TAL2 mount

[jason.p]

It looks like I've got the plastic gearbox.

Worm drive seems OK on the brass cog. I couldn't check the motor as there's a 0.25-0.5amp fuse missing from the power pack. I'll have to search Maplins to find one.

If I'm not using the drive is it best to pull the motor back to disengage the worm drive?

All balancing done, collimation tomorrow then out under the stars.

[AndyH]

For polar alignment I bought from SCS a sighting tube that sits on top of the mount. It's just an aluminium tube about 25cm long and 1.5cm across fixed to an angle plate so it can be positioned correctly on top of the mount. The latitude scale is off by about 2 degrees by my reckoning.

Great to hear from another 2M owner!

Sounds like a very simple and clever device.

Andy.

[AndyH]

If I'm not using the drive is it best to pull the motor back to disengage the worm drive?

Yes. I'd recommend doing so.

Cheers,

Andy.

[jason.p]

For polar alignment I bought from SCS a sighting tube that sits on top of the mount. It's just an aluminium tube about 25cm long and 1.5cm across fixed to an angle plate so it can be positioned correctly on top of the mount. The latitude scale is off by about 2 degrees by my reckoning.

Any chance of a link Richard. I've looked through SCS website and couldn't find it.

Thanks

Jason

[AndyH]

It's possibly a thing SCS made up for the 2M way back then. Hopefully Richard will explain.

You could rig up a sighting device yourself.

Get hold of, preferably, a bit of 'T' shaped bar. Sit that on the top/side of the mounting plate, then use a piece of pipe as the sighting device.

eg:

Andy.

[jason.p]

Thanks, I've got plenty of scrap, should be able to knock something up:)

[RichardL]

I think I bought the polar sighting tube at the same time as the scope. The internal diameter is such that when you look through from the bottom end, the top end makes a circle on the sky which is the same angular diameter as the orbit of Polaris round the true pole. Then you use a chart to tell you where to position Polaris for the current date and time. I've posted the chart before at http://stargazerslounge.com/showthread.php?t=175431 Frankly I'm pleased just to see Polaris at the end of the tube at all. It's harder than you might think - it takes between 30 seconds and 20 minutes to spot it, because your eye tends to focus on the end of the tube rather than at infinity

I lied about the dimensions (well, I guessed wrong). 350mm long by 13mm across. The internal diameter is 9mm.

[jason.p]

Thanks for that Richard. I'm sure I can make something up out of my stock of bits and pieces.

[AndyH]

Reading your other thread, made me remember your pics of the focuser and eyepieces, above.

Your eyepieces look to be possibly be the older 32mm diameter barrel size, rather than the standard 31.75mm(1.25"). If you have a caliper or micrometer, you should check. If they are, it's something to keep in mind if thinking of using modern barlows or eyepieces.

How does the focuser 'hold' the eyepiece/barlow in place. I don't see a thumbscrew. Is there a sprung wire inside? There are various ways round this

Options?

1/ Use the focuser and eyepieces as is.

2/ Using modern std 31.75mm accessories, you'll notice they are a bit loose. The simplest and easiest way to fix is to wrap a single layer of electrical pvc tape round the barrel to give a good fit in the focuser.

2a/ Drill one or two holes at the top, in the side of the focuser, tap the hole to M4 and add thumbscrew(s). This'll hold the newer accessories securely.

2b/ More costly, but would keep the focuser as is - remove the knurled eyepiece holder on the focuser. It should(?) reveal a M42x1 camera thread. Buy a M42x1(female) to M42x0.75(T2 male) adapter. This screws on to the focuser. eg: http://www.teleskop-express.de/shop/product_info.php/info/p5223_TS-Adapter--M42x1-female-to-T2-male-for-russian-objectives.html

Add one of these to that adapter eg: http://www.teleskop-express.de/shop/product_info.php/info/p209_Visual-Back-T2-to-1-25----with-additional-T2-male-thread---short.html

You may or may not need a short extension tube to fit between the above two items, to build up the height. Possibly not.

