Diffraction limits for wide angle lenses?

[joshdaskew]

Hi, I am using a Chamonix 45N-1 and lenses that range from a 65mm Nikon to a 300mm Nikon. I have read in a few posts that diffraction of lenses often kicks in at around f22 or so. For most purposes, this aperture gives me a sharp image and enough depth of field to render the scene sharp from front to back (without really worrying about movements). For lenses on the wide end (I have Nikon 65mm f4 and a Schneider Super Angulon f8) can I effectively shoot more wide open (say f16 or f11) and still obtain sharp depth of field from front to back? Does diffraction start at a more wide open aperture with these lenses? Or is diffraction a common thing that is standard amongst all lenses, provided the format is consistent? I am mainly shooting architecture with these wide angle lenses.

Sorry, I am not sure if that is really phrased well. Thanks for any information, would be greatly appreciated! Best Regards Josh

[Jack Dahlgren]

The longer the focal length the smaller the optimal working aperture. So I'd be more comfortable using f/16 on a 90mm than I would on a 300mm, but "optimum" depends on more than just sharpness and depth of field. Wind or subject movement combined with lighting conditions may dictate a different aperture. And sometimes you do not want the maximum amount of sharpness.

[carverlux]

Hi, I am using a Chamonix 45N-1 and lenses that range from a 65mm Nikon to a 300mm Nikon. I have read in a few posts that diffraction of lenses often kicks in at around f22 or so. For most purposes, this aperture gives me a sharp image and enough depth of field to render the scene sharp from front to back (without really worrying about movements). For lenses on the wide end (I have Nikon 65mm f4 and a Schneider Super Angulon f8) can I effectively shoot more wide open (say f16 or f11) and still obtain sharp depth of field from front to back? Does diffraction start at a more wide open aperture with these lenses? Or is diffraction a common thing that is standard amongst all lenses, provided the format is consistent? I am mainly shooting architecture with these wide angle lenses.

Sorry, I am not sure if that is really phrased well. Thanks for any information, would be greatly appreciated! Best Regards Josh

Josh,

You may find Bob Atkins' calculator handy not only in determining the Diffraction Limit for any lens but its inextricable relationship with Depth of Field and Circle of Confusion. Here it is: http://www.bobatkins.com/photography...ield_calc.html. I am sure you will find a few AHA! moments once you spend some time with it.

Enjoy!
Carver

[Brian Ellis]

Unless you're making really large prints - maybe something in the 30x40 range - diffraction isn't a major problem with prints from 4x5 negatives. I wouldn't worry about it. It's usually more important to get the depth of field you need, even if that involves f64 or smaller, than to lose needed depth of field for the sake of whatever minor effect diffraction will likely have on your print.

There's also another lens aberration the name of which escapes me that increases as the aperture becomes larger (sorry I can't remember the name but I'm sure one of the optical experts here will know). So while photographing at a larger aperture may decrease diffraction it increases this other aberration. Thus there's a trade-off in finding the optimum aperture in a given situation, which is why some people (me included) put a mm scale on their cameras, measure the distance the lens travels when focusing on the near and far, set the lens (or back, if focusing with the back) midway in between, etc. etc., a topic beyond the scope of your question.

It's easy enough to see the effects of diffraction for yourself. Just make two negatives of the same scene with one or more of your lenses, one negative at say f16 or f22 and another at say f64. Make prints from them at different sizes. See whether there's a size at which the effects of diffraction bother you. If so, that's the diffraction limit for that lens at that print size.

[rdenney]

For lenses on the wide end (I have Nikon 65mm f4 and a Schneider Super Angulon f8) can I effectively shoot more wide open (say f16 or f11) and still obtain sharp depth of field from front to back? Does diffraction start at a more wide open aperture with these lenses? Or is diffraction a common thing that is standard amongst all lenses, provided the format is consistent?

Depth of field is a function of focal length and magnification, and whether a given aperture provides enough depends on the scene at hand. DOFMaster, which assumes an 8x10 print as the standard, calculates a depth of field from a little over 6 feet to infinity when focused at about 12 feet, using a 65mm lens on 4x5. If you print to 16x20 and expect the same close scrutiny, the depth of field ranges from 25 feet to infinity when focused at 50 feet.

At f/22, the depth of field increases to about 12.5 feet to infinity when focused at 25 feet, using the tougher 16x20 print-size standard.

That should give you an idea.

