Problems with flats

[MikeB838]

Hi Robin,

I have set backlash to 0 in the Ascom driver of the ZWO EAF.

But I must admit that the problem can be that changing the focus by commanding some steps does move the stars a little bit sideways each time
I command a focus change. Changing the direction does move them in the other direction. I thought that engaging the focuser does only somehow
move the mount, but may be it might move the camera sideways, although it does not look like. I think I will contact the company who has
assembeld it for me (as my Intes Micro did need a special preparation to add accessories: special parts done by lathe).

I have a Maksutov 150mm /1540mm (1:10). The donuts are 140 by 140 pixels, the chip has 2,9umx2,9um Pixels (2712x1538 pixels).
140/2=70*2.9*10=2030 (correct??).
I can see dust specs on the main mirror, but I dare to open it for cleaning as I fear the collimation to be a problem later.
Maksutovs are just closed systems.

Thank you very much that you continue with your help!
I appreciate it very much!

Cheers,
Michael

[admin]

Hi Michael,

depending on the construction of your focuser, a bit of shift as the focus mechanism takes up or releases the load of the camera may be normal. Sometimes there is a tensioning screw for the focuser mechanism that you can tighten a bit (but if you go too far on that it will make it so tight that the motor cannot move the focuser).

cheers,

Robin

[MikeB838]

Hi Robin,

I talked with a person from Astroshop.de today. I have to wait for the technicians to finish their holidays, but as we discussed my problem,
he wondered that a slight touch to the camera (in this tight system) can show up the donuts again. If the system is so sensitive, a swing of
my telescope during the night can show up the donuts. I think that is what had happened to me (in the nights I did not refocus).

It makes me wonder that moving the camera for only a few pixels will show up not only a small ring but a broad ring. Or do I think in the wrong direction? How many pixels shift will be tolerated??

And a new inspection showed that there is some dust on the camera window (I had looked more than once). Oh boy.

BTW: I got a cooled Uranus-C Pro (PlayerOne) today, worked out of the box in SC .
And no donuts on the first look (with refocussing). I'm looking for clear nights now . To continue checking...
And I will ask the technicians, if fiddling with the tension screw(s) can help.

Thanks Robin!

cheers,
Michael

[admin]

Hi Michael,

hope that you have good success with the new camera - one other approach you could take is to buy some sensor wipes (they are not that expensive - you get packs with wet and dry swabs). Typically you would use these on the camera window which will be what has the dust on rather than the sensor itself. I have some and they are fairly good at getting you a clean sensor, although it will inevitably pick up more dust in the end.

cheers,

Robin

[MikeB838]

Hi Robin,

thanks for the tip with the sensor wipes, I may give them a try.

I parked my scope always pointing to polaris. May be I should park it horizontally, so no spurious dust may fall to the mirror or to the
the camera window/sensor.

Thanks I will report my progress with the new camera regarding flats and focus.

cheers,
Michael