Help with new telescope, it will not work with a 9mm lens

[mdstuart]

Good evening

I recently bought a reflecting telescope which I think is an old TAL. It has a 130mm mirror and one eyepiece which is a F25mm.

I tried buying another eyepiece ( a 9mm Celestron ).

But firstly the eyepiece is only just (about 0.5mm) smaller than the focuser tube….Not a problem I thought I will by a thin piece of rubber.

But the main issue is that I cannot focus with the new eyepiece. In order to get it to focus I would need to be able to put the eyepiece further in towards the diagonal mirror by a few more mm.

Perhaps it will work but only with eyepieces down to say 15mm?

Any help would be appreciated.

Regards

Mark

[barkis]

Hi. Mark. If your 25mm eyepiece works ok, then see how much further your focuser can be moved towards the diagonal mirror. I suspect it won't be very far, and that's why you can't focus using your 9mm ocular. Probably, you will have to consider moving the main mirror up the tube a little bit. The only other suggestion I have is getting a Barlow 2x or 3x. The 3x Barlow, and your 25mm eyepiece working together, will give you almost the same magnification as the 9mm. Those on the forum familiar with the Tal 130 may have a better solution for you.

Ron.

[Whippy]

Welcome to SGL Mark . Post up a pic of your scope and I'm sure someone would be able to ID it for you..

Meanwhile, you shouldn't have any trouble focusing with a 9mm eyepiece. Apologies if I sound condesending but I'm guessing you're new to the hobby so I won't get too technical . Where you put the eyepieces into the telescope (the focuser) there should be one or two little screws that should hold the eyepiece in place, you shouldn't need rubber rings to hold them in place.

Otherwise your optics may need to be collimated. All that means that your mirrors may be out of alignment and the need to be put back in place. You can buy various tools that will help you to do this fairly easy job. Have a look here: http://tinyurl.com/yc8j44 .

Tony..

[AndyH]

Mmm.. Tal didn't do a 130mm mirror, i'm sure. 120mm aye, check out http://telescopes.ru/product.html?cat=1∏=11

I have an old Tal M(3" mirror, battleship grey) that has 'old ' style eyepieces. I'll post a pic or two when I'm sober. Sorry, hitting a Heineken mini keg just now. You may have to alter the mirror like i did with the 'M'.

I'll get back to you, when focused on the job.

Burp,

Andy.

[The Warthog]

If you can bring it to focus with a Barlow in it, then the problem is certainly a lack of inward travel.

[mdstuart]

Tube is 132m perhaps mirror is 120mm. Definitely a TAL based on the mount.

25mm lens focuses when moved out by 18mm using focuser. (which is a pretty big about 7cm in length).

9mm lens with focuser right in seems to be about 2mm short of focusing.

I might try a 15mm if I can borrow one and see if that works.

I have a 30mm coming which should work with the 2x barlow I have also bought on e-bay. The 25mm TAL lens is 0.1mm to big to fit in the Celestron Barlow.

By the way the telescope is great I can see M57 but its soooo small.

Mark

[SteelRat]

Hello and welcome Mark

132mm eh? Hmmm the ol' 120mm Tal120 I'm told always had the same OD tube as the 110mm Tal1 - they both used to fit snugly in standard synta 140mm tube rings. All the smaller scopes like the TalM and Alcor had much smaller tubes (sub 100mm)

Without a picture of yer scope here please;

1) What's the colour of the telescope?

2) Does the focuser on y'scope have a pinch screw to hold the eyepiece in place, or does the 25mm eyepiece just push in?

3) What's the length of the telescope tube?

Cheers

Matthew(SR)

[The Warthog]

Sounds like you do have room to move the miirror up the tube a mite.

[peeceeTal2M]

Hi, i had an old TAL-1 made around 1995, it worked fine with the supplied eyepieces but wouldn't focus with any other plossl's i had. I got in touch with TAL and they suggested moving the miror cell forward in order to use these eyepieces.

[SteelRat]

Just been out and measured my Tal1 tube - inner diameter is 133mm.

Sounds like you do have room to move the miirror up the tube a mite.

moving the mirror forward in order to use these eyepieces.

Yeah - I did that with mine so orthos would work with it.

[mdstuart]

So if I want to move the mirror up three mm in the tube how would I go about it.

Do I use the three visible screws at the base of the mirror.

(click to enlarge)

Will I not get the mirror out of alignment (collimation)

Is it really that easy?

By the way I measured the distance from the tube again to the eyepiece right in and it is 70mm. Using the 25mm lens supplied it is at 78mm.

Mark

Mark

[The Warthog]

Yep. Unscrew the screws at the end of the tube, drop the mirror out, and drill three new holes about 15mm up the tube, and then line up the mirror cell and put the screws back in. You will have to recollimate, but that's a fact of life with reflectors.

The measurement you made isn't of any use, unfortunately, as you have to measure to the focal plane of the eyepiece, and that isn't so easy to determine and depends on the optics.

[tom.yates]

Why cant you just have your 1.25 adapter bored out so it will reach focus that's what i did it took the local engineer about 30 seconds to do it at a cost of a pint.

[SteelRat]

Woah Mark - no drilling or engineering required. PM on the way matey.

[The Warthog]

Send me a copy of that PM while you're at it, bud!

[trusty1948]

I am also new to the hobby. Baught an Orion 10" Dobsonian.  Having the same focusing problem.  Would appreciat seeing the PM discussed.

The scope have a 1.5in adapter and came with 1.5 Inch eyepieces.  I suppose buying 2 inch eyepieces would take care of the focus issue.

[Cornelius Varley]

18 minutes ago, trusty1948 said:

I am also new to the hobby. Baught an Orion 10" Dobsonian.  Having the same focusing problem.  Would appreciat seeing the PM discussed.

The scope have a 1.5in adapter and came with 1.5 Inch eyepieces.  I suppose buying 2 inch eyepieces would take care of the focus issue.

It might be better to start your own thread on this subject. This thread is 13 years old and some of the contributors to the thread are no longer active.

22 minutes ago, trusty1948 said:

The scope have a 1.5in adapter and came with 1.5 Inch eyepieces

The eyepieces will be 1.25" not 1.5".

[DaveL59]

I'd agree, especially as this thread relates to the older TAL telescopes that used a non-standard eyepiece range, so any solutions contained here would be completely different than for a modern scope using standard 1.25-inch eyepieces.

Edited May 8, 2020 by DaveL59

[John]

2 hours ago, trusty1948 said:

I am also new to the hobby. Baught an Orion 10" Dobsonian.  Having the same focusing problem.  Would appreciat seeing the PM discussed.

The scope have a 1.5in adapter and came with 1.5 Inch eyepieces.  I suppose buying 2 inch eyepieces would take care of the focus issue.

Hello and welcome to the forum.

You might want to start your own thread with your questions.

It's likely to get overlooked tagged onto the end of this old thread.