first go at auto guiding

[TiffsAndAstro]

48 minutes ago, WolfieGlos said:

NINA should handle it automatically (as long as you enable it), so if it did flip, then well done 👍 I've been doing them for over a year now since I got my HEQ5, but I still watch it when flipping just in case 🙂

I'm also going to be investigating this for myself, along with the multi-star guiding @Clarkey mentioned. I set PHD2 up following a guide (might have been Astrobackyard) early days and it uses single star, and I rarely have issues, but my own guiding last night spent most of the time above 2", which is atrocious. But then none of my images showed trailing and my HFR's ranged between 2.4-2.8...usually they are circa 2.1-2.3. Sometimes we can get obsessed with the numbers, but just looking at the output with your own eyes sometimes can suggest otherwise, but it's definitely best practise to get it as good as possible.

it can't be as easy as just setting it to flip. which i didn't  obviously will try that next.

also i have some sort of mental block about meridian flips. i sort of see when they're happening but i can't picture in my head why it can't just carry on tracking. i think its related to the 'block' so scope can't rotate past + - 90 degress? i guess having a counter weight above camera might be bad its hard to mentally picture. its possible im over thinking it  

as for HFR, i have no idea how it works and have struggled to google a video. i assumed it was for autofocus but clearly not. if you have a link or anything like that it would be much appreciated. i will trawl Cuiv's back collection and be very disapointed if its not covered. 

yeah multi star auto guiding sounds cooler than not, so ill give that a go to. got a bahtinov mask on the way for my guidescope but not really sure its nessecery.

Watching a good video on hfr by chrizzleys observable universe.

I need hfr

Edited April 10 by TiffsAndAstro

[Clarkey]

Meridian flips simply prevent your telescope from crashing into the tripod or pier. If you don't do it, eventually the scope will hit something. (Yes, there are exceptions - but as a general rule).

 

HFR is simply a statistical measure of the size of the stars. In theory stars should be point sources covering one pixel only. However, seeing, poor focus and optics can all make this worse. By getting the HFR (or FWHM) as low as possible this is the 'best focus'. The number will always vary from day-to-day and scope-to-scope, but it just needs to be the lowest possible.

[michael8554]

Time to say what your equipment is - mount, focal lengths, pixel sizes.

Lets say you have one of those tiny guidescopes that give 6arcsec/pixel.

And you're imaging at 2arcsecs/pixel.

A 12 pixel dither on the imaging camera is 2 x 12 = 24arcsecs.

How many pixels does the guidecam have to Dither to make the imaging camera Dither 24arcsecs ?

24/6 = 4 pixels.

If the NINA setting is for the guidecam, your 7 pixel Dithers are too much, and probably increasing Settling times.

If the NINA setting is for the imaging camera, then you should try 12.

Michael

[TiffsAndAstro]

15 hours ago, Clarkey said:

Meridian flips simply prevent your telescope from crashing into the tripod or pier. If you don't do it, eventually the scope will hit something. (Yes, there are exceptions - but as a general rule).

 

HFR is simply a statistical measure of the size of the stars. In theory stars should be point sources covering one pixel only. However, seeing, poor focus and optics can all make this worse. By getting the HFR (or FWHM) as low as possible this is the 'best focus'. The number will always vary from day-to-day and scope-to-scope, but it just needs to be the lowest possible.

yeah watched a decent video on hfr. not entirely sure how to use the graph display of it in nina yet, im assuming higher plots show more stars and tighter stars? which is good ?

I also need that bahtinov grabber. not sure if it an addon or built into nina now, but it looks very very useful

[TiffsAndAstro]

2 hours ago, michael8554 said:

Time to say what your equipment is - mount, focal lengths, pixel sizes.

Lets say you have one of those tiny guidescopes that give 6arcsec/pixel.

And you're imaging at 2arcsecs/pixel.

A 12 pixel dither on the imaging camera is 2 x 12 = 24arcsecs.

How many pixels does the guidecam have to Dither to make the imaging camera Dither 24arcsecs ?

24/6 = 4 pixels.

If the NINA setting is for the guidecam, your 7 pixel Dithers are too much, and probably increasing Settling times.

If the NINA setting is for the imaging camera, then you should try 12.

Michael

Hmm that's not what i worked out by the online tool, but its very likely i did it wrong. https://www.astrohowto.com/interactive-dithering-calculator/

i have a sw 72ed 420mm f5.9 and the zwo miniguide scope f4 120mm with the zwo120mm min guidescope bundle.

