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What solar filter 4 refector with small hole n cap

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#1 Littlegreenman

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Posted 13 February 2013 - 02:38 AM

I have a 90mm Vixen refractor from the 1990's. The objective plastic cap has one of the smaller caps that fits over a smaller opening in the center. How does one use that for solar viewing? Or should I skip that and just get a solar filter that covers the whole objective?

Although, viewing through the small hole would turn the 90mm f/11 into f/ really slow!

LGM

#2 rdandrea

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Posted 13 February 2013 - 12:53 PM

I assume you're talking about a white light filter. If it were my scope, I'd build or buy a filter that used the entire 90mm.

#3 steveward53

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Posted 13 February 2013 - 01:00 PM

I'd be inclined to purchase an A4 sheet of Baader ND5.0 Solar film and make your filter full aperture .

An A4 sheet will give you 6 filters if cut neatly and fitted into a cardboard holder .

Alternatively you could buy a ready made filter for the
scope but these are more expensive.

There are plenty of options/designs for holders online , personally I make mine from 'embroidery rings' .

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#4 Littlegreenman

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Posted 13 February 2013 - 05:55 PM

Thanks, especially for the Baader tip. I like cheap.
Has anyone out there used the smaller hole viewing technique, and if so, how does it compare to full aperature?
LGM

#5 sullij1

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Posted 13 February 2013 - 10:40 PM

Do you have a picture of what you are calling a small hole scope? It may help us.

#6 Zamboni

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Posted 13 February 2013 - 11:02 PM

I think he's referring to an aperture stop. Aperture stops for smallish refractors are largely a carryover from when small telescopes included projection screens and/or HORRENDOUSLY UNSAFE screw-on eyepiece solar filters, largely to reduce internal heat build-up. They can also be used on larger refractors to simulate a smaller, slower f/ ratio scope to reduce chromatic abberation.

To be totally honest, the only good solar use for them these days is for stopping down very large refractors (6" or above) to minimize heat build-up when using a herschel wedge.

#7 Littlegreenman

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Posted 15 February 2013 - 12:49 PM

Ah, yes, an aperture stop. Sorry about the time-delay in getting back to this thread. A picture of the plastic lens cover with the stop removed is included.

LGM

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#8 sullij1

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Posted 15 February 2013 - 08:53 PM

Zamboni, thanks for the history lesson. Before my interest time I guess.

Littlegreenman, yep, an apature stop. Go with the Baader film at full apature. More apature will provide more detail on the active areas. Less apature less detail.






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