2c/ One of these could fit straight onto the focuser screws eg: http://www.teleskop-express.de/shop/product_info.php/info/p1752_Adaptor-from-M42x1-to-T2-and-to-1-25--with-compression-ring.html It would give a lower height compared to the original knurled holder, but there may be enough racking in the focuser to compensate for this?

3/ A bit extreme and probably only cost effective if you can do it yourself or get a friend to do it. I've read of some folk doing this. Skim the 32mm barrels down to size on a lathe, so you can use them in a modern sized barlow.

The above shop is just an example. You may be able to source these adapters here in the UK.

Hope this doesn't confuse. It sounds okay in my head

Andy.

ps: It's obvious, but remember your eyepieces, if they are 32mm o/d, won't fit into a modern std barlow.

[AndyH]

Thanks for the pics Richard !!

On the subject of polar alignment, a sighting device will get you pretty close. If you are going to be leaving the mount in situ, the best thing to do is.........

Align the mount as best you can by eye, then use the 'drift alignment' technique. There are various explanations of this on the web and in the modern Tal manuals. Here's Tal's explanation, cut and pasted from the manual.......

Precise polar alignment

for the MT-1 and MT-1C mounts

For precise polar alignment for MT-1 and MT-1C mounts observe

two bright stars in the west and in the east by turns, using the eyepiece

f’=25mm with reticle.

If during the observation of the star in the east it slowly shifts, so

that you have to lower the top end of the telescope to follow it, then

the northern (upper) side of the R.A. (polar) axis of the mount should

be slightly lifted up.

If you have to lift up the top end of the telescope to follow the star

in the east during the observation, then the northern (upper) side of

the R.A. (polar) axis of the mount should be slightly lowered down.

For the precise azimuth adjustment follow the same procedure to

observe a bright star on a celestial meridian in the south. If during the

observation the star slowly shifts, so that you have to lower the top

end of the telescope to follow it, then the northern (upper) side of the

R.A. (polar) axis of the mount should be slightly moved west.

If you have to lift up the top end of the telescope to follow the star

in the south during the observation, then the northern (upper) side of

the R.A. (polar) axis of the mount should be slightly moved east.

After 20-30 minutes of such observations and adjustments, it is

possible to achieve a precise polar alignment, when any observed

star would stay on the intersection of the crosshairs (reticle) of the

eyepiece for 10-15 minutes without additional correction needed on

the Dec. axis.

The above could do with a couple of illustrations to make it less confusing.

Andy.

[jason.p]

Yes, you're right Andy. The outside diam of EP is 32mm, thanks for pointing it out. I wouldn't have realised till I tried to fit them to a new Barlow!

The EPs are held in the barrel of the focuser by a sprung band on the top edge (same as the Barlow).

As all this is very new to me, I think my best bet is to get used to handling the scope as it is then fine tune when I've got a better idea what I'm doing. In the meantime I'll bear all the advice in mind and come back to it later.

Thanks again

Jason

[AndyH]

Oh !

I had presumed the tube above the knurled piece, was the barlow. So it, including the knurled piece is all part of the focuser then? Does it screw off to reveal an M42 thread below?

I'll take a pic of my 2M's focuser to let you see the difference.

Andy.

[RichardL]

Some while ago I bought a new draw tube - M42 thread at one end to screw onto the focuser, and standard 1.25" barrel the other end complete with thumbscrew. Don't ask me where I got it! I tend to use this all the time now, with a set of Meade eyepieces. You must be able to get such a device from somewhere I would have thought. Not that I have looked ...

[AndyH]

.................As all this is very new to me, I think my best bet is to get used to handling the scope as it is then fine tune when I've got a better idea what I'm doing. In the meantime I'll bear all the advice in mind and come back to it later.

Thanks again

Jason

I'll second that idea

[AndyH]

Some while ago I bought a new draw tube - M42 thread at one end to screw onto the focuser, and standard 1.25" barrel the other end complete with thumbscrew. Don't ask me where I got it! I tend to use this all the time now, with a set of Meade eyepieces. You must be able to get such a device from somewhere I would have thought. Not that I have looked ...

