Using TV paracorr and powermate in fast scope?

[tims]

Could someone please advise if I have got this right. In a fast scope, say f4 where I would want to keep a paracorr on permanently I cannot use a 2X Powermate attached to the top of a paracorr as the bottom of the powermate might touch the paracorr lens.
If this is right that means I would have to attach the powermate first and then the paracorr on top of that. This would mean I couldn't have the paracorr permanently connected? - I would have to keep removing it if I didn't want the powermate on.
Am I right about this? Do others use a standard barlow that (I assume) safely attaches on to the top of a paracorr meaning I could keep (the paracorr) on permanently?
Hmmm, this query is a bit long-winded; hope you can understand what I'm getting at!

[Archy (George)]

Originally Posted by tims

Could someone please advise if I have got this right. In a fast scope, say f4 where I would want to keep a paracorr on permanently I cannot use a 2X Powermate attached to the top of a paracorr as the bottom of the powermate might touch the paracorr lens.
If this is right that means I would have to attach the powermate first and then the paracorr on top of that. This would mean I couldn't have the paracorr permanently connected? - I would have to keep removing it if I didn't want the powermate on.
Am I right about this? Do others use a standard barlow that (I assume) safely attaches on to the top of a paracorr meaning I could keep (the paracorr) on permanently?
Hmmm, this query is a bit long-winded; hope you can understand what I'm getting at!

From Televue via Bintel:
Note for Dobsonian/Newtonian Owners
When using Tele Vue’s Paracorr coma corrector, the 2.5x or 5x Powermate™ should be inserted into the Paracorr’s 1-1/4” adapter (i.e., between the Paracorr and the eyepiece). For 2x and 4x 2” Powermates, first insert the Powermate™ into the focuser, then the Paracorr into the Powermate.

[AstroJunk (Jonathan)]

To be honest, you are just wasting light using a Paracor together with a barlow/powermate. It can be done, but the extra focal ratio given by the barlow rather negates the need.

It **may** be possible to detect a difference with the Paracor in the focusser, and the barlow next, but certainly not the other way round.

[bmitchell82 (Brendan)]

im with you on that one john, i have a fast newt 4.7, when i insert a 2x ed barlow with my photos it almost flattens the image out with only slight flaring at the edges compared to comets in the normal. Have you considered a MPCC..?? they seem to work splendedly for my newt though not so good with the barlow but refer to my first point! a TVPC is what close to 400 a MPCC with all spacers in the kit is 250? easy choice

[tims]

Thanks for your replies.
Would it be fair to generalise then, that using a barlow or powermate with eyepieces of around 13mm and higher would mean that a paracorr/coma correcter wouldn't be necessary?
Do factors such as magnication of the barlow (2X,3X etc) and how fast the mirror is affect what minimum size the eye piece could be before coma correction is necessary?
Again, I appreciate the help you guys are giving me - I'm trying to get as much info as possible before I make any decisions what to buy.

[AstroJunk (Jonathan)]

Yes that generalisation is fine.

The important thing here is f ratio, and a barlow simply multiplies that out to an easier number for eyepieces to handle.

When I first got into astronomy, f6 was considered as fast as one would consider for a newtonian and most scopes were f8. That meant that coma was not an issue, particularly with the unsophisticated eyepieces that were used. Today there is plenty of exotic glass about and short focal length mirrors being produced; but simple physics demands that the more you push it, the deeper you will have to delve into your wallet to overcome the next layer of problems.

I use a paracor about 50% of the time on my f5 dob and I think it is an absolute must have if you are using an ultra wide f.o.v. eyepiece.