Quote:Quote:"Seagulls" would be from coma which is from the primary mirror, not the eyepiece. Coma produces comet-tailed aberrations, not seagulls.Seagulls are astigmatism - very much an eyepiece issue.
Quote:"Seagulls" would be from coma which is from the primary mirror, not the eyepiece.
10" F/4.7 Modified Skywatcher Reflector, 38mm Orion Q70, 17mm Modified Ultima LX, 10mm TeleVue Delos, 7mm Pentax XL.
My eyepieces are made from the waste product of exploding stars.
10XTi 102XLT ST80A(2" Focuser); President, Eypieces Anonymous, Denver Chapter (Hello, I'm an eyepiece junky, what's your excuse?)
DAS Dark Site
“I am the only person to ever ace a 1951 USAF resolution test. My 'to observe' list says 'done'. I do not use charts or atlases when I starhop; men do not use maps. One of my sketches won an SBIG deep sky imaging contest. I am the life of star parties I have never attended. I never say anything looks like a faint fuzzy - not even a faint fuzzy. Pilots aim green laser pointers at me. Don Pensack proofreads my CN forum posts.” - The Most Interesting Astronomer in the Universe
C10NGT, Z8, 150 Rumak, XLT 150, C6, C5, SW5 Newt, 4.5 Ball, C102GT, C90, ST80, A70LF; 15x70, 25x100; Burgess BV; Paracorr II; T6 2.5, XO 2.58/5.1, Ethos-SX 3.7, Delos 4.5, TV Plossl 7.4-26, BCO 10, Hutech HC 12.5, Sterling 12.5-25, ES100 14, CZJ H 16/25, CZJ O 16, M5k UWA 24, T5 31, Ultrascopic 35, Titan-II 40; Bino Pairs M5k UWA 6.7, Baader Zoom 8-24, M5k SWA 24, TV Plossl 26, RKE 28.7; Zooms NZ 2-4, NZ 3-6, Leica ASPH 8.9-17.8, Baader 8-24; Baader Zoom Barlow, VIP Barlow
Quote:Regarding astigmatism:Astigmatism means that an optic has two different focal lengths which are at 90 degrees to one another. In the absence of other aberrations, it means that when one orientation is focused, the other orientation will be out of focus, creating a line. "Best focus" is somewhere in the middle.Anyway I spent the past 4 nights, out under dark skies and did some comparisons and evaluations with the Meade 24mm SWA. Basically it's a good eyepiece.16 inch F/4.42: Without the Paracorr, coma was visible.. maybe some other stuff. With the Paracorr (F/5.07), I saw no field curvature, the edge correction was about as good as it gets in a fast Newtonian.TV NP-101. As previously noted, I saw no obvious field curvature but there are some small off-axis aberrations, sufficient to be noticeable but small enough that I could not determine their nature. Near as I could tell it was probably astigmatism. With the NP-101, I expect the off-axis stars to be as sharp and clean as those in the center, this eyepiece, this eyepiece was very good but not that good. In comparison, the sometimes maligned 22mm Panoptic showed perfect tight stars across the field of view.In another forum, another fellow and I went round and round about the 16mm Series 5000 Meade. He claimed it had coma, I thought it must be astigmatism. I finally purchased a 16mm SWA simply to resolve this question. It did seem like it had coma but that it went away when used with a Paracorr.It does seem unlikely but I wonder if the reverse coma an coma correct adds could also affect the eyepiece. Jon
Quote:John,If the coma corrector corrects the coma from the objective, the image provided to the eyepiece will have no coma
Quote:Dave:What scope(s) are you seeing the field curvature with?I own the 24mm Meade version of this eyepiece and I have used with a number of scopes, most quite fast. It's not a perfect performer in the NP-101 (101mm F/5.4 Petzval), there is some slight residual what I remember to be astigmatism, it's not a clean as the 31mm Nagler, but it is a very good performing eyepiece, there aren't many better.I spent one evening comparing the 24 mm Meade SWA to my 20mm Type 2 Nagler in a 16 inch F/4.42 + Paracorr, it was close... it's a good eyepiece in a fast scope.Jon