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View Full Version : Stupid shutter question (Copal detents & speeds)

seezee
17-Jan-2017, 19:09
I think I know the answer, but can anyone confirm: a typical modern LF shutter, such as a Copal, has detents on the speed adjustment that correspond to the marked speeds. I assume the speed is controlled by a tension spring somewhere in there, so if I set the dial in between detents, e.g., halfway between 1/30th- and 1/60th-second, will I get a 1/45th-second exposure?

Anyone know how this works on mechanical SLRs or rangefinders?

Dan Fromm
17-Jan-2017, 19:42
I think I know the answer, but can anyone confirm: a typical modern LF shutter, such as a Copal, has detents on the speed adjustment that correspond to the marked speeds. I assume the speed is controlled by a tension spring somewhere in there, so if I set the dial in between detents, e.g., halfway between 1/30th- and 1/60th-second, will I get a 1/45th-second exposure?

no

stawastawa
17-Jan-2017, 20:26
nop, you get either 1/30th or 1/45. this is what the detents look like:
159941

If the B is at 3 O'clock then the detents are at about 1-2 o'clock. there are a few more detents at 4/5 o'clock. As you can see they are stair stepped, not continuous.

seezee
18-Jan-2017, 13:03
nop, you get either 1/30th or 1/45. this is what the detents look like:
159941

If the B is at 3 O'clock then the detents are at about 1-2 o'clock. there are a few more detents at 4/5 o'clock. As you can see they are stair stepped, not continuous.

So spring tension isn't what controls the speed? There's something less-direct, like clockwork, based on the stairstep cams?

Luis-F-S
18-Jan-2017, 14:28
I think I know the answer... I assume the speed is controlled by a tension spring somewhere in there, so if I set the dial in between detents, e.g., halfway between 1/30th- and 1/60th-second, will I get a 1/45th-second exposure?

Wrong! it's not a Leica! Sometimes you can "adjust" the speed on older Ilex and Compound shutters, but with the more modern Copal and Compur shutters, it doesn't work.

Bob Salomon
18-Jan-2017, 15:06
Wrong! it's not a Leica! Sometimes you can "adjust" the speed on older Ilex and Compound shutters, but with the more modern Copal and Compur shutters, it doesn't work.

In fact, you can cause damage to the shutter by trying to set intermediate speeds.

Pere Casals
18-Jan-2017, 15:09
I'd add that mechanical shutters often vary from their marked speeds.

Not uncommon that 1/10 is in fact something like 1/14, or 1/25 is 1/30, 1/250 is 1/160. This is specially true with old material and with not regularly serviced units.

Film has a lot of latitude, but if you need precission (with Velvia...) the first you have to do is to buy a shutter tester and check what the real speeds are, you can write down true speeds on a label and place it on the lens board.

You can buy shutter tester as cheap as \$60, or even there is one for \$15 new (ebay... a photocell connected to PC soundcard, then record sound with Audacity software, and measure it)

http://www.kenrockwell.com/tech/exposure-large-format.htm

Regards

RedGreenBlue
18-Jan-2017, 15:26
So spring tension isn't what controls the speed? There's something less-direct, like clockwork, based on the stairstep cams?

The spring tension is essentially constant. Some shutters do have a secondary booster spring to reach the highest speed: 1/500, typically in small and medium format shutters.

Yes, a clockwork type mechanism called an escapement retards the closing of the blades after they reach full-open. Speed cams are stair-stepped, so intermediate speeds can't be set.

seezee
18-Jan-2017, 17:17
In fact, you can cause damage to the shutter by trying to set intermediate speeds.

Good to know!

seezee
18-Jan-2017, 17:18
I'd add that mechanical shutters often vary from their marked speeds.

seezee
18-Jan-2017, 17:19
The spring tension is essentially constant. Some shutters do have a secondary booster spring to reach the highest speed: 1/500, typically in small and medium format shutters.

Yes, a clockwork type mechanism called an escapement retards the closing of the blades after they reach full-open. Speed cams are stair-stepped, so intermediate speeds can't be set.

Bob Salomon
18-Jan-2017, 17:33
I'd add that mechanical shutters often vary from their marked speeds.

Not uncommon that 1/10 is in fact something like 1/14, or 1/25 is 1/30, 1/250 is 1/160. This is specially true with old material and with not regularly serviced units.

Film has a lot of latitude, but if you need precission (with Velvia...) the first you have to do is to buy a shutter tester and check what the real speeds are, you can write down true speeds on a label and place it on the lens board.

You can buy shutter tester as cheap as \$60, or even there is one for \$15 new (ebay... a photocell connected to PC soundcard, then record sound with Audacity software, and measure it)

http://www.kenrockwell.com/tech/exposure-large-format.htm

Regards

As long as the shutter is +\ 30% of the marked speed it is in spec.

Pere Casals
19-Jan-2017, 07:25
As long as the shutter is +\ 30% of the marked speed it is in spec.

Bob, thanks for that interesting information about what is considered under specs.