Hi Richard.

You would have thought so, but I've not seen one:(

If you know of one, do please post it up!

A lot of these adapters seem to have the finer M42x0.75 thread, rather than the courser M42x1 .

Andy.

[jason.p]

Oh !

I had presumed the tube above the knurled piece, was the barlow. So it, including the knurled piece is all part of the focuser then? Does it screw off to reveal an M42 thread below?

I'll take a pic of my 2M's focuser to let you see the difference.

Andy.

Yes, the tube with the knurled piece screws into the focuser body and has the split ring band to grip the EP. Not sure if there's an M42 thread below, I'll have a look in daylight.

(I've just come in from my first look at the moon. I had intended to try out various combinations of EPs and Barlow but I was getting eaten alive by little biting insects and had to abandon it. What I did see was amazing. I've really got the bug now! Unfortunately the moon's gone behind a tree now. I'll be out there with the chainsaw tomorrow:D)

Jason

[jason.p]

I've just had another look at the focuser. The EP holding tube with the knurled collar unscrews. Then there's an adapter with the same thread (looks like 42mm) and a washer. The threads appear to be the same as the EP tube screws onto both threads.

[AndyH]

Righto. That's good. Confirms with what Richard said about his.

It'll probably be an M42x1(1 being the the pitch of the thread), which is the common Russian camera thread(but not so common for adapters available today. M42x0.75 or T2 is a much used thread).

This means, in the future, if you wish to use other std 31.25mm eyepieces etc and have them fit securely, there is a way. Of course you can simply wrap a single layer of elec tape around their barrel and use the focuser as is, which will do the same job, just won't be as pretty. I have looked out a few adapters that would work and I'll take some pics. This is all optional of course and not strictly necessary.

One thing I'd consider, is obtaining an 8mm eyepiece. That'll plug the magnification gap with your current ep's & barlow. It would give you 150x, which can sometimes be a more useful high mag power than the barlowed 25mm ep(192x), especially when the seeing is poor(ie: the air is very turbulent, causing high powers views to be washed out and mucky).

Andy.

[AndyH]

I've put some pics of eyepiece adapters(both the std Tal 2M version for a yr 2000 scope and a 3 piece set) on my flickr pages

http://www.flickr.com/photos/8986911@N08/ (click on the pics to bring up a bigger pic & explanations)

showing how an older Tal could be uprated or if the original adapter was lost.

Thought I'd post a link rather than clog up this thread with pics.

Andy.

[jason.p]

Thanks Andy, it seems I have a few options if I want to upgrade in the future. I think I might go for an 8mm EP as you suggest and pack it out with tape for the time being. Could you recommend one? I don't mind spending a bit, but don't want to over or under do it.

Thanks

Jason

[RichardL]

Here's the standard-sized drawtube alongside the TAL original. Doesn't help much, I know. I probably bought it 10-12 years ago - I suspect from BC&F. You might also try Optical Vision; I know they used to stock lots of TAL accessories.

[AndyH]

Thanks for all these pics Richard(and Jason).

Really helps our understanding of these older 2M's.

[AndyH]

Oh pants.

Richards pics have dissapeared with the software switch

[AndyH]

Jason - I remember you asked about eyepieces for the 2M.

This site here http://www.astrosurf.com/luxorion/reports-epsuggestions.htm gives a good explanation of various types etc. Pretty good read.

Andy.

[jason.p]

Jason - I remember you asked about eyepieces for the 2M.

This site here http://www.astrosurf...suggestions.htm gives a good explanation of various types etc. Pretty good read.

Andy.

Excellent link, thanks. I've still got my eye on that 8mm EP. I think it's still available. Just have to wait and see how much the power pack costs to fix. It's in the hands of my friendly PC tech who sees it as a challenge!!

I'll keep you posted.

Jason