Widefield North American Nebula

[Steve 1962]

This is the result of 15 x 300sec exposures with a modded Canon 1000d and a 50mm EFII lens @ f2.8. The camera was guided on my NEQ6 mount.

I thought focussing a telescope was tricky but this was just ridiculous!..This was the best I could do.

I've also had to crop the image to avoid the worst of the coma in the corners (there's still some there) - what f stop do others use? Also - does anyone know if there's any way to focus this camera remotely from a laptop please?

Just thought it was nice to see this nebula in it's wider surroundings.

Cheers

Steve

[laser_jock99]

Good image of a very interesting are of the sky. There's definately a lot of nebulosity in your photo. I'm guessing you have fairly dark skies for this kind of wide field work? The modded camera certainly is good a picking up the fainter reds.

I also find that using standard camera lenes wide open will generally result in bad coma unless the lens is really good (e.g. a Noct Nikkor) so I tend to shoot at F4 or even F5.6 with some of my Sigma lenses. At some stage I must get hold of an old 50mm F1.2 Nikon lens- these you can reputedly stop down to F2 to F2.8 and start getting round stars (plus they're 1/10th the price of a Noct Nikkor!)

Back to your image- it looked a bit green on my monitor so tried to make the background look more neutral black using curves.

I tried also tried to boost the reds (slightly overcooked)- hope you don't mind me playing?

[Steve 1962]

Hi Laser Jock

Thanks for tinkering - I appreciate the comment about the green ..and I like what you did on the first image! As you say the red stretch is overcooked but it certainly shows what's there.

What do you think of the focus? To me it looks "soft" , but I guess focussing would be easier with the lens stopped down.

As for dark skies - I live to the SW of Taunton, and only have some orange glow to my NE. The rest is nice and dark over the Blackdown Hills - lucky me!

Thanks again

Steve

[laser_jock99]

Regarding the focus- I think the problem with moddified dslr's stem from the wide spectral sensitivty of the filterless CCD. The CCD filter rejects both IR and UV wavelengths- once removed it's impossible to focus both- resulting in the fuzziness you can see. The longer the focal length used the more out of focus the extremes of the spectrum will appear.

To illustrate the problem look at the bloated stars on this image of the Rossette Nebula I took with a full wavelength range Fuji IS Pro camera and 135mm lens. I quickly realised that the main problem was coming mainly from unfocussed UV light as witnessed by the violet fringes (bearing in mind this is with a Nikon ED pro lens).

The way I got round the problem was to use a UV blocking filter (marketed as a Lumicom minus violet) and this tightened up the stars somewhat but still the IR past 700nm causes me focus problems. What I really need is a filter that transmits purely between about 350nm to 700nm.

[Steve 1962]

Hi again Laser Jock

I should have mentioned it earlier - my image was taken through an Astronomik CLS CCD Clip filter..and my Canon has an IR UV filter fitted but you make a good point about the transmission bandwidth of the chip.

I feel more tinkering coming on!

Steve

[laser_jock99]

After a bit on internet searching I came across this filter

diglloyd - Filters - Filter?B+W 486 UV-IR Cut Interfence Filter

which looks like it might do the job of cutting out the UV and most IR beyond 700nm. It is a interference type filter (i.e. not a glass absorber) so may not work well at the wide angles (10mm fisheye!) I sometimes use. But probably worth a try? I still need to get hold a standard 50mm lens too.