M57 - monochrome

Folks - back to the more mundane...

I shot M57 tonight - this is a stack of 12 30 second images. I tried colour but without the IR filter, the DSI is pretty much hobbled. Still, I seem to prefer monochrome - I don't know why.

You can see that I've captured two stars in the central part of the ring. I also have a third star to the upper right of the outer part of the ring.

If you look closely, you may see what could be a fourth star, again to the upper right of centre but just past the inner part of the ring (before you get to the third star descibed above).

If anyone has an inkling to do this, at the very bottom right corner (and apologies, I cropped this image a little too much) you will see a lovely S-shaped galaxy if you crank the levels right up.

Enjoy!

Dave McD

what a very nice shot Dave
regards Darren

Hi Dave,

Nice focus!

How do you determin the correct length for your exposures? I am looking for guidlines on this, do you look at sampe histograms?

Later,

Jed.

Thanks Darren - appreciate it

Jed - that's a very good question to which I don't really have an answer in the form of a table or spreadsheet... Typically, any planets, moon, sun etc are all below 1 second. Bright stars (visible by eye) would be 1 or seconds. Deep sky is usually 5 to 30 seconds with really faint nebulas and very faint stars/asteroids/comets requiring 30 seconds plus.

Luckily, the DSI software has an automatic contrast which tends to be forgiving of overexposures. But then you have an issue processing the results. I'm sure if I spent a little more time researching the data, I could find a simple exposure calculator.

Beware - there are very complex exposure calculators out there. I've seen one that asks for 'air mass', extinction coefficients and the whole shooting match. But the scheme I follow works most times. I usually shoot one image and if it isn't what I want, increase or decrease the exposure time accordingly. The only advantage of stacking images is to reduce the noise and give a smoother image - it doesn't add any more (or less) photon data to the image. Sorry I can't be more defnitive...

Cheers

Dave McD