M77 and NGC 1055 - Galactic Neighbors
Posted 04 December 2012 - 11:55 PM
High Resolution version and more image details available at http://www.astronome...php?c=113&p=471.
This image is a composite image made from a wider frame with both galaxies, and then separate cropped images of M77 and NGC 1055. 435 x 3 minute subs (total exposure time 21 3/4 hours) at ISO 1600 were captured via a Celestron C-8 (orange tube), Celestron focal reducer at f/5.8 (1160mm), and Gary Honis modified Canon 450D. Guiding was with an ONAG On-axis Guider, Lodestar autoguider, and Phd Guiding.
Thanks for looking!
Posted 05 December 2012 - 12:01 AM
Posted 05 December 2012 - 12:47 AM
This shot might convince me to go back to 1600 ISO (sigh -- I've wrestled with myself so many times on this question)
Posted 05 December 2012 - 02:54 AM
Posted 05 December 2012 - 05:04 AM
Posted 05 December 2012 - 08:05 AM
Great shot! Your Celestron FR gave you f/5.8, is that the standard f/6.3 FR modified with a different spacer? What is the spacing?
Posted 05 December 2012 - 10:54 AM
Posted 05 December 2012 - 01:32 PM
Posted 05 December 2012 - 08:20 PM
Posted 05 December 2012 - 10:04 PM
Posted 05 December 2012 - 10:39 PM
@Craig - FYI, the only reason I use ISO 1600 is because I prefer to use relatively short 3 minute subs (for a variety of reasons). Because I'm imaging from fairly dark skies (typically SQM readings around 21.4), I need to use ISO 1600 to bring my background out of the read noise of the camera (i.e., histogram mountain separated from left axis on the back of the camera). Optimally, I'd prefer to shoot at ISO 400 (close to unity gain for my camera), but I'd have to shoot too long a sub to obtain reasonable separation of sky fog and read noise. So, I use the higher ISO. Frankly, I'm not a big believer that different ISOs have a significant effect on image outcome (presuming you don't clip too many bright stars on the highlight end and have adequate separation from the sky background and read noise on the shadow end).
@Mike - Thanks for the suggestion - I had posted over the last month or so the separate portions of the composites for each of the galaxies. Here are links (on my website - not the CN postings) to each of them:
M77 - http://www.astronome...php?c=113&p=467
NGC 1055 - http://www.astronome...php?c=113&p=468
@John - my ONAG on-axis guider forces the FR to focal plane distance to about 120mm. This ends up yielding f/5.8 at 1160mm. The image is somewhat more vignetted with the wider field, and the stars are pretty crummy at the edges (unless you focus for the edges). You can see a little bit of these poor stars in three of the four edges of this image (the upper left is clean because I cropped that corner to frame the galaxies). The wider field isn't terribly usable without doing focus stacking (taking subs focused for different parts of the FOV), but the imaging train is slightly faster (roughly 20%). I think you're better off keeping the nominal spacing of 105mm unless you're forced to the larger spacing (because of something like your guider).
@nikao - the core of M77 is quite bright, so you could probably image it from fairly bright skies. Its a great target because it has some wonderful detail. The outer halo for M77 is really faint and subtle, so I'd plan on dark skies to try to capture that (or an awful lot of time from a brighter sky). NGC 1055 is relatively faint and is a pretty tough target. If you have a focal length of about 1200mm or shorter, you may as well frame in NGC 1055 if you're shooting M77 - they'll fit in the same FOV.
Thanks again everyone!
Posted 06 December 2012 - 03:17 AM
I will keep this on my target list for when I'm able to get to real dark skies as well
Posted 06 December 2012 - 03:10 PM
Posted 07 December 2012 - 09:08 PM
Posted 07 December 2012 - 11:04 PM
Posted 08 December 2012 - 10:59 PM