Stephen65
05-01-2008, 01:02 PM
On Thursday night Ricky came over and we tried my Ethos against his 17T4. Since these have almost exactly the same FOV we were curious to see how they matched up. Test scope was a WO FLT132 refractor (f/7) which produces a nice flat field.
Comparing the Ethos and 17T4 the first thing you notice is that while the Ethos is slightly larger, the 17T4 is noticeably heavier, in fact the 17T4 is as heavy an eyepiece as I have ever held until you start getting up into the 28mm plus widefields.
Optically our conclusion was that the Ethos was superior to the 17t4 in every way. On-axis sharpness and contrast were better (the contrast would follow from the increased magnification if nothing else) and it was perfectly flat and aberration free to the edge of the field - and I mean perfectly flat. Which is quite amazing for a 100 FOV EP. It was also difficult to induce blackouts.
Switching to an 82 degree FOV eyepiece from an Ethos is the only time 82 degrees looks narrow to me. The 17T4 was very good on-axis but the Ethos with higher mag on the same field produced a nicer image and was at least as sharp. Off-axis there were some noticeable aberrations in the last 5-10% or so of the 17t4 field, whether it was astigmatism, field curvature or both was difficult to diagnose. But the stars definitely looked slightly blobbier and spikier than in the centre. The 17T4 also was more finicky with eye placement, it was easier to induce kidney beaning blackouts.
The 17T4 has a longer listed ER (17 v 15) but both had sufficient ER to be comfortable, though neither of us were using glasses.
All in all it was a comprehensive triumph for the Ethos.
Comparing the Ethos and 17T4 the first thing you notice is that while the Ethos is slightly larger, the 17T4 is noticeably heavier, in fact the 17T4 is as heavy an eyepiece as I have ever held until you start getting up into the 28mm plus widefields.
Optically our conclusion was that the Ethos was superior to the 17t4 in every way. On-axis sharpness and contrast were better (the contrast would follow from the increased magnification if nothing else) and it was perfectly flat and aberration free to the edge of the field - and I mean perfectly flat. Which is quite amazing for a 100 FOV EP. It was also difficult to induce blackouts.
Switching to an 82 degree FOV eyepiece from an Ethos is the only time 82 degrees looks narrow to me. The 17T4 was very good on-axis but the Ethos with higher mag on the same field produced a nicer image and was at least as sharp. Off-axis there were some noticeable aberrations in the last 5-10% or so of the 17t4 field, whether it was astigmatism, field curvature or both was difficult to diagnose. But the stars definitely looked slightly blobbier and spikier than in the centre. The 17T4 also was more finicky with eye placement, it was easier to induce kidney beaning blackouts.
The 17T4 has a longer listed ER (17 v 15) but both had sufficient ER to be comfortable, though neither of us were using glasses.
All in all it was a comprehensive triumph for the Ethos.