Hasselblad mystery focus issue?

Arg6442

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Hi all,

I recently came into ownership of a Hasseblad 500c/m rather unexpectedly. Once I got it I sent it out for a CLA and it came back in great shape. However, I'm having a strange issue with focusing. When I focus the 80mm 2.8 t* planar to infinity, the split focusing on the ground glass doesn't quite line up. To test the issue further, I used a digital back (the camera basically came with the back for free) and noticed that focus in the final image is always an amount further than what I see on the ground glass (and when the lens is set to infinity, infinity is in focus). First, I made sure the screen was right side up, and that there weren't any obvious issues with the lens or lens mount. I was under the impression that it could be a mirror alignment issue, but the CLA folks said everything was a-ok. This morning, playing around with the camera, I flipped the focusing screen to be upside down (fresnel lines facing up). Surprisingly, this fixed the infinity focus issue almost entirely (I've never had a camera where the split image ever aligned perfectly). Later today I'll test nearer focuses on the digital back to see if the issue is better across the board. Does anyone have any thoughts as to what could be going on with my camera?

Thanks!
 

Sirius Glass

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Does the focusing screen work better if you rotate it 90°, 180° or 270°?
 

hashtagquack

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Noticed something similar when changing my screen to a split prism. The split prism is very slightly off. I use mounted mine vertically so will need to try in the other orientations to see if that resolves it. When you say you flipped the screen, do you mean you turned the ground glass side upwards?
 
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Arg6442

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Yes, I flipped it over so that the "shiny" side was face down.
 

etn

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Arg6442 said:
Yes, I flipped it over so that the "shiny" side was face down.
Click to expand...
Both my bodies have shiny side "up" i.e. the side you look at through the prism or waist level finder.
Matte side is "down" towards the mirror, inside the camera.
Could you please try this, if it solve your issue?
 
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Arg6442

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etn said:
Both my bodies have shiny side "up" i.e. the side you look at through the prism or waist level finder.
Matte side is "down" towards the mirror, inside the camera.
Could you please try this, if it solve your issue?
Click to expand...
The problem is worse when it is oriented "shiny side up" (which is the correct way), it becomes more accurate when the screen is "shiny side down" (fresnel side is facing you when you look into the viewfinder, this is the "incorrect" way but makes the problem better).
 

Sirius Glass

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You have a problem with the work done on the CLA. Send it back and have them set things right.
 

John Will

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Another possibility. Are you sure the split image screen is a genuine Hasselblad? I ask because a few years ago I had similar problems when I brought a cheap 'knockoff' split image screen which showed a correct image on screen but was out compared with actual distance. The standard Hasselblad screen focused correctly. I eventually brought a genuine Hasselblad split image screen (at exorbitant cost) which also focused correctly.
 
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Arg6442

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Sirius Glass said:
You have a problem with the work done on the CLA. Send it back and have them set things right.
Click to expand...
I think I typed my post originally in a way that didn't make this fully clear. The issue was present prior to the CLA, and I had made a note that there may be a mirror alignment issue or something simmilar. In theory, they've taken care of whatever issue they found (if any), but nonetheless I've contacted them about this and am waiting to hear back from the repairman about exactly what they did/found regarding this issue. If they just ignored it then, yeah, its getting sent back, but I'm wondering what issues besides the lens (ruled out by testing as far as I can tell) could be causing this.
 

mshchem

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Arg6442 said:
Here are some pictures of the screen
View attachment 253474 View attachment 253475 View attachment 253476 View attachment 253477
Click to expand...
That's what my four Hasselblad screens look like. I agree with Sirius. Could be that nothing was adjusted (an oversight ). If things get gummed up, the mirror can get sluggish.
You might try taking the lens off and gently pushing the mirror down with a cotton swab. Then recheck your setup. It could be that the infinity stop on the lens needs attention? ??
 
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Arg6442

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Hooray! I found the problem. The mirror is tilted slightly clockwise. With the lens off I gently pushed on the bottom of the mirror and found that on the left side (facing the camera) it had some downward give, but springs back into its out-of-alignment place. Must be a badly arranged screw. Will be sending the body back to the repairman to get this fixed. Thanks for the help!
 

Sirius Glass

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The repair person needs to put the camera body on a jig and get the box back to the "squared configuration". Do not try this at home.
 

itsdoable

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The mirror carriage on the Hasselblad can twist like that by design. It is the reason the mirror is attached to the carriage by foam pads that have some give. Being able to press the left side of the mirror down is normal.

Facing the camera:
- the right side has a mirror stop that prevents the right end of the mirror from lowering further.
- the left side has a claw that holds down the mirror until it is ready to release.
These 2 items set the mirror position, adjustment is made by bending the 2 tabs.

When you wind the camera, you will see the mirror come down, the right side will stop when it hits the rest, the left side continues down and twists the mirror carriage a bit, the claw on the left then swings into position, and the left side of the mirror then rises to rest on the claw, untwisting the mirror carriage.

All 500 series non-GMS mirrors work this way.


The focus screen you have looks like a non-acute matte 42188, with no glass layer on top. Just to confirm, the 1st picture is the top, the second picture is the bottom. The screen's calibration is made by 4 special headless screws under the screen near the 4 corners in the body, they should be potted, and require a special tool to adjust (they should never need adjustment, but you have no idea what someone may have done to a 50 year old camera).


all of these adjustments should be made by someone that knows what they are doing - there is really only one way to adjust it correctly, and a thousand ways to incorrectly screw it up. ... OK, maybe I exaggerate. a few hundred ways to screw it up?
 
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