Checking Lens-Film Plane Adjustment

R

ruben

Guest
Tomorrow I would like to check the camera lens at infinity, taping something to the film plane, plus magnifier glass to examine the image.

a) Is this the correct proceeding ?

b) What something would be best ? (So Far I am thinking about paper, but I am afraid of the curling).

c) The best magnifier I can think of is a 50mm lens, or an enlarger lens. Is this Ok or not enough magnification ?

d) Anything else ?

Thanks,
Ruben
 
A piece of ground glass is traditional. Almost anything will work as long as it doesn't bow either in or out. In fact, even a thread will work. All you need is something flat and on the film plane to form the image on. If it is too opaque then the image will be dim and difficult to work with. If too clear, you won't get much of an image either.

Do you have tracing paper or kitchen parchment? That might be the best household item to try.

A 50mm lens turned backward (looking through the front element) will give you sufficient magnification. 4x magnification is sufficient to make sure you are in focus... so almost anything will work.
 
Hi Ruben,

I usually use two cameras: the camera to be checked with a ground glass in the film plane, and some pen marks on the ground glass. On a tripod with the lens facing the lens of another camera (an SLR, in my case an OM) with a
lens that I know well and set at infinity (like a 50/1.4 or 85/2). Then I
look through the OM to see if I can see the marks
on the ground glass of the other camera.

Roland.
 
I had a piece of ground glass cut from a larger one to fit the film plane. This is the most accurate method since it is flat and won't curl like paper will plus a good quality 10-15x loupe.
 
Ruben
The ground glass needs to ride on the inner rails, not the outer.
Noel
3M pressure sensitive matt tape is the most convenient.
 
Mike

Almost all cameras will have a mechanism to control the position of the lens mount relative to the film plane. And with a SLR the position of the mirror and the screen relative to the lens mount.

leitz said if you have a noctilux you might need to have the body sent back for registration...

Noel
 
Two questions,

a) what is a ground glass ? Do you mean a flat clear glass or what ? It is an English shorcomming.

b) None of you have mentioned, and perhaps my memory is faulting me, to tape an SLR focusing screen. If this works too, I have several, and could enjoy the microprism center focusing of the screen. But if this is OK I don't now if the mat textured side should face me or the camera lens.

Thanks, so far a lot of contributions!

Ruben

MIKE, with the permission of Xmas I will put it in other words: Your rangefinder, set for infinity, is showing at the viewfinder perfect coincidence between patch and image, but who says that your lens are also aligned at infinity? That's the tricky side of RFs against SLRs.
 
Ruben
Ground glass is just like a SLR focus screen, indeed some SLR plain screens may be ground glass, most will be plastic.
if you want to make your own you need a microscope slide or glass from a slide mount, and auto valve grinding paste, only grind one side, the ground side is placed between the inner film rails.
3m matt tape is just like ground glass.
Please point Mike at the Kiev survivial site.
The lens and the body both needed to be adjusted to the factory registration to allow interchangable lenses to work.
I dont mind you changing my English Ruben. I probably do have a spare for you...
Noel
 
Xmas said:
.....I probably do have a spare for you...
Noel
Click to expand...

A spare ground glass ?

But what about an Olympus OM focusing screen ? I do have several of them in my closet
 
Ruben
No a variable resistor track for a Kiev.

If you use an oly screen you will damage it thay are soft plastic.
Noel
 
Xmas said:
Ruben


If you use an oly screen you will damage it thay are soft plastic.
Noel
Click to expand...

Thanks god among my OM screens I have an already damaged one (broken at one of the corners). But I understand from you that the screen will be as good as a ground glass.
Now, the matt textured side of the screen should face the camera lens or me when looking at it ?

Thanks Noel,
Ruben
 
The matt surface is at the flm plane so that it scatters the image so you can see its position along the axis of the lans system.

A point image in front of the film plane will reach the glass as an out of focus circle.

noel
 
Xmas said:
The matt surface is at the flm plane so that it scatters the image so you can see its position along the axis of the lans system.

A point image in front of the film plane will reach the glass as an out of focus circle.

noel
Click to expand...

I believe that translates as "the matt textured side of the screen should face the camera lens."

:)

The matt surface has to be where the (front of the) film would be.

colin
 
Hi Ruben,

After responding to your initial post, and seeing the types of Qs & As following, might I make a suggestion: if you are questioning the accuracy of your cameras focussing, shoot some slide film at known distances. Slide film will give you a "first generation" image. Then check the film with your loupe (or psuedo-loupe) for focus. An alternative is to shoot negative film and develop-only; look at the negative with the loupe.

If it is a decent camera to begin with you can assume that the film lays reasonably flat at the film plane. Using this method you will not only have your answer, but proof to go with it.

Brian
 
BrianShaw said:
Hi Ruben,

After responding to your initial post, and seeing the types of Qs & As following, might I make a suggestion: if you are questioning the accuracy of your cameras focussing, shoot some slide film at known distances. Slide film will give you a "first generation" image. Then check the film with your loupe (or psuedo-loupe) for focus. An alternative is to shoot negative film and develop-only; look at the negative with the loupe.

If it is a decent camera to begin with you can assume that the film lays reasonably flat at the film plane. Using this method you will not only have your answer, but proof to go with it.

Brian
Click to expand...


Brian,
Thank you indeed for addressing the issues. I just would say I have a lot of oldies, and only lately I catched that viewfinder alignment is not equal to lens ajdusment to film plane, therefore I may be passing though a small counscience crisis. But provided the SLR focusing screen is OK, that't enough for me. In case you question the focusing screen method, then alert me by all means.
BTW the focusing screens hava a micro prism for further accuracy and a "line alignment" within the microprism collar. The only question being if the whole proceeding is OK.

What do you say ?
Cheers,
Ruben

PS
Slide trials are difficult for me, as I have to go to a lab, and due to my location it is a bit annoying.


PS-2,
I don't know why no one here is shouting Yes, use the focusing screen! Until I obtained a shy approval from Noel I felt I had to take him to a torture chamber.
Nor you are jumping of happines about it, and I wonder what is going on.
 
Last edited by a moderator:
Hi Ruben,

If you can get the SLR Focusing screen to lay flat on the film rails, it will work just fine. Give it a try... if it doesn't work to your satisfaction all you'll be out is a little time. Also try taping some tracing or parchment paper to the rails.

If you have more time, look into rigging up the Rick Oleson collimator in the previous post.

Let us know how it works out!

Brian

p.s. I thought Jeruselum had all of the modern conveniences... how far is the lab?
 
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