Long Perng 80mm Carbon Fibre f6.2 Doublet

[dugnsuz (Doug)]

Hello all,
Been ogling the Long Perng 80mm Carbon Fibre f6.2 Doublet on Andrews website.
FPL53 lens element and very sturdy 11:1 crayford focuser - looks very nice for $799AU + free postage!

Has anyone bought one of these scopes - some hands on experience might be nice to hear...particularly with regard to imaging.

Thanks in advance
Doug

[Waxing_Gibbous (Peter)]

I think for $800 you could do better. I haven't seen / read much on these but what I have, has been pretty ordinary. No one has raved about the optics and I suspect most of the price has gone into the tube.
If CF is a must then Dannat's 90mm triplet would be an excellent choice or in a shorter FL the Orion CF80 or I believe there's a Stellarvue 80EDT on a-mart.
A touch more lucre, but definately a cut above I would think.

[dugnsuz (Doug)]

Originally Posted by Waxing_Gibbous

I think for $800 you could do better. I haven't seen / read much on these but what I have, has been pretty ordinary. No one has raved about the optics and I suspect most of the price has gone into the tube.
If CF is a must then Dannat's 90mm triplet would be an excellent choice or in a shorter FL the Orion CF80 or I believe there's a Stellarvue 80EDT on a-mart.
A touch more lucre, but definately a cut above I would think.

Cheers Peter - no, CF isn't a 'must' for me, but as any scope I purchase would be used solely for imaging, decent optics are.
The lack of rave reviews is probably telling, but sometimes newer models take a wee while for the review floodgates to open.
Do you have any links or recall where you read some reviews of this particular scope?
All the best
Doug

[allan gould]

might be better off with this
http://www.williamoptics.com/wo_shop...roducts_id=521

[TrevorW]

or this

http://www.stellarvue.com/svr80ed.html

[dugnsuz (Doug)]

Originally Posted by allan gould

might be better off with this
http://www.williamoptics.com/wo_shop...roducts_id=521

Oooh! very nice Allan - works out about $980AU delivered.

[andrew2008]

Originally Posted by allan gould

might be better off with this
http://www.williamoptics.com/wo_shop...roducts_id=521

That is a great buy at the moment. They were even cheaper over thanksgiving weekend. $698US I think it was. Must be trying to get rid of the last few without the DDG focusers. I ordered one and the price was better than the current price direct from WO from a local dealer.

[dugnsuz (Doug)]

Originally Posted by TrevorW

or this

http://www.stellarvue.com/svr80ed.html

Cheers for link Trevor - price of scope is great but flattener seems a tad high at $265US. Suppose they're a matched pair though.

Originally Posted by andrew2008

That is a great buy at the moment. They were even cheaper over thanksgiving weekend. $698US I think it was. Must be trying to get rid of the last few without the DDG focusers. I ordered one and the price was better than the current price direct from WO from a local dealer.

Great buy Andrew - have you got the scope yet?

Cheers all for input
Doug

[andrew2008]

Originally Posted by dugnsuz

Great buy Andrew - have you got the scope yet?

Cheers all for input
Doug

Was only ordered this week but fingers crossed will be here before Xmas.

[gregbradley]

That sounds like an interesting scope. What are the arguments for and against a CF tube with refractors?

I have heard a few but there are a few refractor makers who offer a CF tube - officina stellare is one.

I wonder if they hold their focus better like they do with mirrored scopes?

I have read before where the lenses change focal point slightly when cooling and this offsets to some degree the contracting aluminium tube reducing the focal shift with temp drops.

Also CF has different thermal characteristics to aluminium -sheds heat slower I believe.

Any data?

Greg.

[Kal (Andrew)]

Originally Posted by gregbradley

I wonder if they hold their focus better like they do with mirrored scopes?

I have read before where the lenses change focal point slightly when cooling and this offsets to some degree the contracting aluminium tube reducing the focal shift with temp drops.

Also CF has different thermal characteristics to aluminium -sheds heat slower I believe.

Any data?

Greg.

Roland Christen has stated that when aluminium tubes change temp they change the focal length, but this is usually a good thing in a refractor since the lens changes it's focal point when it cools, so it helps cancel the effect.

I'll quote something else by Roland:

I have done side by side tests with painted aluminum and black carbon fiber
using a 5" refractor, a 12" Mak-Cass. The unpainted carbon fiber indeed had
terrific tube currents in both scopes, so as to make them rather unusable
in my opinion.

The point to note is that this guy doesn't just design refractors using paper and software, he also goes out and field tests his designs and options for up to a year before finalising his product. The fact that he has tested carbon fiber in a refractor, and not implemented it, says alot.

[gregbradley]

Thanks for finding that Andrew. I remember when Roland was posting about that.

Officina Stellare use filtered fans to help the tube currents with their APOs with carbon fibre tubes. But then that opens the door to the possibility of dust blowing in and getting on the back of the lens where its hard to clean.

Sounds like aluminium is still the way to go.

Greg.