Bob Salomon
19-Jan-2017, 07:52
Bob, thanks for that interesting information about what is considered under specs.

That isn't what is "considered" that is the spec.

Pere Casals
20-Jan-2017, 03:19
That isn't what is "considered" that is the spec.

OK... so it also was the criteria for warranty, perhaps all manufacturers had same level of guaranteed accuracy ( ? )

Recently I've checked all my shutters (some pretty old) I saw differences to marked speeds, but I noted a very good repetitiveness as, at least, speed was allways the same, even in the case of a pneumatic No.5 Compound that is 50 years old.

I feel that those specs are enough for negative film. For Velvia I think that a shutter tester is very interesting. I practiced Velvia with a 35mm F5, with consistent results, while with LF I saw some inconsistency, solution that worked was the shutter tester...

Bob Salomon
20-Jan-2017, 05:13
OK... so it also was the criteria for warranty, perhaps all manufacturers had same level of guaranteed accuracy ( ? )

Recently I've checked all my shutters (some pretty old) I saw differences to marked speeds, but I noted a very good repetitiveness as, at least, speed was allways the same, even in the case of a pneumatic No.5 Compound that is 50 years old.

I feel that those specs are enough for negative film. For Velvia I think that a shutter tester is very interesting. I practiced Velvia with a 35mm F5, with consistent results, while with LF I saw some inconsistency, solution that worked was the shutter tester...
We are talking two different things. A shutter is in spec if it is within +\- 30% of its marked setting. It is consistent if it stays within that tolerance. That does not mean that every time that you fire the shutter that it changes its speed.

Pere Casals
20-Jan-2017, 06:19
We are talking two different things. A shutter is in spec if it is within +\- 30% of its marked setting. It is consistent if it stays within that tolerance. That does not mean that every time that you fire the shutter that it changes its speed.

Hello Bob,

Yes, of course... but I think that repetitiveness is important, specs don't say speed won't vary form +30% to -30%, but happily most shutters repeat same speed time to time, even in the case real speed is one stop beyond the marked one.

A lens can have a shutter with 1/30 -30% (1/20), an another one 1/30+30% (1/40). This is a full stop of difference depending on the lens we use, for slide film this is too much.

Sometimes people talk about the greatness of shooting at box speed or the half, but shutters (in specs) can vary same than that. Just changing the speed or the lens we can have that variation.

Then there is my collection of shutters :), (some salvaged from trash): Absolutely none of higher speeds was in specs!!!!

I bought a cheap photocell and using an oscilloscope I checked all. Now I feel very confident I'm exposing well.

Also I bought a handheld luxometer so I'm also to measure diafragm consistency. I've some boxes of frozen 5x7 Ektachome, and I feel that exposing badly a single one sheet of those may be a major sin!!!!

Anyway I think that testing own shutters is a very good practice, even with new units, specially for great slides...

jnantz
20-Jan-2017, 06:48
old betax shutters allow you to adjust inbetween shutter speeds, just like how you can go inbetween f-stops.
i've also had an old falling plate camera ( the plates it shot were something like a #10 envelope in size ) it had
a shutter speed mechanism worked the same sort of way, a knobthat adjusted a spring to adjust to any shutter speed you wanted
( i can't remember if it turned all the way or a 1/2 circle ) but it was pretty ingenious and helpful if you didn't want the standard or 1/30thS or B/T
while modern glass can be nice, and modern shutters might be thought to be less problematic the older glass and older shutters i have used
were better. less complicated, niceer images .. less to go wrong, and like the regular person fixing his/her tin lizzy
the photographer/user could probably fix his shutter...

YMMV

Bob Salomon
20-Jan-2017, 06:55
old betax shutters allow you to adjust inbetween shutter speeds, just like how you can go inbetween f-stops.
i've also had an old falling plate camera ( the plates it shot were something like a #10 envelope in size ) it had
a shutter speed mechanism worked the same sort of way, a knobthat adjusted a spring to adjust to any shutter speed you wanted
( i can't remember if it turned all the way or a 1/2 circle ) but it was pretty ingenious and helpful if you didn't want the standard or 1/30thS or B/T
while modern glass can be nice, and modern shutters might be thought to be less problematic the older glass and older shutters i have used
were better. less complicated, niceer images .. less to go wrong, and like the regular person fixing his/her tin lizzy
the photographer/user could probably fix his shutter...

YMMV
What matters is the exposure, not testing to death. A working shutter has consistent speeds, otherwise it needs service, if you have two shutters that vary that much from each other then have them serviced to be closer to each other.

jnantz
20-Jan-2017, 07:27
hi bob
i agree .. but there are people who like "testing to death"
and that is how they get their exposure right. i don't ..
BUT i like to be able to fix/adjust my own equipment instead of having
to rely on someone else. less complicated means that i can do just that.

Bob Salomon
20-Jan-2017, 07:53
hi bob
i agree .. but there are people who like "testing to death"
and that is how they get their exposure right. i don't ..
BUT i like to be able to fix/adjust my own equipment instead of having
to rely on someone else. less complicated means that i can do just that.

