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Loose rear lens element 100mm F2 minolta lens

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Alfasud1972 View Drop Down
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Post Options Post Options   Quote Alfasud1972 Quote  Post ReplyReply Direct Link To This Post Topic: Loose rear lens element 100mm F2 minolta lens
    Posted: 17 June 2017 at 19:58
Some time ago i got my hands on a second hand Minolta 100mm F2 lens (the metal one). I had read the reviews here on Dyxum so I had high expectation for this lens. Unfortunately the lens never quite delivered the razor sharp images like the sample pictures I had seen on this website.

Sometimes they images where kind of okay, but at other times they where just not sharp and out of focus.

I did read here from someone that he had to set the AF fine-tuning to -14 to get sharp pictures. So I went and did the AF fine-tuning and found out my lens performed much better at -10.

After I did the fine-tuning to my lens, I took the lens of the camera and noticed a noise, like something was loose. I found out that the rear element of the lens was loose, and that i could press it back with my finger for a millimeter. When I turn my focus ring counter clock wise the inner lens/element pushes the last outer rear element back into place (to the outside).

I have tried to tighten the outer rear element but I do not have the right lens tool (cheap ebay tool).

The repair manual say's that the first 6 lenses are floating, and that the 7-th lens element is supposed to be fixed (well not in my case).

Is anyone familiar with repairing this lens? Is it simply a mater of tightening the last rear element. I must say it is really tight already, I could almost get no movement in it with my (crappy) tool)? I'm kind of worried that the other lenses are touching the last lens element when the focus ring is fully turned counter clock wise , which would get worse if I would tighten it further down.

I know some of you will advice me to send it in for repair. But I already have spend a lot of money buying this lens (can not send it back). I do not have two left hands, and have repaired and cleaned lenses before. So if it is a simple job I would rather do it myself.

I hope I have explained my problem well enough, as I'm not a native English speaker.

Kind regards,

Rody
 



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QuietOC View Drop Down
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Post Options Post Options   Quote QuietOC Quote  Post ReplyReply Direct Link To This Post Posted: 17 June 2017 at 20:06
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Alfasud1972 View Drop Down
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Post Options Post Options   Quote Alfasud1972 Quote  Post ReplyReply Direct Link To This Post Posted: 17 June 2017 at 20:12
Thank you for your reply. You can find most of the repair manuals for free on the internet (http://allphotolenses.com/pdf/c_17.html). As you can read I do have the manual already as I'm referring to it .

I'm was a bit shocked the rear element was loose, maybe someone with more (professional) lens repair experience could be shinning his light on this 'problem'.

I have read on the internet that it is normal for some lenses to have a loose rear element, but than you would not speak of a 'fixed' element I would think.

Maybe some other owners of the Minolta F100 F2 lens would be so kind to check if their rear element is 'loose' or really fixed?


.

Edited by Alfasud1972 - 17 June 2017 at 22:25
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Pete Ganzel View Drop Down
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Post Options Post Options   Quote Pete Ganzel Quote  Post ReplyReply Direct Link To This Post Posted: 18 June 2017 at 08:12
Yea, it looks like the rear element is held by a snap ring inside the tube that is screwed to the rear of the lens. Maybe the snap ring was not seated or the element got pushed so the ring popped out. You just need to unscrew the rear tube (using a spanner or friction tool) and carefully reseat the lens and snap ring.   You can probably fabricate a tool from a plastic tube of the right diameter to slide down inside the rear tube to reseat the snap ring.

Pete

Edited by Pete Ganzel - 18 June 2017 at 08:17
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Alfasud1972 View Drop Down
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Post Options Post Options   Quote Alfasud1972 Quote  Post ReplyReply Direct Link To This Post Posted: 18 June 2017 at 21:22
Thanks Pete, I can not see a snap ring, I will try to make a tool, and open it to see.
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Bob J View Drop Down
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Post Options Post Options   Quote Bob J Quote  Post ReplyReply Direct Link To This Post Posted: 18 June 2017 at 23:57
It is a great lens, so well worth the effort/cost to fix.
 



