Quote:
Originally Posted by Wilso
Hi people's ,
Need suggestions on a 2" eyepiece that would suit a tsa102 frac f8 for DSO.
Currently have only 1.25" eyepieces a 5, 7.5mm Le Tak , 13 nagler ( love it) a 30 mm Le Tak and a Baader zoom type 3. Have on order a Baader clicklock 2" diagonal as well.
Looking for a wide view eyepiece , the 30 Le is only 52 deg.
Any person that has the same size scope any recommendations please? 
Regards
Wilso |
Tele Vue has a lot of useful info on their site. Have a look at eyepiece specifications at
http://www.televue.com/engine/TV3b_page.asp?id=214 and eyepiece calculator at
http://www.televue.com/engine/TV3b_p...212&plain=TRUE
Also look at
http://www.televue.com/engine/TV3b_page.asp?id=154 and
http://www.televue.com/engine/TV3b_p...=Advice&id=220
Unfortunately in the last page above the TV-102 (discontinued) is not listed but the last column for the NP-127 (660mm f.l.) will give you an idea.
The 24mm Panoptic and 32mm Plossl both have 27mm field stop diameters and therefore give the same true fields at different magnifications and exit pupils. These two eyepieces give the maximum true field possible in a 1.25" barrel. As your 30mm LE is similar to the 32mm Plossl you wont gain much true field if any in going with the 24mm Panoptic although the 68 deg apparent field of view is quite pleasing and the sky background too will be a little darker.
If you want maximum field of view that your telescope is capable then in a 2" barrel you have a choice of either 55mm Plossl or 41mm Panoptic which each has a 46mm field stop diameter. I would recommend the 41mm Panoptic over the 55mm Plossl to keep the exit pupil down which will give you a darker sky background and also have a 68 degree field instead of 50 and approx. 20x power instead of 15x.
Note the above two are for maximum true field and if that is your primary goal choose one of these. If you don't mind the 50deg AFOV and want maximum exit pupil because you have dark skies and will be using a narrow band filter then the 55mm Plossl may be worth considering but you will find the 41mm Panoptic a far more enjoyable experience because of the wider AFOV and darker sky background without any filters and quite stunning on Eta Carina with an O-III filter! (I use a Tele Vue Bandmate O-III (now discontinued) which is optimised for smaller apertures but works just as well in larger and works beautifully!)
If your skies are not that dark and you want a bit more magnification and darker sky background (more contrast) then consider a 35mm Panoptic or even 27mm Panoptic. Both are 2" and would give you a wide true field of view. Note the 27mm Panoptic and 22mm T4 Nagler have almost the same FSD so almost the same TFOV with the Nagler just slightly wider and at higher power. The 22mm T4 Nagler would be a good choice and it is slightly less cost than the 41mm Panoptic.
There are lots of options and at the end of the day it comes down to personal preference which unfortunately comes down to money to find out and unless you look through the proposed eyepiece in the same 'scope you wont really know what you like best.
Ask your self the following:
Do you wear glasses at the telescope because of strong astigmatism? If yes then you must look for long eye relief eyepieces. (Tele Vue Dipotrx is an alternative option). Most low power wide field eyepieces will have sufficient eye relief but note e.g. a 31mm Nagler with 82 deg apparent field has 19mm which may appear on paper as being enough and certainly is without glasses but not as convenient with.
Note too if you do have a little astigmatism and observe without glasses then at the low power maximum exit pupil end of the scale that astigmatism will show and stars will not be as sharp as they could be unless you correct the view with glasses or Dioptrx. This is an argument for slightly lesser exit pupil although the effects depend on how much astigmatism you have.
Next question to ask your self is what AFOV do you prefer? You say you really like the 13mm Nagler which has 82 deg AFOV. Will the 68 deg. of the Panoptic appear wide enough for your viewing pleasure? I think the Panoptics are just about perfect but then again so is the 31mm Nagler.
You could easily add the 31mm and 22mm Naglers to complement the 13mm Nagler but you could also choose a 21mm Ethos over the 31/22 combo too for less money than the combo as an alternative although it has a little less eye relief if that matters. However you need to know that 100 deg AFOV is to your liking as you do have to look around to see the edge but that is part of the experience.
I think the 31mm Nagler would be an ideal low power eyepiece for your telescope. If you cannot get it now then either the 41mm Panoptic for maximum TFOV or 22mm Nagler and get the 31mm later for an 82 deg set. Note try not to choose eyepieces that give you the same true field but at different powers since you'll end up with the same amount of sky (true view). i.e. don't choose both 27mm Panoptic and 22mm Nagler as each will show the same amount of sky.
I always like to have an eyepiece that gives me maximum TVOF in the focuser that I have so 24mm Panoptic for 1.25" focuser 'scopes and 41mm Panoptic for 2" focuser 'scopes but I also enjoy the view the 31mm Nagler and also 20mm Nagler (now discontinued) presents. I prefer the 20mm at sites where the sky is not as dark and the 31mm under darker skies. The 41mm is my low power finder eyepiece. I don't care about large exit pupils issues and/or not getting the full aperture of the 'scope through my eye as these issues are really of no consequence to me as my primary goal is maximum field of view for star hopping.
I just re-read your last sentence and you asked for advice from someone with the same scope. Sorry I don't have the same 'scope but I will leave the post for your and others' info should you find it beneficial.
A final thought. Most DSOs are smaller rather than larger so you will more than likely be using the 13mm Nagler on these the most. Of course to find the DSO a wider field eyepiece is desirable. Smaller DSOs will stand out better in say a 22mm Nagler because of the higher power but the search field is narrower. In the 31mm Nagler the search field is wider but a small planetary or say comet may be more difficult to detect and this is where accurate charts and matching star fields with charts comes into play. I think the 22mm Nagler would be a good balance between magnification, field of view and exit pupil; I'm just not sure how it is in a 102mm/f8 telescope as you have.
Whatever you choose, enjoy!
