[Chaos-l] Burgess Finders?

[Mark South]

One more thing as I state the obvious:  :)
Note I said to square the radii, but used the diameters to  
calculate.  You get the same answer either way because of the ratios.
25^2/15^2 = 2.78/1
thanks
Mark
On Aug 20, 2007, at 6:33 AM, Mark South wrote:

> 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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