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Minolta RF 250 5,6
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PostPosted: Sun Mar 13, 2022 4:38 pm    Post subject: Minolta RF 250 5,6 Reply with quote

I would like to disassemble this lens, there are some dusts inside and what could be some mold on the back of the front lens.

I cannot disassemble from the front with the spanner although I thougt it was possible. I have seen long time ago a website showing disassembly that necessitates removal of the rubber grip which I never done. Is that easy to remove? How to maintain proper alignment of the grip when putting back on the lens and are they techniques or tools that should be favoured?

Cheers.


PostPosted: Sun Mar 13, 2022 5:13 pm    Post subject: Re: Minolta RF 250 5,6 Reply with quote

I'm pretty sure I've seen a repair manual for the RF 5.6/250mm somewhere. And there's a Japanese site with repair info for this lens as well. I have downloaded that site, but don't have its link any more. If you contact me via email (stevemark@gmx.ch) I can send you the files.

S


PostPosted: Sun Mar 13, 2022 6:15 pm    Post subject: Reply with quote

I did take this one apart some years ago to remove some fungus from behind the front lens (which is why the price was reasonable, for a change).

I had a quick look for tell-tale signs as to how I opened it.

Indeed, the rubber grip peels off (it sits like a stretchy rubber band/sock around the lens.) Difficult, but doable. Alternatively, you can just roll it up a bit (like you roll down a sock), starting from nearest the focus scale markings. Use a thin flat screwdriver to lift up a little section and then use your fingers to peel up further. There is no glue holding anything down, and the stretchy rubber grips (vinyl actually) that Minolta use are quite robust, they don't tear easily.

You only need to access the 20mm or so nearest the focus scale underneath the rubber grip, where you will find a tape underneath.

- That tape holds together (and hold aligned) the main barrel and the focus scale ring which also has the infinity stop integrated.
- Before removing that tape, mark across the focus barrel and focus scale ring where they meet (at a point where there isn't any tape, or with a sharp knife through the tape) so you know how to re-align them later.
- Before unscrewing the main barrel, measure the barrel length at infinity, so you know that you have screwed it back together again for the correct no. of turns later. However, given the small helicoid pitch, I suspect this is a single-start helicoid, so not much to worry about.
- After removal of the tape, the main focus barrel is no longer constrained by the infinity stop integrated in the focus scale ring, and it can be unscrewed from its single helicoid.

This will render the main and secondary mirrors accessible.

Be careful, the internal cone-shaped light baffle is cemented to the main (rear) mirror, do not try to unscrew this!!

Assembly is in reverse order. After you have re-collimated the lens (or simply re-aligned the marks you made Wink ), use tape again to fix the focus scale ring to the main barrel, and roll back the rubber grip.

Any lenses behind the main mirror (between the main mirror & camera) need to be accessed from the back; there are four screws to take the back of. That probably also releases the infinity stop, so take care.

Good luck! Like 1 small


PostPosted: Mon Mar 14, 2022 1:46 pm    Post subject: Reply with quote

Thank you very much for all the information.

I will wait for a calm moment and experiment.

Cheers.


PostPosted: Tue Mar 15, 2022 3:24 pm    Post subject: Reply with quote

@ RokDoc:

Thanks for explaining the details! I have a RF 5.6/250mm here which looks absolutely like new - the only problem is that one of the two "light baffles" (not sure if this is the correct term!) just behind the front glass has come off. It now sits diagonally inside the large empty space between front lens and rear mirror ... probably best to remove the front lens and try to re-mount it ?!?

S


PostPosted: Tue Mar 15, 2022 8:26 pm    Post subject: Reply with quote

stevemark wrote:
@ RokDoc:

Thanks for explaining the details! I have a RF 5.6/250mm here which looks absolutely like new - the only problem is that one of the two "light baffles" (not sure if this is the correct term!) just behind the front glass has come off. It now sits diagonally inside the large empty space between front lens and rear mirror ... probably best to remove the front lens and try to re-mount it ?!?

S


I would assume so, yes. I imagine it will fit fairly tightly around the secondary mirror, so alignment is probably easy. Not sure what adhesive to advise though, maybe an epoxy for cementing metal to glass.

Good luck Like 1 small