Ok, so I've been scratching my head over this one for a while...
(I've seen the 'nifty fifty' moniker used on 365 several times, so I made up a matching one for the 30mm... ;-p )
I've already got a Sigma AF 30mm f/1.4 EX DC HSM, so why would I also want a 50mm prime lens? There are many 365 members that use and love the 50mm. Why, and what makes it preferable to a 30mm?
I'd really like to know what your thoughts are on this. ;-)
Ugh, @soren beat me to it! Also, your f/1.4 cropped is equal to f/2.1 dof (not speed) on a full frame, and I am a big dof-watcher! Many wide-angle lenses also have a quick drop off between min and max focal distance, so you will get delicious bokeh and dof at 0.4m, but will lose all of that at, say... 3m. Most 50mm I've used have a longer drop off, so I can still get decent dof and bokeh on a target further out. At least, that's my impression. I'm hoping Alexis gets on here and tears my analysis all to shit! ;)
@soren
I originally bought the 30mm because it was supposed to be an equal 'view' to the human eye, or thereabouts. Well, that was one reason. ;-p I didn't really think about the crop factor at that point.
@bankmann Jake and Aaron answered already. On a cropped sensor the 35mm provides about the same angle of view as 50mm on a full frame camera, a 35mm film camera equivalent. That 35 has nothing to do with the focal length of course, just to confuse the issue! For a Nikon D3xxx, 5xxx and 7xxx the "crop factor" is almost exactly 1.5, on Canon it is more like 1.6. 30 is 45 (Canon 48) ffe (full frame equivalent) and 35 is 52 (Canon 56) ffe. The Canon cropped sensor is a little smaller than the Nikon. You can find the exact measurements on a spec sheet.
And of course the 50mm ffe is almost exactly the angle of the human eye. It's actually one reason the old film cameras were made that way.
A 50mm on a cropped sensor camera then becomes 75 on Nikon, 80 on a Canon, an awkward length for a prime lens as a number of people have already mentioned in other places here about the same issue. You don't need at fixed 50 as well, indeed it really is not much use on a cropped sensor camera. You've got to frame your shot before worrying about DoF and "fast."
@frankhymus The number crunching is starting to get dizzy-ing. So...can I check it see if I have it right: If we want something like the old 50mm lens we used to have before digital (and that is close to "natural") we should get a 35mm now?
@houser934 Yep. Or if you shoot Canon, the 30 is closer. That's why Bankmann read that the Sigma 30mm would give him a "natural" angle. And that's indeed absolutely true.
I feel bad when I read these threads because I shoot almost exclusively with a 50 mm / f 1.8 on a cropped sensor camera and I love it. I don't find it to be an awkward length. It makes me think I either don't know what I'm doing or that I would REALLY LOVE a 35 mm/ f 1.4 (which is way too expensive really).
@frankhymus@houser934@rockinrobyn
Your input and information is very much appreciated! ;-) As I was half expecting, a choice of 30/35 or 50 comes down to individual taste. But having the tech details worked through like this is very helpful. I'm starting to get the feeling that as long as I've got the 30mm and am happy with it, not having a 50mm shouldn't bother me. ;-p The crop factor on a Pentax is 1.5, by the way.
@squamloon
Good point, SquamLoon! It would actually be an idea to have a defintion reference here on 365...
Great input and links!
I wonder, too... How much quality lies in the size of the sensor? The larger it gets, the more pixels can be put into it, but too many, too small - and the picture quality suffers...
@squamloon Not better or worse, just different. The Micro Four Thirds specification is exactly a 2:1 factor. Indeed, it is the basis for the small and light lenses for the camera, and the increasing popularity of the specification. A super high quality 35-100 f/2.8 Lumix G lens comes in at less than 16 ounces. It is the equivalent of the classic 70-200 f/2.8 that typically weighs in at 4 pounds for most vendors! Glad you found references explaining the size of digital camera sensors and crop factors in comparison with the negative from an old 35mm film camera.
@rockinrobyn I am glad that you find the 50mm APS-C lens works for you. Especially at f/1.8. Some people, me included, don't find the length so comfortable. Here's a similar thread to this one, and note people other than me commenting about the 50 on an APS-C camera. http://365project.org/discuss/critique/17850/50mm-or-35mm
@bankmann Bingo, this is an ongoing discussion, but with technology developing by leaps and bounds, not the critical one that it was only 2-3 years ago.. It's why camera phones are so "noisy," such tiny sensors with only average quality pixel elements (read cheap) all crammed together bleeding in to each other as the individual analog signals are amplified. And many inexpensive small P&S cameras. It's actually the main reason the algorithms on the camera app on the iPhone 5 with its increased pixel count never drive the ISO above about 120, and also why there is no "open" API for developers to directly manipulate the ISO. Can't have images out there that are grossly noisy with the iPhone logo on them.
The Lumix G series from Panasonic (the GH3 is the "pro" model and it is very, very good) makes the very specific point that its 16MP+ sensor on a 2:1 crop has "state of the art" sensor technology that eliminates this "cramping" effect. The new Nikon D7100 literature similarly is very quick to point out the same for the high pixel count on its APS-C sensor, as the D3200 vs the D3100. Same discussion for a D800 versus a D3, full frame sensors with the D800 three times the pixel count.
