how to seal LX200R ota ?

[astropolak]

Hi
Does anyone have any solution to this problem.
Want to seal the eyepiece end of my LX200R OTA.
This can normally be accomplished with a UV filter of some description etc.
I have no problem in doing that but fear that the filter will reduce the size of the opening (real cell clear diameter) causing less light to go through or vignetting.
Perhaps I can screw a filter to the WO diagonal or something (rather than screwing it to the real cell). I want to be able to permanently leave the filter there of course...
Any thoughts or solutions ?

[jase]

Sorry, I don't actually understand the problem...
Sealing the rear cell opening should be easily achievable with a large clear filter such as a 72mm or more. This will ensure you don't experience any vignetting using 2" (50mm) accessories. You'd need to obtain the appropriate adapters to make this happen. I'm not sure why you'd want to leave the filter there when using the telescope though. If the filter is simply a clear filter, i.e. not a nebula filter which will provide some visual benefits. It is just another piece of glass along your optical path potentially reducing the amount of light reaching the focal plane. Also the addition of adapters to mount the filter will increase you telescope focal length. This may or may not be what you want to achieve.
Can you provide some reasoning/logic behind why you want to do this? Perhaps just a standard 2" plug is a better option.

[[1ponders]]

Hi AP. Bintel sell a dust and moisture seal that will do what you want. It is the Meade #01A Skylight filter/dust seal. Give them a call and see what sizes they have :thumbsup:

[casstony]

36mm clear aperture on the #1A skylight will limit your potential field on a 10" sct. I have one hibernating in the drawer after I figured out it's not really of much use, unless you're changing gear over in an insect swarm or dust storm. Makes a good "made in Japan" dust cap for putting a scope in storage.

[matt]

I have the Celestron Skylight Filter (#93621) permanently in place at the back of my 9.25.

Will I experience similar problems of potential field being limited?

The marketing hype claims it "Improves color saturation and balance" and "Can be used in conjunction with most Celestron photo/visual accessories"

Is this all just bulldust or what?

I have it in place to prevent dust entering the OTA

[[1ponders]]

We have one (the celestron one) an a C11 to help prevent fungal problems.

[Merlin66]

http://www.petersonengineering.com/SkyDiv/vignetting.htm
This link gives some good info on vignetting with SCT's.
Basically the std baffle inside the scope is 50mm diameter (max) and the opening in the back of the scope is 38mm so ANY 2" gear will be affected. Remember also the 2" diagonal will also be vignetted PRIOR to the light getting to the 2" eyepiece. Hence the sales pitch for the "eyeopener"
Any have first hand experience with it? Does it give an un-vignetted field of 2"????????

[casstony]

Don't know about the C9.25, but with the 10" you have the option of the larger visual back.

I can't see that the filter would add anything to the image. Placing more glass/surfaces in the light path could only degrade the image. Unless you have a compelling reason to use it I can't see much point to the filter.

I do tend to change eyepieces over quickly rather than leave the tube open to the outside.

[[1ponders]]

Striker had one for a while.

[Striker]

The peterson works well on 2" eyepieces larger then 35mm anything less and it does nothing.

Its very good for astrophotographgy as it does open up the undersized visual back but there is other ways to do this now such as focusers that screw onto the 3 1/2" rear thread instead of the 1 3/4" currently used.

I cant see any 2" filter affecting you at all.

[astropolak]

Thank you for your replies.
I want to protect the OTA from dust and the like. I had problems in the past with dust in my SCT, even hair - this initially accumulates on the mirror diagonal and then moves onto the secondary or the corrector plate when you rotate the tube for storage...
I would love to have clear UV filter that:
will not degrade the optical path
would seal the tube without restricting it any more than the diagonal does (or the visual back for that matter) - I think 38mm opening.
would not cost an arm and the leg

Joe