Focus tube slop/tilt magically disappears ?

[TiffsAndAstro]

so last night, after 3 goes my calibration result was only acceptable. so i just decided to ignore that and press on.

my guiding was variable with jumps up to 6 at one point, possibly cable related as i had refined my wiring a little earlier on . i also had the best guiding i've ever had. for ngc6888 test 10 min sub i was around 0.9" for the entire 10 mins, for the m33 test it ended one 1.01". 

also i don't understand how my focus tube slop has gone. i did 'check' my focus tube up/down looseness and it seemed solid. did nothing else. maybe the stars aren't round enough in my 10 min sub for siril to be able to measure accurately enough? will try same on 1 min subs when i get a chance later. any thoughts comments would be very welcome.

 

Above are just a stack of same ten minute sub and copy of same with my 1 minute calibration library and a preset auto stretch no crop, pcc or bge or any other process

 

Edited July 17 by TiffsAndAstro

[TiffsAndAstro]

looking at 60 sec subs, tube slop, if that's what it is, is worse than ever on one target and a bit improved on the other.

10 min long subs in future it is, then ;(

[AstroMuni]

15 hours ago, TiffsAndAstro said:

if that's what it is, is worse than ever on one target and a bit improved on the other.

That sounds right. Depending on the direction in which the scope is pointed the focuser tube would be influenced by the weight of the camera in a particular direction causing the tilt.

[TiffsAndAstro]

46 minutes ago, AstroMuni said:

That sounds right. Depending on the direction in which the scope is pointed the focuser tube would be influenced by the weight of the camera in a particular direction causing the tilt.

It feels rock solid though

also it disappears on that 10 minutes sub, which means sub was so bad it hid the slop within the size of the stars?

[900SL]

I wouldn't get too hung up on focuser tilt etc at this stage. And I wouldn't be shooting 10 minute subs unless 3nm narrowband mono. Clouds, wind, wobble, stray light, any of these can cause reject subs and the longer the sub the greater the risk. You'll likely get more blown out highlights too.

Focus on err focus, tracking, dithering,  correct exposure, and total integration. Go for brighter targets higher up, away from LP domes or streetlights

[TiffsAndAstro]

8 minutes ago, 900SL said:

I wouldn't get too hung up on focuser tilt etc at this stage. And I wouldn't be shooting 10 minute subs unless 3nm narrowband mono. Clouds, wind, wobble, stray light, any of these can cause reject subs and the longer the sub the greater the risk. You'll likely get more blown out highlights too.

Focus on err focus, tracking, dithering,  correct exposure, and total integration. Go for brighter targets higher up, away from LP domes or streetlights

I only did a two 10 minutes subs on different targets while my guiding seemed worse than normal. I was shocked they seem (at least to me) ok. Ready for my narrowband filters

Summer time seems to be the time for maintenance and testing.

will concentrate on getting 10 hours on ngc6888 rest of sunny July

I really do appreciate the help, Ty.

[AstroMuni]

22 hours ago, TiffsAndAstro said:

also it disappears on that 10 minutes sub, which means sub was so bad it hid the slop within the size of the stars?

As advised by @900SL 10mins is quite long in my opinion and prone to errors. There is one thing I have realised - with cheaper scopes like mine, tilt/ focuser slop will be something I have to live with. Sigh!

Hence concentrating on the other aspects that I can try to improve, and there are plenty 🙂 

[alacant]

On 17/07/2024 at 13:41, TiffsAndAstro said:

my focus tube slop has gone

Hi

Great effort and excellent progress. I admire your method of experimentation. IMO, very much the key in this game.

The frame you used perhaps just happened to be taken when the angle of the telescope tube cancelled any flexure (?). I don't think the sw focuser (any low end sw focuser?) is capable of holding a camera properly for any great length of time, especially since the load has to be so far from the tube.

The foreground  stars around 6888 are a challenge for any refractor. When the moon has gone, perhaps try loadsa 4 or 5 minute frames? We use a cheepo UHC to help separate the gas from the stars. Maybe worth a try?

Cheers

EDIT** does anyone know of a proper focuser which fits the 72ed? Had a quick search, pero nada.

Edited July 19 by alacant
focuser

[TiffsAndAstro]

15 minutes ago, alacant said:

Hi

Great effort and excellent progress. I admire your method of experimentation. IMO, very much the key in this game.

