First Guiding Attempt in a While

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fatboy1271
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First Guiding Attempt in a While

#1

Post by fatboy1271 » Tue Aug 06, 2019 7:42 pm

The title is a lie because I tried for about 3 minutes a few nights ago... Anyway, getting a late start and knowing that the clouds would be rolling in (It's Always Cloudy in Los Angeles these days) I decided to dedicate what time I had to Guiding.

As was the case the other night my PHD2 live feed was washed out regardless of what exposure setting I used. Instead of beating my head against the wall I did a Reset in PHD2 and so glad I did!!! I do my Polar Alignments with the PoleMaster. My Alignment routine is done through the new CPWI, which I love once I got used to it; although there's not really much of a learning curve.

Once Guiding under RMS Error [px] my Tot would occasionally fluctuate between 0.18 and 0.33; however, it mainly stayed right around 0.18. I'm not very familiar with Guiding but that seems pretty good to me :)

I was taking 300sec at 800ISO and getting round stars as far as I could tell! I still need to do some tests to see if in my Light Pollution 300 at 800ISO is better than at 1600ISO, which gets pretty washed out. Also, I wonder if say 150sec at 1600ISO would be better than 300 at 800ISO...

Attached are two files:

Guiding graph
Guiding 2019-08-05.png
Roundness of star at 300sec (Subject is M14)
M014 Zoom on Stars.png
Thanks to anyone reading this and any comments/suggestions are always welcome!
fat
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
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#2

Post by Juno16 » Wed Aug 07, 2019 12:04 am

I don’t have any suggestions, but just a comment. “That’s Awesome!”

I’ve never seen PHD rms numbers like yours with my AVX. I’d be thrilled with double that!

Good for you!

Thanks,
Jim
Jim

Scopes: Explore Scientific ED102 Triplet APO, Celestron Nexstar 130 SLT.
Mounts: Celestron AVX with Orion MM Autoguider, SLT;
Binoculars: Bushnell 10X50
Camera / Software: Nikon D5300 (Ha mod), IDAS LPS D-1 Filter, Astrophotography Tool, PHD2, SharpCap v3.2, StarTools 1.6 alpha, PE14
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#3

Post by JayTee » Wed Aug 07, 2019 12:42 am

Congrats,

When you "auto guide" the very first thing you do after the image is complete and displays on your screen is to check the shape of your stars. They are either round or they're not. If they are, then YAY, if not then you need to develop a troubleshooting routine. Each imaging system is slightly different so your procedure/routine may or may not mimic mine.

So, what shape were your stars?

Also, in PHD2 don't gauge your guiding by using how many pixels your error is. Instead, use arcseconds, that is a much more meaningful measure of your guiding accuracy. This number is meaningful once you calculate what your imaging scale (not guiding) scale is. This all depends on the image scale of your main system and what you are trying to accomplish. If the RMS guiding error is 0.8 arc-sec, how does that translate to the number of pixels of movement on your main images? If you are working with a long focal length set-up and a main-camera image scale of well under 1 arc-sec/px, you might decide you need better guiding. With a shorter focal length setup for your main camera, this accuracy is probably fine. Measure the star-sizes in your main images and look at the star-sizes and elongation. Those are the only reliable ways to judge if the guiding is truly good enough. We sometimes point to a total guiding RMS of 1 arc-sec as a reasonable target for most set-ups, but that’s only a very rough starting point.

Cheers,
JT
Main: C-stron CPC1100 #2 Scope: 8" f/7.5 Dob mounted Newt AP Scopes: TPO 6" f/9 RC, ES 80mm f/6 APO G&G Scope: Meade 102mm f/7.8, Bresser 102mm f/4.5 Guide Scopes: 70 & 80mm fracs Mounts: C-stron AVX CGEM & GT Alt-Az, Meade DS2000 Cameras: Canon T3i (x2), ASI120MC Binos: 10X50,10.5X70,15X70 (x2), 25X100 EPs: ES: 21 100°, 30 82° X-Cels: 9, 12, 18, 25 Clubs: RCA & HAS
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#4

Post by fatboy1271 » Wed Aug 07, 2019 1:45 am

Juno16 wrote:
Wed Aug 07, 2019 12:04 am
I don’t have any suggestions, but just a comment. “That’s Awesome!”

I’ve never seen PHD rms numbers like yours with my AVX. I’d be thrilled with double that!

Good for you!

