darks flats darkflats

[jonstarrysky]

Can anyone confirm this workflow pls for EAA with a 294MC camera, I was confused last time when the dark flat option was greyed out. Is this correct ?

1. Capture darks at anytime and add to dark library. Needs to be matched vs Lights for temperature, gain and exposure. Hence a library of darks. Darks go into a generic folder under SharpCap captures.

2. Start of an observing session, make sure the Preprocessing Subtract Dark and Subtract Flat boxes are both set to None. If there is a Dark selected before capturing the Flat, the dark flat method isn't available.

3. Click Capture, Capture Flat frame. I am averaging 20 frames, with "Create Monochrome Flat Frame", "Capture and subtract dark flat frames" and "Apply new flat when capture complete" all selected. Unselect "Keep individual flat frame image files". The flat file ends up in a subfolder within the main capture folder for that date

4. Click Start. Flat frame will be captured and immediately followed by dark-flat frame after SharpCap prompts to cover the camera. This will be merged into the flat file. Don't move the camera, the flat is specific to the optical train and its aberrations (not so much the camera aberrations)

4. Preprocessing_Apply Flat: Make sure the new flat is selected. This file automatically incorporates the "dark flat" which in effect doesn't exist as a file.

5. Preprocessing_Apply Dark: Navigate to the dark frame file corresponding to settings for intended lights eg 4 sec, 120 gain

Strategy so far for capturing flats was gain 0, exposure 4 sec, screen illuminated to 50% for main peak. It has worked to varying degrees, though last time it was overcorrected to the right side (linear pattern). Next time I may try a same-gain same-exposure strategy for lights vs flats vs darks. In this case the dark flat will be equivalent to the Dark frame, but the Dark will still need to be added separately from my Darks library or I separately capture a new Dark at the same settings.

"Getting good Flat Frame Correction" section suggests to use the trio of Dark, Flat + Dark Flat. All three. Omitting one or more of these will cause under or over correction eg skipping the dark flat option or skipping the Dark. Initial impressions of the raw camera view (no pre-processing) is I cannot see amp glow so Darks are maybe not essential, but vigneting is quite distracting so Flats will be desired. But anyhow I will need to use all three for avoid under or over correction....

Somehow last time I ended up with huge volumes of data from correction files that got saved automatically, contained in Darks and Flats folders within my image capture folder for that date. Surely it only needed one Flat file and the Dark file should have been in the generic folder for Darks....Bit of learning curve and unticking some boxes maybe....

[admin]

Hi,

the procedure looks good to me. I suspect if you were seeing the dark flat option being unavailable when capturing a flat, you probably accidentally already had a dark frame selected in the 'Subtract Dark' control, so making sure that is 'None' should avoid that problem in future.

On the extra files, those sound like the 'keep individual' dark/flat files options being enabled. Great if you want to do a full reprocess of the data later in another application, but not necessary if you are just going to let SharpCap take care of processing.

cheers,

Robin