Filters

[Fay]

Can someone advise what Astronomik filters should I buy first.

LRGB
HA -(gas & planetary)
or
O III (planetary & emission nebula).

Is it correct that you do not have to use a separate CLS filter with Astronomik filters, as this appears to be built in?

Fay

[JohnP]

Hi Fay,

Chris & Mike are the experts on Narrow band imaging... If you are looking to do straighforward colour imaging with your B&W camera's then if I was you I would buy a set of Astronomik type II RGB filters - you can then use your CLS filter for the L layer & the RGB for the colour. The CLS lets through a lot of Ha anyway & provides effective lightpollution filtering. You don't have to take the RGB images through the CLS - I do just because of the way I have the filters placed in my filter holder.  The Astronomik Type II also block IR so you do not need a separate IRB filter. You can do 'false' colour imaging using Ha & OIII & S2 filters but I think it is a lot trickier... This is where I pass over to Mike or Chris...

Cheers,  John

[Fay]

Thanks, John. When you do LRGB, is there a rule on how long the RGB exposures should be in relation to the L?

Fay

[JohnP]

There probably are but I must admit I don't follow them... Aim for something like a 1/3 or a 1/4. The important bit is the L as this is what will have all the detail in - the R,G,B literally just provide colour information. If I do something like 60 mins for the L then I would aim to do say 15 or 20 mins each for the R,G,B. I try & use the same length subs though so if for example L=30X2mins then I would do say 8X2mins each for R, G & B..

Hope that makes sense - John

[Mike]

"When you do LRGB, is there a rule on how long the RGB exposures should be in relation to the L? "

Fay it tends to be 1/3 of the L, so in other words if you did an hour of L then you would do 20 mins of the R, G and B. Though it is really only a general guide. You can do colour imaging with just R & G and sythesise the B by combinging the R & G. This is good for saving time if you have a bad night. if you do the R, then G before doing the B, then if the clouds roll in you can still create a full colour image.

"Can someone advise what Astronomik filters should I buy first.

LRGB
HA -(gas & planetary)
or
O III (planetary & emission nebula). "

John is right there - I would get the LRGB first, then you can at least start on colour imaging. Using the CLS filter for your L layer will get rid of a lot of the noise from light pollution. Be warned though that a CLS filter lets through a LOT less light than a L filter so you would need to double or triple your exposure length. Ha next, then OIII and SII.

"Is it correct that you do not have to use a separate CLS filter with Astronomik filters, as this appears to be built in? "

No that is not true. The Astronomik filters have a built in IR blocker, but not CLS. CLS filters only let through specific wavelenghts, i.e. Ha, Hb, OIII, etc. and therefore block out the emisions from streetlights.

I can do a chat on filters at the next Imaging Session you get to (I knwo you cant make the one on Friday 12th) if you like.

[Fay]

Thanks for all that info, Mike. I was getting confused there, regarding CLS & IR.Yes that woulkd be a good lesson, filters.

Fay

[Fay]

What is the difference between using a L filter with a CLS on a camera & using a camera with just a CLS filter?

Fay

[Anonymous]

Fay, the L is clear glass, sometimes and IR as well and the CLS is a broadband light polution filter.