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Focusing on focusing

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#1 Renae Gage

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Posted 01 December 2022 - 04:45 PM

As some of you may have gathered, I'm working to improve my planetary imaging set up.  I did okay with an alt-az mount and the Celestron focuser, but I'm heading to a GEM and probably a crayford (although a used FT R/P might be in range).

What I thought I would do is set up an autofocus routine on my planetary pier akin to what I have on my deep sky pier (Mach1-->OAG-->SGP).  It was for this reason that I started the thread on headless computers, thinking that was my route.  I'm gathering that many of you just motor/manually set and lock focus with a Bahtinov.  

 

I would like to hear about your processes for focusing, including hardware, software and routing, starting with the assumption of a polar and sky aligned mount.  If those processes share hardware (e.g. ASI Air or NUC) with your focal process, you can certainly bring that in to the discussion as a relevant perk of your system, but ideally I'd like to walk away from this thread with a plan for focus that I can take, if not to the bank, to our good sponsors at Astronomics or elsewhere.  I assume that anything I learn in this thread will be immensely helpful for EAA/outreach as well, with an eye toward my eventual retirement.

 

For reference, I use an Edge 8.


 

#2 Tulloch

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Posted 01 December 2022 - 05:12 PM

The only people using a Bahtinov mask for planetary imaging are those who already use one for DSO imaging. Anyone who concentrates on planetary imaging focuses by eye and re-adjusts before each and every capture.

 

The FAQ at the top of the forum will give you some more tips about planetary imaging and focusing (sec 14.2).

https://www.cloudyni...ated-july-2022/

 

Andrew


 

#3 kevinbreen

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Posted 01 December 2022 - 05:17 PM

Use a hands-off focuser and ratchet focus in and out and over and over. You'll know when you've nailed it, believe me. Try not to scrutinise the image on screen for detail, rather look at the planet as a whole. Like I said, you'll know.
 

#4 JMP

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Posted 01 December 2022 - 05:22 PM

Some people have experimented with automatic focusing, but in general the best results come from focusing on the planet. When I was using a C8 I used the built in focus knob, when I was using a C11 I had better results with a GSO two speed crayford. I'm currently using a JMI motorized crayford although I may upgrade to something more solid.

 

If the seeing is good you can zoom in on smaller details to focus on. If the seeing is not good enough to do this you're unlikely to get a great image in any case. The last little bit of focus is very small, I like to say I touch the focus knob lightly and think about turning it. Here is the setup I used to take a picture of Mars 2 years ago, this picture is printed in the Feb '23 edition of Sky and Telescope:

 

Jeff Phillips

 

480-obs-3.jpg

 

570-Mars-Print_10-16-2020+g.jpg


 

#5 Jcoogler

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Posted 01 December 2022 - 08:01 PM

As others have stated, most people just go by eye. I still use the focus knob original to my C8. It’s difficult at times but I think after you use it you get the hang of it. I’d like to upgrade to a motorized hands off one eventually but the manual knob works fine in my experience
 

#6 Renae Gage

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Posted 01 December 2022 - 08:04 PM

Up until now, I've just eyeballed it as well, using the Celestron Focus Motor to keep hands off.  With Jupiter, I usually tried to focus on a nearby moon.  I sold that focuser last week along with my Evolution mount.  Those two items fit together pretty well, but I'm also combing the classifieds and shopping the retailers for a GEM.

 

That said, my eyes aren't what they once were, and I find it harder to focus by visualized sharpness these days.  I was hoping autofocusing on nearby stars might make a positive impact.


Edited by Renae Gage, 01 December 2022 - 08:08 PM.

 

#7 Tulloch

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Posted 02 December 2022 - 04:04 AM

Up until now, I've just eyeballed it as well, using the Celestron Focus Motor to keep hands off.  With Jupiter, I usually tried to focus on a nearby moon.  I sold that focuser last week along with my Evolution mount.  Those two items fit together pretty well, but I'm also combing the classifieds and shopping the retailers for a GEM.

