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03-27-2018, 01:37 AM - 1 Like   #1
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Spotmatic Light Seal Specs?

I have a couple of Spotmatics I picked up cheap. One SPII and one SP1000.
The latter is working well, but the former is suffering the old mirror hang problem. I'm working my way through the service manual to give it a CLA myself for the challenge, and if I'm successful I will do the SP1000 too. Part of this is building a shutter tester too, so it's a long process!

Anyway. On both bodies, the light seals and mirror bumper are nothing but a smear of crusty gunk. In the case of the SP1000, the seals are gone from the body and are now a crust on the door! I want to cut my own from some open cell foam, but can't seem to find what thickness they should be, and neither of them has enough left to guess.

Does anyone know?

03-27-2018, 04:59 AM - 1 Like   #2
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You should check out Jon Goodman's site Favorite Classics / Jon Goodman's Seal Replacement Instructions
If you scroll down to the Pentax Spotmatic, he says all the dimensions for the new foam.
I've bought a few of his kits and found them and his instructions to be great.
Probably a lot easier than buying foam and cutting it yourself.
03-27-2018, 07:26 AM - 1 Like   #3
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I use 1mm thick for the door seals, and 2mm for the mirror bumper.

Spotmatics shouldn't need replacement door hinge seals because the fuzzy stuff they use is pretty durable and usually still keeps out light. BTW, the hinge seal is the only really critical seal on the typical vintage SLR. Light can, and does, creep past that hinge, around the corner and onto your exposed film. The rest of the door gasket makes for a nice snug fit, but if it's missing or worn the only issue is the door rattles a bit when handling it. There's usually enough of a light trap where the back door fits into the groove in the frame, that light won't get around those corners and onto film.
03-27-2018, 07:59 AM   #4
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QuoteOriginally posted by blumoon722 Quote
You should check out Jon Goodman's site Favorite Classics / Jon Goodman's Seal Replacement Instructions
If you scroll down to the Pentax Spotmatic, he says all the dimensions for the new foam.
I've bought a few of his kits and found them and his instructions to be great.
Probably a lot easier than buying foam and cutting it yourself.
Great, I'll have a look. This is more about the process than the result, so I'm hapy to make them myself, it's just that I couldn't find a source for the exact dimensions, but this looks perfect.

03-27-2018, 08:31 PM   #5
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QuoteOriginally posted by victormeldrew Quote
I have a couple of Spotmatics I picked up cheap. One SPII and one SP1000.
The latter is working well, but the former is suffering the old mirror hang problem. I'm working my way through the service manual to give it a CLA myself for the challenge, and if I'm successful I will do the SP1000 too. Part of this is building a shutter tester too, so it's a long process!

Anyway. On both bodies, the light seals and mirror bumper are nothing but a smear of crusty gunk. In the case of the SP1000, the seals are gone from the body and are now a crust on the door! I want to cut my own from some open cell foam, but can't seem to find what thickness they should be, and neither of them has enough left to guess.

Does anyone know?
I built myself a shutter speed tester sensor paid radio shack $10 for parts. Got an idea from spotmatic repair manual how to position 2 phototransistors. Placed phototransistors 2mm inward from the edges of the frame, made slits. Can measure curtain speeds 12.5ms and shutter speeds. Had some learning curve with it though.
03-28-2018, 03:30 AM   #6
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QuoteOriginally posted by cameracravings Quote
I built myself a shutter speed tester sensor paid radio shack $10 for parts. Got an idea from spotmatic repair manual how to position 2 phototransistors. Placed phototransistors 2mm inward from the edges of the frame, made slits. Can measure curtain speeds 12.5ms and shutter speeds. Had some learning curve with it though.
I assume you used the audio circuit method then? I had the same idea for a pair of phototransistors rather than the single I've seen elsewhere, but figured I would need a stereo mic or line input so decided against it as I don't have a suitable input on my laptop. But thinking about it now I guess they could go through the same channel, although it would be trickier to read.
03-28-2018, 06:14 AM - 1 Like   #7
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QuoteOriginally posted by victormeldrew Quote
I assume you used the audio circuit method then? I had the same idea for a pair of phototransistors rather than the single I've seen elsewhere, but figured I would need a stereo mic or line input so decided against it as I don't have a suitable input on my laptop. But thinking about it now I guess they could go through the same channel, although it would be trickier to read.
At one point I was ready to purchase one of these kickstarter shutter testers for $160 but I didn't. Chose to experiment building my own tester and I must say everything is very simple. Used schematics from kyphoto.com Test Equipment / Combination Shutter Speed/Curtain Speed Tester bought resistors and phototranistors at Radio Shack for like $1 apiece. Downloaded Soundcard Scope. As I said before there was a learning curve to set everything up, get illumination right and interpret results, but I am confident my tester produces reliable results. I use it just as suggested in Spotmatic service manual to check for shutter bounce, curtain speed, and shutter speed. When I measure shutter speeds I just cover one of the slits and place the other one in the middle of film plane. If you try to build your own, you won't regret it!

