[Chaos-l] Burgess Finders?

[Mark South]

Hi,
Overall, I think you will find the Burgess RACI to be much better  
than your older Orion finder-scope.  It should provide more light  
gathering power.   I personally own an Antares RACI, so I don't have  
experience with a Burgess finder-scope.   However, I do own a Burgess  
7mm eyepiece and have found it to be exceptional, so I would have to  
assume their RACI's would be exceptional as well.

The ratio of light gathering power = the square of the radius of the  
larger object/ the square of the radius of the smaller object.
In your case, (50mm)^2/ (30mm)^2= 2500/900 = 2.78/1 ratio.   So  
that's 278x more light gathering power, or 178% increase of the 50mm  
over the 30mm.  (change/original= % increase-- that is, [2.78-1]/1*100)

With that said, in my experience 50mm will perform really well in  
dark skies, but can be a challenge in light polluted skies due to the  
low overall aperture, knowing which way is north, etc.   Personally,  
I find the RACI more helpful than a straight-through because my map  
will match my views.  I would consider a few things to help you  find  
the harder to locate objects:
1)  When you purchase the finder-scope, try to determine your field  
of view (FOV).  Mine is 7-degrees.
2)  If you are using a traditional map, consider drawing a circle to  
match your FOV with a permanent marker on an overhead.  Cut out the  
overhead to a smaller square to fit your map.   For example for my 7- 
degree FOV, I was able to measure 7 degrees by measuring the  
declination on the right side of the map.   If you have program on  
your palm (i.e. Planetarium), you can program in the circle to the  
appropriate degrees.
3) Know which way is north and orient your map accordingly.   The way  
I determine North is slightly "nudge" your scope toward Polaris.   
With practice, you can orient your map to match what you see in your  
finder-scope quickly so you can know where to hop next.
4) Look for star patterns and orient your map accordingly.   After  
finding that bright star, I like to look for triangles or other  
patterns and jump to them.   The patterns are also helpful to orient  
your map.
5) above is adapted from the Sky and Telescope.  consider taking a  
deeper look here:

   http://www.skyandtelescope.com/howto/visualobserving/ 
Map_at_the_Telescope.html

Best to you.  Hope for clear skies ahead so some of us can star-hop!
Mark



On Aug 20, 2007, at 2:55 AM, Michael Hrivnak wrote:

> Any experience or opinions on the Burgess 8x50 RACI finder?
>
> http://www.burgessoptical.com/Accessories/Finder8x50.html
>
> I realized that I don't use my Orion 6x30 finder very much, and I  
> think it's
> because I just can't see very well with it.  I can barely make out  
> a few
> brighter objects like M13, but it's a real stretch.  My hope is  
> that since an
> 8x50 should gather 2.78 times as much light, I'll have a much  
> easier time
> identifying things in the finder, and thus it will be a more  
> valuable tool.
> Does your experience support that theory?  Do you prefer a  
> different size
> than 8x50?
>
> If I have my math right, I think objects in a perfect 8x50 should  
> be about
> 1.56x brighter than in a perfect 6x30.  If only to help my own  
> understanding,
> I should quickly run through the math.  The saying is that doubling
> magnification reduces brightness by a factor of 4, right?  I think  
> that can
> be formulated to say that the factor by which brightness will  
> change from one
> magnification to the next is equal to (old magnification / new  
> magnification)
> ^2.  In this case, we have (6 / 8)^2 = .5625.  Correct me if I'm  
> abusing the
> laws of physics here.
>
> Then the difference in aperture area = 25^2 / 15^2 = 2.78.
>
> We have two factors by which brightness will change, so we multiply  
> them!
> 2.78 * .5625 = 1.5625.
>
> Object should be bigger, brighter, and thus much easier to locate.   
> What do
> you think?
>
> Thanks,
> Michael
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