TMB Planetary II eyepieces

[Damnit]

^^ slowly coming to the conclusion too that this is not a bad idea and might very well do the same as I know I will not rest till I have tested the full extent of usable magnification of my scope ... but paradigm or TMB, that is my conundrum

[enigma]

Does anyone know if there is a difference in performance between the TMB Designed Planetary and the TMB Planetary II eyepieces? Also, the TMB Designed Planetary look very similar with the TS HR Planetary eyepieces. Could they be the same?

[great_bear]

Almost certainly the same. On the TS web site, they try to hint that theirs are somehow superior by saying they use the latest materials etc. and thus "might" be better than others - but in reality their comments no doubt apply to all TMBs in production at the moment.

My understanding is that years ago, once the design problem was sorted out (and it's arguable I think that there even was a problem, since holding an eyepiece up to the light or shining a torch through it is not a reliable indicator of reflection problems with in-telescope use - and that's what the fuss was about), since then the differences have only been cosmetic I believe.

However, I'd be interested to know if they all come out of the same factory. Does anyone here know which factory makes them?

[johninderby]

Remove the twist-up barrel and they're all identical underneath. It's only the styling of the twist-up barrel that's different.

Watch out for the eBay 6mm TMB II ones though, as some of them don't seem to be as good performers as the "clones".

John

Edit: The earlier TMB ones did have a design flaw that caused internal reflection problems, but that was fixed by replacing the retaining ring that caused the problem.

[great_bear]

but paradigm or TMB, that is my conundrum

If in doubt, it's worth remembering that the TMB is heavilly tried-and-tested by the community. It's one of the very best-selling eyepieces. The Paradigm is much less well-used, and thus more of an unknown quantity. Some people on SGL do like them though.

[paul schofield]

I bought the T.M.B Planetary 5mm, from Skies the limit. Alan of "Skies the limit" was a great help. Knocked £2 off the price, and included a free bolt case so all told £38 cant complain at that. Have not had opportunity the use the new EP yet, clear skies pending.

[Donkeiller]

I bought a TMB 3.2mm to "upgrade" from a 4mm EP from a Celestron EP kit. Tell the truth, apart from the eye-relief, the cheapo Celestron EP was better in every way.

I'm not a fan of TMBs.

[cs1cjc]

I have in front of me to sets of 4mm and 9mm eyepieces, one set marked TMB Optical Planetary II SW and the other marked 1.25"-58 degree wide angle (apparently manufactured by Barsta and commonly called TMB designed) eyepieces. See respectively:

http://www.astronomics.com/main/search.asp?catsearch_header=Astronomics&keyword=tmb

1.25" & 2" Eyepieces

The design of all these eyepieces is with a Konig eye set (see: Eyepiece - Wikipedia, the free encyclopedia) which has three lenses in two groups. This is identical for all focal lengths. The field set is different for the different focal lengths and is generally a cemented doublet. In this format, 5 lenses in 3 groups, it is just about the minimum number of lenses for a well corrected wide angle eyepiece with good eye relief (of around 12mm). Thomas Back wrote that his design works well with telescopes as fast as f4.

Taking the two 4mm eyepieces first, these are apparently the same optical design, having very similar dimensions, but they differ enough to suggest that they come from different production lines. For example the eye lens in the TMB is slight larger, there are mechanical differences and the lens coatings are different with the TMB appearing to be green and the Barsta, magenta.

The two 9mm eyepieces are not to the same optical design. On the TMB 9mm, there are apparently three lenses in two groups in the field set. In the Barsta 9mm the field lens is a bi-concave doublet, the eyepiece is shorter and has a different focal point (the ranges in general are not parfocal).

Physically there are things I like and dislike about both designs. The Barsta design feels more robust and the screw up top has a nicer motion than the TMB. However the Barsta has a chrome barrel with a heavy undercut, whereas the TMB has a, preferable, black satin barrel and undercut with a shoulder. Interior blackening is not perfect in either set of lenses, particularly when compared with (more expensive) Vixen NLV eyepieces.

In use, both sets have sharply defined field stops and give sharp flat images. The TMB eyepieces have less glow round bright objects and consequently show more contrast, though the 9mm shows less contrast than an Antares Ortho (similar to BGO). The large eye lens can show glint (a problem for me observing with spectacles) and this is more pronounced in the Barsta than the TMB. Overall I prefer the TMB models.