Hi,
what is the logic behind AF every x hours?
Which starting point is used for counting x hours? The last AF routine? The start of the imaging session (I hope not)?
Does anyone know?
CS!
Logic behind Autofocus every x hours?
If you don't have properly functioning temp sensor, checking focus regular basis is a good idea.
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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
- Edited
I am fully aware of focus shifing due to temperature changes in the surrounding environment.
ASIAIR even gives an option to refocus based on temperature changes.
However, my question does not concern this in any way.
I wanted to know how ASIAIR "uses" the defined amount of time passed between two AF runs based on the setting "AF after every x hours". The trivial answer would be "time passed between two AF runs", but I have the suspicion that something else is going on here. It seems to me that AF induced by other triggers like filter or temperature change does not interfere with above logic. The setting will AF every x hours no matter how many other triggers activated AF in the meantime.
Allthough you previous answer to me wasn't.... well.... Anyway, my answer is still valid. Used alone, no other focus selections, it ensures that your scope is focused regular basis and focus is good despite the changes in temperature. It IS NOT NEEDED if you have filter wheel and/or temperature sensor and you have set the focus done triggered by them. Why an earth you would like to use all those options same time? it is unnecessary and takes good night time from actual exposures.
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A temperature-based AF routine does not render a time-based routine redundant or overkill.
Shooting an entire night with only one filter with very stable temperature would result in no AF routines at all (maybe one after the meridian flip).
This is the reason both temperature- and time-based routines work together to offer the best of both worlds. That is, if the implementation logic of time-based events is done in a smart way. And I fear this is not the case as of the current OS version, which is why I opened up this thread to find out.
Instead we are speaking about why it is important to refocus during temperature changes...
Why you refocus if filter or temperature has not been changed?