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TMB or Not TMB ... ?


Nightspore

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In July I bought a TS Optics 2.5mm Planetary HR (bad early Mars fever!). These eyepieces are probably made by BST (Barsta) although I’m not sure if they are actual clones of the TMB series originally designed by Thomas Back.

 

https://www.burgessoptical.com/planetary-eyepieces.html

 

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The 'SW 4.5mm' is noticeable as it is the only eyepiece above with a white end cap. Its eye lens cap is actually from a borked TS Optics.

 

However, there are other ‘TMB’ eyepieces on the market. I also have a 4.5mm version. TS Optics don’t have a 4.5mm in their series. Ostensibly similar, these seem to be subtly very different, indicating a different manufacturer. The housingings have matte finishes instead of gloss and almost every aspect of the design is very slightly different.

 

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These alternative eyepieces are usually unbranded although they normally have a ‘TMB Optical’ logo displayed prominently on the adjustable eyecup part of the housing. They also seem to be sold by a plethora of distributors. Often for less than a half of the TS Optics versions. They may actually originate from several different OEM's. 

 

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I couldn’t resist buying the cheapest (34 quid) 2.5mm I could find to compare it with the TS Optics 2.5mm. It was sold under the name Mavis Laven but there were half a dozen other brand names selling something remarkably similar. I suspect that they are all identical.

 

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When it arrived it had no brand name other than the TMB logo and there was a distinct rattle emanating from inside the housing. A cursory examination revealed the FOV was full of debris and dust particles. I know from previous experience that the Smyth/Barlow can be unthreaded so the internal field lens can be accessed.

 

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Five minutes later with a rubber blower and it was almost perfectly clean. The rattle proved a tad more difficult. After a little research I discovered that this is a known problem and the lens element retainers had probably become loosened slightly. Eventually I discovered that by removing (pulling off) the rubber eye guard a flat metal collar is exposed. 

 

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The upper part of this can then be simply threaded out and it is just a matter of tightening the exposed retaining ring around the lens group. I did this manually with my fingers and it did the trick as the EP is now rattle free.   

 

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I used the TS Optics 2.5mm on various scopes while viewing Mars. In my 80ED Evostar it held its own against a much more expensive 3mm Tele Vue DeLite and gave me a sharp 240x. Some of the best images I've had of Mars this year were with the TS Optics 2.5mm. The TS Optics and unbranded 'TMB' type eyepieces also have slightly different focal planes which is indicative of them originating from different manufacturers. However, I find no difference in quality when actually observing with these eyepieces. They are both remarkably sharp and well contrasted not unlike an orthoscopic. 

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They take me back, I had a few true TMBs plus a couple of clones and they were good performers. The fov on the clones were a bit questionable with curvature away from centre but it was only really noticable on lunar close ups.

They are good value for money inmho. I have actually been thinking of getting a pair for my binoscope

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If I remember right, when Thomas Back died the factory making them kept the design and continued production under many names. I believe there was a court case involved. Lots of info on cloudy nights and some heated discussions.

 

Like you Phil, I have been contemplating a couple of higher power ones for my binoviewer.

Edited by tuckstar
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2 hours ago, philjay said:

They take me back, I had a few true TMBs plus a couple of clones and they were good performers. The fov on the clones were a bit questionable with curvature away from centre but it was only really noticable on lunar close ups.

They are good value for money inmho. I have actually been thinking of getting a pair for my binoscope

I've been using the TS ones for years, I'm fairly sure they're BST. The 25mm was far superior to the 25mm StarGuider which had way too many seagulls in a fast refractor lol. I mainly use them for lunar/planetary though.

 

https://agenaastro.com/catalogsearch/result/?q=BST planetary

 

Agena sell them as BST. 

 

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I'm not totally convinced they all come from the same OEM though. 

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2 hours ago, tuckstar said:

If I remember right, when Thomas Back died the factory making them kept the design and continued production under many names. I believe there was a court case involved. Lots of info on cloudy nights and some heated discussions.

 

Like you Phil, I have been contemplating a couple of higher power ones for my binoviewer.

I'd love to know the true story of the TMB one day. It seems a very 'heated' topic on US forums in general.

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I had a closer look at the 4.5mm 'TMB' clone (centre eyepiece below). I've owned this for a couple or three years. It actually always had a very slight rattle which I assumed was the adjustable eyeguard. It didn't impact on viewing as far as I could tell. Although I decided to do a 'Mavis' fix anyway. Oddly, this design is slightly different to the Mavis. The retaining collar has grooves to facilitate threading with some tool. Not unlike the TS Optics version.

 

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Above left to right: 2.5mm TS Optics, 4.5mm unbranded, 2.5mm Mavis Laven.

 

The slight rattle was fixed in the same way as the Mavis EP's. Also, there is no TMB logo on the 4.5mm. The field lens cap is white, and not black like the BST/TS Optics. The eye lens dust cap is the same as the Mavis.

So; this is a bit of an enigma:

Are the Mavis EP's actual clones of the original TMB's?

 

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Are the TS Optics/Barsta a copy of the clones of some sort?

 

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Why is is the 4.5mm a bit sui generis?

Enquiring minds want to know.

I can't discern any difference in optical quality between any of them.

Edited by Nightspore
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  • 3 weeks later...

Mavis 3 (7mm) has landed! She was also a rattler but everything is now fixed and she appears flawless in daylight tests.

 

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Interestingly the slightly battered box was identical to the 'Sky-Watcher' UWA's.

 

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I'm pretty convinced the Sky-Watcher UWA's were actually Barsta (BST).

 

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The plot thickens ...

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  • 5 weeks later...

FWEqfQ0l.jpg

 

The 9mm was also a rattler until I fixed it. I got first light with the 9mm Mavis last night. 44.4x in my ST80 (1.8mm exit pupil). I'm impressed (again). Very nice view of many of the open clusters in Auriga, Gemini, Cassiopeia and Perseus. Great view of M35, M37, M1 and M42 as well. 44.4x seems to suit the ST80 in framing a lot of open clusters. I've used a 9mm Celestron X-Cel LX in the past, which was very good, and around the same FOV. I used to use a 9mm Orion Expanse as well on the ST80, which has a wider field but weird eye placement.

 

gCm3Z5Ol.jpg

 

The field stop is 15mm.

 

uS5ET9Ul.jpg

 

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