Thanks,
Jim
Thanks Jim! I hope to get out again soon to continue working on Guiding. I see JT has some more learnin' for me to do...

fat
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
EPs: Stock Celestron 9mm and 24mm / Celestron Omni 32mm (I love this one!) / Celestron X-Cel LX 3x Barlow (I think 2X would have been smarter...)
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#5

Post by fatboy1271 » Wed Aug 07, 2019 5:11 pm

JayTee wrote:
Wed Aug 07, 2019 12:42 am
Congrats,

When you "auto guide" the very first thing you do after the image is complete and displays on your screen is to check the shape of your stars. They are either round or they're not. If they are, then YAY, if not then you need to develop a troubleshooting routine. Each imaging system is slightly different so your procedure/routine may or may not mimic mine.

So, what shape were your stars?

Also, in PHD2 don't gauge your guiding by using how many pixels your error is. Instead, use arcseconds, that is a much more meaningful measure of your guiding accuracy. This number is meaningful once you calculate what your imaging scale (not guiding) scale is. This all depends on the image scale of your main system and what you are trying to accomplish. If the RMS guiding error is 0.8 arc-sec, how does that translate to the number of pixels of movement on your main images? If you are working with a long focal length set-up and a main-camera image scale of well under 1 arc-sec/px, you might decide you need better guiding. With a shorter focal length setup for your main camera, this accuracy is probably fine. Measure the star-sizes in your main images and look at the star-sizes and elongation. Those are the only reliable ways to judge if the guiding is truly good enough. We sometimes point to a total guiding RMS of 1 arc-sec as a reasonable target for most set-ups, but that’s only a very rough starting point.

Cheers,
JT
Hey JT,

Thanks for the info; I appreciate your time writing all that up. I understand what you mean by guiding numbers don't mean squat if you don't have round stars.

Last night I was tracking for 600sec! I'm hoping to try again tonight and see if I can get another batch of M31. Separate question is whether or not shooting at 600sec x 400ISO is better than 300sec x 800ISO.

Anyway, as to PHD2 numbers, is this the arcsecond setting you are talking about?
Arc-seconds vs Pixels.png
Here is a screenshot of a couple stars near M51. It's zoomed in at 328% in BYEOS:
M051 600s 400ISO 328Percent.PNG
They look round to me... What do you think? Am I on the right track?

Thanks again,
fat
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
EPs: Stock Celestron 9mm and 24mm / Celestron Omni 32mm (I love this one!) / Celestron X-Cel LX 3x Barlow (I think 2X would have been smarter...)
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#6

Post by Jennifer Christine » Tue Aug 20, 2019 3:31 pm

Check the smallest stars for elongation.
I notice in your original image that thetre is a lot of noise and stars are suffering from compression artifacts. Make sure you process in tiff format at 16 bit.
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#7

Post by JayTee » Tue Aug 20, 2019 9:28 pm

Here's my philosophy on exposure time and ISO. I try to use 1600 ISO whenever possible. It means that my exposure time will be shorter. I can process out the noise from the higher ISO but I can't fix the guiding errors that inherently pop-up with longer and longer exposures. It is a trade-off though because I believe the SNR is better on longer exposures, but the issue once again is that shorter exposures are less prone to guiding errors.

Plus, when you screw up a 10 minute exposure you've lost 10 minutes of imaging time, but if you screw up a three-minute exposure you've only lost three minutes and there's still seven more minutes to go in that 10 minute period where you could get in 2 more images.

Cheers,
JT
Main: C-stron CPC1100 #2 Scope: 8" f/7.5 Dob mounted Newt AP Scopes: TPO 6" f/9 RC, ES 80mm f/6 APO G&G Scope: Meade 102mm f/7.8, Bresser 102mm f/4.5 Guide Scopes: 70 & 80mm fracs Mounts: C-stron AVX CGEM & GT Alt-Az, Meade DS2000 Cameras: Canon T3i (x2), ASI120MC Binos: 10X50,10.5X70,15X70 (x2), 25X100 EPs: ES: 21 100°, 30 82° X-Cels: 9, 12, 18, 25 Clubs: RCA & HAS
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#8

Post by fatboy1271 » Wed Aug 21, 2019 12:50 am

JayTee wrote:
Tue Aug 20, 2019 9:28 pm
Here's my philosophy on exposure time and ISO. I try to use 1600 ISO whenever possible. It means that my exposure time will be shorter. I can process out the noise from the higher ISO but I can't fix the guiding errors that inherently pop-up with longer and longer exposures. It is a trade-off though because I believe the SNR is better on longer exposures, but the issue once again is that shorter exposures are less prone to guiding errors.

Plus, when you screw up a 10 minute exposure you've lost 10 minutes of imaging time, but if you screw up a three-minute exposure you've only lost three minutes and there's still seven more minutes to go in that 10 minute period where you could get in 2 more images.

Cheers,
JT
Hey JT!

Earlier today I posted My Exposure+ISO Test and pretty much found the same answer that you just gave! The 600sec x 400ISO has less noise but I think the 180sec x 800ISO has slightly more detail. Therefore, the extra time spent imaging one shot is not worth it. Especially with PI's capabilities...

