Diffraction?

Sirius Glass · Dec 16, 2014

Lens manufacturers design lenses with the smallest aperture possible without suffering from significant diffraction degradation. There are diffraction effects at every aperture, and these effects increase as the aperture decrease in size. At the next smaller aperture than the lens is built with the diffraction starts to dominate, hence that aperture is not available to be used.

The sweet spots for 35mm lenses is f/8 to f/11, for medium format f/11 to f/16 and for 4"x5" f/16 to f/32.

LJH · Dec 17, 2014

Sirius Glass said:
Lens manufacturers design lenses with the smallest aperture possible without suffering from significant diffraction degradation.

I'm not convinced that this is true.

In terms of LF lenses, how do they know what format the lens is to be used on? For example, a 14" lens will have different (visual) diffraction character on 4x5 compared to 8x10.

Sirius Glass · Dec 17, 2014

LJH said:
I'm not convinced that this is true.

In terms of LF lenses, how do they know what format the lens is to be used on? For example, a 14" lens will have different (visual) diffraction character on 4x5 compared to 8x10.

That is accounted for in what I posted. I learned this from studying and using optics to build space borne optical instruments.

LJH · Dec 17, 2014

Sirius Glass said:
That is accounted for in what I posted. I learned this from studying and using optics to build space borne optical instruments.

Where? I didn't see format mentioned, only the blanket statement.

A 355mm G Claron will stop down to f90 (barrel). This will be usable for 11x14", but possibly not for 4x5. Which format did Schneider design this for?

Dan Fromm · Dec 17, 2014

LJH said:
For example, a 14" lens will have different (visual) diffraction character on 4x5 compared to 8x10.

Stuff and nonsense.

Jim Jones · Dec 17, 2014

Most small format lenses can be stopped down to where diffraction certainly does limit visual sharpness in large prints. However, even the diffraction in my Micro-Nikkor at f/32 is acceptable with some subjects in smaller print sizes, while f/11 is noticeably less sharp than f/8 with other subjects in larger prints. Harold Merklinger has written extensively and lucidly on the subject. Links to some of this information are available at http://www.trenholm.org/hmmerk/HMArtls.html.

Sirius Glass · Dec 17, 2014

LJH said:
For example, a 14" lens will have different (visual) diffraction character on 4x5 compared to 8x10.

Dan Fromm said:

Stuff and nonsense.

Click to expand...

I am with Dan on this.

DREW WILEY · Dec 17, 2014

You can't change the laws of optical physics. This is not like a vote in congress. Diffraction is a fact. And in general, it's impossible to make
a truly sharp 16x20 print from 35mm film, due to the sheer degree of enlargement. Whether the effects of diffraction are critical to you or
not depends a lot on subject matter and personal printing style, and what your final expectations are. I sometimes make 30x40 Fuji Supergloss prints from 8x10 film, and even with that modest degree of enlargement, or even with 20x24's, I can easily detect the effect of
unduly small f-stops. Not everybody is as nitpicky as I am... but if you do have the ability to make truly sharp prints, viewers will indeed put there noses right up to them to study the detail. I've had people study a big print of a large meadow of wildflowers, for example, and suddenly spot a mosquito sitting on one of the flower petals out there, fully in focus. I don't believe in that "normal viewing distance" nonsense.

LJH · Dec 17, 2014

Sirius Glass said:
I am with Dan on this.

Insomuch as you both make unsubstantiated statements?

Dan Fromm · Dec 17, 2014

LJH said:
Insomuch as you both make unsubstantiated statements?

Cropping changes nothing in the image. Now do you understand why your unsubstantiated statement is wrong?

Sirius Glass · Dec 17, 2014

LJH said:
Insomuch as you both make unsubstantiated statements?

No it is well documented on books on optical engineering and lens design. See Kingleslake for examples. Also Modern Optical Engineering by Warren Smith. Optics Eugene Hecht. Try doing your homework in advance instead of shooting from the hip sonny.

E. von Hoegh · Dec 17, 2014

Diffraction takes place in the enlarger, too. Use the grain focusser and watch that nice crisp grain turn to mush as you go past f:8 or so.

Sirius Glass · Dec 17, 2014

E. von Hoegh said:
Diffraction takes place in the enlarger, too. Use the grain focusser and watch that nice crisp grain turn to mush as you go past f:8 or so.

Good point. If one buys the top quality camera lenses then they should top quality enlarger lenses.

DREW WILEY · Dec 17, 2014

There's no right or wrong to any of this, aesthetically. But diffraction is a genuine optical issue which should be taken into account just like any other tool or choice we make in our workflow. At it is relative to the focal length and design of the lens. So you can't just go around making blanket statement about stopping down two stops or whatever. Robots make lousy photographers unless they're designed to do just one thing well, like making printed circuits. And you might buy any number of optical textbooks and complicated app programs to tell you
what to do, while I'd prefer simply to look at the groundglass and see if image is the way I like it or not, without all the fuss.

E. von Hoegh · Dec 17, 2014

Sirius Glass said:
Good point. If one buys the top quality camera lenses then they should top quality enlarger lenses.

