Question about PHD2 and camera bit depth

[John Nagy]

A friend and I both have ZWO ASI120mm-S guide cameras and we both use PHD2. I've always operated mine with the PHD2 setting of 16 bit. The camera isn't 16 bit though, the ZWO website says it's a 12 bit ADC. There's no choice in PHD2 for 12 bit. Does that make a difference?

I noticed the other day that my friend has his PHD2 set to 8 bit. I went back and looked at his guide logs from the past year and he's always had it set to 8 bit. Does this low setting have a negative effect on guiding accuracy?

Thanks,

John

[bw_msgboard]

Hi John, see below.

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of John Nagy
Sent: Monday, June 07, 2021 3:37 PM
To: open-phd...@googlegroups.com
Subject: [open-phd-guiding] Question about PHD2 and camera bit depth

A friend and I both have ZWO ASI120mm-S guide cameras and we both use PHD2. I've always operated mine with the PHD2 setting of 16 bit. The camera isn't 16 bit though, the ZWO website says it's a 12 bit ADC. There's no choice in PHD2 for 12 bit. Does that make a difference?

 

The drivers convert the internal camera data into either 8-bit or 16-bit data streams because that’s how the data will be stored and manipulated by the applications.

 

I noticed the other day that my friend has his PHD2 set to 8 bit. I went back and looked at his guide logs from the past year and he's always had it set to 8 bit. Does this low setting have a negative effect on guiding accuracy?

 

It doesn’t necessarily have an effect on guiding, but the loss of depth makes the frames more vulnerable to bright sky backgrounds or mis-matched dark frames.  In general, it’s better to use 16-bit mode with one known caveat: Some of the ZWO cameras/drivers don’t support it correctly and will silently drop into 8-bit mode.  At that point, guiding will be impacted and may fail altogether.

 

Bruce

 

Thanks,

John

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[John Nagy]

Thanks Bruce. I'll pass this along and remind him next clear night to make the change.

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