31mm or 26mm Nagler Type 5??????

I have a brand new never used 31mm nagler type 5. I am waiting on delivery of my new discovery 15" PDHQ F5 scope so i can try out the 31mm nagler. I should recieve the scope on or around the 26th of august. I am concerned that the exit pupil on the 31mm might be to large. I am 41 years old & am told that the older you get the smaller your exit pupil gets. I had a f4.8 12.5" scope a couple of years ago & used a 30mm widscan 2 & really liked it without any noticable problems. I need some expert opinions on this matter! Id really appreciate your response.
thanks David L

Hi David! I'm in the same boat. My 47 year old eyes have pupils that don't open much more than 5-5.5mm. With my fast scopes, I get a big exit pupil with long focal length eyepieces. Much bigger than my eye can admit. So I'm wasting light. I've done all of the calculations and I'm going with a 26mm. Now if I had a long focus refractor, that would be another thing. But with my "fast" reflectors, I have a perfect match if I use the 26mm. I'd bet the view with the 31 will be great so use it for a while to make sure you really want to get rid of it. Even though you might lose some light, it might be worth it for those nice, wide views. Let us know how it works out.
Bill

Hi Dave...

I have used my 31 t% on a 16" f/ 3.9 with a 4" or larger secondary and saw no problems.... the secondary was not visible. I am 38... so we should be close to the same. I think you'll love the 31. Hang on to it.

If the 30mm Widescan II worked well at f/4.8 then I think the 31mm Nagler would work well at f/5. Having used both eyepieces, I can certainly say that the 31mm Nagler is a world away from the 30mm Apogee Widescan II for edge of field sharpness. Contrast, I don't know, but I would tentatively guess that the Widescan would be a tad brighter due to less air to glass surfaces and less total glass thickness to absorb light.

I commend you for the choice of the Discovery 15" f/5 dob. Eyepiece height not too high, step stool necessary perhaps but no ladders, and a lot of aperture to satisfy your deep sky endeavors for many years. Just don't get aperture fever! It is a bad, bad disease!

Hi David,

I just recently experienced your 31N/26N dilemma. I used a 31N in my 24" F/4 from a very dark site (Chiefland, FL) and immediately fell in love with it. Decided right then and there that I would buy one as soon as I could afford it. This eyepiece was just right for me.

Then of course, along comes the announcement of the 26N and the exit pupil issue (I'm 47) begins to introduce doubt into my plan. Spending six-hudred dollars on an eyepiece is a situation not to be taken lightly.

I called or wrote to just about everyone who's opinion I valued and got just about a fifty-fifty split on which eyepiece would be best suited to me. But there was one particular suggestion that made the most sense, and in the end that's the one that helped me make up my mind.

This person, well known and somewhere in my age bracket, uses a 35 Panoptic on her 20" F/4, knowing that it produces a nearly 9mm exit pupil. However, even though it cuts down the effective aperture of the scope, it provides an incredibly wide field for those objects that just cry for "the big view".

And of course it becomes the ultimate "finder" eyepiece. But, once the object is located, you are most likely going to jump to considerably higher magnification in order to darken the sky background and make the object large enough to see details within it. The 26N would not give you as large of a field of view initially (as the 31N), nor would it provide a substantial increase in object size or darken the sky background like something in the range of a 12mm to 16mm eyepiece.

As I said, the suggestions out there seem to run evenly for both, but looking at it in this light made the most sense to me. I ended up buying the 31N and I believe it will remain in my eyepiece case for a very long time. Good luck on your decision.

Pat Rochford

You might want to have your pupils checked by an ophthalmologist first. Not everyone follows the "rule" and your pupil may still dilate large enough to take full advantage of the 31 Nagler.

Personally, I'd keep the 31, then jump down to the 22 Nagler.

Paul Gustafson