Tal 1 Revamp

[Alfian]

This all started with  a growing frustration with the Tal1 focuser. I was fortunate in some respects that I had the later focuser which took 1.25 “ eyepieces and not the earlier one that was slightly smaller and could only use the standard Tal issue EPs. However I had two issues. Firstly, because of the limited travel of the focuser I was still pretty much limited in eyepiece choice, for example I could not bring my  20mm Maxvision EP to focus. Secondly, the focuser was quite stiff to use and no matter how I adjusted it, stripped it apart and reassembled, greased etc, I could not improve matters much. The Tal1 focuser like most Tal stuff is well engineered, over engineered if anything, but I decided it needed replacing. The question was, given that the Tal has an odd (110mm) aperture and hence tube diameter,  with what?

I had an old Konus 114/f5 reflector and looked and measured things up and concluded that a focuser off a 114 scope would probably fit, so not wanting to butcher perfectly usable scope I bought a R&P focuser off a 114mm from ABS quite cheaply and dutifully set about modifying it to fit the Tal. The immediate presenting problem with trying to fit a "normal" round based focuser to a Tal1 is that the focuser base obscures one of the secondary spider vane attachment/adjuster bolt heads. This called for some careful reshaping of the new focuser body. I am no engineer but I've done enough over the years to plan things out and take it one careful step at a time, but on this occasion the determination to get it just right resulted in it being just plain wrong. It would have worked, probably, but would have looked - not good.  Start again. This time, with the rationale that the Konus cost me next to nothing second hand and that I very rarely used it, I decided to sacrifice it to the Tal. This mean decision turned out to be an extremely fortuitous one for reasons that will become clear later. The Konus focuser, which was in any event a better sturdier unit than the first, was very carefully adapted to fit the Tal. Additional holes were drilled for the fixing bolts (incorporating existing ones)  and the result looked promising. 

The next presenting issue was the Tal's tube. The hole that the old Tal focuser butted against, not through, needed opening out by about 2mm all round plus a cut out at the bottom for the focuser's rack.  At this point its worth a little diversion to explain that Tal 1s are left handed, that is to say they are laid out the opposite way round from most other scopes. This is not with respect to the focuser, much of an issue, but the optical finder perched above the focuser is arranged so you view with your left eye. I always found this awkward and more so because my right eye is my best one and does not need (much) correction. So here was an opportunity to make the Tal 1 right handed by turning the focuser upside down and repositioning the finder. This was obviously a consideration in terms of cut out positions and bolt holes. With the tube stripped out,  I was conscious when carefully filing, drilling  and cutting away at the Tal that the focuser needed to remain square on to the secondary. It was also the point of no return, no pressure then, this was going to have to work. With the focuser mounted on the bare tube with everything tightened up everything worked very smoothly and it seemed strange to see the focuser tube protruding into the telescope tube when racked fully in. The new finder shoe was also fitted in its right handed position.

Now to the primary mirror mounting. I was aware from the word go, (from stuff I'd read on line, indeed from this forum) that by changing the focuser, the primary would need repositioning slightly further into the telescope tube in order that images could be brought to focus. This presents a few issues. The existing  mounting system is one where the mirror cell is held by three bolts to the rear mounting plate which with the tensioning springs provide a means of collimating the primary mirror. Changing the position of the primary means using longer bolts and different springs. Andy (the SG oracle on things Tal) gave me some advice on how to go about this. Thanks Andy(H). The other tempting way to (NOT) achieve this is to simply to hack off say 20mm of the tube and re-mount the existing cell etc complete. This will not work as the tube at the very bottom end where the rear mounting plate is inserted is reamed out a fraction, so it wont work because it wont fit anymore!  When I started to look at replacing the mirror cell mounting bolts with longer ones, I was surprised, given how Tal tend to over engineer things, how skinny they were, 4mm I think. Adding what I estimated to be another 20mm to the length, even with stronger springs slightly worried me. I thought I'd have a look at the Konus mirror cell and mounting plate to see how it compared. The Konus was much more substantial in just about every way plus it had those nice knurled adjusters so collimating the primary can be done with your fingers instead of a screw driver. It didn't take much of  a "Ping" to make me wonder whether the Tal mirror could be mounted into the Konus set up and fitted into the Tal tube.  To cut a longish story short, with some messing, fiddling, dremmelling, and some cursing (not too much)  - yes it could and did. One of the benefits of fitting the Tal mirror cell into the Konus  mount was that it, at a stroke, gave me the near 20mm spacing that I needed. No need to change anything else.  One of the big differences was that the Konus rear cell assembly was effectively a rear cap type fitting from the outside of the tube whereas the Tal assembly, as said, fits snugly inside. This was eventually and easily solved by drilling three new mounting holes and tapping threads to take new securing bolts. I also used the Konus front cap assembly on the Tal. The plastic front cap of the Tal was, at least on mine, incredibly tight, so I did yet another transplant. Given all the Konus bits I used I thought I'd put a Konus sticker on the finder shoe, so the name still survives.

