M57 in false colour

[Kaptain Klevtsov]

In totally nasty seeing conditions 24th October I had my first bash at emmission line composite imaging. None of the subs were good, so Registaxing them didn't give good sharp images, not even the CLS filter one that I used for the L channel.

Here's the whys and wherefores.

300mm f/5.3 Newtonian Skelescope with SC3 webcam at prime focus with filterwheel.

L channel 16 subs at 20 seconds CLS filter

R channel 25 subs at 90 seconds Ha filter

B channel 16 subs at 25 seconds OIII filter

Each channel aligned in Registax.

R and B images copied on top of L channel in Photoshop.

Images manually aligned and cropped in Photoshop

R and B layers colourised and given 50% opacity in "normal" blending mode.

Image flattened and Noel's Actions used to reduce space noise, lighten only DSOs and dimmer stars.

Tweak in levels.

Any and all tips welcome chaps and chapesses as to the processing of these composites as I'm guessing here.

I already know that I need to do darks to get rid of the hot pixels (couldn't be bothered as the raw images were so poor) so I rushed this one off to see if there's a chance of it working with my gear. I did notice that the exposure times through the narrow band filters are nowhere near long enough but due to the polar alignment being off a hair I pressed on and then overstretched them.

One for the learning section I feel, if its going to happen.

Captain Chaos

[CELESCOPE]

HI CC , a good go at it mate , ok , narrow band as you rightly said do need a lot of exposure time , if you can get down maybe to f4 you may have some better luck with the shorter exposures , also as it was bad weather CC i would,nt even try rgb or narrow band , conditions have to be spot on , else we do get frustrating results , but you have had a go at it ,and first steps are encouraging , keep at it you are getting there .

Rog

[lunator]

CC

It shows a very good representation of M57.

As a starter image it is good and showws that the equipment will be able to deliver when conditions allow.

Cheers

ian

[Kaptain Klevtsov]

This was done when MartinB posted the "clear but murky" thread, and the sky looked as if it hadn't got dark though it should have done. I at least learned that you can't easily do f/14 (OMC140) whilst using narrow band filters, as the sub-exposures were into the minutes. With my HEQ5 mount this doesn't work yet, as its got no guiding and hasn't been PEC trained.

On the Skelescope the aperture was just enough to get an image in view with K3CCD without the skid marks caused by poor alignment. I think Roger's comment about getting down to f/4 or less means that I need to get the focal reducer in on the act, as that could get the Skelescope down to around f/2.something depending on the chip to FR distance. All I need to do now is to reconfigure the setup so that the FR is in there too. I'm guessing that the filter wheel stays as is on the T thread on the (Synta) focusser, and the SC3 camera gets the FR added to a nosepiece which slips into the EP adapter for the filter wheel. Also I need to get the polar alignment tuned in better with the EQ6 as the ring was sliding down the frame all the time. Tomorrow's job is to work out which knobs to twiddle to get the alignment of the EQ6 sorted out, or use another webcam to guide the shots. Anybody had a go with an unmodified Toucam pro for guiding?

Captain Chaos

[MartinB]

I think it was the seeing that knobbled you CC. Can't remember all the details of your scope but imagine you are probably under 2 arc seconds per pixel. The seeing was so bad that night that the finest resolution you could hope for was probably around 5 arc seconds per pixel. Your image was bound to be blurred. Your DSLR has much bigger pixels than your web cam which would give you more acr secs per pixel. The lesson is to use the DSLR when seeing is bad and the web cam when conditions are good. It was a crazy night - great transparency and the worst seeing I have seen.

The other thing you could do CC is to create a synthetic green channel. You can do this with Noel's actions.

Having said all that there is some very promising detail beneath all that fuzz. Given steady conditions you are on your way to turning out something a bit special.