Picking just one eyepiece for a 12" dob+powermate

[discardedastro]

So I currently have my 8" Newt and that's permanently on imaging duty. I'm trying to now design a complete new rig centred on a Skywatcher 300P non-goto scope (which will be my first non-goto scope) for a telescope I can take out and use for visual observing while my imaging rig does its thing. Plus I'm going to an event (EMFcamp) in July where I want to have something a bit more outreach-friendly alongside the imaging rig! A 12" truss feels about right in terms of portability and storage space requirements.

That kit list includes a Powermate 2x which I might use on the imaging rig but I'm mostly thinking of it as a more versatile way to get more flexibility out of a good eyepiece. I've also thrown in a Paracorr though this is mostly for the 8" to replace an MPCC Mk3 for imaging, and a Baader Steeltrak NT because the 300P only comes with a pretty basic focuser and I've liked the Steeltrak on the 8". While I'm trying not to break the bank I'm keen to go for a good-quality eyepiece - I much prefer doing a couple of things well rather than lots of things "okay" and I don't like buying something I know I'm going to upgrade/replace when I can!

To avoid things becoming too expensive (more than they already are) I'm only looking to pick up one good eyepiece to start things off on this rig. I've got the 28mm that came free with the 200PDS, plus a Pentax 12mm. I don't find myself reaching for the 12mm often. However, I'm struggling to visualise how, say, a 17mm TV Nagler would look in that dob compared to my 28mm in the 8". I've got little experience with "serious" eyepieces like the Televues and not so much experience in visual observing anyway.

Basically - any advice for the best focal length to go for as an all-rounder EP given access to a 2x Powermate?

Edit: Forgot to add, I'm also keen to stick to the TV eyepieces for the Dioptrx support as I wear glasses but would prefer not to and use a Dioptrx lens to correct my astigmatism...

Edited February 22, 2020 by discardedastro

[bingevader]

22 hours ago, discardedastro said:

However, I'm struggling to visualise how, say, a 17mm TV Nagler would look in that dob compared to my 28mm in the 8".

I'd suggest, as a very rough comparison, to stick both 'scopes and EPs into Stellarium and have a look.

As you've probably already worked out, the 17mm in the 300p would give a magnification of 88x at an aFOV of 82° and the 28mm in the 200pds would give a mag of 36x at an aFOV of 56°.

So, not an east comparison to make really.

However, you won't fit all of M42 for example, in the FOV, but it would be at a much higher magnification in the 300p with the 17mm.

Whereas, M42 would fit comfortably in the smaller FOV at a much lower magnification in the 200pds with the 28mm.

You wouldn't get all of M42 in the 300p with the 28mm either though!

My 82° 30mm EP would just about do it.

[Sagitta]

Both scopes are about FR5 so that's 1000mm vs 1500mm.
The Nagler 17 has 82° AFoV, that SW28 56°(?).

1000mm/28mm=35.7x and 56°/37.7=1.48° TFoV

1500mm/17mm=88.2x and 82°/88.2=0.93° TFoV

a 25mm 100° eyepiece (ES) in the 12" would give you about the same TFoV (object framing), but part of the field would be peripheral vision.

Have you taken the parameters to Stelvision or Telescopium?
You could take screenshots and paste them side by side in post to compare.

Do you not reach for the 12mm very often because of bad seeing or are you not into higher powers observing?

In that case, and for the purpose of outreach, my choice might be the Panoptic 35. I find it very comfortble and when barlowed is like a 17.5mm.
Or consider a cheaper alternative for outreach.

 

[ollypenrice]

I'm not persuaded by the 'lots of eyepieces' approach and could live with just two, or a third for shorter FL scopes when observing planets.

The two which I have used as 'defaults' in both a 20 inch Dob and a 14 inch SCT are the TV Ethos 13mm and the TV 26mm Nagler.  A longer FL Ethos might be even nicer than the Nagler but I'll probably never know!!

A very wide field is a big, big bonus in a non-tracking mount.

Olly

[NGC 1502]

13 hours ago, ollypenrice said:

I'm not persuaded by the 'lots of eyepieces' approach and could live with just two, or a third for shorter FL scopes when observing planets.

Agree that generally most observing could be done with 3 eyepieces for low medium and high power.  But for some observers trying to squeeze all they can from a scope maybe one or two extra eyepieces could be useful.  For instance, I’m a double star fan, sometimes I need extra high power to get a split.  Even if the view is a bit fuzzy due to very high mag, if I can confirm the secondary in a binary or triple system, I’m happy.

I tried once to just use just a 24mm Panoptic and a 9mm Nagler for my 10” Dob, that’s 50x and 133x.  But that doesn’t use all of the potential of the scope, even though just two eyepieces is nice and simple.

Ed.

 

 

[discardedastro]

Thanks for all the comments and suggestions - loading everything into Stellarium definitely helped get my eye in!

I'm thinking that to get "one eyepiece to rule them all" then spending a bit more and going for the 21mm Ethos might be the right approach to start with - it frames a lot of targets well and using the Powermate would give me a lot of flexibility. It's a bunch more than the Naglers of course, but I can just about cost it in (especially if I leave the Powermate for now and just get the Paracorr).

My only worry with the Ethos is just how much of the field ends up being in the periphery and therefore how much of a practical upgrade it would be from the Naglers.

Looking around the Explore Scientific 82 degree series also look interesting at considerably less cost but the lack of the Dioptrx corrector is a downside.

[ollypenrice]

7 hours ago, discardedastro said:

Thanks for all the comments and suggestions - loading everything into Stellarium definitely helped get my eye in!

I'm thinking that to get "one eyepiece to rule them all" then spending a bit more and going for the 21mm Ethos might be the right approach to start with - it frames a lot of targets well and using the Powermate would give me a lot of flexibility. It's a bunch more than the Naglers of course, but I can just about cost it in (especially if I leave the Powermate for now and just get the Paracorr).

My only worry with the Ethos is just how much of the field ends up being in the periphery and therefore how much of a practical upgrade it would be from the Naglers.

Looking around the Explore Scientific 82 degree series also look interesting at considerably less cost but the lack of the Dioptrx corrector is a downside.

There is more to the Ethos than its staggering FOV, though in a Dob this is very useful in prolonging the time between nudges. I'm only talking about the 13mm here, since it's the only one I know, but it has an extraordinary clarity or transparency. I've never used any EP in which I was so unaware of the glass in front of my eye. This is hard to define but I'm not alone in having this feeling. Without any doubt at all it is the best EP I've ever used. Also, moving your head to peer into the edge of field is an immersive and exciting experience.

Olly

[John]

I agree with Olly. I have the Ethos in 21mm, 13mm, 8mm and 6mm focal lengths and they are superb eyepieces and not just in terms of their field of view.

The 21mm is eye-wateringly expensive if bought new though. The APM 20mm HDC-XWA is an excellent alternative at substantially less cost.

 

[Second Time Around]

I think I'm right in saying that the 20mm Explore Scientific 100 deg accepts a Dioptrx.  

Can anyone confirm?