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Tips for removing lens cell from AP130

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#1 johndgaul

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Posted 23 April 2013 - 08:43 AM

Hi all

I've noticed what looks like a cloudy film when holding the lens of an AP130GT up at a slight angle to a bright light. It looks a bit like condensation fog, but I'm pretty sure it's not. My suspicion is that it's the early stages of fungus growth on the rear side of the lens. I don't remember it being there before, and would like to make a closer inspection.

Could you give advice on the removal of the lens cell from the optical tube? I've removed the dew shield, but not gone any further. How does the lens cell attach to the OTA - is it threaded on, and held in place by grub screws? It seems to have three screws around its circumference - will it unthread if these are loosened? There are also some screws on the front face of the lens cell, which I imagine are for collimation adjustment - are they? I don't want to do anything that would affect collimation, so thought it would be wise to ask before doing anything! :)

Being based in the UK, I'm hoping to deal with this myself rather than ship back to Illinois.

I've emailed Astro-Physics for guidance and haven't heard back yet. But it would be GREAT to get your views and practical tips on this.

Thanks very much in advance

John

#2 Starhawk

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Posted 23 April 2013 - 09:05 AM

The ap guys have been at NEAF. Give them a chance to get back and answer- they'll tell you exactly what to do or not. If you want to do something good while you wait, dry out the OTA with desiccant.

-Rich

#3 Paul G

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Posted 23 April 2013 - 11:30 AM

Check this out:

How to clean an AP refractor objective (video)

I've removed objectives from AP scopes numerous times for cleaning, never had any problems. I always contact AP first to confirm which set of 3 screws to remove just to be on the safe side. This post tells which screws are which:

Which screws do what on an AP objective cell



#4 johndgaul

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Posted 23 April 2013 - 05:44 PM

Rich, yep, George at AP got back to me, with a nice recipe for home-made cleaning fluid as well.

Gus, thanks for the links and positive experience! I admit I'm a bit nervous with this, as I'm quite inexperienced in dealing with scopes. I'm sure I'll get over it!

I hope there's no permanent etching of the coatings.

I'm waiting now for some Purosol (already have Baader Optical Wonder stuff) and lint free optical wipes to arrive, then I'll get at it, in daylight. I'll post back here with my experience, and a beginner's guide to the process.

Thanks again

John

#5 johndgaul

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Posted 23 April 2013 - 06:13 PM

On the 130GT, there are two circular holes on the face of the lens cell:
(photo)
Presumably, for an optical wrench...

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#6 johndgaul

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Posted 23 April 2013 - 06:15 PM

And three evenly-spaced hex-head screws around the circumference (photo):

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#7 johndgaul

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Posted 23 April 2013 - 06:28 PM

Not sure how it comes off the OTA. I'm guessing by loosening the screws around the edge.

#8 johndgaul

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Posted 25 April 2013 - 04:12 AM

I'm heartened by reading the success story in this thread:
http://www.cloudynig...2565988/page...

My scope doesn't _look_ nearly as bad, so hopeful it will come out OK.

Still haven't got a definite answer on how to remove the 130GT cell from the OTA. I don't want lenses falling out :)

I think I'm going to get on with it this evening, if I can get home from work in daylight.

#9 dedo

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Posted 26 April 2013 - 05:11 AM

I would advise not to touch the three side screws by any means without beeing sure about what you're doing.

#10 johndgaul

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Posted 26 April 2013 - 12:50 PM

dedo, you're right to suggest that - better safe than sorry :)

I've found out more about this now. The AP130GT is different to many of the other AP soopes, in that the lens cell is integrated to the OTA, and can't easily be detached.

To get access to the rear of the lens, the lens assembly itself needs to be removed.

I found some great instructions for this in a PDF on the AP Yahoo user group.

The three hex head set screws around the edge of the lens cell press (gently!) against the retaining ring for the lens - the part with STARFIRE EDF APOCHROMAT etc. engraved on it.

With the set screws removed, the retaining ring can be removed and the lens glass assembly pushed out of the cell. eek!

I haven't done this bit yet, as I'm a bit wary of handling the glass outside of a cell :)

#11 dedo

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Posted 26 April 2013 - 04:32 PM

mmmm I can see a lot of fun with collimation :p

#12 APtelephoto

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Posted 26 April 2013 - 06:01 PM

No worries! The only consideration in this design with respect to collimation is seating the sections of the scope together. I've broken down the scope into the three main sections many many times for transport. I extensively employ it as a "long lens" for daytime wildlife photography and my main scope for cruising the night sky. With all the pollen and debri I encounter, I've also removed the cleaned the lens 3 times over the last 4 years. :smash:

Only once did I have an apparent slight collimation issue which turned out to be one of the section collars not being snugged up :foreheadslap:, just BE SURE TO NEVER TIGHTEN THE LENS RETAINING RING! :shameonyou: :shameonyou: :shameonyou: You thread it until it touches the lens and then back it off. Use a marker on the ring and the anodized portion of the tube as an index mark before you dissassemble it, that way you have a visual reference of how far to back it off after contact. Call Howard at AP if you have other concerns!

It has proven to be an extremely durable system in my experience. :bow: :bow: :bow:

Pete

#13 johndgaul

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Posted 27 April 2013 - 02:02 PM

Thanks, Pete. It was your instructions that I found on the AP Yahoo user group. I always enjoy looking at your photos - just amazing.

I just took it all apart a few minutes ago, and put it back together. In the end, I didn't touch the optic's surfaces with any cleaning fluids! Just a dust with a blower and a very light touch with a camel hair brush. It all went back together beautifully as it was. I marked the cell with the orientation of the lens and put it back the same (don't know if this was necessary, but just in case), also the retaining ring to its original position which I'd noted - so as not to pinch the lens.

I suspect I might be suffering from scope hypochondria reading scare stories about fungus and mould on these forums :) The glass looks super clean!

Pete (or anyone else with a similar scope), is it possible that the "haziness" I'm seeing when held at an angle to bright light is just a reflection from the glass/oil interface in the triplet lens assembly?

Anyway, I enjoyed getting to know this fine instrument better. The closer I look, the more I can appreciate the workmanship that went into it. And I'd feel confident with this procedure in future should the lens really need cleaning.

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#14 johndgaul

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Posted 27 April 2013 - 02:09 PM

In the background on the right, the "tower" I made to push the lens out of the cell, by lowering the telescope's tube over the tower. A toilet roll taped on to a plastic tub containing coins to weight it down, with Kleenex (plain, no additives) tissues and lint-free PEC pads on top to contact the lens surface.

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#15 johndgaul

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Posted 27 April 2013 - 02:14 PM

The lens retaining ring, lens side with pads.

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#16 johndgaul

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Posted 27 April 2013 - 02:15 PM

Optic safely back in the cell

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