Large refractors and dew systems
Posted 25 October 2013 - 12:53 AM
Looks like the heat might influence the correct focus, so some people use a temperature sensor
Probably best to place it behind the lens (lens system for an Apo-refractor) onto the OTA... placing it in front of the lens might cause more easliy some warmth into the dewshield tube
Posted 25 October 2013 - 02:13 AM
There seams to be some misunderstanding with that terms in recent thread (same topic).
Posted 25 October 2013 - 03:08 AM
If the dew cap is isolated from the cell by something thermally more insulating, like felt, velvet, etc., a heater on the dew cap will tend to keep the heat more localized there.
The dew heater does its job via conduction of heat to the glass and radiation from the warmed tube. Depending such on factors as;
- objective diameter/mass,
- degree of thermal contact between tube/cell and glass, and
- heater efficiency (more efficient when wrapped so as to reduce losses to air/sky),
the 'mode' of heat transfer (condictive or radiative) will be more one or the other.
Posted 25 October 2013 - 05:17 AM
Posted 06 November 2013 - 12:34 PM
Posted 06 November 2013 - 05:05 PM
Posted 06 November 2013 - 07:08 PM
Posted 07 November 2013 - 02:15 PM
Posted 08 November 2013 - 02:00 AM
You might try extending the dewshield for a 3:1 ratio. I've never had a dew issue with that ratio. No electrics.
Jim, Is that 3x the objective size? Sorry if it's a dumb question….I should know but the brain is elsewhere and a dew shield is looming on the horizon along with a large number of clouds as the f12 frac nears completion.