@lisabell exactly! I thought I was set with lenses but since I use a crop sensor, now I either need to move up to a full-frame or get a 'dirty thirty'! Too bad no birthday anytime soon!
@taffy What do you shoot with, Taffy? Nikon has a really great little f/1.8 35mm for US$200. It's my go to lens for atrocious light conditions. I don't know about Canon.
Having an underused nifty fifty on a Canon cropped sensor, I' m liking the sound of the 30mm. Though I think I would prefer the moniker "flirty thirty".
@frankhymus
You give us great info, Frank, and present it very well! ;-) Thanx!
@taffy
Me, I'm not sweating the 50mm from now on - unless I find one that's on sale, I guess... ;-p
I've got a Sigma 18-200mm I'm really pleased with, anyway, so I've got the range covered... ;-p
@ipost4u
Good alternative, Chris. ;-) Never even crossed my mind. But I'm sticking to my guns on that one... ;-p
@rockinrobyn Don't feel bad -- 50mm on a crop frame camera isn't an awkward length at all. It's a very common length for a portrait lens -- 85mm lenses have long been considered superb for portraiture in the film days (and still today for full-frame users, where 85mm f/1.2 lenses are something almost every professional portrait photographer owns). Your 50mm lens has a very similar focal length, when you take into account the crop factor.
I don't particularly like such categorisation of lenses anyway, nor do I believe that there are 'awkward' focal lengths. Photography is about creating a result, and that can be done in a number of ways with a number of lenses. Yes, shooting a portrait with a super-wide angle lens is probably best avoided in general, as is shooting landscapes with a telephoto, but apart from these extreme angles, pick a lens that works for you and enjoy it. Whatever next -- are you only allowed to use your zoom lens at certain focal lengths?
I go into a far more technical discussion about why a 'normal' focal length is dependant on the size the photo is viewed at below, but in short, on a site like this where photos are displayed at relatively small sizes, you're actually replicating more closely what a 'normal' lens is than you might think!
@grizzlysghost Hah! That's a pretty accurate description of the results. It's not the easiest thing in the world to explain.
Depth of field, contrary to what an awful lot of photographers think, is not actually materially affected by focal length (except in some specific and unusual situations). If you take a shot of the same subject *framed in the same way* with two lenses of a different focal length, the depth of field will be, within a small margin of error, identical.
However, what does change is the magnification of the lens. A lens with a larger focal length provides more magnification (this is, of course, why if you switch from a 24mm lens to a 85mm lens, you need to step back considerably to get your subject to be the same size in the frame). This magnification alters the *apparent* depth of field -- the background is no more blurred, but it is magnified so that it *appears* blurrier.
This is a pretty complex aspect of optical theory to understand, so it's pretty OK to stick to the simpler, albeit slightly incorrect, assumption that a longer focal length has a narrower depth of field. If you do want to try and get your head around it, there are a couple of links that explain it in more detail here:
But don't worry if you can't -- I think it would be an incredibly technically-minded photographer that believed that knowing this would make you better at photography!
@frankhymus There's a few myths mixed up in that as well, although they are extremely common and widely-purported, even by experts. The angle of the human eye is far, far wider than 50mm -- we can actually see slightly behind us at the sides of our eyes (try waving your hand about level with your ear while looking straight ahead). The individual field of view of each eye is just over 100 degrees. Talking about the angle of the human eye is a bit of a difficult thing to pin down anyway -- we only see detail in an incredibly narrow area called the fovea centralis (which is why we need to constantly move our eyes to read). The area this covers is about 2 degrees, or roughly the field of view of a 1200mm lens (on a 35mm camera).
Of course, while the simplified explanation that it is equal to the field of view of the eye isn't quite correct, there is certainly truth to the fact that certain focal lengths render images similar to how we see them with the eye when *viewed at a typical size*. Understanding exactly how this happens is probably a degree in itself (I personally suspect it is related to how the brain maps the fisheye output from our eye into the rectilinear view our brains interpret), but in the early days of photography, photographers had already worked out that a focal length equal to the diagonal length of the film size produced an image that our eyes found pleasing when printed -- because we will naturally view a printed photo from a distance approximately equal to the diagonal length of the print. That's the key -- it's the *size the photo is viewed at that* determines what focal length looks correct to our eye, not the focal length per-se.
Sadly, for 35mm film, the diagonal length of the film is 43mm, not 50mm. So why did we end up with 50mm lenses? Unfortunately, rather than because of how it was the correct 'normal' focal length, mundane manufacturing issues instead came into play.
When SLRs first came out, it was desirable to have a cheap lens that could be sold with them (an SLR without a lens isn't much use), and cheap means simple, so the manufacturers were limited by simple and easy to manufacture lens designs. It was also desirable to have a wide aperture, not only for depth of field reasons, but also simply because film wasn't all that sensitive, and you needed all the light you could get.
