Next eyepiece purchase help

[andrew2008]

I'm looking to get one or two good eyepieces for use at lower powers in my 12" F5 dob. Currently use a 11 & 7T6 naglers, 17 stratus and TV 32mm plossl. The stratus rarely gets used as it's performance is disappointing so it will probably get sold. The jump then from the 32 to 11 is pretty big. 46x to 136x.

Not sure if 1 eyepiece or 2 will suffice. And then what to get? I've considered nags (16t5), panoptics (19 & 24), denkmeier 21, xw20 and others. Some I'm willing to wait and buy second hand to save a bit. Which of these or others should I be looking at?

Cheers

[Waxing_Gibbous]

A hearty vote hear for the Panoptics. Absolutely perfect for your telescope. fantastic clear, flat fields all the way to the edge. Either or both will leave you feeling warm and fuzzy for years.
The Nagler 16 gives the same FoV as the 19 panoptic, but at a higher mag. The field isn't quite as flat and there is a tiny bit of coma at the edge, at least with my old 12", but its not objectionable.
Same could be said of the 20mm Nagler, which gives the same FoV as the 24 Pan, again at a higher magnification.
I also have a 26mm SWA APM eyepiece, which gives very satisfying views. Not as sharp ar contrasty as the TVs, but more than adequate for a quick scan. Its also about 1/3 the price and is sold under a variety of different logos (APM, University Optics, etc.)
I have both Televue types, but with my newt. I keep coming back to the panoptics. Ya' just can't go wrong.
Hope this helps.
Peter

[Sylvain]

I've got a TV 24mm panopic too - it's a real beauty! Really really a nice eyepiece to use and keep for years. It comes at a premium price, but more affordable than larger FOV TV eyepieces.

[Max Vondel]

I have a 22mm Panoptic and it's still one of my favoured EP's. I should sell it as I have a 22mm Nagler Type 4, but somehow it always finds use in one of my smaller guide and finderscopes! Having both the 1.25 and 2" skirts makes the old style more useful than the 24mm, which only comes in 1.25 I think?!
Go Pan Galactic Gargle Blasters!
:rofl:

[norm]

Another vote for the 24mm Panoptic. Something about that eyepiece, I keep returning back for it.:thumbsup:

Have a 10mm Pentax XW and 17mm Nagler.

Another one to consider could be the 20mm Scientific Explorer 100 degree FOV. Haven't used or seen it personally, buy reading some articles, its got favourably reviews and a hell of a lot cheaper than the 21mm Ethos. Just bear in mind the weight.

BTW: the 24mm pan is a 1 1/4 barrel size.

Cheers, Norm

[Steffen]

The 16mm Stratus has about the same true field as the TV 32mm Plössl (about 50 minutes) and as such is probably not a good fit. Something with a field stop of about 15mm would be a good next stop, so the 11mm Nagler seems well placed. It gives you 34 minutes true field. If you want less magnification you could bridge the gap with an 18mm Radian (42 minutes true field, 83x).

Cheers
Steffen.

[andrew2008]

Think you mean the 16 nagler there? From my maths the 32mm (47x) and 24 Pan (62.5x) offer the same FOV, around 1.1 degrees. The 16 nagler (93x) and 19 Pan (78x) are very close also. Both around 52 to 53' . I had thought of the Radians but the 18mm is only about 6' bigger than than the 11T6.

From the advice so far it seems the Pans are the way to go. Tick most of my boxes which are 1.25" , light, & fairly good eye relief. They also get great reports and are highly recommended in the Backyard Astronomers Guide.

[Steffen]

How so? According to the tech specs their field stop diameters and the resulting TFOVs and magnifications on a 1500mm focal length scope are:

TV Plössl 32 - 27mm - 62' - 47x
TV Radian 18 - 18.3mm - 42' - 83x
TV Nagler 11 - 14.9mm - 34' - 136x

Cheers
Steffen.

[andrew2008]

I didn't use the field stop in my calcs for TFOV. Generally i just use AFOV / magnification. The mag for the 32 is only 46x

The televue website advocates the use of the formula you used and just about every other site i've found uses the AFOV/mag. Backyard Astronomers Guide lists both but states the AFOV/mag is generally ok as Televue are about the only company that releases field stop. Will have to do some more reading on this. Thanks Steffen.

[Steffen]

Sorry, my bad, I must have divided by 22 for whatever reason… :screwy:



The formula "field stop / focal length * 57.3" is the correct one (57.3 being the conversion factor between radians and degrees: 180/π). The "AFOV / mag" formula is an approximation for simple eyepiece designs and smallish AFOVs.

EDIT: You're right, not many eyepiece makers publish field stop sizes. I usually measure them myself where possible.

Cheers
Steffen.