Film holder tests

[Damon Kocherhans]

I read the article by Jack East in PhotoTechniques (May/June 1999) recently beca use I have noticed that my black and white negs have been unacceptably sharp. I used the Kodak Readyload series 3 holder for the negs in question. So I did wh at the article suggested. I took a ruler and set it across opposite corners and slid a toothpick down the ruler till it just touched the groundglass and held t he toothpick in place with a clamp. When I put piece of film in the Readyload and put it in the camera and checked it with the toothpick, the toothpick wouldn 't reach the film, and not by a little. The toothpick was 1/16 of an inch or mo re from the film. Can this be true? That seems like a lot or error. Am I doin g the test wrong? The camera I am using is the Arca-Swiss Discovery. Could I h ave a faulty back? This is very frustrating.

[Wayne_6692]

Were you holding the pack horizontal or vertical?

[Walter Glover]

Hi Damon,

At the outset let me say that I went down the Readyload route and trashed it ? film plane position is just ONE of its problems.

The earlier response posted regarding orientation is valid but on top of that there is another consideration: Arca-Swiss make great kit and it is highly unlikely that you have a faulty back .... however, Arca-Swiss place the fresnel in front of, rather than behind, the ground-glass. That is, in terms of you veiwing from behind the camera. Where this gets complicated is that the ground surface of the viewing screen is inaccessible and further more there is possibly an allowance made for the refractive index of the fresnel. I had similar problems years back with a Boss Screen.

If your 'Discovery' doesn't have a fresnell fitted then try a comaprison with regular double darks (try a few and find an average, they'll all be different.)

Cheers .... Walter Glover

[Don Wong]

Damon:

I wonder if a field test might settle your doubts about focus accuracy, since final results on film are all you really care about, not a test that might involve any number of variables (such as where the matte surface of the groundglass is, or what the Fresnel might be doing to throw off your focus.

Focus a subject on the groundglass and shoot a number of sheets with a long lens wide open, using Kodak film in your Kodak holder. However, on successive shots, refocus the rear standard by 1/16 inch away from the plane of sharp visual focus.

Keep good notes on how each sheet was focused, and when you examine the sheets, the one that's the sharpest will tell you where your focus plane is.

Just a thought.

[Robert A. Zeichner]

I think you should read the other current post on film holder measurement and then try to get your hands on an article I authored for ViewCamera back in Nov./Dec. 1996 that deals with film testing your camera's ground glass alignment. I know Jack East and he is a talented photographer and a nice guy, but I just don't buy toothpicks, rulers and clamps for making any kind of meaningful measurements of tolerances in the +/- thousandths of an inch realm. Not only are those the wrong tools for the job, but the test procedure fails to take into consideration, the overall "flexibility" of the holder and the fact that depth needs to be referenced to the entire perimeter of the holder's frame, not just two points that you arbitrarily select to lay your ruler across. I look forward to hearing the results of the other poster's test results with his mil. spec. gauge set up. Had I those resources, this is the kind of tool set I would have built to do this testing.