Measuring it should not be a great problem: just take-out the retardment and measure I gues.....
(measuring opening and closing times)
(measuring opening and closing times)
*******Measuring it should not be a great problem: just take-out the retardment and measure I gues.....
(measuring opening and closing times)
Philippe,
If you let them set the fastest speed of your H-lenses to 1/350, you're more than 1 full stop off.
...
When high speed is needed, take (rent, borrow) a focal plane shutter camera, that is why it is made for.
Well... considering the mass of the shutter blade elements, and the spring power available to overcome that mass ...
I've GOT to avoid falling into a trap here: trying to argue without one shred of objective data. Myself, I'd be more confident in the Hasselblad/ Prontor/ Compur/ Engeering organizations.
One question: If you tech IS able to "set" your 1/500th shutter speed to 1/350th ... why would you not have him/her set it to 1/500th?
I've GOT to avoid falling into a trap here: trying to argue without one shred of objective data. Myself, I'd be more confident in the Hasselblad/ Prontor/ Compur/ Engeering organizations.
Between 1/250 and a little more than 1/400 — close to 1/500 —, 1/350 is more a 1/2 than a full stop. [...]
*******John, you need to study up on "shutter efficiency." It has nothing to do with overcoming inertia. It has to do with a hole uncovering another hole, as you say. Suggest you look at the google book link I posted earlier (you need to back up to the "previous page" for the discussion of leaf shutters), or even better read Ansel Adams "The Camera" in which he describes shutter efficiency.
*****
This thread began with problems with a cold-crank Compur shutter and has gotten muddled. My attempt in my last post was to attempt to point out that it is basic geometry which is the bete noir is this, such as it is. And although I am a poor benighted former history major with no scientific training, common sense (and least my own, I think) tells me that if there is a given amount of inertial "drag" of an opening shutter, and that self-same shutter is opening with the same geometry as the aperture, then the smaller the aperture, the greater the percentage of effect (however slight) the smaller the aperture being "uncovered." I would suggest to anyone wishing to try this out, that they would find that the exposure of a leaf shutter given at, say an actual shutter speed of 1/500 sec at f/22, will not be precisely linear with the exposure given by the same shutter at an actual shutter speed of 1/250 at f/22.
Now we all know that, for various reasons, many shutters at the higher speeds are not dead on accurate--which is, I think, what Phillippe is talking about. But that is a different issue, is it not?
Shutter efficiency and the resulting "relative exposure" resulting from the phenomenon has been an issue since the development of the first leaf shutter.
****
Yup
It has nothing to do with "ego" of Hassy, Rollei or even Yashika owners and users. I hope your tongue was in your cheek when you typed that.
******
I reckoned that the Ngh, Ngh, and the vbg (very big grin) might have been a giveaway on that point. "Course, you are probably just chagrined that you do not have an Argoflex!!! (VBG)
p.s. it will also help if you start believing that shutter timing does NOT start when the shutter is fully open.
Indeed. Brian is absolutely right in all he wrote.
Another thing is that, though it may appear to be, it is not a big practical problem.
******
Thank heaven for the latitude of modern films.
That is not to say that it is not a real phenomenon. It certainly is.
But also really not that big a deal.
*****
Quite correct.
The deviation of the actual speed from what it should be is small.
We know when it happens, so can adjust for it.
*****
Yup. And, obviously, spending a coupla thousand bucks for a camera system that requires us to make those kinds of adjustments under those conditions is no big deal, either.
And it is not that often that you are shooting the fastest speed at small enough apertures for this to be a problem to begin with.
*****
Very true. I still have AGFA APX 25 in the freezer, so this is not a big deal with this dinosaur.
And when you consider that leaf shutters have been in use for many years, in many different cameras/lenses, and are still being sold and used new, it really cannot be that big a problem. Else we wouldn't have put up with it for so long, nor still put up with it today, would we?
******
It would be great if someone could give us some numbers.
OK, who has measured the difference on a negative? I'm guessing no one.
****
Yup.
I'll try to remember to shoot two frames at the same EV and different apertures and measure the negs with a Xrite 810 next time I have the Hassy out. Measuring negatives might have saved about 15 posts in this thread.
Mike
It is both.
There would be a difference between f/22 at 1/500 and f/8 at 1/60.
But, the efficiency being better at slower speeds, you should also try to see the difference between, say, f/22 at 1/500 and f/22 at 1/250 or f/22 at 1/125.
Which is why it is hard to test: the latter test would require being able to control the amount of light precisely, such that different EVs lead to the same exposure.
I test my shutters now and again, on transparancy film (i stull have a stash, which i do not use for anything else - no need for transparencies these days), shooting all speeds at constant EV (actually, i need to shoot two series - one for the slower speeds, one for the faster speeds - with some overlap).
I never noticed a considerable difference. Just noticeable, about 1/2 stop maximum, at most. And that only between all other (fast) speeds and 1/500.
You should run a similar test for your focal plane shutters too, by the way.
Odds are on that the fastest speed isn't quite what it should be.
Not because of a similar efficiency problem, but because the faster the speed, the more the inevitable error margin (in setting up and adjusting the thing) shows itself.
It is both.
There would be a difference between f/22 at 1/500 and f/8 at 1/60.
But, the efficiency being better at slower speeds, you should also try to see the difference between, say, f/22 at 1/500 and f/22 at 1/250 or f/22 at most. And that only between all other (fast) speeds and 1/500.
******
Envision, for the moment, a shutter that is perfectly timed at 1/250 and 1/500.The point the old timers made was that---with a leaf shutter--- there would be no detectable difference in density between 1/250 at f/22 and 1/500 at f/22--even though we all KNOW there should be one stop difference.
Lets not get carried away with nostalgia Mr. Leica of the 5 iteration of M. Some of those old time exposures would have been better having been kept under the hat and in some cases it would have been a good idea to save the film and protect the head from sunburn.
I never noticed a considerable difference. Just noticeable, about 1/2 stop maximum, at most. And that only between all other (fast) speeds and 1/500.
Q.G.;733063You should run a similar test for your focal plane shutters too said:Don't confuse shutter ACCURACY with shutter EFFICIENCY. But your point remains valid that testing of FP shutters is warranted if one is concerned about teh shutter efficiency issue... there is indeed a shutter efficiency effect with FP shutters too. The physics of the timed opening/closing of a hole across other various sized holes shares certain similarities with the physics of sliding various sized slits across various sized holes... to put it in the fully-acccurate language of a history major.
As Phillipe sez: let's not get carried away...
*******
I wonder how that crept in?
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