First attempt at M31 with 2 sec. subs

[stevedodkins]

Here's my attempt at capturing the Andromeda Galaxy. I only have a standard tripod, no equatorial mount or astrotrac, so was limited to 2 sec exposures using a 200mm lens. I'm quite pleased with how it turned out, as the overall exposure time is relatively short, so definitely something i'll go back to another night when i have more time.

372 x 2 Seconds exposures + 220 darks. (Total 12 min 24 sec)

Canon 40d + 70-200mm L IS lens @ f/2.8, 200mm, ISO 3200.

Stacked in DSS, processed in CS4 with a final tweak in Lightroom.

I welcome any advice or suggestions (particularly regarding processing).

Steve

[RogerTheDodger]

That's pretty good considering the limitations, just shows what can be done...

roger

[Superewza]

That's great, just imagine what it could be like with the poor mans astrotrac

Make a Scotch Mount: From Star Ware 1st edition

[Orion_the_Hunter]

Nice! What scope did you use?

[stevedodkins]

Thanks.

Superewza, i do plan on making a scotch mount, not sure the ball head i've got would support my lens though, but it would be good for widefield.

Orion_the_hunter, this was taken with a 200mm lens for my canon dslr, no telescope.

[RobH]

Great result

You don't need as many darks as you've taken....50 will be enough.

Cheers

Rob

[carastro]

Can't believe you've got that with 2 sec subs.

(well what I mean is I believe you of course, but it's amazing).

Processing looks fine too.

Just think what you could achieve with the right kit.

Carole

[Glen]

Brilliant result! Maybe think about deducting bias shots and a little time between exposures for the chip to cool, may not significantly produce a better result , just throwing it out there. Did you crop this at all? All the same well done!

Glen

[LukeSkywatcher]

WOW. All this with a fixed tripod etc.

I am really going to have to give my zoom lens a bit more outside time.

[jgs001]

Wow Steve... good work... that's excellent for 2 second exposures

[RobH]

Brilliant result! Maybe think about deducting bias shots and a little time between exposures for the chip to cool, may not significantly produce a better result , just throwing it out there. Did you crop this at all? All the same well done!

Glen

If you're subtracting darks, you don't need to subtract bias as all the bias information is in the darks.

At 2 seconds, the darks are not far from being bias frames anyway!

Rob.

[Glen]

Oh, thanks Rob, apologies all for any confusion caused. That'll clear up allot, i was only trying to help stevedodkins with (what i thought maybe) noise in the post. So under a certain exposure time bias becomes unnecessary?

Regards Glen

[stevedodkins]

Thanks everyone.

Glen, this is the cropped version. there was a 1 or 2 second interval between exposures. do you know the optimal interval? it's something i'll have to look into, but if it just creates more noise then wouldn't that be picked up by the dark frames which i took at the end?

[Pete Presland]

thats a great effort just shows what can be done

[Glen]

stevedodkins, from my understanding when the chip heats up it creates noise seen as hot pixles, giving the chip time to cool may help, but for 2 sec subs it may not count..

As for time between subs theres another post running atm and seems like whatever works for your setup , trail and error see here

http://stargazerslounge.com/imaging-discussion/129530-how-long-between-dslr-exposures.html

[Glen]

to add the high iso i believe will add noise to a pic (3200 compared to say 400-800iso) so a longer exposure is needed to get a similer result. without a motorised mount youve done a fine job sir:icon_salut:

Glen

[Fay]

That is really good for 2 secs, Steve. Do you reside on the ISS?

Fay

[LukeSkywatcher]

I'd imagine that the time between subs for 2 second subs should be about 5 seconds?. Unless the mirror is locked up. Then i'd imagine you can fire off subs til the cows come home because there will be no internal shake and the heat build up will not be that high anyway.

I dont know really,. Its just me. I'd give the camera a few seconds to settle down again before firing off the next 2 second sub.

[Glen]

Good point Paul. Would firing off 320 2 sec subs create heat in the chip if not left to cool a little? i dont know how long the 40D takes to write. interesting though.

Glen

[RobH]

Oh, thanks Rob, apologies all for any confusion caused. That'll clear up allot, i was only trying to help stevedodkins with (what i thought maybe) noise in the post. So under a certain exposure time bias becomes unnecessary?

Regards Glen

Hello Glen.

Most of the noise is caused by reading the sensor etc. Because the subs are so short, this noise is a significant factor. With longer subs, it becomes less important as the signal to noise ratio will be better.

If you're applying dark frames, you never need to apply bias, as the bias information is contained in the darks, no matter what the exposure length, be it 2 seconds or 20 minutes.

If you also apply bias, you end up actually adding noise.

If you apply flats though, you need to bias subtract them before applying them to the subs.

The improvement in the S/N ratio that you get from stacking lots of subs tends to be very slight after you pass 100 subs or so, so adding many more subs to this image would hardly affect the S/N, as it has a lot of subs already.

In very short subs like this, it might work well to ' dither', which means slightly shifting the target on the sensor each shot or few shots.

Then use a stacking algorithm like sigma clip or SD mask, or median combine. These are 'sigma reject' methods, and what will happen is that everything that is common to all subs will come through ok, but random elements, like a lot of the noise, will be rejected.

Cheers

Rob

[Psychobilly]

Hi Steve a might fine result for such short subs

That lot must have taken DSS a while to process...

DSS uses a slightly different terminology for its calibration frames its best to have a look at the claibration section of the DSS help files...

I just dug these process images out again they are taken form the DSS help files...

Billy...

[Glen]

If you're applying dark frames, you never need to apply bias, as the bias information is contained in the darks, no matter what the exposure length, be it 2 seconds or 20 minutes.

If you also apply bias, you end up actually adding noise.

....

If you apply flats though, you need to bias subtract them before applying them to the subs.

Rob

thanks Rob, im shure the op will find this helpfull also.

many thanks

Glen

[RobH]

Peter,

Thanks for the info about DSS...I didn't know it did it like that and there would have been some confusion I'm sure .

Cheers

Rob

[LukeSkywatcher]

Good point Paul. Would firing off 320 2 sec subs create heat in the chip if not left to cool a little? i dont know how long the 40D takes to write. interesting though.

Glen

I just think i'd prefer to let the camera rest for a few seconds between each shot,.

[Glen]

Billy, thanks for uploading the pictures. I do see that the last mentions any other combination leads to improper cal.

thanks again and humbled

Glen