Calling Tal 100RS owners - what 2" diagonal?

[Dodge]

Anyone got any recommendations on a 2" diagonal for a new Tal 100RS? I tried the SW Deluxe 2" Dielectric one, but it was too big and wouldn't allow my EP's to come into focus.

What do you guys use?

ta

[Marki]

I have a Williams Optics dialectric 2", and have the same problem when its fitted to my TAL100RS . Works fine with my shorter focal length refractors, though.

[John]

The TAL 100's seem to use a number of different focuser designs, some of which don't have enough inwards focuser travel to allow a 2" diagonal to be used. If it's any consolation I found the same when I tested the much more expensive and exotic TAL Apolar 125 apochromat. I guess the only solution would be to shorten the tube length a bit

The light path through a 2" diagonal is quite a bit longer than a 1.25" diagonal which is why the former need more inward focuser travel.

[Marki]

Thanks John - I thought it must be something to do with that. Rather than cut my tube or change focusser, I could just get a 1.25" dialetric as well. Having said that, the TAL diagonal is pretty nice anyway (at least once I blew all the dust and stuff out with a puffer ).

[Coco]

I have a TAL 100RS, I shortened the tube so I could use a 2" diagonal with my 14mm Explore Scientific 100 degree eye piece, I found it was enough when I barlowed it so I'll shorten it a bit more, I took my tube to an engineering shop where they put the tube in a band cutter nice and square.. I wouldnt expect your local engineering shop to charge more than £20 for doing this.. it takes just 5 minutes to square the tube up and cut it..

[Caldwell 14]

Seems to be a common problem, I stuck to 1.25 when I had one.

[Stardust]

I had the same problem. Bowled up at a star party to find I couldn't use most of what I'd taken. Didn't occur to me to check the 2" diagonal beforehand, oops.

[nightfisher]

My 100rs comes to focus with a skywatcher 2" and a 32mm 2"plossl type ep

[moriniboy]

Can just about make it focus using a Televue 2" and a Baader Aspheric 36mm.

Will therefore be shortening the tube, can any one advise how much to cut off?

[Astro_Baby]

I can only assume mine is unique - a fact I have long suspcetd as its focuser seems much shorter than any others I have seen and its optics look slightly different too (pale green coatings rather than purple).

I tested mine when it was new and it would come to focus on all EPs using a Revelation 2" Dielectric Diagonal.

EPs Tested were

TAL S2 25mm Plossl - No problems

TAL S2 10mm Plossl - No Problems

Celestron 32mm Plossl - No problems

Baader Hyperion 13mm - No problems

Baader Hyperion 5mm - No problems

Skywatcher Panaview 26mm - No problems

Skywatcher Panaview 38mm - Could focus but only just - focuser almost fully racked in.

Explore Scientific 14mm 100' FOV - No problems

All EPs could come to focus with a Skywatcher 2" ED Barlow.

Seeing this post made me get off my ass and run a test today with the TAL 100RS and the 2" Dielecteric Diagonal again.

Heres the results with a different batch of EPs as I have changed almost all my EPs since I firts tested.

These were tested against a radio mast thats approximately 8 miles away.

University Optics Ortho 15mm - No problems

University Optics Ortho 18mm - No problems

University Optics Ortho 12.5mm - No problems

University Optics Ortho 9mm - No problems

Explore Scientific 14mm 100' FOV - No problems - retested to be sure

Explore Scientific 30mm 82' FOV - No problems but inward focus travel is tight with perhaps only 1/4" to 1/8th of inward travel left over.

Pentax XW 10mm - No problems

Pentax XW 5mm - No problems

TAL S2 25mm - No problems - retested for completeness

SV 26mm Plossl - No problems

All were tested with the Revelation 2" Diagonal. It may be because the diagonals 2" to 1.25" adapter is recessed but I doubt it - the recess is less than 1/8" in depth and the inward focus travle avail;able at focus on all of the EPs is a lot more than 1/8" apart from with the EXplore Scientific 30mm where inward travel is down to the last turn of the focus wheels at focus.

Hope thats of some use to you all or at least food for thought.

Mel

[Marki]

Thanks Mel, thats very helpful. Isn't the green coating more usual with the 100R? Or maybe they changed the spec later in the RS run (my serial number is 1523).

I'll try the WO 2" dialectric diagonal again with some different eps and see if I can get anything into focus. I'd only tried the TAL supplied 25mm, with the 1.25" adapter still in the diagonal. Think I'll try the Baader zoom, as that can be fitted direct into the diagonal without the 1.25" adaptor (I have no other 2" eps as yet, although contemplating a 2" 32-35mm wide field of some sort).

[Stardust]

It was the WO 2" diag that wouldn't focus with my Pentax eyepieces.

My 100RS has nice purple coatings where my friends new scope has the pale green.

It does seem odd that there are variations out of the same factory.

