A question about multi session captures and DSLR. - Forums

Topic starter

Mar 13, 2019

Hi there,
i have recently got my setup to the point where i can guide and plate solve giving me the opportunity to capture data over multiple sessions. I was wondering whats the best way to capture and process the data. The issue I have is I don't have a dedicated astro camera so i cant leave it connected and its a DSLR so no cooling. How can i do multi day shoots and get a clean image?
Hope someone can help!
Thanks Mike.

Engaging

Carastro

Mar 13, 2019

Why can't you leave your DSLR connected provided it is covered up well? Are you also using it in the daytime?

Carole

AwesomeAstro

Mar 13, 2019

I take my DSLR off all the time and collect data on multiple nights, no problem. You have the plate solver so make sure you're always at the same angle. If you don't, you'll end up losing the edges of the stack (sometimes a lot of data) where the frames didn't overlap from all nights. Otherwise you simply combine the different nights' data like normal. You will need to take new flats every time you change the camera angle, however. I recommend trying to keep the same ISO and exposure time (unless you find a better combination) each night, however, because preprocessing is easier when the ISO is the same (same bias frames), and there are no "weighting" or noise issues when the exposures are the same.

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Michael

Topic starter

Mar 13, 2019

Carastro:
Why can't you leave your DSLR connected provided it is covered up well? Are you also using it in the daytime?Carole

Yes, it's my main daytime shooter, that's also why i haven't astro modded it.

I take my DSLR off all the time and collect data on multiple nights, no problem. You have the plate solver so make sure you're always at the same angle. If you don't, you'll end up losing the edges of the stack (sometimes a lot of data) where the frames didn't overlap from all nights. Otherwise you simply combine the different nights' data like normal. You will need to take new flats every time you change the camera angle, however. I recommend trying to keep the same ISO and exposure time (unless you find a better combination) each night, however, because preprocessing is easier when the ISO is the same (same bias frames), and there are no "weighting" or noise issues when the exposures are the same.

Oh good good! I do try to keep my camera mounted in the same way. Just so I'm clear, because the flats will be different from night to night i process each night separately and at the end combine them all in to one image?

AwesomeAstro

Mar 13, 2019

Michael:
Oh good good! I do try to keep my camera mounted in the same way. Just so I'm clear, because the flats will be different from night to night i process each night separately and at the end combine them all in to one image?

Correct, preprocessing (calibration with bias, flat, and- although I don't use them anymore and you probably don't need to either- darks) occurs based on the individual image's needs. You may have a lot of images that require the same bias frame (ISO dependent only) or flat frame (depending on the optical train configuration and camera angle), in which case you could do them as a batch all together, but every calibration must occur based on the individual image's needs. Postprocessing (background extraction, color calibration, noise reduction, stretching, etc..) occurs after the stack. The best workflow is calibration (based on the needs of the bias and flat frames), cosmetic correction (hot/cold pixels, mostly the former for DSLRs), debayering, frame selection and weighting, registering, then integrating, then processing.

The only issue you could have across multiple days is if you change focal lengths, exposure, ISO (not a huge issue), or don't take new flats.

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Thomas

IOTD Staff

Mar 14, 2019

I would take flats each night along with the darks, if you use them, and use some painter's tape or something similar to mark your camera orientation. I put a piece of tape that spans the camera to telescope interface and then cut it so I can separate the two. This way all you have to do is line up the two pieces of tape and your camera orientation will be the same as the previous night.

As for processing, you will want to bias, flat, and dark calibrate each night separately. Once each night is calibrated, you can align and integrate all nights together at once.

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Michael

Topic starter

Mar 15, 2019

Thanks everyone for the advice! Now I just need clear skies!

Thomas:
I put a piece of tape that spans the camera to telescope interface and then cut it so I can separate the two. This way all you have to do is line up the two pieces of tape and your camera orientation will be the same as the previous night.

Grate tip! I'm definitely going to give it a go!

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