The frame you used perhaps just happened to be taken when the angle of the telescope tube cancelled any flexure (?). I don't think the sw focuser (any low end sw focuser?) is capable of holding a camera properly for any great length of time, especially since the load has to be so far from the tube.

The foreground  stars around 6888 are a challenge for any refractor. When the moon has gone, perhaps try loadsa 4 or 5 minute frames? We use a cheepo UHC to help separate the gas from the stars. Maybe worth a try?

Cheers

EDIT** does anyone know of a proper focuser which fits the 72ed? Had a quick search, pero nada.

Uhc filter ? Is this a UV/ir cut one?

Not sure can replace focus tube on 72ed and probably not worthwhile compared to cost of better scope?

[alacant]

4 minutes ago, TiffsAndAstro said:

Is this a UV/ir cut one?

Hi, No.

https://es.aliexpress.com/item/1005007352153949.html?spm=a2g0o.productlist.main.3.14287ksf7ksfym&algo_pvid=b8975814-0ebe-49a0-9c13-0dc7c4498861&algo_exp_id=b8975814-0ebe-49a0-9c13-0dc7c4498861-1&pdp_npi=4%40dis!EUR!26.26!26.26!!!203.28!203.28!%402103919917213810310008087e9a2d!12000040387621293!sea!ES!168948195!&curPageLogUid=DKWrZVz4zFUO&utparam-url=scene%3Asearch|query_from%3A

Edited July 19 by alacant

[900SL]

16 hours ago, TiffsAndAstro said:

I only did a two 10 minutes subs on different targets while my guiding seemed worse than normal. I was shocked they seem (at least to me) ok. Ready for my narrowband filters

Summer time seems to be the time for maintenance and testing.

will concentrate on getting 10 hours on ngc6888 rest of sunny July

I really do appreciate the help, Ty.

What is your set up? It's helpful if you can add a footnote to these posts.. camera, gain/ISO, exposure, scope focal length and F number (or lens information) etc

[TiffsAndAstro]

1 hour ago, AstroMuni said:

As advised by @900SL 10mins is quite long in my opinion and prone to errors. There is one thing I have realised - with cheaper scopes like mine, tilt/ focuser slop will be something I have to live with. Sigh!

Hence concentrating on the other aspects that I can try to improve, and there are plenty 🙂 

I only did 10mins as a test. Just aircraft seems enough reason to not do them.

[TiffsAndAstro]

53 minutes ago, alacant said:

Hi, No.

https://es.aliexpress.com/item/1005007352153949.html?spm=a2g0o.productlist.main.3.14287ksf7ksfym&algo_pvid=b8975814-0ebe-49a0-9c13-0dc7c4498861&algo_exp_id=b8975814-0ebe-49a0-9c13-0dc7c4498861-1&pdp_npi=4%40dis!EUR!26.26!26.26!!!203.28!203.28!%402103919917213810310008087e9a2d!12000040387621293!sea!ES!168948195!&curPageLogUid=DKWrZVz4zFUO&utparam-url=scene%3Asearch|query_from%3A

That's cheap but from what I've read LP filter best avoided, but quad band might be good. £26 though might be worth a try?

[TiffsAndAstro]

54 minutes ago, 900SL said:

What is your set up? It's helpful if you can add a footnote to these posts.. camera, gain/ISO, exposure, scope focal length and F number (or lens information) etc

Should be in my Sig but doesn't seem to appear here

72ed flattener UV IR cut sv605cc usually 60 sec subs plus darks bias and flats, sw SA GTi f5.83 101 gain 5 offset -5c

[900SL]

Your 5 offset might be clipping dark signal, resulting in noisy backgrounds that stacking cannot remove, I'd crank that up a bit on the 533 IMX. Mine runs at 70 by default on the AsiAirPro, which is too high, somewhere around 30 should see you good

I ran your numbers through a 533IMX spreadsheet for exposure and 60s is more than enough for Bortle 5 to swamp read noise. Having said that, I run min 533 OSC at 90s exposures because I'm usually not clipping highlights, and my mount can track guided at 0.4"/px

Do you check individual subs for wobble, clouds, elongation etc? Wind and cloud can really mess up a stack if not removed

https://www.cloudynights.com/topic/685994-gain-and-sub-exposure-calculation-spreadsheet-for-the-zwo-asi533/page-2

 

 

 

Edited July 19 by 900SL

[alacant]

1 hour ago, TiffsAndAstro said:

quad band

We prefer the uhc to the current trend of such. You can split and combine channels just the same. 

