Tele Vue 11mm Plossl vs 9mm and 7mm Orthoscopic Eyepieces

I specifically compared these EPs over 3 nights. The ones I have aren't exactly the same focal length (I bought them to complement or "complete" my set of EPs so they are deliberately different FLs). Having said that they are pretty close, the TV plossl is 11mm and the Ortho's are 9mm and 7mm. So 11mm vs 9mm is not too bad for a comparison, could be closer but that's all I've got.

General thoughs:

I'm not sure which ones look better, build quality or aesthetically, but my wife thinks the Ortho's look "pretty". The TV plossl is bigger than the Ortho's and looks slightly awkward, it's hard to explain but the inside of the eye cup and top metal surface of the EP look quite flat. The top lens is quite small for an EP (typical plossl) or at least is made to look small by all that metal and eye cup rubber flat arcoss the top of the EP. Both were approximately the same price, $95 for both Ortho's (Telescope Shed) and $105 for the TV Plossl (Bintel).

The TV plossl comes with top and bottom plastic covers, the Ortho's do not have any covers. The lack of at least a top cover for the Ortho's is a bit annoying (standard 1.25" EP covers are a bit too lose to fit on the top of the EP as well, I still haven't come up with a solution to cover the top of my Ortho's).

Practicality:

The Ortho's don't come with eye cups so I thought it was going to make viewing more awkward, but it actually made viewing easier. In comparison, the TV plossls eye cup kind of felt odd. But, I would still probably prefer an eye cup on the Ortho's because it helps block out stray light from around the sides of your eye. I don't think either eye piece type wins or loses here.

The biggest difference between the two EP's came as a bit of a surprise. The TV plossl fogged up REALLY easily. Like within a few seconds of viewing. Each night wasn't overly dewy, mostly the moisture came from my eye. The EP's were cold, because I keep them sitting in their boxes next to the scope when I'm viewing, but only the TV plossl seemed to fog up. Initially, this made comparing the EP's difficult. I felt that I only had a few seconds to judge when looking through the plossl, any longer and I'd risk the dew giving a false impression of the view. In the end I made sure that the EP was kept in my pocket when I wasn't using it and even taken back to the house to warm up evey now and then.

Optical Performance:

There's not much difference between the two types of EP's but my feeling is the Ortho's probably come out on top. The TV plossls have a slightly larger FOV (50 degrees as apposed to 45 in the Ortho's) but it doesn't actually make that much of a difference when viewing. Neither of these types of EP's are going to challenge a Nagler. The only point to mention here is that because they both have a small fields of view so they are best used with telescopes that have some from of tracking.

Using 47Tuc as a target (NGC104), when switching from the 9mm Ortho to the 11mm Plossl, my first thought was that the Ortho had better contrast. But switch back the other way (to the Ortho) and I couldn't tell the difference. Actually the longer I looked at 47Tuc the less I could differentiate between the two EP's.

On bright doubles like Acrux both EP's performed pretty well and I couldn't really tell the difference. I spent a lot of time looking at Canopus (-0.6 mag) and placing the star just outside the FOV to see if there was any stray light difference between the two types of EP's. Again I couldn't see any difference. When looking for the airy disk (on the third night of comparison, the seeing was maybe 8/10) both the 9mm Ortho and the 11mm TV plossl were both pretty similar except the TV plossl definitely had more pronounced rays emitting from the focused star. There wasn't any dew that I could see of the TV plossl at this time, so I think the effect was real. Having said that both EP's did show this phenomenon quite faintly, but I only noticed it in the Ortho's after I went looking for it. The plossl was not as good here, but I'm not sure if it matters. I don't know what the effect is called, but it wasn't too much of a big deal.

Overall I liked both types of EP and I will keep them. I couldn't find any obvious abberations in either and only thing that I can really complain about is the propensity of the TV plossl to dew up. Apart from that they are both pretty damn good.

Scope used: 150mm F12 Intes Maksutov-Rukman-Cassegrain.

by stu