Hello,

Into the tab Guide of guide options, the parameter "Min error (arcsec)" could be calculate by Ekos as the ration between imaging sampling and guiding sampling.

Imaging sampling=206* Pixel imaging camera/mount focal
Guide sampling=206-Pixel guiding camera/ guide focal

Min error = Imaging sampling/Imaging guide

Best regards

I cannot follow this. What is 'imaging guide'? Or should that read 'guide sampling'? Then your ratio would not have units, and I have no clue why it should refer to some minimum error. What am I missing?

I apologize because I don't know all the right technical word.
I wanted to speak of scale image instead of image sampling.

I think this parameter is the same as Motion minimal on PHD2. Right ?

So in this case, the value is the fraction of a pixel, in percent, under wich no correction is sended to the mount. This value is the ratio of scale image between main caméra and guide camera.

Am I right ?

No apologies needed - I just wanted to make sure I understand what you want
In PHD2 indeed the min move is given in pixels, not in arcsec. And it's indeed pixels on the guide cam. But (IMO) you would not want to set it based on the image scale ratio, else you would only send a correction if the error on the main camera is already more than a pixel.
Now, in EKOS internal guider that min move is actually in arcsec, not in pixels. So you don't have to worry about conversions. Just specify the min move based on your camera image scale, using maybe a third or a quarter of that value at most.

Peter, is it possible to provide an example with numbers for your last sentence - suggestion for better understanding? (I just try to follow you both )

The idea is that a shift of, e.g., a quarter pixel on the main cam is still acceptable. My setup has 928mm FL and 3.76μ pixels, i.e., an image scale of 0.83"/px. A quarter of that is ~0.2". So this is the value I'd put in as min move.

For PHD2 I would have to know the FL and pixel size of the guide setup, too. It is 3.8μ/476mm or 1.65"/px. So the ratio as Morelli wants is 0.5. But you do not want to use that as min move in PHD2, it would be way too large (IMO). You should multiply the guide ratio with the allowed main cam pixel error, so for the example above 0.5*1/4 or 0.125

Did that help? I hope I'm not overdoing things

Thanks for that Peter!

I am not quite familiar with PHD2, I use only internal guider, but I got interested for this min value, cause I've never touched it before.

I'll do the maths to see if I can get something out of this too.

For example my main cam is 3.76μ / 400mm = 1.94 and the guide is 3.8μ / 120mm = 6.53

OK I understand the meaning of the field "Min error". The tooltip of this field must be rewrited with an example as your Peter.