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Cmedin
Tinkerer
Username: Cmedin
Post Number: 1
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 02, 2007 - 01:00 pm: | 
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Hi all. I am in possession of a Kodak six-20 folder with the Anastigmat lens in a Dakor shutter. Everything seems to be fine mechanically, but the lens is pretty dirty and I'd like to disassemble and clean it. The rear element unscrews easily, and there appears to be a ring that can be removed that holds the lens assembly to the camera. I gather that once the pin/screw is removed from the front of the lens, the front element can be removed as well. Once that's done, I should have sufficient access to clean the middle element, right? (Are there more than three?)
Being new to this I don't want to screw anything up, so I was hoping for some guidance as to the best way to get the front element back on properly; I read that because of the focusing helical it can't just be removed and put back on without caring about proper positioning and whatnot. How do I do this?
Also, what's a safe solution for cleaning the lens elements on this beast?
Thanks much! |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 363
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 02, 2007 - 04:31 pm: |
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There will be 3 elements in the lens. The front one is on the focusing helical so it will come out easily, you have already gotten the rear one out, so you have access to all 6 surfaces. Kodak lens cleaning solution on a lens tissue is fine for cleaning them; wrap the tissue around the end of a cotton swab to reach the small glass surfaces.
You will have to reset the focus when you're finished. You'll need a focusing surface in the film plane .... glass with a strip of frosted Scotch tape on the front side (facing the lens) is good, but you may be able to get by with tracing paper, wax paper or a strip of Scotch tape stretched across the film rails. Make sure it is straight across the rails in the same plane that the film will be in. You want to set the lens at infinity, so go outdoors and find the most distant clear subject you can see; viewing the image on the focusing surface with a magnifier, adjust the lens to correct focus before you reattach the distance scale to the lens... then attach it in the infinity position.
You can also do the adjustment indoors, using another camera to create the infinity target, as described here: http://rick_oleson.tripod.com/index-123.html |
Cmedin
Tinkerer
Username: Cmedin
Post Number: 2
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 02, 2007 - 06:04 pm: |
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Thanks! I've never had a lens apart before so have no clue what the focusing helical even looks like or how it works. Figured I'd start with this antique since it won't break my heart if I can't get it back together right. :-)
So far the most complicated thing I've done is light seals and mirror damper foam, but I hope to work my way up to more advanced stuff down the road.
By the way, you have an excellent site; I used the tape trick on a couple of rangefinders and it did make a noticable difference. |
Cmedin
Tinkerer
Username: Cmedin
Post Number: 3
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 02, 2007 - 06:12 pm: |
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PS: is the front element supposed to move in/out when focusing? It just spins and I can't see any movement at all otherwise. Could it be that it's stuck to the middle element and I'm just spinning both together? I was googling for repair info earlier and somebody had that happen due to the grease getting so stiff it basically stuck the two together... |
Cmedin
Tinkerer
Username: Cmedin
Post Number: 4
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 03, 2007 - 08:17 am: |
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OK, got the front off and it is just screwed on with a very fine pitch thread. When I reassembly can I count on the infinity position being in the same spot and I just need to find the right # of turns to get the lens to focus right?
Also, just curious; how can the lens focus from 3.5ft to oo with such a small movement? |
Cmedin
Tinkerer
Username: Cmedin
Post Number: 5
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 03, 2007 - 08:59 am: |
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Responding to my own post again :-) I put it back together -- the infinity stop pin can only be in one spot so it was just a matter of finding the right 'turn' for the lens. Put some scotch tape on the film plane and went outside, found a nice big metal power line tower far away and just turned until it snapped into place. Went inside and set the focus at 10 feet and focused on an item roughly that distance away, it snapped in and out of focus on the tape as I moved to/away from the 10 ft mark on the lens.
Now I just need to spool some 120 onto the 620 spools I have sitting around and I can try it out! |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 364
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 03, 2007 - 11:41 am: |
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Sorry for not getting back for your questions, sounds like you've got it taken care of. The focusing helical is just a fine thread, but with several starts rather than just one. Generally, the distance scale is removable from the lens so you just ignore where it started, get it back to correct focus and then reattach the scale to suit. If you leave the scale on and remove the stop pin (some cameras are like that), then if you get it back onto the same thread start that it was on originally it will come back to the correct position.