Because the mirror of an SLR swings upwards, it limits the distance the rear element of a lens can get to the film without the mirror hitting the lens as it swings. This also limits the widest focal length you can create using simple lens designs -- to go wider, you need to position the rear lens elements closer to the film. There's a good breakdown of the maths and difficulty of producing a 43mm lens with a sufficiently wide aperture (the aperture width affecting the size of the elements, and hence the thickness) while sticking to simple lens design techniques here.
Of course, retrofocus lens designs allow us to use wide angle lenses even though the rear of the lens cannot get closer to the film, but these designs require many more elements and are far more expensive to manufacture (they are also less sharp, due to these extra elements). This is why 50mm lenses are typically very cheap, very light and very sharp -- they have very few elements in them (because they don't need a retrofocus design), and they use less glass than longer focal lengths with equivalent apertures (because aperture is related to focal length, so longer focal length lenses need to be wider).
This is the rather mundane reason that SLRs historically came with 50mm lenses rather than 43mm lenses which would be considered 'normal' by photographers. Of course, now 50mm lenses are so common that they are now seen as a 'normal' lens simply because of that popularity! (50mm also has the benefit of being the size Oskar Barnack chose for his first Leica camera, although it is often claimed that this is simply what he had available at the time!)
And as I said earlier, the reason the 'normal' lens focal length (the diagonal of the film size) was chosen is because people typically view decent-sized prints at a distance of approximately the diagonal of the print size. As you probably figured out earlier, with the Internet now being used so much for photography, that of course is no longer the case -- on this site, you have to get pretty close to the screen to view a photo from the same distance as it is diagonally across.
All this means that actually, while if you print an image at a decent size a 43mm lens would look about right to the eye -- but when viewed relatively small on a screen, what appears 'normal' to the eye is actually a considerably longer focal length. It turns out that a 50mm lens on a crop camera is, while not what most photographers who used film are used to, actually a pretty good 'normal' lens to use if you primarily post photos on the 'net (especially at small sizes like on this site!), and appears more natural to the eye than a 35mm lens would! Funny how technology works out like that sometimes. (Of course, if you view photos on a decent-sized desktop monitor full-screen then again, the 'normal' focal length would go back to being closer to 50mm on 35mm film -- but if you view them on a mobile phone then you might need a focal length closer to 100mm for it to appear 'normal'!)
The same argument applies in the opposite way, of course. If the viewing surface you are using is considerably larger than average, then you will need to use a wider angle lens than the simple diagonal rule would dictate to make the image appear 'normal'. That's why IMAX films are filmed on lenses with a wider field of view than normal films -- because the IMAX screen is so much larger.
So, in short, 43mm is the 'correct' focal length based on how people view images printed at a decent size (i.e. in a gallery). 50mm is a roughly-close estimate that was chosen because it could be manufactured cheaply. With photos much more commonly being shared online and being viewed on a variety of screen sizes, the simple reality is that it doesn't matter if you use a 35mm, 50mm or 85mm lens -- they will all look 'normal' to some people on some devices, and not to others.
(Incidentally, the retrofocus design issues are one of several key reasons why the days of SLRs are probably numbered. Mirrorless cameras remove the need for retrofocus lenses, which means that lenses under 50mm can be made much cheaper, much lighter and much sharper. Once the other issues with mirrorless cameras are solved, expect to see true DSLRs with mirrors start to dwindle in popularity)
A larger sensor size results in a greater apparent depth of field, but also means that the lenses require more glass to project a sufficiently large image circle, which makes them heavier and more expensive.
The quality issue is harder to define -- it depends on your point of view. The size of each individual pixel on a sensor determines the per-pixel noise levels of the sensor, but it's not that simple. Take two sensors of the same generation (sensors improve as technology advances), one of which is half the size of the other. If you make the pixels on each sensor the same size, the larger sensor has twice the resolution than the smaller sensor, but the same amount of noise. If you make the resolution of each sensor the same, the larger sensor has (roughly) half the noise of the smaller sensor, but the same resolution.
This is the reason why many people upgrade to newer, higher-megapixel cameras and complain that the noise is the same or worse than it was on their old camera. To check noise, they are zooming in to 100% and looking at it, and indeed it is worse. However, a fairer comparison is to resize the two photos to be the same size -- at that point, the newer, higher-megapixel camera should perform better than the old one, even though when 'pixel-peeping' the results look worse.
What this means is that, if you take the overall quality of a photograph, a larger sensor is always better (assuming the larger sensor is using the same or newer technology than the smaller sensor). If you pixel-peep, then the quality will depend on the pixel size, not the sensor size. Many photographers become obsessed with noise and lens sharpness and constantly 'pixel-peep', hence why you hear noise complaints of high-megapixel cameras like the D800, even though in comparison to other cameras when reproduced at equivalent sizes it's pretty astonishing.
Here endeth the lesson in lens optics and camera design!
@frankhymus I use a Nikon D90 so the 35mm you're talking about sounds like something within reach. I have a 14-24 mm so have always just figured that's what I should use, but it's large and heavy so doesn't really work as a walk-around lens. BTW, did you send me a challenge this week? I may have miseed it.
@frankhymus quick question -- is the 35mm only in a dx version or is there a full frame one as well? If both, which are you referring to? Thanks in advance.
