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Comments on Eyepieces and Planets

Started by Rod Kaufman, 05/04/2003 10:25AM
Posted 05/04/2003 10:25AM Opening Post
I have some comments regarding the application of various eyepieces relative to performance issues on the planets.
Over many nights of observations on Jupiter and Saturn with a Discovery 12.5" dob and an 16" Astrosystems dob, I attempted to discern subtle differences in performance among the eyepieces in my collection.
I have general comments that may be of benefit to some amateurs, First, I am convinced that a battery of eyepieces are necessary to obtain the maximum amount of detail, color variation,and resolution. However,cost effectiveness is an important issue as expensive eyepieces do not necessarily equate to the best performing eyepieces. After re-reading the cloudy nights review on planetary eyepieces and reflecting back on my recent experiences, I have recognised that some relatively inexpensive eyepieces can outperform more expensive units on specific details on the planets. For example, I found that my seibert 7mm eyepiece gave the best overall resolution on the rings of Saturn as compared to my pentax XL, UO ortho and ultima eyepieces. The difference was not subtle but rather obvious. I found that a 7mm pro-optic eyepiece gave the best color rendition on the globe of Saturn with the Pentax unit close but not as good. The overall contrast between the rings of Saturn and the globe was best in the pentax and UO orthos, giving that nice optical snap every amateur loves to see. The ultimas were also very favorable in this regard.On Jupiter, the differences were apparent but more subtle. I found the pentax eyepiece and the UO orthos to give highly resolved details of the belts, bands and festoons. Color variation was more difficult to discern but the pro-optic widefield 7mm unit and the pentax XL were quite close with perhaps the pentax revealing the best color fidelity. The ultimas were also good in this regard,and also quite good in resolution but not quite as good in revealing subtle color variations.
I would like to read comments from other amateurs who have applied a variety of eyepieces in the observation of the aforementioned planets over many hours with similar instruments. Perhaps some kind of a consensus of opinion or at least a trend of recommenmded use of eyepieces for various surface details may start to be realized. Up to now, it's been pretty much, "this eyepiece is better than another". It just doesn't work that way, in my opinion.
Posted 05/04/2003 12:58PM #1
I don't think people should get so hung up on color rendition. You will notice these differences primarily when switching back and forth during eyepiece comparisons. If you will just make a choice and stay with it for an extended time, I very much doubt that the amount of discernable detail and color differences will be significantly different, but you must give your eye/brain system time to adjust. I'm not saying that it doesn't make a difference--in fact it does slightly increase the contrast of some colors at the expense of others, just like a very weak color filter, but WEAK is the operative word.

For people who can't hold their head and eye steady, sometimes long eye relief is a bad idea because it leads to substandard performance that other observers with a steadier gaze needn't suffer. For example, you can generate "lateral" color on-axis in many eyepieces by moving your eye a bit off-axis. Not much detail is lost, generally, but this can't be good.

Sharpness does vary a bit, particularly at fast focal ratios where many designs may end up being a bit undercorrected. Smoothness of polish, quality of coatings, and design affect contrast and internal reflections. I sometimes do not like a very wide field when doing lunar viewing because the extra light will scatter a bit in my eye. It's the whole system, from objective/primary to the eyepiece to the eyeball and brain that we care about in visual astronomy. It may not be any technical fault of the eyepiece that it isn't the best choice for me in a certain situation.

Among currently available production eyepieces an inexpensive eyepiece may be the best choice in some cases. But I think it's just that rarely have eyepiece manufacturers devoted themselves to the task of designing and manufacturing planetary eyepieces that deliver uncompromised performance, particularly at today's faster focal ratios. That's why many of us are excited that TMB and AP are BOTH moving into the void. I really expect that the new TMB Monocentrics, which are better corrected with modern glass than classical monocentrics, will outperform all the inexpensive competition for planetary use, probably all the expensive competition as well, but that will no doubt be a hot topic of future debates, and I exclude the AP eyepieces being designed now from this comment because no sample currently exists and so no comparison has been done. However, we do expect great things from AP as well.