Leaf Shutter Efficiency Compensation

[Todd Barlow]

Is there some sort of standard for compensating for a leaf shutter when using the shutter speed and apeture in various combinations:
1) high SS, small f stop (small opening)
2) high ss, large f stop


Thanks

Todd

 

[David A. Goldfarb]

There is probably just too much variability in shutter types and lens combinations for there to be a standard way of compensating for this, not to mention the question of the condition of any particular shutter on any particular day. If you're concerned about it, I'd run some tests on slide film with continuous lighting (with strobes there should be no effect, except in a few very limited situations) and see if there is enough variation from what is expected to worry about it. There might be more variation from the temperature of the shutter, for instance, than the shutter speed effect you are describing.

 

[Ed Sukach]

This is another one of those things I've heard of ... but.
The theory is that the mechanical opening of a leaf shutter is "more gradual" that the travel of a slit across the film, a la focal plane shutter, would be.

I have never found that to be a factor, not as inherent design artifact. If there is a difference in the opening times of certain localized areas of a leaf shutter, I think it would only be of interest to those who *scream*for "1/10 stop" exposure accuracy... something far beyond other limiting factors: film speed accuracy, aperture calibration (linearity), exposure meter accuracy, development time/ temperature accuracy - the particular phase of the moon ... and a bunch of others I probably have left out.

When one stops to consider it all - it's pretty damn miraculous that we get as close to the "correct" exposure as we do.

 

[Max Power]

Hey Todd,
I remember asking this same question about a year ago after coming across a chart on Exposure Correction for Leaf Shutters in the KODAK Professional Photoguide. Basically, the chart notes that at 1/125 and f16, you need to reduce the lens opening by 1/3 stop.

1/250 @ f11 = -1/3
1/250 @ f16 = -2/3
1/500 @ f8 = -1/3
1/500 @ f11 = -2/3
1/500 @ f16 = -1

Basically, look at it as a sort of right angle triangle with the right angle at the south-east and you can picture the chart.

I hope that this helps.

Kent

 

[David H. Bebbington]

This is one of those things that apply in theory but are seldom a problem in practice. I think the reason is this: Leaf shutter efficiency is greatest with a small stop (whole of opening is uncovered right at the start of exposure, stays uncovered until the end). Efficiency would be lowest with a large stop, but in practice large stops are almost always used with a high speed, and so the potential underexposure is compensated by the fact that the actual exposure at high speeds is going to be longer than the marked value.

 

[Diapositivo]

A normal sunny day is somewhere, with 100 ISO, between 1/125 @ f/11 and 1/125 @ f/16 (between EV 14 and EV 15).
The "sunny 16" rule is seldom verified in my experience. It's more "sunny 11 and 1/2" (EV 14,5). EV 15 is of rare use with ISO 100.
So my rule of thumb is: even though I use slides with an external light meter, when using 100 ISO I can afford to forget shutter efficiency issues. If really I have a EV15 situation I should try to remember to close 0,3 stops more, but no big problem if I forget.

If using a high-speed film, such as a ISO 400, and if using it in daylight on a sunny day, then the problem would get quite real. A "100 ISO/EV15" situation requires 1/500 @ f/16 which would lead to 1 full stop overexposure, which is likely to spoil a slide.

So the easy rule of life is: no high-iso with leaf shutter for sunny outdoors.

And in any case, if I needed high-iso for sunny outdoors, that's probably sport or nature photography and I would be using a SLR with focal plane shutter.

The matter is in any case very interesting and I am glad it was raised because one can happen to have a 400 ISO in one's Canonet or Vito and might use it outside in daylight just to complete the roll. In that case, one must be wary of this shutter efficiency issue.

Fabrizio

PS I know it's a 5-years old thread, but it's very interesting stuff indeed.

 

[picker77]

If you're talking about non-electronically controlled leaf shutters, all of this quickly becomes moot if you put the shutter on an accurate electronic shutter tester. That 1/500 speed on the dial is probably more like 1/250-300 at best. Of the ones I've tested, none came anywhere near 1/500, and very few could even do an honest 1/400. Speeds were pretty accurate up to around 1/125, but they all seemed to plateau at around 1/250-1/300 or so. This was as much true of older Kodaks and Graflexes as it was newer Copals. At a setting of 1/400 or 1/500, shutter speed numbers pretty much became wishful thinking for all of them.

I haven't had the opportunity to test a new Copal, or for that matter one that was fresh back from a complete CLA by a good shutter shop. I would hope in those cases higher speeds would be more accurate than I've measured on my older lenses. But I wouldn't bet the farm on speeds above 1/250 in any case.

Worrying about 1/3 or 1/6 stop exposure accuracy gets to be a little silly if the actual shutter speed is some unknown 50-70% of the speed you're setting on that dial. It's amazing we get any good exposures at all using mechanical shutters at higher shutter speeds, and the fact that we do is a tribute to the wide exposure latitudes afforded us by modern film manufacturers.

 

[benjiboy]

Even though It's five years since the OPs post, these are the sort of theoretical questions asked by people who have never used a leaf shutter.