The Collimation Saga : Part 2

[Charic]

Also looking back at your secondary pics, because the corrector is part of the secondary mirror, it looks as if it will self align when re-installed, so whatever your task, it may be easier to do than you imagine.

[bambuko]

One of the problems with collimating this design is that the Barlow/corrector gives a very reduced image of the optical components making it difficult to judge by eye in what manner components need adjusting...

Yes, it is a bit fiddly, but on the other hand spherical primary and fixed focuser and primary will make it fairly tolerant anyway?

...To be honest, Ive really only had success doing this on a star image whilst adjusting the secondary. 

I have tried adjusting it using star image and to be honest made a right pig of it, so I took it back and leisurely adjusted it using sight tube.

I am sure it could be better   but it is OK for now.

Seeing is affecting it far more at the moment than collimation (at least in my humble view).

[Charic]

Peter Drew...........yeah, it can make it slightly awkward. I believe these type of scopes are made for low cost, mass production, and ease of use, in as much that collimation isn't so critical with a spherical mirror(Newtonian) I can strip down completely and re`assemble my 127EQ in about 40 mins now, That's everything out, even the primary mirror( Centre marked it last time for the fun of it) I may even 'Bling' this scope just for Lunar use when friends or enthusiasts are over. maybe they'll  be able to take the scope away with them. I`ve offered it out before, for keeps.

One other thing, so that members don't get confused. The Barlow corrector fitted to these telescopes, don't allow the Laser spot to hit the centre of the primary mirror, as the beam is scattered. However, if using a Barlow after secondary mirror alignment, A Barlow is very effective in setting the primary mirror, because the laser beam is now scattered, its easier to see the shadow of the primary doughnut as an image in the Laser tool. 

[bambuko]

Also looking back at your secondary pics, because the corrector is part of the secondary mirror, it looks as if it will self align when re-installed, so whatever your task, it may be easier to do than you imagine.

Assuming we have now drifted to TAL-120

Corrector is fixed/glued to focuser assembly and not part of secondary mirror.

Now you've done it!..............F1Bird is the clue?

You mean "...I don't think yesterday was the best day to be asking for collimation advice! Think I'll keep a low profile for a bit!..."

I hope she is not keeping low profile - there is no need for it

[Charic]

bambuko..........just looks like a lens holder in the pic on your thread?

[andyman]

Glad i steered clear of this design....too much faffing about for my liking

[itmo]

hate to think what a cheap corrector does in a cheap telescope. Usually cheap barlows are a total catastrophe for image quality and I assume these corrector designs arent that much better. 

[bambuko]

bambuko..........just looks like a lens holder in the pic on your thread?

There are two photos and one is a bit deceiving because it only shows the lens holder with spider arms secured to the secondary (here), but this is not my pic and I don't know how to do it without breaking the glue that fixes the corrector lens holder to the focuser (the second picture here shows my assembly) - I guess this is PITA part of this design.

On the other hand once you get secondary right there is nothing else to adjust (primary is fixed in TAL-120) and all TALs are built like tanks and seldom require any collimation anyway.

My problem was not the collimation but the play in focuser.

[Charic]

andyman.............No-one tells you, till its too late. I bought the 127EQ last October. very cheap though, got some great books in the deal, but soon learnt that telescopes pitfalls. Its in the shed now. Only learnt from the help and advice from SGL. The telescope blew me away looking at the Moon for the first time, no doubt, but thats about its limit for me. Theres not enough aperture to get the bigger better views, for anything else, hence my upgrade after only 10 Days

[bambuko]

hate to think what a cheap corrector does in a cheap telescope. Usually cheap barlows are a total catastrophe for image quality and I assume these corrector designs arent that much better. 

Those that are bad are really bad, TAL-120 is actually OK.

Having said so, given a choice between TAL-1 (full tube length, without corrector) and TAL-120(shorter tube with corrector) I would not hesitate and choose  TAL-1.

[Charic]

bambuko..............I`m missing the point somewhere? The secondary looks the same in both pics, just disassembled in one, although attached to the focuser? I`ll have another look

[andyman]

andyman.............No-one tells you, till its too late. I bought the 127EQ last October. very cheap though, got some great books in the deal, but soon learnt that telescopes pitfalls. Its in the shed now. Only learnt from the help and advice from SGL. The telescope blew me away looking at the Moon for the first time, no doubt, but thats about its limit for me. Theres not enough aperture to get the bigger better views, for anything else, hence my upgrade after only 10 Days

Before i picked my first scope i did a fair bit of research...about 2 months worth to be exact.took into account the size,weight,aperture, transportation and it certainly pays to do your homework when choosing your first scope

[Charic]

andyman..........absolutely. Its always a recommendation now for folk to try before you buy  and study ect.  I've been into astronomy for over 30 years, but its all been with binoculars. To be honest, a telescope never really interested me, due to its bulk and sensitive construction, so always used binos, from 10x50 to 20x80 to my preferred choice now of 7x50's. And working nights for the last 13 Years allowed many views of the night skies, but only last Year during Leonids, did  I ask my self, Maybe its time to get the telescope, now I've settled down in one area. The advice was sought here, and I've no regrets so far.

[englishmike]

I have had a number of Tal 1 Tal 120 Tal 150 Tal M  Tal 65 ....

I have found the TAL1(s) ( I have had about 10 of these)  to be suberb , very easy to work with, the later ones with the conventional focus control and suberb BArlow and lens being the one to get. BUT early ones with sprung eyepiece clips didnt focus with conventional eyepieces. Shaving 15mm of the length of the tube ( primary end) solved all that. Tal1 optics always suberb.

Tal 150 was fantastic , Tal M punched much above its weight (see attach if Clavius), Biggest prob with the Tal1 and the Tal m is the flimsy clamp hinges which break ! Easy to fix though..

Then theres the 120.!

I bought this really for the motor and the handy  tube clamp design. BUT I also found the images a little out of focus AND colimation is impossible as the primary is factory set  glued in its carrier and cant be adjusted without a boj! Another worry is the spider holding the secondary does not sit in the middle of the tube , making the secondary 5mm of centre ! What a dissapointment. I am now going  to see what I can do about this. I also think the image might be better if the intergral corrector and barlow are removed from the focuser. (why include an external barlow with the scope when it already has an integral one.) More later ....

TalM BArlow Webcam 640 480 2 Clavius .bmp