Ha! I tried using a CGEM, but went back to my Celestron Evolution 9.25 + focus motor as the GEM was too unwieldy for me :)


 

#8 RedLionNJ

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Posted 02 December 2022 - 07:22 AM

 I'm gathering that many of you just motor/manually set and lock focus with a Bahtinov.  

 

I would like to hear about your processes for focusing, including hardware, software and routing, starting with the assumption of a polar and sky aligned mount.  If those processes share hardware (e.g. ASI Air or NUC) with your focal process, you can certainly bring that in to the discussion as a relevant perk of your system, but ideally I'd like to walk away from this thread with a plan for focus that I can take, if not to the bank, to our good sponsors at Astronomics or elsewhere.  I assume that anything I learn in this thread will be immensely helpful for EAA/outreach as well, with an eye toward my eventual retirement.

 

For reference, I use an Edge 8.

You could not be more incorrect.  I have no idea where you got this impression from. No serious planetary imager focuses with a Bahtinov mask.

 

If you have a moveable primary mirror, then locking it is definitely a good idea. This will minimize (but not totally prevent) shift as you move the scope around on its mount to point to different areas of the sky. It doesn't take a whole lot of shift to require refocusing or even recollimation sometimes.

 

Once you have the target comfortably within your sensor, ideally very close to the center of the optical axis, and have taken into account ADC settings, then it's time to start fine focus.

 

Using a hands-off focusing mechanism (ideally Crayford-style with remote control, but still sitting beside the scope so visual feedback is "instant"), roll through what you judge to be "best focus" a few times from either direction. You judge best focus by the daintiest features you can detect when previewing at perhaps 200%. (this only applies when the seeing is good, it's a lot harder when it's not).

 

Eventually you get a feel for where exactly the best focus lays and that's when you stop.  This process is pretty quick with experience and good seeing. It can be nearly impossible in poor seeing. And there are many types of intermediate seeing, all with their own challenges. Sometimes the image appears to be at optimum focus for only a fraction of a second at a time - this is when NOT moving the focuser. You still have to judge where the focus lays for the maximum contrast and finest features detectable. You'll just find it a lot tougher under these conditions. You might spend ten minutes just trying to nail focus in order to take one capture, only to repeat the process all over again before the next capture. There is no compromise. There's no point in recording data if you haven't nailed the focus to the best of your ability, given the conditions.

 

The focus may or may not change from capture to capture. If you find it's not changing measurably, then keep the same focus for a few capture runs. If you find it's changing from capture to capture, then assume it's going to do that for the entire session and expect the worst.  Many nights, the focus on an SCT is going to change slowly throughout the night. You come back out next night and find you're remarkably far from focus at the start of the new session, due to where it ended up that morning, It may even be far enough out you need to unlock the mirror and adjust again prior to relocking.

 

Focus is a fickle friend (or fiend, depending on your seeing conditions). It really does pay to nail it, but that can take considerable time and effort to do until you're very, very experienced.


 

#9 bunyon

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Posted 02 December 2022 - 09:11 AM

I get what you're saying about the eyes going soft and share the problem/concern. Unfortunately, none of the automated tools or tricks (like a B. mask) used in DSO imaging work well for planets.

 

I increase gamma (or is it decrease?), anyway, I change gamma to increase contrast. Then sit far back from the screen. The temptation is to get up close, but you want a "smooth" look to the planet. Then...do your best. I know it sounds weird when we all say "you'll know it when you hit it" but, um, you'll know it when you hit it.  


 

#10 Borodog

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Posted 02 December 2022 - 11:48 AM

As usual, I will offer a contrarian voice.

 

I hate focusing by eye. I hate it, I hate it, I hate it. I loath it entirely. It is too subjective and I suffer from intense FOMCF: Fear Of Missing Critical Focus. I will waste endless time rolling back and forth through critical trying to decide what is better.

 

I have been pushing very hard on getting automatic focusing for planetary imaging using SharpCap working well, and I can now say that it works, it works well, and it certainly does a better job than I can by eye, and I go so far as to say it does a good of a job as any of you could. It took a lot of back and forth with Robin Glover (developer of SharpCap) to get it working properly, but as of my last time out, it just works.

