Diffraction. When does it really matter with LF?

[Mark Sawyer]

But it isn't affected by focal length. Effective aperture, a dimensionless number, is what matters.

That makes sense. But the diffraction limits calculators I've seen go by f/stops, not actual aperture size. And of course, f/stop dimensions change with focal length, as that's the "f" in "f/stop".

[Dan Fromm]

focal length/entrance pupil is dimensionless.

[Kirk Gittings]

Only you can choose between slight diffraction and lack of depth of field. Me? I'll take diffraction!

I was giving a talk many years ago with Mark Citret, out in CA somewhere on architectural photography (Not commercial but more art/personal AP), maybe it was at the VC Conference in Carmel. We both repeatedly referred to the aperture in many of our 4x5 exposures as f/32. After the talk someone came up to us, somewhat aghast, saying that the diffraction would ruin our images as if at an aperture smaller than f/22 there was some cliff of unacceptable unsharpness you fell off of. Believe your experience. Try it out and see what works for you and your type of imagery.

I really like what Bruce said "Everything in LF is a trade off. If you open up too far you have shallow DOF. If you stop down too far you soften the image through diffraction. Etc.

The bottom line as you'll find eventually,
is to artfully walk all the trade offs."

nice.

[Drew Wiley]

Gosh. It's been a couple decades since I've bumped into to Mark. Some well-known 4x5 landscape photographers routinely use f/32 because it provides enough depth to generally make up for film sag or flatness issues in the holder, yet the amount of diffraction is still barely noticeable even in really big enlargements. Wide angle or shorter focal length lenses tend to be affected by diffraction a little sooner, but their images are also affected more by any lens to film distance deviation; so for all practical purposes, it's a wash. And it's too nonsensically complicated to figure out on the fly every hypothetically ideal this or that. If one is a scientific photographer and working with truly flat glass plates in a lab, that might be a different story.

[Serge S]

And the tools shape the artist as well as the art..

Yes!

"We shape our tools and thereafter our tools shape us."
Marshall McLuhan

[Alan Klein]

Gosh. It's been a couple decades since I've bumped into to Mark. Some well-known 4x5 landscape photographers routinely use f/32 because it provides enough depth to generally make up for film sag or flatness issues in the holder, yet the amount of diffraction is still barely noticeable even in really big enlargements. Wide angle or shorter focal length lenses tend to be affected by diffraction a little sooner, but their images are also affected more by any lens to film distance deviation; so for all practical purposes, it's a wash. And it's too nonsensically complicated to figure out on the fly every hypothetically ideal this or that. If one is a scientific photographer and working with truly flat glass plates in a lab, that might be a different story.

As you know I recently started shooting LF. Mainly I've been shooting medium format 6x7 landscape. My general practice with MF was to calculate the DOF range using the DOF scale on the lens or a handy chart. Then stop down one additional stop for good measure. I used to enlarge (commercially) to 16x20". If there was diffraction, I didn't notice probably because I didn't know what I'd be looking for. But everything was in focus most of the time that I wanted to be in focus.

So now that I've taken up LF I read that f22 is a good f stop to work with. Every shot I took this year has been at f22. Of course, with tilts, the whole formula I had been using with MF is probably thrown out the door. So how do people decide the best f stops on the fly. I know there are some special LF tables you can look up. But the whole process seems too arcane and I'm having enough trouble focusing and seeing things upside down to figure out a better stop other than f/22.

Anyone with simple suggestions?

[Bernice Loui]

Chronic f22 syndrome. Did this back in the mid 1980's at the beginning of learning how to use a view camera (4x5). This came about from reading about how view camera lenses were optimized at f22 (Rodenstock Sironar N, Schneider Super Angulon at that time). It was a struggle to learn how to view the upside down and backwards image on the dim (perception from that time) ground glass image. This brought about a variety of viewing aids from reflex viewers to fresnel lenses to different brands of ground glass. Struggled desperately with trying to figure out how camera movements work and what they did. By default, it was compose, focus best guess-possible, apply cameras movements with mixed confusion if it helped or made the image worst, stop the lens down to f22 or so and ... accept what happened.