Everything together now, I set about collimating the Tal. Fortunately at F7.3 this is a very easy task, both secondary and primary. A collimation cap is all that is necessary though I did check it with my Cheshire. In daylight I focused on a distant object - result, very big smiles.  This reassuring objective achieved I now completely stripped it back down to the tube for its cosmetic work. Following advice offered on the forum I had three options. One was to do a proper DIY paint job. I do not have the appropriate indoor space for this so warm calm  warm outdoor days would be needed so given the waiting game I passed on this one. The second was to get the tube powder coated. A given estimate was not especially expensive and in retrospect I should have gone for this, but wanting to complete this revamp DIY style, I eventually opted for the third option,   carbon fibre vinyl wrapping. Having not tried this before, I dutifully studied youtube videos and had a practice run on the now lonely Konus tube, no problem.  Confidently wrapping the Tal tube, I was somewhat overzealous with the heat gun and irreversibly wrinkled things.  Second attempt went better, but given what I had left of the roll, it went on in several sections. I was pleased with how the joins went but inevitably it did not look as good as it should have done but for fun a  couple of  Russian red stars were applied to signify the Tals  origins. The overall result depending on your tastes is pretty reasonable, but at some point in the future if  I have the time and spare cash I'll probably get it it powder coated. Last job was to flock the tube which I'd not done before but was surprised how easy it was, so shiny black outside, very matt black inside.  Everything was reassembled, optics re-collimated and job done.

Last night I had the Tal out for a quick session just to check after everything it still worked where it counted. A bright moon lit the sky but M42 looked good with the the four main stars of the Trapezium an easy target. The moon at 133x was really nice too with deep shadows on the terminator. Comparing it to my newly acquired ED100 is a bit unfair but the Tal 1 acquits itself very well for a small reflector.

For those who have endured this long screed, well done, and thanks for sticking with me! Photos speak for themselves bare bones before and after with a close up of the new Tal/Konus mirror primary mirror assembly.

[nightfisher]

Quite a job done there, and now you can take pride in owning a very unique telescope

[Alfian]

Thanks Jules,unique is one word for it, here and there I've thought of a few more.

[iPeace]

On 3/9/2017 at 19:56, Alfian said:

...for fun a couple of Russian red stars were applied to signify the Tals origins. The overall result depending on your tastes is pretty reasonable...

I like it. A lot. Don't tell anyone, but you've inspired me to do something similar. Purists will cringe, but I couldn't resist.

[Alfian]

LIke it, if it feels right, why not? A very individual scope! Purists are either so shocked they are stuck for words or are keeping feelings to themselves. Probably good either way! Excuse tardy reply, wifi access dicky.

[iPeace]

13 hours ago, Alfian said:

LIke it, if it feels right, why not? A very individual scope! Purists are either so shocked they are stuck for words or are keeping feelings to themselves. Probably good either way! Excuse tardy reply, wifi access dicky.

I certainly won't disapprove of anyone preferring a pure white tube, that's just as beautiful in its own way.

Do you still have the Tal Mutant?

[Alfian]

9 hours ago, iPeace said:

Do you still have the Tal Mutant?

No, I don't have it anymore Mike. After I bought the ED100 it became clear that as much as I liked it, and despite the work I had put in, the Tal1 was always going to get sidelined. I tried to sell it for what I thought was reasonable but got no takers and on principle I refused to let it go for less, so I decided to donate it to a school astronomy club where its bullet proof nature would work well. In the end however I did, by way of thanks, get a 10mm BCO which I really like, (thanks Shane)  so I'm a happy bunny. That GSO 150/f6 just has to be such a good all rounder.

[iPeace]

3 hours ago, Alfian said:

I decided to donate it to a school astronomy club

Nice one.

[Telescope40]

Tidy work. Looks excellent. Enjoy 

 

John