Coma Correctors

[Solanum]

I have an F5 dob and I was wondering about coma correctors. I note that both the MPCC and the Televue ones increase the F ratio, is this how they work, simply by acting as a low power barlow lens (presumably bringing a broader part of the light cone to the focal plane)? Or are they more complicated than that and doing more with the light to reduce coma?

Note that I barely know what I'm talking about here!

[Alchemy (Clive)]

ifou are going visual probably the best is the televue paracor which multiplies by about 1.4 i think

if you are imaging the MPCC is the go and does not multiply the size.

[Satchmo]

Originally Posted by Solanum

Or are they more complicated than that and doing more with the light to reduce coma?

Thats correct.

[toryglen-boy (Duncan)]

Originally Posted by Solanum

I have an F5 dob and I was wondering about coma correctors. I note that both the MPCC and the Televue ones increase the F ratio, is this how they work, simply by acting as a low power barlow lens (presumably bringing a broader part of the light cone to the focal plane)? Or are they more complicated than that and doing more with the light to reduce coma?

Note that I barely know what I'm talking about here!

The Televue increases the focal length by about 1.4, the MPCC does not. From looking at my MPCC it appears that the middle is uncorrected, and only the edges are changed, when i move the MPCC across a page of text, the middle text is always fine, and the text on the edges changes, this backs up the fact that its optimzed for F4-F6 scopes.

after i finally figured out the spacers etc, its a good piece of kit, and i would recommend it, although if you are gonna just use it purely visually, then i would recommend the Paracorr

[Paddy (Patrick)]

Originally Posted by Alchemy

ifou are going visual probably the best is the televue paracor which multiplies by about 1.4 i think

if you are imaging the MPCC is the go and does not multiply the size.

I think the paracorr increases magnification by 15%.

http://www.televue.com/engine/page.asp?ID=56

Definitely a good investment - I never observe without mine in situ

[Geoff45 (Geoff)]

The Baader paracorr doesn't change the focal length and is a lot cheaper that the Televue
Geoff

[Robh (Rob)]

Originally Posted by ghsmith45

The Baader paracorr doesn't change the focal length and is a lot cheaper that the Televue
Geoff

Excuse my ignorance on this, but I take it that the coma corrector is only useful on a f/4-f/6 scope in a wide-field low-power eyepiece. On higher power, the field is much reduced so the corrector is less effective and coma is less of a problem anyway.

Rob.

[Starkler (Geoff)]

Originally Posted by ghsmith45

The Baader paracorr doesn't change the focal length and is a lot cheaper that the Televue
Geoff

Pedants point of order. Paracorr is a trademark of the televue coma corrector product.

The Baader product is suited to photography use, whilst the paracorr is optimised for visual use.

The paracorr acts like a like 1.15x barlow as a side effect of its optical design. The barlow effect is not what coma correction is about, else you would just use a barlow.

I own 3 scopes. Two at f5 and one at f4.8 and I use my paracorr in all of them.