First proper astrophoto, M51 from suburbia in a quarter moon

Taken Wednesday night/Thursday morning Feb 1st-2nd at about 00.30 or so onwards.
Unguided LXD-75, Celestron Onyx 80ED, Canon 600D.
14 subs of 60 seconds, at ISO 800, using the onboard dark frame removal and no ISO smoothing. I know that the lack of flats is ovbious, but it's a start
I was lazy and at the end of my viewing session, and the camera was running out of battery, so I just went for lights and to see how the internal dark subtraction worked. I'll be taking proper flats and proper darks and proper bias frames the next time I'm out but I'm quite impressed with this pic. 14 minutes with an 80mm f6 lens and I can see past mag 16 stars, and I can just make out some non-NGC galaxies (I4263) in the region. I haven't completed my attempts to process the raw files in IRIS yet, and it's a quick jpg export from the .fit file in IRIS. There is still more detail or at least more visibility to get out of it.

Link to the photo and there's a link to the full size jpg

It's hard to belive that this pic came from raw frames that were bright orange, with the faintest hint of the spiral arms, though I could just get the arm in a 10 sec exposure. IRIS is a wonderful tool.

( it seems that the forum software needs a .jpg file extension to work with the image links...)

Hi Cathal. You're right to be pleased with that image, you've done well for 14 minutes total exposure from a light polluted site. Unfortunately, with poor skies much longer exposure times would be required to tease out more detail of the fainter parts of the spiral arms. Nevertheless, you will see a marked improvement if you can add another hour of exposure time.
I'm not a very experienced DSO imager, but my experience was that using a simple autoguider was the biggest single factor in getting better images. I was not able to take substantially longer exposures, because of the brightness of the sky, but a much much lower percentage of the exposures were ruined by tracking errors. That made a bigger difference than the use of dark, flats, bias frames etc., though, of course, they certainly do help the final image quality. I think you've done a good job with the processing. IRIS is a great tool, and its reputation for being difficult to use is not deserved.

The stars in the corners of your image are elongated; it is of no consequence for a small object near the centre of the image, but a field flattener would help if you tackle large targets. I would also recommend a Bahtinov mask to really nail the focusing.

Keep up the good work. The galaxy hunting season is around the corner, so keep those fuzzies coming.

Mike

A nice attempt Cathal, it's all part of the learning curve. I too am still at the unguided stage, so as mike says, more exposures will help out a lot, though that's not easy on a cold night

How do you find the 600D for noise? I was thinking of getting one

Keith..

Congrats on a great start Cathal. Clearly your mount is able to handle 60s unguided which is great. You'll be amazed at the difference flats make, not only will you remove the vignetting but also you'll be able to remove the light polluted background MUCH better. Well done!

Noise of the 600D? There are not many bad pixels at all on my camera.
I took darks when I was going for a widefield of Orion on the last clear night I had out just after Christmas. Using IRIS to see how many hot pixels I had, I think I had something like 15 pixels noted after running "find_hot cosme 300" - I'll re-run that to get the proper numbers and I'll report back here. Very few anyway. Overall in a dark frame at 1 minute, I counted 4 obvious pixels, and about 15 that were a bit brighter then the background. Pretty good with 18,000 pixels to play with, and they're easy enough to clear up afterwards.
I did read that the sensor in the 600D works at its most sensitive and with the least sgnal to instrument noise at about ISO 800 so that's what I've been using all of the time.
One thing that's fantastic about the 600D is the video mode, as the 3x zoom is actual native sensor resolution. it'll take the centre 1920x1080 of the chip with pixel width of 4.3 micrometres. For my 8" newt with 2x barlow, I've got approx 0.38 arcsec/pixel which is close to ideal for planetary capture though a 2.5x powermate would be better. It would be perfect for a 10"/11" SCT for planet capture. Chroma noise in the videos can be noticable though, but the stacking does help an awful lot with it.

I did a little more simple processing on the image in Paint.net, and the result is here . Not that much of an improvement but I went looking through my atlases (the TriAtlas by JR rocks by the way) to see what I could tease out of the pic. I can identify two IC galaxies nearby - IC 4263 and IC 4276 (barely) as well as noting that the circled star is mag 16.33. I should put up one of the raw subs - you'd probably cry.



Thanks for the pointers and good words

Cathal. Don't confuse noise with Hot Pixels. Hot Pixels are just one (very small) component of noise. The biggest component of noise is the grainy colour you see when you zoom right in. This pervades all of the image, and it is this which defines 99% of the noise. Also remember that to be most effective, darks need to be taken with the camera at ethe same temperature as when the lights were taken. With a DSLR this really means that you should if possible take a new set at the end of each imaging session. Yes I know this is easier said than done at 3 in the morning when you are cold and tired!