I've been playing with long nighttime exposures for a while now and I'm starting to wonder how I can avoid the starburst streetlamp look. Now, I know that this is caused by Fraunhofer diffraction at the aperture blades and there's little I can do about that directly.
However, it occurs to me that if I had a lens that didn't have blades and instead had a fixed, round aperture, then I'd not get the starburst spikes. (IIRC - and it's been a long time since University THB so I'm a bit fuzzy on the optics involved - I'd see halos instead? Which could be a nice change ;)
Now I have a little lensbaby which has drop in aperture rings - which are round - so I can try this out... a bit. Problem is I'm pretty sure that a little toy lens isn't going be anything like sharp. And I'd really prefer sharp.
Which brings me to my question: Are there any fixed, round aperture primes out there?
Fairly wide would be good, somewhere around 15-25mm? At f11-ish? Also it's be nice if it had, or could be adapted to, a K mount (so that's pretty much anything but Canon then). Manual'd be fine.
My guess is that there isn't, but you never know... Or, of course, there may be another way of solving this that I've not thought of...?
I'm not sure there are any for SLR type lenses - never come accross one in all my years of buying/selling/collecting camera stuff (a few of my older TLR and Box cameras do use something similar)
The other thing would be to make (well adapt) a lens.
Obvious choice would be the Industar 50/2 - as it is better than many modern lenses, is very simple to take apart, and can be got for £10/$15 on a good day on ebay.
(indeed, it has a firm place as the number 2 lens in my bag)
A few details/sample pics I threw up on another forum, for those that dont know it.
I recon you could fashion something internally by way of a fixed aperture - and at a price roughly that of a sandwich and a cup of coffee - it's worth a play.
Surely you'll only get the starburst effect with the lens stopped-down, though? At maximum aperture the iris is close enough to circular for this effect to disappear. This will be at the expense of DOF though.
@styru Thanks - I had a feeling it would come down to a cut and shut. I'll investigate that lens :)
@smalbon Maybe, dunno. There are still points where the blades overlap - even with rounded blades - so the effect may still be present, albeit less pronounced. I'd have to experiment, I guess.
Also I'd need to mess about with ND filters to get the exposure times as high as I'd like... and, well, I want to keep the DoF. :)
Lens baby would certainly be out I believe- they are brilliant if you like blurry type pictures ( http://www.flickr.com/photos/calanais/2158763594/in/photostream for example is taken with the smallest ring.). I have one and love it.. but beauty in the eye of beholder.
Matthew got it right. The only fixed aperture lenses I ever heard of are mirror lenses, they're usually f8. There's a couple of tamron, sigma or tokina ones from the 1980s which will be reasonable and are K mount, and you will get nice donuts or rings like Matt said, however, they will be 300mm, and 500mm. Look into lenses a bit though there are a ton of different kinds and you might just need to buy one from pre 1980 or something. And a wide open lens like Stephen said, below F2 you might still get patterning, but if you get the SMC 50mm pentax f1.4 I bet you don't.
@intymalcolm@chewyteeth I routinely use a Nikkor AF 50mm f/1.8D on my D300 and that's got to be stopped-down to at least f/8 before "sunstars" start appearing strongly, it has a 7-bladed diaphragm so there's 14 points. There's an 85mm version which has 9 blades.
I do have a vague recollection of seeing some old, vintage possibly, lenses that had diaphragms with a much greater number of strongly curved, heavily overlapping blades such that the aperture was a good approximation to circular at all stops.
@calanais@chewyteeth Not sure about mirror 'lenses', they tend to be far, far too long for the tasks I have in mind for them. Also, I know the bokeh would be doughnut shaped (and possibly a bit distracting) but that's a caused by a different optical phenomenon... not sure the long exposure diffraction would do the same, would it?
As it goes, I've got an old manual Tokina 28mm f2.8 that looks like it'll come apart easy enough. 28mm at f10/11 is, what, a 2.5/3mm aperture - I'll see if I can fit a small washer inside it somehow, I think :)
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The other thing would be to make (well adapt) a lens.
Obvious choice would be the Industar 50/2 - as it is better than many modern lenses, is very simple to take apart, and can be got for £10/$15 on a good day on ebay.
(indeed, it has a firm place as the number 2 lens in my bag)
A few details/sample pics I threw up on another forum, for those that dont know it.
My Industar
I recon you could fashion something internally by way of a fixed aperture - and at a price roughly that of a sandwich and a cup of coffee - it's worth a play.
...............................
>>Feeling Blue - my 365
@smalbon Maybe, dunno. There are still points where the blades overlap - even with rounded blades - so the effect may still be present, albeit less pronounced. I'd have to experiment, I guess.
Also I'd need to mess about with ND filters to get the exposure times as high as I'd like... and, well, I want to keep the DoF. :)
Lens baby would certainly be out I believe- they are brilliant if you like blurry type pictures ( http://www.flickr.com/photos/calanais/2158763594/in/photostream for example is taken with the smallest ring.). I have one and love it.. but beauty in the eye of beholder.
I do have a vague recollection of seeing some old, vintage possibly, lenses that had diaphragms with a much greater number of strongly curved, heavily overlapping blades such that the aperture was a good approximation to circular at all stops.
@calanais @chewyteeth Not sure about mirror 'lenses', they tend to be far, far too long for the tasks I have in mind for them. Also, I know the bokeh would be doughnut shaped (and possibly a bit distracting) but that's a caused by a different optical phenomenon... not sure the long exposure diffraction would do the same, would it?
As it goes, I've got an old manual Tokina 28mm f2.8 that looks like it'll come apart easy enough. 28mm at f10/11 is, what, a 2.5/3mm aperture - I'll see if I can fit a small washer inside it somehow, I think :)