manually choosing star seems to improve my guiding

[TiffsAndAstro]

i seem to get better guiding when i manually select a star to guide on in phd2. does this suggest i've mucked up my settings somewhere and should reset try again?

over last few sessions, i'd guesstimate auto select gets me around 1.2 - 1.5 (occasionally much much worse) and manually selecting one gets me 0.6 - 1.1

for example, tonight i forgot to even balance in dec properly because i was hurrying and manually choosing star seems to have dropped my guiding from 1.7 to 1.05 over 400 0.5 sec exposures

Edited August 3 by TiffsAndAstro

[Budgie1]

There shouldn't be any need to reset but you could try running the Guiding Assistant for over 3 minutes and run with the settings it suggests. Make sure the mount is balanced correctly first and also do a recalibration run as well.

I also use guide camera exposure of 2 - 2.5 seconds.

[TiffsAndAstro]

im using 0.5sec and have tried everything up to 3.0sec

i did see a good you tuber say they used 0.5sec and it was conventionally bad but didn't really go into it much more

don't like the guiding assistant because last time i used it some time ago, it said bad things  

Edited August 3 by TiffsAndAstro

[Elp]

Short guide exposures are suited to HD mounts though by doing so with any mount you're fighting the seeing so your mount may correct though it doesn't need to. 1-2s is more suitable, if seeing is bad maybe more but in such conditions the images may not turn out so good.

[TiffsAndAstro]

2 minutes ago, Elp said:

Short guide exposures are suited to HD mounts though by doing so with any mount you're fighting the seeing so your mount may correct though it doesn't need to. 1-2s is more suitable, if seeing is bad maybe more but in such conditions the images may not turn out so good.

tonight has lots of cloud patches and possible high cloud so maybe not best time to try and tweak. or do anything  

i am getting my lowest ever hfr though. this is starting to seem very random

Edited August 3 by TiffsAndAstro

[Elp]

If you visually look at a star up close during bad seeing you'll know what I mean, it'll dance all over it's central point which is something you don't want your mount to correct for, I think during longer guide exposures it averages out the movement then issues a pulse.

[TiffsAndAstro]

meh cloud is here. maybe later it will clear a little

[Elp]

I'm hoping tomorrow holds but we'll see.

[Budgie1]

21 minutes ago, TiffsAndAstro said:

im using 0.5sec and have tried everything up to 3.0sec

i did see a good you tuber say they used 0.5sec and it was conventionally bad but didn't really go into it much more

don't like the guiding assistant because last time i used it some time ago, it said bad things  

Sometimes sub-1 second exposures work but, as @Elp has said, you may be chasing the seeing. Also, a longer exposure (even 1-1.5 sec) gives you better SNR on the guide star and makes it easier for PHD2 to follow, so you don't get as many "Star Lost" warnings.

Are you using multi-star guiding? If not then give it a go and see if that improves things.

Also make sure your guide scope focal length & guide camera pixel size are correct in the PHD2 settings. I thought I was getting great guiding last night, until I noticed I hadn't changed the focal length setting from the 765mm when I was using an OAG, to the 242mm for the EvoGuide I was using on the current scope!

[TiffsAndAstro]

25 minutes ago, Elp said:

I'm hoping tomorrow holds but we'll see.

jinx alert

[TiffsAndAstro]

Just now, Budgie1 said:

Sometimes sub-1 second exposures work but, as @Elp has said, you may be chasing the seeing. Also, a longer exposure (even 1-1.5 sec) gives you better SNR on the guide star and makes it easier for PHD2 to follow, so you don't get as many "Star Lost" warnings.

Are you using multi-star guiding? If not then give it a go and see if that improves things.

Also make sure your guide scope focal length & guide camera pixel size are correct in the PHD2 settings. I thought I was getting great guiding last night, until I noticed I hadn't changed the focal length setting from the 765mm when I was using an OAG, to the 242mm for the EvoGuide I was using on the current scope!

when i leave phd2 to it, it  auto selects a star and 4 others are circled. i think this is the multistars

when i manually choose a star, i don't see any stars circled, so i assume multi star guiding is off. i assumed multi star would be better from averaging but for me it seems not. which makes me think i've mucked up a setting. target snr is set to 6 which seems low? its only thing sticking out  

[Budgie1]

2 minutes ago, TiffsAndAstro said:

when i leave phd2 to it, it  auto selects a star and 4 others are circled. i think this is the multistars

when i manually choose a star, i don't see any stars circled, so i assume multi star guiding is off. i assumed multi star would be better from averaging but for me it seems not. which makes me think i've mucked up a setting. target snr is set to 6 which seems low? its only thing sticking out  

Yep, that's about right for multi-star guiding.

6 is the default minimum SNR, when you're guiding I think you want to see something around 30+, which will show in the bottom right of the PHD2 screen.

[TiffsAndAstro]

7 minutes ago, Budgie1 said:

Yep, that's about right for multi-star guiding.

