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cpsTN
Pooh-Bah
Reged: 04/26/07
Posts: 1198
Loc: Murfreesboro, TN 37129
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At what aperture is it recommended to use an off-axis white light solar filter? Would I be better to use full aperture with an 8" scope?
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Charles P. Sands
Observing since 12/29/86
8" f/5.9 dobsonian (Zhumell DSH-8), with 8x50 RACI
70mm f/5 achromatic refractor (Orion GoScope)
GSO plossls (12 15 20 40), Orion barlows (2x 3x)
10x50 bushnell binos
15x70 Celestron StarMaster binos
S&T's POCKET SKY ATLAS
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The heavens declare the glory of God;
and the firmament sheweth His handywork
Psalm 19:1
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ragebot
Carpal Tunnel
Reged: 08/26/05
Posts: 1671
Loc: Tallahassee, FL, USA
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Quote:
At what aperture is it recommended to use an off-axis white light solar filter? Would I be better to use full aperture with an 8" scope?
It depends on who you ask.
The official Baader page says a stopped down off axis is the way to go.
Lots of very experienced guys in this forum say a full aperture Baader filter is the way to go.
You pay your money and take your chances.
here is a link to an off axis diy project.
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Meade ETX 90, Meade AR5, Orion ED80, Atlas GT, 8 in Newt, Coronado DS SM40, Garrett 10.5X70, Sigma SD10, SD14, Canon 1D2, Xti, Nikon CP4500, C-14
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Solar B
scholastic sledgehammer
Reged: 02/28/07
Posts: 906
Loc: By Edinburgh , Scotland
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I think that seeing will come into it.
It might be an idea to try both options but
if your seeing is generally OK to Good id say full Aper.
Brian
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" Gentlemen only ever use Refractors "
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brianb11213
Carpal Tunnel
Reged: 02/25/09
Posts: 2075
Loc: 55.215N 6.554W
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Quote:
if your seeing is generally OK to Good id say full Aper.
Especially in winter when there is less light (and heat) about.
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2150
Loc: CA
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I don't understand why reduced aperture has never helped me. How ever that has been the case. The theory says it should. Make up some masks and try different experiments.
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Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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cpsTN
Pooh-Bah
Reged: 04/26/07
Posts: 1198
Loc: Murfreesboro, TN 37129
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I will try different things. Thanks guys!
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Charles P. Sands
Observing since 12/29/86
8" f/5.9 dobsonian (Zhumell DSH-8), with 8x50 RACI
70mm f/5 achromatic refractor (Orion GoScope)
GSO plossls (12 15 20 40), Orion barlows (2x 3x)
10x50 bushnell binos
15x70 Celestron StarMaster binos
S&T's POCKET SKY ATLAS
--------------------
The heavens declare the glory of God;
and the firmament sheweth His handywork
Psalm 19:1
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DAVIDG
Carpal Tunnel
Reged: 12/02/04
Posts: 1985
Loc: Hockessin, De
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There are a couple of reasons to go off axis in a scope which has a central obstruction, when you go off axis the obstruction is taken out of the light path, so contrast is improved, second when you stop a telescope down, any optical abberation in the system is also reduced.
Also daytime seeing rarely allows resolution higher then what a 4" telescope can produce so an off-axis aperture filter in the 3" to 4" range, in theory can deliver better images then full aperture telescope of large size with a central obstruction.
Finally the larger the filter, the higher the odds that it will introduce more optical abberations into the system. To obtain a high quality glass filter that is flat to at least 1/8 wave across a 4" aperture will cost at least $300. Zeiss and Questar were the only two manufactures that I know of that offer such a filter. Any size over that would cost $1000 or more. Baader film is pretty good but not perfect so in the range of 3" to 4" the wavefront distortion is good. When you start going larger then that things can start to fall apart pretty quickly.
With the cost of Baader film being very reasonable, just make a full aperture filter from it and an additional off axis mask and try it both ways. When seeing allows go full aperture.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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jcf2001
member
Reged: 03/27/09
Posts: 18
Loc: Beavercreek, Ohio
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I use a 4" off axis filter on my home built 8" and 6" reflectors. Both work fine.
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old_frankland
professor emeritus
Reged: 03/28/05
Posts: 507
Loc: San Francisco Bay Area
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I think a lot has to do with your expectations. My experience with a C9 is I can see more filtering full aperture....though I need to work at it.
If you want to go out and take a quick tour of the photosphere, perhaps a quick close up look at spots or pores, etc., then the smaller aperture filter will likely be the more pleasing. However, if you want to spend time studying a spot group, looking for fine structure, then the full aperture filter will ultimately show you more.
You will, of course, need to be patient looking for those split seconds when seeing steadies over the features you are observing, but fleeting details will be higher resolution than you would see with the reduced scope aperture.
....your mileage may vary.
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Cheers,
Jim
Livermore CA
http://www.lafterhall.com/astro.html
3" APO, 4" ED refractor, 9" SCT, GM8
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