How do I fix/improve my focusing issues?

[Quetzalcoatl72]

I have most of my problems sorted out now but it seems when I do go out on the rare occasion, focusing seems to be the main issue. I use a batinov mask for my RCT 8/f8 scope because it's impossible to tell focus otherwise when looking at the diffraction spikes I notice they move around a lot so when I think the middle spike is centered the left or right part of it seems to move up and down so I can never get it to stay still to make sure I know it's 100%.

I have a lot of broadband cables across the sky so I think that's causing the problem, which I can't avoid obviously, They also make collimating difficult as I see it distorting the ring pattern. I always thought you focus on the brightest stars which is what I do, but I've also been told you focus on the target which could be impossible as the stars are usually smaller and hard to tell the diffraction spikes. Bright stars would have to be above 30º in the azimuth to clear any wires. My images have looked fine through the cables above f6 otherwise.

[powerlord]

I always focus on a bright star with a bahtinov. it's effectively infinity - don't see why you'd try to focus on the target. I suppose the argument is atmospheric disturbance, etc-  but frankly I've never had any issues focusing on a bright star. If you don't have one, get an electric focuser - its sooo much easier when the mount and scope is stable. And I suppose, make sure you have the right grill spacing for your OTA for the bahtinov.

certainly mine never 'move around'. I always get a clean 6 spikes.

[vlaiv]

I have two Bahtinov masks - one large and one small (for 8" and 80mm scopes) - and they gather dust. I never really warmed up to using them and for me FWHM / HFR was always reliable measure of focus.

In fact - I focused most of my sessions by simply looking at the stars - make them pin point - you have focus, or make them small enough so that any tweak of focus in or out makes them larger - you have focus.

I guess it is easier to do with astro cameras and laptop then it is with DSLR camera and looking at camera screen even with zoom.

[Quetzalcoatl72]

1 hour ago, powerlord said:

I always focus on a bright star with a bahtinov. it's effectively infinity - don't see why you'd try to focus on the target. I suppose the argument is atmospheric disturbance, etc-  but frankly I've never had any issues focusing on a bright star. If you don't have one, get an electric focuser - its sooo much easier when the mount and scope is stable. And I suppose, make sure you have the right grill spacing for your OTA for the bahtinov.

certainly mine never 'move around'. I always get a clean 6 spikes.

I assumed auto focusers were for people who do everything indoors, do they know when a star is out and correct it?

[powerlord]

well, the zwo eaf one with asiair pro does actually auto focus, but the cheap ones don't - it's just a way of focusing without touching the scope. hence no wobbling around all over the place while you try and tweak the focus and try to work out if it's focused while wobbling around everywhere. For your ED80 probably not an issue, but certainly my longer FLs became much easier to focus when I could use the electric focuser and see a nice stable image as i twiddled

[scotty38]

I use the ZWO EAF and getting it set up/understanding it is not trivial either imo. There are plenty of videos to help but I struggled massively getting a nice curve etc until I read a post on here with some suggested settings. I've since tried to find it again to thank the author but failed.. Will have another look but anyway I think the focuser is a great tool.

[Quetzalcoatl72]

7 hours ago, scotty38 said:

I use the ZWO EAF and getting it set up/understanding it is not trivial either imo. There are plenty of videos to help but I struggled massively getting a nice curve etc until I read a post on here with some suggested settings. I've since tried to find it again to thank the author but failed.. Will have another look but anyway I think the focuser is a great tool.

That's the problem, I don't want to learn algebra to improve my images. I've seen tutorials on FWHM / HFR curves and stuff it goes right over my head, I'm incapable of understanding maths and equations 

[scotty38]

4 minutes ago, Quetzalcoatl72 said:

That's the problem, I don't want to learn algebra to improve my images. I've seen tutorials on FWHM / HFR curves and stuff it goes right over my head, I'm incapable of understanding maths and equations 

Well it can be a bit involved but like I said once I input the settings I found it's all worked fine and dandy. To be fair the whole astro lark is complex and riddled with maths and what have you so it shouldn't be much of a surprise. I will find that post though 🙂

[City9Town0]

No maths or equations required... visual representation on laptop screen... Get the 'graph bars or numerical value displayed' as high/low as possible (depending on system). Doesn't take long, and isn't expensive😉.

