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Refractors vs SCTs and Maks for uneven doubles

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#51 WRAK

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Posted 21 January 2013 - 07:40 AM

... A question - why have you set the CO for 254mm at 33% ? This would be unusual for a Newtonian unless of short focal ratio. Lord's 10 1/4-inch reflector mentioned in his paper is of long focal ratio, therefore is likely to have a smaller CO...

Fred, the advertised data of this mixed bag of observations point rather to the mid of the last century and these are probably not Lord's own observations but some from the Lewis collection. Another hint are 254mm = 10" aperture. But this would maybe even the more suggest a smaller CO. The reason why I assumed despite this a rather large CO is the heavy overperformance for very close equal bright doubles in relation to the Dawes criterion even when modified for CO. May be the unknown observer even used a trick described by Taylor in Argyle's book on "Observing ..." - intentionally increasing the CO for a better chance to split very close equal bright doubles.
Wilfried

#52 Asbytec

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Posted 21 January 2013 - 09:03 AM

STT 517AB, a very close, 7th magnitude pair.
http://www.cloudynig...ber=5634514&...






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