Author Topic: Exposure measurement above 30 seconds and beyond  (Read 4745 times)

mlguest

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Exposure measurement above 30 seconds and beyond
« on: July 12, 2014, 10:30:19 PM »
It would be nice, if ML could enable an exposure measurement above the 30 second limit from canon. Is this possible?

a1ex

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Re: Exposure measurement above 30 seconds and beyond
« Reply #1 on: July 13, 2014, 09:28:22 PM »
The easiest automated method is bracketing - it will just keep trying until it gets a correct exposure.

Alternative: take a test picture at 1-5 seconds, for example, and look at the ETTR hint. Set the bulb timer to as many stops as indicated (for example, test picture at 5 seconds, ETTR hint 4 EV => 80 seconds), and it should work.

Problem: if the test image is very dark, the ETTR hint is far from accurate. The fix is hard (deconvolution on the histogram or something similar), but easier approximations can be found.

a1ex

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Re: Exposure measurement above 30 seconds and beyond
« Reply #2 on: June 12, 2015, 06:03:46 AM »

garry23

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Re: Exposure measurement above 30 seconds and beyond
« Reply #3 on: June 12, 2015, 02:36:52 PM »
Great news about the ETTR.

When I'm doing LE work I simply use a high ISO to set the exposure using the RAW histogram, say at 3 shops up, ie ISO 800, then reset ISO to 100. 

Thus if I want an LE of, say, 120s, I set an exposure of 15s at 800, then reset to 120 in bulb at ISO. 100.

Danne

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Re: Exposure measurement above 30 seconds and beyond
« Reply #4 on: June 12, 2015, 03:17:59 PM »
nice one.

DeafEyeJedi

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Re: Exposure measurement above 30 seconds and beyond
« Reply #5 on: June 13, 2015, 05:10:19 AM »
I like the math of this... Definitely a nice one!
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halbmoki

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Re: Exposure measurement above 30 seconds and beyond
« Reply #6 on: June 13, 2015, 03:16:27 PM »
That's how I do it as well,  if the exposure for low ISOs shows "more than 30sec". I usually use ISO 3200, which gives me good reading up to 15min at ISO 100. Since such long exposures need to be prepared carefully anyway, a few more seconds spent calculating the correct time don't hurt at all.

It would be nice to have that step automated in some way, though.
There could be a setting in the bulb timer options, like "use high ISO metering" that would use a high ISO (say, 6400, to not exclude the older/cheaper cameras) when pressing the metering button, automatically calculate the TV for the currently set ISO from the measured value and set that for the bulb timer, which could then be triggered the normal way - no need to go into any menus after activating the initial setting.
Sadly, I have no idea, if it's that easy to program, but temporarilly raising the ISO when a button is pressed seems doable and the rest is basically like the "exposure lock" function and stuff that happens in ML anyway... just my little idea, in case any of the devs feel like adding another feature right now.