My best shot of M83 yet

tornado33 · #1 10-05-2005, 08:17 AM

Hi
Last night I took 2 of the longest exposures Ive ever taken of M83, two 17 minute ISO 200 shots with my EOS300d and 10 inch F5.6 scope, using the new off axis guider. Stacked and processed the images with Photoshop, converted them from the original RAW to 16 bit Tiffs before working on them.
http://www.users.on.net/~josiah/temp/m83small.jpg
The air was very moist, water was running off the telescope tube when I started to pack up.

iceman (Mike) · #2 10-05-2005, 08:25 AM

Beautiful shot Scott, lovely colours! It must be nice to image at such a low ISO!

Robby · #3 10-05-2005, 08:36 AM

17mins...! I've never heard of anyone going so long with a 300D. However the results prove that it was a worthwhile excersise. Well done!
For comparison I did M83 on Friday night, but with 5x3min shots. http://www.star-mate.com/DSO/M83_Pro2_web.jpg
Your image is brighter and has a bit more detail in the outer rings.
Keep it up.
Cheers

tornado33 · #4 10-05-2005, 08:49 AM

Thanks for the feedback folks. Robby, yours shows nice accurate guiding there. I didnt do dark subtraction, as when I stack the images with Photoshop , noisy pixels (except the amp glow on extreme right side of images, dissapear) What I do is offset the 2nd image slightly (by moving the guide star slightly between the 1st and 2nd shot by, say a dozen or so pixels). This ensures that any hot pixels dont appear at the same place when the 2 images are aligned and stacked, they then get averaged out. In future I might even go as far as 1/2 hour shots and see what happens

Scott

Robby · #5 10-05-2005, 08:54 AM

Hey Scott,
Do a dark frame! You'll be amazed at the difference. While your technique works, you can't beat the dark frame. Instead of just averaging away your nasty pixels, you will eliminate them!
Although I appreciate at longer exposure the dark frame is more time consuming!
Be interesting to see the difference in a shot at ISO400 and 8mins exposure time. I wonder which would be better?
I almost always image at ISO1600. Mainly because I'm lazy I think!

...
Cheers

tornado33 · #6 10-05-2005, 12:32 PM

Howdy.
Thanks for the tips.
I did a dark and subtracted it with Photoshop. It got rid of the Amp glow, but seemed to reduce the contrast a bit, geting the image to similar appearance as the one without dark subtraction seemed to introduce more noise. Ive never had much luck dark subtracting, or flat flielding for that matter. I can dark subtract with Photoshop and Registax, and flat field with registax, but Registax doesnt like 16 bit Tiffs. Flatfielding also seems to reduce contrast, givng rather flat images as a result. There must be an art to it (and better software), I was shocked at how expensive the good astro image processing software is, beyond my budget.

atalas · #7 10-05-2005, 03:35 PM

Plenty of detail tornado, well done .

Louie

[1ponders] (Paul) · #8 10-05-2005, 06:10 PM

Nice tornado, very nice. Good to see people stretching the limits of what's normally done and showing what can be done.

acropolite (Phil) · #9 10-05-2005, 06:53 PM

Nice shot Scott. What did you use for guiding? I can't wait to strap my SLR on to the LX. Now if I can just figure a way to get the necessary extras past the minister for household affairs.........

tornado33 · #10 11-05-2005, 09:13 AM

Thanks.
I used to use a 70mmm refractor guide scope, but was getting flexure induced guide errors, now I use a combination 2 inch focusser/off axis guider , images of it set up here http://www.users.on.net/~josiah/focuser/
and the company site
http://www.aeroquest-machining.com/page9.html
I get no flexure errors now, only downside is the guide stars arent round due to the off axis coma you get in newtonians.
I "hand guide", looking at the guide star with an illuminated recticle, making RA adjustments with push buttons on a drive corrector, dec adjustments with a slow motion manual hand control, the "old fashioned" way hehehehe.

ving (David) · #11 11-05-2005, 09:44 AM

Quote:

Originally posted by acropolite
Nice shot Scott. What did you use for guiding? I can't wait to strap my SLR on to the LX. Now if I can just figure a way to get the necessary extras past the minister for household affairs.........

mission control has tighened budgetary constraints... no such ventures shall be made by me till the financial advisor gives me the go ahead

but I do have a motorised focuser now!

thnx laurie!

tornado33 · #12 19-05-2005, 11:51 PM

Howdy
For the guiding I used a 12mm illuminated recticle eyepiece and a 2.8x Barlow