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Minolta lenses focusing past infinity
Old 02-05-2019   #1
retinax
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Minolta lenses focusing past infinity

Hi all,
I only have the one functioning XD-7 body right now, but several lenses. I've adjusted the mirror stop, so focus on matte screen and film are reasonably close. It still focuses past infinity with all my lenses. Very significantly so, several millimeters on the focus ring of a 50, a negative focused with the infinity setting on the lens scale looks soft to the naked eye.
Do Minolta (MD and MC) lenses just focus way past infinity? Is the stop adjustable? Or should the lens mounting flange on the body normally have shims? I lean in favor of the latter explanation, but there are no signs of shims on this body, nor on my parts donor body. And with shims, close focus would change, too. Because the weirdest part is that at close distances, the marks on the focusing scale are spot on! Measured to the film plane, that is. Or did Minolta have a different way, do they refer to the front element or the lens mount or something?
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Old 02-05-2019   #2
Sumarongi
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Do I understand correctly, the *lenses* can be focussed beyond the infinity mark, physically, by turning the focussing collar?
—— Who was the previous owner of the lenses in question? Was s/he e.g. an astrophotographer, an Antarctica scientist, or the like? Then it would be explainable that s/he had modified their lenses, IMHO.
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Old 02-05-2019   #3
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Can't help you directly as to what the problem may be but I have an XG-M and XD5 and the 50mm/1.7 and 28mm/2.8 Minolta lenses plus a 28-200 zoom (Tokina) and they all focus just as I'd expect. I don't think the distance sales are deadly accurate but I've never noticed an ability to focus beyond infinity.
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Old 02-05-2019   #4
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The point on the focus ring where infinity focus happens can depend on temperature (expansion, contraction), so it makes sense that some lenses would have some room for adjustment beyond the infinity marking. Whether this is intentionally the case here I don't know.
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Old 02-05-2019   #5
retinax
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Quote:
Originally Posted by Sumarongi View Post
Do I understand correctly, the *lenses* can be focussed beyond the infinity mark, physically, by turning the focussing collar?
—— Who was the previous owner of the lenses in question? Was s/he e.g. an astrophotographer, an Antarctica scientist, or the like? Then it would be explainable that s/he had modified their lenses, IMHO.
The lenses stop at the infinity mark. However infinity focus is reached before that, around halfway between the infinity and the 10m marks on the 50.

I don't know what previous owners did, but I have bought lenses from different people. So it must be the body or something that all the lenses have in common.
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Old 02-05-2019   #6
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Quote:
Originally Posted by retinax View Post
The lenses stop at the infinity mark. However infinity focus is reached before that, around halfway between the infinity and the 10m marks on the 50.

I don't know what previous owners did, but I have bought lenses from different people. So it must be the body or something that all the lenses have in common.
Thats a long way off what would be expected.

Think it through - lenses all have different sources but same issue with all: it has to be the camera.
Close focus on the lens means the lens is further from the film. Correct focus is consistently achieved when the lens is set closer than infinity, meaning additional distance from the film is required to bring the lens to focus.
This means the mount is too close to the film.
Most are shimmed, usually with paper, to bring to calibration. Use rings of fine paper to reshim, under the mount on the camera.
(That is, remove the mount, place an appropriate cut 'shim' underneath and reattach the mount - test. Keep going until near enough to correct.)
Check to ensure the mount is square - that focus is correct across the frame side-to-side and top-to-bottom.
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Old 02-05-2019   #7
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This isn't normal for Minolta lenses. I have 13 Minolta lenses (MC and MD) and 5 SLR bodies (three SR-Ts and two X-570s) and all of my lenses focus correctly at infinity (with all bodies).

It sounds to me like the problem is with the camera, likely the mirror, as you suspected, or possibly the focusing screen.

Does the focus at infinity look correct on film?

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Old 02-05-2019   #8
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Quote:
Originally Posted by Scrambler View Post
Thats a long way off what would be expected.

