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Matching darks... AC > Battery?

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#1 Footbag

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Posted 06 April 2013 - 03:18 PM

I was about to take some darks in my refrigerator and I realized something. My AC adapter cables are running through my Mach 1. Normally, I like taking my darks with the AC adapter just as I took my lights.

Is there any damage in using the battery for the darks after using the AC adapter for the lights?

I know the battery generates some heat, but I will still be matching the darks by temp afterwards.

#2 Falcon-

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Posted 06 April 2013 - 07:55 PM

My intuition says there should be no real effect since your are matching based on EXIF/sensor temp rather then ambient temperature.

In theory the battery heat being somewhat localized may produce a gradient in the dark frame, but given the distance away from the sensor the battery is vs items directly on the circuit board I doubt it will be a problem.

#3 Footbag

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Posted 06 April 2013 - 09:20 PM

Well... We'll see.

#4 Tom and Beth

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Posted 06 April 2013 - 11:05 PM

It would be interesting to hear your results, including which of the many AC adapters you have. Mind you, this is based on several threads read here that some adapters (Switching type particularly) could lead to induced noise in the current, perhaps leading to more noise in the camera?

#5 Footbag

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Posted 07 April 2013 - 08:54 AM

OK. I took dark's (on battery) last night and applied them to my image(AC). My AC adapter is the cheap E-Bay $16 one. It has broken multiple times and I've patched/shortened the cables.

At first glance, the image appears well calibrated. My streaks that were in my old image seem to have disappeared. I';m pretty OC with my calibration, but I don't see any real disadvantages.

I only did a quick and dirty stretch to look for noise, if my later results come out different; I'll update this thread.

#6 Alex McConahay

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Posted 07 April 2013 - 04:49 PM

The real test would be a set of averaged dark taken with a battery, compared with a set taken on AC converter. And the results would be determined by how much the different systems heated the internal parts of the camera.

Alex

#7 Footbag

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Posted 07 April 2013 - 05:02 PM

The real test would be a set of averaged dark taken with a battery, compared with a set taken on AC converter. And the results would be determined by how much the different systems heated the internal parts of the camera.

Alex


That's a good idea. I can make a master dark of each. Actually, it would be better to create a more controlled environment and do say 5or more on battery and AC. Unfortunately the AC adapter is still running through the mount, so that will limit my control. It'll happen in the garage.

How would I compare the results?

#8 Alex McConahay

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Posted 07 April 2013 - 09:21 PM

Open one in Photosohop.
Open the other. Select all. Copy.

Go back to the first and Paste.
Change the blend mode to difference.

If there is any difference between the two pictures, it will show up.

Alternative 1.....

Open both in your favorite processing/viewing program. Change the histogram so that you have a sharp cutoff at some level that shows clear bright and dark areas. Apply that exact same curve to the other shot.

Alternative 2....

Open both shots in photoshop.
Image/Adjust/Threshold

Move the Threshold slider to separate the black and white portions in one of your images. Do the same on your other image (with the same slider setting). Differences will be obvious.

Alex

#9 Alex McConahay

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Posted 07 April 2013 - 09:22 PM

In dong the above, remember that you may have some random differences. The big differences, or patterns is what you are probably looking for.

Alex

#10 Footbag

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Posted 07 April 2013 - 09:33 PM

I was thinking difference in Photoshop, but didn't know what to look for. I guess any pattern is bad.

EDIT:I actually found a matched dark from a previous session, so I did the difference method in photoshop. No apparent difference. No pattern. If I stretched the difference image there was random noise.

Just based off this, and my results after stacking I'd say it's safe.

#11 Tom and Beth

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Posted 07 April 2013 - 10:24 PM

I was thinking difference in Photoshop, but didn't know what to look for. I guess any pattern is bad.

EDIT:I actually found a matched dark from a previous session, so I did the difference method in photoshop. No apparent difference. No pattern. If I stretched the difference image there was random noise.

Just based off this, and my results after stacking I'd say it's safe.


Interesting. Especially with your description of the AC adapter. Also means you don't have to worry about taking the wiring out of the mount.






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