Minimum f-stop?

[Leigh]

Diffraction is one of those monsters that parents use to frighten their kids, like the headless horseman.

In any normal image diffraction effects are slight, though measurable, and indistinguishable from poor focus.

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To answer the OP...
Most of my lenses are f/5.6, and I typically shoot them at f/16 or f/22.
If the manufacturer states an optimum aperture, I use that value when possible, or adjacent settings.
I would not hesitate to go smaller if dictated by image considerations.

I shoot wide open if that setting produces the desired effect in the image.

- Leigh

[Vaughn]

Photographing in the dense redwood forests where camera movements have to be kept to a minimum and a deep requirement for DoF -- usually f64 or f90.

8x10 and 11x14. Contact printed.

[Bernice Loui]

This is a question of what the image maker wants in the image to be in focus.

One of the great advantages of a view camera is the ability to alter and change the plane of focus which is a very powerful tool in the image making process.

When I first began using a 4x5 the typical rule was to stop down to f16 or f22 to "optimize" the lens and get everything in the image in focus (actually apparent focus). After many thousands sheets of film past. Using both aperture and camera movement evolved to a wonderful selective focus tool. This also drove my preferences in optics in ways I never imagined.

Initially all my lenses were the latest modern multi coated on the market. In time most of them were passed on to new owners and the optics became a mix of vintage, and modern.

I do use vintage optics wide open and stopped down to not more than f32.. almost as a rule. I have tried the smaller than f45 routine and did not like the reduction of image quality. This was one of factors why I stopped using 8x10 film. I do believe 8x10 and larger makes wonderful contact prints (my 8x10 days with AZO paper) and this can reduces some of the requirements on optics.

If the image requirements were "everything in the image sharp" modern lenses stopped down to f22 or so with 5-7 bladed iris shutters would be fine, but once one develops a taste and need for highly selective focus, preferences for out of focus rendition, tonality and all those other qualities in the image, the expectations of how a lens behaves at a given aperture does matters a lot.

There appears to be a fashion trend among digital and smaller format image makers to produce Bokeh based images where the points of light becomes out of focus shapes in the background. This is not new as film makers have done this for a long time and no reason why LF based images cannot use the same technique for similar effect.

I did post an image like this in another thread about Goerz lenses.. That color image was made at f16, at almost life size (1:1).
http://www.largeformatphotography.in...rz#post1008090


Bernice

[C. D. Keth]

Diffraction is one of those monsters that parents use to frighten their kids, like the headless horseman.

In any normal image diffraction effects are slight, though measurable, and indistinguishable from poor focus.
- Leigh

That's a good way to put it. I do pay attention to it and I don't shoot deeper on stop than I need to. That said, I'll come home with a slightly less sharp negative because I had to stop down further rather than come home empty handed. I won't avoid pictures because the setup will require a deep stop.

[Mark Sawyer]

Diffraction is one of those monsters that parents use to frighten their kids, like the headless horseman.

Pretty much what Leigh said... Apo-Ronars close down to f/256, and when I first got one for my 8x10 I just had to try it. Contact printing, the negative was still as sharp as the eye could resolve, and I'm sure it could have handled moderate enlargement well.

[IanG]

Pretty much what Leigh said... Apo-Ronars close down to f/256, and when I first got one for my 8x10 I just had to try it. Contact printing, the negative was still as sharp as the eye could resolve, and I'm sure it could have handled moderate enlargement well.

I have to agree with you and Leigh.

While I usually use f22 for 5c4 work I have used f32 quite a bit and f45 on the odd ocassion - some of my 5x4 lenses stop down to f64. It's so dependant on what the lens is, focal length etc taht there's no hard and fast rule. In practice it's usually fine to use up to 1 stop off the minimum aperture with no discernible loss of quality and even the last stop isn't bad. Many of my lenses stop down past the minimum aperture.

It's really about knowing your own lkenses and their capabilities.

Somewhere there's a breakdown of the apertures used by John Sexton and he goes past the f22 recommendation with stunning results/

Ian

[Lffbug]

Seems to me that you have the tail wagging the dog by asking what we use.

Fair enough statement, and some further clarification. One area that I am interested/curious about is portraiture. I'm curious about how large an aperture setting you use (i.e. lowest f-stop value) and successfully get good results.

Available light portraits would have painfully slow shutter speeds even with ISO 400 film, so I figure that's out except for extremely still subjects.

I have some low powered monolights, 150 w-s actual, but I figure that I can only get to about f/11 with 400 speed film. Forget 100 speed film, unless I shoot nearly wide open. I really don't want to buy higher power strobes, and would like to see what I can do with what I have. I supposed I could push the film, but that seems to go against the point of using studio lighting.

Probably I just need to try some things out, first. But I am curious how others deal with this (I know - buy a bigger light - but I am cheap, uh, frugal).

[ic-racer]

I read that LF photography is often performed at very small apertures.

You can (and should) read the much better information on selection of the aperture on this site's home page : http://www.largeformatphotography.info/fstop.html

[Bernice Loui]

This brings up an interesting bit of view camera and photographic history. The first common photographic lenses were single element or "landscape" lenses. They had less than ideal color correction, small effective f-numbers, a good number of lens aberration and limited field of view. When these single element lenses were used for portraiture along with the slow speed plates of the day, head clamps and sitting chairs were invented to deal with the long exposure times.

In time Jozef Petzval invented a lens with two groups corrected for color, spherical aberration with a wide enough aperture (effective f-stop) to reduce exposure time required for portraiture. This was a very significant advance for photography.

Eventually the Petzval evolved along with other lens designs like the Triplet and Dagor..

This is likely the origins of a portraiture style that lives on to this day.

As lens development proceeded, soft focus lenses and others were developed to meet the needs and demands of portrait and other photographic image makers.



Bernice

Fair enough statement, and some further clarification. One area that I am interested/curious about is portraiture. I'm curious about how large an aperture setting you use (i.e. lowest f-stop value) and successfully get good results.

Available light portraits would have painfully slow shutter speeds even with ISO 400 film, so I figure that's out except for extremely still subjects.

[paulr]

Diffraction is generally better than defocus blur, if you have to choose. If you're working with any digital steps, diffraction is much more amenable to reversal by sharpening. The slopes of the airy disk mimic the gaussian function of a standard unsharp mask fairly well. More advanced deconvolution sharpening algorithms, like those used in Lightroom and in Photoshop's Smart Sharpen, handle it even better. Defocus blur has a much more variable and complex point spread function, and so it's probably not going away.

Here are some charts that show actual MTF effects of diffraction, both in pure form, and when diffraction is combined with the MTF of a typical sensorand various degrees of defocus blur (COC stands for circle of confusion, if you haven't already guessed).








The short of it is that with circles of confusion greater that 10 microns (this is really small) there are only benefits to being stopped down to f22.

These are interesting especially if you consider that with low-noise images, detail rendered at 10% MTF should be completely recoverable (meaning, you can make it sharp). For film that's faster than ISO 100, I imagine you could recover most detail as low as 20% MTF. I'd like to find charts calculated for smaller apertures. From these we can extrapolate that at f32, MTF will drop below 20% somewhere around 35-40 lp/mm, which means that it will start irrecoverably eating detail in larger prints from 4x5.