@abirkill Hats off to you yet again Alexis! You certainly have a talent for explaining anything is easily understandable terms and without sounding like a know it all! :) Thanks again!
I had to google the bit about a crop sensor affect DoF as it didnt seem correct when I read it...
My 5 cents worth for @bankmann is that you may want a 50mm on your crop sensor to shoot portraits. Personally, I've started thinking of the 50mm 1.8 canon not as a "nifty fifty" but more as a "shifty fifty" - thats how much I hate it. If you were shooting canon, I would personally say spend a tiny bit more and get the 50mm F1.4... not sure how the pentax / sigma offerings fare
"Our central angle of view — around 40-60° — is what most impacts our perception. Subjectively, this would correspond with the angle over which you could recall objects without moving your eyes. Incidentally, this is close to a 50 mm "normal" focal length lens on a full frame camera (43 mm to be precise), or a 27 mm focal length on a camera with a 1.6X crop factor. Although this doesn't reproduce the full angle of view at which we see, it does correspond well with what we perceive as having the best trade-off between different types of distortion."
I don't really have any technical knowledge but can say I love the two prime lenses that I have. 50mm and 100mm macro. Absolutely love the 100mm macro. What would you call a hundred? Lol
@abirkill
Hot damn, but that was educational! ;-) Thanx for the input!
@toast
There's a Sigma 50mm (Sigma 50mm f1.4 EX DG HSM) and a Pentax 50mm (Pentax SMC FA 50mm f/1.4) that cost about the same, and then there's a cheaper Pentax (Pentax SMC DA 50mm f/1.8). I would probably go for the Sigma lens, because it would be familiar, as I have the 30mm Sigma already. But as I read the comments in this thread, I feel that there is no real need for it in particular; as I've got other equipment that 'covers it'. It would be a 'nice to have' thing. I see that people's choice of 30, 35, or 50 is indeed a personal preference. This is indeed educational for me. ;-) (There are other 50's with added functionality, such as macro, but I'm disregarding those here.)
@abhijit
A 'handsome hundred'? A 'hunky hundred'? ;-p Or a 'handy hundred'?
@frankhymus Frank I have that lens bought it same time as my D7100, and loving it. Already had a few other lens but no fixed and didn't want the kit lens as already had equivalents and better in my camera bag:-)
@toast Yes, that's not immediately evident at first either! It does, of course, have the corollary is that it happens when you frame the objects identically (which means standing a different distance from the subject). Merely putting a lens on a different camera doesn't directly affect the DoF, it's the movement you have to make to get the same shot that is the underlying cause.
@frankhymus It's a nice simplification but again misses the actual point, I feel. (It also comes worryingly close to the 'focal length alters perspective' fallacy).
Here's another way to think about it that might help explain what's actually going on. Imagine that a printed photograph is a window to the scene that it photographed. With a normal window, the field of view you see is determined by how close you are to the window -- when you press your nose against it you can see almost directly up or down, when you are 20 feet away you can only see a few degrees up or down.
Obviously, when we move closer or further from a printed photograph, that does not happen -- we can't see a wider field of view than the photographer captured, regardless of how close we get (we merely 'stretch' the field of view of the photograph over a wider area of our eye).
It therefore clearly follows that, for a given focal length, there is a distance to view it from which matches that focal length, and that is the distance where the photograph looks 'normal'.
As I said, humans instinctively view a printed photo at a distance equal to the diagonal if possible. (You'll find that humans do this a lot, actually -- if you have a decent-sized monitor you'll find that you've almost certainly naturally positioned it so that you are approximately the distance of the diagonal away from it. Go around an office to see how almost everyone else has also naturally chosen this!)
This is why a 'normal' lens gives the right appearance for gallery prints. But if you (or something else) controls the distance the photo is viewed from (and therefore the apparent field of view of the photograph), then that 'normal' lens changes completely.
If you force someone to stand 2 feet away from a 20 foot wide photograph, then a super-wide lens will be the lens that appears 'normal' -- all those 'distortions' you get at the edge of the lens are exactly cancelled out by the fact that edges of the photo are, to the viewer, so much further away, and hence smaller.
Similarly, if you force someone to stand 20 feet away from a 2 foot photo, an extreme telephoto lens will be 'normal'.
That's exactly what many websites (and devices) do force -- viewing a photo on here from the distance of the diagonal size of the photo requires getting much closer to the screen than most people do, so a lens much longer than 50mm is needed for the photo to look normal. And on a mobile phone or other small-screened device (even a laptop where people are rarely able to get as close to the screen as they normally would) the effect is even worse.
Articles like the one linked always seem to tackle the issue from the photographer's viewpoint -- literally. A 50mm lens may look 'normal' through the viewfinder of a 35mm camera (although that in itself is affected by the viewfinder magnification), but the only person seeing a photo through the viewfinder of a camera is the photographer. To everyone else, the 'normal' focal length depends on their distance from the photo as they view it. (And remember, all this was discovered before viewfinders were commonly used in photography)
If you shoot gallery prints, by all means choose a 43mm/50mm lens on a full-frame camera, or cropped equivalent, and it'll be about right (if you want that 'normal' appearance of looking through a window). If you shoot photos that end up online then it really doesn't matter -- there is no 'right' or 'wrong' answer. If you want to shoot photos that will look 'normal' to people when viewed on this particular site, you need a focal length of approximately 75mm-100mm, as I suspect most people on here view the photos from a distance of between 1.5 to 2 times the length of the photograph's diagonal (more if they don't press the 'view large' button).
