erick
02-12-2009, 12:41 AM
I don't know much about refractors, so maybe I should have kept my hands in my pockets :ashamed:
But I bought this nice short tube 102mm refractor and it looked pretty good when I had a quick look.
But I thought, that objective lens has a few too many spots for my liking - I think I'll give it a clean.
I removed the objective from its support - a bit of screwing and pushing and pulling.
Then gave it a wash.
Discovered what an "air spaced doublet" means! OK, spend quite a while with the bulb blower and sliding thin paper in the air gap to remove the water :screwy: Ended up with some visible water marks but thought I'll come back to those in future. The surface spots had all come nicely off. So I rebuilt the front end.
This evening I fitted a new dovetail mount to the rings so it sits beautifully on my EQ5. Point it at Canopus and.........Yuck! the view was horrible.
After a fair amount of fiddling around, I figure that the objective lens is now not properly aligned with the optical axis. One give away was that the adjustments on the GSO-type finderscope were hard over to not quite align with the image in the eyepiece. But I had pulled the finderscope off its mount (playing with O-rings) so I didn't twig to that early - I thought I had just stuffed up remounting it - but on close inspection it was mounted just fine.
I think the other giveaway is the view. I've attached an out-of-focus webcam shot - this does not look right! In fact it looks very wrong! I took a video as I wound the focusser through (sort of ) the focus point. See here:-
[EDIT - removed - too embarrassing!]
I think focus point is approximately 27 or 28 sec in. But, at that point, the star is sort of small, but not pinpoint, and there is a glare of light around it, not symmetric.
I'd like to confirm that is the problem before I pull the objective back out of the cell and have a good look. When I dismantled first time, I did not observe any shimming of the lens. I presumed it just mounted flat in the cell.
I must also try to remove the residual water stains in the air gap. But there are three spacers that look like they are stuck to each lens and I don't think I should but pushing any alcohol through the gap in case it loosens the adhesive? Might just have to push distilled water through and leave on edge to air dry?
Another thought? In trying to remove the water in the air gap, have I maybe changed the spacing on one side, between the two lenses? But they should have pulled back together again when I wound down the locking ring?
A good learning exercise for me. Thanks a lot! :rolleyes:
Grateful for any help. Especially grateful if there is a Melbourne IISer who just loves pulling refractors apart and fixing them! Feel free to get in touch.
But I bought this nice short tube 102mm refractor and it looked pretty good when I had a quick look.
But I thought, that objective lens has a few too many spots for my liking - I think I'll give it a clean.
I removed the objective from its support - a bit of screwing and pushing and pulling.
Then gave it a wash.
Discovered what an "air spaced doublet" means! OK, spend quite a while with the bulb blower and sliding thin paper in the air gap to remove the water :screwy: Ended up with some visible water marks but thought I'll come back to those in future. The surface spots had all come nicely off. So I rebuilt the front end.
This evening I fitted a new dovetail mount to the rings so it sits beautifully on my EQ5. Point it at Canopus and.........Yuck! the view was horrible.
After a fair amount of fiddling around, I figure that the objective lens is now not properly aligned with the optical axis. One give away was that the adjustments on the GSO-type finderscope were hard over to not quite align with the image in the eyepiece. But I had pulled the finderscope off its mount (playing with O-rings) so I didn't twig to that early - I thought I had just stuffed up remounting it - but on close inspection it was mounted just fine.
I think the other giveaway is the view. I've attached an out-of-focus webcam shot - this does not look right! In fact it looks very wrong! I took a video as I wound the focusser through (sort of ) the focus point. See here:-
[EDIT - removed - too embarrassing!]
I think focus point is approximately 27 or 28 sec in. But, at that point, the star is sort of small, but not pinpoint, and there is a glare of light around it, not symmetric.
I'd like to confirm that is the problem before I pull the objective back out of the cell and have a good look. When I dismantled first time, I did not observe any shimming of the lens. I presumed it just mounted flat in the cell.
I must also try to remove the residual water stains in the air gap. But there are three spacers that look like they are stuck to each lens and I don't think I should but pushing any alcohol through the gap in case it loosens the adhesive? Might just have to push distilled water through and leave on edge to air dry?
Another thought? In trying to remove the water in the air gap, have I maybe changed the spacing on one side, between the two lenses? But they should have pulled back together again when I wound down the locking ring?
A good learning exercise for me. Thanks a lot! :rolleyes:
Grateful for any help. Especially grateful if there is a Melbourne IISer who just loves pulling refractors apart and fixing them! Feel free to get in touch.