Can I use an all sky camera for Newt collimation?

[900SL]

I have an ASI 178mm planetary camera (with the all sky lens still in the box).

A Google search indicates that you can use same with software to generate concentric circles for secondary collimation, alignment etc, by putting the camera in the focuser

I'm also aware that the camera chip needs to be centered in the focuser

Anybody use something similar?  Recommended software/idiots guide? 

Edited Tuesday at 14:22 by 900SL

[happy-kat]

als colimation tool gives concentric circles, I used a webcam when I used it in a scope focuser, I ran the tool just over a jpg too to see if circles were concentric

[900SL]

Cheers Kat. Looks like Sharpcap has some collimation functions, and there's another called 'collimation circles'. I'll have a look at all three

 

In the meantime I tried the 178+allsky lens. Fits into the 2" eyepiece holder. I think I'll get a Cheshire to see what is going on here. The camera cross hairs on the ASIAir app seem to be off center. Not sure if this is sensor or scope related. Here's two screenshots 180 degrees rotation. Not sure that range I'm focused at here, need to play around a bit

Edited Wednesday at 07:19 by 900SL

[AstroKeith]

14 minutes ago, 900SL said:

Cheers Kat. Looks like Sharpcap has some collimation functions, and there's another called 'collimation circles'. I'll have a look at all three

 

In the meantime I tried the 178+allsky lens. Fits into the 2" eyepiece holder. I think I'll get a Cheshire to see what is going on here. The camera cross hairs on the ASIAir app seem to be off center. Not sure if this is sensor or scope related. