Film flatness of a Sinar Zoom II holder? Can't get sharp images wide open?

[joshdaskew]

Hi, I currently own a Chamonix 45N-1 and was one of the first people on here to report problems I was having with this camera with getting in focus images while shooting with the Schneider Xenotar 135mm 3.5 wide open. So as everyone here probably already knows, this was deemed to be due to the fresnel being on the lens side of the groundglass and therefore, somewhat acting as a lens itself and causing a focus shift. I have had since had a Maxwell screen put in ( the latest one that is almost halfway between the bright and the super bright ) and am very happy with (apart from the extremely cut corners but that is in my next thread) and have also had the camera back aligned by Bill Moretz at pro camera to ensure it is spot on. Further tests with the camera and my new Maxwell screen came back right on the money!! This was also being tested with my new 150mm 2.8 Xenotar which has even shallower D.O.F. I then bought a Shen Hao roll film back and after doing some tests wide open on the 150mm Xenotar, could not get a whole roll film consistantly in focus? This was shooting at a variety of distances from close up to mid range, long etc etc. Some were in focus and some werent. I came to the coclusion that the groove that was in the cameras back was not aligning with the groove in the film back. I finally sent it back and while i was in Japan had the chance to use a Horseman 67 back. Same test and the same result, some were in and some were out. I have since received my Sinar back and done the same thing and while the results have been a little better, basically the same thing, some are in and some are out..

My intention is mainly for portraits where you might want to be shooting wide open, am I expecting too much from roll film backs? Even if stopping down I would still like to know that what I am primarily focusing on is in focus! Any others had these problems? Any advice? I can get sharp images with my Pentax 67 at 2.4 and that is when objects are prone to movement, considering that these tests have all been static, then I don't see the issue and the fact that some are in and some are out (although always very close to being in focus) is reall confusing me..

Any thoughts, comments or advice would be greatly appreciated!

Best Regards Josh

[ic-racer]

I'd waste a frame and see if the film center is bulging from the pressureplate of the rollfilm back. Touch it with the tip of a pencil. If it indents then it was not firmly against the pressure plate. I suspect sometimes it bulges and sometimes not, just like in a medium format camera. If I want precise focus, I'll always try to use sheet film.

[rdenney]

I have a Vario (and also a Shen-Hao) and have made 6x12 images with both. Both were absolutely as sharp as I would have expected from sheet film. The Sinar is known for film flatness (the Calumet is not). The Vario is the previous model to the Zoom/Zoom2.

I would not assume it's the holder until you are sure that the holders are mounting in the camera properly, which seems to be an issue.

I focus mine using a Maxwell screen on a Sinar F with a 6x loupe. I installed the screen myself, but that was easy on that camera.

Rick "who would check to insure the holder is really seating properly" Denney

[tlitody]

two possibilities:

Firstly a zoom II is very thick and takes some pushing into the camera back. I don't know your camera, but if has any movements on the rear standard, then its possible the force of inserting the holder will shift the rear standard out of focus. I think cameras with fixed rear standards are best for roll fim holders but it depends on how firmly they lock down.

Secondly, if you leave the film for any time, especially in warm weather, it can get a bulge in it from where it is rolled round the roller at the end of the holder. When you wind on the film that can can be in the image somewhere. So check what exactly is out of focus. Is it a vertical line through the image. And are the images that are out of focus just the ones where the film has been in the holder for a while without being wound on. Images taken quickly afterwards don't get that bulge set in the film. Same can happen with medium format cameras such as hasselblads.

[joshdaskew]

Hmmm, very interesting indeed... First of all, thanks for all the comments and advice, much appreciated! So, all the shots have been taken in the same session and I have been winding the film on before I have taken the next shot. So the actual time sitting there wouldn't be more than 10 minutes or so.. IC-Racer I will take your advice and waste a couple of frames and see if it is bulging at all but I think by memory from when I first inspected it that it was fine..

rdenney when you say that you have inspected your 612 images against 5 x 4 images I presume that you are talking about images that have been stopped down somewhat and therefore critical focus is not as important? Or have i got that wrong?

So my main reasoning for using a roll film back is to shoot wide open portraits at f2.8 or so and still have some ability for movements (and to have a cheaper option to coincide with shooting 5x4 portraits) Am I barking up the wrong tree or are you guys saying that it is possible i would miss a couple of frames shooting wide open portraits with a medium format body (was thinking the Pentax 67 with the 105mm 2.4)?

Will shoot a few more test shots and see if i can get some more consistent results... Thanks once again for all your help and input. Best Regards Josh

[Oren Grad]

Secondly, if you leave the film for any time, especially in warm weather, it can get a bulge in it from where it is rolled round the roller at the end of the holder. When you wind on the film that can can be in the image somewhere.

In the Sinar rollholders the tight curve at the end of the holder comes after the film is exposed, not before.

[tlitody]

In the Sinar rollholders the tight curve at the end of the holder comes after the film is exposed, not before.

I remember it being the other way but I sold mine years ago so it could be my memory playing up.

[rdenney]

I remember it being the other way but I sold mine years ago so it could be my memory playing up.

No, Oren is right. The film feeds off the supply spool straight into the frame area, then around the roller at the end, across the back, and onto the take-up spool. But even that roller on the far end is as large in diameter as a full roll, as opposed to the narrow rollers in, say, a Hasselblad back.

Rick "thinking the Sinar only suffers from being a bit fiddly" Denney

[rdenney]

rdenney when you say that you have inspected your 612 images against 5 x 4 images I presume that you are talking about images that have been stopped down somewhat and therefore critical focus is not as important? Or have i got that wrong?

Here is an example where I didn't stop down all that much. There was enough of a breeze that I needed to keep the exposure down to a second or so. Aperture was f/16 on a 121mm Schneider Super Angulon. That's probably about as wide open as it gets for landscape photography. I used tilts and swings to get three points on the main branches in perfect focus. The leaves along the left edge were also in focus.



Even with smaller apertures, however, depth of field doesn't make the image as sharp as the plane of focus, it just makes it acceptably sharp.

This situation above isn't as shallow as when one is using selective focus with a long, fast lens. But scanned at 4000 spi in my Nikon scanner, or viewed on the light table with a 10x loupe, it's easy enough to see the difference between the focus plane and what isn't in the focus plane.

This image was made using the Shen-Hao holder:



The lens was a 47mm Super Angulon. The depth of focus at the film plane is so narrow with the short lens that any ripples in the film would be visible. This one has no such issues. The parts of the cannon in perfect focus are sharp even viewed at actual pixels after scanning at 4000 spi.

The issue of the weight of the Sinar holder is one I would not have considered, because my Sinar camera is more than solid enough to support it. I don't have experience with cameras designed primarily to be light and portable, but I wonder if the Sinar Zoom holder fulfills a requirement to be light and compact. For that, the Shen-Hao is actually pretty good.

Rick "confident in this piece of kit" Denney

[tlitody]

Well that still leaves the possibility of the back moving on the track when you insert the holder.