2" Vs 1.25"

[cjmarsh81]

Hello All.

I am currently saving up for a wide field EP such as a Nagler type 6 or a pentax XW or even a Vixen LVW. Somewhere in the 20-30mm range.

I am just wondering what is the advantage of getting a 2" over a 1.25" EP. I would assume that being much larger in diameter it allows more light and you can see more. Is this the case? Or does it just give you a wider FOV?

All responses welcome

Chris

[janoskiss (Steve H)]

I would assume that being much larger in diameter it allows more light and you can see more. Is this the case? Or does it just give you a wider FOV?

No on all counts. Just consider the FOV specs for the eyepiece and forget about barrel size when choosing EPs. (but fyi: 2" barrel is needed for wide FOV with long focal length EPs or when a particular EP design uses large lenses.) The only reason to buy all 2" or all 1.25" is to not have to bother swapping out a 2"-to-1.25" adapter. If that does not worry you then ignore the barrel size when choosing EPs.

[Dave47tuc (David)]

I can not put this on every eyepiece thread but have a look at this site,
http://www.astrosurf.com/lombry/repo...uggestions.htm

Plenty of information on eyepieces. Hope that helps.

[h0ughy (David)]

for me i love 2" EP's. they allow me to view comfortably at the eyepiece. For others they prefer 1.25". Have you tried some 2"ers? I might suggest if you can, do so. Fo me 2" all the way! But thats only my preference. There are excellent 1.25" EP's out there. you may end up with mixing them.

[janoskiss (Steve H)]

Houghy, sorry but what you are saying makes no sense to me at all. What does the size of the barrel have to do with viewing comfort? ... unless you look through your eyepieces back-to-front

[ausastronomer (John Bambury)]

Steve,

2" eyepieces invariably have a much larger eye lens and longer eye relief which makes them a lot easier and more comfortable to use. Kidney beaning and blackout are also rarely an issue with 2" eyepieces. The 27mm Panoptic compared to the 24mm Panoptic is a classic comparison. Only 3mm difference in focal length but the 27mm has a lot more eye relief and is a lot easier to use. The downside is that 2" eyepieces are much larger and heavier so its not a good option for "toy" telescopes.

FWIW Houghy's approach is fine when your visual scope has a long focal length. Houghy uses a 12" LX 200 GPS (not a toy), so medium focal length 2" eyepieces give him high power and the long focal length 2" eyepieces give him low/medium power. His scope has a 3 metre focal length so an eyepiece like the 2" 17mm Nagler T4 gives him 180X. At the low end of the scale, the 41mm TV Panoptic gives 75X with almost a 1 degree TFOV. You then use a 2" barlow with your 2" eyepieces for planetary work. This is also a very good way to go if you own a large DOB with a focal length over 2.5 metres.

Of course its an expensive journey if you head down that road, as EVERYTHING 2" is very expensive (over $400 for an Astronomiks OIII filter for example), but practically and optically it's the right way to go. It doesn't help the guy with a 4" refractor or an 8" dob as the 2" eyepieces are really only suited to low/medium power widefield views, and you need to go a lot shorter in focal length to get high powers.

CS-John B


CS-John B

[janoskiss (Steve H)]

Originally Posted by ausastronomer

2" eyepieces invariably have a much larger eye lens and longer eye relief which makes them a lot easier and more comfortable to use.

That is a bit of a misconception. Few examples: 13mm Stratus has a larger eye lens than either the 17mm T4 Nagler or the 27mm Panoptic. All the 1.25" Stratus from 3.5mm to 21mm have a large lens like this. Geoff's 1.25" XLs seem to have a pretty big eye lens too (probably at least as big as the 27mm Pano but I did not compare side-by-side). Ditto many of the Meade 1.25" UWAs, SWAs and at least one of the 5000 Plossls. My 26mm 5000 Plossl has exactly the same size eye lens as the 27mm Panoptic.

Kidney beaning and blackout are also rarely an issue with 2" eyepieces.

The 17mm T4 has got a severe case of the kidney beans no matter where I put that adjustable eyecup. I know that many people have no problems with this eyepiece, so probably my eyes have something to do with this.

[cjmarsh81]

No I have not seen through a 2" EP yet. I am hoping to tag along to the next Newcastle Astro viewing night in Shortland and look through some other people's scopes while I'm there. I was going to go to the last one but I forgot it was on.

I probably will end up mixing 1.25" and 2" EP's in my collection. Doesn't really matter except I will have to keep changing the reducer and my Barlow won't work on all EP's. As the 2" will only be a widefield I don't need to use it with a barlow anyway so that doesn't matter either.