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# Thread: Newbie help with exposure

1. 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.

2. 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!

3. FWIW, when your box of Velvia is done, maybe try the Provia, which has excellent reciprocity characteristics. Maybe the Velvia does, too, but I have not tried it.

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