Siebert Ultra EPs vs. Radian or Pentax

Started by stuper1, 10/23/2002 01:38PM
Posted 10/23/2002 01:38PM Opening Post
I posted this on the eyepieces forum but didn't get much response, so I will try here. Has anyone done a comparo between the Siebert Ultra EPs and something like a Radian or Pentax XL? Specifically, I am thinking of buying the 13mm 1.25" Siebert Ultra, and I am wondering how it compares against a 14mm Radian or Pentax. The reason I would prefer the Ultras, other than price, if they provide comparable performance, is that they are lighter, which will be an issue with the 12.5" f/5 dob I am building (the lightweight design tends toward top-heaviness). Harry Siebert told me by e-mail that his EP would outperform the Radian or Pentax, but I am wondering if any of you can independently verify or refute this claim based on actual use. Thanks.
Posted 10/23/2002 04:03PM #1
I haven't used one of the newer Ultra series Sieberts, but do have his 4.9.. and the 1.5~2.5x barlow. Both are very good and perform very well in my 8 and 10 in f/6 dobs. I used to have a 6mm Radian and found it useless due to ghosting and kidney beaning.

Walter
Posted 10/23/2002 06:32PM #2
I can't comment on the Siebert Ultra. The 14mm Pentax XL does has some field curvature and so isn't sharp to the edge at f/5 if you focus the center of the field properly. The 14mm Radian is fine but with a narrower field, of course.

Maybe the 13mm Ultra will outperform the Radian and Pentax--I wouldn't know until I tried. It's possible. But Siebert's been saying stuff like that for a long time now. I tried the 7mm Standard Siebert out of curiosity because of similar hype, and while good for the money it was nowhere near as good as an 8mm Radian or 7mm Pentax XL. My apologies to antiestablishmentarians, but it just wasn't close. If all you want is performance in the center of field at f/5, though, your possibilities are almost limitless. It's wanting full-field sharpness (or close to it) at f/5 that will pare down your options dramatically.

I have a 14mm Radian now for my 10" f/5, but I hear good things about the 13mm Nagler T6. If you really are curious about the Siebert and you can't get the kind of direct comparison you're looking for here, then maybe you should try it and tell us how it works out for you. Be a trailblazer. :-)
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Mike