Temperature sensor

[Bottletopburly]

Is anyone using a temperature sensor with auto focus using Apt, how much of a temperature drop do you need for the need to refocus ,I mean would you set it to refocus for every 1 degree fluctuation  can’t seem to find any info with regards to using a temp sensor with an autofocuser on the web . 

Edited April 3, 2019 by Bottletopburly

[red dwalf]

i know some people would do it every 1 or 2 degrees but i don`t usually bother unless 3 or 4 degrees

[+Ibbo]

Depends on which scope I'm using.

The Tak 102 is pretty stable as is the TS IS71, the WO 132 and the SCT need more attention.

[Bottletopburly]

3 hours ago, Ibbo said:

Depends on which scope I'm using.

The Tak 102 is pretty stable as is the TS IS71, the WO 132 and the SCT need more attention.

Steve never gave a thought how temp fluctuations  may be different depending on scope or type of scope , what sort of temperature fluctuations would be needed before you would need to refocus on an 8” newt  same with the 5” mak ,would the mak be more stable than the  newt . Also may be a dumb question when your using a temp sensor and you have done initial focus and you have setup your software for temp sensor in my case APT and temp drops say 2degrees do you have to physically stop to refocus or does the software adjust focus to suit on the fly  I’m assuming it changes on the fly or in between imaging subs depending how software is configured ?

[+Ibbo]

With the Tak I am looking at 2-3 °C with the SCT its every degree or so.

I dont think it is scope tyepe rather focal length.

 

But I am guessing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[red dwalf]

Easiest way to find out if you need to re focus is to check the images every no and again, zoom in on a star and it'll show if the focus is out.

[Bottletopburly]

31 minutes ago, Ibbo said:

With the Tak I am looking at 2-3 °C with the SCT its every degree or so.

I dont think it is scope tyepe rather focal length.

 

But I am guessing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3 minutes ago, red dwalf said:

Easiest way to find out if you need to re focus is to check the images every no and again, zoom in on a star and it'll show if the focus is out.

Thanks guys every days a school day.

[+Ibbo]

29 minutes ago, red dwalf said:

Easiest way to find out if you need to re focus is to check the images every no and again, zoom in on a star and it'll show if the focus is out.

Yes that is one way but I would rather not loose a sub esp if its one of my stupidly long 1800sec ones ?

[red dwalf]

I don't go that long Steve for that very reason, although my guiding is getting better every year, so might try one or two mega length exposures one day

[philjay]

Actually in theory, the longer the focal length the longer the decent focus point, therefore a longer focal length scope shouldnt need tweaking as much due to temperature change. However the longer fl gives a bigger image scale on the chip, eg magnification, so any drift in focus is magnified.

I spent a long time mulling ovef this when imaging with my old c11. Thats why I moved to refractors, I lost a lot of images with  the c11

[Bottletopburly]

12 hours ago, philjay said:

Actually in theory, the longer the focal length the longer the decent focus point, therefore a longer focal length scope shouldnt need tweaking as much due to temperature change. However the longer fl gives a bigger image scale on the chip, eg magnification, so any drift in focus is magnified.

I spent a long time mulling ovef this when imaging with my old c11. Thats why I moved to refractors, I lost a lot of images with  the c11

Thanks phil it will be a bit of trial and error ,i will refocus a at every one degree drop and measure the stepper change as i need an average to input into APT settings ,hopefully i will get a minute to swap af1 for af2 on the scope and be ready to roll 

[+Ibbo]

On 05/04/2019 at 20:43, philjay said:

Actually in theory, the longer the focal length the longer the decent focus point, therefore a longer focal length scope shouldnt need tweaking as much due to temperature change. However the longer fl gives a bigger image scale on the chip, eg magnification, so any drift in focus is magnified.

I spent a long time mulling ovef this when imaging with my old c11. Thats why I moved to refractors, I lost a lot of images with  the c11

I agree Phil, also it might be the smaller pixels on the modern cams comes into it as well.

[Bottletopburly]

Well I have set up APT to utilise the temp sensor and is now adjusting focus on the fly , stepper average I found for a 1 deg change was 17 steps , input this into settings in APT and it seems to be working fine so far stars looking tight ??

[Bottletopburly]

To get a better average I am going to start off checking focus with bahtinov mask after focus with autofocus, then re  autofocus  after 2deg temp change and double check with bahtinov mask then work out the step movement for 2degrees do this a couple of times should give me a more accurate average reading for step change due to temperature change , last time I was out I turned real time autofocus off and after 2degree drop focus is visibly out slightly.