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Tak LE vs RKE vs TV Plossl

Started by jeyjey, 10/15/2005 10:00AM
Posted 10/15/2005 10:00AM | Edited 10/15/2005 10:02AM Opening Post
I was out observing Mars the other night, and wanted to get the best view I could. I've been comparing a 7.5mm Tak LE with an 8mm RKE and an 8mm TV Plossl -- so these were my candidates. Seeing was fluctuating from minute to minute between a Pickering 6 and 8, so they were actually quite hard to compare.

Subjectively, three things pop up immediately. The RKE feels brightest. Now, I didn't do any limiting magnitude tests (my goal here was Mars, not an eyepiece review), so this isn't necessarily due to better transmission -- it could, for instance, be a result of more light scatter.

Next, the RKE has what I find to be a claustrophobic view. I just don't find 45° comfortable, whether it frames what I'm looking at or not.

And finally, the Plossl's short eye relief combined with its rubber eyeguard result in a lot of eyelash scraping and jamming for me. I don't think the RKE has any more eye relief, but the volcano top at least keeps my eyelashes out of the view.

Now, like I say, the seeing was fluctuating quite a bit. So I had to keep popping them all in and out to try and confirm any differences. I believe that I got crisper lines between the Northern lowlands and Southern highlands more often with the RKE and the Plossl, than with the Tak. But the view was pretty fuzzy in all 3 most of the time, and all three managed moments of great sharpness.

Just about the time this trade-off between obvious comfort (the Tak LE) and perhaps better views (the RKE and Plossl) was becoming a real delimma, the seeing settled down to Pickering 7 or 8, with moments of 9. Our three contestants were duly retired in favor of a 5mm Tak LE, and I was able to get on with viewing Mars without worrying whether or not I had the right occular in the scope.

The 5mm is that much better than the 7.5, you ask? No, there's just no competition at that focal length in my kit. wink

(It should probably be mentioned that the 8mm RKE and the 8mm TV Plossly each represent the shortest focal lengths in their respective ranges.)

-- Jeff.
Posted 10/15/2005 03:31PM #1
Interesting report, Jeff. Thanks for sharing your perspectives. Which scope did this particular Martian "cruise" utilize?

I just realized: My "shortest" eyepiece with a rubber eyeguard is an 18mm Superwide. 8O I used to have a 7.5mm LE, but I didn't find myself using it as often as it deserved -- not for any comfort- or view-related issues, of course (great comfort & fidelity). Rather, the 7.5mm focal length simply "favored" one particular scope (150mm f/12 Maksutov), and nights which support 240x in my area (north suburban Denver) are uncommon. Planet views through my other (shorter) scopes typically rely on the 4mm-6mm range.

Cheers & best wishes.
-Dan
Posted 10/19/2005 06:58PM #2
While viewing Mars the other night I had a chance to compare my new Tak 5mm LE to a Meade 6.4mm 4000 Plossl. This was with a TV 102 on a Gibraltor Mount (I know, I know, it's not the steadest thing for high power viewing.)

Interestingly, the Meade seemed to give a bit more contrast. However, the larger field of view in the Tak more than made up for a difference that could have been due to atmospherics. Still, it had me wondering what the view would be like through an Ortho such as the UO 4.8mm - fewer lens but much, much smaller field of view.