<p>I have an old (nearly 50 years old)alt-azimuth three-inch (7.6cm) refracting telescope that someone else made. They ground the lens, created the cylindrical body and added a rack and pinion style focusing slider. It is mounted on a homemade tripod.</p>

<p>This has been poorly stored for several years in damp conditions and has developed mould on the main lens elements. The main lens elements comprise a convex and concave combination (presumably to reduce achromatic aberration?)</p>

<p><strong>Question:</strong></p>

<p>I've cleaned the main lens elements in soapy water and removed the mould using a soft cloth. </p>

<p>How would you now test this lens? 
Would you reassemble the telescope and check resolution against known double stars or are their tests I can apply to the lens before reassembling the telescope?</p>

CC BY-SA 4.0
2019-12-09T16:57:22.797Z
Sometimes doublets will have marks to show how one lens was rotated to best match the other. This wouldn't matter for perfect lenses, but for imperfect (real world) lenses it's important. Did you notice any such marks? I don't know if the telescope maker would have made any, but it's possible.
uhoh
CC BY-SA 4.0
2019-12-10T02:22:46.087Z
ebv make your comment an answer. That about what I was going to say.
TazAstroSpacial
<telescope><refractor-telescope>
Methods for testing a refracting telescope lens
MiguelH
# Methods for testing a refracting telescope lens

(Asked by: username_0 on 2019-12-09)

I have an old (nearly 50 years old)alt-azimuth three-inch (7.6cm) refracting telescope that someone else made. They ground the lens, created the cylindrical body and added a rack and pinion style focusing slider. It is mounted on a homemade tripod.

This has been poorly stored for several years in damp conditions and has developed mould on the main lens elements. The main lens elements comprise a convex and concave combination (presumably to reduce achromatic aberration?)

**Question:**

I've cleaned the main lens elements in soapy water and removed the mould using a soft cloth.

How would you now test this lens?
Would you reassemble the telescope and check resolution against known double stars or are their tests I can apply to the lens before reassembling the telescope?

**Tags:** telescope, refractor-telescope

> **Comments:**
> **username_1**: Sometimes doublets will have marks to show how one lens was rotated to best match the other. This wouldn't matter for perfect lenses, but for imperfect (real world) lenses it's important. Did you notice any such marks? I don't know if the telescope maker would have made any, but it's possible.  
> **username_2**: ebv make your comment an answer. That about what I was going to say.  

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## 0 answers

