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Off axis WL Filter Question

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#1 Special Ed

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Posted 11 January 2017 - 11:34 AM

Hello,

 

I tried asking this question in the Cat forum but didn't get a response.  Does anyone here know?

 

Thanks in advance.



#2 George Bailey

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Posted 11 January 2017 - 01:09 PM

I don't think it would make a difference

(I never noticed a difference with my C8),

but it would be simple enough to test it out at different positions and see if you get a better view

at one of them with your scope.



#3 Special Ed

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Posted 11 January 2017 - 02:37 PM

Thanks for the response, George.  I'd like to experiment with it but the Sun won't cooperate by producing an AR.  Wouldn't matter anyway--cloudy forecast here through next Tuesday...



#4 David Gray

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Posted 12 January 2017 - 06:13 AM

Hi Michael….

 

I’m not really a solar observer but I use a 6” off-axis (clear) mask/diaphragm with my 16.3” scope on occasion for other objects and not found an optical issue.

 

However for your solar-mask pursuits I wonder about how much (if) the sun would heat the opaque area of the device – thus possibly rising thermals across the filter in some instances....(the 9 to 3-o-clock positions ???) – so perhaps a 6-o-clock position might be in order.  

 

Or wind-directed thermals might be the factor to consider/address….?

 

Just my speculations on the matter…….

 

Dave.



#5 Special Ed

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Posted 12 January 2017 - 08:54 AM

Hi Dave,

 

Thanks for the thoughts.  The opaque part of the filter is white so it should reflect away a lot of the Daystar's heat but probably not all.  It makes sense to keep the filtered opening at the bottom (6 o'clock) of the objective.  Good to hear from you.



#6 marktownley

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Posted 12 January 2017 - 02:40 PM

I don't think you will see any difference.  With a blank sun you will get an easier full disk with your 50mm scope.



#7 Special Ed

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Posted 13 January 2017 - 06:53 PM

Thanks, Mark.  You're probably correct.  As far as seeing the full disk, I have other telescopes (and my 15x70's) for that).  My 2" ep's give me very close to a full disk, but I am more interested in a high power view with the C14.

 

As luck would have it, a (sort of) break in the clouds this afternoon coincided with the emergence of AR2625 so I was able to try out my new off-axis filter.  It worked great.  Sketch can be seen here.

 

[Edit: AR2625 is now followed by newly designated AR2626 ]


Edited by Special Ed, 14 January 2017 - 10:35 AM.


#8 Special Ed

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Posted 22 January 2017 - 02:56 PM

Got a brief chance to try out the off-axis filter again yesterday, the 21st, with the Daystar shining weakly through overcast.  It worked well enough for me to detect one of the new sunspot groups (AR2628) even though I didn't know it had developed.

 

Using my 2" 55mm Televue Plossl @71x,the clouds prevented me from getting the sunspots into sharp focus but I was happy to see that the solar disk fit completely inside the FOV so I guess my calculation of a 40* TFOV for the ep is correct.

 

These new AR's are flaring mildly with some C-class activity so hoping for clear skies for all.  :)


Edited by Special Ed, 22 January 2017 - 02:57 PM.


#9 Special Ed

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Posted 25 January 2017 - 09:33 PM

Got to try out my new filter this morning (25 Jan.) with clear skies and excellent transparency.  Unfortunately, the seeing was Wilson 1.0 (as bad as it gets).  It's always something.

 

Even with the very poor seeing and resulting difficulties in achieving fine focus, I was able to detect the new sunspot group, AR2629, that just emerged on the eastern limb--I wasn't aware of its existence.  Could also see AR2628, Its umbra had a very thin line that trailed out to the following (east) side.  Seeing was too poor to detect the remnants of the other AR's.  Seeing was also too poor to attempt a sketch.




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