M6 50mm lens problem, please help!

[alice]

Guys,
I seem to be having a bit of hard luck with my M6, first it was the strange non-responding shutter problem (it seems ok now)

Now here is another problem that I have and would like to ask all the experts here if you know the cause.....

for some reasons, the 50mm lens is just not sharp! the center portion of the photo always appear less sharp than the non-center portion of the photo (considered that the center is where i focus on). it looks to me some sort of front-focus problem is appearing, i try to attach a photo here to demonstrate, this photo was shot at 1/250 with F8 aperture, and focused on the center rusted post with an inverted hook. But the photo turns out that the short stone pillar in front of the rusted post appears sharper. Since they are in close proximity and i set my lens at F8, i was expecting both to be sharp.

can someone enlighten me......please.

thanks a lot!

 

[felipe]

Have you ruled out the scanner as a culprit?
If you're using glasless slides and it's hot,humid or whatnot the film might curl and give you those neat out of focus effects. 🙂

Another reason might be a loose film pressure plate but when I had my M6 it appeared rather solid if I remember correctly..

Good luck,
Phil

 

[Flyfisher Tom]

Alice,

It is somewhat difficult to tell from the photo whether the center is sharp ... it certainly looks sharp to me, but that might be due to the small size of the jpeg. Does it look that way on the chrome or negative?

Might be a possible rangefinder misalignment, has it had a CLA in the past few years? If you've been having other techincal problems with the M6, might be worth looking into sending it to DAG (Don Goldberg) for a routine CLA.

 

[denishr]

Alice, to rule out (camera and lens) focusing problem, you should shoot a test roll - shooting a "test target", consisting of a picket fence or something. Just to give you an idea what I'm talking about, check out these links:

http://www.photo.net/learn/focustest (Focus testing)
http://www.normankoren.com/Tutorials/MTF5.html (Lens testing)
http://www3.telus.net/public/kaylalyn/checking lens working distance.html (Focus test, also shows a neat "focus test target).

After you shoot one roll with different f-stops (or only wide open, since this is where any errors will be obvious), you'll be sure whether it's the lens+camera or scanning.

Denis

 

[alice]

Tom,
you just reminded me of something! I had the 50mm lens cleaned a couple of weeks ago, could it be that the Mamiya technician somehow messed it up during the cleaning......
maybe I should call up that guy today.....

 

[nksyoon]

Would setting the flim pressure plate to 220 instead of 120 cause such a problem with 120 film?

Also, once I didn't extend the bellows fully and was wondering why I couldn't focus to infinity.

Nick

 

[alice]

Nick,
Ummmmm, i am not sure about the pressure plate to 220, this problem doesn't appear to my 75mm lens.

here is another example where i focused at the center red little flower but it turns out that the bunch of flowers on the left are sharper.....

I think its probably because of my lens or camera or both because when i investigated the negatives, the center is always softer.....

maybe my M6 got jealous of me for not using it in years and are giving me these problems when i wanted to use it now....

 

[FrankS]

Hi Alice, to check your rangefinder, find something on the horizon far away (over 1/2 mile) and focus on it using the camera's rangefinder patch. Then see what the lens distance scale reads.

Put the camera on a tripod and do the same test with an object that you have set a measured (make sure you measure) 4ft away (or whatever the closest marked distance is on the lens distance scale). Focus on it using the rangefinder and check what the lens distance scale reads.

 

[akitadog]

Hi,

I had all 3 of my Mamiya 6 lenses and the camera body checked for focus accuracy. The camera service department can adjust the focus on each lens by changing the shims on the lens. First you insure that the camera body is adjusted properly, and then each lens can be set to match the body. It wasn't cheap to do but it insured all my lenses are spot on with my camera body. A good service shop should be able to check all this and tell you what if any adjustment is needed.
Regards

HHK