But, diffraction is dependent on the aperture you choose and the reproduction ratio you're using the lens at - be it a magnifying glass or the best lens available. Use that enlarging lens at the widest practical aperture and within the ratios it was designed for; if you need time to d&b put a dimmer bulb in.

SchwinnParamount · Dec 17, 2014

Lacking a dimmer bulb, do you suppose a neutral density filter or two would be Ok?

Dan Fromm · Dec 17, 2014

SchwinnParamount said:
Lacking a dimmer bulb, do you suppose a neutral density filter or two would be Ok?

Shorter exposure will do the job too.

David Allen · Dec 17, 2014

I know the theory but do not have much truck with it in real world usage. I have worked with 10 x 8 transparencies, X-rays, Ultra violet, infra-red, etc (at the National Gallery of Great Britain), 21mm wide angle on a Leica, 38 Biogon on a Hasselblad SWC, 65mm on a Mamiya 7, 90mm Super Angulon XL on a 5 x 4" and a 'bog standard' Angulon on 5 x 7" not to mention tne Ektar 210mm stopped all the way down on 10 x 8". I have never experienced a situation where the desired Depth of Field resulted in a loss of a significant or image degrading critical sharpness because of diffraction.

I believe that it is only an issue for those analogue equivalents of pixel peepers . I make all my photographs with a Mamiya 7 and 65mm lens using apertures f11 plus. My images are very sharp and meet my requirements for how the image should look. Maybe someone with a lupe could see something wrong but, come on, is that how you want to view images?

So no, I have never had a problem with Diffraction. Depth of Field with required sharpness from front to back is much more important to my image making than any 'technical' considerations about Diffraction. I think these 'clearly based in objective science' questions should simply be answered by the idea of 'look at my photograph, does it have sufficient levels of detail and sharpness to make the image work?"

I do accept that Bayer sensors are more sensitive to the problem but, F**k them they have to live with their choice of using a digital medium.

Bests,

David.
www.dsallen.de

Dan Fromm · Dec 17, 2014

David, in closeup (up to 1:1) work and photomacrography (above 1:1) diffraction is a killer. See:

Gibson, H. Lou. Close-Up Photography and Photomacrography. 1970. Publication N-16. Eastman Kodak Co. Rochester, NY. 98+95+6 pp. The two sections were published separately as Kodak Publications N-12A and N-12B respectively. Republished in 1977 with changes and without the 6 page analytic supplement, which was published separately as Kodak Publication N-15. 1977 edition is ISBN 0-87985-206-2.

for examples of loss of depth of field on stopping down.

It is real and is not an issue that only pixel peepers and grain sniffers care about.

David Allen · Dec 17, 2014

OK Fine - as everyone who has seen my posts I am not driven by technical theory. I assert that my photos are sharp enough for my purposes and are, keeping with what I want to convey, absolutely what I want. What else does one need?

David.
www.dsallen.de

Sirius Glass · Dec 17, 2014

David Allen said:
OK Fine - as everyone who has seen my posts I am not driven by technical theory. I assert that my photos are sharp enough for my purposes and are, keeping with what I want to convey, absolutely what I want. What else does one need?

David.
www.dsallen.de

Nicely said. I certainly do not worry about diffraction.

DREW WILEY · Dec 17, 2014

We all set our own standards, and even so, might handle different kinds of subject matter itself differently in this respect. If you're getting the
look you want in your images, that's all that counts.

M Carter · Dec 17, 2014

Sheesh folks - theory, arguments, and general "I've always heard". It's a damn rabbit hole.

If you're concerned, test your own gear.

Get a focus chart or setup a still life. (I usually just grab a software box, it's got various sizes of print and stands up all by itself). Stick post-it notes on with the aperture noted.

If you have a DSLR your lens will function on, shoot a properly exposed shot at every aperture. Hell, do halves or thirds. You'll know in approximately 7 minutes where the sweet spot of any given lens is.

Or shoot a roll of film, develop it, and do some prints. Go to town, use 5x7 paper and enlarge the daylights out of the same area on each neg. Grab a 10X loupe.

I have a blast in the darkroom, but much of my rent is paid shooting digital stills and footage. I have a pretty solid idea of where my lenses are at their best (and how neutral my neutral densities are and how diffuse my diffusion is and what color temp my daylight fixtures **really** are and what my gels really do) because it's really easy to test this stuff, especially if you have a DSLR handy.

No offense to the OP, but I'm amazed at questions that get asked that have a zillion possible answers (due to specific gear and workflow and preference) when it's possible to remove all the mystery in a matter of minutes (or a couple hours) and in most cases, learn a thing or two in the process.

TEST TEST TEST!!! OK, offa my soapbox now!

SchwinnParamount · Dec 17, 2014

M Carter, where do you get software boxes? Didn't those go out with CDs? We're all about downloading software today. Maybe you meant you were grabbing a soapbox (which you can still find in abundance at the grocery store)

M Carter · Dec 18, 2014

I still seem to have a stack of 'em on a bookshelf... maybe it's because Adobe Cloud pisses me off regularly?

Diffraction?

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