Example:

 

Edited July 19 by alacant

[TiffsAndAstro]

16 minutes ago, alacant said:

We prefer the uhc to the current trend of such. You can split and combine channels just the same. 

Example:

 

That's a fantastic image. I'm as keen on the cloud structures as brain itself but I have a little less fov. My framing is ok I think.

Er splitting channels is a term I associate with mono. I'll have a Google on it as I doubt I'm doing that.

[alacant]

42 minutes ago, TiffsAndAstro said:

cloud structures

TBH, I'm not a fan of of obliterating stars. For me, the stars are the best part of any image, also perhaps the most difficult  bit to get right. Removing them removes structure and life. I did this one to illustrate that you don't need to spend €silly on narrow filters to see the dust and gas. The uhc separates them well.

But hey, That's what's trending so...

Edited July 19 by alacant

[TiffsAndAstro]

14 minutes ago, alacant said:

TBH, I'm not a fan of of obliterating stars. For me, the stars are the best part of any image, and I believe the most difficult  bit to get right. Removing them removes structure and life. I did this one to illustrate that you don't need to spend €silly on narrow filters to see the dust and gas. The uhc separates them well.

But hey, That's what's trending so...

So far for me, I want some imperfection in my results. I'm not perfect and my gear definitely isn't :). 

but not too much

the balance of star field to everything else seems to be different for every image I take and even then is very subjective.

I wonder what an image that kept luminosity (?) relative between each star and the nebulosity would look like? An unstretched 10sec sub?

[TiffsAndAstro]

Could my disappearing tilt be due to me not tightening the focuser locking screw? I think this could be the main cause.

[WolfieGlos]

51 minutes ago, TiffsAndAstro said:

Could my disappearing tilt be due to me not tightening the focuser locking screw? I think this could be the main cause.

Hmmm, interesting. I don’t recall testing that on my 72ed, I always ensured it was tight. Might be worth experimenting with. 

[TiffsAndAstro]

12 minutes ago, WolfieGlos said:

Hmmm, interesting. I don’t recall testing that on my 72ed, I always ensured it was tight. Might be worth experimenting with. 

that's my plan i *think* i barely tightened it when i got a lack of eggy stars along one side. focus tube itself seemed and seems pretty stable with my optical train on it. if i try to wiggle it, it feels rock solid. 

on the good news front, that last session i had of 40 minutes between clouds and after doing a bit more re-wiring, my auto guiding seemed to be under 1" mostly. until clouds. might be coincidence of course also i think i'm getting close to the weight limit of my sw gti, cw are really near the end of the cw bar

[WolfieGlos]

12 hours ago, TiffsAndAstro said:

that's my plan i *think* i barely tightened it when i got a lack of eggy stars along one side. focus tube itself seemed and seems pretty stable with my optical train on it. if i try to wiggle it, it feels rock solid. 

Let us know how you get on. I always tightened mine in the fear that the drawtube would slip whilst the mount naturally moves, and so lose focus. But perhaps that screw is forcing the drawtube in slightly, causing it to be slightly out of alignment with the glass.

You can always take your rig off of the mount and put it onto some scales. 👍

[TiffsAndAstro]

1 hour ago, WolfieGlos said:

Let us know how you get on. I always tightened mine in the fear that the drawtube would slip whilst the mount naturally moves, and so lose focus. But perhaps that screw is forcing the drawtube in slightly, causing it to be slightly out of alignment with the glass.

You can always take your rig off of the mount and put it onto some scales. 👍

Well I tried between clouds last night, but was having auto guiding issues which must be wiring related.

400" rms error is bad, right?

Maybe tonight...

[TiffsAndAstro]

so through clouds last night i was trying to add more time to my ngc 6888. i tightened the screw and got tube slop/tilt. i loosened it a bit and still got slop/tilt. i loosened it completely and....the slop/tilt seemed to go away, or at least very much reduced.

my focus tube didn't seem to move much, i was shooting near zenith, so this might account for lack of slop/tilt but is probably worse case for focus tube dropping out/down under weight of optical train? even with very variable guiding (not 400" rms thankfully) i was getting hfr in nina as low as 2.09 which is about 0.5 better than my previous lowest hfr.