Then you should be using a densitometer to read your exposures. Not spending all your time testing. Go use the equipment. Just because you find your actual shutter speeds doesn't mean that you are properly exposing your film.

Pere Casals
20-Jan-2017, 07:59
hi bob
i agree .. but there are people who like "testing to death"
and that is how they get their exposure right. i don't ..
BUT i like to be able to fix/adjust my own equipment instead of having
to rely on someone else. less complicated means that i can do just that.

Bob just says the truth, a shutter is in specs for 1/30 if it delivers 1/20, and also if it delivers 1/40. This is a full stop, and this can be important or not for you.

Then... well, not necessary testing to death, I've tested my 7 shutters in some 2 hours

My "best" shutter is a Compur 3 with a Sironar-N 300 MC, then I've three Compur 1, two Seiko#0 and a No.5 Compound of a Symmar 360/620 (I use it because 620mm 8x10 )

I found for example that the Compur 3 1/200 was 1/120. I wrote down all real speeds for each marked speed on a label in each lens board.

This is one of best things I made to get consistency with transparencies, very happy with results, and very well invested 2 hours. It is not testing to death, just 2 hours to know very, very well how personal gear is working.

Really I absolutely recommend that procedure to anybody that is shooting transparencies and/or he owns "vintage" shutters like me.

To me it was extremly useful, really, because metering for Velvia can be challenging and knowing the real speeds of shutters is a major advantage for that. An overexposed 8x10 slide is something very painful, one remembers it for years !!!

Also for negative film with "very good" shutters that has less importance, of course, but still it is good practice to check shutters from time to time.

Pere Casals
20-Jan-2017, 08:34
I'd add that with Nikon F5 and Velvia I was having very consistent results. The F5's Copal is electronically adjusted, say service free, the electronics measures real speeds and makes automatic corrections, Even 20 years after camera was manufactured, mine is 97'. Exposures are just exact. (even at 1/8000)

When I moved to Velvia LF I saw unexpected inconsistency after checking all. With the shutter tester now I feel I've same control than with F5.

...and now I ask myself... How was I shooting LF slides without checking shutters? (that's the pain from [1 stop] 3 overexposed Velvia sheets :) )

jnantz
20-Jan-2017, 09:12
Then you should be using a densitometer to read your exposures. Not spending all your time testing. Go use the equipment. Just because you find your actual shutter speeds doesn't mean that you are properly exposing your film.

i am perfectly happy doing what i do, without a densitometer, and without spending a lot of effort testing
some may like to do tests and desitometer "stuff" but i don't ..
i do a simple bracket+develop test first to find out where i think my best exposure/iso/developer time is, i also develop by inspection sometimes
and that is pretty much it, i've come to the conclusion that there is no such thing as perfection, so
i don't waste my time/effort to find perfect exposures &c ... but if someone else wants to test and use a densitometer, good i'm glad they are having fun
i also don't use a spot meter, but an ambient meter ( when i have to ) and have been judging light with
experience/sunny 11 for slides, c41 and b/w film in all formats from miniature ( 1/2 frame 35mm ) to hand made 4x5-5x7 dry plates 11x14 sheets of hand coated paper
for long enough that i don't sweat the small stuff. never had a problem .. once in a while i will see what my shutters are firing at
and if they are off i make adjustments when i expose ...

YMMV

Pere Casals
20-Jan-2017, 09:27
i am perfectly happy doing what i do, without a densitometer, and without spending a lot of effort testing
some may like to do tests and desitometer "stuff" but i don't ...
YMMV

Of course, negative film has a lot of latitude and overexposing a bit can allways be corrected when printing...

But... imagine you have two different lenses, one (a 210mm) at 1/30 fires at 1/20, if you use the 240mm perhaps it can fire at 1/40... this is a full stop !! and both lenses are in specs, say new. Then there are old shutters there...

Also different speeds of the same shutter may have errors in different directions. One will never be able to adjust process with accuracy, because every speed of every shutter lives in a different world.

Well... one stop is not important in a lot of situations, that's true !!! specially if shooting under box speed, but IMHO it can matter a lot in case of reciprocity failure or with slides, then measuring real speeds is an interesting option.

Luis-F-S
20-Jan-2017, 09:54
Then you should be using a densitometer to read your exposures. Not spending all your time testing.

+1!!!! Bob you can lead a horse to the well.......... L

jnantz
20-Jan-2017, 10:03
it's helpful, but for me at least, it is not on my list of priorities to have and use a densitometer
and to be doing speed tests all of ( or some of ) the time, even when shooting slide film, and i've never really worried.
i have a healthy contempt for my materials.

Pere Casals
20-Jan-2017, 10:33
What is true is that a true artist has no time to loss in too much technical accuracy, and at the end it is better Sunny 16 with a good idea that all technical metering in the world without creative ideas.

The rule of not underexposing negative film and not overexposing slides is very powerful for a lot of situations.

jnantz
20-Jan-2017, 10:43
the rule of not underexposing negative film and not overexposing slides is very powerful for a lot of situations.

amen !!