Hey all. Im curious to learn the math behind depth of field. So far, all of my knowledge has been trial and error and for the most part, that works ok. I find however that a lot of times I have people out of focus when i really wish they were in focus, and I tend to shoot from fairly close so I know that I need to change the f-stop to account for that.
Are there easy charts to learn or ways to figure out what will be in focus/ out of focus from certain distances using certain lenses? Any tips or suggestions on where to start that research as well?
Shooting close to the subject with far more distance behind the main subject to the background than from the camera to the subject will always get you a blurred background, irrespective of the aperture. "Hyperfocal Distance" if you care to google for the subject. Basically 1/3 in front of the subject and 2/3 behind the subject, so you can see that if the behind distance is more than 3 times the in front distance, you'll get blur. That's what all those numbers in the table in the link really say.
Many (not all) lenses have numbers (in feet or metres) printed on them that give you an idea of what depth of field you will get. Anything either side of those figure will be out of focus
To add to John and Frank, there is a fourth factor: focal length. So, in summary, DOF is controlled by 1) aperture, 2) distance from camera to subject, 3) distance from subject to background, and 4) focal length.
@rellimdj Perhaps we should say *apparent* DoF. The "rules" and absolute distances remain the same but a long telephoto tends to pull the subject forward in the frame and separate it from the background
@katiebrenkert OK might get a bit of slating but, considering I'm an engineer and could if required work out loads of stuff to do with this, I would recommend getting a subject camera and lens then experiment. There is no better thing than experience and experiment :-)
@frankhymus but would anyone really stop calculate the perceived depth of field then set aperture speed etc set the distance on the lens oh lights gone subjects moved?
By all means understand what it means but to get a feel for the depth of field and be able to make snap decisions experience counts for more than any calculator.
A bit of advice a good friend gave me was stop reading about taking photos a go take them!
Many older (and higher-end) prime lenses have depth of field scales on the lens itself, to allow you to quickly determine the appropriate depth of field for the photo without needing to get out calculators or charts:
Here, the yellow line indicates where the lens is focused, with the lines to the left and right indicating the depth of field at different apertures. So you can see at a glance that at f/8, everything between approximately 0.9 metres and 2.5 metres will be in focus.
This was particularly useful in the film days, of course, where you couldn't simply fire off a quick shot, zoom in, and make sure everything you needed to be in focus was actually in focus!
Sadly, these are often missing off prime lenses, especially cheaper ones, today.
Today, if you don't want to mess about with depth of field charts and want to get the shot right first time, the depth of field preview button on your camera, combined with magnified live view, can be very useful. I frequently use this for my wide angle seascape work, where I want as wide an aperture as possible, while still making sure that everything from the foreground rocks to the horizon is in focus. I can set the lens to f/8, hold down the depth of field preview button, adjust the focus so that the horizon is just sharp, and then check the foreground to see if that's sharp. If it's not, then I can stop down to f/11 and try again (and again to f/16 or f/22, if necessary). This sounds a bit time-consuming, but with a bit of practice it's very easy, and I can usually do this in 30 seconds or less.
@katiebrenkert On older cameras there was nearly always a "stop down" button... It effectively provided a 'through the lens' preview of the DOF expected on the taken photo! I'm sure most modern DSLR's have this function.... A rather useful little gizmo!! :)
@abirkill The DoF preview button was a really nice surprise when I upgraded to the Nikon D7100. I use it quite a bit it in Live View. The button is reasonably close to my Fn button one which I have programmed Auto Focus Hold, so its only a few centimeters away for my finger to find. The combination works well for me.
@frankhymus Well kind of Frank. Depends on how close they are. Long telephotos actually compress the scene, and make things that are far apart seem closer.
@abirkill Do you have a post from the past where you discuss using the DOF preview button? I still find that most of the time I can't see well enough inside the view finder to be able to tell, even after my eye adjusts to the light. Any tips on that? I'm sure live view would help as well.
@adambralston Actually I think you need to pick up the image from the sensor, so for a DSLR Live View with the mirror raised is necessary? I would guess on the mirror-less systems, you'd see it in the electronic viewfinder though. Alexis? @abirkill
@adambralston I don't think I've discussed it in depth (so to speak!) before, but I'm happy to answer any questions.
The depth of field preview button is functional and will correctly show the actual depth of field of the image through the optical viewfinder, but the combination of the relatively small image in the viewfinder, even on a full-frame camera, combined with the darkness when a significant stop-down is done, means that I don't find it much use in that way, either. (Of course, back in the film days this was the only way to do this, so it certainly can be useful)
The darkness is, of course, caused by the aperture closing down -- when looking through an optical viewfinder without holding the depth of field preview button you are looking through the lens when it is wide open, regardless of the aperture the photograph will be taken with -- the lens will only be stopped down when the photo is taken. However, when you hold down the DOF preview button, the lens is stopped down there and then. If you have an f/2.8 lens and hold down the DOF preview button with the camera set to f/16, the viewfinder image will suddenly be only 1/32 the brightness!
For these reasons I pretty much exclusively combine the DOF preview button with Live View, which will automatically keep the exposure the same so the only change is the increased depth of field (and possibly a little more noise in the Live View image in low light conditions). Because you can also zoom into any area in live view, I find this a lot more useful.