---------- Post added 03-28-18 at 06:18 AM ----------

QuoteOriginally posted by victormeldrew Quote
I assume you used the audio circuit method then? I had the same idea for a pair of phototransistors rather than the single I've seen elsewhere, but figured I would need a stereo mic or line input so decided against it as I don't have a suitable input on my laptop. But thinking about it now I guess they could go through the same channel, although it would be trickier to read.
Your laptop should have input for a stereo microphone.
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03-28-2018, 06:25 AM   #8
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This is the circuit I was going for originally...the LED is just an indicator to show that it's working and aligned:


I found a stereo option, but with a simpler circuit, just a simple pair of phototransistors in parallel connected to each side of a stereo jack. I think a combination of the two is probably best...I can do without the LED, but I think the capacitor will improve the graph slightly (and protect the transistors somewhat). But I would need to get a USB sound interface with a stereo line in. I'm seriously regretting selling my oscilloscope!

I think a Schmitt trigger would help out the graph no end. It would iron out the various rise/fall times into clean voltage switches at fixed times. But then it might iron out shutter bounce... Probably I'm overthinking it at this point.

QuoteOriginally posted by cameracravings Quote
Your laptop should have input for a stereo microphone.
It might well do, I just assumed the mic input was mono. I shall investigate.

03-28-2018, 06:47 AM   #9
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QuoteOriginally posted by victormeldrew Quote
This is the circuit I was going for originally...the LED is just an indicator to show that it's working and aligned:


I found a stereo option, but with a simpler circuit, just a simple pair of phototransistors in parallel connected to each side of a stereo jack. I think a combination of the two is probably best...I can do without the LED, but I think the capacitor will improve the graph slightly (and protect the transistors somewhat). But I would need to get a USB sound interface with a stereo line in. I'm seriously regretting selling my oscilloscope!

I think a Schmitt trigger would help out the graph no end. It would iron out the various rise/fall times into clean voltage switches at fixed times. But then it might iron out shutter bounce... Probably I'm overthinking it at this point.



It might well do, I just assumed the mic input was mono. I shall investigate.
If you go in sound settings on your laptop there should be an option to test your input devices. If you have a stereo microphone jack you should be able to see 2 channels.

---------- Post added 03-28-18 at 07:02 AM ----------

QuoteOriginally posted by victormeldrew Quote
This is the circuit I was going for originally...the LED is just an indicator to show that it's working and aligned:


I found a stereo option, but with a simpler circuit, just a simple pair of phototransistors in parallel connected to each side of a stereo jack. I think a combination of the two is probably best...I can do without the LED, but I think the capacitor will improve the graph slightly (and protect the transistors somewhat). But I would need to get a USB sound interface with a stereo line in. I'm seriously regretting selling my oscilloscope!

I think a Schmitt trigger would help out the graph no end. It would iron out the various rise/fall times into clean voltage switches at fixed times. But then it might iron out shutter bounce... Probably I'm overthinking it at this point.



It might well do, I just assumed the mic input was mono. I shall investigate.
Unfortunately, I don't know that much about electronic parts and capacitors in particular. What do they do? How do they improve signal? I know I can benefit from improved signal
03-28-2018, 07:54 AM   #10
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QuoteOriginally posted by cameracravings Quote
How do they improve signal? I know I can benefit from improved signal
In the case of the circuit above, firstly it prevents DC from flowing, thus eliminating any DC offset in the signal (making sure zero is actually zero) - plus protecting the transistors if you happen to accidentally connect it to something you shouldn't. Secondly it will reduce noise.
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