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Nigella Bryant

My first telescope image M42

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Hi all, I know I need to improve on this but had to share my first telescope image of M42 taken in January with my Orion UK 12inch f4 Newtonian 

M42-43-small.jpg

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Well it is way better than my first telescope image.

What camera are you using? Is it a single-shot image, or has it been stacked (wih calibration frames)?

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Posted (edited)

Hi, I use a Canon 1000dm for lights,  image was a stack of 10x30second exposure at iso800. Stacked in DSS and photo shop CS2. Taken using APT. Mount Neq6 unguided. Only used four 30th of a second darks, no flat's which is something I need to apply and take next time I take a deep sky object. 

Edited by Nigella Bryant

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Darks should be the same length and temperature as the lights. If not, you are adding more noise than you are calibrating out.

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So I'd have to take 10x30secs darks at iso 800 to match the light's?  Also what about flat's and bios, I've read about? Thanks.

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10 hours ago, Nigella Bryant said:

So I'd have to take 10x30secs darks at iso 800 to match the light's?  Also what about flat's and bios, I've read about? Thanks.

Yes, 10-20 dark frames, each the same length as the lights and, most problematical for DSLRs, the same temperature (and ISO setting). You are capturing the "heat" signature of the chip ... how many electrons are generated, which increases with increasing temperature. I'm a bit OCD when it comes to this sort of thing, so I used to do my darks in two batches when I used a DSLR ... half immediately before the lights and half immediately after, on the (probably mistaken) view that they would even out.

Flats: You take a series of 10-20 images using a "flat" light source. The aim is to catch any imperfections in the optical train (vignetting at the corners, dust-bunnies, etc). The main thing is that nothing should be physically changed (e.g. focus) between taking the flats and the lights. The stacking program then takes these imperfections into account and corrects for them. The exposure length is determined by the intensity of your light source (some programs, like APT and Sharpcap, will work this out for you). Some people also go to the trouble of taking "dark flats", which are a set of darks at the exposure length of your flat subs.

Bias: These are a series of "dark" subs taken with the shortest exposure length you have. The aim is to capture the "read noise" of the camera. As the content of the chip (after the exposure) is read-out and interpreted, this generates extra signal and this is what you are getting. These can be done in advance and a "master bias" produced by the stacking program can be used for quite a while.

If you ever move onto a "cooled" camera, that takes images at a particular temperature, darks can also be prepared in advance.

HTH

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10 hours ago, Nigella Bryant said:
3 minutes ago, Demonperformer said:

Yes, 10-20 dark frames, each the same length as the lights and, most problematical for DSLRs, the same temperature (and ISO setting). You are capturing the "heat" signature of the chip ... how many electrons are generated, which increases with increasing temperature. I'm a bit OCD when it comes to this sort of thing, so I used to do my darks in two batches when I used a DSLR ... half immediately before the lights and half immediately after, on the (probably mistaken) view that they would even out.

Flats: You take a series of 10-20 images using a "flat" light source. The aim is to catch any imperfections in the optical train (vignetting at the corners, dust-bunnies, etc). The main thing is that nothing should be physically changed (e.g. focus) between taking the flats and the lights. The stacking program then takes these imperfections into account and corrects for them. The exposure length is determined by the intensity of your light source (some programs, like APT and Sharpcap, will work this out for you). Some people also go to the trouble of taking "dark flats", which are a set of darks at the exposure length of your flat subs.

Bias: These are a series of "dark" subs taken with the shortest exposure length you have. The aim is to capture the "read noise" of the camera. As the content of the chip (after the exposure) is read-out and interpreted, this generates extra signal and this is what you are getting. These can be done in advance and a "master bias" produced by the stacking program can be used for quite a while.

If you ever move onto a "cooled" camera, that takes images at a particular temperature, darks can also be prepared in advance.

HTH

 

Being a relatively new DSLR imager with my own problems, haha, I'm curious about the doubling in the image, and surely Nigella Bryant must wonder though no mention was made. Would that be caused by poor polar alignment or somehow bad stacking? It looks to me like maybe only one sub is misaligned. Even unguided as the subs were, with the Neq6 mount 30 second subs should be a breeze, no? I use the Heq5 Pro and before I got my PHD2 running correctly I was getting 60 second subs no problem.

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Poor polar alignment will cause tracking of stars rather than a double image. It looks to me like a stacking issue, although I don't know enough about the way that is done to explain why it is happening.

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Hi

If my first image had looked like that, I'd have been happy. As it is, all I got was some greenish fuzz, otherwise known as the Andromeda Galaxy. Way to go. I used to take my DSLR flats after a session, in the morning in brighter twilight, scope pointed at an evenly illuminated clear sky. Dunno whether I'd take darks half before a session, why introduce heating of the chip right off the bat? I may be totally off here, but the doubled-up stars don't seem to be a stacking problem to me, rather something due to a sudden very small mount movement (gust of wind? Cable snag? Something slightly banging against the mount?) At 10 images (lights), the "reject sigma" algorithm in Deepsky Stacker should be able to filter out small imperfections.

- Andy -

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21 minutes ago, AstroAndy said:

Hi

If my first image had looked like that, I'd have been happy. As it is, all I got was some greenish fuzz, otherwise known as the Andromeda Galaxy. Way to go. I used to take my DSLR flats after a session, in the morning in brighter twilight, scope pointed at an evenly illuminated clear sky. Dunno whether I'd take darks half before a session, why introduce heating of the chip right off the bat? I may be totally off here, but the doubled-up stars don't seem to be a stacking problem to me, rather something due to a sudden very small mount movement (gust of wind? Cable snag? Something slightly banging against the mount?) At 10 images (lights), the "reject sigma" algorithm in Deepsky Stacker should be able to filter out small imperfections.

- Andy -

I hadn't noticed the double star problem but is more likely due to layering one image of a shorter exposure on top where I didn't match the layer's of the core properly. I really struggled to understand the techniques of layering in photo shop,  I still do. Sorry I didn't mention that I tried layering a shorter exposure of the core of the nebula. 

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Easily remedied :) With the move tool, on can align layers properly. Or >edit > transform, if they are of different sizes.

Capture.PNG

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21 minutes ago, AstroAndy said:

Easily remedied :) With the move tool, on can align layers properly. Or >edit > transform, if they are of different sizes.

Capture.PNG

Thanks, I'll have another go at the layer's. 

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