Author Topic: "Minumum" size of solar aperture mask?  (Read 73 times)

Zachary Tenk

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"Minumum" size of solar aperture mask?
« on: December 27, 2017, 02:53:59 PM »
Hi guys! I haven't done any solar observing yet so I'd like to get ready for the Mercury transit next month. I think I've got a good handle on the safety info and I need something further.

My 12" has a aperture cap with a 2" removable cap in it. I've used it successfully on the moon so far. I've been thinking of getting either a Baader solar film or even a D-ERF filter. As the second option is expensive I'd like to buy only once and get the right size. In short, is a 50mm aperture filter sufficient? Is there an advantage to going for a larger filter? I think up to a 100mm will fit, but what are the pluses / minuses? (Aside from the obvious expense)

How about comparing a Lunt 50mm ERF to a 100mm regular solar filter? Price wise they are about the same.

Many thanksFlorian



xgamodrakmu

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Re: "Minumum" size of solar aperture mask?
« Reply #1 on: December 28, 2017, 09:54:02 AM »
The ERF filters are not safe when used by themselves for visual observations. They need to be used with an additional H-Alpha filter.The Baader solar film is safe for visual use since it has an Optical Density of 5. The 100mm aperture would work well.
     Dave

trodnenwisen

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Re: "Minumum" size of solar aperture mask?
« Reply #2 on: December 29, 2017, 09:40:02 PM »
Thanks Dave, I wan't aware of that!

knucareaslo

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Re: "Minumum" size of solar aperture mask?
« Reply #3 on: January 07, 2018, 11:08:30 PM »
If you want to customize and optimize for your reflector, you can make your own off-axis filter from Baader film.

You could go for the largest diameter that just fits between the outside of your secondary and the inside of your primary, and position it so that it sees no obstructions. This would maximize the resolution possible and at a reasonable brightness level. Adding color filters at the eyepiece is also possible for increasing contrast of various features and reducing overall brightness if you want.

I've done this before and just received a piece of Baader film for doing it again on my current 10" dob.

Deandre Fulce

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Re: "Minumum" size of solar aperture mask?
« Reply #4 on: January 09, 2018, 09:15:06 PM »
If maximizing aperture is good, I could even make 4 identical circular cutouts to avoid the spider vanes. Would that be beneficial in noticeably increased resolution? I assume 4x100mm aperture cutouts wouldn't be a problem as far as too much light getting in?

Jason Meyer

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Re: "Minumum" size of solar aperture mask?
« Reply #5 on: January 11, 2018, 08:53:34 AM »
I'm pretty sure that you'd find that to be a rather bright arrangement using Baader film. You're proposing more than 50 square inches of area. I've used Baader film in various apertures and suspect that you wouldn't want more than half of that.

As far as resolution goes, I'm sure a lot depends on the accuracy of your mirror, too. One four inch aperture should make your scope pretty much perform like a 4" apo. That's nothing to sneeze at, particularly for the relatively low power you'd probably want to use on the sun.

Randy Wiggins

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Re: "Minumum" size of solar aperture mask?
« Reply #6 on: January 12, 2018, 03:39:33 AM »
Just to be absolutely clear before you order:

There are two types of Baader Astro-Solar safety film.

The correct one is the normal visual type. OD5.0

The other is the photographic. OD3.8.
This last one needs extra filters for visual safety so avoid.

Check out some of the YouTube guides to making your sun filter.
Remove your finder to avoid accidental use!
Never leave a telescope unattended in daylight!

If you cut out the Baader filter sheet with care you can make extra filters for your binos.
Or even for your sunglasses. With care to avoid dislodgement. [Is that even a word?]

The sun is really tiny when you look directly through a finished solar filter.
I'm now wondering whether Mercury is remotely visible to the eye when using the Baader filter for safe viewing.
I never thought to try last time there was a Mercury transit.
Venus should be no problem at all but is 5x bigger than Mercury appears.
Searching online suggests the eye needs an aperture of 7.5mm to glimpse Mercury.
This is hardly likely when using Baader Solar film visually in bright daylight.

Paul Melo

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Re: "Minumum" size of solar aperture mask?
« Reply #7 on: January 13, 2018, 05:14:16 AM »
Quote
If maximizing aperture is good, I could even make 4 identical circular cutouts to avoid the spider vanes. Would that be beneficial in noticeably increased resolution? I assume 4x100mm aperture cutouts wouldn't be a problem as far as too much light getting in?

You definitely do NOT want to observe this way (...if I understand what you're saying,,, I apologize if I misinterpreted this).
4 different cutouts used SIMULTANEOUSLY would emphasize the slightest shift from ideal focus so could be helpful for achieving critical focus but I'd say bad for actual observing.

highdanmyne

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Re: "Minumum" size of solar aperture mask?
« Reply #8 on: January 13, 2018, 10:42:36 AM »
In effect what 4 apertures does is make 4 gigantic spider vanes.

colzefuli

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Re: "Minumum" size of solar aperture mask?
« Reply #9 on: January 17, 2018, 12:25:30 AM »
Four identical apertures will make a focusing mask. Better to use only one off-axis aperture or go full aperture film.

--Christian

Randy Wiggins

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Re: "Minumum" size of solar aperture mask?
« Reply #10 on: January 18, 2018, 01:55:04 AM »
I would say four inches of aperture is perfect for the Baader film in the optical grade. It would make your scope an excellent off-axis reflector.

Randy Ott

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Re: "Minumum" size of solar aperture mask?
« Reply #11 on: January 23, 2018, 01:08:20 AM »
Thank you guys, I appreciate all your inputs. I ordered a Baader continuum (dark green solar) filter and both kinds of solar foil. Baader recommends that for <150mm apertures I should use the photo foil, the image might be too dim with the visual filter. I'm going to make 2x100mm apertures, one with photo foil + filter, one for visual foil and no filter. Only one aperture will be in use at a time. I hope I'll be ready in time, I'll post some pics of the setup when ready.

Cheers!

Florian