All on a sw gti with a proper tripod now. using nina.

 

Edited April 11 by TiffsAndAstro

[TiffsAndAstro]

i did some test subs 60, 120, 180 and 300 seconds with guiding going. I think my stars are a little oval shaped, but they seem exactly same oval shape in all those test subs. so i suspect the alignment of my camera/reducer/focus tube is a tiny bit out. next clear skies i have a plan to fix or reduce this shape.

also i reduced the wait to settle time from 10sec to 6sec to improve speed but will change that back, as i had a yellow nina warning about camera not being ready. 

 

Also any good suggestions for a 'final' test run. Ideally something high up and not a boring cluster

I'm thinking m101 as it's about the biggest spiral visible all night?

Also other people will be a decent judge of what's possible with my gear and so any remaining major issues?

 

Edited April 11 by TiffsAndAstro
jpg replacing dng

[Clarkey]

Looking at the subs, I would say a combination of backfocus from the flattener and a bit of tilt.

[TiffsAndAstro]

37 minutes ago, Clarkey said:

Looking at the subs, I would say a combination of backfocus from the flattener and a bit of tilt.

So...about back focus....

I assumed sort of, that as long as i can move the focus tube via the focus knobs in and out past focus and back, then if its in focus, its in focus.

But now im wondering if i have to get the exact back focus right before i then move the focus knobs? i can't see what difference it would make, but then there's lots of things i can't imagine that do actually happen  I mean, if the back focus is spot on, there's no need for focus knobs, surely? and yet they exist

any chance you know of a good video or link which would explain this? especially with a dslr if its much different from a osc.

Edited April 11 by TiffsAndAstro

[Elp]

It's to do with where the plane of focus is where it focuses light to a point, if you didn't have a focuser you'd be stuck when trying to use different equipment. You don't think about it when doing visual as the diagonal takes up most of the backfocus, but if you use different manufacturers eyepieces you'll see the effect as they're not usually parfocal and you have to make slight focus adjustments to get them again into the plane of focus.

[Clarkey]

1 hour ago, TiffsAndAstro said:

But now im wondering if i have to get the exact back focus right before i then move the focus knobs?

The back focus is the distance from the flattener to the sensor - not normal focus. For most flatteners this is 55mm. (I am assuming you are using a field flattener with the 72ED). For a 600D this is normally the Canon T-ring plus the distance from the front of the camera to the sensor. But it is always approximate and may need extending by a fraction. (You can buy M42 and M48 spacers such as these Astrodymium Colour Coded Fine Tuning Spacer Rings for M42 Threads (12x) | First Light Optics). Ideally to avoid any tilt try to get screw fittings. Any sort of compression fitting is likely to introduce tilt.

[TiffsAndAstro]

9 minutes ago, Clarkey said:

The back focus is the distance from the flattener to the sensor - not normal focus. For most flatteners this is 55mm. (I am assuming you are using a field flattener with the 72ED). For a 600D this is normally the Canon T-ring plus the distance from the front of the camera to the sensor. But it is always approximate and may need extending by a fraction. (You can buy M42 and M48 spacers such as these Astrodymium Colour Coded Fine Tuning Spacer Rings for M42 Threads (12x) | First Light Optics). Ideally to avoid any tilt try to get screw fittings. Any sort of compression fitting is likely to introduce tilt.

Ty for this. I've watched a few videos and my t ring should give exactly 55mm.

But what if it doesn't? Not sure how I'd order a possible fraction of a millimeter spacer.

I think for now, I'll try and improve the tilt and then ask if anyone can see a back focus issue, but I'm open to suggestions:)

Ok then, after looking at your link they go down to 0.4mm. is it just a case of trial and error, slowly building up the spacers and looking at the results?

[TiffsAndAstro]

1 hour ago, Elp said:

It's to do with where the plane of focus is where it focuses light to a point, if you didn't have a focuser you'd be stuck when trying to use different equipment. You don't think about it when doing visual as the diagonal takes up most of the backfocus, but if you use different manufacturers eyepieces you'll see the effect as they're not usually parfocal and you have to make slight focus adjustments to get them again into the plane of focus.

So I don't need exact back focus as long as I can focus the stars? Ie moving the focus tube will compensate for incorrect back focus?

Or is perfect back for required to get stars In Focus and not egg shaped?

