Newbie help with exposure
You all inspired me to try pinhole photography, so I just purchased my first pinhole 4x5 off of eBay. I also have some Fuji Velvia 100F on its way.
My question is about exposure and reciprocity failure.
I know that I take my meter reading with a regular meter, then convert that for my f-stop (f/160). I'm using the convertor on Mr Pinhole, so I should be fine there. (although the times I'm seeing seem very short compared with what I see some of you using - a few seconds vs minutes.)
So how do I take that and factor in the film? According to the data sheet, I add 1/3 stop at 2 minutes, 1/2 stop at 4 minutes and 2/3 stop at 8 minutes.
Here's the newbie questions:
1. How do I "Add stops" or partial stops?
2. How do I handle exposures longer than the 8 minutes they mention?
By the way, I live in the Pacific Northwest, north of Seattle, so I'll be photographing rocky beaches, plus maybe some forests, if that factors into anything.
(I also posted this question on f295, but thought I'd try here as well, just in case)
Thanks in advance,
With a fixed f-stop, obviously (hence your question) you can only change exposure time.
to increase time by n stops, multiply the 'uncorrected' time by 2^n.
1/3 stop = 2^0.333 = 1.26 (multiply by 1.26)
1/2 stop = 1^0.5 = 1.414 (square root of 2)
2/3 stop = 2^0.67 = 1.59
For longer times, I can see a simple trend but can't think of a simple tway to explain it. I'll think about it & maybe someone else will come along too.
OK, at the risk of approximating, not a crime with pinhole, you will find with b/w films that many people do not agree with mfr's posted reciprocity data.
With color, sometimes a mfr suggests a color correction filter and a correction in fractions of stops. It sometimes includes the correction needed for that additional color correction filtration. It's not always clear in the datasheet.
Personally, I think mfrs give convenient fractions of stops because it is more practical to correct by a 1/3 or 1/2, 2/3 or 1 stop on a lens f-stop ring than it is 0.301, 0.602, 0.903, etc.
Here's my ballpark suggestion for times >8 seconds.
Reciprocity Failure correction stops = log(t), where log is log base ten
multiplier = 2^log(t)
You would probably be fine using this in the 1-8 second range too under my unsubstantiated theory of manufacturer data manipulation for practicality.
Good luck with pinhole photography. I'm sure you'll find it both rewarding and fun. I've only been shooting pinhole for a couple years and probably have a much more casual attitude than most. Like you I shoot reversal film although I usually shoot Ektrachrome 100ASA. I got a handy exposure wheel with my camera from Zero Image to help convert exposure values at f/16 to f/225 which is the size of the pinhole I use. I've found that for converted exposures 2 seconds or less, I don't compensate for reciprocity at all and from 2-8 seconds usually add 50% to the exposure time. This means that if the exposure is 4 seconds at f/225 - add 50% (2 seconds) for an exposure of 6 seconds. This has worked really well for me with both reversal and black and white.
Keep in mind, I always shoot in daylight. If you're shooting in dim light, reciprocity will play a much bigger factor. My best advice would be to load up a few sheets of 4x5 and try some shots. Record your exposure time and see how the transparencies look. Then adjust from there. But most importantly, have fun.
A few comments. The answer also depends on your media and desired final output/purpose. I usually shoot B&W negatives so I err on the side of overexposure. With Velvia maybe you want to err on the side of underexposure per Doug's comments re not worrying too much if you are under 10 seconds. Also, do you want to enlarge, scan, make contact prints, or just look at the cool transparencies etc?
As Murray says the only "stop" you can play with is time. Once you get into longer exposure times it's important to remember doubling the time is only one stop. 4 minutes is one stop more than 2 minutes and 8 minutes is 2 stops more. Once in this territory you can often safely double time without major implications and lighting conditions can change in any case, so gut feel based on experience becomes as good a guide as anything once you know your chosen materials.
I second Doug's advice to have fun. It's a nice way to get back to the fundamentals of thinking about photography and letting accidents, good and bad, happen.
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Thanks everyone, this helps quite a bit. Regarding my desired final output/purpose. Well, eventually (and I stress that word) I'd like to do very large prints with the 4x5, ending up in a gallery.
Right now though, the emphasis is on fun, learning and just enjoying the creative process (as well as the spontaneity) with pinhole.
i use the pinhole designer and put in "no reciprocity" correction for E6 films. i then do a bit of testing. in daylight i have pretty much been dead on with the exposure doing this. i think you should be in the 2-5 sec range on most sunny days. check for your self. i had a great 4x5 E6 photo up in the f295 gallery but i lost it when the gallery went down. here are a few i found. they were taken with a 25mm pinhole. (not the ones i was thinking of. i will dig them out) it is a f 125 and i think it was about .5-2 sec. i forget.
Doug's advice is good, from my experience with a 4x5 pinhole (a great custom-made yellow cedar and brass one made by a photographer in Vancouver, Canada under the name "Binary Box").
I googled the info, and found a conversion table for various f-stops (f/8, f/11, f/16) upwards to f/200. Printed it off, keep it with me always, and it's worked flawlessly with both B&W film and chromes.
by the way, an f/160 camera needs exposure 100 x that of an f/16 meter reading or estimate.
You could shift the decimal place over two positions, then do whatever quick reciprocity failure correction you chose, if you aren't the preprinted-chart kind of guy.
Converting f-stops is relatively easy...
Lets say you have your "regular" camera or light meter with you and meter the scene as f-16 1/125th. And you know your pinhole is f-180.
To get a conversion factor in time for your exposure (Fstop_pinhole / Fstop_meter) ^ 2
(180 / 16) ^ 2 = 127 (rounding up from 126.5625, close enough)
Multiply the exposure time by 127
127 * 1/125 = 1.016, call it 1 second. Now apply any filter factors, then finally apply the reciprocity factor correction. Murry gave you a reasonable way to guess at the factor in the absence of any other information.
Simple, isn't it? What I would do is make yourself a chart based on the good-ole Sunny-16 rule and then scale it for -1, +1, +2 and +4 stops (snow/sand, hazybright, distinct shadow/backlight, kinda gloomy) and pre-figure in the reciprocity failures. Then keep these charts tucked in your camera bag or just taped to the camera!