Ethos 17mm vs 21mm

[GavStar]

I'm very impressed with the Ethos 17mm in my tv85 but have the option to exchange it (plus a bit more cash) for a 21mm. Clearly the additional weight and size of the 21mm is a consideration but I've also seen some comments on cloudynights that the 17mm is easier and more comfortable to use.

Any views on whether this is the cas- if not then I am tempted to upgrade?

Thanks

Gavin

[estwing]

I can't say about the 17 but the 21e is simply sublime go for it

[John]

I don't have a 17mm Ethos but I do have the 6mm, 8mm, 13mm and 21mm and they are all superb within their focal length niches. The only hesitation might be if you are concerned about the weight of the 17mm because the 21mm is around 40% heavier - 2.2 lbs v's 1.55 lbs.

[alan potts]

I do find the 17mm slightly easier to use and it is easier for me to see the full FOV but that is something that many do not want. As already stated they are are both superb eyepieces. I have been using my 21mm a bit more of late as I have sold my 20mm Nagler, something I said I would not do, I hope that I do not regret it. The only downside with the 21mm is the size of it but most of my scopes are fairly big so that is less of an issue, it looks funny in the 70mm ED though, where the eyepiece is almost the same size as the telescope.

[Stu]

I have both, and love them both, not that that helps you! When I bought them I intended to sell one, but could never decide which.

Which scopes would this be for, other than the TV85? I think I probably use the 17 more in the 85, smaller exit pupil but still 2.8 degree fov. The 21 is lump and the balance is challenging, particularly on a giro. I use this more at dark sites.

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[GavStar]

Thanks for the comments. I would also be using it on a fc100df and a 120ed, but currently it's mostly the tv85. Given the comments about the 17 being slightly easier for some people and the 'lump' comment re the 21 I think I will stick with the 17.

Gavin

[alan potts]

It is a very nice lump to have though. I think based on your scope of choice the 17mm would be best based on the reasons given by Stu. The trouble with the Ethos range I find is, it is a bit like a nice bar of chocolate, you never seem to able to just break off one piece, I am sure you will add to 17mm as and when.

Alan

[Don Pensack]

I own all the Ethos range, but have a few favorites, based on my scope size (12.5") and focal ratio (f/5.75 when including the Paracorr).

In my scope, the best contrast and images are with the 17, 10, and 8mm.  They are superb in every way and match my eye's aberrations well.

The 21 is excellent, though I do not see star images quite as tiny at such low power and I see, perhaps, a little more astigmatism.

The 13mm is superb, but the slightly darker background of the 10mm is a little more entrancing.  I admit to spending entire nights with

either just the 13 or just the 10 in the focuser (when such a choice matched my pre-selected targets).

The 6 and 4.7 are excellent, but seeing isn't always good enough to use them a lot.  It can take a lot of patience, waiting for good seeing.

One recent night with superb seeing, I used the 6, 4.7, and 3.7 to good measure on a lot of small targets.

With a non-driven dob, though, those last two required a lot of scope pushing.

Note also that the 21 and 17 are well-corrected for coma with the newer Paracorr-II, but not perfectly corrected with the Paracorr  I

That's because the in-most setting of the Paracorr I isn't quite far enough in for the 31 Nagler, or 21 and 17 Ethos.

Of course, correcting 96% of the coma is still way better than correcting zero.