New Toys - 13mm ETHOS and 18" UC Obsession

ausastronomer (John Bambury) · #1 08-10-2007, 10:16 AM

As some of you may be aware Gary Kopff, Andrew Murrell and I are entertaining some visiting American Astronomers, including Dave Kriege from Obsession telescopes, out at Coonabarabran for some dark skies observing.

Dave brought with him an 18"/F4.2 Ultra Compact Obsession and 2 x 13mm Televue Ethos eyepieces. We are awaiting delivery in Coonabarabran of one more piece (QANTAS lost it somewhere) for the 18" UC before we can fully assemble it and give it 1st light. This scope will end up in Melbourne as an additional 3RF scope, after we give it a good shakedown

One of the 13mm ETHOS eyepieces will also remain here with us and has generously been given as a gift by our US visitors to Gary, Andrew and myself, for the hospitality we have extended them. This eyepiece is for the 3 of us to share, which suits us fine as we do a lot of our observing together. All 3 of us used a prototype of this eyepiece in a variety of scopes at 2007 Texas Star Party and loved it. We gave the production model plenty of focuser time in my 18" Obsession on Saturday night. It works beautifully in the 18"/F4.5 Obsession giving 160X and a true FOV of 38', with a 2.9mm exit pupil. It's quite amazing to think you can observe the full moon at over 150X and fit it all easily into the FOV of an eyepiece. This eyepiece is something absolutely special and worth the very high asking price if you own a premium scope.

Cheers
John B

RB (Andrew) · #2 08-10-2007, 10:23 AM

Great to hear John, looking forward to having a look through the Ethos when we next meet.
Hope you get the missing part back soon for the scope.

wavelandscott (Scott) · #3 08-10-2007, 11:00 AM

Wow! What a great token of appreciation!...maybe I need to start being nicer to people...

I look forward to looking through that eyepiece/scope combination...

Or maybe I should not...in ignorance there is bliss

Rodstar (Rod) · #4 08-10-2007, 01:40 PM

I am salivating at the thought.....

Does the Ethos benefit from a Paracorr, John, or is it pretty sharp across the FOV in your f/4.5 without?

Stephen65 · #5 08-10-2007, 04:09 PM

I was just going to ask that - did you use a Paracorr? There has been some discussion recently on CN about visible coma if used in a fast scope without a Paracorr.

wavelandscott (Scott) · #6 08-10-2007, 05:40 PM

Only my speculation on my part...but, I would imagine that a Parracor would be helpful on faster scopes for the Ethos (like other eyepieces)...a slight increase in magnification might be kind of nifty too...

skies2clear · #7 08-10-2007, 05:45 PM

Quote:

Originally Posted by Stephen65

I was just going to ask that - did you use a Paracorr? There has been some discussion recently on CN about visible coma if used in a fast scope without a Paracorr.

....and ditto for me too. Very curious to know.

Sounds like you're having a ball with all this new gear John,

Clear skies,
Nick

wavelandscott (Scott) · #8 08-10-2007, 05:59 PM

Quote:

Originally Posted by wavelandscott

Only my speculation on my part...but, I would imagine that a Parracor would be helpful on faster scopes for the Ethos (like other eyepieces)...a slight increase in magnification might be kind of nifty too...

I say this not that I suspect that there is anything at all wrong with the Ethos design...and I am sure that someday (not soon) I will own one

But assuming that coma is inherent in a fast mirror and thinking about a much wider field of view in the Ethos...I would imagine that one might "see" more coma and therefore a tool that eliminates (reduces) coma in a fast newtonian scope would seem to me to have merit.

Stephen65 · #9 08-10-2007, 06:39 PM

Quote:

But assuming that coma is inherent in a fast mirror and thinking about a much wider field of view in the Ethos...I would imagine that one might "see" more coma and therefore a tool that eliminates (reduces) coma in a fast newtonian scope would seem to me to have merit.

That's pretty much what the CN discussion was about - the review of the EP in a 20" f/4.5 is about 2/3rds down this page:

http://www.cloudynights.com/ubbthrea...l/fpart/3/vc/1

ausastronomer (John Bambury) · #10 09-10-2007, 12:07 PM

Cloudy last night guys. I will try it out tonight in the paracorr if the weather stays good.

I didn't perceive a need to use the paracorr with it last Saturday however.

Cheers,
John B

ausastronomer (John Bambury) · #11 10-10-2007, 10:15 AM

We had an absolutely outstanding nights observing last night. Seeing wasn't the greatest but transparency was excellent and the skies were very dark and clear. I was able to see 8 Pleiades naked eye. M33 was visible naked eye and the Gegenschein was clearly visible. I got an average reading of 21.89 on the Unihedron Sky Quality meter. At SPSP site at Ilford I normally get 21.4 to 21.5.

Unfortunately I couldn't get the ETHOS to reach focus when combined with the paracorr, so I didn't waste time with it. Without the paracorr stars are not quite as sharp in the ETHOS at EOF as they are in the centre due to coma, but it is certainly not objectionable. None of the dozen experienced observers present, perceived a need to use a paracorr.

A paracorr may improve the view with the ETHOS but it isn't 1/2 bad without it

Cheers,
John B

Rodstar (Rod) · #12 10-10-2007, 01:39 PM

John, would it not come to focus in the Paracorr through lack of in-travel, or lack of out-travel?

I find with my 22 Panoptic + Paracorr, the view will not come to focus unless I tighten the positioning of the Paracorr in such a way that it is sitting about 15mm out from the stop position in the Moonlite focuser. That is, there is insufficient out-travel to bring it to focus by a bit less than about 15mm. I am wondering if I can expect the same sort of situation from the Ethos?

Satchmo · #13 10-10-2007, 03:29 PM

Quote:

Originally Posted by ausastronomer

Unfortunately I couldn't get the ETHOS to reach focus when combined with the paracorr, so I didn't waste time with it.

Thats interesting. The televue website lists the `virtual' field stop position to be 0.27" below the EP shoulder which is only 0.5mm further than the common 0.25" spec most of the eyepieces come in now. Similar to yours I heard of case where a guy had two Ethos to try in his 10" binoscope and could not get enough in travel though no problemwith other EP's . Go figure ..

I'm really hoping there will be some physical reason why the Ethos will not be suitable for binoviewing aside from minimum OPD limit which is oK ( my eyes are 67mm and it has 64mm diameter), otherwise I will have to get a second job to pay for a pair

Mark

skies2clear · #14 10-10-2007, 06:24 PM

John,

seeing how you value transmission performance too when viewing very faint DSO's, how do you rate the Ethos against other premium glass, like XW's for eg.?

I'd also be interested to hear how much you like the UC Obsession scope, and what it's strengths/weaknesses are, say compared with a standard Obsession, when it arrives of course!

Clear skies,
Nick