10 replies to this topic

[Lentini]

I donated an ST80 and the recipient has suffered front lens scratches. They are asking if they can get a replacement lens. I assume just the outer/front lens.
 

Sounds like a No to me. First, not sure how you’d find a proper lens. Second, not sure how user-replaceable an ST80 front lens is. And not sure how hard it would be to find an entire lens set replacement. Sounds more like a replace-the-scope. 
 

Problem is they’re in Uganda, so logistics aren’t standard.

 

Anyhow… I was curious if anyone had tried replacing lenses like this.

[Polyphemos]

The first thing will be to see if a replacement can be sourced. The owner will need to remove the lens set to measure the diameter of the lenses, and then see if an appropriate replacement size and focal length (400mm) is available. AliExpress is one possible source though every lens set I’ve found there is a cemented doublet and what is really wanted is an air spaced doublet pair.

 

The lens set can be removed by pulling off the dew shield and unscrewing the black lens retaining ring from the lens cell. Removing the lens cell from the optical tube is optional but advised, and is easily achieved by unscrewing and removing the three Phillips retaining screws.

 

Alternatively, and preferably, perhaps a want ad here on CloudyNights will turn up a used ST80 lens cell that can be sent to the owner for a simple swap out.

[Jon Isaacs]

A scratched lens on an ST-80 might not be much of a problem.. 

 

Jon

[Chris1485]

I once bought a low cost 80mm scope off ebay to salvage the object lens.

It's easy to remove the lens on an ST80, you can find advice on the web about this.

A bit of care is need obviously, but it shouldn't be beyond most people..

[Polyphemos]

A scratched lens on an ST-80 might not be much of a problem.. 

 

Jon

  

[Jon Isaacs]

  

 

It depends on how bad the scratches are and how many of there are.. The views could be just fine.  

 

There is always the Surplus Shed:

 

https://www.surpluss...item/L2196.html

 

Jon

Edited by Jon Isaacs, 08 April 2025 - 06:36 AM.

[Polyphemos]

It depends on how bad the scratches are and how many of there are.. The views could be just fine.  

 

….

Or at least not much different  .

 

All kidding aside, I enjoyed the moon this evening through an old ST80 I’ve been restoring. I’d installed a GSO #8 filter in the nose of the diagonal to tame chromatic aberration and I thought the view of the moon was more than completely acceptable and surprisingly sharp and contrasty through the SV135 7-21 zoom eyepiece I had in the diagonal. I was pleasantly surprised and impressed.

 

Nice work finding a replacement 80mm objective and lens cell package at the Surplus Shed. I hadn’t thought of that and AliExpress had nothing compatible I could find.

[Jon Isaacs]

Jim:

 

The moon is one object that I find is relatively insensitive to CA, ST-80s do a decent job at 100x or more..  The Surplus shed has a lot of objectives.. 

 

Jon

[Gonariu]

A few years ago I dropped my Celestron Travelscope 70 and the achromatic doublet chipped very laterally. This bothered me and I bought without too many problems a new achromatic doublet here in Italy from a well-known company that sells and repairs astronomical telescopes. With the new doublet I think the Travelscope has improved!

[SporadicGazer]

I once bought a low cost 80mm scope off ebay to salvage the object lens.

It's easy to remove the lens on an ST80, you can find advice on the web about this.

A bit of care is need obviously, but it shouldn't be beyond most people..

I immediately thought of a used donor scope too.

 

Does anyone know if the optics in the cheaper variations, e.g. CT80, are the same as the ST80.  (My vague thought is keeping the better ST80 mechanicals and harvesting equivalent optics from one of the cheaper versions as a more budget friendly fix.)

[RichA]

It depends on how bad the scratches are and how many of there are.. The views could be just fine.  

 

There is always the Surplus Shed:

 

https://www.surpluss...item/L2196.html

 

Jon

I've got an AP field flattener that someone gave me, it's scratched badly (real scratches).  When I use it, you cannot see any impact at all, it's pretty remarkable.  It's also better than a Chinese flattener-compressor I have.