# Thread: Length, width and diagonal measurements for exposed windows of various film holders?

1. ## Length, width and diagonal measurements for exposed windows of various film holders?

I am looking to better define what the exposed diagonal for various film formats, with the aim of creating an accurate representation of what the image circle demand for various lenses would need to be. I am guessing the best way to determine this is to actually measure the exposed film area for various film holders across various formats? Alternatively, is there an accepted margin for various formats that has been referenced elsewhere?

2. ## Re: Length, width and diagonal measurements for exposed windows of various film holde

It makes more sense to use the overall dimensions of the film, since
image quality drops off near the edges of the image circle.

Also, the image circle changes with different aperture settings.

- Leigh

3. ## Re: Length, width and diagonal measurements for exposed windows of various film holde

Your post should propagate some interesting responses on this FORUM. My solution has been to shoot a standard scene which includes some elements approaching "infinity" using a larger format than the lens will be used for. Then make a contact print and from that print determine the optic's useful coverage. Some of my vintage wide angle lenses project an enormous image but only the central part has enough sharpness to be useable, and other lenses (usually telephoto optics) project an image that the sharpness cuts off abruptly relative to the image they project. Of course this works for only the film formats that I make contact prints from. For the 4x5 format which I enlarge the negatives, shoot a whole plate negative and judge the sharpness of the image on a lightbox with a magnifier. I have one extreme wide angle optic that I use on my 11x14 that its sharpness is majorly degraded in the corners of the 11x14 format but I am totally able to subjectively live with it in the contact prints that I make... Objectively (sharpness wise), I would nave not judged it to cover the 11x14 format. Something to consider is the coverage diagonal: Do you determine it from the full size of the film negative, corner to corner, or from only the central image portion of the negative that you print from?

4. ## Re: Length, width and diagonal measurements for exposed windows of various film holde

I have a fidelity deluxe 4x5 holder in my hands...
the window is 4 3/4" x 3 15/16", diag is 6 1/8"

hope that helps

5. ## Re: Length, width and diagonal measurements for exposed windows of various film holde

This link may help: https://www.largeformatphotography.i...der+dimensions. Go to post #20.

6. ## Re: Length, width and diagonal measurements for exposed windows of various film holde

Originally Posted by l2oBiN
I am looking to better define what the exposed diagonal for various film formats, with the aim of creating an accurate representation of what the image circle demand for various lenses would need to be. I am guessing the best way to determine this is to actually measure the exposed film area for various film holders across various formats? Alternatively, is there an accepted margin for various formats that has been referenced elsewhere?
4x5: 153.7mm
5x7: 208.7mm
8x10:312.5mm

Don't think that image circles of lenses are amazingly well defined, the illumination circle is larger than the manufacturer's specified image circle. It's not clear what criterions manufacturers used to say the image circle, at some off-axis distance the image qualty has degradated enough for the manufacturer to say what the image circle is, and of course the image circle grows depending on aperture and on bellows extension...

...but IMHO many times nobody would complain if the manufacturer had specified 6mm (3mm per corner) more or less for the image circle, so being the circle specification that "elastic" IMHO it's not worth investigating if the different holders clip 1mm less or more on the sheet...

7. ## Re: Length, width and diagonal measurements for exposed windows of various film holde

For every format there are minor variations - a few millimeters or fractions of a millimeter - in the format diagonal that arise from variations in the film holders made by different manufacturers or at different times. If you are trying to figure out *exactly* what you can get away with, you will need to reference a specific holder. If you are just trying to get a reasonable general guide for each format, with a very small safety margin built in, you don't need to catalog holder variations in each size - just use the diagonal of the nominal sheet size. If you want to be really finicky you can subtract 2.25 mm from the calculated diagonal for larger sizes or 1.12 mm for smaller ones to account for the nominal amount by which cut sheets are supposed to be smaller than plates.

8. ## Re: Length, width and diagonal measurements for exposed windows of various film holde

When you measure, you have to figure out if you incorporate useful image in the gaps for the film slots near the flap-end. That increases your diagonal measurement. I assume I'll overlap the projected image on the easel blades a few millimeters when I calculate lens coverage and angle of view.

Those "In the American West" images of Avadon looked great printed full-frame. But in my own work (that is almost never on a white background devoid of detail) there are too many potential irregularities near the film edge, so I crop it out on the baseboard.

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