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SBKOO 21mm finder
Old 3 Days Ago   #1
Dez
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SBKOO 21mm finder

I recently bought one of these Leitz finders cheaply, as it was in sorry shape The rear inner element, which has the mirror surface, is out of position, leading to a very blurry image. These finders have a bad reputation for being extremely difficult to disassemble, but every reference I can find is about the eyepiece. Well, it wasn't easy to remove, but I have done the deed. So, how do I get the rest of the elements out the front to be able to clean and properly mount them? Anyone have some experience with this little beast?



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Old 3 Days Ago   #2
HuubL
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I was told it was impossible to get the front glass out without breaking it.
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Old 3 Days Ago   #3
Vickko
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yep. From the investigations that I've done, the front element is glued on. You essentially need to press it all out from the rear. And I have no idea how you space things to get it to work again.

So maybe if you soak the front 3 mm in some solvent to dissolve the adhesive, you might loosen things up and make the "pushing out of the lens" easier.

Good luck
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Old 3 Days Ago   #4
Phil_F_NM
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The front group is indeed cemented in ad after this many years, the glue is probably as hard as amber. A solvent may work but an ultrasonic cleaner might be better as the cement becomes very brittle with this much age and may simply crumble out.

Regarding the spacing, the glass should just sit on a little shelf. There could be a shim/s under the glass but I think it's unlikely. The fine focus would be done with the rear element but seeing as these were static optics there shouldn't be any shimming necessary.

Phil Forrest
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Old 3 Days Ago   #5
Landshark
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Been there, done that. Never again!

The elements are held in by fear, gravity and paint. That's the only adhesive used, no glue is involved.
Acetone was suggested by a well regarded Leica repairman. With a WARNING, it's something he really doesn't like to do because of the delicacy involved.

OK, so I used Acetone to soften it and used a thin piece of spring steel to clear any remainder of paint out..The paint of the frame is also softened by the Acetone......................and
Acetone is really thin and flows quickly and everywhere. Did I mention the spring steel? You're going to need that to sort of dig the front lens loose.

Get the point?

The glass BTW doesn't simply push out from the rear either, there's separation between the lenses but once you have the front element out, everything else just sort of drops out
Anyway, if you've taken the glass out etc. etc. stick everything back in place and carefully paint around the edges of the glass.......Viola! Fini!
Did I mention there's a cemented pair in there? Or that Acetone flows every where?..........Want to guess how I figured that one out?

Yeah, I know it's Voila I just happen to like violas.
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Old 3 Days Ago   #6
JMQ
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Phil, there is a reason why Sherry and DAG would not touch this finder with a 10-foot pole.
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Old 3 Days Ago   #7
Phil_F_NM
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Quote:
Originally Posted by JMQ View Post
Phil, there is a reason why Sherry and DAG would not touch this finder with a 10-foot pole.
It was made by the hand of man. It can be fixed.

Phil Forrest
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Old 3 Days Ago   #8
Dez
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I have the front element loose and flopping around, but the lower part of it will not move forward. It appears there is a steel framework in there which slides in and snaps into place. There is a channel in the bottom of the shell with a sharp lip at the front. I think this frame is sliding forward and stopping at this lip.

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Dez
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Old 3 Days Ago   #9
JMQ
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Quote:
Originally Posted by Phil_F_NM View Post
It was made by the hand of man. It can be fixed.

Phil Forrest
Indeed Phil, Indeed, but not by those 2.
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Old 3 Days Ago   #10
mdarnton
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Not by Leica, either. I sent one in for a cleaning, 40 years ago when they were still current, and they charged me a pretty fair price for the job and sent me a brand new finder.
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Old 3 Days Ago   #11
Dez
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Well, I managed to get it apart. It was just paint and glue holding the front elements in. I've cleaned everything up, and the paint is drying where I re-blackened the surfaces that had been painted (dissolved in the solvent). There was one good size chip in a corner of the front element when I started; now there are two. I can see why repair people don't want to mess with these things. Hopefully, I'll be able to get everything back together tomorrow while keeping all the bits clean. Lots of work, but I ended up with a decent Leitz 21mm finder for under fifty bucks!

Oh, and the blur wan't caused by the misplaced rear element. The major fault was that one of the big internal elements was in backwards! So someone else has had this beastie apart. That's probably where the first chip came from.

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Dez
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Old 2 Days Ago   #12
sc_rufctr
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I serviced mine when I first got it. I used a very small scalpel knife to release the front element.
It worked fine for me but it's risky doing it this way.

