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Zerochromat 8 inch refractor

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#1 wiseone

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Posted 12 March 2010 - 10:43 AM

Several people have been asking questions about this design, so I am posting some spot diagrams and the wavefront error. There has also been a question about the upsides and downsides of this design. To answer this, I will first give the downsides - although it has been designed to have as much mechanical tolerance as possible, it is sensitive to movement of the corrector train. With proper mechanical design, this isn't too much of a problem, though it needs careful thought about supporting the tube; if it is squashed slightly when mounting, it can cause astigmatism. The mechanical allowance is 100 microns (about 4 thou') for the corrector assembly. The corrector lenses themselves are mounted on a rigid aluminium rail, and are in individual cells, accurate to +/- 25 microns. The inequalities in the OG placement and the small fold flat are taken into account by the adjustable large flat. By tweaking this flat mirror, you can take out atmospheric refraction when viewing objects low in the sky.
The upsides to the design are low cost and very good performance - the theoretical Strehl is 0.999+. There is no visible chromatic aberration, even at 500x on a bright star. The diffractions rings are gratifyingly weak, with nearly all the energy in the Airy disc. I welcome any serious questions.

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#2 wiseone

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Posted 18 March 2010 - 07:33 AM

422nm spot diagram

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#3 wiseone

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Posted 18 March 2010 - 07:34 AM

450nm spot diagram

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#4 wiseone

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Posted 18 March 2010 - 07:35 AM

500nm spot diagram

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#5 wiseone

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Posted 18 March 2010 - 07:36 AM

550nm spot diagram

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#6 wiseone

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Posted 18 March 2010 - 07:36 AM

600nm spot diagram

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#7 wiseone

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Posted 18 March 2010 - 07:37 AM

700nm spot diagram

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#8 wiseone

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Posted 18 March 2010 - 07:38 AM

Finally, the 800nm spot diagram

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#9 Crayfordjon

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Posted 19 March 2010 - 11:11 AM

Better than a Tak!, would you say?

#10 wiseone

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Posted 19 March 2010 - 11:53 AM

I really couldn't comment! It depends on the figures that they have.

One interesting feature is the very flat field of view, as it was designed that way. Traditional refractors need a field flattener, so the Zerochromat needs to be compared to a system complete with field flattener.

#11 jrbarnett

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Posted 19 March 2010 - 11:58 AM

Only in theory.

Design is important, but execution is what counts.

Will the prototypes and more importantly production units achieve close to the theoretically possible figure quality?

Takahashi consistently delivers actual quality approaching the theoretical maximum quality for their designs. That consistency is why they command premium prices in the marketplace. If this new entrant can deliver similar quality consistently, then yes I might say "better than Tak".

Until then, however, it's all talk. Best of luck with the new venture.

- Jim

#12 wiseone

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Posted 19 March 2010 - 12:02 PM

Thanks for the useful comment. Of course the proof is in the execution. I am working on productionising the telescope, but moving quite deliberately and without haste. Only time will tell...... :question:






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