Which one to get?

Sometime this year I plan on replacing my 35mm Pan and 27mm Pan with a 26mm T6. Probably after tax time. I also have a 17mm T4.

Let's suppose that having gaining some experience with the 26mm, I feel that I want an EP bewteen the 26 and the 17. What would you recommend, a 20mm T5 or a 22mm T4? Why?

I have a 10" Xti (f/4.7) and a C6 SE (f/10.

Thanks for your opinions.

I liked the 22 T-4 better, mainly because it just seemed to be more emersive in the view. Plus it splits the difference between the 31mm and 17mm for me.
However, with the 26mm, the split would be more equal, but still rather close with the 22mm.
The other good choice is the 20mm T-2, which again was a little better view than the 20mm T-5 to me. It is also heavier though, so that is a consideration.
I have the 20mm T-2 and the 22mm T-4 and it is a hard choice, but I would not sell the 20mm T-2 before the 22mm T-4, because the T-2 is just special.
The 22mm has a longer eye relief too, but the 20mm T-5 is comfortable too. The 22mm is slightly smaller than the 17mm but the 20mm T-5 is even smaller.
So, size, weight and eye relief as well as focal length spread should be the determining factors for your choice.

Hi Dennis
I can't argue with Floyd, he has looked through more eyepieces than I've ever seen in magazines. However, I did switch from a Pan35 to the 26T5, never looked back. I also have the 20T5 and it is one of my favorite eyepieces. The 20T5 seems to hit a sweet spot in my NP101 and Starmaster 11" f/5.4 telescopes. Very comfortable and sucks my eyeball right out the end of the scope, awesome eyepiece. However, since you already have the 17T4, I'm not sure you would gain that much by adding the 20T5. In my case the 20T6 nicely fills in between the 26T5 and a 13T6. I dought you can go wrong with any of them and it may boil down eyerelief, Tfov, or weight preferences depending on your scope.
Just my $.02
Buck

Hi Dennis. And gang.
I almost let this one slip by me.
I would say wait until you've used the 26T5 a bit,
but in the meantime keep an eye on the ads, and like Floyd said,
if you get a deal on either one, snap it up! You'll be happy.
Personally, I had the 20T5 early on, and I've always liked it.
I added the 26T5 a little later (sold my 27 Pan),
and then added the 31T5 and sold my 41 Pan.
The 17T4 came along just last year, after having the 12T4 for a while.
I liked the 12T4 so much, I decided to add the 17T4 too.
Based on those, plus my viewing through Floyd's 22T4,
I'd say that one would be a fine choice, too.
I just couldn't justify getting the 22T4 with all the others.
Don't want to over do it now, do we?
I did however, get a 20T2 at one point, just so
I could evaluate it vs. the 20T5 for a while,
but it had messed up filter threads, and I had to let it go.
Another fine choice, though, as well.
There. That cleared things up a lot, huh? 8)
Linton

Let's suppose that having gaining some experience with the 26mm, I feel that I want an EP bewteen the 26 and the 17.

I won't humour you; I have a 26T5 and 16T5 and I don't feel I need anything in between .

The cheapest solution to your "problem" would be to sell the 17T4, get a 20T5 and get something shorter than 17mm (like a 13T6 or even 12T4 if you want more eye relief), but I have a feeling they couldn't pry the 17T4 from your cold, dead fingers.

Dennis Freeman said:

Sometime this year I plan on replacing my 35mm Pan and 27mm Pan with a 26mm T6. Probably after tax time. I also have a 17mm T4.

Let's suppose that having gaining some experience with the 26mm, I feel that I want an EP bewteen the 26 and the 17. What would you recommend, a 20mm T5 or a 22mm T4? Why?

I have a 10" Xti (f/4.7) and a C6 SE (f/10.

Dennis,

Excellent plan IMO replacing the 35+27Pan with the 26 Nagler. The 35 Pan in the 10XT has a 7.4mm exit pupil so you are probably getting some light loss - not good if you plan to use your wide fields for DSO hunting. For this reason the 40 Paragon should not be considered either since exit pupil would be over 8mm. The 26 Nagler gives you a good exit of 5.5mm so darker background and only losing 0.12deg TFOV over the 35 Pan.

As for your question, when you look at the magnification increase and TFOV decrease when you go from 26mm to 17mm, there should really be no need for an intermediate eyepiece. Going from 26mm to 17mm is a 50% (or traditional 1/2 step) increase in power and your TFOV is reduced by a little more than a 1/3. This is about perfect. If we were talking about higher magnifications (i.e., if you had a much longer focal length scope) then stepping up in magnification less than 50% would make sense since the atmosphere comes into play. At these lower powers though it does not. So I'd save the cash and not get something in between the 26 and 17, and instead opt to use the money saved to enhance the short FL range of your EPs....or go the other way and opt for the 31Nagler instead of something in between the 17 and 26 as the 31 Nagler would give you .35deg more TFOV and still keeps the exit pupil at only 6.55mm so you'll get full light.

Good luck!
-Bill