As @frankhymus says, on mirrorless cameras with electronic viewfinders, both the rear screen and viewfinder are fed from the live view data, so you don't have to worry about the viewfinder dimming in these cases. Indeed, I think that Sony NEX mirrorless cameras will, by default, automatically stop down the lens and show the final image's depth of field whenever the shutter release is half-depressed, negating the need for a separate button.
@frankhymus@abirkill Awesome detail as always. Thanks for that. I have a Rebel XT - it has the Auto DOF setting. And, actually, I find sometimes it's awesome. Still, not always sure how to use it.
@adambralston Is that the A-DEP mode? It's a neat trick, although I usually found that it gave me a different answer each time I half-pressed the shutter, which didn't fill me with confidence. It may be significant that (from memory) it's not an option on any of Canon's full-frame cameras (nor, I think, the 7D or 70D)...
Thanks everyone for all the responses. Alexis- your tip is exactly what Im looking for- just a reference to get me started so I dont screw up the shot every time. I find that when Im shooting groups of people (and not posed groups of people) and I want someone slightly behind in focus, I always manage to screw it up. As mentioned earlier though, I tend to shoot from fairly close, closing that range so I never seemed to go far enough with my f-stop. According to what I looked up last night it would have to be around 16 to keep someone in focus.
Im going to try your trick and see how it works for me. I havent ever used the DOF button because I never noticed a difference, didnt think to use it with live view. Thank you!
This is a fantastic discussion. Thank you all have commented, I was wondering about this idea a few weeks ago. I have since started to use th DOF button and find It works great
I have a DOF button on my camera? Damn I must try that. I am having a great time with depth of field and what was said about practice makes perfect is sooo right. Loved this discussion.
I was given this tip by a professional landscape photographer - the higher the f stop the greater the DOF, the lower the f stop the shallower the DOF. Works for me every time and is really easy to remember.
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By all means understand what it means but to get a feel for the depth of field and be able to make snap decisions experience counts for more than any calculator.
A bit of advice a good friend gave me was stop reading about taking photos a go take them!
Here, the yellow line indicates where the lens is focused, with the lines to the left and right indicating the depth of field at different apertures. So you can see at a glance that at f/8, everything between approximately 0.9 metres and 2.5 metres will be in focus.
This was particularly useful in the film days, of course, where you couldn't simply fire off a quick shot, zoom in, and make sure everything you needed to be in focus was actually in focus!
Sadly, these are often missing off prime lenses, especially cheaper ones, today.
Today, if you don't want to mess about with depth of field charts and want to get the shot right first time, the depth of field preview button on your camera, combined with magnified live view, can be very useful. I frequently use this for my wide angle seascape work, where I want as wide an aperture as possible, while still making sure that everything from the foreground rocks to the horizon is in focus. I can set the lens to f/8, hold down the depth of field preview button, adjust the focus so that the horizon is just sharp, and then check the foreground to see if that's sharp. If it's not, then I can stop down to f/11 and try again (and again to f/16 or f/22, if necessary). This sounds a bit time-consuming, but with a bit of practice it's very easy, and I can usually do this in 30 seconds or less.
@abirkill Do you have a post from the past where you discuss using the DOF preview button? I still find that most of the time I can't see well enough inside the view finder to be able to tell, even after my eye adjusts to the light. Any tips on that? I'm sure live view would help as well.
The depth of field preview button is functional and will correctly show the actual depth of field of the image through the optical viewfinder, but the combination of the relatively small image in the viewfinder, even on a full-frame camera, combined with the darkness when a significant stop-down is done, means that I don't find it much use in that way, either. (Of course, back in the film days this was the only way to do this, so it certainly can be useful)
The darkness is, of course, caused by the aperture closing down -- when looking through an optical viewfinder without holding the depth of field preview button you are looking through the lens when it is wide open, regardless of the aperture the photograph will be taken with -- the lens will only be stopped down when the photo is taken. However, when you hold down the DOF preview button, the lens is stopped down there and then. If you have an f/2.8 lens and hold down the DOF preview button with the camera set to f/16, the viewfinder image will suddenly be only 1/32 the brightness!
For these reasons I pretty much exclusively combine the DOF preview button with Live View, which will automatically keep the exposure the same so the only change is the increased depth of field (and possibly a little more noise in the Live View image in low light conditions). Because you can also zoom into any area in live view, I find this a lot more useful.
As @frankhymus says, on mirrorless cameras with electronic viewfinders, both the rear screen and viewfinder are fed from the live view data, so you don't have to worry about the viewfinder dimming in these cases. Indeed, I think that Sony NEX mirrorless cameras will, by default, automatically stop down the lens and show the final image's depth of field whenever the shutter release is half-depressed, negating the need for a separate button.
Thanks everyone for all the responses. Alexis- your tip is exactly what Im looking for- just a reference to get me started so I dont screw up the shot every time. I find that when Im shooting groups of people (and not posed groups of people) and I want someone slightly behind in focus, I always manage to screw it up. As mentioned earlier though, I tend to shoot from fairly close, closing that range so I never seemed to go far enough with my f-stop. According to what I looked up last night it would have to be around 16 to keep someone in focus.
Im going to try your trick and see how it works for me. I havent ever used the DOF button because I never noticed a difference, didnt think to use it with live view. Thank you!