The biggest issue is that if I shoot at 1600ISO I will be stuck most likely around 60 seconds. I haven't confirmed that but my LP is pretty bad; 8.5 to 9 Bortle looking SE and 7 to 8 looking W/NW :(

Thanks for your time!
fat
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
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#9

Post by JayTee » Wed Aug 21, 2019 3:08 am

For a Canon sensor, the conventional wisdom is to use either 800 or 1600 as your lowest noise ISO setting. This is based on some of the older models - T5i and older. So you need to do some more testing of your local environment and weigh ISO/Exposure duration against the level of background noise using the histogram as your guide. Ideally, you would like to keep the histogram in the left hand third of the scale and certainly no more than about halfway into the scale.

Hope this helps,
JT
Main: C-stron CPC1100 #2 Scope: 8" f/7.5 Dob mounted Newt AP Scopes: TPO 6" f/9 RC, ES 80mm f/6 APO G&G Scope: Meade 102mm f/7.8, Bresser 102mm f/4.5 Guide Scopes: 70 & 80mm fracs Mounts: C-stron AVX CGEM & GT Alt-Az, Meade DS2000 Cameras: Canon T3i (x2), ASI120MC Binos: 10X50,10.5X70,15X70 (x2), 25X100 EPs: ES: 21 100°, 30 82° X-Cels: 9, 12, 18, 25 Clubs: RCA & HAS
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#10

Post by Juno16 » Wed Aug 21, 2019 11:23 am

Hey fat,

I saw the histogram for a 600 second iso 400 image in your post. Somebody help me out here, but I always thought that you should shoot for 1/4 to 1/3 from the left. Yours are way up there close to 3/4. That explains why you are shooting much longer exposures than I am. I recently had some images where the histogram peak was almost halfway shooting at iso 400 for 150 seconds.
My thinking could be way off. Can anyone comment?

Thanks,
Jim
Jim

Scopes: Explore Scientific ED102 Triplet APO, Celestron Nexstar 130 SLT.
Mounts: Celestron AVX with Orion MM Autoguider, SLT;
Binoculars: Bushnell 10X50
Camera / Software: Nikon D5300 (Ha mod), IDAS LPS D-1 Filter, Astrophotography Tool, PHD2, SharpCap v3.2, StarTools 1.6 alpha, PE14
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#11

Post by JayTee » Wed Aug 21, 2019 11:25 am

Hi Jim,

Look at the post right above yours!

JT
Main: C-stron CPC1100 #2 Scope: 8" f/7.5 Dob mounted Newt AP Scopes: TPO 6" f/9 RC, ES 80mm f/6 APO G&G Scope: Meade 102mm f/7.8, Bresser 102mm f/4.5 Guide Scopes: 70 & 80mm fracs Mounts: C-stron AVX CGEM & GT Alt-Az, Meade DS2000 Cameras: Canon T3i (x2), ASI120MC Binos: 10X50,10.5X70,15X70 (x2), 25X100 EPs: ES: 21 100°, 30 82° X-Cels: 9, 12, 18, 25 Clubs: RCA & HAS
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#12

Post by Juno16 » Wed Aug 21, 2019 11:28 am

Thanks JT!

Still have sleep in my eyes! Answers my question though, thanks!

Jim
Jim

Scopes: Explore Scientific ED102 Triplet APO, Celestron Nexstar 130 SLT.
Mounts: Celestron AVX with Orion MM Autoguider, SLT;
Binoculars: Bushnell 10X50
Camera / Software: Nikon D5300 (Ha mod), IDAS LPS D-1 Filter, Astrophotography Tool, PHD2, SharpCap v3.2, StarTools 1.6 alpha, PE14
Dog: Jack
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Astro Photos https://flickr.com/photos/157183480@N07 ... 7681236785
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#13

Post by fatboy1271 » Wed Aug 21, 2019 3:48 pm

Thanks JT! I am ignorant to where the RAW should lie in the Histogram so this is again very helpful! With that said... My LP is killing me!!!

At 60sec x 1600ISO I can't get to the Left 1/3. I'm at 1/2, slightly left. At 180sec x 800ISO I'm at 1/2, slightly right. 60 seconds seems awfully short when I can easily achieve 180sec+. How would you approach my situation?

60sec x 1600ISO
NGC 6822 60sec x 1600ISO.png
180sec x 800ISO
NGC 6822 180sec x 800ISO.png
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
EPs: Stock Celestron 9mm and 24mm / Celestron Omni 32mm (I love this one!) / Celestron X-Cel LX 3x Barlow (I think 2X would have been smarter...)
Support Staff (Loved Ones!): CeCe, Ro, and Geno
Let's Go Pens!!!
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