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JMO
13-Jan-2018, 20:24
I have recently obtained a Phochron XA digital shutter speed tester and have made a little jig to mount my dozen or so lenses (all on Technika-style boards) so I can quickly test them through the various shutter speed settings. Luckily, only one of my lenses/shutters is off, and a bit too inconsistent, on certain speeds such that I will need to send it out for CLA or repair. All the other lenses seem to be quite consistent from one click to the next, and fairly close to the various speeds indicated on the shutter dials -- BUT OF COURSE THERE ARE SOME VARIANCES!

My test data are speeds expressed as fractions like 1/28.4 seconds (where the target was 1/30), and these data can be easily converted to milliseconds. My question is how do I determine the aperture exposure corrections to apply when taking photos with these lenses, in order to correct for the results of my shutter speed tests (whether the lens in question was found to be a bit fast, or slow)? My Compur or Copal lenses shutters allow me to add or subtract exposure in 1/3 stop increments, but how do I relate those increments to the shutter speed test data (which are on an arithmetic scale)?

Finally, if someone might have, and be willing to share, an Excel spreadsheet set-up for this purpose, it would be greatly appreciated.

torashi
14-Jan-2018, 00:33
I have recently obtained a Phochron XA digital shutter speed tester and have made a little jig to mount my dozen or so lenses (all on Technika-style boards) so I can quickly test them through the various shutter speed settings. Luckily, only one of my lenses/shutters is off, and a bit too inconsistent, on certain speeds such that I will need to send it out for CLA or repair. All the other lenses seem to be quite consistent from one click to the next, and fairly close to the various speeds indicated on the shutter dials -- BUT OF COURSE THERE ARE SOME VARIANCES!

My test data are speeds expressed as fractions like 1/28.4 seconds (where the target was 1/30), and these data can be easily converted to milliseconds. My question is how do I determine the aperture exposure corrections to apply when taking photos with these lenses, in order to correct for the results of my shutter speed tests (whether the lens in question was found to be a bit fast, or slow)? My Compur or Copal lenses shutters allow me to add or subtract exposure in 1/3 stop increments, but how do I relate those increments to the shutter speed test data (which are on an arithmetic scale)?

Finally, if someone might have, and be willing to share, an Excel spreadsheet set-up for this purpose, it would be greatly appreciated.I wrote an Excel spreadsheet for you. I can email it to you, if you send me your address through a private message. For some reason I can't attach an .xlsx file here.
I'd suggest not to worry too much, if it's within the shutter's speed tolerance specs. I would suggest, if your work is very critical, that you could also test the shutters at different temperatures. For example by putting them in the freezer inside a sealed plastic bag (dew & moisture barrier, you know) or heating them a bit up with an incandescent bulb (and always with a thermometer) so as to mimic real environmental situations.
This should also let you know beforehand how they should behave in different weather conditions during summer/winter.

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torashi
14-Jan-2018, 00:51
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.https://uploads.tapatalk-cdn.com/20180114/99f8e26dfab236337a5b78368e0f7131.jpg

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ic-racer
14-Jan-2018, 04:51
No compensation is needed if one uses meter that displays shutter speeds at 1/3 stop intervals.

Doremus Scudder
14-Jan-2018, 11:21
I simply made a sticker for my lens board with the marked shutter speeds and an indication of compensation rounded to the nearest 1/3 stop. Example: say the 1/30 second speed is about 1/3 stop too slow. I'll mark this as 1/30- (minus to indicate slower). I have a few shutters marked in old speeds. With these I'll use modern standard speeds with an adjustment marking. E.g., 1/5 sec becomes 1/4+ (plus indicates faster).

Then, when exposing I simply make an appropriate adjustment with the aperture. 1/30- needs 1/3-stop less exposure from the aperture as 1/30.

FWIW, I figure everything from milliseconds and have made tables to show where the 1/3-stop speeds are. I fire my shutter at f/22 (where I work most) several times and take an average. Of course, if the shutter is erratic, it goes in for a CLA.

Hope that makes sense.

Best,

Doremus

JMO
14-Jan-2018, 18:32
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....

Dan Fromm
15-Jan-2018, 05:59
If you have a spreadsheet package, here's the magic formula:

exposure error in stops = log10(measured shutter speed in seconds/ideal shutter speed in seconds)/log10(2)

jp
15-Jan-2018, 07:17
My light meter has a dial... If my lens is setup for 1/250 and I know it's more like 1/200 because of cold, age, etc.. I use the aperture that corresponds with 1/200 on the light meter dial.

JMO
15-Jan-2018, 09:28
These last three answers are what I was looking for - THANK YOU ALL. I plan to use the Excel spreadsheet, with function from Dan, and then make little labels to put on each lens board with the aperture stop corrections. I have thought that another useful bit of info to put on these sticker labels will be the lens image circle, so I'll know in the field how much room I have for movements.

Jerry Bodine
15-Jan-2018, 14:04
...I am not clear on how I should make judgments on what aperture corrections to make in relation to the shutter speed test results...

One can never have enough data, I believe. If you're still interested in an Excel spreadsheet to answer you needs, I can provide you with one if I, too, have your email address via PM.

Jac@stafford.net
15-Jan-2018, 14:34
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
15-Jan-2018, 15:03
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
15-Jan-2018, 15:41
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
15-Jan-2018, 16:56
aperture stop corrections.

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

JMO
15-Jan-2018, 18:44
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
15-Jan-2018, 19:20
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
16-Jan-2018, 03:23
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
16-Jan-2018, 21:37
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.