Cleaning inside faces of objective lenses

[Chunky Wheeler (Chris)]

I have been out of the country for 3 months and upon my return I am dismayed to find mould spots inside the objectives of my Skywatcher ED 120mm Black Diamond refractor and my 70mm William Optics Zenithstar refractor.

Both scopes were stored in their cases in the house, and with anti-mould dessicant pakets sitting beside them. The garden is so wet it's like a quadmire, and it seems like it never stopped raining all the while I have been away.

Anyone out there got any ideas of how to get the objective lens cells out, cleaned and put back properly collimated? If this is a job for the experts, who and where are they?

Thanks a million

Chunky Wheeler

[astro_nutt]

Hi Chris. Bad luck with the mould forming on the objectives.
I would suggest contacting one of the Astronomy Clubs in Queensland and see what they reccommend.
Cheers!

[OzEclipse (Joe Cali)]

Hi Chris,

Bad luck about the mould. The first thing you should do is put the lenses in the Sun.

Don't point the scope at the Sun. Just put the OTA's flat on a table facing north with lens hoods removed or retracted and leave them there for a 4-5 hours in the middle of the day, for both days of a weekend. If you have a plain piece of flat mirror glass, put them on this to double the light intensity entering the lens. This should kill or slow the mould and it may even disappear if growth is only light.

If there is mould between the lenses, they are probably air spaced. Some times the cell needs to be removed, sometimes the lens can be removed from the cell with the cell in the tube.

I'm not familiar with the bigger OTA you describe and though I have a Z70, I haven't ever removed the lens so I can't give you specific directions for cell removal. The important thing is to mark the orientation of the lens cell in the tube, the lens in the cell and most importantly the orientation of the lenses with respect to each other. In the case of the lenses, take out the lens in one piece and draw a line down the edge of both elements. The lenses may have small adhesive spacers. Make sure you don't lose these. If there are symmetrical elements eg a biconvex crown element, make sure you mark the direction as well as the radial orientation of the lenses.

Plain soap and water can be used to clean the lenses. Don't use anything abrasive. I'd just soap and wash my hands before touching the lens, rinse off hands then re-soap my hands and use the pads on the palms of my hands to soap the lens. Try not to use a soap with moisturizers. Plain sunlight kitchen soap is good. You can also use isopropyl alcohol or soap then finish with isopropyl alcohol. When buying, note that isopropyl alcohol and Propan-2-ol are the same solvent.

Good luck!

Joe

[MattT]

On my 100ED Saxon the lens cell unscrews from the tube, pull off the dew shield and give the cell a twist...see what happens.