EPs for Tak 90mm APO (Ethos vs Naglers)

[jamespierce]

Here's my dilemma folks I'm looking to buy a simple set of 'nice' EPs to go with our Tak SKY 90mm which is basically our do everything, traveling and get out there and look at stuff scope. Lets say the budget is a little over $1K AUD.

Combos I'm considering:

TV Ethos 10mm
TV Nagler 3-6mm

TV Nagler 16mm
TV Nagler 9mm
TV Nagler 3-6mm

TV Nagler 13mm
TV Nagler 7mm
TV Nagler 2-4mm

The combinations are much the same price, my heart says get the ethos and a zoom for planetary and high power work with the ethos being the 90% usage case. 50x mag and a 2 degree field is really versatile for a smallish refractor.

My logical brain worries about the huge size difference and issues with balance etc switching between EPs, also the naglers give a bit more flexibility with magnification also. Is there another option I'm missing ?

For the nerds - here are the calcs on the various EPs I've considered. The 13mm Ethos and 17mm Nagler were in the mix for a while, but a true field of more than 2 degrees can wait I think, perhaps later we'll add a really wide EP like a 17mm Ethos etc or a 20+mm Nagler later.

http://posterous.com/getfile/files.posterous.com/james-3fa20/JeVseN2134Ex8I0dCNucCoqNafmum9FvH3k QuS2Gl5QCpGQTb7dC1HXdeGQO/EPs.jpg.scaled.1000.jpg

[casstony]

Hi James, I think you should try a bunch of different eyepieces to see what you like before buying. If eye relief/comfort is important consider Pentax XW's. Are you anywhere near a club that has public viewing nights?

However, if the Aussie dollar starts to plummet run into Bintel and grab 10mm Ethos and Nagler zoom :)

[dannat]

are you going to buy the optional focal reducer & extender (can you still get them) - might be better than buying really short f/l ep's lie the 3-6mm nagler

[jamespierce]

The 1.6x is about $500, so basically the price of a nice EP anyway - The high mag EP is really what's driving me to change our EP setup for this scope, but I figure the 1.6x is quite specific to this scope, unless someone can tell me it works way better, I don't see the point really ? (so far I've been told don't bother, get the EP, more flexible etc).

Currently I have 40,25,17 and 10mm EPs, all good plossls - So with this scope life really starts at about 17 or 10mm and the eye relief on the 10mm is really tight (7 or 8mm I think). I figure if I'm going to buy more EPs, I might as well get a few seriously nice ones for the long term, the question is just which combo !

[astro744]

You will find that you will crave for a bit more light once your exit pupil below drops below 0.5mm. Therefore 3mm is about you smallest practical focal length. The Nagler zooms are amazing and you will find the 3-6 gets a lot of use for dialling in just the right power for the seeing.

At 3mm you get 168x and this is sufficient for large enough images of planets. If you feel you could push the boundaries a little further you can add a 2 element quality Barlow to the zoom and your total elements will still only be 7 which is the same as all the T6 Naglers but a much smaller apparent and therefore true field.

If using your 'scope without tracking I would suggest the Naglers or Ethos (you never know a 4mm Ethos may be out in the future but 4mm is just a little low in power for the planets on your 'scope but workable). You can get two naglers for one Ethos though.

A 2.5mm or 3.5mm (or both) would be great for your 'scope and maybe complement those two with a 7 & 13.

At 3.5mm you will get 144x which will give you a nice sharp Jupiter and Saturn but you will feel you want a little more image size hence the 2.5mm T6 or back to one or both of the Nagler Zooms. Choices, choices! You could buy a zoom now and once you find the focal length you prefer most of the time then buy a T6 or Radian closest to that focal length for a wider field of view.

You may find you will use your 'scope more for low power viewing which it was really designed for so start thinking about a quality 2" diagonal (if you don't already have one) and your low power sweeping eyepiece.

If your heart is set on the Ethos/Zoom combo then go with it and add more Ethos eyepieces later. If you stay with Naglers consider the 20mm T5 as it is relatively light (2") and will give you 3deg at 25x

Note too the Ethos eyepieces are relatively light considering their size. Have a look at http://www.televue.com/engine/page.asp?ID=144 for the specs.

Whatever you choose, enjoy!

[jamespierce]

So in the end I've decided on the Ethos 10mm for a start, 2mm exit pupil, 2 degree field of view and 50x. Seems like a good all round 'do everything' EP. I'll try some high max pieces and decide what to do, but the 3-6mm Nagler is looking good on that front. Down the track we'll add in something really wide, either perhaps a 17mm Ethos or a 20mm+ Nagler - Trying to avoid super heavy EPs so as not to overpower the scopes balance on the mount.

I'll let you all know how it goes once I get in a few sessions.

[beren]

:thumbsup: Congrats with your Sky90, love mine {makes a great little astrograph too}
Mostly use a 24mm pano/ 16mm /9mm nagler and 6mm radian with mine. After switching to a EQ mount I found using 2 inch eyepieces a pain with rebalancing :P

[dannat]

james have you looked at the tak Le eyepieces - or the orthos in small focal lengths -would give sharp views on planets