[vlaiv]

4 minutes ago, Quetzalcoatl72 said:

That's the problem, I don't want to learn algebra to improve my images. I've seen tutorials on FWHM / HFR curves and stuff it goes right over my head, I'm incapable of understanding maths and equations 

What sort of equations?

1. Tweak focus

2. Look at FWHM / HFR value produced by imaging software

3. Repeat above procedure until you get smallest reading in point number two

This is how motor focuser works as well - it takes series of snaps and measures FWHM / HFR in each and produces "curve" - but actual curve or its production is really not important to you - it just lets software find best focus spot - with smalles FWHM/HFR values.

Best focus must be where arrow is pointing as moving either to the left or right increases FWHM / HFR value.

[Quetzalcoatl72]

18 minutes ago, vlaiv said:

What sort of equations?

this headache here

[City9Town0]

https://astrophotography.app/usersguide/focusing_aid.htm#

 

[Quetzalcoatl72]

23 minutes ago, vlaiv said:

2. Look at FWHM / HFR value produced by imaging software

In nina are the graphs available for manual focus right away or only with a focuser plugged in?

[Quetzalcoatl72]

8 hours ago, scotty38 said:

I use the ZWO EAF and getting it set up/understanding it is not trivial either imo. There are plenty of videos to help but I struggled massively getting a nice curve etc until I read a post on here with some suggested settings. I've since tried to find it again to thank the author but failed.. Will have another look but anyway I think the focuser is a great tool.

not sure my stellar lyra is supported with ZWO EAF, it's also a feather touch focuser. As for my ed80 well, the focuser is incredibly bad on that, just moves a lot when tightening the locking bolt. An autofocuser should keep it in one place right, don't need to lock the bolts?

[City9Town0]

I'm fully manual focus and APT... don't use NINA but found this in two seconds...

 

 

[vlaiv]

51 minutes ago, Quetzalcoatl72 said:

this headache here

Yeah, don't need those at all.

42 minutes ago, Quetzalcoatl72 said:

In nina are the graphs available for manual focus right away or only with a focuser plugged in?

You don't need graphs at all - there is stats panel for each sub you make. You should have frame and focus type of sub (just few seconds long) that you can take - or even loop.

Stats window has basic statistics of the sub - number of stars detected, mean, median, min, max and so on - and HFR.

Note HFR number and try to make it as small as possible by tweaking focuser.

Workflow is - adjust focuser just a tad - take exposure. Don't adjust focus while you are exposing - but between exposures. Compare HFR to previous and adjust - (if tweaking focus makes number larger - change direction).

There is often graph of HFR history between subs. Above bar graph looks like that - but I can't be 100% certain as I'm not using NINA.

If you have such graph - you'll have visual representation of current HFR and its relation to past values. SharpCap has this:

It shows graph with bars moving to the left to make room for new exposures and also best and last reading (either FWHM or HFR).

[Quetzalcoatl72]

6 minutes ago, vlaiv said:

Workflow is - adjust focuser just a tad - take exposure. Don't adjust focus while you are exposing - but between exposures. Compare HFR to previous and adjust - (if tweaking focus makes number larger - change direction).

I see now thanks, it's just like adjusting az alt bolts when precise polar aligning 

29 minutes ago, City9Town0 said:

I'm fully manual focus and APT... don't use NINA but found this in two seconds...

I based most of my methods/settings from him. I avoided this one because I didn't have a focuser, but if you can do it manually, then that's great 

[powerlord]

2 hours ago, scotty38 said:

Well it can be a bit involved but like I said once I input the settings I found it's all worked fine and dandy. To be fair the whole astro lark is complex and riddled with maths and what have you so it shouldn't be much of a surprise. I will find that post though 🙂

can you post your settings. I just attached new zwo eaf and it appears to have a mind of it's own - sometime your press up and it moves a bit, sometimes it doesn't, sometimes it just keeps going. and even a small movement is large. it's fine on my C8, but a movement like that on my 72ED is no good at all. I got it because i need it for doing automated focusing between filter changes with the asi1600 - so far it appears like its not going to be staight forward 😕

[scotty38]

43 minutes ago, powerlord said:

can you post your settings.