 

If anyone is interested in the proper way to do it, I'll outline it. It is not exactly obvious.


 

#11 RickD_99

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Posted 02 December 2022 - 02:30 PM

As usual, I will offer a contrarian voice.

 

I hate focusing by eye. I hate it, I hate it, I hate it. I loath it entirely. It is too subjective and I suffer from intense FOMCF: Fear Of Missing Critical Focus. I will waste endless time rolling back and forth through critical trying to decide what is better.

 

I have been pushing very hard on getting automatic focusing for planetary imaging using SharpCap working well, and I can now say that it works, it works well, and it certainly does a better job than I can by eye, and I go so far as to say it does a good of a job as any of you could. It took a lot of back and forth with Robin Glover (developer of SharpCap) to get it working properly, but as of my last time out, it just works.

 

If anyone is interested in the proper way to do it, I'll outline it. It is not exactly obvious.

Please do! I have the Celestron electronic focuser and also have a SharpCap Pro license and would love to hear about your method for automating planetary focusing…


 

#12 bunyon

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Posted 02 December 2022 - 03:47 PM

As usual, I will offer a contrarian voice.

 

I hate focusing by eye. I hate it, I hate it, I hate it. I loath it entirely. It is too subjective and I suffer from intense FOMCF: Fear Of Missing Critical Focus. I will waste endless time rolling back and forth through critical trying to decide what is better.

 

I have been pushing very hard on getting automatic focusing for planetary imaging using SharpCap working well, and I can now say that it works, it works well, and it certainly does a better job than I can by eye, and I go so far as to say it does a good of a job as any of you could. It took a lot of back and forth with Robin Glover (developer of SharpCap) to get it working properly, but as of my last time out, it just works.

 

If anyone is interested in the proper way to do it, I'll outline it. It is not exactly obvious.

I mean, yeah. It isn't that I like focusing by eye. It's that I find it works best. If you find me a button to push that does it better, I'd be cool with it.


 

#13 Ittaku

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Posted 02 December 2022 - 03:59 PM

As usual, I will offer a contrarian voice.

 

I hate focusing by eye. I hate it, I hate it, I hate it. I loath it entirely. It is too subjective and I suffer from intense FOMCF: Fear Of Missing Critical Focus. I will waste endless time rolling back and forth through critical trying to decide what is better.

 

I have been pushing very hard on getting automatic focusing for planetary imaging using SharpCap working well, and I can now say that it works, it works well, and it certainly does a better job than I can by eye, and I go so far as to say it does a good of a job as any of you could. It took a lot of back and forth with Robin Glover (developer of SharpCap) to get it working properly, but as of my last time out, it just works.

 

If anyone is interested in the proper way to do it, I'll outline it. It is not exactly obvious.

Would you say it's a big enough win to jump ship from firecapture?
 


 

#14 Borodog

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Posted 02 December 2022 - 05:49 PM

Would you say it's a big enough win to jump ship from firecapture?
 

Well, I already no longer use FireCapture for planetary, so . . .

 

Ok, here's how to make it work, in my experience. You mileage may vary. It might take you a significant amount of tweaking until you work out the kinks. I worked on it for a couple of months and Robin has implemented several changes based on my experience and recommendations. This all presumes you have a motorized focuser set up properly that SharpCap can control.

 

0) Be running the latest beta 4.1

1) If you have an ASCOM mount, use feature tracking via the mount, COG method to keep the planet centered on the sensor. If not, make sure your polar alignment is good (you should have good polar alignment anyway if possible) to minimize drift. The focus ROI box no longer conflicts with feature tracking.

2) Use planet stabilization; planet stabilization now works with feature tracking. This is mandatory to keep the planet centered on the focus box

3) Use the Edge Detection/Contrast based focus method

4) Set the averaging to 20 frames

5) Black level and noise reduction shouldn't really matter much

6) Set the focus ROI box to be entirely contained within the disk of the planet; in other words the box is in the planet, not the planet in the box (note that you can try it the other way too; it may not matter so much since my last request was implemented; if you do this black level may become more important)

7) TURN OFF BRIGHTNESS COMPENSATION - this is key

8) You'll have to experiment a bit to figure out how far upstream of critical focus to start your sweep and what step size to use. It's going to depend on your focuser. For my Celestron Focus Motor and 1100 EdgeHD, being inside of critical focus by 50 steps and sweeping with a step size of 10 seems to work well.

