Plane wave have said that with the cdk design it's a compromise between vignetting and F ratio. Hence they went with F6.8 which is what most CDK designs have had (more or less).
F6.8 is still pretty fast. Planewave's reducer is .66X a pretty savage and takes the F ratio down to F4.5 or so. The problem with that with this iteration of reducer is optimum spacing is something like 54mm which means I can't use my current OAG and I would have to do guide scope autoguiding which is hit and miss.
I may switch to a zwo or qhy OAG they are thinner than my MMOAG (40mm thick).
I have found my Planewave very easy to collimate and it holds collimation well.
The whole design seems very user friendly.
Greg.
Quote:
Originally Posted by OzEclipse
Greg,
This is a smaller aperture than the 260:
Vixen VC200L 8" f9 f6.4 (1280mm FL) with dedicated reducer.
Mechanically very sound, holds collimation well
No front corrector plate so optics resistant to dew/fog
Corrected image circle just clips the corners of a full frame sensor
Joe
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Quote:
Originally Posted by Stefan Buda
Thanks Greg,
They probably tried to reduce vignetting by not making the primary baffle fully cut off direct view of the sky from the sensor. The SCA260 is a bit faster than my CDK250 and that would've made full cutoff more difficult.
Thanks Ben,
It seems that they pushed the design into very difficult territory that is very unforgiving for any misalignments.
When I designed the CDK250, I wanted to make it f/5.6 and it turned out that it was impossible to achieve full correction over a full size sensor by using only two lens elements. I'm sure that is why they had to use 3 lens elements and that makes the design even more prone to alignment problems.
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