Again, this is relatively complex optical theory so can be a bit tricky to get your head around. Hopefully it at least explains why 50mm/43mm lenses were originally considered normal, and gives insight that there is no 'normal' lens any more if you post primarily online, where the size you photos are viewed at cannot be controlled. (Or at least that the normal focal length ranges from about 45mm-150mm).
@abirkill
I'm very impressed with your explanations. True, this is very 'far field' for me, but I get what you're saying. Thank you for this information! ;-)
@shadesofgrey
That's great! ;-) I wasn't aware of your work on a guide... ;-p Very cool!
@suelaubscher The f/1.8? Yes, it's a great buy at $200. A little edge distortion, but easily fixed. AF is great in bad light. It should give you wonderful images on your D7100.
I think the reason most get the 50 is because you can get one for around $120 bucks US for the canon or nikon. My 35 1.8 for nikon was $230 or something. I have the 50 and 35 1.8's but usually the 35 is more useful for me on crop senor.
Think it all depends on what/where/how you like to shoot. I got the canon 50mm 1.8 for my crop body because it was affordable and a vast improvement over my kit lenses. It was the lens that was on my camera about 80% of the time, and I got some excellent portrait shots of my daughter with it. However, it definitely felt cramped at times, indoors especially (and as my daughter grew and started walking, it was getting super hard to get far enough away from her to get good photos with the 50mm). If I hadn't just upgraded to full frame, I probably would have been looking for a wider angle fast prime for portraits.
For a "walking around" lens, though, I found the 50mm on my crop to be pretty versatile. If you are using your 30mm and finding you feel cramped-like you have to be too close to your subjects to frame them how you like, then the 50mm might be a good way to go. Otherwise, your 30mm is probably just as good!
@frankhymus@lbjefferies@soia@cassiadawn
Sorry I haven't had the time to follow up on your comments in this thread! ;-p
I'm very grateful for the input. I'm sticking with my 'dirty thirty' for now... ;-p
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On my crop sensor camera i like my 35mm better then my 50mm
I originally bought the 30mm because it was supposed to be an equal 'view' to the human eye, or thereabouts. Well, that was one reason. ;-p I didn't really think about the crop factor at that point.
That was a good, point, actually. Never considered the DOF 'quality' of these lenses.
;-D Cheers! I'm just the same... Plus, Aaron ( @grizzlysghost ) has managed to 'inspire' me a couple of times... ;-p
And of course the 50mm ffe is almost exactly the angle of the human eye. It's actually one reason the old film cameras were made that way.
A 50mm on a cropped sensor camera then becomes 75 on Nikon, 80 on a Canon, an awkward length for a prime lens as a number of people have already mentioned in other places here about the same issue. You don't need at fixed 50 as well, indeed it really is not much use on a cropped sensor camera. You've got to frame your shot before worrying about DoF and "fast."
Your input and information is very much appreciated! ;-) As I was half expecting, a choice of 30/35 or 50 comes down to individual taste. But having the tech details worked through like this is very helpful. I'm starting to get the feeling that as long as I've got the 30mm and am happy with it, not having a 50mm shouldn't bother me. ;-p The crop factor on a Pentax is 1.5, by the way.
I, for one, had no idea what you all meant by "cropped sensor", and was enlightened by this explanation at Digital Photography School....
http://digital-photography-school.com/full-frame-sensor-vs-crop-sensor-which-is-right-for-you
...and by this Wiki explanation of Crop Factor: http://en.wikipedia.org/wiki/Crop_factor
So is my new Canon T4i with a 1.6 crop factor "better" than my old 4/3 Olympus, at 1.84—2?
Good point, SquamLoon! It would actually be an idea to have a defintion reference here on 365...
Great input and links!
I wonder, too... How much quality lies in the size of the sensor? The larger it gets, the more pixels can be put into it, but too many, too small - and the picture quality suffers...
@rockinrobyn I am glad that you find the 50mm APS-C lens works for you. Especially at f/1.8. Some people, me included, don't find the length so comfortable. Here's a similar thread to this one, and note people other than me commenting about the 50 on an APS-C camera. http://365project.org/discuss/critique/17850/50mm-or-35mm
@bankmann Bingo, this is an ongoing discussion, but with technology developing by leaps and bounds, not the critical one that it was only 2-3 years ago.. It's why camera phones are so "noisy," such tiny sensors with only average quality pixel elements (read cheap) all crammed together bleeding in to each other as the individual analog signals are amplified. And many inexpensive small P&S cameras. It's actually the main reason the algorithms on the camera app on the iPhone 5 with its increased pixel count never drive the ISO above about 120, and also why there is no "open" API for developers to directly manipulate the ISO. Can't have images out there that are grossly noisy with the iPhone logo on them.
