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What size threads for front of 3.5" Questar?

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#1 Erinsimaging

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Posted 26 May 2012 - 08:50 PM

Anyone know what the specificans/size/threads are for the front of the 3.5" Questar? I was thinking about purchasing the correct size UV photo filter to screw into the front and using it as a bit of added protection when I take my Field model out birding.

Erin

#2 Suk Lee

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Posted 26 May 2012 - 09:39 PM

Don't know the thread count, but highly doubt you can find a UV filter of the right gigantic size. Questar offers a protective flat with the requisite flatness but it isn't cheap. Ironically flat is harder to make than curved...

#3 Terry_McComas

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Posted 31 July 2012 - 08:18 PM

I don't have a clue as to the thread specifications, either, but wanted a UV filter for my 50th Anniversary model, as I do a lot of public outreach and am nervous about little fingers, covered in peanut-butter. The 95 mm. filter, from B + W, fits perfectly, is superb quality has a bomb-proof coating and costs considerably less than Mother's flat. (I ordered mine from B + H, in New York.)

#4 MBoys

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Posted 18 February 2014 - 01:30 PM

My 1975 3.5" Questar front threads are 95mm... so any 95mm filter should work.

#5 munirocks

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Posted 03 March 2014 - 03:12 PM

I don't have my Questar yet but I purchased the B+W filter ahead of time, for public outreach events, based on the testimony from others that the fit was good. There are several reasons that I opted for the B+W:

The optics are very good, and they use high-quality Schott glass.

There are two types of coatings available: a single coating (SC) and a multi-resistant coating (MRC). Make sure you buy the one you want. The MRC is actually harder than glass so is very scratch resistant, and you don't need to clean the MRC very often anyway because it is water-repellent. Good for dewy nights and wet days.

The B+W ring is made of brass, so is very strong and resistant to corrosion/oxidation.

The brass won’t cold-weld to steel or aluminium, so won’t get stuck on the scope if it gets left on for a long time.

The brass makes it easy to spot a fake. There are apparently cheap Chinese fake filters in the market made of aluminium, so buyer beware! Buy from a reputable source. The brass is noticeably heavy in the hand (the filter weighs 68 grams) and you can see the yellow brass colour coming through the fine laser-etched lettering on the front of the filter ring.

The B+W filter is also available in both Clear MRC and UV MRC versions. I got the UV MRC because I’ll usually be looking through miles of atmosphere (either in daytime or nighttime). If I was going to use it mostly as a long-distance microscope or other short-range activities I’d consider the Clear version.

#6 ChristianG

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Posted 04 March 2014 - 03:05 PM

I got the UV MRC because I’ll usually be looking through miles of atmosphere (either in daytime or nighttime). If I was going to use it mostly as a long-distance microscope or other short-range activities I’d consider the Clear version.


Well, you made the good choice!

In a Questar 3.5 with R1 secondary, the light passes twice through a thick meniscus lens made out of glass that is a good UV absorber.

So I doubt there would be any difference between the 362$ Clear MRC 'filter' (it does not filter anything) and the 325$ Clear UV Haze MRC filter.

But you are saving 37$ with the UV Haze, since it is made of regular glass which absorbs UV like the meniscus lens, and the Clear one has to be made of some special glass so as not to filter out UV...

But both are nice filters, no question.

--Christian






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