exposure calculator for night shots

Discussions regarding Phase One 645 AF and Mamiya 645AFDIII Camera

exposure calculator for night shots

Postby Mike1111 » Thu Jul 09, 2009 1:56 pm

I am 'numerically dyslexic' and would like something (a card wheel / slide rule or an program/app) to help calcuate exposures at different ASA's?

For example i want to do a night shot on 50asa at f11, but i have to guess the exposure time as it is off the metering scale. So using the meter I do an exposure at 800asa at f2.8 and get say 2 seconds. I would like something that would instantly tell me that the equivalent at 50 asa and f11 would be say 60 seconds.

Is there such a product?

I have a http://fotosharp.com/day_night_exposure_calculator.html

but it cant be used for converting.

I ask because my camera automatically does a dark frame subtraction and waiting sometime for 20 mins exposure then another 20 mins may mean you miss the shot.

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Re: exposure calculator for night shots

Postby Peter9 » Thu Jul 16, 2009 9:32 pm

Hi Mike

I have not seen a chart like the one you linked to, so I’m not sure entirely how it works, but I can tell you how I do when I’m doing long exposures.

If I remember my “old trusted” light meter I can do zone metering for the shot (an absolute must when shooting with Cambo or Horeseman as they doesn’t have a light meter build in) but if I forgot the meter I select custom function 01 on the camera body and set the aperture/Shutter step to full step (we might as well enjoy the benefit of the high dynamic range of the P+ back :wink: ) then I measure the light at say ISO 800 (remember to use average light metering) and note the time.

I then change the ISO setting to the preferred setting, noting how many steps I moved it down.

I can now move the exposure setting dial the same number of steps (towards longer exposure) and that gives me the right exposure.

The only problem with the approach above is that if you need exposure times longer than 30 sec you will run out of range on the exposure dial, but if you like I can send you an excel sheet with the exposure value table (EV table) or you can use the first line of the chart found on this web page http://www.carlmcmillan.com/ev_chart.htm and just count the steps on that and use a stopwatch using bulb mode.

If I have missed the point or there is anything you would like to have clarified, please do let me know.

All the best

Peter Tirsgaard

Ohh by the way! I should mention that when shooting in M mode the AEL button now works as a set the correct exposure time button, which makes selecting the right shutter time much faster than clicking the exposure dial and observing the light meter.

And when shooting in bulb mode you can use custom function 22 to select how the bulb function should work, you can select that the bulb mode should turn off when the exposure button is released, or if you want the camera to keep exposing and stop when you press the shutter button again .
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