Hi all
Finally there has been a bit of clear weather where I live, albeit for half a night. I didn't get out till late so I had a go at IC 405 (flaming star nebula) with my trusty Ha filter. As with previous Ha images I used 10 minute subframes unguided. I only managed 6 subframes as it was getting very close to the horizon where there was some cloud creeping up hence the image being quite noisy.
TMB 115 with Starlight Xpress H36 and Astronomik 13nm Ha filter on Paramount ME unguided, simple autodark subtraction done in Maxim DL, with curves, levels and contrast done in Photoshop CS2.
There is a better quality image on my website http://www.imagingtheheavens.co.uk
Regards
Gordon

Gordon,

Nice shot and nice processing. 10 minutes unguided! I wouldn't dream of that with my CGE unless it was a piggy-back shot.

--Andy

__________________
Observatorio de la Ballona

When one says 'unguided' does it mean that you manually followed that area of sky by slowly turning the fine adjustment 'wheel'? Or does it mean motor driven but not actually tracked with a second CCD camera and guide scope?

Very nice picture by the way

A great shot!, Very nice frame and lots of details. Welldone Gorden and Clear Skies.

Hi Ashdown
Unguided means that you allow the mount to guide using its motors without using an external camera to provide corrections for periodic error. Some mounts have to be guided with anything longer than 30 second exposures because the periodic error is so erratic it would cause the image to be blurred
Hope this was the answer you were looking for
Kind regards
Gordon

Well it was a concise answer like I was looking for, but I was hoping you were going to say you guided it yourself :P oh well, I have a long time left to work up to gear and results like yours Thank you Gordon!

Hi Ashdown

I am sorry to disappoint you, but I leave the tracking accuracy to the Paramount, I am hoping to try for 20 minutes unguided next time and I will post the results here as they come. If ever you have the funds to buy a Paramount I can thouroughly recommend it, it has surpassed all my expectations already and I haven't even started trying out all of its capabilities.
Best wishes and clear skies
Gordon

I easly go 10 minutes at 3560mm focal length with mine with 1" pixels. With my 6" f/4 using slightly more than 3" pixels I never did find a limit. Longest I went was 30 minutes and that was fine. After 50 years of fighting my mounts it's sure nice to have one that really does its job. I do use a 400 star T-Point map which helped my accuracy greatly. With that, not only can I do 10 minute subs I can stack them without alignment most of the time. I do have to resize them however due to temperature really changing image scale. Can't blame the mount for that.

Rick

Hi Rick
Nice to see a fellow Paramount owner, I generally do two 15 star T-point mapping runs mainly due to time constraints and the changeable weather here, also I use a portable setup so I do this each night I image. I dream for a permanent setup in an observatory but that may have to wait. Originally I had a Meade LX200GPS so I was used to a maximum of 30 seconds unguided. Since changing to the Paramount and starting with 1 then 2, 4 and now 10 minute unguided subs I can see what you mean by not finding a limit. The only limiting factor that I can see is a cloud or the accuracy of the polar alignment. It will be 20 minute subs for me next time.
Best wishes
Gordon

Lovely. Incredible exposure times from my perspective. Is there a standard formula for calculating pixel sizes, (arc), given camera and telescope specs?

Kind regards
Matt

Hi Matt
There is a calculation which works for all cameras and scopes and it is
Arcseconds/pixel = pixel size/focal length * 206
Ideally you should be aiming for a figure of about 2 to 2.5. The lower the number the higher the resolution but this will only be of benefit if the seeing is very good.
As an example my main telescope has a focal length of 850mm and I am using a pixel size of 7.5um so the equation will be
arcsec/pixel = 7.5/850 * 206 which gives 1.818
This means I am probably not making best use of the extra resolution due to the poor seeing. What I might do is use 2x2 binning which will give me an arcsec/pixel figure of 3.6 which may be better for the seeing conditions but it will also increase the sensitivity of the camera by a factor of 4. A good place to look for more info on this and a calculator that you can download is by entering Ron Wodaski in a search engine, his books are very informative.
Kind regards
Gordon

Thanks, My DSI II should then give me 2.13"/pixel at a focal length of 814mm, well within your reccomended range. Thanks so much. No Binning available on that cam but at f/4 I have enough light.

Kind regards
Matt