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Sensor not central to camera

Posted: Fri Jun 29, 2018 8:37 pm
by robertm
Hi,

I’ve just received an ASI183MM Pro but have noticed that the sensor is not centred in the camera body. Is this normal ?

I think this will have quite an impact on things like polar alignment (using stars) and also collimation of my telescopes so I want to know if this is normal or not.

Many thanks
Robert

Re: Sensor not central to camera

Posted: Tue Jul 03, 2018 2:08 am
by Support@ZWO
Could you send us a picture? I will let our engineer take a look.

Re: Sensor not central to camera

Posted: Wed Jul 04, 2018 2:19 pm
by robertm
Hi Sean,

I've added a file to show what it looks like. I've added a few rough lines to help show what I mean.

The sensor also doesn't seem to be perfectly orthogonal though I've yet to see how much difference this makes at f/3 in practice (I've not enough backfocus for the tilt adjuster.

Many thanks for taking look at this.
Robert

Re: Sensor not central to camera

Posted: Thu Jul 05, 2018 9:00 am
by Sam
This is not a correct way to tell the sensor is center or not
you can use a lens to check if you wish to

the tolerance is around 0.1-0.2mm during assembly

Re: Sensor not central to camera

Posted: Thu Jul 05, 2018 3:19 pm
by robertm
Thanks Sam I’ll check that out.

Robert

Re: Sensor not central to camera

Posted: Thu Jul 05, 2018 11:03 pm
by robertm
Hi Sam,

You're right. Even though the sensor looks way out by eye I've confirmed it is actually 252 microns (0.252mm) off (that's 105 pixels * 2.4 microns) i.e. slightly off spec. In an ideal world it would have been nice to have it perfectly central but I shouldn't think that will matter too much in practice.

Sorry for taking up some of your time.

Robert

Re: Sensor not central to camera

Posted: Fri Jul 06, 2018 10:50 am
by Sam
robertm wrote:Hi Sam,

You're right. Even though the sensor looks way out by eye I've confirmed it is actually 252 microns (0.252mm) off (that's 105 pixels * 2.4 microns) i.e. slightly off spec. In an ideal world it would have been nice to have it perfectly central but I shouldn't think that will matter too much in practice.

Sorry for taking up some of your time.

Robert
0.2mm sounds reasonable and is under the tolerance of our control
we will try to do better in the future, thank you

Re: Sensor not central to camera

Posted: Mon Jul 30, 2018 2:33 pm
by Konihlav
0.2mm is very, very, very large number.

With DSLR camera lenses, I have to sometimes tune them with 0.05mm and 0.02mm "washer" to make the bayonet square to my camera (that also must be perfect between chip and bayonet), for this a "washer" like thin foil could be used, see, e.g.:
https://www.ebay.com/itm/Brass-Metal-Th ... SwwVRZjC7n

I prefer if the camera is perfect, if the lenses are perfect etc. then you need less effort to make it work and make every pixel sharp, focus and count! with perfect gear you can combine it without issues and a need to re-fix-for-tilt.

Also, with my F/3.6 astrograph (ASA 10") I use 0.025mm focuser STEP to focus my telescope - hence I can see a difference of 0.05mm, definitively!

Re: Sensor not central to camera

Posted: Mon Jul 30, 2018 3:24 pm
by Support@ZWO
Konihlav wrote:0.2mm is very, very, very large number.

With DSLR camera lenses, I have to sometimes tune them with 0.05mm and 0.02mm "washer" to make the bayonet square to my camera (that also must be perfect between chip and bayonet), for this a "washer" like thin foil could be used, see, e.g.:
https://www.ebay.com/itm/Brass-Metal-Th ... SwwVRZjC7n

I prefer if the camera is perfect, if the lenses are perfect etc. then you need less effort to make it work and make every pixel sharp, focus and count! with perfect gear you can combine it without issues and a need to re-fix-for-tilt.

Also, with my F/3.6 astrograph (ASA 10") I use 0.025mm focuser STEP to focus my telescope - hence I can see a difference of 0.05mm, definitively!
It's better to check the result of real shooting, I don't think it would be a big problem.