Solanum
29-04-2008, 12:03 AM
Despite clouds earlier on this evening, they cleared off in time to allow me some viewing before bedtime. Remarkable considering that I only took delivery of my used Siebert 15 mm Ultra and 2x Barlow two days ago, courtesy of Rob Skelton.
When I was considering the purchase I didn't see a huge amount of comment on Siebert eyepieces here (except for Astronut), so I thought I'd add my comments for the sake of the next person looking.
Transparency tonight was good, but seeing pretty poor, consequently I didn't give the 2x Telecentric Barlow much of a work out. I tried the 15 mm Ultra on several objects: Saturn, Omega Centuri, Rigel Kent, Eta Carina nebula, 47 Tuc, and lots of open clusters.
Two things struck me whilst using this EP. Firstly the contrast was superb, easily better than my Televue 20 mm Plossl, which really surprised me. Stars were slightly sharper in the TV 20 mm Plossl, but this may be due to the poor seeing and higher magnification of the 15 mm. My 6mm LV was totally unusable tonight.
Secondly the lack of visible coma, stars were sharp as far as my eye could see towards the edge of the view. The difference in coma between the 15 mm Ultra and my 30 mm 2" MAS was astounding, even though I would expect less coma in a 15 mm than a 30 mm EP.
Big open clusters looked great, sharp stars to the edge, and Eta Carina was a sight to behold, really good contrast. The best view though was Omega Centuari, hundreds of of resolved stars all sharp and the whole clusters filled the field of view perfectly. I spent a long time looking at this and came back to it more than once.
Now nothing is perfect and having a look at Saturn and Rigel Kent (clearly seperated despite the seeing), demonstrated this. There were distinct internal reflections, definitely not reflections from my eye, and with the brighter objects there was more than one visible as well. You could almost work out the internal lens structure from them. On the other hand they weren't very bright and were always away from the object itself, so whilst a little distracting they didn't interfere with what you were actually interested in.
In reality a 15 mm 70 deg AFoV wouldn't be my first choice for planetary viewing anyway, so this isn't too big a problem.
The good points:
despite appearances in some images, the build quality is very solid.
and despite the build quality, the eyepiece is really light.
the pop up eye-cup is very comfortable, the perfect size for my eye, more comfortable than any 1.25" EP I've tried.
excellent contrast.
almost no visible coma across the entire FoV (in an F5 scope).
almost no edge brightening.The bad points:
distinct internal reflections with bright objects.
if you look at Omega Centuari through it you may never bother looking at anything else :DNote that my eyepiece experience has been limited to what I currently own, so I can't compare the Siebert to a top of the line EP.
When I was considering the purchase I didn't see a huge amount of comment on Siebert eyepieces here (except for Astronut), so I thought I'd add my comments for the sake of the next person looking.
Transparency tonight was good, but seeing pretty poor, consequently I didn't give the 2x Telecentric Barlow much of a work out. I tried the 15 mm Ultra on several objects: Saturn, Omega Centuri, Rigel Kent, Eta Carina nebula, 47 Tuc, and lots of open clusters.
Two things struck me whilst using this EP. Firstly the contrast was superb, easily better than my Televue 20 mm Plossl, which really surprised me. Stars were slightly sharper in the TV 20 mm Plossl, but this may be due to the poor seeing and higher magnification of the 15 mm. My 6mm LV was totally unusable tonight.
Secondly the lack of visible coma, stars were sharp as far as my eye could see towards the edge of the view. The difference in coma between the 15 mm Ultra and my 30 mm 2" MAS was astounding, even though I would expect less coma in a 15 mm than a 30 mm EP.
Big open clusters looked great, sharp stars to the edge, and Eta Carina was a sight to behold, really good contrast. The best view though was Omega Centuari, hundreds of of resolved stars all sharp and the whole clusters filled the field of view perfectly. I spent a long time looking at this and came back to it more than once.
Now nothing is perfect and having a look at Saturn and Rigel Kent (clearly seperated despite the seeing), demonstrated this. There were distinct internal reflections, definitely not reflections from my eye, and with the brighter objects there was more than one visible as well. You could almost work out the internal lens structure from them. On the other hand they weren't very bright and were always away from the object itself, so whilst a little distracting they didn't interfere with what you were actually interested in.
In reality a 15 mm 70 deg AFoV wouldn't be my first choice for planetary viewing anyway, so this isn't too big a problem.
The good points:
despite appearances in some images, the build quality is very solid.
and despite the build quality, the eyepiece is really light.
the pop up eye-cup is very comfortable, the perfect size for my eye, more comfortable than any 1.25" EP I've tried.
excellent contrast.
almost no visible coma across the entire FoV (in an F5 scope).
almost no edge brightening.The bad points:
distinct internal reflections with bright objects.
if you look at Omega Centuari through it you may never bother looking at anything else :DNote that my eyepiece experience has been limited to what I currently own, so I can't compare the Siebert to a top of the line EP.