Meanwhile the order of components in the finder. It's certainly not as simple as some of the other focal lengths.

The biggest issue you will have is getting it back together with no dust inside.
I used a silicon based craft glue (softish when cured) to secure the front element. I would not use epoxy because that will make it very difficult to disassemble without damaging something.

*** Note the chip on the edge of my front element. It was like that when I removed it.





Good luck with yours.
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Old 2 Days Ago   #13
Erik van Straten
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Great pictures, Peter! I never knew this finder was so complicated. I remember however it was new three times as expensive as the 28mm finder back in the early seventies.

By the way, mine rattles when I shake it, but it works fine, so I'll leave it as it is.

Erik.
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Old 1 Day Ago   #14
Dez
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Thank you very much, Peter. Your illustration is just what I needed. It is now obvious why I cannot get good focus from my SBKOO finder: the front element and spacer are missing!

I may be able to salvage something yet. I understand the position of the two strong concave elements, but not their correct orientation. Which way does the flat surface of each element go? Can you give me an estimate of the focal length or dioptre strength of the front element? I may be able to cobble something up.

At the moment, I have the two concave elements oriented so the flat sides are facing towards the ends of the finder (i.e. almost a sphere of air in the middle). It appears to give approximately the field of a 17mm lens, but some of the field is vignetted by the front of the housing, and it focuses to the eye a bit beyond infinity. With both flat sides facing forward, and the two lenses appear to be identical, it's pretty close to being right; could the front element be a simple flat that I could make out of something like a microscope slide??

Thanks for your help,
Dez
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Old 1 Day Ago   #15
sc_rufctr
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Quote:
Originally Posted by Dez View Post
Thank you very much, Peter. Your illustration is just what I needed. It is now obvious why I cannot get good focus from my SBKOO finder: the front element and spacer are missing!

I may be able to salvage something yet. I understand the position of the two strong concave elements, but not their correct orientation. Which way does the flat surface of each element go? Can you give me an estimate of the focal length or dioptre strength of the front element? I may be able to cobble something up.

At the moment, I have the two concave elements oriented so the flat sides are facing towards the ends of the finder (i.e. almost a sphere of air in the middle). It appears to give approximately the field of a 17mm lens, but some of the field is vignetted by the front of the housing, and it focuses to the eye a bit beyond infinity. With both flat sides facing forward, and the two lenses appear to be identical, it's pretty close to being right; could the front element be a simple flat that I could make out of something like a microscope slide??

Thanks for your help,
Dez
Looking at your photo in your OP your front element seems to be there. Although it looks turned around. (It's in backward. It should concave in)

The flat surface of the both of the central elements should face towards the front. They "Spoon" each other
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Old 1 Day Ago   #16
sc_rufctr
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If it helps I could disassemble mine and line up the components upright to give you a better understanding of how they are placed.

I'll only do this if you ask me to and it's not a big deal. Let me know.
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Old 1 Day Ago   #17
Dez
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Quote:
Originally Posted by sc_rufctr View Post
If it helps I could disassemble mine and line up the components upright to give you a better understanding of how they are placed.

I'll only do this if you ask me to and it's not a big deal. Let me know.
Thanks very much for your kind offer, but it won't be necessary. Actually, what had happened to the finder is rather complex. The front element and the thin spacer behind it were missing. The second and third element were pushed up to the front; whether or not this was done to give the impression that the finder was complete, I don't know. The rear mirrored element was flopping around inside. The result was a quite fuzzy image, with framelines that appeared and disappeared. Reversing one of the elements resulted in a less fuzzy image, but with a fisheye coverage.

I have now put the rear spacer back where it belongs and pushed the two remaining elements to their correct position, and tacked the corners of the front one with silicone glue. It now provides a sharp image which is quite close to the correct coverage, but is slightly vignetted by the shell. I have blackened the inside of the shell to eliminate reflections, which helps. So it is usable, but only just.

From your picture, it appears that the front element is a very weak concave lens, maybe -1 diopter. I am going to try to find some appropriate glass that I can grind down to make a new one, but that will be quite tricky. the front spacer should not be hard to fabricate.

Thanks for all your help- this turned out to be more difficult than I had anticipated, and the several misconceptions I came up with along the way didn't help a bit. I guess I can't complain too much; it was very cheap.

Cheers,
Dez
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Old 23 Hours Ago   #18
sc_rufctr
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Good luck Dez.
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