[wombat2go]

This induced me to run a shutter time test on the MX.
It is rather good!

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[stevebrot]

This induced me to run a shutter time test on the MX.
It is rather good!

Cool! I forgot that you were set up to actually measure the timing of the full shutter event as well as the light per exposure. Am I correct that ideally, the penumbra times should be constant at all speeds in a well-adjusted shutter?


Steve

[wombat2go]

Cool! I forgot that you were set up to actually measure the timing of the full shutter event as well as the light per exposure. Am I correct that ideally, the penumbra times should be constant at all speeds in a well-adjusted shutter?

Hi Steve,
You raise a few issues in one sentence!

The photodiode here is in the photo-current ( reverse bias ) mode
which has response time in microsecond range but ( I think)
the current is a logarithm of the incident photons.

Photodiode is mounted at the end of a "pipe" in black acetal of 1.2 mm dia and 10mm length
to give a grazing angle of 7 degree.
I originally made this to pick up scatter from ground glass on the Graflex cameras
when testing the leaf shutters and also the 4x5 focal plane shutter.
The "pipe" was pressed against the gg.
But I found it seems to work just as well on medium format shutters when
the ground glass is removed , and the "pipe" is approx at the focal plane ( ie "aerial focus")

I am fairly sure that the penumbra of the LF and MF leaf shutters
that i have measured here is dominated by the motion of the leaves, and not by my photodetector.

Today was the first time I measured a 35mm curtain shutter and i immediately noticed
1) a different shape to the rise and fall edges.

2) The brightness (40mm -M pancake wide open) was about 20%
of the brightness typically measured on a medium format lens.

3)There was a risk that the photodiode assembly would fall against
the Pentax MX shutter so i quickly measured the approx times and
did not record a trace off the storage scope.

So I have some work to do before measuring 35mm focal plane shutters at above about 1/125th second.

To truly measure the shutter speed/penumbra of a small film camera, I suppose I have to replicate:
The maximum angle of photons that will bring the film grains above recombination.
The floor brightness that will bring the film grains above recombination.
The sensor junction more accurately at the film plane but so it can't damage the shutter.
The photodiode current run through a transfer function to replicate film exposure.

regards

(Yikes, I hope Rupert and Otis don't get hold of this little diatribe!)

[stevebrot]

(Yikes, I hope Rupert and Otis don't get hold of this little diatribe!)

A very valid fear


Steve

[pathdoc]

Hi Steve,
You raise a few issues in one sentence!

The photodiode here is in the photo-current ( reverse bias ) mode
which has response time in microsecond range but ( I think)
the current is a logarithm of the incident photons.

Photodiode is mounted at the end of a "pipe" in black acetal of 1.2 mm dia and 10mm length
to give a grazing angle of 7 degree.
I originally made this to pick up scatter from ground glass on the Graflex cameras
when testing the leaf shutters and also the 4x5 focal plane shutter.
The "pipe" was pressed against the gg.
But I found it seems to work just as well on medium format shutters when
the ground glass is removed , and the "pipe" is approx at the focal plane ( ie "aerial focus")

I am fairly sure that the penumbra of the LF and MF leaf shutters
that i have measured here is dominated by the motion of the leaves, and not by my photodetector.

Today was the first time I measured a 35mm curtain shutter and i immediately noticed
1) a different shape to the rise and fall edges.

2) The brightness (40mm -M pancake wide open) was about 20%
of the brightness typically measured on a medium format lens.

3)There was a risk that the photodiode assembly would fall against
the Pentax MX shutter so i quickly measured the approx times and
did not record a trace off the storage scope.

So I have some work to do before measuring 35mm focal plane shutters at above about 1/125th second.

To truly measure the shutter speed/penumbra of a small film camera, I suppose I have to replicate:
The maximum angle of photons that will bring the film grains above recombination.
The floor brightness that will bring the film grains above recombination.
The sensor junction more accurately at the film plane but so it can't damage the shutter.
The photodiode current run through a transfer function to replicate film exposure.

regards

(Yikes, I hope Rupert and Otis don't get hold of this little diatribe!)

Given that Eric would have to be able to measure these things in order to adjust the timing of deranged shutters that he repairs, I imagine he would have all the answers. Why don't you check your suppositions with him and report back? I'm actually finding this quite interesting, even if I don't have the gear to do it. I'd be very interested to see what the differences were pre- and post-CLA even in a camera which wasn't obviously defective and which was giving reasonable shutter speeds "to the ear".

[Johnny Rod]

I would too. My shutter tester is a single phototransistor so not sure it's well suited to curtain shutters. I found my MX the best of mine, at the high speeds. The Super Program perhaps also needs a look as I've replaced a couple of foam bits. I was going to try to clean out the shutter tracks in the K2 as per RayUK's notes in the thread I linked above, but it looked far from simple, and I worried about solvent/dirt going everywhere.

[stevebrot]

I was going to try to clean out the shutter tracks in the K2 as per RayUK's notes in the thread I linked above, but it looked far from simple, and I worried about solvent/dirt going everywhere.

That is a very valid concern. A good rule of thumb is to not fiddle with the clean/lube of a vertical metal shutter unless you know what you are doing. If damaged in the attempt, it may well be toast and difficult to replace.


Steve