Hi clayne. Thank you for pointing out this possibility. I don't reposition the camera body between focusing for the film plane and the viewing screen. During this testing I focus on exactly the same point in space on the object each time, so the scenario of focusing on two different cannon balls at different distances from the lens plane doesn't apply.
Originally Posted by clayne
Ignoring temporarily the fact that my results are inconsistent, there is clearly more to aligning two lenses than I understood and the fact that half the time I establish focal discrepancies at close, medium and far distances is motivating me to do more research.
Through searching, I am discovering that calibrating the focus of a TLR is not necessarily an easy job, well I mean it doesn't seem to be documented fully in one place (except I assume in my camera's service manual which I really need to purchase for about $35 on eBay - yet by the time it arrives I probably would have solved the problem !!).
Up until now I haven't worried about ensuring the taking lens focuses properly at infinity. (see here , here and here). Some posts also indicate the distance scale needs to be correctly aligned. I don't even use my distance scale. I'm learning about backsighting, collimation etc. etc.
Problem solved !
I think I've finally solved the problems causing a discrepancy between the viewing screen and film plane focus
The top of the lens plate needed to be tilted away from the body so that the plate had no gap between it and the retaining spring. Previously I was pushing it flat against the body with a spacer btwn the spring and the plate, that was the wrong direction. The height of the spacer plus adhesive (black tack) is 0.6mm.
I have confirmed that both lenses now focus together for distances of 0.6m, 3m and infinity.
Another way to give similar results would be to add another 0.6mm shim under the viewing lens. The current solution provides a tilt, while a lens shim would provide a planar offset. At least the solution I used also addresses my concurrent problem of the top retaining spring not touching the lens plate.
In response to Christiaan's suggestion to swap or remove the thicker shim, firstly it was not possible to swap them because they are keyed to fit each lens specifically using the position of the head of a very small screw. Secondly when I removed the 0.4mm shim from the viewing lens, it made the focus discrepancy worse. This is when I realised that I could fix the spring issue in the manner described above.
I thought I might have to adjust the focus of the front element of the taking lens at infinity with the distance scale set there too, but it now appears I don't have to.
I suspect that the repeatability issue I had (making it harder to diagnose the real problem) was that the tracing paper I was using for a lens plane viewing screen wasn't taut enough at times since I was manually arming the shutter and not winding on the tracing paper to both tighten it and arm the shutter. To solve that problem I went back to using the following screen in the film gate comprising perspex sheet with some translucent tape on the lens side (e.g. Scotch magic tape).
BTW speaking of non-flat film causing focus problems, check out the posts about film bulge here. (the word "bulge" should be highlighted)
Last edited by PeterB; 01-26-2012 at 05:49 AM. Click to view previous post history.
That makes me think that the lens panel is not plane parallel to the film plane. But if the adjustment works, I'd live with it.
I feel, therefore I photograph.
I finally received the repair manual for the C330f. It only has two sections relating to adjustment of the focus. The first ensures the Lens Guide is parallel to the film plane, the second ensures the bellows extends the same distance when focusing through the viewing screen or at the film plane.
I'm attemting to follow the first section. refer to the page 7 attached.
It isn't clear to me how to remove the focussing knobs or camera's side covers to adjust the guide plate at step 6-1.B.c and fig 18.
Can any C330f owners tell me how I can remove the knobs and side covers ? The service manual is light on details and doesn't even mention that.
BTW instead of using a Dial Gauge, I opted for two steel rulers (see . The horizontally fixed one has been levelled and held in place with a vice. I tried using some vernier calipers rather than a 2nd steel ruler but for some reason I wasn't getting sufficiently repeatable results.
I also need to fabricate a small raised block to place the camera on (marked F-1 in figure 17). I think F-1 rests on the film rails. When the camera's door is open, the rear external edges of the body are not parallel with the front which is why the camera must be supported by the film rails resting on a special block.
Sponsored Ad. (Subscribers to APUG have the option to remove this ad.)
I realised that the exploded views in the rear of the manual are to be used to guide one in disassembling this camera. The leatherette side skins must be peeled off to reveal the first layer of screws. This is a shame as I will have to glue it back on again. Anyway at least I am making progress.
I also will find an Outside Calliper http://goo.gl/eYKx1 or large micrometer to measure the parallelism to save me locating a very flat block to rest the film gate on.
I got one side panel off. Some screws are really hard to remove, so off to my local electronics store tomorrow to get a precision PH screwdriver with a fat handle so I can exert lots of torque. Tip needs to be hardened to prevent it shearing off like the cheap one did last night.
I think the OP needs a different focusing screen, or needs to shim the focusing screen.
Firstly, you're not attacking the problem by addressing/eliminating the simplest, or most common area that causes focusing problems, and that is usually the focusing screen..
Rack the lens board/bellows to get the taking lens in focus on the film plane, then shim the focusing screen for viewing lens focus.
If you haven't already lost shims from behind the front elements of the lens, put the lens back together and leave it alone.
You can use "Scotch Tape," spread across the film plane, (like lap-siding on a house), to imitate a ground glass for focusing the taking lens.
Marc, are you replying to Sully75 or myself?