SCHNEIDER SYMMAR-S 240MM QUESTION. PLEASE HELP!!!

[Apple]

Hi Leon,

You've dragged this one up from the archives!

Correct me if I'm wrong, but I don't see why you need to set hyperfocal distance if you've got the ability to perform movements with the camera. Even with hyperfocal distance settings on "fixed" cameras, not everything will be sharp - technically there's only one point actually sharp in a photograph - the distance at which the lens is focused - the rest varies in "acceptable" sharpness. Hyperfocal sets the focus / aperture to give the best option and gives you a better chance of people not noticing that something isn't sharp - it's how much you can get away with!

With movements, you can play with planes of focus and depth of field to put more or less in acceptable focus - the method Joanna mentions above is probably the easiest if you want to keep the perspective "natural" by using the front standard for the tilt / swing (works on either or both.) If you want the perspective to be altered, use the rear standard for the swings / tilts.

I have heard of hyperfocal distance on LF cameras but I guess it would involve a fair amount of measuring bellows extensions, tables and pretty decent distance reckoning to get the settings. Using movements is done by eye for most people. Certain cameras, e.g. Sinar etc have full asymmetric movements which can speed up the process.

Andrew

[Emmanuel Bigler]

Hello from France, Léon

If I may add 0,02 continental euros to this discussion, I would start by suggesting that
you should not be afraid of stopping down any lens beyond what is supposed-to-be reasonable.
After all, LF photography in 2007 in itself is something definitely eccentric. So let's be a little bit more eccentric than others

For sure you can, and definitely should, use tilts to benefit from all the advantages of the view camera, but one of the joys of LF photography is also to experiment.

Using tilts at a wider aperture will deliver superior sharpness.. if your subject is properly located in a wedge-shaped portion of landscape.
If your subject is "tunnel-shaped" like this advertising image for a famous cheese cellar in Franche-Comté,
http://www.tourisme-metabief.com/photo. ... &width=200
Scheimpflug and slanted planes are useless. The only thing that you can do in this situation is to stop down if you want to increase depth of field. And eventually suffer from diffraction, but then you'll get an image where smoothness will be homogeneous from the foreground to the background, this might be more pleasant than an image with a severly blurred foreground and a sharp background.

You'll note that this image is perfectly unacceptable since verticals are converging. Digital phtotographers have really no excuse since they can easily correct converging verticals by post-processing... But cheese aficionados do not care for that

There is an article in French by Jean-Marie Solichon about what happens when you stop down too much, and how an image, potentially degraded by diffraction, will look.

http://www.galerie-photo.com/diffraction.html

You'll see in the article how miracles can be obtained by post-processing using a digital sharpening tool. Yes, the uncompromising LF photographer will definitely object, but this is another option for those who prefer to spend hours and hours in front of a computer to minutes adjusting the controls in the field

If fact for a lens like the 240mm Symmar-S, the manufacturer probably recommends f/22 or f/32 as the best f-stop.
I have no idea about which exact criterium or combination of criteria are used by manufacturers to define the best aperture, but my understanding is that it is a compromise between sharpness and coverage.
At the widest aperture, coverage and sharpness are not the best, but you have the best brightness to help you properly focusing.
When stopping down, sharpness increases first at the centre of the image, stopping down further makes the image more homogeneous from the centre to the corners without noticeable sharpness progress at the centre, and beyond a certain point, say F/32-F/45, there is no longer any progress in coverage and a visible degradation due to diffraction appears. This is easily visible between f/16 and f/45 in J.M. Solichon's article.

Certainly, depth of field continues to increase when stopping down past the best aperture, but since the image becomes less sharp and affected by diffraction usual formulae based on pure diffraction-free geometrical optics are, strictly sepaking, no longer valid.

If we stop down to, say, an improbable f/128, the image sharpness will be limited by diffraction effects to a resolution around 128 microns, it means that if you demand 100 microns as your limit of accpetable sharpness (the diameter of the circle of confusion in DOF calculators) you come to the conclusion that no point of the object field can be projected to a spot smaller than 128 microns, hence no point of the object field is acceptably sharp, depth of field in this condition is... nil, and not at all "infinite" as you could think if you know what people say about pinhole images !

So, Léon, feel free to stop down to the mechanical limits of you iris and see what happens.
Beware however that the precision on the f-number will probably be not very good at those very small apertures. However you can try and check with a spotmeter aiming at the ground glass how the intensity of light varies when you stop down beyond what is engraved. You should verify that each click or step of one f-number moves the spotmeter reading accordingly ; so you can easily extrapolate beyond what is engraved.

This spotmeter procedure is discussed in this recent thread on the Northern-American LF forum. (sorry for a self-citation

http://www.largeformatphotography.info/ ... hp?t=32332

In the thread, I suggest a geometrical method to determine the actual f-number on a lens without aperture scale, but the spotmeter-on-ground-glass method seems to work fine and is worth testing first.