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05-23-2019, 06:31 PM   #1
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Spotmatic underexposed band on negative on take up spool side

Hi need some help. Has anybody seen on Spotmatic, SPII or SP F a straight or a diagonal underexposed band running by the edge of the negative closer to speed selector? This only happens at 1/1000. Please check my photos attached. Apart from that one underexposed band the rest of the negative exposed evenly.

I am wondering what may this be? It is clear that one of the curtains does something at the beginning of its travel.

I recently overhauled this Spotmatic and I deliberately overlapped curtains more than 1 bar (let's say 1 and a half bar) in an attempt to get shutter speed perform at 1/1000.

Thanks for all suggestions!
Alex

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05-24-2019, 12:45 AM   #2
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I had a similar problem when my battery started to get weak.
05-24-2019, 01:00 AM   #3
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That is known as Capping. It means the slot between the two curtains doesn't stay the same during the travel. Sometimes, one curtain catching up enough to close the slot completely. I have found that a touch of lubricant (remove bottom plate) in the gears will solve the problem. I can't say anything about your overlapping issue.
05-24-2019, 06:02 AM   #4
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QuoteOriginally posted by arnold Quote
That is known as Capping. It means the slot between the two curtains doesn't stay the same during the travel. Sometimes, one curtain catching up enough to close the slot completely. I have found that a touch of lubricant (remove bottom plate) in the gears will solve the problem. I can't say anything about your overlapping issue.
Excellent, thanks Arnold for pointing me in the right direction. I am back to square 1 with my Spotty. I was pretty sure I've adjusted curtain travel accurately according to service manual. It seems i have to reset curtain overlapping back to 1 bar. But then i will have 1/1000 as 1/500. Really hate this!

Thanks again

---------- Post added 05-24-19 at 06:04 AM ----------

QuoteOriginally posted by sp500 Quote
I had a similar problem when my battery started to get weak.
Thanks for reply. Battery issue does not affect shutter mechanism on Spotmatics as it only powers exposure meter.

05-24-2019, 07:34 AM   #5
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If I read your images properly, then the curtain problem is happening at the beginning of the exposure - at the right side of the camera where the shutter curtains start their travel. This is because the image is inverted at the film plane, and left is right.

Usually capping occurs when the closing curtain catches up with the opening curtain, and exposure gets blanked off, or fades out. But what's happening with your shutter is the two curtains are starting too much together, and then opening up properly after those first few millimeters of travel. This would suggest the opening curtain is sticky and is taking too long to get up to speed.

Lubrication is likely the culprit.
05-24-2019, 08:18 AM   #6
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Hi Ontarian thanks! You are absolutely right! Let me explain as now I do understand what the problem is.

When I was restoring my Spotmatic (actually 3 of them) the cameras were performing at 1/1000 speed as 1/500. If adjusted fastest speeds I'd lose 1/60 sec. It would be firing as 1/125. I began to look for ways to get my cameras as close to spec as possible. Even though Pentax service manual stated that curtains should overlap by 1 bar, i thought if I overlapped curtains a bit more I'd increase top speeds without losing 1/60. And it did! The problem though i am getting shutter capping at 1/1000 now at the beginning of curtain travel.

So I will have to disassemble the camera again and set curtain overlap to 1 bar. Unfortunately I will have to leave with fastest shutter speeds being too slow.

On the other hand I lost some dear frames to shutter capping which is not acceptable.
05-24-2019, 11:14 AM - 1 Like   #7
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Sad to say it's very common to find old cameras not actually delivering on their top shutter speeds.

The Japan Camera Inspection Institute set tolerances for cameras to meet their marked shutter speeds. If a camera was marked as having a 1/1000th top speed, it had to be within a certain percentage of that to be eligible for export. However, going from my experience with all the 35mm SLRs I've tested over the years, very, very few of the old manual mechanical bodies actually reached a full 1/1000th when the slower speeds were properly adjusted. Seeing a 1/800th or 1/750th was far more common - and that was probably good enough for export (who's going to notice a third of a stop extra exposure anyway on an old manually metered camera?).