At some point, the opportunity to use a Sinar P in studio happened with a VERY experienced photographer. This experience plus LOTs of Polaroid film and LOTs of film burned taught me the value of Polaroid proofing (Ha!) and the value of a camera with precision as a teaching tool. The other skill that must be learned and acquired is how to view the ground glass without viewing aids. This takes time to learn and develop. As eyes age, this compounds the problem. While there are times when trying to achieve every item in the image to be in apparent focus means stopping the lens down lots, there are often times when this is excessive. It is driven by items in the image and image composition and the ability-skill of the image maker to apply camera movements as needed to achieve overall focus. This does mean evaluating the image with the lens stopped down to taking aperture and camera movements (as needed, if used) applied. This is why the preference for no fresnel lens as the grooves work hard against this, a camera with precision of camera movements and stability, a 7x ground glass loupe with a GOOD dark cloth. Much of this is about blocking out ambient light then allowing your eyes to adjust to the available light on the GG.

Growing out of the chronic f22 habit can be a good thing.


Bernice

As you know I recently started shooting LF. Mainly I've been shooting medium format 6x7 landscape. My general practice with MF was to calculate the DOF range using the DOF scale on the lens or a handy chart. Then stop down one additional stop for good measure. I used to enlarge (commercially) to 16x20". If there was diffraction, I didn't notice probably because I didn't know what I'd be looking for. But everything was in focus most of the time that I wanted to be in focus.

So now that I've taken up LF I read that f22 is a good f stop to work with. Every shot I took this year has been at f22. Of course, with tilts, the whole formula I had been using with MF is probably thrown out the door. So how do people decide the best f stops on the fly. I know there are some special LF tables you can look up. But the whole process seems too arcane and I'm having enough trouble focusing and seeing things upside down to figure out a better stop other than f/22.

Anyone with simple suggestions?

[Vaughn]

I never thought of f22 as a magic number...now f64, that's a different beastie! Early on, my images usually required the DoF generated by f64 and I did not know about diffraction issues...ignorance was bliss.

Alan, you might benefit from some strong reading glasses -- ones that can get your face within a foot of the GG so you can study the entire image under the darkcloth. I remember the time I pulled my head out from underneath the darkcloth and for an instant, thought the rest of the world was upside down...neat. I started using a Rolleiflex, I guess since everything was backwards, I got use to everything being upside down with the 4x5 quickly.

[Alan Klein]

Chronic f22 syndrome. Did this back in the mid 1980's at the beginning of learning how to use a view camera (4x5). This came about from reading about how view camera lenses were optimized at f22 (Rodenstock Sironar N, Schneider Super Angulon at that time). It was a struggle to learn how to view the upside down and backwards image on the dim (perception from that time) ground glass image. This brought about a variety of viewing aids from reflex viewers to fresnel lenses to different brands of ground glass. Struggled desperately with trying to figure out how camera movements work and what they did. By default, it was compose, focus best guess-possible, apply cameras movements with mixed confusion if it helped or made the image worst, stop the lens down to f22 or so and ... accept what happened.

At some point, the opportunity to use a Sinar P in studio happened with a VERY experienced photographer. This experience plus LOTs of Polaroid film and LOTs of film burned taught me the value of Polaroid proofing (Ha!) and the value of a camera with precision as a teaching tool. The other skill that must be learned and acquired is how to view the ground glass without viewing aids. This takes time to learn and develop. As eyes age, this compounds the problem. While there are times when trying to achieve every item in the image to be in apparent focus means stopping the lens down lots, there are often times when this is excessive. It is driven by items in the image and image composition and the ability-skill of the image maker to apply camera movements as needed to achieve overall focus. This does mean evaluating the image with the lens stopped down to taking aperture and camera movements (as needed, if used) applied. This is why the preference for no fresnel lens as the grooves work hard against this, a camera with precision of camera movements and stability, a 7x ground glass loupe with a GOOD dark cloth. Much of this is about blocking out ambient light then allowing your eyes to adjust to the available light on the GG.

Growing out of the chronic f22 habit can be a good thing.


Bernice

Well it's nice that someone else suffered through the same things I'm suffering through now. At least I don't feel like a dope.

Maybe I'll remove the fresnel from my Chamonix 45H-1 if I can focus better and easier. How does a GG without the fresnel work better? How do you approach focusing without the fresnel vs. with it?

[Bob Salomon]

Well it's nice that someone else suffered through the same things I'm suffering through now. At least I don't feel like a dope.

Maybe I'll remove the fresnel from my Chamonix 45H-1 if I can focus better and easier. How does a GG without the fresnel work better? How do you approach focusing without the fresnel vs. with it?

It doesn’t. The fresnel does 2 things. One it evens the light spread across the gg diminishing the fall off across the gg and secondly it brightens the gg image.