Cleaning a Celestron Ultima Barlow

I had a close look at my Celestron Ultima 2x barlow the other day having spent a few nights out imaging Jupiter and Mars and discovered that it was disgustingly filthy. No idea how it should have got so dirty given that when it’s not in use it’s stored in an eyepiece case with end-caps on, but there you go. This was more than just a couple of specks of dust that would probably get lost in the overall image, so I had to do something about it. Fortunately some time back I purchased some Baader Optical Wonder cloth and cleaning fluid for just such an occasion.

Dismantling the barlow was pretty straightforward, though I had no idea what to expect. I first unscrewed the two halves to leave just the lower metal barrel section containing the optics. From the bottom I then unscrewed the lens retaining ring by putting my thumbnail into one of the notches in the ring and turning it anti-clockwise. With that removed all the elements could be pushed out from the other end of the barrel. First item out is what appears to be a thick lens, but is actually two lenses cemented together, with the thinner one at what would normally be the open end of the barrel. Next was a thin spacer, and finally another lens that is convex side uppermost in the barrel. In this photo the parts are in the order they came out, left to right.

I following the instructions for using the cleaning fluid and it was immediately obvious that the lenses were much improved afterwards. It’s not particularly easy to get them all back into the barrel one at a time however, so I first stacked all the pieces up on the table, and then slid the barrel down over them before screwing in the retaining ring:

I mainly use this barlow for imaging and I’ve not had much time for that in the last few days, but I look forward to improved images next time I can get out.

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