PHD2 auto selects a bright star?

[Andy56]

Hi,

Looking for help on PHD2 guiding.

Something has changed in my PHD2 setup and when it auto selects a star it chooses a relatively bright one with flat topped star profile. As I understand the flat top can lead to inaccuracies in guiding.

It used to, by default, select a small star with a pointed top for the star profile.

A difference between the manual and my set up is the Minimum star SNR for AutoFind. Mine is 6 the manual is 25.

Is this likely to be the cause. I can experiment tonight as it's predicted to be clear for quite a few hours, but I would like to know if I'm going in the right direction.

 

Many thanks,

Andy

Edited November 18, 2022 by Andy56

[Andy56]

Ah found a possible.

The Star Saturation Detection is set to Max-ADU value. Would this be better using Saturation Via Star-profile as this is what seems to be the issue.

Having said that I've not tried guiding using a flat topped star profile, I've just assumed that it would be poor.

Cheers

Andy

[symmetal]

If you enable 16-bit mode in the guide camera driver setup you should achieve much higher SNR figures which may assist PHD2 in choosing a star.

Also it's worth selecting multi-star guiding in the 'Brain' guiding tab as this will use many stars to derive the guiding corrections so having one of them saturated won't affect the result to any noticeable degree.

Alan

[newbie alert]

6 hours ago, Andy56 said:

Ah found a possible.

The Star Saturation Detection is set to Max-ADU value. Would this be better using Saturation Via Star-profile as this is what seems to be the issue.

Having said that I've not tried guiding using a flat topped star profile, I've just assumed that it would be poor.

Cheers

Andy

Won't be poor, just not as good.... means the fwhm reading will be inaccurate 

[Andy56]

To close this with feedback, the change I made to use Saturation Via Star-profile worked.

I think the multi-star guiding is selected but it only selects one star.

I'll experiment with this on the next clear night.

Many thanks for your assistance.

Andy

[david_taurus83]

I found in the past that if gain is set high on the camera it tends to pick faint stars that are more affected by seeing wobbles. If I lowered the gain it tended to select brighter stars that wouldn't saturate and were not as wobbly if seeing was poor.

[The Lazy Astronomer]

On 24/11/2022 at 08:06, Andy56 said:

To close this with feedback, the change I made to use Saturation Via Star-profile worked.

I think the multi-star guiding is selected but it only selects one star.

I'll experiment with this on the next clear night.

Many thanks for your assistance.

Andy

Phd2 will only show the guiding cross on one star, but if it's using multi star guiding, it should show circles around 5 - 10ish other stars within the FOV

[michael8554]

"I think the multi-star guiding is selected but it only selects one star."

If you have selected MultiStar, but have manually selected a guide star, MultiStar is disabled.

Michael