And a body with a lot of miles on it, might only see small increases in actual shutter speed above 1/250th - so a 1/1000th ends up being closer to 1/500th. The cam surfaces for the higher speeds do wear down with time.


It's not until electromagnetically controlled and electronically timed shutters turned up where the higher speeds were much more accurate, and could be dialed in spot-on after service.

My advice to you is to get your Spotmatic shutter adjusted so it delivers even exposure, even if it is a bit slower than marked at the top end. Trying to squeeze that 1/1000th out of it will likely lead to issues like capping, curtain bounce, or uneven exposure across the frame.
05-24-2019, 01:03 PM   #8
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QuoteOriginally posted by cameracravings Quote
Excellent, thanks Arnold for pointing me in the right direction. I am back to square 1 with my Spotty. I was pretty sure I've adjusted curtain travel accurately according to service manual. It seems i have to reset curtain overlapping back to 1 bar. But then i will have 1/1000 as 1/500. Really hate this!

Thanks again

---------- Post added 05-24-19 at 06:04 AM ----------



Thanks for reply. Battery issue does not affect shutter mechanism on Spotmatics as it only powers exposure meter.
Without going into too much detail, how hard is it to adjust your shutter curtains? Do you have to strip it right down to get at them? And what method do you use to determine timings?

05-25-2019, 05:34 AM   #9
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QuoteOriginally posted by Ontarian50 Quote
Sad to say it's very common to find old cameras not actually delivering on their top shutter speeds.

The Japan Camera Inspection Institute set tolerances for cameras to meet their marked shutter speeds. If a camera was marked as having a 1/1000th top speed, it had to be within a certain percentage of that to be eligible for export. However, going from my experience with all the 35mm SLRs I've tested over the years, very, very few of the old manual mechanical bodies actually reached a full 1/1000th when the slower speeds were properly adjusted. Seeing a 1/800th or 1/750th was far more common - and that was probably good enough for export (who's going to notice a third of a stop extra exposure anyway on an old manually metered camera?).

And a body with a lot of miles on it, might only see small increases in actual shutter speed above 1/250th - so a 1/1000th ends up being closer to 1/500th. The cam surfaces for the higher speeds do wear down with time.


It's not until electromagnetically controlled and electronically timed shutters turned up where the higher speeds were much more accurate, and could be dialed in spot-on after service.

My advice to you is to get your Spotmatic shutter adjusted so it delivers even exposure, even if it is a bit slower than marked at the top end. Trying to squeeze that 1/1000th out of it will likely lead to issues like capping, curtain bounce, or uneven exposure across the frame.
I agree with you, no more "overclocking" the curtains for me! My guess based on careful examination is that the fastest shutter speed is not achieved due to wear on the release cam and cam follower. If only I could fabricate a new release cam I would cure the problem. But this cannot be done. I will readjust my camera and will be happy with what I have. My Kodak Medalist II gives me only 1/250 instead of 1/400, and I am very happy with it.

Thanks again for you insightful advice!
Alex

---------- Post added 05-25-19 at 05:48 AM ----------

QuoteOriginally posted by dsmithhfx Quote
Without going into too much detail, how hard is it to adjust your shutter curtains? Do you have to strip it right down to get at them? And what method do you use to determine timings?
Curtain adjustment screws are located behind the bottom plate, so adjusting the curtains travel speed is easy. I would only do so after complete teardown, cleaning and lubrication. Most Spotmatics were last serviced in the 80s-90s and usually have pretty dirty mechanisms. A very common symptom of this is sticky mirror.

I made myself a curtain speed tester just as it was described in Asahi Pentax 23102 Service Manual. My shutter speed tester has 2 photo diodes which allows me to measure travel speed for both curtains in the beginning of travel and in the end of travel.
05-25-2019, 12:09 PM   #10
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QuoteOriginally posted by cameracravings Quote
A very common symptom of this is sticky mirror
Well a sticky mirror is itself also an easy fix with only bottom plate removal required (I've done it on a Spotmatic SP, it took about 15-minutes):

How to Fix a Ceased/"stuck" Mirror on a Pentax ES Spotmatic: 8 Steps
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