Although, the below image is crap I am pleased as it is my most technically challenging image so far. The image is a dark nebula in Cepheus - It represents the sum of 30 X 90 Secs guided exposures. In order to capture this image I had to modify a 2nd Toucam for LX guide control & then figure out how to get the guide cam & imaging cam all working at the same time on my laptop... I'm sure Chris, Mike, Paul & Fay can all sympathise... Anyway after about a month of trying I managed it & below is the first image. This was taken with a Ha filter - I should now be able to take 2 to 3 mins images which hopefully means I can go after fainter objects. Residual Ampglow is still a problem with this length of exposure on the SC3 even though I have done the mod.
The image doesn't come anywhere close to Mike's from a few months ago but for long exposure narrow band imaging from what essentially is a webcam I think it's pretty good... I'd still love a camera like Mike's though :-) I should be able to improve on this if I try more longer exposures - should also help with the noise - remember my SC3 is not cooled so it gets pretty hot with 2 min exposures...
Anyway here is the image:
(http://homepage.ntlworld.com/john.punnett/graphics/oas/VDB142.jpg)
Cheers, John
John I agree, with a modified webcam that is a very impressive image. Yes it is very noisy, but with a longer exposure as you say it should improve. What did you do in the way of bias and dark frame reduction?
For what is a technically challenging and very dim object your image is well impressive. Well done.
Hi Mike,
Thanks for your comments...
Normally with all my processing I tend to take approx 10% dark frames at the end of the imaging session - this seems to work OK with the relatively short 10-20 secs exposures I normally do.... However, it didn't work for this image last night & Chris told me why... Basically I grabbed 5 X 90 secs dark frames at the end of the session but when I subtracted these from the stacked frames it made the image a lot worse & not better as usual. The reason is to do with the thermal noise in the darks... i.e. the camera (CCD) was at a different temp when the darks & lights were taken - The imaging session lasted over one hour...
It seems I now need to take darks before & after getting the lights... I guess this is the disadvantage of using an camera for long exposure that has no CCD temp control...
I have never taken bias or flats... I guess I need to start looking at these as well now I'm increasing exposure length...
Cheers, John
John,
I really like that one, I can understand the challenge!!!
I was trying to have a go at either M51 or M101, but could not see anything at all. I think the viewing conditions would have to be really good. Have you an unprocessed frame of both of these that I could look at to see what I should expect to see on the screen. I am dying to get a spiral.
Fay
I'll try & send you a raw for M51... It may take me a while as I will have to search my archive files.. M51 is a lot easier than M101..
By the way I finished up imaging at about 1 last night -I gave my laser pointer a quick try (no neighbours lights on etc. & no moon) & it was great - I'm well chuffed with it.. :-)
Cheers, John