Sensor not central to camera

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robertm
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Sensor not central to camera

Post by robertm » Fri Jun 29, 2018 8:37 pm

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

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Support@ZWO
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Re: Sensor not central to camera

Post by Support@ZWO » Tue Jul 03, 2018 2:08 am

Could you send us a picture? I will let our engineer take a look.
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robertm
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Re: Sensor not central to camera

Post by robertm » Wed Jul 04, 2018 2:19 pm

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
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ASI183MM-PRO_chip_off_centre.jpg

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Sam
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Re: Sensor not central to camera

Post by Sam » Thu Jul 05, 2018 9:00 am

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
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183.jpg
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robertm
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Re: Sensor not central to camera

Post by robertm » Thu Jul 05, 2018 3:19 pm

Thanks Sam I’ll check that out.

Robert

robertm
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Re: Sensor not central to camera

Post by robertm » Thu Jul 05, 2018 11:03 pm

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
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sensor centred.JPG

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Sam
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Re: Sensor not central to camera

Post by Sam » Fri Jul 06, 2018 10:50 am

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
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Konihlav
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Re: Sensor not central to camera

Post by Konihlav » Mon Jul 30, 2018 2:33 pm

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!

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Support@ZWO
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Re: Sensor not central to camera

Post by Support@ZWO » Mon Jul 30, 2018 3:24 pm

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.
Location:lon=120.6 lat=31.3
Suzhou China

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