Here you go. I'm not saying these are correct or whatever just that they have worked for me and I get a great looking curve. It hasn't improved my images but at least they look sharp, so yeah I guess that is an improvement 🤣

 

 

[Budgie1]

With your Bahtinov Mask, I assume you're using live view on your 600D to try and focus?

If so, the central spike is dancing around due to the atmospheric turbulence. If you get it close using live view and then start taking 2 or 3 second exposures, these will "freeze" the seeing so you can see where the central spike is. Then adjust the focuser in or out and take another exposure to see where it's moved too. Continue this until it's centred correctly.

It's the same method vlaiv described above for FWHM & HFR.

[fifeskies]

I use a 600D and use APT to run my imaging

Just like Budgie 1 suggests , I have an "imaging plan" set up , choose it as focussing so no images get stored.

Set for 100 exposures at 3 seconds and fast-ish ISO. (find 100 exposures is plenty but set as many as you need)

I have a cloned monitor near the mount so can see the test exposures and the spikes as they change every 3 seconds.

I open the Bahtinov helper in APT and set it over the target , every 3 seconds the image is given a value and you can see this change as you tweak focus.

 

Get close by eye then make micro adjustments from below to above the best value , I usually rack through both directions to make sure I hit the minimum.

Once you get an idea of the range of values,  despite wobbly seeing you can home in on the best value.

 

If seeing is very wobbly let it sit at "best" focus for a good few exposures to see if it is averaging out at a value you can work with.

 

Edited June 26, 2021 by fifeskies

[Budgie1]

1 hour ago, fifeskies said:

Get close by eye then make micro adjustments from below to above the best value , I usually rack through both directions to make sure I hit the minimum.

I also use APT and the Balhtinov Aid is good. The "Distance" figure also gives you the direction to correct the focus, + to lengthen the focus tube out and - if it needs shortened.

I didn't realise that it also has a built-in stacking function for DSLR's with live view, so you can use that rather than setting up an imaging plan.

[Quetzalcoatl72]

On 25/06/2021 at 23:59, Budgie1 said:

With your Bahtinov Mask, I assume you're using live view on your 600D to try and focus?

If so, the central spike is dancing around due to the atmospheric turbulence. If you get it close using live view and then start taking 2 or 3 second exposures, these will "freeze" the seeing so you can see where the central spike is. Then adjust the focuser in or out and take another exposure to see where it's moved too. Continue this until it's centred correctly.

It's the same method vlaiv described above for FWHM & HFR.

I don't use that camera anymore, this site wont update my setups, was using asi533 on nina, tried the focus assist on that program too was really struggling with the spikes bouncing everywhere

[Quetzalcoatl72]

On 26/06/2021 at 11:32, Budgie1 said:

I also use APT and the Balhtinov Aid is good. The "Distance" figure also gives you the direction to correct the focus, + to lengthen the focus tube out and - if it needs shortened.

I didn't realise that it also has a built-in stacking function for DSLR's with live view, so you can use that rather than setting up an imaging plan.

whaaa? wheres this stacking option that sounds cool

[old_eyes]

I moved to a motor-focuser to get away from having to touch the scope. I think a lot of people must have a much more delicate touch than me.

I use autofocus for extended imaging runs, but I also do a bit of quick manual setting up to get in the right area after I have changed something in the optical train. I use NINA, set it to repeat short exposures without storing, and then remotely move hte focuser until I get the stars as small as possible. You can eyeball it or look at the HFR/HFD or whatever. If you don't have a lot of backlash it works fine. I have tried Bhatinov masks, but don't get a better result and it is an extra thing to fiddle with, drop, lose in the dark.

I have done the same thing with APT and it works fine.

After some recent troubles with a new scope, I have got autofocusing working again and find that the most convenient, whether I am under the stars or in my warm room.