5 replies to this topic

[hikerdave]

I'm been using an ASIAIR with an ASI533MC Pro camera with a re-purposed (from visual to astrophotography) 600mm focal length refractor with nice results. However, for some reason I looked at the calibration Flat subs from last nite's imaging. The ASIAIR saves images as stretched JPEG and linear FITS. I saw a few dust spots on the JPEG but the FITS were all grey (viewed in ASIFitsView on my Windows computer and stretched in PI). I also viewed the same Flat subs from the ASIAIR app on my tablet and the dust spots were clearly visible.

 

Why can't I see the spots in the FITS Flat sub after stretching in PI or viewing in ASIFitsView?

 

I enclosed 4 screen shots of the sub (each with adequately sufficient names I hope). I've received some very insightful and helpful responses in my previous posts. Looking forward to learning more. Thank you.

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[Dynan]

Can you upload an link a single raw, unprocessed flat?

[hikerdave]

Sure, thanks for the assist. Here is a link to a Flat FITS sub, about 18MB:

https://drive.google...?usp=drive_link

[sharkmelley]

The FITS file is from a colour camera and therefore has the "chequerboard" effect from the bayer matrix.  It is also well exposed.  These properties will both will prevent the stretching algorithm from doing much stretching.

 

Since you are using PixInsight, use the IntegerResample process to downsample by a factor of 2 to remove the chequerboard.  Then stretch.  Divide the binned values by 10 using the PixelMath process.  Then stretch.

[Dynan]

The flat looks good. stats about half scale (Even though I used 16-bit depth, it scales), as is the histogram. The Flat Contour Plot (found in Scripts) shows your dust motes.

 

Were you using a dual-band filter? Shows two peaks.

 

[hikerdave]

Just the UV/IR cut filter. The flats are effective for removing the motes artifacts - so far anyway. Presently a curiosity, which is a bit unsettling in this hobby IMO (e.g., the ASIAIR can display the flats showing the motes tho, so I can determine the appropriate exposure time for flats anyway).

 

Thank you!