Contax focus problem - can someone help?

<p>I have had this Contax 137 MA for quite some time. Last year I noticed a discrepancy between successive shots - with some pictures being out of focus (usually a successive shot). It doesn't seem to be a lens problem. In example 2, I took some shots of the same scene with my CZ 28 mm, an M42 Super-Tak with adapter (usually also an excellent performer), and you can see the differences. Could there be some sort of mirror slap in the camera? My local tech didn't see anything wrong. Can anyone help/explain?<br>

Thanks,<br>

Allen Gross</p><div></div>

<p>Allen, first of all you don't need to start a new thread to post a new image, just click on "contribute a response" in the existing thread. And if you resize the images down to 700 pixels, they will appear directly in the thread, not as links.</p>

<p>It certainly looks like a focusing issue. I would ask, does the focus scale on the Takumar agree with the actual subject distance? And is the mirror moving freely and resting on its stop?</p>

<p>I think your second pair of photos is more telling. In the clear photo of the pair, everything in the photo is in focus, indicative of the 28mm lens being stopped down a ways. Then in the second photo of the pair, everything in the photo is equally blurry. If it were just missed focus, you would expect to see areas out of focus and areas in focus -- just not the right ones. But in your example(s), everything is equally blurry. It's as if the lens or film plane were somehow displaced by a certain small amount.</p>

<p>I don't think I'm clear on your wording. Are you stating that the first pic in each set is taken with a CZ and the second (blurry) one is taken with a Super Tak? Or is the first set taken with the CZ and second taken with the Super Tak? Or? And you're using the Super Tak with an adapter for CY bayonet mount?</p>

<p> </p>

<p>Well if it is not a lens problem there is really only one thing it could be - a film flatness problem. If the lens and camera are not moving, then the film would have to move for the focus to change. <br>

Or is the problem only happening when you swap lenses? Or is it only happening with a particular lens? You need to eliminate variables, rather than introduce new ones. Does it happen if you use one lens through a whole roll?</p>

<p>Put a lens on the camera, but don't bother loading any film. Put on a tripod, or otherwise in a stable location. Lay down a yard stick so you're looking at it from the end. Put something to focus on at the 18 inch mark. Now, take a picture, and wind on, and see if the same place is in focus. (Take several pictures to be sure.)<br>

What you're checking is that the reflex mirror comes back down to exactly the same place after each shot. If it doesn't, it will be "telling" you to mis-focus the lens.<br>

I can't image film flatness problems severe enough to cause that amount of out-of-focus, that would take an error of several millimeters of lens position. But I can image a gummed-up mirror system.</p>

Let's see if I can get these to show up on this one thread.<div></div>

1st of several<div></div>

Example No2 (CZ)<div></div>

Pentax M42 SuperTakumar - out of focus<div></div>

Post by David Bebbington Mar 28, 2015; 05:55 a.m.

 

What Contax model? How is the Pentax M42 lens attached?

<p>Firstly, thanks for the quick responses. As you might guess, this is my favorite forum on Pnet and I’m always impressed how helpful people are.<br>

John: Thanks for the advice on avoiding starting a new thread to post successive comments.<br>

Michael: Apologies for not being clear about the examples and the lenses used. I first noticed the problem using the CZ lens taking pictures of the Rodin statues at the Norton Simon Museum (it affected other photos as well). The same thing happened on a subsequent occasion: occasional shots with everything equally out of focus (normal daylight, aperture and shutter speed).<br>

I then thought of shooting with different lenses to see whether the problem was with the CZ – hence the use of the Super Tak, which I usually use with my M 42 Pentacon but have also used with the Contax with the M42- to C/Y adapter. I also shot with a Vivitar 19-35 at 28 mm and got similar results. So I think it’s something with the camera.<br>

Dave: The original problem was noticed while using a single lens throughout the roll (Ex. 1).Ex. 2 used different lenses to ascertain that it wasn’t the CZ causing the problem.<br>

James: Thanks for putting the photos on one thread. It’s a Contax 137 MA, with the speed selection ring having long been broken, making the camera essentially an MD in operation. The M42 lens is attached with an M42 to C/Y adapter. As mentioned, this lens has functioned fine before on both my Pentacon and the Contax.<br>

Michel, Dave and John:<br>

<strong>“It's as if the lens or film plane were somehow displaced by a certain small amount.” </strong>What would cause this?<br>

<strong>“film flatness problem.”</strong> This I doubt, as I’m always impressed when loading film into the camera how flat the film appears. And it’s happened with several rolls, so it couldn’t be a faulty roll. <br>

<strong>“gummed-up mirror system.” </strong>Seals and foam look fine – looking at it while repeatedly firing the shutter without a lens, everything looks fine.<br>

John: I will try your approach. Should your hypothesis be true, what would have to be done?<br>

Any other ideas based on the info I gave you?<br>

Thanks,<br>

Allen</p>

 

<p>John: I tried your suggestion. Mirror returns to this same place each time - no need to re-focus. Also tried it with different lenses - same result.</p>

<p>The focusing screen is firmly in place, no chance of it moving slightly and causing the problem? I had a similar issue caused by this situation in a Contaflex . I'd check the focusing system from mirror to viewfinder.</p>

<p>I have an older SLR where the mirror does not return to the focussing position completely until the shutter has been cocked. It will sit about 1mm out of place when returning until the film is wound on. The only way to tell really is to put the camera on a tripod, focus on some close point, fire the shutter, check the focus again (now slightly off), then cock the shutter (focus now dead on again). But if you focus before cocking the shutter the result is slightly missing focus when you actually the the shot. <br>

The only related problem might be a focus screen which is not held in place securely, if this could move around the result would be missing focus too.<br>

One way to see if it is a problem with the focusing system or something else would be to put the camera on a tripod, focus on a fixed point - and fire off a few shots without changing any settings. If the focus changes without you touching anything, then it's something other than the mirror or screen moving around.</p>

<p>I think my original question, does the distance scale on the lens agree with the actual subject distance, still needs answering. For example if you focus on an object 10 feet away, the focus scale should indicate near enough ten feet. Or better probably at infinity. Check that the scale is at infinity when you focus on a distant object. If it isn't then there is a problem with either the position of the mirror, or the position of the focusing screen.</p>

<p>In working on a number of 137's many years ago, I recall one of the causes of focus problems.</p>

<p>If you raise the mirror and look into the mirror box, you will see that the mirror rests on a small pin on the rewind side of the box.<br>

The pin is actually covered by a plastic bushing, which sometimes goes missing, causing a noticeable mis-focus by allowing the mirror to rest at a lower position. There are other potential reasons for the pin to be out of position, but that is the one I recall.</p>

<p>A short focal length lens, stopped well down, might compensate, but as I recall (just relying on distant recall!) the error is very noticeable.</p>

John: yes, the distance scale agrees with the measured distance. Tried it at 6 ft. And distance (which reads @ infinity.

 

Michael: I'll try to get a picture of that bushing and pin for you . I think the mirror is in its proper position, but you may be

able to tell.

 

 

-Allen

Does this occur sporadically or can you reproduce it reliably? Just looking at the thread it appears to me that the camera

is the problem. Just. wondering if there is something that gets hung up occasionally or if there is specific part that

behaves in a predictable way.