cleaning SCT glass front

[red dwalf]

what do you use to clean the front glass plate on an SCT scope ?

i`ve tried a little washing up liquid on a sponge and screen cleaner for my LCD tv, but they still seem to smear even when i use a soft towel to dry it, driving me mad.

wife says i never take this much time and effort when doing the house windows !

cheers Rob

[Paxo]

Unless it is really really bad, don't touch it at all, modern sct's have a variety of exotic light transmitting coatings which could be easily damaged by cleaning. You'll be amazed how dirty they can look and not effect what you are seeing. How bad is the corrector plate?

Steve..

[FLO]

Steve is right. Consider that in the middle of your correcter lens is a secondary mirror which is effectively invisible when observing at the eyepiece so you certainly don't need to worry about dust-specks or other minor marks.

Having said that, you can clean dust simply by huffing (the condensation formed is distilled water) on the correcter lens and wiping with a micro-fibre cloth. If that isn't enough then use (sparingly) some Baader Optical Wonder (dreadful name but excellent results). The fluid and cloth cannot harm the glass or coatings but do be careful to first check that the cloth and lens are free from grit or anything else abrasive.

HTH

PS: Baader Optical Wonder is not suitable for mirrors.

[Talitha]

Also, be sure never to use canned, pressurized air to loosen debris from any type of optical surface before cleaning it. These cans contain a propellant whose oily droplets can be discharged during spraying.

IMO, the best way to keep a corrector plate clean is by preventing dew from forming on it. Even a very thin layer of fog-like moisture will allow airborn debris to stick to the glass.

[red dwalf]

do you think a little washing up liquid would damage the coatings ? I hope not. i thought it was the mirrors that had the coatings on.

[Talitha]

See if you can detect any difference next time you're out, Red... time will tell. By way of encouragement, i've read that there's more danger of scratching the coatings than there is of damaging them. Of course, this assumes that care be taken when choosing a cleaning product. IIRC, a very diluted application of Dawn dish detergent was once used by someone whose plate had droplets of springtime sap on it. Might have read about it in CN or the MAPUG archives.

TBH though, i wouldn't do anything else to it. I've never cleaned the corrector plate on my LX-10 since purchasing it in Nov 2001, and last year (25 Aug 2008) some exceptionally transparent skies allowed me to avertedly attain a telescopic limiting magnitude of 14.2.

[FLO]

It is common practice to use mild washing-up liquid diluted with water when cleaning Newtonian mirrors but I wouldn't want to use it for lenses. If it was a mild liquid, diluted with plenty of water and used sparingly then I am guessing no harm was done. If all you can see are a few smears then I wouldn't worry about it.

Are you going to the Salisbury Star Party? I'd be happy to take a look if you are.

[red dwalf]

very decent of you Steve offering to have a look but i`m away in Scotland for family holiday so can`t make it this year, was planing to go with DOC, i.e. Mick as he lives close to me but dates have clashed.

[red dwalf]

is there anything i could look for myself, I take it I`d be looking for scratches ?

[Jarndyce]

I had to remove tree sap from my C6 corrector plate recently (only left it for a few minutes - damn!).

A friend of mine is a conservation scientist and has to deal with all manner of difficult but extremely delicate (and expensive) cleaning issues. They had just spent 4 months cleaning a Roman vase....

He recommended distilled water with no additives. It worked a treat. However, as others have said it's vital that anything abrasive - dust, grit etc is removed first, and very little pressure is applied. The coatings on modern lenses and glass are not water soluble and will not be harmed by this. Soap, detergents and wetting agents can leave a residue, but again this won't harm your glass.

As had been said, if you don't need to, don't clean it. Hope this helps.

[BlueAstra]

If its fingerprints or other greasy marks there is a method known as drop and drag that can be used to clean optics. Its normally used on lenses or flat optics, and can be quite difficult to do on an SCT because of the circular edges and recessed nature of the glass.

Basically get some IPA or optical glass cleaning fluid (suitable for coated optics) and a pack of optical (important) cleaning tissues. Imagine holding a rectangular tissue by the corners at the short dimension. Take one tissue, check it has no grit on it (very important) and fold up this edge with a narrow fold. Lay it flat on the optics and put one or two drops of liquid on the tissue along (important) the folded edge where it touches the glass. The liquid will soak into the tissue along the edge and contact the glass, hopefully in a continuous line. Now take the folded up edge and drag the tissue across the optics (do not apply pressure). The tissue will smear some of the fluid across the optic and the dry part of the tissue will mop up the residue. This will clean the glass without leaving any reidue on it. Discard tissue after each try. I recommend you practise on some fingerprints on 'spare' flat glass first.

This is really a last resort. As mentioned above, small marks, scratches etc will have minimal effect on the image, and the optic should normally be left alone. A very large smear or scratch defect could give rise to some scattering and perhaps affect the contrast produce a blemish in the image.

[TwuMirrors]

I saw this method on youtube, a polymer is spread, dried then peeled.

The example is on a meade 8" SCT corrector plate.

 

[Peter Drew]

I've used a drop of washing up liquid to a cup of luke warm water to clean SCT correctors including our two 16" for many years, final rinse off with distilled water. Not had any problems, yet.  😀