disappointed with 7mm PentaxXW vs 13mmEthos + x1.6

Tests with my xx12" Orion Truss Dobson


I have a brand new 13mm Ethos that I bought a week ago along with an 8mm Ethos and a x1.6 2" Antares Barlow.

I fitted the TV 2" rings on both Ethos and gave the a run for their money. Excellent EP's. Outstanding. But then I tried the famous x1.6 2" Antares Barlow with the 13mmE and compared it to the 8mmE. And compared...ad compared...and compared. And sold the 8mm Ethos for there was on difference in image quality between the 13mm + x1.6B combo and the 8mmE. Got the money and decided to give the 7mm Pentax XW a chance. Went out to a star meeting and started testing (double stars and Jupiter), and tested, and tested and tested. And arrived at the conclusion that there's nothing special about the 7mm XW that the 13mm + x1.6B combo doesn't have. There was no improvement. (I know I compared 8.1mm vs 7mm (100º AFOV vs 70º AFOV). So now I feel like selling this Pentax bought on Friday...(I think I'm going to trade it for a 2x Powermate and a Giro Alt/Az mount)

Conclusion: the 13mm Ethos is clearly the best from the Ethos range and probably the best EP on the Market. And so is the x1.6 Antares barlow.

What a team!!!

opinions please.

opinions please.

My thinking: The differences between eyepieces are subtle at best, it's not like the differences between various telescopes where orders of magnitude are possible.

With the 13mm Ethos and the 1.6x barlow, your nominal magnification is 187x with a 1.6mm exit pupil, with the 7 mm XW you are looking at 217x and a 1.4mm exit pupil. For planetary views, neither of these is near pushing a 12 inch scope, the view should be bright and dependent upon the steadiness of the seeing. Likewise for double stars, you scope and eyepieces are not really getting started in this range, to see differences, I would want to be working with very good seeing, a well cooled scope, a tight double star that challenges that scope where the magnifications would be over 400x and maybe double that.

But again... differences between eyepieces are subtle. How did the 7mm XW work with the barlow? That should have been about 350x and the increased magnification should provide a different view though not necessarily a "better" view.

Jon

Hi Paulo--

I agree, the 13E plus the 1.6 antares barlow makes an awesome 8mm eyepiece. But a very heavy one! Also, I get a little ticked at the extremely tight tolerance on the barlow, trying to get the 13E in and out of the thing. So because of the inconvenience I wind up not using this combo very often--and put my 16 T5 in a 2x TV barlow instead!

The Pentax 7XW has more eye relief than my 13Ethos. I use the 7XW for public star parties to accommodate eyeglass wearers. However, if I had to sell one it wouldn't be the 13Ethos.

Milt