Tele Vue Pronto - I messed up! :-(

[DRT]

This post is long overdue as the error I made happened about a year ago and the Pronto has sat doing nothing ever since.

I bought this scope second hand about two to three years ago. After a while I noticed that there was some fungus stuck to the inside face of the objective. Not wanting to mess around with the sealed collimation screws I released the retaining ring from the front of the lens cell and carefully removed the two lens elements. This is where things started to go wrong.

Firstly, I very carefully washed the lens elements in warm soapy water to remove the fungus. I also managed to remove most of the blackening around the edges of the lenses

Then I tried to re-assemble the lens cell but had forgotten to mark the edge of the two elements to ensure I put them back in the same alignment. The washing had removed any trace of helpful marks that could have been used to work this out so there is a 359 out of 360 degree chance that they are now in a different place to where they were when Tele Vue put the scope together

I have checked the collimation of the re-assembled scope and that is fine but the views just don't seem to be as sharp as they were previously and CA is definitely more apparent than it once was. This could be either the lack of blackened edges or the misalignment of the objective elements - or possibly both  

I thought about calling TV to see if I can send it to them to fix but that's going to cost £100+ just for the postage and would no doubt have a repair bill to pay. So I have decided to post this question in the hope that the collective knowledge of SGL can perhaps advise me on how to go about sorting the alignment of the lens elements.

Any suggestions?

Edited January 18, 2017 by DRT

[ollypenrice]

I would check the time zones and give TV a call on the phone. I had a problem with an accident-damaged TV scope once and they were absolutely marvellous on the phone. They gave me full instructions on how to sort it out and, when followed, these instructions worked. Have pen and paper to hand.

Best of luck,

Olly

[Cjg]

Olly's advice is sound ;-)

If that doesn't work for you, then I wonder if the dude who fixes / tests the scopes for FLO could help? he'll have the kit and the knowledge to sort....is based in Cambs I think, so less £££ to post?

Good luck,

 

Chris

[ollypenrice]

8 minutes ago, Cjg said:

Olly's advice is sound ;-)

If that doesn't work for you, then I wonder if the dude who fixes / tests the scopes for FLO could help? he'll have the kit and the knowledge to sort....is based in Cambs I think, so less £££ to post?

Good luck,

 

Chris

Es Reid. Good idea!

Olly

[Moonshane]

I'd have thought blackened edges might reduce contrast ever so slightly (possibly imperceptibly?) but of course alignment / putting in the right way round etc might cause problems as might not putting in foil spacers etc.

 

[Peter Drew]

Only a few simple things to go wrong. In correct orientation of the lens components, incorrect spacers, overtightening of the lens after reassembly. In most cases the plano-concave element goes into the cell first with the concave curve facing the sky. This is followed by whatever spacers were originally provided. Last of all. the biconvex lens with the shallower curve facing the sky. The outer retaining ring should be replaced such that it just touches the lens assembly.   

[DRT]

7 minutes ago, Peter Drew said:

Only a few simple things to go wrong. In correct orientation of the lens components, incorrect spacers, overtightening of the lens after reassembly. In most cases the plano-concave element goes into the cell first with the concave curve facing the sky. This is followed by whatever spacers were originally provided. Last of all. the biconvex lens with the shallower curve facing the sky. The outer retaining ring should be replaced such that it just touches the lens assembly.   

I am certain that I put the lenses in the correct configuration (i.e. both facing the right way and in the correct order). The cell has a metal spacing ring rather than foil spacers and I made sure the outer retaining ring was only just touching the lens so that is three variables ruled out.

I'm pretty sure it is the rotational alignment of the lenses that is the issue. I am making an assumption that in a good quality telescope someone would send a bit of time optimising this to get the sharpest possible image?

 

 

 

[Stu]

I suspect it may come down to just the relative rotation between the two elements Derek, assuming you reassembled them the correct way round? The TVs are wide air spaced doublets as I recall, no foil spacers but a metal band which sits between the two. So long as this is seated correctly along with the lenses then it may be a case of testing with an artificial star and rotating the front element until you get to a best result?

I did a similar job with my old Genesis and got it pretty good in the end.

[DRT]

6 minutes ago, Stu said:

I suspect it may come down to just the relative rotation between the two elements Derek, assuming you reassembled them the correct way round? The TVs are wide air spaced doublets as I recall, no foil spacers but a metal band which sits between the two. So long as this is seated correctly along with the lenses then it may be a case of testing with an artificial star and rotating the front element until you get to a best result?

I did a similar job with my old Genesis and got it pretty good in the end.

Yes,that's the design of this one, Stu. I'll give the artificial star thing a go. How did you go about making the small rotations of the front element without covering it in grubby fingerprints?

[Stu]

If I recall correctly, I used something slightly rubberised, possibly a glove just to give good grip without leaving a mark

[DRT]

8 minutes ago, Stu said:

If I recall correctly, I used something slightly rubberised, possibly a glove just to give good grip without leaving a mark

I'll steal one of Mrs T's pink Marigolds

 

[Chris]

Stu has a point, you probably don't have much to lose. Try turning the front element until it hopefully improves. I'd go for the thin latex/nitril gloves, the type you get from the hardware store for painting etc, they will be a lot more tactile than the marigolds (I know you were probably joking about the marigolds really  ).

If it really goes down hill from there, then E S Reid might need calling on the Bat phone.

Edited January 18, 2017 by Chris Lock

[DRT]

2 minutes ago, Chris Lock said:

I'd go for the thin latex/nitril gloves, the type you get from the hardware store for painting etc, they will be a lot more tactile than the marigolds

Cheers - I'll try to get some of those

 

[Moonshane]

hi mate

I have some I can post if you want although I think I got a pack of 100 pairs for about £3.

[DRT]

43 minutes ago, Moonshane said:

hi mate

I have some I can post if you want although I think I got a pack of 100 pairs for about £3.

Thanks for the offer, Shane, but I'll pick some up from Wilkos around the corner from me.

Cheers

[Peter Drew]

I think TV would be most put out to hear someone suggesting that rotating the elements of their objects would improve the performance. The tolerances adhered to by the top end manufacturers should ensure that radial  positioning of the elements is unimportant. However, if I remove an objective and the orientation is unmarked I always mark it just in case. Whenever I had objectives made to order I always asked the opticians to mark the orientation of the components as they were to the final testing. 

[DRT]

1 hour ago, Peter Drew said:

I think TV would be most put out to hear someone suggesting that rotating the elements of their objects would improve the performance. The tolerances adhered to by the top end manufacturers should ensure that radial  positioning of the elements is unimportant.

Oops! Fear not - I am taking full responsibility for this mess and wouldn't dream of suggesting it was TV's lenses that were at fault.

Let's just agree that I have put them in squint or the wrong way round