Skylight filter or not?

[Victor Meldrew]

Just bought a new scope (Zeiss Diascope 85) and I'm wondering whether I should protect the big objective lens from the start. I can obviously see the advantage of doing so but the things that are worrying me are:

1. does it make sense to go to the expense of buying a scope with fluorite glass throughout only to put another layer of non-fluorite 'glass' in front of it?

2. you create an enclosed space which isn't nitrogen-filled and that will contain a certain amount of moisture.

Any thoughts?

I'm not intending to do any sea-watching by the way.

[Charles Harper]

It generally protects the objective from dust and other intrusions. One thread suggested it's best NEVER to wipe the objective at all (to save scratching), so a cheaper cover lens would be a good idea. It could be removed at home to dry out inside. On another thread, we were looking for a sky or UV cover lens for the Swaro ATS65HD, but were not able to find one. I'm still in the market.

Don't know about the fluorite/non-fluorite argument except in the case of toothpaste.

[redshift]

The lens in an apo refractor is made using special glass (e.g. flourite) because of the special light-bending properties of such glass (and therefore avoidance of colour-fringing in the image), rather than anything to do with light transmission. Since the filter is flat and is not a lens, this is not an issue, "ordinary" glass is fine.

I would protect the surface of your lens with your life! Any scratch here WILL degrade your image quality.

[walwyn]

As with others I've always use a skylight filter to protect the lens.

[grahams]

Here in the UK Jessops sell skylight and uv filters that will fit scopes. I purchase an 82mm filter for my Swaro ATS 80HD. I believe that Hoya make them so you should be able to obtain in Japan.

[Charles Harper]

Andrew checked with both Jessups and Swaro on his own and my behalf back at the end of August, and came up with no filter that would fit the 65. I'm not familiar with Hoya, but I'll google it, thanks.

[Charles Harper]

Oops. Google got me a homepage convertible to English, but the links to optics, etc. are all in a foreign tongue. Rats. Well, I'll think of something...

[BirdWatcher]

Grahams, could you please confirm the appropriate filter thread size for use on a Swarovski ATS 80 HD spotting scope?

Is the 82mm size, mentioned in your previous post, correct? I am a bit confused, as I thought the ATS 80 HD used 80mm filters.

The reason I am asking, is that I am considering buying a new Swarovski ATS 80 HD spotting scope and I would want to buy a Skylight filter (of the correct size) at the time of purchase so the objective lens on the new scope would be protected right from the start.

I currently have a KOWA TSN-824, straight through, spotting scope with 82mm objective.

I was also very glad to read in another post in this thread that using a Skylight filter would not degrade the image seen through the scope, as using the filter virtually eliminates the question of how to properly clean the exterior glass of a scope's objective lens without doing damage to the glass or its coatings.

One last question .. does using a Skylight filter on a spotting scope objective while DigiScoping with a digital camera also NOT interfere with the resulting photo quality .. or the camera's focusing capability?

BirdWatcher

[Victor Meldrew]

Mmmm.... the thread size on the Zeiss is 86mm which probably makes it even more unlikely that I'll find one.

Thanks for your opinions everyone. I'm convinced.

[falco]

I recently tried a skylight filter on my ATS 65 HD. I think i was called Hoya HMC super or something like that (their best filter I was told). Surprisingly I experienced a decrease in both clarity and sharpness with the filter on! The decrease was really obvious too! (especially on high magnification) So I didn't bought it. After have bought a really expensive scope for its nice sharpness I don't want to make the view look less good than it can be.
Maby other filters are better. Make sure you try one before you buy it is my advice.

[GR Triever]

Originally posted by Victor Meldrew
Mmmm.... the thread size on the Zeiss is 86mm which probably makes it even more unlikely that I'll find one.

Thanks for your opinions everyone. I'm convinced.


86mm is a common filter size; B&H Photo in New York can provide that if you don't find it locally. They are an excellent company to deal with, by the way.


GR

[Charles Harper]

Thanks, Falco-- you may have saved me some money! Welcome to Bird Forum, too-- we need lots more Continental members, so it's good to have you aboard. If I find a good filter, I'll certainly let you know, because we have the same scope.

[mak]

The filter thread for the 85mm Diascope is M 86x1.
There are filters available for this model (but not directly from Zeiss, certainly not in the UK).

[grahams]

Birdwatcher - I will check tonight but I am almost 100% sure that the filter thread is 82mm

[grahams]

Birdwatcher - I have checked the filter that I bought and it is a Hoyta 82.0s UV filter both sides coated.

[grahams]

Sorry the previous post should say Hoya not Hoyta