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prvivozac
23-Jul-2008, 01:45
HEllo everyone,

I work on exhibition, so I borrowed Sinar P from a friend. but, it has some focusing problem: it focuses on some different plane - for example, I focus on a three, and then develop a film, and the house 15 meters behind will be on focus, not a three. The fosuc mistake is so strong that aperture f22 or f32 doesn't help. Lens is Sironar 150/5.6, in perfect condition, and focus mistake is so big you see everything on film. I was on service and guy put it on kalimator, and it was same mistake.
Only place the mistake can be is focusing screen, it must be out of focus. But everything seems normal! I'm frustrated and searching here for help, because I have no other place to search for.
P.S. there's no problem in film holder, I tried on 10 of them.

Thanks a lot
Prvi Vozac

David A. Goldfarb
23-Jul-2008, 05:30
Is the focusing screen backward? The ground side of the glass should be toward the lens.

Is there a fresnel lens installed? On a Sinar back, the groundglass is usually between the fresnel and the lens, but I don't know that this is the case with all Sinar backs. I think I had one once where the fresnel was under the groundglass, but I don't know if it came that way from Sinar, or if the back was adjusted to be used that way, but it focused properly. If the fresnel is in the wrong position, then the groundglass will be out of register with the film plane.

Jan Nieuwenhuysen
23-Jul-2008, 12:45
The first thing I would suspect is a focus shift caused by the rear carrier of the camera not being locked properly before installing the film holder.
In other words: you may inadvertently move the back carrier with the focussing screen attached to it slightly forwards when you put in the film holder under the focusing screen. This is not an uncommon mistake.

If you are sure this is not the cause of the problem I suggest you ask your friend if he has the ground glass replaced or added a bossscreen recently or a fresnell lens, or something...
I would then think that the focussing screen is not in the right position. If things further away from the camera then your subject (like the house behind the tree) are in focus instead the subject that means the bellows are actually extended not far enough for proper focus on your subject. This would indicate the groundglass is placed a bit too far from the lens in relation to the proper plane of focus.

prvivozac
23-Jul-2008, 13:51
Is the focusing screen backward? The ground side of the glass should be toward the lens.

Is there a fresnel lens installed? On a Sinar back, the groundglass is usually between the fresnel and the lens, but I don't know that this is the case with all Sinar backs. I think I had one once where the fresnel was under the groundglass, but I don't know if it came that way from Sinar, or if the back was adjusted to be used that way, but it focused properly. If the fresnel is in the wrong position, then the groundglass will be out of register with the film plane.


matted side of the glass was toward back, and the service guy told me it should be toward the lens, so we turned it. But kalimator shew it was out of focus.
focusing back looks same as on this picure(form the internet, not mine, but the same position of the glass).http://img360.imageshack.us/my.php?image=backwg9.jpg After this I didn't make test, will tomorrow.
Fresnel lens isn't toward thel lens, it is on the back, it goes in the hole arrows is showing. I didn't make test without fressnel too. I'll do it without fresnel. tomorrow will make shots an then I'll see.
thanks goldfarb!

prvivozac
23-Jul-2008, 14:07
The first thing I would suspect is a focus shift caused by the rear carrier of the camera not being locked properly before installing the film holder.
In other words: you may inadvertently move the back carrier with the focussing screen attached to it slightly forwards when you put in the film holder under the focusing screen. This is not an uncommon mistake.

If you are sure this is not the cause of the problem I suggest you ask your friend if he has the ground glass replaced or added a bossscreen recently or a fresnell lens, or something...
I would then think that the focussing screen is not in the right position. If things further away from the camera then your subject (like the house behind the tree) are in focus instead the subject that means the bellows are actually extended not far enough for proper focus on your subject. This would indicate the groundglass is placed a bit too far from the lens in relation to the proper plane of focus.


Locker I checked every time, and was carefully looking for a smallest possible movement of the standard/back during insetring of the film holder.
THe friend's friend broke the gorund glass and replaced it with other of Sinar, I checked it many times, but everything seems OK, it looks identically as on this picture.

Focusing screen is definitely (if I'm not crazy) in right position, on milimeter.
I tested the camera first when I was making tests of film - I was making shots of rough textured wall, on tripod, 1/60sec, f16-32. most of 7 shots look very similarly unfocused, with little difference. It was about 1,5 from the camera.
second test I made on the little hill in front of my house, three was on 15 meters and house on 40m.
Third test I made was on 1-2 meters. I focused on thing 1 meter from camera, and then thing on 1,5 was sharp. Then I purposely put f5.6 too clearly see mistake. Some shots wasnt so blury but none was sharp.

Now I was measuring eventually difference in distance of ground glass and film in the holder, and it is the same! on milimeter, everything seems OK. I thougt that there's some mistake in the glass holder, but there isn't.

Oh... tomorrow I'll notify what tests show. Tell me if you have some smart to tell ;-) please, and thanks on your answers!
ciao
Prvi Vozac

Bjorn Nilsson
25-Jul-2008, 11:59
If you still are having problems, it could be of use to know how much the focus is off, and in which direction. For this you must shoot at f/5.6.
Set up a clinical (read boring) shot of a measure tape or similar. Place the start of the tape at the filmplane (or if it's more practical, at exactly 1 meter in front of the filmplane. Now focus at a given measurement on the measure tape. (For example 1 meter.) You will see exactly where the focus falls.
In one of your tests so far seem to say that the film will be sharp at 1.5 meters when you focused on 1 meter which sounds like a lot of error, but anyhow you can measure the difference on the camera (from the front to the back standart) when focusing on these two points respectively. The difference in bellows draw between the two setups (1 meter and 1.5 meter respectively) is around 12-13 millimeters, so something is definitely very wrong. (If there was something wrong with the ground glass, the error could be maybe 1-3 millimeters.)
I also find it very strange that a Sinar P could have such a great error. That is, you have to check what you are doing. Are you putting the film cassettes in the camera in a correct way? (Please don't be offended by us asking "obvious" questions. We just need to know in order to help you.)

//Björn

Peter De Smidt
25-Jul-2008, 19:52
The matte side of the ground glass should be towards the lens. (I've used Sinar Ps since about 1992.) If that leads to improper focus, then there's a seating problem. Either the ground glass is not set right in the frame, or the film holder isn't set correctly in the back. The proper areas are machined metal, and it seems unlikely that there could be such an error without obvious damage.

prvivozac
26-Jul-2008, 01:23
Thanks a lot everyone. It was mat glass. I turned it, moved the fresnel, and made the test. on one meter, f5.6, perfect sharpness. But, I don't understand how it was such a big mistake, things wasn't lot sharper at f22? And the glass is 3mm thin.

thanks a lot, sorry if I bother you with such a small problem. But, I'm very happy I solved it.

Ciao
Prvi Vozac