Apologies if this is a particularly dumb question 

[bosun21]

The correct back focus is  the distance between the reducer/flattener and the camera sensor. This is totally independent of the focal point of the telescope which is reached by racking the focuser in and out. If you don't have a reducer/flattener in the optical train then you can totally forget about it. The reason they are almost universally used is to flatten the field and reduce the focal ratio of the telescope providing a larger FOV.

[Clarkey]

27 minutes ago, TiffsAndAstro said:

Ok then, after looking at your link they go down to 0.4mm. is it just a case of trial and error, slowly building up the spacers and looking at the results?

Pretty much. It is pretty common to need the odd spacer in an imaging train. Basically, you need the focus tube > field flattener >55mm >sensor. As @bosun21 says the 55mm (+/- a few mm) is totally separate to the normal focus point.

[TiffsAndAstro]

Ty all for all this. I'll try and sort the tilt next, and then see if back focus issue is still visible.

Of course I'll try not mess with any tilt fix while playing with spacers.

Doesn't sound terribly fun, but I think it's a plan

[Elp]

This explains it well:

https://optcorp.com/blogs/deep-sky-imaging/how-to-set-the-correct-back-focus

[TiffsAndAstro]

58 minutes ago, Elp said:

This explains it well:

https://optcorp.com/blogs/deep-sky-imaging/how-to-set-the-correct-back-focus

Ty for this. Added to my list to read.

I wonder if there's some Nina plugin to help? Will have a search

Lol already read that, phew those examples images look really useful.

 

Edited April 11 by TiffsAndAstro

[900SL]

As you are a noob, don't sweat backfocus or tilt too much at this stage. If the recommended backfocus is 55mm from flattener/reducer, use that. 

Similarly main focus: use the bahtinov mask and focus using the focuser. Using on screen FWHM or HFR can be a struggle due to seeing 'wobble'. FWHM is useful for indicating focus drift however, as time goes on and temperatures change. FWHM also tends to improve with elevation, and change with seeing and high cloud

Don't expect perfect stars across the field. Starter level mounts and scopes have all sorts of optical and mechanical issues which prevent this.

So, for noob:

KISS. accurate PA, good focus, short focal length and fast focal ratio, shorter exposures, and if guiding, make sure you understand things like pixel scale, calibration, the relative speed and vector of stars depending on location etc

 

Edited April 12 by 900SL

[woldsman]

On 10/04/2024 at 20:29, Clarkey said:

Meridian flips simply prevent your telescope from crashing into the tripod or pier. If you don't do it, eventually the scope will hit something. (Yes, there are exceptions - but as a general rule).

 

HFR is simply a statistical measure of the size of the stars. In theory stars should be point sources covering one pixel only. However, seeing, poor focus and optics can all make this worse. By getting the HFR (or FWHM) as low as possible this is the 'best focus'. The number will always vary from day-to-day and scope-to-scope, but it just needs to be the lowest possible.

It’s important to callibrate guiding on the same side as the meridian as your target. Although after the target transits you can in theory retain calibration by checking “reverse Dec output  after a meridian flip”, in practice I find I need to re-callibrate. Maybe this is due to not having a premium mount. I’m not 100% sure but suspect that in addition to the risk of your counterweight crashing into the leg of the tripod, if you go on a long way past transit your guiding may also deteriorate. This would potentially be caused by the East/West balance being slightly different. You could perhaps rebalance after transit but it is simpler to do the flip and to recalibrate as it does not take long.

I try to plan it so a change of filter is due after the target transits.  Meridian flipping for me involves sending the mount to the home position, slewing to the new callibration spot, recalibrating phd2 and in between changing the filter and refocusing. There are other methods (eg setting meridian flip commands) but I keep it simple. It doesn’t take long. You need to make sure there are no cable snag issues and it is worth making sure the guiding is good before you recommence imaging. 
 

A big advantage of mastering meridian flips is you can image targets that spend longer high in the sky where seeing conditions are better. You image the target either side of its zenith. 

[TiffsAndAstro]

1 hour ago, 900SL said:

As you are a noob, don't sweat backfocus or tilt too much at this stage. If the recommended backfocus is 55mm from flattener/reducer, use that. 

Similarly main focus: use the bahtinov mask and focus using the focuser. Using on screen FWHM or HFR can be a struggle due to seeing 'wobble'. FWHM is useful for indicating focus drift however, as time goes on and temperatures change. FWHM also tends to improve with elevation, and change with seeing and high cloud

Don't expect perfect stars across the field. Starter level mounts and scopes have all sorts of optical and mechanical issues which prevent this.

