Temp sensor EAF

[xelasnave]

Where do you place the temperature sensor for the ZWO EAF ? In the camera? On the tube?

Alex

[JA]

Hi Alex,

whilst I don't use one, what I can suggest is that the temperature compensation is used to account for the change in optical path length caused by temperature changes in the telescope materials and more likely manifest in the tube assembly. That is the way it would be modelled from first principles using the coefficients of linear expansion of the material/s.

I'd therefore try to monitor the tube temperature, typically the longest component, being careful to discount any air temperature/wind effects, by careful placement of the sensor on the tube assembly and insulating it so that the heat transfer is largely form the tube side, not the environment.

Best
JA

[xelasnave]

Thanks J A..talking of temperatures there was ice in the observatory last night on most everything. .
Alex

[Drac0 (Mark)]

Never really considered it too much. I've just had mine sitting down the side of the scope but not fixed to it, just the end hanging out of my cable run. Probably is something I should look at more & JA is probably heading in the right direction with trying to focus on the temp of the scope itself.

Cheers,
Mark

[RyanJones]

JA is bang on.

[Drac0 (Mark)]

I guess the next question is where along the tube would be the best location?
Cheers.
Mark

[mswhin63 (Malcolm)]

The idea for measuring the temperature is to configure the automated process for re-focus, realistically the probe can be set in most places even if for example a refractor has no access to the optical path.
For me, I wouldn't need t go to the wiring path, only look at ambient temperature as based on thermal conduction principles the optical path will eventually cool within a thermal constant.

In short, I would measure every delta at 3 degrees ambient. In turn, this could be every 3 degrees in the tube or whatever your setup will be. Eventually it will all balance out.

[xelasnave]

I think the only thing to do is drill a hole in the mirror and set it in there with epoxy

But I am going to stick it in a little block of foam such that it will be in contact with the tube and stick it on the tube but near the back and on the top so everyone will ask "what's that?" Together with the remote temperature sensor that came with my camping fridge with the readout in the van so I can monitor temperate in the observatory all the time..that will be handy...

Alex

[Startrek (Martin)]

Alex,
I’ve been using my EAF’s both autonomously with the handcontroller and with APT for more than 12 months now at both locations with both Newts and never used a temp probe
Never had any issues with focus drift at all and I’m not going to bother using it with the big 10” CF Newt either

Do RASA’s suffer from focus drift in extremes of temp and humidity ?

I’ve never had severe problems with focus drift

Martin

[JA]

Originally Posted by Startrek

Do RASA’s suffer from focus drift in extremes of temp and humidity ?

Hi Martin,

I think that focus is simply more critical at lower f-ratios, probably because of the increased field curvature that the flat sensor has to deal with, resulting in a reduced (acceptable) range of the plane of focus. As a result external influences like temperature, which change the optical path length will be even more apparent.

Best
JA

[Dave882 (David)]

I’ve never used a rasa but with the c14 I need to refocus at least every 1hr till midnight, after which it remains fairly stable. I’ve heard people recommend a refocus every 1degree shift, I reckon that’s generous. I always approach focus from same c/clockwise direction and have mirror locks, and tube is 110% insulated now, but still needs fairly regular attention. Refocus are always in the same direction for me (clockwise adjustment, with c/clockwise final approach of course) so not sure how that reflects on tube contraction.

[Startrek (Martin)]

Originally Posted by JA

Hi Martin,

I think that focus is simply more critical at lower f-ratios, probably because of the increased field curvature that the flat sensor has to deal with, resulting in a reduced (acceptable) range of the plane of focus. As a result external influences like temperature, which change the optical path length will be even more apparent.

Best
JA

Thanks for the optical explanation for focus shift
Glad I’m not imaging at f2
My f5 Newts up to 1250mm fl are obviously more forgiving

Cheers
Martin

[xelasnave]

Originally Posted by Startrek

Alex,
I’ve been using my EAF’s both autonomously with the handcontroller and with APT for more than 12 months now at both locations with both Newts and never used a temp probe
Never had any issues with focus drift at all and I’m not going to bother using it with the big 10” CF Newt either

Do RASA’s suffer from focus drift in extremes of temp and humidity ?

I’ve never had severe problems with focus drift

Martin

I am only using it because it was in the box
But given the issues I am finding with focus I will bet that temp change may be an issue ...hopefully the day will come where I can comment from experience.
Alex

[Nikolas (Nik)]

I let my temperature probe hang freely as it is near the OTA it measures the ambient temperature and I set it to refocus every 2C temperature drop, it works perfectly

[LonelySpoon (Neville)]

I've got a Celestron autofocuser and to be honest I don't know if it is compensating or not!

Just got the ZWO EAF and am considering the sensor.

If the critical focus of your setup is very narrow, I'd guess temperature compensation becomes, well, critical?

As the whole setup cools down, the more massive components change least, so my plan is to put the sensor near the focuser on my refractor, and on the top of the tube of my SC. On the other hand, bigger components move more physically, as a percentage of change.

Just guessing, though.

I got a sensor with my Pegasus box which is useless 'cos I can no longer communicate with the box- it just distributes power now, so I don't know what the temperature is doing at the scope.

Neville
LSO