The reason that the lens can focus so far with so little movement is that you are only moving the front element, not the entire lens. Separating the front element away from the lens changes the lens itself, reducing its focal length... a 105mm lens suddenly becomes a 95mm lens. But being mounted 105mm from the film, it now behaves as if it was a 95mm lens racked out 10mm on a focus rack. This is not the ideal way to focus a lens optically, but it's very simple and compact and inexpensive to do it that way. As long as you don't try focusing closer than about 1 meter this way, it's generally quite acceptable. |
Cmedin
Tinkerer
Username: Cmedin
Post Number: 6
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 03, 2007 - 12:11 pm: |
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Ah, so that is how the helical works. I wonder if I just got lucky and hit the right one the first time. Since infinity focus seems perfectly fine, and the 10 foot setting was sharp with merely a small twist in either direction throwing the object 10' away out of focus it sure seems like it.
Thanks for the explanations. I can't wait to go shoot some with this guy now. Really need to put together a shutter speed tester too if I'm going to keep playing with these oldies... |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 365
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 03, 2007 - 07:38 pm: |
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Have you tried the "TV" method? It's tricky with a leaf shutter, best to remove the lens for testing if you can. With focal plane shutters it's very quick and pretty accurate once you get used to it.... certainly good enough for photographic purposes. Any type of shutter tester is easier to use with the lens removed, though. http://rick_oleson.tripod.com/index-135.html |
Cmedin
Tinkerer
Username: Cmedin
Post Number: 7
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 04, 2007 - 04:39 am: |
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I'll give that one a go...thanks! |
Adrian
Tinkerer
Username: Adrian
Post Number: 77
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 04, 2007 - 05:24 am: |
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Rick,
Very interesting to see you shutter tester in use - like the use of available technology!
At risk of being an ignoramus, why does the presence or absence of the lens make a difference
And I'm interested in why it's trickier with a leaf shutter - presumably you get a different shaped area with the opening and closing leaves (a circle? Oblong?) rather than the stripe as the focal plane shutter goes across? Apart from my two OM10s, most things I'd fiddle with have leaf shutter so it would be a useful trick to be able to use .
Adrian |
Charlie
Tinkerer
Username: Charlie
Post Number: 93
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 04, 2007 - 06:12 am: |
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A leaf shutter is exposing the whole frame at one time while a focal plane shutter is exposing only a slit at one time which is dragged across the frame. The electronic flash synch time is an indication of the time it takes to expose the whole frame with a F/P shutter. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 366
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 04, 2007 - 04:49 pm: |
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If you can remove the lens from the leaf shutter, it's not much of a problem. The image you get is a horizontal band, similar to the one on the right hand side of the screen in my cartoon, with one exception: instead of being a straight stripe, the band bows out, fatter in the center and thinner at both ends. This is because the shutter speed through a leaf shutter is different in different parts of the circle... it's open longer in the center than it is near the edges. Judging whether you have a "correct" speed with a leaf shutter is therefore tricky, but this is not a quirk of the test method - this is just the way leaf shutters behave. There is no such thing as accurate, consistent speeds in a leaf shutter. But that is another rant for another day. They are accurate and consistent enough for photographis purposes, as a century of experience has proven.
If you leave the lens in, whether you're looking at a leaf shutter or a focal plane shutter, it's hard to see the image. You need to squint at a tiny virtual image of the monitor screen within the circle of the glass of the lens, and it's very hard to judge just because of the small size. The easiest way to overcome this limitation is to just load up a roll of film and take pictures of the screen: your images will look just like the test shots, and you can read your shutter's performance off of the photos. |
Adrian
Tinkerer
Username: Adrian
Post Number: 78
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 06, 2007 - 01:47 am: |
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Thanks, gents, I'll bear that in mind. I guess I have a mental block about "camera = lens", which is silly if you think about pinholes.
I should also have realised the difference with the focal plane shutter myself - especially the slit! I've spent enough time watching my Purma Special work that I should have remembered. In fact, I got it out again last night and had another look just to remind myself!
I feel educated and chastised...
Adrian |
