Sticky layer on corrector plate

Post by **weixing** » Mon Oct 20, 2003 12:42 am

Hi,
Today late afternoon as I was cleaning my scope exterior, I accidentally brush over part of the corrector plate of my MCT. To my surprise, the part of corrector plate that the brush touch show a sticky substance. I'm sure that the substance is not from my camera brush.

After checking with a red touch light, I found out that the sticky substance was part of a thin layer on the corrector plate which I discover when I got the scope and it seem not causing any image degrade, so I leave it alone(I thought it was the imperfection of the corrector plate glass, because it was not obvious at all, you need to face the corrector to a light source and look at an angle to see it).

Anyway, I use my LenPen to generally clean off the sticky portion as much as possible(it getting late and not enough illumination). I test the telescope tonight(19 Oct) and discover that my scope can now focus even more sharply... may be also tonight sky was very clear.... I plan to get a new LenPen tomorrow and do a thorough check and cleaning if needed...

By the way, do any of you guys have this on your corrector/lens??? My initial conclusion is that this layer is cause by the water vapor in the air that trap the dust and "stick" to my corrector plate when I was doing observation.

Post by **Airconvent** » Mon Oct 20, 2003 2:17 am

I try not to touch the corrector plate but if I had to do some cleaning, a quick way is either a lens pen or a 3M Optical Len cleaning cloth.
Its a whole lot easier than the "authorised" method of using diluted isopropyl alcohol....but only for light smudges...

rich

chris shaw · Post by **chris shaw** » Tue Oct 21, 2003 3:07 pm

I do have a few 'spots' on my corrector plate caused by water vapor or dew, I think, but have not cleaned it as they are quite small and does not really degrade image quality. I don't think I have any sticky smudge but if you do shine a light down at the corrector plate you may see streaks and signs of uneven coating, although this is quite normal (does not affect optical performance) according to the ETX manual. Such 'flashlight' tests are usually not used to judge quality of optics....Better to worry about collimation...although for MCT, there is nothing you can really do about collimation....

Chris

harlequin2902 · Post by **harlequin2902** » Tue Oct 21, 2003 3:13 pm

Though I've never really opened up any ETX myself, my guess is that to collimate the ETX, you'll need to remove the entire rear assembly (the part that covers the flip mirror system) to reach the collimation screws for the primary mirror at the back - at least that's what I had to do for my Nexstar 4 when it needed collimation.

chris shaw · Post by **chris shaw** » Tue Oct 21, 2003 4:04 pm

HIGH RISK...

Post by nF » Tue Oct 21, 2003 6:35 pm

Ask Mr Au to teach you how to collimate a scope. He's the expert for this. =P

Post by **Airconvent** » Wed Oct 22, 2003 12:42 am

harlequin2902 wrote:Though I've never really opened up any ETX myself, my guess is that to collimate the ETX, you'll need to remove the entire rear assembly (the part that covers the flip mirror system) to reach the collimation screws for the primary mirror at the back - at least that's what I had to do for my Nexstar 4 when it needed collimation.

Hi Sam,
No need for that. You are supposed to remove the visual back cover and using a round head allen key, turn the 3 screws on the inside OTA (the ones with paint on them). Jeff did it before but highly recommend NOT doing it...

rich

Post by **Airconvent** » Wed Oct 22, 2003 12:45 am

NovaFusion wrote:Ask Mr Au to teach you how to collimate a scope. He's the expert for this. =P

So far, I've understand that Mr Au specialises in SCTs and not Maks...
Unlike the SCT where there are 3 collimation screws on secondary mirror of the correctot plate, Maks' collimation screws are more difficult to access...

rich

Post by **weixing** » Wed Oct 22, 2003 12:57 am

Hi,
Sky-Watcher or Orion MCT's collimation screw are on the back of the OTA and are easy to access. Due to the design, most MCT do not require collimation, so most MCT manufacturer do not include the collimation screw....

Post by **Airconvent** » Wed Oct 22, 2003 1:35 am

weixing wrote:Hi,
Sky-Watcher or Orion MCT's collimation screw are on the back of the OTA and are easy to access. Due to the design, most MCT do not require collimation, so most MCT manufacturer do not include the collimation screw....

Hi Weixing,
That's interesting. Disadvantage I suppose of having the screws too accessible is people may eventually be tempted to push the collimation a little more closer to perfection , with disastrous results.

rich