9) Set the number of samples per focus score to at least 3; this means that each focus score is an average of 60 frames (3x20). You can increase this if you want, 5 would be 100 frames, etc.

10) Let 'er rip.

 

Please note that if you are confident in your manual focusing, automatic focus is probably not for you. You can probably do it faster by hand. I just can't.

 

I may try to record a tutorial video at some point on this.


 

#15 Ittaku

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Posted 02 December 2022 - 06:01 PM

Well, I already no longer use FireCapture for planetary, so . . .

 

Ok, here's how to make it work, in my experience. You mileage may vary. It might take you a significant amount of tweaking until you work out the kinks. I worked on it for a couple of months and Robin has implemented several changes based on my experience and recommendations. This all presumes you have a motorized focuser set up properly that SharpCap can control.

 

0) Be running the latest beta 4.1

1) If you have an ASCOM mount, use feature tracking via the mount, COG method to keep the planet centered on the sensor. If not, make sure your polar alignment is good (you should have good polar alignment anyway if possible) to minimize drift. The focus ROI box no longer conflicts with feature tracking.

2) Use planet stabilization; planet stabilization now works with feature tracking. This is mandatory to keep the planet centered on the focus box

3) Use the Edge Detection/Contrast based focus method

4) Set the averaging to 20 frames

5) Black level and noise reduction shouldn't really matter much

6) Set the focus ROI box to be entirely contained within the disk of the planet; in other words the box is in the planet, not the planet in the box (note that you can try it the other way too; it may not matter so much since my last request was implemented; if you do this black level may become more important)

7) TURN OFF BRIGHTNESS COMPENSATION - this is key

8) You'll have to experiment a bit to figure out how far upstream of critical focus to start your sweep and what step size to use. It's going to depend on your focuser. For my Celestron Focus Motor and 1100 EdgeHD, being inside of critical focus by 50 steps and sweeping with a step size of 10 seems to work well.

9) Set the number of samples per focus score to at least 3; this means that each focus score is an average of 60 frames (3x20). You can increase this if you want, 5 would be 100 frames, etc.

10) Let 'er rip.

 

Please note that if you are confident in your manual focusing, automatic focus is probably not for you. You can probably do it faster by hand. I just can't.

 

I may try to record a tutorial video at some point on this.

Thanks for that.

 

You got me at 2 unfortunately, as I neither have an ascom mount, nor am I using equatorial movement.


 

#16 Renae Gage

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Posted 02 December 2022 - 07:38 PM

Ha! I tried using a CGEM, but went back to my Celestron Evolution 9.25 + focus motor as the GEM was too unwieldy for me smile.gif

Been there, done that, but when setting up on a permanent pier in an observatory, a mount is only unwieldy once.


 

#17 SHaley

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Posted 02 December 2022 - 07:43 PM

Thanks for that.

 

You got me at 2 unfortunately, as I neither have an ascom mount, nor am I using equatorial movement.

I thought there is a ASCOM driver w/focuser for the Meade LX200. 


 

#18 Ittaku

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Posted 02 December 2022 - 07:48 PM

I thought there is a ASCOM driver w/focuser for the Meade LX200.

I've been unable to get mine to budge in response to commands. I just use the rs232 port now to read off coordinates to drive the altaz decorator.
 

#19 Borodog

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Posted 02 December 2022 - 08:27 PM

Thanks for that.

 

You got me at 2 unfortunately, as I neither have an ascom mount, nor am I using equatorial movement.

Neither is critical as long as your polar alignment is good and you are using planet stabilization.


 

#20 Ittaku

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Posted 02 December 2022 - 08:35 PM

Neither is critical as long as your polar alignment is good and you are using planet stabilization.

