M31 First Attempt

[Jaydippy]

Hey all, finally got around to processing some data I'd captured on a recent holiday to rural Wales (slightly more astro-friendly than London). Not too sure what I'm doing when it comes to post processing, so any advice is greatly appreciated. Happy to send over the data if anyone wants to mess around with it, see what comes out. 

Here it is, my first attempt:

(had to rescale image to 1MB posting limit).

Cheers,

Jay

[xtreemchaos]

thats a great first go mate,well done.thanks for posting. charl.

[Stargazer33]

That is a very impressive picture Jay. Made even more so as it is your first attempt. Well done!

[orion25]

Bravo, Jay, on your first attempt. Great dust lanes there. How many subs/darks/flats?

Cheers,

Reggie 

[laudropb]

Very nice image. Especially for a first attempt. Thanks for sharing.

[nightster]

Great job. That will keep you hungry for photons!

[nightster]

Great job. That will keep you hungry for photons!

[angelmnegron]

Very nice. What are your details?

Scope

Camera

Lenses

Exposure times

Software used to combine

[Jaydippy]

Thanks for the comments all! It was nice to finally get an image out after such a steep learning curve.

Thanks Reggie, I can't remember exactly but I think the subs were 4x60s, 8x90s and 2x120s. Bit of a mixed bag, but I was trying to see how far I could stretch the subs given my fairly poor alignment. I'm ashamed to say I didn't take any darks/flats...still all seems like witchcraft to me.

Cheers angel, being a student the equipment is all on a fairly tight budget. The scope was an Opticstar ARC102 f/6.6 (great scope for the price) on an eq5 with dual motors (unguided). The camera is an unmodded Canon 400d and subs stacked in DSS with GIMP for some light post processing.

[pyrasanth]

That is a great first image.

This is what you need to do to improve it. If you have a mono CCD camera the tips below will work but if your shooting with a DSLR I have little experience of them preferring dedicated astronomy CCD cameras.

Increase your signal to noise ratio. Signal data increases much faster than noise. So take lots of very short exposures. Flat field correct them then stack. You also would do good to get a good light pollution reject filter like the IDAS sold by FLO.

If you use a mono CCD camera  take lots of L data using quite short exposures & take 3 times as much L as the RGB data. The L is much more important than the RGB data so get more of it. The difference in your results will be quite spectacular & don't forget to refocus frequently & especially between changes of filter.

I guess with a DSLR you could still take loads of shorter exposures to minimise the noise.

[Jaydippy]

thanks for the advice pyrasanth. I'm only imaging with DLSRs for the time being, though a CCD might on the horizon after I have a little clear-out.

I tend to use a UHC filter for when the light pollution gets intolerably bad (nearer the horizon etc.) but it doesn't work so well on some objects. A decent lp filter is on the Christmas list, but I'm told that they can be quite hit-and-miss, dependent on the type of street lighting nearby. I'll certainly give the IDAS a look though.

I'm still trying to get my head around S/N, but I thought it scaled by the square root? Surely longer exposures would be better, assuming your tracking is good enough and you aren't overexposing. Also, wouldn't overly short exposures increase the effect of read/bias noise?

[pyrasanth]

thanks for the advice pyrasanth. I'm only imaging with DLSRs for the time being, though a CCD might on the horizon after I have a little clear-out.

I tend to use a UHC filter for when the light pollution gets intolerably bad (nearer the horizon etc.) but it doesn't work so well on some objects. A decent lp filter is on the Christmas list, but I'm told that they can be quite hit-and-miss, dependent on the type of street lighting nearby. I'll certainly give the IDAS a look though.

I'm still trying to get my head around S/N, but I thought it scaled by the square root? Surely longer exposures would be better, assuming your tracking is good enough and you aren't overexposing. Also, wouldn't overly short exposures increase the effect of read/bias noise?

Hi Jaydippy- some info to help you along- get the book mentioned later.

Signal increases much faster than noise. They initially start off as linear then the noise stays fairly constant or increasing slowly but the signal ramps up- it certainly climbs very fast. I suggest, as I have recommended many times, read the book The Deep Sky imaging primer (Bracken)- it will tell you a lot about the techniques you seek.

When you get a dedicated CCD mono astro camera you can experiment with narrow band filters- when you pick the appropriate imaging target they will remove a lot of undesirable noise data. However narrow band is not a substitute for dark skies but they are certainly a tool worthy of consideration-target dependent.

My imaging targets are deep sky so I need very fast optics & thus use the Celestron RASA at F2.1 but it captures signal & noise data at an alarming rate hence I take hundreds of 120 second exposures then stack. If I see noise I just take more data. The sample below is what I am currently imaging & so far is 125 120 sec subs. The pre stack images have noise but the sheer quantity using CCDStack2 averages out the noise.

It takes a lot of practice but as your results get better people will admire your work & wish they could do the same. Clear Skies to you & all.

[Jaydippy]

Thanks for all the info pyrasanth, I'll put the Bracken on the to-buy list long with Making Every Photon Count, which I've also seen recommended quite often.

Wrt. using narrowband filters to reduce noise, I thought noise was an unwanted effect of the electronics being used, in which case the filters wouldn't reduce noise but only light pollution and unwanted wavelengths right? Again, I'm not too savvy with this, so let me know if I'm thinking about this in the wrong way.

I've heard great things about the RASA and if that image above is anything to go by, it deserves the praise. Wonderful image mate 

[pyrasanth]

I wish noise in the camera was the only thing I had to worry about when taking my pictures.

Noise is generally classed as any information that is undesireable. Noise can come, as you identified, from the camera electronics but there are many other forms which serve to annoy the hell out of us. Light pollution is probably the worst culprit & can range from banding to mult-coloured gradients which require careful correction. If you take many exposures you will be hit with sat & meteor trails which again require correction. The dreaded gamma ray also can show as a zig zag on the CCD.

Narrow band filters whilst never a substitute for dark skies help by rejecting light pollution and only pass a narrow band of light being radiated or reflected from the object being imaged. However you won't get true colours but the results can be very satisfying.

[Jaydippy]

Ahhh right, I hadn't come across this definition of noise before. I quite like the idea of picking up the occasional gamma ray, terrible for the sub, but satisfying to see when you think of how they come about

Living in London, I can definitely sympathise when it comes to light pollution, especially from the new broad spectrum LED street lighting that they seem to be installing everywhere. Luckily they aren't too keen on making the transition in my area but it seems to render most LP filters useless.

That being said, narrowband filters should still work on LED lighting to some extent right?

[seo]

Very nice first attempt ! Bravo !

[Guest]

Very nice 1st attempt & thanks for sharing it..

Martin

[Jaydippy]

thanks guys!