Help me diagnose a shutter (I think) Issue. SRT 101

Brett Rogers · Mar 19, 2019

It's likely to be a band of underexposure caused by the mirror not retracting quickly enough. Can't possibly be the shutter, that's horizontal, can't be aperture of course due to the size and shape. Other owners have had the issue with SRT101s. It shouldn't be too problematic to fix. The curtain times should be checked and adjusted though because if the mirror is sticking it may relate to need for lubrication or lack of tension.

For example reflex mirror hanging up can often be insufficient second curtain tension in case of a 101. Various 101s also used either a plastic (nylon) or metal mirror gear under the lower cover. The plastic ones can fail occasionally. Had to swap one over for a metal type for an owner a couple of years ago actually. Not a bad idea to inspect this part also just in case it is on the way out and causing problems.

If there is no parts failure, cleaning and lubrucating the lower cover mechanisms and, if needed, adjusting the curtain tensions should effect a fix. It's basically a very well made, durable and reliable design.

Arbitrarium · Mar 19, 2019

Looks to me like the only explanation is the mirror bouncing back down a bit after lifting. Explains why it only shows on slower speeds, fast speeds would open and close before the mirror bounces.

If it was the mirror not retracting fully, it would show on all shutter speeds, or even be worse at faster speeds.

Brett Rogers · Mar 19, 2019

Arbitrarium said:
Looks to me like the only explanation is the mirror bouncing back down a bit after lifting. Explains why it only shows on slower speeds, fast speeds would open and close before the mirror bounces.

If it was the mirror not retracting fully, it would show on all shutter speeds, or even be worse at faster speeds.

You raise some valid points above and it's possible you might be correct. As a percentage of the overal exposure time, any capping effect from a lethargic or bouncing mirror is only going to be more pronounced at higher speeds.

Remember, though, that the elapsed time needed for the curtains to fully traverse the film gate should be the same at 1/1000 as it is at say 1/60 or 1/30. It's the relative timing of the two curtains aka the slit width that's different, not their running velocity. If the mirror was behaving identically at, say, 1/1000 the effects should still be visible, but perhaps not over the entire length of the film gate.

From experience though I can inform that these now up to fifty-something year old SLRs may not always manifest mirror problems at every shutter speed. Eg one which arrived last year would operate correctly at high speeds however when fired at medium or slower speeds only, the mirror would stick up. The cause for that one was insufficient second curtain tension and needing lubrication, because the curtain shaft wasn't always tripping the mirror release lever enthusiastically enough when the curtain was closing.

In summary, then, I agree with some of what you suggest—but you're assuming the mirror is malfunctioning at every shutter speed, which may or may not actually be the case.

I'd give the mechanism beneath the lower cover a clean and lube and if needed adjust shutter accuracy first—it may well benefit from these things anyway.

I rather like the 101s and have a few. The most recent which arrived last week was also in need of some basic adjustment, but after getting this it passed a check on my Kyoritsu shutter tester with flying colours. If the OPs camera remains recalcitrant following some basic maintenance as outlined above, it may be necessary to investigate further of course, but I suspect this may get it sorted.

Cholentpot · Mar 19, 2019

Brett Rogers said:
You raise some valid points above and it's possible you might be correct. As a percentage of the overal exposure time, any capping effect from a lethargic or bouncing mirror is only going to be more pronounced at higher speeds.

Remember, though, that the elapsed time needed for the curtains to fully traverse the film gate should be the same at 1/1000 as it is at say 1/60 or 1/30. It's the relative timing of the two curtains aka the slit width that's different, not their running velocity. If the mirror was behaving identically at, say, 1/1000 the effects should still be visible, but perhaps not over the entire length of the film gate.

From experience though I can inform that these now up to fifty-something year old SLRs may not always manifest mirror problems at every shutter speed. Eg one which arrived last year would operate correctly at high speeds however when fired at medium or slower speeds only, the mirror would stick up. The cause for that one was insufficient second curtain tension and needing lubrication, because the curtain shaft wasn't always tripping the mirror release lever enthusiastically enough when the curtain was closing.

In summary, then, I agree with some of what you suggest—but you're assuming the mirror is malfunctioning at every shutter speed, which may or may not actually be the case.

I'd give the mechanism beneath the lower cover a clean and lube and if needed adjust shutter accuracy first—it may well benefit from these things anyway.

I rather like the 101s and have a few. The most recent which arrived last week was also in need of some basic adjustment, but after getting this it passed a check on my Kyoritsu shutter tester with flying colours. If the OPs camera remains recalcitrant following some basic maintenance as outlined above, it may be necessary to investigate further of course, but I suspect this may get it sorted.

I have no qualms working on my own cameras. I got a Pentax ES yesterday and fixed a sticking mirror problem. Electronics seem shot though as the batteries are heating up when I put them in.

Any charts which levers and gears should get my attention for a light lubrication for the 101?

Help me diagnose a shutter (I think) Issue. SRT 101

Brett Rogers

Arbitrarium

Brett Rogers

Cholentpot

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