The Lumix G series from Panasonic (the GH3 is the "pro" model and it is very, very good) makes the very specific point that its 16MP+ sensor on a 2:1 crop has "state of the art" sensor technology that eliminates this "cramping" effect. The new Nikon D7100 literature similarly is very quick to point out the same for the high pixel count on its APS-C sensor, as the D3200 vs the D3100. Same discussion for a D800 versus a D3, full frame sensors with the D800 three times the pixel count.
You give us great info, Frank, and present it very well! ;-) Thanx!
@taffy
Me, I'm not sweating the 50mm from now on - unless I find one that's on sale, I guess... ;-p
I've got a Sigma 18-200mm I'm really pleased with, anyway, so I've got the range covered... ;-p
@ipost4u
Good alternative, Chris. ;-) Never even crossed my mind. But I'm sticking to my guns on that one... ;-p
I don't particularly like such categorisation of lenses anyway, nor do I believe that there are 'awkward' focal lengths. Photography is about creating a result, and that can be done in a number of ways with a number of lenses. Yes, shooting a portrait with a super-wide angle lens is probably best avoided in general, as is shooting landscapes with a telephoto, but apart from these extreme angles, pick a lens that works for you and enjoy it. Whatever next -- are you only allowed to use your zoom lens at certain focal lengths?
I go into a far more technical discussion about why a 'normal' focal length is dependant on the size the photo is viewed at below, but in short, on a site like this where photos are displayed at relatively small sizes, you're actually replicating more closely what a 'normal' lens is than you might think!
@grizzlysghost Hah! That's a pretty accurate description of the results. It's not the easiest thing in the world to explain.
Depth of field, contrary to what an awful lot of photographers think, is not actually materially affected by focal length (except in some specific and unusual situations). If you take a shot of the same subject *framed in the same way* with two lenses of a different focal length, the depth of field will be, within a small margin of error, identical.
However, what does change is the magnification of the lens. A lens with a larger focal length provides more magnification (this is, of course, why if you switch from a 24mm lens to a 85mm lens, you need to step back considerably to get your subject to be the same size in the frame). This magnification alters the *apparent* depth of field -- the background is no more blurred, but it is magnified so that it *appears* blurrier.
This is a pretty complex aspect of optical theory to understand, so it's pretty OK to stick to the simpler, albeit slightly incorrect, assumption that a longer focal length has a narrower depth of field. If you do want to try and get your head around it, there are a couple of links that explain it in more detail here:
http://www.worth1000.com/tutorials/162260/theory-depth-of-field-vs-focal-length
http://www.luminous-landscape.com/tutorials/dof2.shtml
But don't worry if you can't -- I think it would be an incredibly technically-minded photographer that believed that knowing this would make you better at photography!
@frankhymus There's a few myths mixed up in that as well, although they are extremely common and widely-purported, even by experts. The angle of the human eye is far, far wider than 50mm -- we can actually see slightly behind us at the sides of our eyes (try waving your hand about level with your ear while looking straight ahead). The individual field of view of each eye is just over 100 degrees. Talking about the angle of the human eye is a bit of a difficult thing to pin down anyway -- we only see detail in an incredibly narrow area called the fovea centralis (which is why we need to constantly move our eyes to read). The area this covers is about 2 degrees, or roughly the field of view of a 1200mm lens (on a 35mm camera).
Of course, while the simplified explanation that it is equal to the field of view of the eye isn't quite correct, there is certainly truth to the fact that certain focal lengths render images similar to how we see them with the eye when *viewed at a typical size*. Understanding exactly how this happens is probably a degree in itself (I personally suspect it is related to how the brain maps the fisheye output from our eye into the rectilinear view our brains interpret), but in the early days of photography, photographers had already worked out that a focal length equal to the diagonal length of the film size produced an image that our eyes found pleasing when printed -- because we will naturally view a printed photo from a distance approximately equal to the diagonal length of the print. That's the key -- it's the *size the photo is viewed at that* determines what focal length looks correct to our eye, not the focal length per-se.
Sadly, for 35mm film, the diagonal length of the film is 43mm, not 50mm. So why did we end up with 50mm lenses? Unfortunately, rather than because of how it was the correct 'normal' focal length, mundane manufacturing issues instead came into play.
When SLRs first came out, it was desirable to have a cheap lens that could be sold with them (an SLR without a lens isn't much use), and cheap means simple, so the manufacturers were limited by simple and easy to manufacture lens designs. It was also desirable to have a wide aperture, not only for depth of field reasons, but also simply because film wasn't all that sensitive, and you needed all the light you could get.
Because the mirror of an SLR swings upwards, it limits the distance the rear element of a lens can get to the film without the mirror hitting the lens as it swings. This also limits the widest focal length you can create using simple lens designs -- to go wider, you need to position the rear lens elements closer to the film. There's a good breakdown of the maths and difficulty of producing a 43mm lens with a sufficiently wide aperture (the aperture width affecting the size of the elements, and hence the thickness) while sticking to simple lens design techniques here.
