Focus accuracy issue with Intrepid 8x10

[Sam L]

My friend and I set up some studio lighting and shot 12 portraits of each other using my Intrepid 8x10 and a schneider 360mm f/6.8 lens wide open on Fuji HR-U x-ray film.

We did our best to level the camera and make sure the standards were parallel. We carefully focused on the eye lashes with a loupe. The photos are good but they are uniformly slightly front focused -- the eyebrows are sharp instead of the eyelashes.



I would think the model moved a half inch or there was focusing error except it affected 11 of the 12 photos in the same way. Two photographers, 3 different brands of film holders, 12 shots over 2 hours, refocusing after every other photo.

Thoughts?

[Ari]

I, too, always had a consistency problem when calibrating focus, so I bought this and it's worked out great: https://www.bhphotovideo.com/c/produ...tion_tool.html
No more guesswork or other variables.

[Sam L]

That looks like a useful tool. Can you calibrate the focus on one of these cameras? I assume you would move the ground glass resting position a bit, perhaps by shimming it?

[Bob Salomon]

Wide open is one of your problems. You should be at least 2 stops down. Best performance would be at 22.

[Kiwi7475]

Wide open is one of your problems. You should be at least 2 stops down. Best performance would be at 22.

Errrr…. For portraiture a lot of people shoot wide open. Maximum sharpness is not the goal. And it’s sharp enough, just not where they focused.

[Kiwi7475]

Do you change aperture after focusing? Some lenses do suffer a shift when stepping up or down, like Imagons, etc

[Sam L]

Indeed, I was going for shallow DOF on just the eyes. No change in aperture between focusing and shooting. But good to know about focus shift on some lenses.

I'm going to do a more controlled test with newspaper text taped flat to a at 45 degrees to the camera to eliminate the moving subject issue.

[Tin Can]

I try to focus on the closest eyeball highlight

I also made a rig for a head brace that is out of sightline, very often used by wet plate artists

[Sam L]

Tin Can, do you have a picture of your head brace?

[Bernice Loui]

Check the accuracy/precision of the ground glass location to film holder back plate with film thickness. This dimension is crucial to hold what is focused on the ground glass to be recorded on film. If the ground glass location is different (ideally in 0.0X inches or better) than where the film sits in the film holder this out of focus behavior will be the result.
https://www.largeformatphotography.i...f-ground-glass

This aspect of any view camera becomes critical as lens apertures become large. Too many rely on "stopping" down the lens to gain apparent focus to make up for lack of accuracy/precision in the camera and lens mounting.

Given this is a modern Plasmat lens, focus shift will be nil.

As for portrait sitter moving, not likely given the number of missed focused images.


Bernice