Okay. No polar alignment with alt/az movement. Tracking is pretty good though.


 

#21 Borodog

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Posted 02 December 2022 - 11:01 PM

Okay. No polar alignment with alt/az movement. Tracking is pretty good though.

 

Oh, yes. Derp.


 

#22 Borodog

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Posted 02 December 2022 - 11:07 PM

Ok; forget everything I said. Planetary autofocus in SharpCap is still not ready for prime time.

 

I installed the latest 4.1 beta that dropped on November 28th, and the Edge Detection/Contrast method is 100% broken now. Perfect inverted parabolas, i.e. the focus parabola is supposed to have a maximum. The new beta returns a minimum instead at critical focus, so of course no fit is found. No idea what happened. I did switch to the Fourier Detail method and that focused right away, but I need it to be bullet proof. I'll keep the forum posted if there is any improvement.


 

#23 Kokatha man

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Posted 03 December 2022 - 04:56 AM

blahblah.gif fingertap.gif rolleyes.gif  rofl2.gif  To the OP & anyone else who is interested in reality, Grant's comments (RLNJ) & Jeff's (JMP) are the voices of experience & relevant approach to focusing in this thread waytogo.gif ...but Kev's comments (kevinbreen) <"Try not to scrutinise the image on screen for detail, rather look at the planet as a whole,,."> bear some truth even if they seem to run counter to Jeff's comments <"If the seeing is good you can zoom in on smaller details to focus on...">

 

Kev won't mind me echoing his comments about the constantly poor seeing he appears to experience...& his comments about focusing are particularly relevant in poorer seeing: in our last thread where Pattie & I encountered pretty poor seeing for Mars (& only 30° elevation btw) I described the approach for gauging best focus as a type of "gestalt" phenomenon, where the sum of the parts apparent provides a better appraisal of optimum focus than trying to concentrate too much on any specific "feature." This accords with Kevin's comments I quote here of course.

 

In better seeing, concentrating upon some of the finer dark features such as V. Marineris or the Oxus extension etc gives a more accurate appraisal...but then again Mars is a relatively easy target where it is mainly quite simple albedo variations. In other words it doesn't take a whole lot of experience to capture a relatively decent-focused image.

 

Incidentally, the captures we made the other night which I'll post sometime soon were in sufficiently good seeing for us to use the V. Marineris markings for accurate focus... smile.gif

 

But accurate focus of Jupiter for instance is much harder...the fine detail of whispy festoons & small storm "bubbles" or other minutiae etc require a far greater degree of focus appraisal & dexterity, something that no automated system could hope to approach atm! wink.gif

 

Saturn is another "simple" planet for focusing - the Cassini Division is at its darkest (or "blackest") when you hit optimum focus...you can watch it (the CD) shift from a lesser tone (with more fuzziness also) towards a darker (blacker) as well as sharper appearance as you home in on focus...mimicking the 256-bit grayscale with its varying shades from white to black. (remembering that a white Cassini Division will mean you've inverted your planet's image somehow! lol.gif


 

#24 Renae Gage

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Posted 03 December 2022 - 05:21 PM

You could not be more incorrect.  I have no idea where you got this impression from. No serious planetary imager focuses with a Bahtinov mask.

 

 

Thank you for that.  The boldface type made it easier to see.

 

As much as I am Jonesing on the discussion so far, nobody is really addressing the original request, i.e. to describe your focal process, including hardware and software.  That I omitted in that request the role for using one's eyes is on me, but I hope you'll understand that I do know what good focus looks like and how to approach it bidirectionally, allowing us to move past that part of the discussion.

 

I believe this to be a forum populated by imagers who have arrived at their current focal setup as an improvement on previous setups that were less optimal.  I was hoping that a few of you would describe your configuration and how they interact with it (knob, HC, software [which], etc).   


Edited by Renae Gage, 03 December 2022 - 05:21 PM.

 

#25 Renae Gage

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Posted 03 December 2022 - 05:25 PM

Great Mars, Jeff.  Worthy of an S&T publication.


 


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