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First image M45


bjarnit

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Hi

Just had my first imaging session completed and i want to show you the results, and ask a few questions.

The equipment i have is skywathcer eq3 mount unguided and a SW 150pds.

My first target was M45 and the photo below is the result after stacking 17 X 90sek subs with dark and bias frames.

I used pixinsight for processing the image and followed a youtube video on what to do as i have no experience with image editing programs

 

 

I can see from the photo that my scope is not 100% collimated and that is something i can fix. but what i find strange is that in the lower left corner the image is realy black like it is a dead zone eventhoug there are some stars on that area.

Also you see some star drifting around the edge of the photo, but the stars in the middle seem ok for a first attempt. maybe shoot shorter subs sence i dont have a guide camera.

Also i think the image is a bit grainy, is that something that can be fixed with more images (longer exposure)?

 

Any input is highly appreciated.

 

Regards Bjarni

m45-pleiades-test-2-–-Kopi.jpg

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Hello, that's a good first anyway. To try some answers at your questions:

  • about darker or lighter corners: which camera do you use ? with large sensors you have more vignetting, which needs flats to correct (given your FoV and focal I could bet on APS)
  • about noise (grain) : 17 subs is probably quite low, depending on the ISO used;
    • I see your stars are saturated so it may be your processing (learn and practice the art of stretching !) or too high exposure; If the latter I can suggest a higher number of shorter subs (with same other settings).
    • How many darks did you use ? I read from many DSLR users that a too low number can actually degrade your subs before stacking, hence more noise. Try processing without any darks or bias to check the resulting noise
    • Also, unless you want to scale a master dark, or calibrate flats, bias are redundant with darks and one of the two is useless IIRC, so eliminate one and use the other; For me I kept darks to handle thermal noise, but I have read most other DSLR users rather keep and use bias (because of thermal instability of DSLR sensors leading to uneffective darks) and eliminate the thermal gradient later with image processing software as a 'background removal' step.

PS: please upload jpeg images unless you're sure it deserves an uncompressed version, detail- and quality-wise, it will save our and sgl's network bandwidth ?

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1 hour ago, bjarnit said:

input is highly appreciated.

Hi. Excellent shot.

You could try a coma corrector. If you have one already, make sure that it is at the correct distance from the camera sensor. If not, coma is easy to correct in software.

Maybe you could fix the secondary tilt, rotation and position up-down and take flat frames to correct what's left. But hey, it's good s it is:)

HTH

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2 hours ago, bjarnit said:

I can see from the photo that my scope is not 100% collimated and that is something i can fix. but what i find strange is that in the lower left corner the image is realy black like it is a dead zone eventhoug there are some stars on that area.

Also you see some star drifting around the edge of the photo, but the stars in the middle seem ok for a first attempt. maybe shoot shorter subs sence i dont have a guide camera.

Also i think the image is a bit grainy, is that something that can be fixed with more images (longer exposure)?

 

Very Nice start! :)
As per stars in the corners: You need coma corrector to get rid of the egg shaped stars in the corners, - at the moment that form is caused by parabolic primary mirror, - all newtonians suffer from it.

Collimation: I would say it is close to perfect, - do not touch it for a while. At least, do Not touch the secondary mirror, it will cause more headache than improvement. To Collimate primary is easy, but I am almost sure, you do not need it at the moment, unless you been transporting the scope and etc.

Grainy background is what all astrophotographers fighting against, and there is no short way... unless jumping straight to Mono astro camera.

More exposures, more calibration subs, darker skies, colder nights (sensor) and guiding with dithering will help a lot. 

Also some experience with Dynamic Background Extraction in Pixinisght will reduce gradient and uneven corners, which may be caused by the Moon or even by CMOS sensor amp glow.

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