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Equipment Discussions >> ATM, Optics and DIY Forum

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Reged: 10/07/09

Loc: USA
Re: Secondary Size Revisited - A New Realization? new [Re: dvb]
      #6169811 - 11/01/13 08:47 AM


I would not reduce the tube diameter to make decrease the secondary size - at least 1" is needed in addition to the radius of the primary to ensure proper air flow to deal with thermal currents in the tube.

Tube currents are probably the dominant factor in picking a tube size for tube OTAs, unless forced air cooling removes the need for the extra room. The need for additional UTA diameter for cooling or airflow considerations for truss telescopes is much less clear. I've seen no statement that a problem exists that needs to be addressed.

I was trying to inform on the purely optical tradeoffs. If people want a larger secondary and bigger OTA or taller focuser so the eyepiece height is lower, that's another tradeoff.

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