New 20" Dob, I'm now officially obsessed !

That's also what they say about these big mirrors, about once in ten years.

I used tap water to clean the grit off the mirrors, but then used purified water from a chemists and 1 drop of washing up liquid to polish it with, I also used surgical cotton wool which does a great job, much better then paper towels.

I personally wouldn't use rain water, as it catches all the gunk in the atmosphere an the way down, it might even be slightly acidic which is the big killer to mirror optics.

I used tap water to clean the grit off the mirrors, but then used purified water from a chemists to clean it polish it with, I also used surgical cotton wool which does a great job, much better then paper towels.

Oh God, never use paper towels to wipe a mirror! :!:

I personally wouldn't use rain water, as it catches all the gunk in the atmosphere an the way down, it might even be slightly acidic which is the big killer to mirror optics.

From our geographical perspective, we have good rain water. The thing would be to leave a plastic basin/bucket out in the open to catch the rain water (less grit etc from the roof via the drain pipe). Then, having let it settle in a cool room for a day afterwards, gently submerge a glass jar/beaker into it, cap it, and store it that way. The pH of rain water here (Ireland) is between 6.5 to 7, which means it is a tiny bit more acidic than pure/distilled water (pH of an even 7) - that amount is negligible for the amount of times you will be 'washing' your mirror over time. Tap water is anywhere from 7.5 to 8.5 - more lethal to such sensitive coatings due to the alkalies and metals dissolved in it. Acid rain is from 0 to 5.

Seanie.

Funny thing there (and at the risk of been shot for angering the rain gods), it hasn't rained in nearly 3 weeks. the longest spell of dry for a long time.

Funny thing there (and at the risk of been shot for angering the rain gods), it hasn't rained in nearly 3 weeks. the longest spell of dry for a long time.

And totally uncharacteristic for this time of year. Saturday hit 20 degrees C by the way - 6 degrees above the average max for this time of year.

Imagine using tap water from Galway, given the outbreak there, what would you see through the eyepiece :lol:

After cleaning my mirror, I prevented more dust settling on it by applying several layers of clingfilm. When one layer gets dirty, I just remove it, exposing a new layer of clean clingfilm.

Unconnected to this, but I've recently noted that my recent imaging sessions haven't been very productive.