Of course, retrofocus lens designs allow us to use wide angle lenses even though the rear of the lens cannot get closer to the film, but these designs require many more elements and are far more expensive to manufacture (they are also less sharp, due to these extra elements). This is why 50mm lenses are typically very cheap, very light and very sharp -- they have very few elements in them (because they don't need a retrofocus design), and they use less glass than longer focal lengths with equivalent apertures (because aperture is related to focal length, so longer focal length lenses need to be wider).
This is the rather mundane reason that SLRs historically came with 50mm lenses rather than 43mm lenses which would be considered 'normal' by photographers. Of course, now 50mm lenses are so common that they are now seen as a 'normal' lens simply because of that popularity! (50mm also has the benefit of being the size Oskar Barnack chose for his first Leica camera, although it is often claimed that this is simply what he had available at the time!)
And as I said earlier, the reason the 'normal' lens focal length (the diagonal of the film size) was chosen is because people typically view decent-sized prints at a distance of approximately the diagonal of the print size. As you probably figured out earlier, with the Internet now being used so much for photography, that of course is no longer the case -- on this site, you have to get pretty close to the screen to view a photo from the same distance as it is diagonally across.
All this means that actually, while if you print an image at a decent size a 43mm lens would look about right to the eye -- but when viewed relatively small on a screen, what appears 'normal' to the eye is actually a considerably longer focal length. It turns out that a 50mm lens on a crop camera is, while not what most photographers who used film are used to, actually a pretty good 'normal' lens to use if you primarily post photos on the 'net (especially at small sizes like on this site!), and appears more natural to the eye than a 35mm lens would! Funny how technology works out like that sometimes. (Of course, if you view photos on a decent-sized desktop monitor full-screen then again, the 'normal' focal length would go back to being closer to 50mm on 35mm film -- but if you view them on a mobile phone then you might need a focal length closer to 100mm for it to appear 'normal'!)
The same argument applies in the opposite way, of course. If the viewing surface you are using is considerably larger than average, then you will need to use a wider angle lens than the simple diagonal rule would dictate to make the image appear 'normal'. That's why IMAX films are filmed on lenses with a wider field of view than normal films -- because the IMAX screen is so much larger.
So, in short, 43mm is the 'correct' focal length based on how people view images printed at a decent size (i.e. in a gallery). 50mm is a roughly-close estimate that was chosen because it could be manufactured cheaply. With photos much more commonly being shared online and being viewed on a variety of screen sizes, the simple reality is that it doesn't matter if you use a 35mm, 50mm or 85mm lens -- they will all look 'normal' to some people on some devices, and not to others.
(Incidentally, the retrofocus design issues are one of several key reasons why the days of SLRs are probably numbered. Mirrorless cameras remove the need for retrofocus lenses, which means that lenses under 50mm can be made much cheaper, much lighter and much sharper. Once the other issues with mirrorless cameras are solved, expect to see true DSLRs with mirrors start to dwindle in popularity)
@squamloon @bankmann Define 'better'!
A larger sensor size results in a greater apparent depth of field, but also means that the lenses require more glass to project a sufficiently large image circle, which makes them heavier and more expensive.
The quality issue is harder to define -- it depends on your point of view. The size of each individual pixel on a sensor determines the per-pixel noise levels of the sensor, but it's not that simple. Take two sensors of the same generation (sensors improve as technology advances), one of which is half the size of the other. If you make the pixels on each sensor the same size, the larger sensor has twice the resolution than the smaller sensor, but the same amount of noise. If you make the resolution of each sensor the same, the larger sensor has (roughly) half the noise of the smaller sensor, but the same resolution.
This is the reason why many people upgrade to newer, higher-megapixel cameras and complain that the noise is the same or worse than it was on their old camera. To check noise, they are zooming in to 100% and looking at it, and indeed it is worse. However, a fairer comparison is to resize the two photos to be the same size -- at that point, the newer, higher-megapixel camera should perform better than the old one, even though when 'pixel-peeping' the results look worse.
What this means is that, if you take the overall quality of a photograph, a larger sensor is always better (assuming the larger sensor is using the same or newer technology than the smaller sensor). If you pixel-peep, then the quality will depend on the pixel size, not the sensor size. Many photographers become obsessed with noise and lens sharpness and constantly 'pixel-peep', hence why you hear noise complaints of high-megapixel cameras like the D800, even though in comparison to other cameras when reproduced at equivalent sizes it's pretty astonishing.
Here endeth the lesson in lens optics and camera design!
I get confused my your Canon stuff....
I had to google the bit about a crop sensor affect DoF as it didnt seem correct when I read it...
My 5 cents worth for @bankmann is that you may want a 50mm on your crop sensor to shoot portraits. Personally, I've started thinking of the 50mm 1.8 canon not as a "nifty fifty" but more as a "shifty fifty" - thats how much I hate it. If you were shooting canon, I would personally say spend a tiny bit more and get the 50mm F1.4... not sure how the pentax / sigma offerings fare
"Our central angle of view — around 40-60° — is what most impacts our perception. Subjectively, this would correspond with the angle over which you could recall objects without moving your eyes. Incidentally, this is close to a 50 mm "normal" focal length lens on a full frame camera (43 mm to be precise), or a 27 mm focal length on a camera with a 1.6X crop factor. Although this doesn't reproduce the full angle of view at which we see, it does correspond well with what we perceive as having the best trade-off between different types of distortion."
