How should I determine lens aperture corrections for tested shutter speed variances?

[Jac@stafford.net]

OP - you have had all the responses necessary. My little advise: ignore those who fall into insignificant, minuscule metrics. An exposure difference of 1/3rd is entirely insignificant. In fact an exposure error of two stops is unlikely to ruin your image. Screw the Excel stuff. Do your pictures and make gross adjustments, refining them as they work for you.

Some people have more keyboard time than making pictures.
.

[Dan Fromm]

OP - you have had all the responses necessary. My little advise: ignore those who fall into insignificant, minuscule metrics. An exposure difference of 1/3rd is entirely insignificant. In fact an exposure error of two stops is unlikely to ruin your image.

Good point, for work in black/white negative film. With reversal film -- I shoot E6 almost exclusively -- a 2 stop error is a catastrophe. 1/3 stop, however, is negligible. You're right, unless the OP is shooting reversal film he's being compulsive.

[Jac@stafford.net]

Good point, for work in black/white negative film. With reversal film -- I shoot E6 almost exclusively -- a 2 stop error is a catastrophe. 1/3 stop, however, is negligible. You're right, unless the OP is shooting reversal film he's being compulsive.

Ah, of course using reversal film is critical. I did not consider that because I never use it. My lack of insight.

To everyone - what Dan wrote.

[ic-racer]

aperture stop corrections.

Apertures are off? Maybe I'm missing something. Why not identify the measured shutter speeds on the shutters?

[JMO]

Apertures are off? Maybe I'm missing something. Why not identify the measured shutter speeds on the shutters?

ic-racer, In my OP I explained that I tested my shutter speeds for all my LF lenses, and (as could be expected) most were off to greater or (mostly) lesser degrees at various of the speed settings. So in order to compensate for those variances one must adjust the aperture settings accordingly (if not send the shutter out for CLA or repair). However, I wasn't sure how to determine what aperture corrections to apply - but now, thanks to the help provided above, I am clear on that and have made an Excel spreadsheet to use my shutter test data to derive aperture setting adjustments. I am mindful of the cautions by jp and others that I needn't over react to these data when I use B&W film, as there is plenty of latitude in the overall process. I was also aware that more precise exposure control is critical when using E6 film; but, contrary to what I expected when I got into this LF hobby several years ago, I rarely use my E6 film these days as I generally prefer my digital camera when the endpoint will be a color print. My sincere thanks to all who have contributed above.

[ic-racer]

So in order to compensate for those variances one must adjust the aperture settings accordingly

If you are using an exposure meter and your shutter has values for example 1/5, 1/13, 1/40, 1/100, 1/160 use those values in your meter. You can read the aperture directly off the meter.

You did not mention what your actual aperture measurements were when these were tested, so I assumed they perfectly matched the aperture scale for your lens. In that case no aperture compensation is needed.

[Doremus Scudder]

Doremus, Thank you for your answer, but how do you decide which variances in measured shutter speeds require 1/3 stop correction, versus 2/3 stop, versus some other level of exposure correction? I don't want to make more of this than what it is, but at this stage in my relatively neophyte LF career I am not sure how to convert the shutter tester results into aperture adjustments. How do you make those adjustments? I have sent a PM to torahsi with my email address, so I can receive the Excel spreadsheet, but I am not clear on how I should make judgments on what aperture corrections to make in relation to the shutter speed test results. Thank you....

JMO,

I simply made a chart that correlated shutter speeds in milliseconds to 1/3-stop intervals (it's attached below FYI). I could mark the speeds to the closest fraction, e.g., 1/5, 1/8, 1/10, etc. but chose the + or - signs instead, for no real overriding reason. You can do it however you like. Keep in mind, when you round to the nearest 1/3 stop, your margin of error shrinks to 1/6 stop. That's more than accurate enough even for transparency films. Heck, it's likely that other factors introduce a lot more error than that.

Best,

Doremus

[JMO]

JMO,

I simply made a chart that correlated shutter speeds in milliseconds to 1/3-stop intervals (it's attached below FYI). I could mark the speeds to the closest fraction, e.g., 1/5, 1/8, 1/10, etc. but chose the + or - signs instead, for no real overriding reason. You can do it however you like. Keep in mind, when you round to the nearest 1/3 stop, your margin of error shrinks to 1/6 stop. That's more than accurate enough even for transparency films. Heck, it's likely that other factors introduce a lot more error than that.

Best,

Doremus

PERFECT, many thanks.

[Ricardo Maydana]

Here's how the sheet looks like. It's really simple. First, the exposure time percent difference is calculated as the difference between the theoretical and the experimental values, divided by the theoretical. Then it's just converted to tenths of stop in the next row by simply applying a format.
A positive number indicates compensation by closing of the aperture (think plus, bigger number) and a negative the opening. If you prefer it the other way around, I can change that, too.

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un punto la columna "E", como se calcula o que formato se usa..