crackout I don't see how that adds anything to question above.
You need to refocus the optical train when temperature changes cause the OTA tube to change length, and thus change focusing -- remember that a 5 micron change would cause you to go out of critical focus zone, especially with fast optics.
The usual (what people like Hara and I use) method is to tape a temperature sensor to the optical tube. Depending on the optical design, often, a 1º C change will require a refocus, and if you are very critical, even 0.5ºC change.
What Hara is telling you is that if you do not install a temperature probe, instead of using temperature to determine when you need to refocus, then you will need to blindly check focus periodically (often unnecessarily), perhaps every half hour or hour, depending on how fast temperature is changing.
Hara's answer is a perfectly good answer to me. Best not to bite the finger that feeds you. He was kind enough to answer you while the rest of us just think that it is so obvious that we don't bother to answer. An apology might cause him to continue to help you.
Chen
