Maximum sharpness

[ic-racer]

DOF depends on reproduction ratio.

...and the viewing distance...and the acceptable CoC size...and the aperture diameter...and the subject distance...and the amount of front tilt or swing...ad nauseam

[Joe O'Hara]

Wouldn't it be better to set the focus point at appr 1/3th away from the nearest distance instead of halfway?

Stefan

Stefan,

Nathan stated it correctly. What you need is a scale (like a mm ruler) on the camera bed and a marker next to it on the focus rail. Some cameras come with this, many field cameras don't. I made one for mine. Focus on the most distant object you want sharp. Note where the index is on the ruler (say, 36 mm). Then focus on the closest object you want sharp and note where the index is, say, 40 mm. Then set the focus bed in the middle of those two numbers, in this case, 38mm. Then stop down. At some point the image will start to suffer from diffraction but if you're not enlarging it much it may not matter. In any case, this method finds the optimum place to put the focal plane.

The rule of "1/3 away from the nearest distance" is only strictly correct for one particular distance (I don't recall which). The above procedure works for all situations (when it can work; sometimes you have to give up and move the camera back, or make a different picture).

Nathan is also correct that there's nothing to be gained from movements here, because your subject is "3-dimensional"-- you can optimize either of the walls, the ceiling, or the floor, at the cost of making the opposite surface drastically worse.

[E. von Hoegh]

...and the viewing distance...and the acceptable CoC size...and the aperture diameter...and the subject distance...and the amount of front tilt or swing...ad nauseam

Which is why I included the caveat "all other things being equal". They rarely are. This scene is a good candidate for a smaller format, say 6x7. I don't know what the OP considers acceptable, or what he intends to do with the image.

[miesnert]

Thanks for all the responses. Very nice!

I am working on a series of images in which this image might be. If it will be in the series, the end product will be a large (120cm wide) analogue c-print.

[Leonard Evens]

Stefan,

The rule of "1/3 away from the nearest distance" is only strictly correct for one particular distance (I don't recall which).

It is important to distinguish distances along the rail from distances into the scene.

The one third rule refers to distances into the scene, not those along the rail. It works only when you are focusing at one third the hyperfocal distance from the lens.

In principle, you should always focus along the rail at the midpoint between where the near point and far point focus are along the rail. If you do that, the circles of confusion from the near point and far point will be equal. If you move the focus point nearer the near point on the rail, then you will be aiming for greater sharpness at the near point than at the far point. There may be circumstances in which you want to do that, but you shouldn't do it as a general rule.

[Nathan Potter]

Leonard, thanks for pointing that out. I use a TK 45 which has mm. markings along the rail so it simplifies establishing the near and far focus points and makes it easy to find the midpoint. Careful use of a loupe is essential.

This 1/3 near setting I need to look into to understand why that should be. Seems counter intuitive since the incoming ray bundles are all in a straight line so the acute angle on either side of the hyperfocal distance is equal. Of course it's zero on optical axis and gets progressively less acute as one moves away from the optical axis so this implies a non linearity across the FOV. Also that non linearity varies with the focal length of the lens. Dunno.

Nate Potter, Austin TX

[Doremus Scudder]

Which is why I included the caveat "all other things being equal". They rarely are. This scene is a good candidate for a smaller format, say 6x7. I don't know what the OP considers acceptable, or what he intends to do with the image.

Or simply use a wider lens and crop to achieve the desired image. Exactly the same as using a smaller format (assuming the lens quality is the same and film alignment comparable) and is a lot less to carry around.

Take a look here for a great system for determining your optimum f-stop: http://www.largeformatphotography.info/fstop.html

Best

Doremus

[Leigh]

a 6x9CM thats stopped down would yield a sharper neg in the center.

Not true at all.

By what mechanism does a lens know what film or sensor lies behind it?

For example, consider a Crown Graphic.
Take a photo on 4x5 film. Then install a 6x9 roll film holder and take a photo.

How will the 6x9 photo be sharper than the 4x5?

- Leigh

[E. von Hoegh]

Not true at all.

By what mechanism does a lens know what film or sensor lies behind it?

For example, consider a Crown Graphic.
Take a photo on 4x5 film. Then install a 6x9 roll film holder and take a photo.

How will the 6x9 photo be sharper than the 4x5?

- Leigh

If you put a 6x9 back on the camera and reframe so that (neglecting the change in aspect ratio) you are recording the same scene as you were with 4x5, the available DOF will be greater (all other things being equal, and if you have the room to move the camera back) and more of the scene will be acceptably sharp on the film.

[Leigh]

You didn't say anything about reframing.

We're talking about the image recorded on the film with the same lens at the same distance from the film.

- Leigh