Can't say I fancy cutting the tube down, just stick with a decent 1.25" diagonal

[Dodge]

Can't say I fancy cutting the tube down, just stick with a decent 1.25" diagonal

Likewise - I won't be cutting anything. I just fancied trying my 28mm Nirvana with the Tal. I suppose I could always not bother with the diagonal and sit behind it.

[Coco]

Mel... measure your tube for me will you

I cant see how a lens cell would effect this, my diagonal is a Moonfish 2" job, very big so that could have a bearing..

The ES 14/100 looks sweat through it doesn't it

[John]

Just out of interest I assembled this little montage of 3 TAL 100 focuser designs. The oldest (not now fitted) is bottom left. Astro_Baby's is the top one and the 3rd design seems to be the most commonly found. Astro_Baby's focuser is broadly the same design as the ones used on the TAL Apolar 125 apochromat but the Apolar used an extended housing to hold a group of the 6 lenses it uses and also had the issue of not coming to focus with 2" accessories. I'm sure at one point TAL were putting 2" Skywatcher Evostar focussers on the TAL 100's as yet another alternative but I could not find a photo of one of those.

[AndyH]

Hi.

That bottom right pic is of the original rack & pinion 100 RS's. I had one of them on my mine.

Dave(F15Rules) had an RS, with a long bodied crayford. Pic here, in his album.....

http://stargazerslounge.com/album.php?albumid=464

Hope he doesn't mind me pinching it to paste on here, for the benefit of this discussion?

That crayford focuser looks a lot like the ones that the newest 125R achro uses(or at least those pics I've seen of those scopes, on a couple of Russian forums). The 125's that we in the UK had imported, years back, used the old rack & pinion, same as the 100RS, as in the pic in John's post.

The majority of the new 100RS pics I've seen on SGL, are the short body ones, as in Astro_Baby's pic.

Andy.

ps: Useless info time - I remember reading on the TalScopes Yahoo Group that whilst many folk(inc me) presumed those early 2" RS R&P focusers were chinese made, the godfather of the yahoo group, Bill Brady, asked the factory & they totally refuted this, saying they were Russian made.

[John]

Thats interesting Andy. Dave's focuser seems to be a long bodied version of Astro_Baby's crayford so another variant

I had one of the 1st TAL 100's to come into the UK back in 1999. It had the "original" R&P which was 1.25" only and had rather short travel focuser. Some 1.25" eyepieces such as the Ultima 35mm and a UO Konig 32mm would not come to focus in that because of the limited inwards focuser travel available. That scope had purple objective coatings and a machined metal dew shield. Wish I still had it, despite it's quirks ......

[AndyH]

Yeah, the original R was a lovely scope. It just looked nice. Can't really explain it.

They were the 100R. The S was added to the name, when the scope had the 2" R&P focuser added. Both 'R' & 'RS' types were manufactered together, for a while, before the old 'R' was finally discontinued. Exactly when the 2" R&P was replaced with the 2" crayford, I'm not certain, but mid to late 2000's rings a bell.

The purple coatings were replaced years back with a modern, new improved(so say the designers) coating system that has that greenish hue.

Mind you, there is something that screams RUSSIAN optics, when I see that deep purple coating on scopes.

To confuse matters even further, I noticed a few months back, that the Tal website(npzoptics.com) has now designated the RS as now simply S.

Andy.

[nightfisher]

If its any help my 100rs has green hue to lens coating and short crayford like astro baby`s, mine is pictured on flo`s website, showing the crayford

[Astro_Baby]

Measurements of 'Tanya' my 100RS

Length of tube from most forward point of lens cell to start of large knurled part of focuser (the knurled ring which acts as the focuser rotation lock)

81 cm

Distance between start of knurled rotation lock to rear of main Crayford block

6.7 cm

Distance between end of Crayford main block and start of focus tube (2") element at maximum in-focus

1.5cm

Length of 2" to 1.25" Adapter when installed

2.3cm

So when the 1.25 adapter is fitted the scope is 91.5cm long from the the start of the lens cell to the end of the focus tube at full in-focus

With the 2" adapter removed the scope measures 89.2cm from start of lens cell to end of the 2" focus tube with full in-focus.

Hope that helps.

[Caldwell 14]

Measurements of 'Tanya' my 100RS

Tanya? I thought I was the only one who did that, My son named mine Sasha, although she was mainly known in our house as Comrade Scope I may buy another, 3 weeks after selling her (that was a mistake) although I did see a cheap Lyra going for sale and now I'm torn

[nightfisher]

Go for another Tal, you know you want to!

[Caldwell 14]

The Lyra has been sold, I'll sleep on it, pointless really, I'm going to buy another TAL anyway aren't I!

[nightfisher]

On a more serious note, most lyra owners feel that the f11 is a touch better than the tal100, but i wonder is this just down to the slightly higher f no, also with the lyra from new, you have to factor in the cost of a diagonal and a finder scope

[Caldwell 14]

Yeah I thought about that too, well over a ton on top eh!