Vibration-Induced Micro-Blur

[Captain Scarlet]

I was chatting to a fellow SGL friend today about this, and relating how convenient “tracking” is for observing at very high magnification. You simply sit and stare and do not have to break contact at regular, frequent, intervals.

But always, right by my ear, there is this bzzzzzzzz of the motors gently running to keep on target. I was wondering how much of this bzzzzzzz finds its way to the OTA and induces a vibration-induced blurring. I should add I am talking here from a strictly observer’s viewpoint.

My main go-to mount (in both senses of the phrase) is an az-eq6, especially for my bigger scopes which will more likely be used at high magnification. I think it’s belt-driven, but even so the belts will be in tension and therefore of limited damping use?

I wonder, does anyone have experience or views or links about this?

I might attach an accelerometer set-up (if I can find it) to my rig to see what that shows between tracking and stopping tracking. Maybe even a guide log from imagers might yield useful info? Even my iPhone has some apps that might be able to show a frequency spectrum.

Cheers, Magnus

Edited March 27, 2023 by Captain Scarlet

[andrew s]

For any reasonable system the damping due to the inertia of the mount/telescope system should put any drive induced blurring well below the seeing psf.

Regards Andrew 

[Paz]

I have thought about this in the past when observing with an eq5 with the RA motor going but I couldn't detect this effect myself.

[bosun21]

I reckon that if any vibration was transferred to the telescope and optics then our astrophotography friends would have discovered it and wrote about it long ago.

[Captain Scarlet]

29 minutes ago, bosun21 said:

I reckon that if any vibration was transferred to the telescope and optics then our astrophotography friends would have discovered it and wrote about it long ago.

Well I have to say that even when I look at the supposedly very best astro-photos, and for extended objects they are incredible, I always think to myself: wow stars look so so much better through an eyepiece than ever they do on a photo.

Edited March 27, 2023 by Captain Scarlet

[bosun21]

1 minute ago, Captain Scarlet said:

Well I have to say that even when I look at the supposedly very best astro-photos, and for extended objects they are incredible, I always think to myself: wow stars look so so much better through an eyepiece than ever they do on a photo.

That may be the case due to slight bloating of the stars due to long exposures but with things like planetary videos definitely shows great intricate details. Saying that I am glad i only do visual astronomy now.

[jetstream]

42 minutes ago, bosun21 said:

I reckon that if any vibration was transferred to the telescope and optics then our astrophotography friends would have discovered it and wrote about it long ago.

Imagers spend much time and a whole pile of cash on their mounts to minimize a whole host of issues, such as PEC which only accounts for a portion of the error.check out the prices of a 10 Micron or A-P mount... the 10 Micron goes up to 27000 pounds...

https://www.firstlightoptics.com/10micron-mounts/10micron_1454010.html

 

9 minutes ago, bosun21 said:

like planetary videos definitely shows great intricate details

the lunar/planetary imagers use "lucky imaging" ie the use of a dedicated (mostly) video camera and then use programming to choose the best frames and then stack them to reduce noise and so on. Without this whole process the images would be much worse than visual.

Edited March 27, 2023 by jetstream

[jetstream]

13 minutes ago, bosun21 said:

That may be the case due to slight bloating of the stars

Imagers go to great length and expense to reduce star bloat and IIRC blue bloat. Scopes like the TOA130 are designed to help give nice tight stars.

Edited March 27, 2023 by jetstream

[bosun21]

Just now, jetstream said:

Images go to great length and expense to reduce star bloat and IIRC blue bloat. Scopes like the TOA130 are designed to help give nice tight stars.

You still get star bloat with long exposures, albeit dramatically reduced or eliminated by processing. It’s not so much the telescope optics but rather it’s physics with an accumulation of  light from a point source. 

[jetstream]

Just now, bosun21 said:

but rather it’s physics with an accumulation of  light from a point source. 

This is interesting to me can you explain it further? Do all stars in an image bloat?

[bosun21]

4 minutes ago, jetstream said:

This is interesting to me can you explain it further? Do all stars in an image bloat?

It depends on the magnitude of the stars. This is what I was taught by a seasoned astrophotographer. I am open to correction however from someone with a good knowledge of AP.

[andrew s]

12 hours ago, jetstream said:

This is interesting to me can you explain it further? Do all stars in an image bloat?

The image of a star formed by a telescope is not a point but a diffraction pattern created by the optics of the telescope.  It's called the point spread function.  It's central bit is similar to a gaussian function. The longer you expose the more the wings of the function get above the noise so the apparant diameter of the star increases.  Star bloat.  

Atmospheric seeing can also spread out the image as can wind gusts. 

Regards Andrew 

[jetstream]

2 hours ago, andrew s said:

The image of a star formed by a telescope is not a point but a diffraction pattern created by the optics of the telescope.  It's called the point spread function.  It's central bit is similar to a gaussian function. The longer you expose the more the wings of the function get above the noise so the apparant diameter of the star increases.  Star bloat.  

Atmospheric seeing can also spread out the image as can wind gusts. 

Regards Andrew 

Of course. Can the optics of a telescope play a role in the bloat?

[Captain Scarlet]

17 hours ago, andrew s said:

For any reasonable system the damping due to the inertia of the mount/telescope system should put any drive induced blurring well below the seeing psf.

Regards Andrew 

I'm not sure I'm completely convinced. I'll go away and experiment, I have some useful tools which should shed some light.

M