Quote:
Originally Posted by AG Hybrid
I have to say Greg. Your sudden interest in visual/observational astronomy and all the threads you've made has brought back some life into the eyepiece forums.
In regards to your post, I think you should look into how much deeper you can see with certain eyepieces at similar focal lengths, and have a better understanding about eyepiece design can affect how well you can see objects. Not just in field correction but also light scatter.
My case in point is this. The target I chose with a mag 10 star cluster. Normally cake from dark sky but from the middle of Sydney - oddly difficult even in my 12".
I tested a 9mm ES 100 against a Delos 8mm and Pentax XW 10mm.
I found in both cases the Delos 8 and Pentax XW10 could see deeper than the 9mm 100. When I say deep I mean stars that needed averted vision in the 9mm 100 could be seen with direct vision in the 8 and 10.
I attributed this to the ES 9 have 12-13 pieces of glass in it and the Delos and Pentax XW only having 6-7, maybe also better coatings and a finer polish on top of that. All these little things start to add up.
You have a few eyepieces around 7-9mm. I'd be interested to see what results you find if any you can discern.
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ES 9x100=9 elements in 6 groups
ES 9x120=12 elements in 6 groups
Pentax XW = 6 to 8 elements depending on focal length (40mm 6 elements in 4 groups, 3.5mm 8 elements in 5 groups, 7mm 8 elements in 6 groups)
Delos = 8 elements in middle focal lengths, unknown at the ends
Ethos = 8 to 10 elements depending on focal length
All these eyepieces have about the same number of air-to-glass surfaces, so what's the difference?
Coatings. Pentax and TeleVue use very sophisticated coatings and also multi-coat the cemented surfaces.
Polish. Higher polish results in less light scatter
Design parameters. Different eyepieces have different spot sizes and this results in superior focus to fainter stars.