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Tal-1 nightmare in Worksop


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Oh my...where to begin? looking for advice really.  

Last year I purchased an inexpensive second hand TAL-1 reflector..purchase online..came via Currier in working condition if a little bit dirty...but no bother.. it worked :-) On odd nights since last December when it arrived I have dragged it out into the back garden and loved every minute pointing it around the skies...its been like a return to younger days. okay..thats the romance out of the way. 

Last week I decided to give the whole telescope a deep clean..the mirrors were well dusty so I found the resolve to have a crack at cleaning them..looked at astrobabies  web site and her tutorial..the job looked within my grasp so I went for it...had the OTA apart..cleaned the mirrors..gave the whole thing light lube and spit and polish...it was all going brilliantly...then I tried putting the thing back together again...went well...went through my notes about collimating..followed them to the letter..............A week later I am still playing around with this Russian nightmare!! why oh why oh why oh why did I start down this road to hell??? While you can get the telescope to within reasonable focus at lower magnification the sharp images at high magnification that I got previously are unattainable.....so today ( monday) I decided to throw money and technology at the blumming thing...yes!! a laser collimator would solve the problem..that's what's missing here!!..so off I toddled to Rothervalley optics purchased a Sky watcher model and brought it home and set about righting my bad deeds with the TAL......4 hours Ive been here faffing around with this monstrosity!!..Ive followed the instructions to the letter...christ..the end result is worse than if you attempt to align it by line of sight!!

Tonight Ive just managed to stop short of pulling the whisky bottle out..getting hammered..calling the telescope rude names in the shed before sleeping off my booze induced coma out in the passageway with the dog!! Why oh why is something that should be so easy so ridiculously complicated!!!!!!!!!!!!!!!!!!!!

( now sobbing uncontrolled ) please someone help!...I promise never to do this again! I just want my telescope back to how it was and be able to look at the moon again....I feel it must be something simple that I am over looking...but its gonna have to be pointed out to me...and I am not one for admitting defeat usually...but on this occasion...I AM!!!!

Standard Tal-1, not the motor driven version.. made in 1996...it has a 1.25 inch focuser and EP'S.....

davsim66@googlemail.com

with best regards

David

p.s have posted this in eastmidlands section as well as that is where I live.

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I don't know the tal model but on the skywatcher scopes, you have two sets of primary scrws. One set are the collimating screws, the other set are the locking screws. Your collimating screws move the primary up and down the tube so if this is off, it can make things difficult at either end of the magnification spectrum. To move it up the tube a bit, give each of the collimating screws a full turn, to move it down the tube a bit, do it the other way. Take your time, be patient and make notes of the results. I had to do this when I upgraded to 2" EPs.

Make a collimating cap. Take a focuser blanking cap and drill a small hole (no bigger then a couple of mm) in the middle. By blocking the primary with a bit of paper make sure your secondary is circular and central (as in Astrobaby's guide). If it isn't use the secondary adjustment screws to change it. They don't need to be tight so undoing them a bit can be used as well as doing them up. Take the paper away and you should just be able to see all of your primary clips and the centre spot should be about central. If not, use the primary collimating screws to adjust as needed. Small and slow. The locking screws only need to touch the surface, they do not need to be tight.

If using a laser, put it in the focuser and tighten it up. When it's turned on, first check that it is in the middle of the centre spot on your primary. If not, you need to adjust the secondary until it is in the middle. Once it is central the beam should reflect back along the tube, hit the secondary, travel up the focuser and disappear up the hole in the laser. If it doesn't you need to adjust your primary with the primary collimating screws. Watch the laser collimator to guide the beam to where it needs to be as you adjust the primary.

If any of this doesn't make sense, let me know. Take it slow and steady, make notes and don't get annoyed. It can take a while if you are not used to it. Also, you need to make sure that your laser is collimated. Rest it in two v shapes pointed at a wall a few meters away then rotate it. The red spot should not move. If it does, your laser is out and needs sorting. If it is, you can collimate reasonably well with just the collimating cap described above in conjunction with a star test.

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my starting point was the tals own instruction manual...some interesting translations in there I can tell you,  but I understand the principles. when looking down the focuser the secondary should appear round and be central to the walls of the focuser tube..the primary should be central in the secondary s  reflection...check...done all of this and in gradual steps.. but the image seen at high magnification is still a long way off sharp.. using the collimator I have laser spotted the centre of the primary by adjusting the secondary screws..check...then have adjusted the primary via the screws to find the centre of the target on the laser collimator..that's achievable.....how ever...when this is done the reflection of the secondary and the spiders veins are no longer central when looking down the focuser tube...the secondary appears a long way off centre..??? go figure??? this is my dilemma! i have considered the secondary and how its positioned under the focuser...have done very gradual adjustment there...I have also considered the primary and how far advanced up the tube it is towards the secondary...I understand the principle of focal length...but the adjustment screws at the back of the primary are so short that there isnt that much length to adversely affect the focal length of the telescope...or paerhaps this may be the case...?????? Guessing I am tired at this time of night...I will have another crack at it in the morning with a fresh approach............

thankyou for you imput :-) appreciated...as are any of thoughts from contributers :-)

David

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Firstly... the reflection of the secondary doesn't matter as long as the secondary is central in the focuser using the colli cap and the primary is circular in the resulting image with all the primary mounts visible. Don't confuse yourself unecessarily.  Secondly... even small movements of the primary screws can have a big effect on apparent focal length. When I had to move my mirror, two turns of the screws was way too much. It moved the focus completely out of reach. 1 turn was all that was needed.

If all of the above is correct, it may simply be the seeing. That can make a massive difference. Moving the primary up or down the tube a little may sort it though. Try a full rotation of the screws one way then recollimate. If it makes it better then all good, if it makes it worse, undo and go a full turn the other way then retest.

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Ok, maybe this will help a bit.   Using a simple collimation cap, get the secondary central under the focuser and pointing at the primary, so that the reflection of the primary is central in the secondary.

Whilst you are doing this, IGNORE the reflection of the spider and secondary.  When you have sorted the secondary as above, then leave it alone for the next bit.

The reflection of the spider and secondary can then be centered using the adjustments on the primary mirror ONLY.  Leave the secondary alone, you have already sorted that.........

When you are happy and everything looks ok, then you can fine tune the collimation on a defocused star at high power, say 150 - 200x.  The fine tuning can be achieved by adjusting the primary mirror only.

Yes I know that collimation can be bring up differences of opinion, and at the risk of being wrong, what I've just described should sort your Tal 1 with its fairly forgiving F 7.3 focal ratio.

Good luck, Ed.

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try my guide to collimation http://stargazerslounge.com/topic/197640-collimation-and-star-hopping/

others are very good but sometimes go into a little bit more detail than necessary. I tried to mention what's important and what's not.

does the mirror sdtill look in good condition after cleaning? if it does, then you'll be fine.

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