Poor experience with TMB 6mm planetary eyepiece

[Martin-Devon]

I know this posts flies against the grain of several recent SGL reports, but I just want to share my experience. I've been looking to buy a decent planetary eyepiece and had been mainly looking into Televue and Pentax 5-6mm options - they come at a steep price though. Then I picked up that several people were raving about the TMB 6mm EP, and the price was about 1/3rd-1/4th the cost - so I plumped for one.

My scope is the Celestron CPC800 (8" aperture, with 2032mm FL), and I already have Baader Hyperion 36mm and Celestron Axiom 10mm EPs. The TMB 6mm would give me 338x magnification, the Axion 203x. Anyhow, the TMB EP arrived last week and on 2 consecutive nights I spent several hours focusing in on Jupiter and making comparisons. On the 2nd night, conditions were absolutely perfect and my main viewing time was from midnight -2.00am in the morning.

With the Axiom 10mm, Jupiter was very sharp and crisp in focus, I could easily see nice precise banding and the moons were also nicely in focus with deep black background fields. Switching to the TMB 6mm was disappointing - Jupiter was about 50% bigger, but the image was not sharp at all. I took a long time tweaking very gently the focusing, but over the 2 hour period could never see any sharpness or clear resolution. The moons also were somewhat fuzzy and as I switched back-forth with the Axiom, I began to appreciate just how good the Axiom actually was.

I'm not saying that the TMB 6mm is a bad EP, maybe I had a duff one, or maybe on my CPC800 pushing to 338x was beyond it's limit, but I have since returned the TMB and got a refund.

[Moonshane]

I don't know what this scope can reasonably handle but I'd say that it's the magnification / seeing and not the eyepiece. I'd suggest even an Ethos 6mm would struggle in your scope except on the sharpest nights? due to atmosphere etc, 338x I would say, based on my experience, is much more than most scopes can produce on most nights except on the moon. For example, last night I was only managing to get the best views at 125x on Jupiter with a 6" f11 dob. I could have pushed this to 160x (but don't have a 10mm eyepiece - this will be remedied as soon as possible) and with my 8mm at 200x the seeing was occasionally good enough but not often. even with 125x I was getting truly awesome detail and seeing features I had never seen before.

I'd suggest you try an 8mm rather than a 6mm and you might get more use out of this.

[Moonshane]

ps I have no axe to grind re TMBs but think they are good for the money. I sold mine when I bought my 8mm Radian.

[Hypernova]

I'd say that the high magnification was too much for the seeing conditions that night. The magnification provided by the 6mm would only be of use on nights of very good seeing so it's not surprising that you say the image was not sharp. Even if the sky seems clear, there may upper level cloud or atmospheric turbulence that could be interfering with the views. I would say that 200-250x would be a maximum on most nights of average-good seeing in the UK but i may be wrong.

[Capricorn]

Would say that 338x is simply too much.

Probably a combination of at or beyond the scopes ability and beyond the viewing ability of the UK in general.

Seems to be often said that in the UK much beyond 200x is pushing it. 338x is somewhat above that.

To get 338x I would have said that everything would have to be "just right".

And although nice the TMB's (about £55 if I recall) are not up in the £200-400 realm in which the quality may just be good enough to produce anything.

[johninderby]

Simply too much magnification. I found that when I had a C8 I very rarely went lower than a 9mm Nagler. Sometimes on the Moon a 7mm Nagler, but on Jupiter or Saturn the views were just too soft under normal seeing conditions.

John

[Ben Ritchie]

Seems to be often said that in the UK much beyond 200x is pushing it. 338x is somewhat above that.

200x is certainly what I find to be maximum useful power under normal conditions, sometimes I don't even get there. I sometimes get to 300x power for double-star work, but only on those very rare nights where the seeing is Pickering 8+

Agree with the others, sounds just like too much power for the conditions.

[ollypenrice]

Another the same. The C8 usually has very good but not excellent optics, it needs to be in perfect collimation, and 250x would be the limiit I would personally set. In a 10inch SCT, very early in the morning, I just once went to nearly 500x on the moon when the seeing was beyond belief. The image held up and the scale was fun but I was not seeing anything I couldn't see at about 300x. I'm afraid I can't remember all the details.

I have read of QA issues with lots of post Thomas Back TMB products, which is a terrible shame, but I woud not blame the EP here, necessarily.

Olly

[michael.h.f.wilkinson]

I have a C8, and rarely go beyond or even to 250. As was said above, 338 is just too much, except when the seeing is perfect, AND you have collimated the scope properly. Two nights ago, even my TV Radian showed mushy views, which I know has nothing to do with the EP. In practice, you really only compare EPs fairly if you use the same focal length in the same scope, under the same viewing conditions.

[russ]

I agree with the others, the 6mm is too much for the C8, except on the rare ultra steady nights. And even then, for some reason, only really Mars takes the high power. I find 250x to be the highest i go with Jupiter.