Help with Baader mk3 coma corrector spacing

[SimonfromSussex]

I'd be very grateful if anyone has any good ideas how to resolve a focus issue I have with my new baader mk3 coma corrector.

I'm using it with a 16" lightbridge and I went for the baader (over a paracorr) partly on price but mainly because the baader doesn't affect the field of view (I was desperate to maintain the 100deg!!!).

If I screw the coma corrector directly to the base of the eyepiece (with the relevant spacing rings to give me near as dam it 55mm) it slots into my lightbridge focuser no problem and I can reach focus.

However I'd like to switch between eyepieces quickly (rather than keep having to unscrew) so I thought I'd try a push fit adapter instead. However with the push fit adapter it pushes the eyepiece further away from the focuser and consequently I cannot get it to focus (there is not enough inward travel).

Here is a pic of it screwed on and this works fine:

Then here is what I'm trying to do with the adapter but cannot reach focus like this.

Please does anyone know a way to quickly change between eyepieces but maintain the focus ability?

Please don't say buy a paracorr 

[alan potts]

I am not sure about this but I believe there is an extention with a click lock made by Baader and available from TS in Germany, if anyone one can help they will be able to as they seem to sell an adapter for everything.

I have the 1.25 inch version in my Vario finder, there must be a 2 inch version. Mine has three little thumb screws but I am sure there are others.

I guess the TV version of the Parrcorr don't need such things.

Alan

[Scooot]

Hi Simon,

Cancel that, just realist its a 1.25" doh

[crashtestdummy]

This is why I purchased the paracorr,I didn't fancy the idea of fiddling in the dark swapping spacers.

Can you get a slightly shorter spacer ring?are you using the standard focuser on your lightbridge?

[Damo636]

This page may be of some use Simon...

http://www.alpineastro.com/optical_accessories/MPCC/mpcc_visual.htm

[Mike73]

I think the only way you could do it Simon is to buy another Baader mk3 CC and permanently keep them on your lowest/widest power EP's?

I hope I'm wrong and you find away to do it but looking on the bright side it would be cheaper than a Paracorr, less fiddling about in the dark and you'll keep all the benefits of using the Baader over the Paracorr.

[Rustysplit]

Hi Si, Just looked at the TV specs and the measurement you are using for the field stop is the diameter of it, not it's position. TV state that that is actually -.38" ABOVE the EP shoulder, ie into the main body. This may sort your travel out? Worth a go.

[SimonfromSussex]

Thanks everyone for the replies.

Al, well spotted. Yes I was reading the diameter from the TV site...doh!

This looks to be backed up by Damo's link which puts the coma corrector flush with the 21 ethos (i.e. no spacing).

However I'm pretty sure I tried it without the spacing ring (i.e. just the 35mm adaptor) and it still wouldn't reach focus 

Of course that also means I shouldn't really be using the 35mm spacer either, as this will be making the gap too big?

If I don't need the spacer though I wonder if I can just screw the CC onto the standard adapter that fits into the focuser. I'm sure I have screwed 2" filters to this in the past so it should take the corrector?

This would be near enough the correct spacing then and might just do it. 

I will have a fiddle later, skies looking promising for tonight. 

If not then another corrector would solve the problem, or maybe a low profile focuser?