haydencoffin

hi Steve, thanks for that reassuring advice. (i did try the scope under the sky on both of the apparently clear nights we've had in the last three months (!) and was disappointed in the clarity of the image. that's when I looked at the optical parts through the open front and the eyepiece hole and thought i saw deposits on the secondary lens, This house is unoccupied for much of the year and I though maybe damp had damaged it ( even though it is kept in an airtight bag). Turns out what i saw is spotting on the mirroring at the back, but i couldn't have seen that that's what it was without removing the back. Best wishes Gael PS clear night, for a couple of hours, all's well, nice crisp and clear views of Moon, and Mars even with a 7mm eyepiece. I'm happy, it doesn't take much there days. Thanks everyone for advice,

Hi Ed, I wasn't clear enough. I did remove the backplate, its back on now, hopefully the manual and the other chap in this group whose post i can no longer find are right and I haven't messed up the collimation, but its too late now. I'm just saying that as a result I has a good view of the secondary unit and the lens surface was perfect but in daylight the silvering is greyish and is spotty although when i look at my face in it it is gin clear. My question is , will i notice that when there's a clear night and i can actually use the scope, or should i try to find someone to re-sliver it. apparently if you remove the secondary its a bit hard to recollimate

Thank you Ed. Since my oroginal post I found the TAL200K service manual and also another thread about the 200K which said one could remove the back plate and mirror assembly as a unit without disturbing the collimation because of the accuracy of machining. So I did. The primary lens is absolutely clean and shiny, the surface of the secondary lens is equally clean shiny and spotless. Its the mirroring buried down in the back of the the secondary lens unit which is spotty, though it produces a gin clear view of my face. do you think I'd notice any fall off in viewing quality or should i have it serviced ? ( I did track down Steve Collingwood earlier, he says he's not taking any telescopes in at the moment and doesn't know if he'll return to doing so. I do hope that's from choice and he isn't affected by the current emergency) anyway if you've a moment to advise I'd be grateful.

I think my TAL200K is not as sharp as it used to be ( although the viewing weather has been poor - I only do Mk1 eyeball viewing and am a very amateur astronomer). The primary mirror looks perfect as does the star diagonal mirror and the eyepieces but the lens on the secondary looks as if sand has been scattered on it ( its quite difficult to see). I've very very gently wiped it several times with a microfibre cloth with isopropyl alcohol on it but it has made absolutely no difference/ I don't want to remove the secondary for closer inspection, I'll take it to a pro ( if I can find one I live in Rochester , Kent) I attach a photo taken through the focuser hole. what i am talking about is the (slightly blurry, poor shot, swirl around the bright disk in the centre in the photo ( the bright disk which is the reflection of my camera light). The secondary assembly on these telescopes consists of a mirror and two lenses I understand and I'm wondering if there is dirt or some sort of growth inside the assembly, it looks just as if a few hundred grains of sand have landed on it. They are not as regular as the photo implies so i don think they are an image of part of the telescope

Thanks, I'll think about that.

(also posted in a reply thread elsewhere) Hello there! I'm a newbie to this forum so I apologise if my question has been answered already elsewhere. I've been using a TAL200K for about 15 years but getting fed up with the rack and pinion focuser so i treated myself to beautifully made in Germany 2" thread adaptor plate and a generic 10:1 SGT crayford focuser ( these are branded Skywatcher, Lacerta, OVL but I think they are all the same. ) turns out this is much longer than the original TAL and only near terrestrial objects can be bought into focus. Unless there's an easy fix i'm sending the focuser back for a refund, soooo, is there a low profile crayford or other smooth action focuser that will fit the 50.8mm threaded plate which has a similar low profile to the original TAL ? best wishes.