NGC4755 region - preliminary image - worth continuing?

[erick (Eric)]

I'm going to try and get a reasonable image of this region in the next month, as good as I can within the limits of my equipment.

I think this first shot says it is worthwhile pushing ahead? Maybe?

Equipment:- GSO 8" f4 reflector on an EQ5 mount, simple RA drive tracking. DSLR is a Pentax K100D. Using B setting, 2 sec mirror-up delay and remote shutter operation. Using a lightshield extending some 30cm from front of the tube.

I have set up just inside the entrance of my garage. Set up the mount where I can park the scope (tube vertical) so that the roller door just misses it on closing! For the next month, I can get a clear view of Crux for a few hours each night. Have spend a few nights getting it positioned, laying out power for heating (finderscope and secondary mirror), getting the AutoStar hand set running again, power to camera etc. Also have spent a while getting the setup balanced. Then have spent time getting the scope as precisely collimated as I can.

Conditions:- Full Moon and fair number of local street lights etc.

Image:- ASA 1600, single shot of about 5 seconds, shooting JPEG with ICNR. Presented full frame. Tweaked levels a little in a cutdown version of Photoshop. Some image resizing and compression to get down to 200kbyte limit for attachment.

Now there are a million things wrong (eg. nowhere near polar aligned as yet, and the Pentax DSLR is never going to perform particularly well), but I think some things look good? I have good enough resolution of the stars, plenty of colour in them, nothing strange appears to be going on with the star shapes across the frame (ignoring the elliptical shape due to trailing over 5 seconds - yikes!).

Shall I push ahead?

Next steps?

1. Try to get much better polar alignment. Going to be fun since I cannot see much of the sky. Perhaps time I got down on the ground and looked through the polar scope in the mount - ouch, my back!

2. Wait until the Moon goes away and until minimal local light pollution (Sports lights out).

3. Focus will remain trial and error - nothing fancy on the Pentax to help with this. I seem to be able to pick pretty good focus on a bright star (Mimosa) through the viewfinder.

4. Then shoot at the lowest ASA I can to keep the camera noise down - 400? Shoot multiple subs of at least a minute duration (probably mount and polar alignment limited?). Try JPGs, but also shoot RAWS (but they are a proprietary Pentax file type, as I recall, annoying to handle) plus darks.

Eric - the non-astrophotographer

[Moon (James)]

Eric,
Sounds like a plan. Practice makes perfect I say.
It would be interesting to test if DeepSkyStacker can open up your RAW files from your camera - the online help indicates that it can.
You could also save some time and skip the ICNR and use standard darks instead.
Good luck
James

[bojan]

Erick,
This is nice first try, you are on your way for much better job and it is definitely worth continuing :-)

As far as ASA setting is concerned, I found it best to stay at highest value (Canon), but it is not a rule, and in some cases the dynamic range may be compromised (depending on camera model).
There was a thread on IIS, discussing this.. someone showed (by means of mathematical analysis) that the best S/N is at high ISO, which, for me, was not surprise.
When I find it, I will post a link.
Avandonk (Bert) knows a lot about this subject (middle of the page):
http://www.iceinspace.com.au/forum/s...ight=S%2FN+ISO

[erick (Eric)]

The only night I tried to shoot RAWs, I think I did shoot at the max the Pentax has - 3200. It looked like I was shooting through a Scottish tartan! I see if I can find the image.

Here is it, nope I was shooting at ISO 800 - 30 sec (me standing very still!)

I'll experiment, thanks Boojan. At least now I'm not looking for an animation, but a single image.

James, I'll try DeepSkyStacker.

And thanks guys, you've made me track down last year's threads and I got a lot of good advice then on acquiring and processing with my camera. I'll re-read all that now.

[gbeal]

Of course it is Eric, most of the hard work is done, with basic alignment etc, so yes, carry on.
In a round about way I have had a similar experience myself. I got a new to me scope recently, and decided to try the DSLR with it, instead of the usual camera I use. I tried a few shots of Omega Cent, but also tried The JewelBox as well.
Focus was always going to be an uphill battle, as I am so used to software focus. I tried a Bahtinov mask, and it got me close enough.
Keep at it, try a B mask, get the alignment a bit better if you feel it is "off". Try varying ISO settings. I like the lower ones, but if Bogan says high is good, I am not going to argue. I used ISO640 in this case.
I will trial this concept some more too.
Gary

[erick (Eric)]

Thanks Gary

OK - a B mask next. I was thinking whether I should bother.

[gbeal]

Well, like I said I am software assist all the way, but with my DSLR (Sony a700) it is impossible, so I tried the B Mask. Up until now I had only tried one the once, and when I did it seemed a complete waste of time. I ended up with a mask when I bought the new scope and thought "what the heck, nothing to lose by trying it", and was glad I did. Sure LiveView would help even further but this, and a few others I took all seem pretty close to focus. AND, they are at about 2000mm focal length.
Give it a go. When you are being driven crazy think about canning it then, but until then keep trying.
Gary

[bojan]

Originally Posted by erick

Thanks Gary

OK - a B mask next. I was thinking whether I should bother.

Bakhtinov mask is great help.. but not something you MUST have.
I managed to achieve good focus without it as well.
The trick is in exposure time, it should be short enough not to saturate the star image - then you can see how big the image is and correct until the circle is smallest.
That assumes using laptop running something like FocusAssist, and screen magnifier (plenty of freeware available on the web).

I imagine the live view is very helpful here as well.. with screen magnifier of course

[erick (Eric)]

Well, I persisted.

Worked hard to get the polar alignment as good as I could - but still not great. I reckon the polar scope wasn't properly aligned with the mount axis (probably cause I pulled it out and replaced it while I was mucking around!)

Focus much better thanks to a Bakhtinov mask.

Unfortunately the only night I had to shoot photos, the nearby football oval decided to turn on its floodlights. Couldn't wait, the targets were dropping fast in the sky. So I put up a screen to stop direct light getting into the end of the tube and pushed ahead.

Star trailing restricted my exposure times to about 15-20 seconds. ISO 800 for most frames. Shooting with ICNR and saving as JPEGs.

Finally had 10 useful frames of the region I most wanted - The Jewel Box through to Estelle's Star.

(Estelle's star - What's that you say - see here:- http://www.iceinspace.com.au/forum/s...ad.php?t=62524 )

4 useful frames of Omega Centauri. 5 useful frames of Mimosa and Ruby Crucis.

Many thanks to Ken for helping stack the frames with Registax and to Ken and John for working some magic on my poor data with Photoshop 3.0. (And I have to admit, I did sunsequently hit the widefield with a little Star Rounder magic.)

I'm very pleased with my "happy snaps".

ps. I typed f4 below - I should have said f5 for the scope.

[ballaratdragons (Ken)]

They came up a treat, Eric.

It was a pleasure to help.
Keep at it coz I think you have a knack for detail
and you are off to a great start.

[multiweb (Marc)]

Very nicely done. Sharp with great colors.