So, for noob:

KISS. accurate PA, good focus, short focal length and fast focal ratio, shorter exposures, and if guiding, make sure you understand things like pixel scale, calibration, the relative speed and vector of stars depending on location etc

 

Ty for this it's good advice. I like KISS and try to practice it in general :))

Not gonnaa think of back focus until I reseat the flattener. I took it out and didn't pay much attention when put it back. If I reseat it again with more care to slowly tighten up each of the two bolts holding it in, alternating every 1/4 turn it should reduce the tilt a bit. I need a way of screwing the flattener on though, those two bolts don't inspire confidence in accuracy or security. I think my back focus will be acceptable then. If not I can maybe try the cheap spacer set on flo.

I'll keep any eye on the hfr grap. Higher plot for star numbers and lower plot for hfr. In my last session I did see a big drop in hfr and number of stars but want sure what it meant. Now I do Ty

also I'm definitely managing my expectations. I'm viewing my current setup as good practice for if I ever bought a more grown up setup while also being a very portable battery powered rig for travel to darker sites. In theory.

really appreciate your help with all this. This site's users (and  you tube) have helped this not be overwhelming. At least not yet.

Also, saw one you tubers 2 hours total integration time of bodes and cigar galaxies. My 13 minute attempt was not massively worse, so I'm optimistic:)

Edited April 12 by TiffsAndAstro

[TiffsAndAstro]

1 hour ago, woldsman said:

It’s important to callibrate guiding on the same side as the meridian as your target. Although after the target transits you can in theory retain calibration by checking “reverse Dec output  after a meridian flip”, in practice I find I need to re-callibrate. Maybe this is due to not having a premium mount. I’m not 100% sure but suspect that in addition to the risk of your counterweight crashing into the leg of the tripod, if you go on a long way past transit your guiding may also deteriorate. This would potentially be caused by the East/West balance being slightly different. You could perhaps rebalance after transit but it is simpler to do the flip and to recalibrate as it does not take long.

I try to plan it so a change of filter is due after the target transits.  Meridian flipping for me involves sending the mount to the home position, slewing to the new callibration spot, recalibrating phd2 and in between changing the filter and refocusing. There are other methods (eg setting meridian flip commands) but I keep it simple. It doesn’t take long. You need to make sure there are no cable snag issues and it is worth making sure the guiding is good before you recommence imaging. 
 

A big advantage of mastering meridian flips is you can image targets that spend longer high in the sky where seeing conditions are better. You image the target either side of its zenith. 

That's a really good point about higher targets. Previously I would wait for M42 to pass meridian before starting imaging but this is harder to do on higher up ones for the reasons you said. 

I think my next test maybe tonight and/tomorrow on m101/106 (none cluster test target suggestions welcome, unless clusters have a good property to test like maybe star separation?)

I'll tick meridian flip in sequence and I think I can add a calibrate guider into the sequence too? Calibration seems to take about 5 mins. I really just want to do one target for as long as I can for a nice result.

Edited April 12 by TiffsAndAstro

[900SL]

I usually do manual meridian flip, as i babysit my mount. I can track 15 degrees past meridian before risk of scope/tripod collision. 

Then I do flip, check focus (which can shift during flip),  and recalibrate guiding, then off we go. Takes 5 minutes

Good if you can automate it all though. I have issues with Asi Air pro random disconnect from guide camera, so keep an eye on it during imaging

Edited April 12 by 900SL

[Elp]

Once I've been present with it a few times I allow the air to auto meridian flip. I simply make sure the cables have enough slack to not catch onto anything (don't care much about tidying it up as I setup and breakdown most sessions), and when setting up make sure the east/west balance is fine so it doesn't fall over (not a thing you usually check with a CW mount though I suppose you auto check it when doing Ra balancing). The main issue is usually when using larger/longer scopes as they have a higher chance of hitting, or your camera out back hitting the tripod, at which point you usually need a pier to lift it into clearance.

Edited April 12 by Elp

[Clarkey]

3 hours ago, 900SL said:

I usually do manual meridian flip, as i babysit my mount. I can track 15 degrees past meridian before risk of scope/tripod collision.

I'm tucked up in bed normally😄

[Anne S]

Returning to calibration, I see you're using Phd2. As long as you're using pulse guiding, ie using the mount connection, you only need to recalibrate if you take down your setup. Phd2 can do the calibration for you by slewing to a good position and moving the scope to do the calibration. You don't need to do one after a meridian flip as Phd2 will adjust the corrections as it will know it's now working on the other side of the meridian.