Hot damn, but that was educational! ;-) Thanx for the input!
@toast
There's a Sigma 50mm (Sigma 50mm f1.4 EX DG HSM) and a Pentax 50mm (Pentax SMC FA 50mm f/1.4) that cost about the same, and then there's a cheaper Pentax (Pentax SMC DA 50mm f/1.8). I would probably go for the Sigma lens, because it would be familiar, as I have the 30mm Sigma already. But as I read the comments in this thread, I feel that there is no real need for it in particular; as I've got other equipment that 'covers it'. It would be a 'nice to have' thing. I see that people's choice of 30, 35, or 50 is indeed a personal preference. This is indeed educational for me. ;-) (There are other 50's with added functionality, such as macro, but I'm disregarding those here.)
@abhijit
A 'handsome hundred'? A 'hunky hundred'? ;-p Or a 'handy hundred'?
@frankhymus It's a nice simplification but again misses the actual point, I feel. (It also comes worryingly close to the 'focal length alters perspective' fallacy).
Here's another way to think about it that might help explain what's actually going on. Imagine that a printed photograph is a window to the scene that it photographed. With a normal window, the field of view you see is determined by how close you are to the window -- when you press your nose against it you can see almost directly up or down, when you are 20 feet away you can only see a few degrees up or down.
Obviously, when we move closer or further from a printed photograph, that does not happen -- we can't see a wider field of view than the photographer captured, regardless of how close we get (we merely 'stretch' the field of view of the photograph over a wider area of our eye).
It therefore clearly follows that, for a given focal length, there is a distance to view it from which matches that focal length, and that is the distance where the photograph looks 'normal'.
As I said, humans instinctively view a printed photo at a distance equal to the diagonal if possible. (You'll find that humans do this a lot, actually -- if you have a decent-sized monitor you'll find that you've almost certainly naturally positioned it so that you are approximately the distance of the diagonal away from it. Go around an office to see how almost everyone else has also naturally chosen this!)
This is why a 'normal' lens gives the right appearance for gallery prints. But if you (or something else) controls the distance the photo is viewed from (and therefore the apparent field of view of the photograph), then that 'normal' lens changes completely.
If you force someone to stand 2 feet away from a 20 foot wide photograph, then a super-wide lens will be the lens that appears 'normal' -- all those 'distortions' you get at the edge of the lens are exactly cancelled out by the fact that edges of the photo are, to the viewer, so much further away, and hence smaller.
Similarly, if you force someone to stand 20 feet away from a 2 foot photo, an extreme telephoto lens will be 'normal'.
That's exactly what many websites (and devices) do force -- viewing a photo on here from the distance of the diagonal size of the photo requires getting much closer to the screen than most people do, so a lens much longer than 50mm is needed for the photo to look normal. And on a mobile phone or other small-screened device (even a laptop where people are rarely able to get as close to the screen as they normally would) the effect is even worse.
Articles like the one linked always seem to tackle the issue from the photographer's viewpoint -- literally. A 50mm lens may look 'normal' through the viewfinder of a 35mm camera (although that in itself is affected by the viewfinder magnification), but the only person seeing a photo through the viewfinder of a camera is the photographer. To everyone else, the 'normal' focal length depends on their distance from the photo as they view it. (And remember, all this was discovered before viewfinders were commonly used in photography)
If you shoot gallery prints, by all means choose a 43mm/50mm lens on a full-frame camera, or cropped equivalent, and it'll be about right (if you want that 'normal' appearance of looking through a window). If you shoot photos that end up online then it really doesn't matter -- there is no 'right' or 'wrong' answer. If you want to shoot photos that will look 'normal' to people when viewed on this particular site, you need a focal length of approximately 75mm-100mm, as I suspect most people on here view the photos from a distance of between 1.5 to 2 times the length of the photograph's diagonal (more if they don't press the 'view large' button).
Again, this is relatively complex optical theory so can be a bit tricky to get your head around. Hopefully it at least explains why 50mm/43mm lenses were originally considered normal, and gives insight that there is no 'normal' lens any more if you post primarily online, where the size you photos are viewed at cannot be controlled. (Or at least that the normal focal length ranges from about 45mm-150mm).
http://365project.org/discuss/general/9968/getting-started-guide-for-new-users
I'm very impressed with your explanations. True, this is very 'far field' for me, but I get what you're saying. Thank you for this information! ;-)
@shadesofgrey
That's great! ;-) I wasn't aware of your work on a guide... ;-p Very cool!
For a "walking around" lens, though, I found the 50mm on my crop to be pretty versatile. If you are using your 30mm and finding you feel cramped-like you have to be too close to your subjects to frame them how you like, then the 50mm might be a good way to go. Otherwise, your 30mm is probably just as good!
Sorry I haven't had the time to follow up on your comments in this thread! ;-p
I'm very grateful for the input. I'm sticking with my 'dirty thirty' for now... ;-p