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Re: [OM] New Camera - Sony digital noise processing for long exposures +

Subject: Re: [OM] New Camera - Sony digital noise processing for long exposures + camera/lens rental
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Thu, 01 May 2014 09:32:39 -0400
I started digging into this image stacking stuff for deep sky photography and immediately started running into terms I didn't understand as in this passage
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4 Capture your light and calibration frames

Start your imaging run, aiming for as many images as possible. Unless you already have a library of bias and dark frames (at the correct exposure length), leave time for these. Flat frames must be taken on the night or the next day without touching the camera or focus.
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I have no idea what "bias" and "flat" frames are but assume that I do know what a "dark" frame is. I assume that a dark frame is an "exposure" taken with the shutter closed or sensor otherwise blocked from light. It's to be taken at the same exposure time as other shots where you want to subtract digital noise from a long exposure.

I was reminded that my Canon 5D has a noise reduction option for exposures over 1 second that causes all exposures to be twice as long. I assume that this is for generation of the dark frame whose noise will be subtracted from the image frame. I've only ever used this feature once and had forgotten about it. So I decided to check the OM-D E-M5 and see that it also has such a feature as does the Sony SLT-A65. The Sony also has a high ISO noise reduction feature which is not described in the SLT-A65 manual. So I downloaded the manual for the SLT-A99 thinking the "more professional model" might have more info. Indeed it does but not much. It simply describes it as a multi-exposure mode which produces a single image from multiple exposures. No info at all on how many exposures or how they are combined.

Maybe this will help point you to some other areas for research.

At the risk of using up some of your limited camera funds you could rent an A65 right here ($52 for 4 days)
<http://www.lensrentals.com/rent/sony/a-mount/cameras>
but you'll also need a lens
<http://www.lensrentals.com/rent/sony/a-mount/lenses>
There are no Sony kit lenses but there are 3 Tamrons available at under $30 for 4 days. But it will cost you an extra $25 for each item for shipping (maybe they'll give you a break when sent together).

Contact me off-list. I have some film era Minolta AF lenses which might be usable. Minolta 50/1.7, Sigma 28-70, 70-210 and 75-300. I also have some other Minolta stuff. 1x-2x right angle adapter, small flash units, Cambron AF extension tubes, "Photoco" AF 1.7X Tele Converter, wired remote shutter release, + 2 MAXXUM 5000 AF film camera bodies and owner's manuals (wierd: program and manual modes only)

I assume the 50/1.7 will work on a modern Sony AF body. Dunno how the Sigmas will do. The 75-300 has bad zoom creep. None of these items have been tested with film in the cameras.

Good luck,
Chuck Norcutt


On 4/30/2014 11:00 PM, Chuck Norcutt wrote:
Maybe this will help.  Haven't read it myself yet.  There's also a
YouTube tutorial available.
<http://deepskystacker.free.fr/english/index.html>
<https://www.youtube.com/watch?v=UWWaKkCUm6c>

Chuck Norcutt

On 4/30/2014 9:27 PM, Chuck Norcutt wrote:
Also, although I don't know how it's done, there are techniques used in
deep-sky astro photography of combining several short exposure digital
images to get the equivalent of one image at long exposure.  I don't
know if that would work for your own long exposure needs but you might
want to chase that down... and tell me about it afterwards as I'd like
to know about it myself. :-)

Good luck, hard decision yet to come
Chuck Norcutt
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