Take a look at DOFMaster.com, but remember that it is based on a standard 8x10 print, which is too small and too forgiving for most large-format applications.

Regarding diffraction, it has some effect at all apertures, and the issue is whether the effect of diffraction becomes a constraint. But I would say that, in general, don't worry about it. Insufficient depth of field will cause a lot more blurriness than diffraction, even at f/45. I have certainly made images at f/45, and printed them large with good sharpness, using 90mm lenses on 4x5. So, use the largest aperture that provides the depth of field you need, as viewed with a strong loupe on the ground glass, and don't worry about diffraction.

Remember also that the movements make it possible to adjust the focus plane, which can help you get the things you want in focus without depending on depth of field to do so. Depth of field describes the distance in front of and behind the focus plane that will appear to be sharp given a stated standard of sharpness. The focus plane will be sharp no matter what, even if you tilt it using camera movements. You'll be limited by the coverage of your lenses somewhat, but it doesn't take much tilt at short focal lengths to have a big effect.

Here's an example, made with a 121mm f/8 Super Angulon:



The lens was tilted to the right very strongly to get the window opening at right into the focus plane along with the tower. The left side was outside the depth of field, but that was not a problem for me. The aperture was f/45, and the image is plenty sharp.

Rick "for whom diffraction is what it is" Denney

[timparkin]

Does diffraction start at a more wide open aperture with these lenses?

No... diffraction is a constant regardless of aperture

If you use f/22, you can get a typical enlargement of 9x for typical circles of confusion..

If you use f/64 you can get a typical enlargement of 3.2x

So, yes, diffraction still has a large effect for 4x5 ...

However, like a previous poster has mentioned, it's always a trade off. Only stuff on the focal plane can be enlarged 9x at f/22 - if something is out of focus, it's out of focus regardless of diffraction..

Tim

p.s. - great page on this very site - http://www.largeformatphotography.info/fstop.html

[Lynn Jones]

Josh,

Stop paying attention to "psuedo science" and deal with reality. Realistically, good quality lenses will start to significantly soften with an aperture of about 2mm. We don't care about focal length or anything else.

Lynn

[timparkin]

Josh,

Stop paying attention to "psuedo science" and deal with reality. Realistically, good quality lenses will start to significantly soften with an aperture of about 2mm. We don't care about focal length or anything else.

Lynn

So for a Canon G1 at a focal length of 6.1mm, f/6 s on the edge of diffraction but on a Schneider 1000XL, f/500 is well within diffraction limits...

You'll have to excuse me if I don't agree with this..

[Emmanuel BIGLER]

For lenses on the wide end (I have Nikon 65mm f4 and a Schneider Super Angulon f8) can I effectively shoot more wide open (say f16 or f11) and still obtain sharp depth of field from front to back?

Hello !
Each of your excellent wide-angle lenses probably has a best f-stop as recommended by the manufacturer.
For the Schneider Super Angulon f-8, I assume a 75 or 90mm, the best f-stop is probably 22.
If you shoot at f/11 or f/16, you may get a slightly sharper image at the centre, du to slightly less difraction, but this will be very hard to notice, you'll loose some sharpness an probably some light in the corners. So it is a trade-off between coverage and sharpness at the centre, you have to somewhat sacrifice the centre in order to get the full coverage (about 100° for the f/8 "old" SA series).
I have seen pictures taken with a 90mm f/8 super angulon on 6x9, at f/11 those images are as sharp as you might dream of, but cropped by the 6x9 (56x82 mm) format you do not use the corners.

Regarding shorter focal lengths like the 65, it is a general rule that the recommended f-stop is wider, e.g. 11 or 16 when focal lenghts are shorter. However for their 65mm grandagon N Rodenstock still recommend 16-22 ; check for the 65mm Nikon, for example here the general spreadsheet quotes the image circle @f/16, which is probably the best f-stop.
http://www.largeformatphotography.in...s/LF4x5in.html
For the shorter Rodentock apo-grandagon series (35, 45, 55) the recommended f-stop is 8-11, not 22.

[Chauncey Walden]

Lynn's saying that diffraction becomes serious at a 2mm aperture goes along with something I heard years ago called the "Rule of 4" (which is just a rule of thumb, of course.) That is you will be happiest if you limit your minimum f/stop to the focal length divided by 4, which also goes along with what Emmanuel was saying about the shorter focal lengths. So, 4mm not too bad, 2mm bad at least as far as large format lenses are concerned.