6 is the default minimum SNR, when you're guiding I think you want to see something around 30+, which will show in the bottom right of the PHD2 screen.

hmm i (for no real reason tbh) thought the 20+ i got was fine. i have nothing to judge it by. i will try and see if i can get them above 30

cheers for all this btw

[Budgie1]

1 hour ago, TiffsAndAstro said:

hmm i (for no real reason tbh) thought the 20+ i got was fine. i have nothing to judge it by. i will try and see if i can get them above 30

cheers for all this btw

I wouldn't get too hung up about the exact number, I've seen 18-30ish mentioned but others have seen it as high as 120. The secret is not to let the star get saturated.

Looking on the PHD2 user guide it says:

Quote

Target SNR - this is the average SNR value that PHD2 will attempt to achieve by adjusting the exposure time. SNR often fluctuates from frame to frame even with a fixed exposure duration, so be sure to account for that when choosing a target SNR value. PHD2 will always reject frames when SNR drops below 3.0. The default value of 6.0 may provide enough of a cushion to prevent fluctuations from causing the SNR to go below 3.0 - but double-digit values are recommended.

For the main screen the SNR figure it says:

Quote

SNR of the primary (or single) star in the guiding star list. If the SNR value drops below 10, its value will be shown in yellow as a warning that you may encounter some 'lost-star' events.  In single-star guiding mode, if the guide star is saturated, the field to the left of SNR will show 'Saturated' in a red typeface.

This may also be worth a watch :

 

[TiffsAndAstro]

24 minutes ago, Budgie1 said:

I wouldn't get too hung up about the exact number, I've seen 18-30ish mentioned but others have seen it as high as 120. The secret is not to let the star get saturated.

Looking on the PHD2 user guide it says:

For the main screen the SNR figure it says:

This may also be worth a watch :

 

already watched it, but will watch it again tomorrow.  shorter exposure times to compensate for what i think are over saturated stars ? drop the gain from default?

[Clarkey]

If you manually choose a star the chances are it will be saturated which will affect guiding and give false results terms of accuracy. Auto and multi star will give the best result in my opinion.

As for the guiding assistant, use it and take note. It is there to help - but it is sometimes a little too honest. "Your guiding is pants - give up now" or words to that effect 😁

[TiffsAndAstro]

12 minutes ago, Clarkey said:

If you manually choose a star the chances are it will be saturated which will affect guiding and give false results terms of accuracy. Auto and multi star will give the best result in my opinion.

As for the guiding assistant, use it and take note. It is there to help - but it is sometimes a little too honest. "Your guiding is pants - give up now" or words to that effect 😁

Last time I ran it it said my Dec (might have been Ra lol) had one billion microseconds of back lash.

If it clears at all tonight I reckon run it seems what it says

Not sure how I can get less saturated stars though. The  guide scope is pretty nasty to focus.

also when I manually chose a star, my hfr seemed noticeably smaller. Not exactly scientific test though.

Edited August 4 by TiffsAndAstro

[Clarkey]

Just now, TiffsAndAstro said:

Not sure how I can get less saturated stars though. The  guide scope is pretty nasty to focus

What guide scope?

[TiffsAndAstro]

1 minute ago, Clarkey said:

What guide scope?

Zwo f4 120mm

Pointing it at a bright star with 10sec exposure gives tiny bahtinov diffraction patterns.

I'll try using the asi app and zooming in.

[Clarkey]

I have one and they are not great to focus. I find the SW finders pretty good with a C adaptor. However, they are a bit heavier. You can pick them up cheap. It is worth persevering with the focus though as it will help.

[TiffsAndAstro]

2 minutes ago, Clarkey said:

I have one and they are not great to focus. I find the SW finders pretty good with a C adaptor. However, they are a bit heavier. You can pick them up cheap. It is worth persevering with the focus though as it will help.

Btw run calibration before guiding assistant and keep same exposure time?

[Clarkey]

Yes. As a rule the suggested times are 1 to 3 secs which I would generally go with for UK seeing. Make sure you leave the camera to guide and settle before running though.

[Pompey Monkey]

To home in on an issue, always, always,  change only one thing at a time.

Do exactly what you did before, but just tweak one setting.

If you change more than one variable at a time, you'll never know what caused the change in the outcome. Nor will the good people who want to help you,  me included. 😃

This is an engineering 101 principle.

 

[TiffsAndAstro]

9 minutes ago, Pompey Monkey said:

To home in on an issue, always, always,  change only one thing at a time.

Do exactly what you did before, but just tweak one setting.

If you change more than one variable at a time, you'll never know what caused the change in the outcome. Nor will the good people who want to help you,  me included. 😃

This is an engineering 101 principle.

 

well i've been playing with one thing at a time mostly, but i think stuff interacts a lot so it doesn't seem that straight forward. plus wind and clouds. 

my guiding numbers are below my average but my hfr has been the lowest i've managed. 

did some flaming skull but clouds so now m27 lol

 

Edited August 5 by TiffsAndAstro

[TiffsAndAstro]

and m27 is bright lol. on the first plate solve 5sec image i said wow out loud lol