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C11 vs. EdgeHD11 vs. VMC260l

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#1 Scott Rose

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Posted 04 February 2010 - 08:11 PM

Looking for a larger portable cat mostly for visual and maybe some AP. Any insights from users of these scopes would be appreciated, especially someone who has used both.

#2 Patrick

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Posted 05 February 2010 - 07:24 AM

There aren't that many EdgeHD's out there yet, and probably not too many folks have a VMC260, so you may get limited responses from folks who've actually used all three (which includes me).

In general, the word is that the EdgeHD's can put out a very good image all the way to the edge of field and has a very flat field. A standard C11 will have some field curvature and more aberrations towards the edge of the field. How important that is to you only you can decide. With a tracking mount capable of keeping an object in the center of the field it may be less important.

The main benefit of the EdgeHD's will be seen in astrophotography...long focal length astrophotography...with flatter fields and round stars all the way to the edge of the field.

The VMC260 is a much more expensive scope and does not have a corrector plate on the front of the scope. The corrector sits in front of the secondary mirror. It has a flat field as well and is highly regarded as an excellent astrograph. Unlike most SCT's, the secondary is held in place with a spider, so diffraction spikes when looking at bright objects or when imaging will be apparent.

All three of the scopes will require a beefy mount at least in the CGEM class range.

Patrick

#3 mikefulb

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Posted 05 February 2010 - 06:13 PM

Hopefully another advantage of the EdgeHD11 over the C11 for imaging will be the mirror locks. My C11 mirror shifts about 1 arc-minute per hour when tracking from East to West. I'm very curious how well the mirror locks on the Edge work and if 10-15 minute exposures are possible at prime focus with 9 micron pixels, for example.

Michael

#4 dickbill

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Posted 05 February 2010 - 06:27 PM

The main benefit of the EdgeHD's will be seen in astrophotography...long focal length astrophotography...with flatter fields and round stars all the way to the edge of the field.

Hi Patrick, wouldn't you expect the opposite, that at long focal lenght and therefore reduced field of view, the advantages of the HD diminish?

#5 Patrick

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Posted 06 February 2010 - 12:18 AM

Hi Patrick, wouldn't you expect the opposite, that at long focal lenght and therefore reduced field of view, the advantages of the HD diminish?



The focal length for an EdgeHD is the same as a standard SCT which is about 2800mm. Since the corrector is built into the draw tube of the EdgeHD the main benefit of the correction (flat field, round stars) is only gained when imaging at the scopes native focal length (or with a reducer when one becomes available). The Edge will have tighter stars all the way to the edge of the field of view than a standard SCT.

Patrick






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