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minimum focusing distance with SE series

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#1 Ekyprotic

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Posted 20 June 2013 - 01:59 AM

Hi all, what's the minimum focusing distance with all the SE series scopes? I'm trying to figure out if I can use them as spotter scopes and for terrestrial photography.

#2 Atl

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Posted 20 June 2013 - 02:54 PM

I have focused on a caterpillar on a mesquite bush about 18ft away and the caterpillar covered the frame at about 100X with a 6SE.

#3 Ekyprotic

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Posted 20 June 2013 - 11:22 PM

I have the 8 SE I wonder if the minimum focusing distance is about the same? I found literature on the ETX90 that says it's minimum focusing distance is about 11 feet.

#4 Ekyprotic

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Posted 21 June 2013 - 03:48 AM

Alright, so I downloaded the manuals for a bunch of different scopes and here is what I found-

minimum focusing distance for the entire Nexstar series besides the 8 SE is 20 feet

for the 8 SE it's 25 feet

This still makes the 8 SE the best scope of this group for telemacro as its focal length of 2032mm more than makes up for the extra 5 feet.

In the ETX range, the best telemacro scope is the ETX 90 with a close focusing distance of 11.5 feet. The ETX 125's is 18 feet but its longer focal length of 1900mm does not completely make up the difference. However, both are better at telemacro than any of the scopes in the Nexstar range.

What really surprised me is that when I looked up the size of the central obstruction of the various SCT, the 8 SE, had far and away the smallest central obstruction (by diameter or by area) of any Celestron SCT- this includes the 9.25, 11 and 14 inch versions. There is a typo in the manual, but on Celestron's website it correctly lists the CO as 31 percent (by diameter) or 9.77 percent (by area) - 2.5" out of 8" (so you can do the math yourself.) This small percentage of CO is almost on the level of Meade's ETX MAK's (which are around 9.4-9.6 percent by area.) What this means is that the Nexstar 8 SE has the contrast of a 5.5" APO and the 6 SE of a 3.8" APO.... the 5 SE is more like a 3.15" APO

The Meade SCT CO that I looked up were MUCH larger- up to 14 percent (by area!) for the 8 inch.

One other thing I found is that a scope I had previously been considering as a secondary scope, the Star Navigator 102, only has a clear aperture of 90mm! So that idea is definitely out.






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