[Chaos-l] Burgess Finders?
md_south at mac.com
Tue Aug 21 10:27:52 EDT 2007
1 more correction to yesterday's email.
I said the 50mm has 278 times more light gathering power.
Correction: Based on the formula below, that is actually 2.78 times
more...and that still is a 178% increase from 30mm to 50mm.
Remember, however, 50mm is still small aperture as a finderscope, so
still don't expect to be "wowed" by this scope, unless you are in
really transparent, dark skies.
On Aug 20, 2007, at 7:32 AM, Mark South wrote:
> 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
> On Aug 20, 2007, at 6:33 AM, Mark South wrote:
>> 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,
>> 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:
>> Best to you. Hope for clear skies ahead so some of us can star-hop!
>> On Aug 20, 2007, at 2:55 AM, Michael Hrivnak wrote:
>>> Any experience or opinions on the Burgess 8x50 RACI finder?
>>> 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
>>> 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
>>> ^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?
>>> Chaos-l mailing list
>>> Chaos-l at rtpnet.org
>> Chaos-l mailing list
>> Chaos-l at rtpnet.org
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