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11-15-2012, 01:03 AM   #1
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Hello from Taiwan

Hi,

I live in Taiwan and my Pentax is a very old 6x7 with a yellowing glass lens.

Check out some slide film and polaroids I've shot on the thing at my blog more MSG!

Thanks!

11-15-2012, 02:03 AM   #2
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Don't worry abotut he radioactivity of thorium - its half life is so long that it will not hurt us. If it had a short half life it would have been useless as an element in optical glass since the glass composition would have changed too quickly. That also means it will not damage film. Nice pictures around Taipei.
11-15-2012, 02:50 AM   #3
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Thanks, the radioactivity doesn't bother me, it's the tint. It steals 1/2 stop of light and makes my color photos too warm.
11-15-2012, 04:45 AM   #4
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Enjoy the forum. Not too much can be done about the yellowing, but colour balance might be able to assist.

11-15-2012, 09:29 AM   #5
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QuoteOriginally posted by Mgarber Quote
Thanks, the radioactivity doesn't bother me, it's the tint. It steals 1/2 stop of light and makes my color photos too warm.
Do a forum search on yellowing. Some people here have ideas on a fix.
11-16-2012, 10:27 AM   #6
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Big news! I wasn't losing light due to yellowing, although some is present. I've discovered that my shutter is slightly too fast. I did extensive tests, and made an animation to time the shutter. The results can be seen here (using my 5D as control) more MSG!

The Pentax 6x7 shutter is slightly too fast. Now, the question is how to fix it.
11-16-2012, 12:25 PM   #7
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QuoteOriginally posted by Mgarber Quote
Big news! I wasn't losing light due to yellowing, although some is present. I've discovered that my shutter is slightly too fast. I did extensive tests, and made an animation to time the shutter. The results can be seen here (using my 5D as control) more MSG!

The Pentax 6x7 shutter is slightly too fast. Now, the question is how to fix it.
On your other page you say the shutter is electronically controlled, and 1969. That date pre-dates the IC timing devices such as 555, so my guess is that the design is an analog circuit. It probably relies on discrete components - resistors, capacitors and a voltage threshold switching device. If the problem occurs at all shutter speeds the problem would be in the devices in common. I would suspect the design has different resistors, one for each shutter speed, and one capacitor and one threshold device. You would need to open the camera, determine the circuit diagram, and component types. The challenge would be if it was the semiconductor to source and equivalent given that the function is somewhat subtle. (An exact replacement is probably also going to be very old, if you could find it. It is old enough that it might have been a germanium device, rather than silicon - and that would make difficulty because of the the differnt juction voltage. There are very few germanium devices made now.) If it is the capacitor it would be possible to source an alternate relatively easily.

The alternative is to use a work-around, and over expose (according to meter) by the required amount, but that is likely to be of limited value over time, because now the component has started to deteriorate I would expect it to continue to get worse.

Do you speak Chinese? If so I would recommend finding a camera service place. You will need to work out a way of judging whether they really know what they are doing or just have practiced a bit.
11-16-2012, 07:46 PM   #8
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QuoteOriginally posted by tim60 Quote
The challenge would be if it was the semiconductor to source and equivalent given that the function is somewhat subtle. (An exact replacement is probably also going to be very old, if you could find it. It is old enough that it might have been a germanium device, rather than silicon - and that would make difficulty because of the the differnt juction voltage. There are very few germanium devices made now.) If it is the capacitor it would be possible to source an alternate relatively easily.
Lucky for me, whatever the component is, they probably still make them somewhere in Taiwan. But Mystery Onion had the following to say in another forum:
QuoteOriginally posted by MysteryOnion Quote
The board for speed control is located on the shutter speed dial side under the mirror.
To access is going to be quite a few leatherettes and screws to be removed the lower middle shell.

Three adjusters should be on the board and control the span of speeds from 1/1000 side (VR1) and 1 sec. side (VR2) and the battery check threshold (VR3).
The adjustment will cause shifts and compression to the overall speeds... from what I'm observed.

I would say that adjustments should not be done casually, a constant test must be done. The push and pull of speeds have happened suddenly and is touchy to set.
So that gives me some clues. And I do speak Chinese, and I know a repair shop owned by and old guy who will either fix it or send it to somebody who knows how to fix it. The problem is parting with the camera for the several weeks that will take

11-17-2012, 03:38 AM   #9
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You are a lot better off than me, I do not speak Chinese, and I visit Taiwan fairly often. Was there a month ago for a week. Parts do seem easier to get there - some really unusual stuff is availabel if you know where to look.

I put a couple pictures related to Taiwan in Takumar Club thread recently:
https://www.pentaxforums.com/forums/lens-clubs/31601-takumar-club-740.html#post2164760
https://www.pentaxforums.com/forums/lens-clubs/31601-takumar-club-732.html#post2137427

The girl running last week was near home. That was a nicer part of the support of Taiwanese people who visit.
11-17-2012, 04:02 AM   #10
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Cool. Let me know if you need help searching for something or if you're stopping in.
12-02-2012, 05:32 AM   #11
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Welcome to PF. I'm also in Taiwan (Kaohsiung) and regularly share photos in the lens clubs. Have fun on here. Kirk
12-03-2012, 12:53 AM   #12
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Hello.
Probably you have already see the topic:
Post your medium format photos!
where you can post shoot taken with your MF.
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