Astro-Professional TMB 80mm f/11.25 Achromatic Refractor

[johninderby]

I recently got hold of another of the now discontinued Astro-Professional TMB 80mm f/11.25 achromats. Never should have sold the old one! This was the very last new one available and I got it directly from Astro-Professional.

CA is very well controlled and similar to what would be found with one of the f/6 80mm APOs with FPL-51 glass, in other words not really noticeable for visual use. A fringe or minus violet filter is definitely not required. The TMB doublet lens is much sharper with better contrast and with more depth of focus and gives a very steady image and totally outclasses the previously mentioned 80mm APO for planetary use. An in-focus star shows very clear and stable diffraction rings in the Airy disk.

The scope comes with a single speed GSO crayford, but I decided to upgrade the focuser to one of the new TS Monorail dual speed crayfords, which is Telescope Service's own branded version of new GSO Linear crayford. Nearly twice the weight capacity of the older GSO and is very rigid with no noticeable flex and very smooth as well. Very similar to the WO linear focuser. Also replaced the standard tube rings with CNC ones and added a carry handle and replaced the standard focuser bracket with a Baader bracket that takes a standard Synta foot.

According to the manufacturer the scope was a very poor seller as very few buyers realised just what a special scope it was, and weren't prepared to pay the extra for the TMB lens. Now that the supply of lenses has run out (the TMB estate won't authorise further production of the lenses) production has ceased for good. I can imagine now that it's discontinued prices of the scope second hand will be more than it was new.

I will be using it primarily for white light solar observing with a Herschel wedge.

John

[A McEwan]

Wow - that looks very nice indeed! Lovely solar setup and that focuser looks pretty special too. Nifty use of the carry-handle there!

[ollypenrice]

I knew nothing of this instrument and found your description fascinating. In view of recent threads on long focal length refractors being ready for a comeback you may be ahead of the game here! It looks lovely, anyway.

Olly

[johninderby]

I think it's only now that this scope is starting to get some attention. It seemed that everyone was rushing to buy cheap 80mm APOs, and as you could buy something like a Celestron C80-ED APO for less, an 80mm achromat was dismissed out of hand and few people bothered to take a closer look.

It is a "niche market" telescope though, and while it gives those remarkably sharp and steady images with great depth of focus that make it great for planetary and solar observing, it isn't as portable as a small and fast APO nor is it as suitable for wide field use.

John

[Solar B]

Quality set-up there John,from the Zoom/AE Wedge to Objective

Only thing i could add is one of the AE solar shades.

Brian

Mmmmm just wondering how this would compare with your FLT98

on the Sun,faster but more ap.

[johninderby]

Just by coincidence an AE solar shade is sitting in the workshop just waiting for some foam strip to be added to stop it scratching the OTA.

The zoom is a Pentax XF 6.5 to 19.5, very impressed with it for solar observing both in white light and Ha. It has actually replaced a couple of Baader orthos as the best they could do was match the zoom. I suppose the optical characteristics of the zoom just happen to be ideal for solar use.

For night time observing the 80mm put up a good fight with some lovely and very steady planetary views, but in the end just couldn't compete with the FLT98 for sharpness and contrast, so it'll be interesting to see what happens when I compare the two for solar (sun this weekend please)

John

[johninderby]

More pics

This time with a SkyWatcher pillar (HEQ5 type) to give it more stability as the long OTA did tend to cause some longer lasting vibrations with the photo tripod. The modified Manfrotto 405 geared head is still used though. An A&E solar shade fitted as well.

Do you think that the Lunt60 looks a little bit over-mounted ?

John

P.S.

Before anyone asks SkyWatcher has now changed the colour of the pillar to white to suit the newer HEQ5 and 6 mounts.

[Solar B]

Smart that pillar looks the Biz i could do with one of those.

Brian

[darkstar]

Hi John

I have just bought the last one of these scopes and i am looking for a dual focuser, do telescope servises still sell the one you have on your scope?

Best regards

John

[F15Rules]

Hi John,

That's a really nice looking scope..I almost bought one three months ago, and admit that the price (I was quoted about £300, I seem to recall) put me off a bit...also, I have a lovely Pentax j-80 F12 so asked myself why I would need another scope of probably very similar performance?..but I was tempted as it has a TMB lens and looks very well made.

In the end I bought a clearance Celestron ED100 Apo complete on a CG-5 mount and stainless 2" tripod for £475, which was a bargain. The ED100 is excellent, but in a direct shootout when Mars was better placed, the Pentax showed all that the ED100 could, just the ED was that bit brighter.

Thanks for sharing your new scope, I predict it could become a valuable collectors' item of tomorrow.

cheers

Dave

[johninderby]

Hi John

I have just bought the last one of these scopes and i am looking for a dual focuser, do telescope servises still sell the one you have on your scope?

Best regards

John

Hi

Yes, this is the one.

http://www.teleskop-express.de/shop/product_info.php/info/p3946_MONORAIL-2--Refractor-focuser---e-g--for-Skywatcher-86mm-flange.html

I did find however than the flange was a very, very tight fit in the OTA tube. I put the flange in a lathe and skimmed about 0.5mm off it so that it would fit properly. It might be a good idea to email Telescope Services first and explain the potential problem.

John

P.S.

You could always fit the new focuser to the old flange f you didn't mind the fact that the old flange is satin finished and the new focuser is more glossy finished.