Orion 102ED f7- how good?

[allan gould]

Anyone out there purchased/used an Orion 102mm ED f7 scope either visually or photographically? Specifically I'm interested in the amount of CA as well as usable magnification.

[chris lewis]

Hi cannot add any first hand experience but have been reading some forum comments and reviews. The summary being: The Orion 102mm f/7 is made by Kunming Optical. It's an FK-61 doublet. FK-61 glass has a higher dispersion than FPL-53 and thus, typically results in lesser color correction, especially in a faster f/ratio scope. FK-61 has an Abbe number (dispersion) of 81.6 which is equivalent to FPL-51 and PK-52. FPL-53 has an Abbe number of 95.0 which is far superior to these glasses and is actually quite close to Fluorite’s Abbe of 95.6. With a 102mm FK-61 based doublet at f/7 you can expect it to be solidly in the semi-Apo category but not having actual Apo performance. The 102mm f/7 does have a dual-speed Crayford focuser and retractable dewshade, which makes it more desirable as a travel scope. It's shorter focal length better suits it to wider field observing over the ED100. For deepsky imaging and portability, the 102mm f/7 would also have an advantage. The longer focal ratio (F/9) of the Synta series 100 ED with FPL-53 glass makes this scope more suited to Lunar and Planetary Observing. The ED 102 (F/7) has a faster focal length which allows it to observe larger areas of the sky with the same size eyepiece. Magnification wise it is lower then the Synta ED 100 ie. 150x to 180x - whereas the ED100 goes higher to 240x [all approx. and depending on 'seeing']. The actual Orion sites list the ED102 F/7 as having a max. mag of 143X where as the ED100 f/9 has a max. of 230x. Hope this helps.

[allan gould]

Chris
Thanks for that - most informative. I was unaware that it had FK-61 glass and not FPL-53. Your comments were spot on and it looks like I will continue looking for that 4" scope for astrophotography elsewhere.
Allan