Experimenting with blue filter

[CraigT82]

Seeing seemed pretty decent last night with the moon up about as high as it gets, so thought I'd try something I have been wanting to have a go at for a while: shooting through a blue filter to maximise the resolving power of the scope. 

Here is Clavius, 10k frames shot and 30% stacked.  Not sure I like the aesthetics of the blue channel (highlights were particularly 'high') but can't deny it really brings out the fine detail.

8.75" Fullerscope,  APM 2.7x barlow, Altair 290m, Baader blue CCD filter. 

[Roy Foreman]

Very nice shot. Clavius is my favourite crater. I always assumed a red filter was the one to use to minimise the effects of atmospheric turbulence, but your shot through a blue filter has worked really well.

[CraigT82]

Here is a softer processed version which I prefer... It's got a bit of an Apollo imagery feel to it.  The version in the OP is a bit harshly done I think.

 

[CraigT82]

On 24/01/2021 at 13:52, Roy Foreman said:

Very nice shot. Clavius is my favourite crater. I always assumed a red filter was the one to use to minimise the effects of atmospheric turbulence, but your shot through a blue filter has worked really well.

Thanks, yes the red filter is often the best to use in normal (poor!) seeing, however in decent seeing you can go to green and in excellent seeing you can use blue.  The idea is that you can resolve smaller feature with the shorter wavelengths (resolving power is dependent on the objective diameter and the wavelength of the light). 

Edited January 29, 2021 by CraigT82

[jetstream]

3 hours ago, CraigT82 said:

Thanks, yes the red filter is often the best to use in normal (poor!) seeing, however in decent seeing you can go to green and in excellent seeing you can use blue.  The idea is that you can resolve smaller feature with the shorter wavelengths (resolving power is a function of the objective diameter and the wavelength of the light). 

Excellent image Craig and I prefer the first, sharpest one which I don't find harsh. So critical sampling - where were you at for this image and set up if you don't mind me asking?Did you barlow for the blue?

[CraigT82]

Thanks Gerry. I'm normally well oversampled with my set-up - around f/20 usually whereas proper sampling would be f/12 for my GPCAM3 290mono. 

This is simply because I don't have a 1.6x barlow, only a 2.7x APM barlow.  I screw the APM cell directly onto the nosepiece of my filter wheel and it gives me about 2.3x amplification this way. This way is light weight and keeps the imaging train short.  I do have an ES 2x focal extender but it doesn't have a removable cell and so using that would get me closer to critical sampling but it would also add length and weight to the imaging train which is something I want to avoid as the plastic tube of the Fullerscope is very flexible.

[jetstream]

2 minutes ago, CraigT82 said:

I'm normally well oversampled with my set-up - around f/20 usually whereas proper sampling would be f/12 for my GPCAM3 290mono

Your welcome Craig, and thanks for the info- it will be used down the road once I get some concepts pounded in the old noggin. Keep the images coming!