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12-03-2012, 02:00 PM   #1
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Sigma 600mm Mirror Parts

One of the great things about the Pentax DSLR lineup is the backwards compatibility for lenses. True, the older manual lenses for 35mm lack some functionality, but if you have a good lens in the bag, and can make do with having to actually manually focus, etc., why spend money needlessly?

So I have this Sigma 600mm Mirror lens, that has worked great since I bought it about 30 years ago for $300. I have used it on my *iStDL and K10D, with good results.

The other day I was cleaning it, and when I tried to pull the filter carrier out (it inserts at the back of the lens, between the last element and the mount) it refused to budge. I pulled a bit harder, and the thing came out in pieces. Apparently one side had cracked and the warped a bit, and became caught as I tried to pull it out, and then broke in two pieces.

I contacted Sigma, sent them pictures, and the best they say they can do is to offer me a "trade up" deal.

Um, sure.

The SLR film to DSLR conversion factor means that it is essentially about a 900mm focal length lens. They no longer produce a compact, lightweight folded mirror type lens, and the closest thing they have is several thousand dollars.

I don't think so.

I'm not that great of a photographer.

I've tried finding "parts" lenses, but no luck there. I might try to glue the parts back together, but there is not much meat where the thing broke, so it may not stay together.

I also considered using the pieces to make a mold and maybe cast a new part from plastic resin, or perhaps metal using the lost wax casting process. But if I can simply find a usable replacement, why bother.

Any suggestions?





12-03-2012, 02:21 PM   #2
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I've never done this work on lens parts, but I've glued together even smaller things with a tiny amount of 500kg/cm^2 rated epoxy glue. You could try that and sandpaper away the excess.
The only problem I can see is that one side doesn't seem to be a clean break but rather a bit bent?
12-03-2012, 02:33 PM   #3
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There are lots of similar lenses out there on eBay, i.e.:
Super Telephoto 500mm F 8 Mirror Lens for Pentax PK K M KM K100D K110D K10D K20D | eBay
800mm Mirror Lens for Pentax K 30 K 7 K 5 K 01 K R Digital SLR Camera 084438151404 | eBay

Shouldn't be too hard to find an affordable replacement

Adam
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12-03-2012, 02:33 PM   #4
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QuoteOriginally posted by enemix Quote
The only problem I can see is that one side doesn't seem to be a clean break but rather a bit bent?
It is, exactly. What it looks like is that the plastic was under a bit of stress from the threaded metal ring that the filter screws into, and that it fractured on the side farthest from the camera in the images. Over time it warped some, and when I tried to pull the thing out it caught on the slot. I then tugged on it not really taking the time to see what was amiss, and it broke in two.

What really bites is how Sigma doesn't have repair parts available. They told me they have a carrier for 30.5mm filters, but not for the 22.5mm.

Another reason I would be reluctant to lay down a couple grand for a new lens that would have an equivalent focal length. Support is important to me, even for such "old" equipment.

12-03-2012, 02:36 PM   #5
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I've thought about how I would repair that. I have two of those lenses, and I took one out and gave it a once over.

Since I have a metal lathe and mill, take that into consideration as to my recommendation.

1)First I would get another filter (or step up/down ring) in the same diameter as the one used in the Sigma - 30.5mm.

Vivitar 30 5mm UV Ultra Violet HD Protective Glass Filter | eBay

2) I would take out the glass in the replacement filter so that I could use the threads/shell as the foundation for the repair.

3) Then, knowing the outer diameter of the empty shell, I would bore that diameter into an aluminum piece and duplicate as closely as possible the broken sigma piece. The Sigma piece is a relatively simple thing that just slides in and holds the filter in place.

The hard part of making a duplicate part is the threads for the filter, and in buying a spare ( or stepup/down) and taking the glass out, makes for an easy replacement/fabrication.

Last edited by LaurenOE; 12-03-2012 at 02:44 PM.
12-03-2012, 02:46 PM   #6
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Hmm..so there is a metal ring embeded in the plastic?
Even better now that the plastic cracked!

Drop me a PM if you want me to attempt to make something using your broken parts.

12-03-2012, 03:01 PM   #7
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QuoteOriginally posted by Racer X 69 Quote
What really bites is how Sigma doesn't have repair parts available. They told me they have a carrier for 30.5mm filters, but not for the 22.5mm.
Another reason I would be reluctant to lay down a couple grand for a new lens that would have an equivalent focal length. Support is important to me, even for such "old" equipment.
That is quite crappy of them, such a cheap part shouldn't be a problem to keep stocked.

Can the lens be used without a rear filter? In that case you could get some front-mounted filters instead and keep using it that way? Should at least be less expensive than getting a new lens.
12-03-2012, 04:34 PM   #8
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QuoteOriginally posted by enemix Quote
That is quite crappy of them, such a cheap part shouldn't be a problem to keep stocked.

Can the lens be used without a rear filter? In that case you could get some front-mounted filters instead and keep using it that way? Should at least be less expensive than getting a new lens.
Most mirror lenses are HUGE up front so I doubt you could.

12-03-2012, 06:47 PM   #9
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QuoteOriginally posted by enemix Quote
Can the lens be used without a rear filter?
Of course it can. There should be enough over-run to still focus at infinity. The filter is not needed.
12-03-2012, 06:48 PM   #10
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QuoteOriginally posted by Corto-PA Quote
Most mirror lenses are HUGE up front so I doubt you could.
I don't know how big the Sigma is but my 3M-5CA uses front-mounted 72mm filters.
12-03-2012, 09:24 PM   #11
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QuoteOriginally posted by enemix Quote
That is quite crappy of them, such a cheap part shouldn't be a problem to keep stocked.
Yes it is, and yes they should.

QuoteOriginally posted by enemix Quote
Can the lens be used without a rear filter? In that case you could get some front-mounted filters instead and keep using it that way? Should at least be less expensive than getting a new lens.
QuoteOriginally posted by Corto-PA Quote
Most mirror lenses are HUGE up front so I doubt you could.
QuoteOriginally posted by kh1234567890 Quote
Of course it can. There should be enough over-run to still focus at infinity. The filter is not needed.
QuoteOriginally posted by enemix Quote
I don't know how big the Sigma is but my 3M-5CA uses front-mounted 72mm filters.
The threads on the front of the lens for the hood are 86mm Ø. I've tried to find a clear or UV filter before just to protect the front element, or a polarizer, but no luck.

Wait. That was then.

I just did a Google search, and there are plenty of 86mm Ø filters! Woot! Woot!

At the very least I guess I can stick the remains of the outer part into the slot to keep stray light from entering the light path, and grab a circular polarizer, and a clear glass for protection, and continue to give a second life to this useful piece of equipment.
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