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Pete Ganzel View Drop Down
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Post Options Post Options   Quote Pete Ganzel Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 01:13
Originally posted by Alfasud1972 Alfasud1972 wrote:

Thanks Pete, I can not see a snap ring, I will try to make a tool, and open it to see.


The snap ring or "pressure spring" is on the inside of the rear tube which you need to unscrew. The part is shown in the cross section just in front of the rear element (2598-1422-01). The cross section shows a zig-zag pattern on the inside of the tube which is actually light baffling, not screw threads and the "floating" section passes back and forth through the rear tube to focus but is unconnected to it.

Pete
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Alfasud1972 View Drop Down
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Post Options Post Options   Quote Alfasud1972 Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 01:30
Thank you Pete, now I see it :) ! The rear tube is stuck really tight. I will try to fabricate a good tool tomorrow. Would it be okay to apply some indirect heat to the rear tube, to make it easier to unscrew?

I was thinking to put it in a sealed fridge bag, and than gently heat it up with a blow dryer (so I will not blow dust in it). Or is this a bad idea?

On classic bycicle's you can loosen lockring's with a hammer and a screwdriver, but I think I will not try this method on a lens ;-)...

Edited by Alfasud1972 - 19 June 2017 at 01:41
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Pete Ganzel View Drop Down
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Post Options Post Options   Quote Pete Ganzel Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 02:04
Originally posted by Alfasud1972 Alfasud1972 wrote:

Thank you Pete, now I see it :) ! The rear tube is stuck really tight. I will try to fabricate a good tool tomorrow. Would it be okay to apply some indirect heat to the rear tube, to make it easier to unscrew?

I was thinking to put it in a sealed fridge bag, and than gently heat it up with a blow dryer (so I will not blow dust in it). Or is this a bad idea?

On classic bycicle's you can loosen lockring's with a hammer and a screwdriver, but I think I will not try this method on a lens ;-)...


You might try a little acetone around the edge of the tube with an eyedropper, let evaporate and do again, this will soften any sealing lacquer. Do not apply heat or hammers!

Pete
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Maxxuman View Drop Down
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Post Options Post Options   Quote Maxxuman Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 16:18
Pete, since you checked in I have an issue I wonder if you can offer any advice on.

I dropped my KM 28-75/2.8 and the focus gears have been damaged internally, while the elements are fine. I was disappointed to see there wasn't a manual included in your disk I have (although I understand why, with it being a late Tamron rebadge).

I'd like to have it repaired but the place I contacted said they couldn't help because it's such a rare lens and they don't have parts. I have a feeling the focus gears may be identical to the Tamron versions but have no way to confirm that. Do you have any suggestions on how I could go about getting it repaired?
Barry
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Alfasud1972 View Drop Down
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Post Options Post Options   Quote Alfasud1972 Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 17:44
Thanks Pete, aceton and a self fabricated tool did the job to unscrew the tube. I carefully pushed the snap ring back into to place with a plastic tool. Now I'm going to AF fine tune this lens and make some sample pictures.

For future reference, after 'soaking' lightly in acetone, clean the remains of the acetone and sealing lacquer very very well. You don't want to get this on your lens I think.

Cheers,

Rody

@maxxuman, maybe it is better to start your own thread, to keep the forum clean and also for better future reference.
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Maxxuman View Drop Down
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Post Options Post Options   Quote Maxxuman Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2017 at 20:39
Originally posted by Alfasud1972 Alfasud1972 wrote:


@maxxuman, maybe it is better to start your own thread, to keep the forum clean and also for better future reference.


Sorry, you're probably right. I just thought it was such an obscure thing, which perhaps only Pete may have any insight to, that I wasn't sure how to seek his input. Plus I have a rotten cold so I'm probably not thinking straight!

Glad you got your issue sorted.
Barry
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Alfasud1972 View Drop Down
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Post Options Post Options   Quote Alfasud1972 Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2017 at 00:54
Thanks, yes, from quick testing it is a lot sharper at lower F stops. At first it was only sharp at F5,6 and now it is sharp from F2.8.

I did the AF fine tuning process again as I hurried it a bit the first time, so I hope it performs even better now. I will shoot with it tomorrow in daylight to check it out again.
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