[RCC] My second attempt at astrophotography and need some critique. - Forums

Topic starter

Dec 1, 2020

Hello all,

This is my second try at astrophotography. I think it's better than my first but still has some issues. My first was the same target. I wanted to stick with the same target so I could better see the differences/improvements.

For this one i took 350ish subs, 60 darks, flats, and bias frames. I used a Nexstar 5se scope and tracking mount, and a Nikon d7000. No filters. Iso 1000, 5 second exposures. I stacked in sequator and adjusted some curves in GIMP. I'm not very confident in my post-processing yet.

I took the subs when the moon was nearly full and sitting right next to Pleiades and orion was fairly low in the sky.

When I first looked at the stacked image I thought i was having some tracking issues but someone pointed out that the stars in the lower right looked ok.

Don't be gentle, I need the critique to learn!

Thank you,

Chris

https://www.astrobin.com/lzv1g9/?nc=user

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Joel85

Dec 2, 2020 · Edited: Dec 2, 2020

Hello Chris

Congratulation for your first and second picture , welcome in this wonderfull and deliciously horrible hobby

About your second picture :

- well framed image

- Stars : try to control backfocus +collimation + (if possible) tilt in this order . From time to time, there are several reasons why stars are not round and it's difficult to explain the reason why (cumulative reasons for one result sometime)
- may be a tracking issue but 5 " is a very short exposure (this is probably not the main reason)
- For backfocus here is a sample for help (stars form)

(We do not see these default on your picture but you may need this later one of these day, once other controlled will have been made)
BAckfocus control is made durng the day first : distance between captor and coma corrector (if coma corrector is used)
- Tilt is a very difficult setting : I am just controlling that rings are tight, not too much, but without play that's all (I can leave with a small tilt ...)
- About processing : we can see vignetting in corners (more black). Control your masterflat, or flats if you can see the same (the flat should have corrected it in part ). I agree with you ( post-processing)
- exposure time : try a longer exposure for getting more signal around nebula if possible , all the picture is nebula, even corners, and there is no sky around m42 (yours is not so bad with 5" ! congratulation ! you can be happy with your first picture)
- With more signal, post-processing is easier : may be can you try next time 15" or more than alf an hour (n x5")
- Post -processing : it is a long way ... to learn it (and to explain ) You will need to build masks (object mask, background mask, starmarsk ) for a good post processing (so that, you will be able to "touch" background without "touching" nebula and vice versa )
- Post processing is a never ending story ... i am still learning every day ... in astronomy too

I hope these few informations will help you

Clear skies and thank your for sharing these first pictures !
(and sorry for my "franglais"

)

Supportive

andrea tasselli

Frequent contributor

Dec 2, 2020

Hi,

Where to start… First things first I suppose:

1. The camera is mounted tilted with respect to the optical plane, that is why you have astigmatic star shapes at the centre and the round ones at the far right hand side. You need to control that. This is critical at your focal length.

2. ISO is too high for a Nikon D7000. Best ISO is 200. Maybe 400 for 5". And that is it. You're burning the core of M42 at ISO 1000.

3. Acquiring and applying a flat is critical to astrophotography. You need to shoot at dusk. 20 frames would do. Point the scope near to the zenith after the Sun has set and take the shots. Leave the camera in place until you start taking photos of the subject you want, if you can.

4. Don't waste your time taking zillions of bias frame or darks. That isn't where your problems are, they are in having a correct flat frame and applying it. At 5" you wouldn't even need a dark (I know, I have a D7000 too) at this stage. Leave it for later.

5. Get DeepSkyStacker. It is free. And it is very good. Follow their guidelines in processing deep sky imagery, that is a good start.

Hope it helps

Helpful

Chris Barnes

Topic starter

Dec 2, 2020

Thank you all for your input!

In reference to the tilt: I am currently using a generic barrel type t adapter. One that slides into the visual back of the scope, and secured with two little set screws. (Does that make sense?) Could that be the source of the tilt?
@Joel85 I will go for a longer exposure next time. The reason I didn't this time was because this was the first time I've used tracking and I wanted to make sure that i had it set up properly.

@andrea tasselli thank you. I'll lower that iso next time. I do have DSS. The reason I haven't used it on my first two images is because sequator outputs an image that seems to require less processing. DSS gives me a mostly black image and sequator gives me a nebula (@Michael Timm calls it "already stretched") and so I just felt more comfortable working with that. He had also suggested i switch to DSS and I'm currently in the process of trying to re-stack with DSS.

I haven't been with astrobin for very long but in the short time that I have been, I have been amazed at the kindness and generosity of this community. Thank you all

P.s. I think I just figured out how to add my image to the thread instead of just the link

2nd M42

Respectful Supportive

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