Think it through - lenses all have different sources but same issue with all: it has to be the camera.
Close focus on the lens means the lens is further form the film. So correct focus consistently at closer than infinity means additional distance required to bring the lens to focus.
This means the mount is too close to the film.
Most are shimmed, usually with paper, to bring to calibration. Use rings of fine paper to reshim, under the mount on the camera.
(That is, remove the mount, place an appropriate cut 'shim' underneath and reattach the mount - test. Keep going until near enough to correct.)
Thanks. Yeah I know that shimming would solve it at least for infinity focus, I just wasn't sure if the closer distances wouldn't be off the scale, considering they're correct now. But I realize now that the difference wouldn't be noticed, seeing that the distance between the 0.45 and 0.5 marks is a lot more than between the 10m and infinity marks.
The riddle that remains is why are there no signs of shims? the lens mount rests of four posts that would need individual shims, and their distinctive shapes have left faint marks on the mount, so there either never were any or someone removed them long ago.
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Old 02-05-2019   #9
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Quote:
Originally Posted by CMur12 View Post
This isn't normal for Minolta lenses. I have 13 Minolta lenses (MC and MD) and 5 SLR bodies (three SR-Ts and two X-570s) and all of my lenses focus correctly at infinity (with all bodies).

It sounds to me like the problem is with the camera, likely the mirror, as you suspected, or possibly the focusing screen.

Does the focus at infinity look correct on film?

- Murray

Thank you, yes I have adjusted the mirror stop and checked focus with a ground glass on the film rails, image on focusing screen and focus on film plane correspond very closely. The focusing screen can only go in one way around, the tab is off center. I've taken test pictures that I've only examined with a (somewhat weak) loupe so far, I'll take them to the dark room tomorrow to see if focus is really spot on. But as I wrote in the original post, that it's off when the lens is set to the infinity mark is clear.
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Old 02-05-2019   #10
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Quote:
Originally Posted by retinax View Post
Thanks. Yeah I know that shimming would solve it at least for infinity focus, I just wasn't sure if the closer distances wouldn't be off the scale, considering they're correct now. But I realize now that the difference wouldn't be noticed, seeing that the distance between the 0.45 and 0.5 marks is a lot more than between the 10m and infinity marks.
The riddle that remains is why are there no signs of shims? the lens mount rests of four posts that would need individual shims, and their distinctive shapes have left faint marks on the mount, so there either never were any or someone removed them long ago.
One possibility is that the camera got dropped and struck either into a lens or from on the back with a lens attached - so the entire front of the camera is pushed in. So make sure the focus is even across the film as you shim!

With an SLR you focus based on identical distance lens to film and lens to ground glass. So provided this is correct, the focus works regardless of what the distance marks show. Everything else is getting the distance marks to line up for depth of field assessment, distance estimation etc.
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Old 02-05-2019   #11
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Quote:
Originally Posted by Scrambler View Post
One possibility is that the camera got dropped and struck either into a lens or from on the back with a lens attached - so the entire front of the camera is pushed in. So make sure the focus is even across the film as you shim!

With an SLR you focus based on identical distance lens to film and lens to ground glass. So provided this is correct, the focus works regardless of what the distance marks show. Everything else is getting the distance marks to line up for depth of field assessment, distance estimation etc.
Yes that might be it. On the focusing screen, focus is definitely different for bottom and top of the frame. I'll need to check if that translates to the film plane. The problem with these cameras is that it's almost expected for the focusing screen - the screen itself can't be adjusted, only the mirror stop, which leads to a swing sort of effect, you can only get it right for the center if it needs to be adjusted a bit off factory spec.
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Old 02-05-2019   #12
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Quote:
Originally Posted by retinax View Post
Yes that might be it. On the focusing screen, focus is definitely different for bottom and top of the frame. I'll need to check if that translates to the film plane. The problem with these cameras is that it's almost expected for the focusing screen - the screen itself can't be adjusted, only the mirror stop, which leads to a swing sort of effect, you can only get it right for the center if it needs to be adjusted a bit off factory spec.
If you believe it may have had an impact, I suggest placing the body onto a surface plate and using a depth gauge to check the parallelism of the mount to the film rails. It sounds like at least some of the corners are low. If the body is otherwise fully functional it would be worth checking as you should be able to shim them back to the correct register. If this is indeed the problem, calibrating the body will then fix both the over infinity focus and the finder view, (although you will have to re-set the mirror height again as the final step in the calibration process).

I have seven or eight Rokkor lenses from 28mm to 200mm in focal length, and three or four Minolta bodies, mostly SRTs. All my lenses reach infinity at the stop, which is exactly where they're meant to.
Cheers,
Brett
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Old 02-06-2019   #13
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Wink

Quote:
Originally Posted by Sarcophilus Harrisii View Post
If you believe it may have had an impact, I suggest placing the body onto a surface plate and using a depth gauge to check the parallelism of the mount to the film rails. It sounds like at least some of the corners are low. If the body is otherwise fully functional it would be worth checking as you should be able to shim them back to the correct register. If this is indeed the problem, calibrating the body will then fix both the over infinity focus and the finder view, (although you will have to re-set the mirror height again as the final step in the calibration process).

