5x4 - How to measure film /plate register ?

I have a 5x4 MPP Microtechnical camera Mk. VI. I'd like advice on how to
measure the register, or more specifically between which points should the
measurements be taken. Data on the MPP user's club website states 0.2"
(5.08mm) for my model. My measurements using a checked digital caliper
(averages of very many readings) suggest 5.23mm for the ground glass
assembly, and 5.31mm average over 6 DDS with film holders.
Many thanks for any insight.
--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

Malcolm Stewart wrote:
I have a 5x4 MPP Microtechnical camera Mk. VI. I'd like advice on how to
measure the register, or more specifically between which points should the
measurements be taken. Data on the MPP user's club website states 0.2"
(5.08mm) for my model. My measurements using a checked digital caliper
(averages of very many readings) suggest 5.23mm for the ground glass
assembly, and 5.31mm average over 6 DDS with film holders.
Many thanks for any insight.

I'm not familiar with your camera, but I think you would be better off
testing photgraphically. Focus on a target with the lens axis making a
45 degree angle with the target. Some people use rulers, but I've
found that anything with a lot of detail will work. I use a newspaper
taped to a vertical wall. I place the camera about 10 times the focal
length away from the lens and make sure it is level. You focus as best
you can with a high power loupe, e.g. 7 to 10 X. You then make an
exposure. You repeat the process several times, and develop the film
and examine it under high magnification.

You will almost certainly find that you are some distance off from where
you intended to focus. Measure that distance in the target (not on the
film) and take 70 percent of it to account for the 45 degree angle.
Take the resulting quantity and multiply it by the square of the
magnification, and that will give you the amount the gg and film planes
differ. The magnification is the ratio of image size to subject size.
It can be calculated by taking the distance from the lens to the
target, dividing by the focal length, subtracting one, and finally
taking the reciprocal of that. If the subject is 10 times the focal
length from the lens, the magnification is 1/9.

You should do these calculations for each exposure you made and take the
average.

For comparison sake, note that if you are using an f/5.6 lens, and you
normally look at the gg with a 7 X loupe for focusing, you would expect
not to be able to focus better than about 0.2-0.3 mm along the rail or
camera bed. With a lower power loupe, it would be proportionately
larger. You seem to have found that you are off by about 0.08 mm, which
seems a small fractions of the normal focusing error when using the camera.

"Leonard Evens" wrote in message
...
snipped

For comparison sake, note that if you are using an f/5.6 lens, and you
normally look at the gg with a 7 X loupe for focusing, you would expect
not to be able to focus better than about 0.2-0.3 mm along the rail or
camera bed. With a lower power loupe, it would be proportionately
larger. You seem to have found that you are off by about 0.08 mm, which
seems a small fractions of the normal focusing error when using the
camera.

Thanks for your suggestions, and "Yes" - I can correct that by packing out
the ground glass.
However, I am still somewhat surprised by the difference between my
measurements and those quoted in a variety of places for this model.

--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

"Malcolm Stewart"
wrote in message ...
I have a 5x4 MPP Microtechnical camera Mk. VI. I'd like
advice on how to
measure the register, or more specifically between which
points should the
measurements be taken. Data on the MPP user's club
website states 0.2"
(5.08mm) for my model. My measurements using a checked
digital caliper
(averages of very many readings) suggest 5.23mm for the
ground glass
assembly, and 5.31mm average over 6 DDS with film holders.
Many thanks for any insight.
--
M Stewart
Milton Keynes, UK
http://www.megalith.freeserve.co.uk/oddimage.htm

I think you are asking if the distance of the ground
glass matches that of the lens.
If you can remove the back of the camera its easy.
Measure the depth to the ground glass from some convenient
referece point, insert a film holder with film in it and
measure again.
The standard distance for the film from the edge of the
holder for common sizes is:

ANSI Standards for film plane placement in sheet film
cameras.
Size Location Tolerance + or -

4x5 0.197 0.007

5x7 0.228 0.010

8x10 0.260 0.016

Dimensions in inches.
Film thickness is 0.007 The above does not include
film thickness.
Smaller formats than 4x5 are the same as for 4x5.

You can check the holders by laying a flat plate across
them and using a depth micrometer to measure the distance.
Remember to subtract the thickness of the plate.
0.190 will be the distance from the reference surface for
the film holders to the ground glass.
If you can remove the ground glass panel you can measure
this directly. Most spring backs hold the film holders at
the corners, you will be able to tell by looking. Meauring
from this point to the ground side of the GG will tell you
if its in the right place.
Its important to check the holders because they cam
become warped or the centers can get displaced.



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Richard Knoppow
Los Angeles, CA, USA