I have seven or eight Rokkor lenses from 28mm to 200mm in focal length, and three or four Minolta bodies, mostly SRTs. All my lenses reach infinity at the stop, which is exactly where they're meant to.
Cheers,
Brett
Unfortunately I don't have access to these measuring tools. I've looked at a ground glass on the film rails and the issue is certainly less than on the focusing screen. I'll need to examine again with more time and shoot some test frames of a line of trees across the whole frame at infinity or something. In any case today I printed some crops from test shots on T-Max 100 at maximum enlargement I can do, focus is ok in the middle at least. As a matter of fact, this film at this enlargement shows that the whole system isn't good enough to focus the excellent MD II 50 1.4 wide open consistently enough for this magnification - I ended up with the focus floating around the targets a bit. In practice though, I don't enlarge as large as that (would be around 40x60cm), I don't take shots of flat targets or objects at infinity wide open, so I won't worry much for now, just use it and include some test shots on the next roll.


I'll need to try an SRT, too. I've held off because I'm afraid it'll lose the comparison to my beloved Spotmatic; the XD is a different sort of camera, it doesn't compete . But the Spotmatic can focus more precisely with its finer microprism...
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Old 02-06-2019   #14
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The SRT-202 is the top of the line, last version SRT. Has an acute matte bright screen with rangefinder and microprism. It also shows the F/stop and shutter speed in the viewfinder, and does double exposures. I bought one in the classifieds here for $40 and it was (is) perfect.

Minolta SRT 100 and 202 by Nokton48, on Flickr

https://www.rangefinderforum.com/for...ht=Minolta+SRT

If you can find a good one the XK is a good option, too. That camera is pro in every respect and was way ahead of it's time. I've had plenty of F2s and F3s and F1s and I would take this over those anyday.


HugoStudios Tan Morocco XK (2) by Nokton48, on Flickr

001 by Nokton48, on Flickr

DSC04450 (1) by Nokton48, on Flickr


Plenty of Minolta Love on this forum. See my ongoing SRT thread here:

https://www.rangefinderforum.com/for...ht=Minolta+SRT
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Old 02-06-2019   #15
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Quote:
Originally Posted by Nokton48 View Post
The SRT-202 is the top of the line, last version SRT. Has an acute matte bright screen with rangefinder and microprism. It also shows the F/stop and shutter speed in the viewfinder, and does double exposures. I bought one in the classifieds here for $40 and it was (is) perfect.
You should also look for Minolta SR-T Super (for the Japanese market) = SR-T 303 elsewhere (including Europe of course)
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Old 02-06-2019   #16
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The SR-T 101 has the focusing screen with the finer central microprism, like the Pentax Spotmatic. That was the norm at that time. The 101 finder shows the match-needles and the shutter speed. Most 101s have mirror-lock-up, except for the last of the model run.

My favorite is the SR-T 102, with the newer focusing screen (split-image rangefinder in the center, surrounded by a coarser, snappier microprism collar. This focusing screen provides easier focusing with faster lenses, while the finer microprism of the 101 is better with slower lenses.) The 102 finder includes the match-needles, shutter speed, and aperture. Earlier 102s also have mirror lock-up (MLU).

The successor to the SR-T102 is the SR-T 202 referenced by Nokton48. The 202 has no MLU, but is otherwise similar to the 102. It has a display that shows that the film is advancing, but I never valued this feature, as I had other ways to confirm this.

Nokton48 claims to have a 202 with an Acute Matte focusing screen. I have not been able to find corroborating evidence of this anywhere else, so I am inclined to believe that he has a special 202.

Compared to the Pentax Spotmatic, more of the finder in SR-Ts can be seen with glasses on. Also, the SR-Ts all have full-aperture metering.

I have a Minolta SR-T 101, an SR-T 102, and an SR-T 201. I also have a Pentax H1a, a Spotmatic II, and a Spotmatic F. These Minoltas and Pentaxes are similar, but there are differences, too. I am a little more partial to the SR-Ts, but I have very great appreciation for all of these cameras.

Get a Minolta SR-T, get to know it one its own terms, and appreciate it for what it is. You will then have two great families of lenses.

- Murray
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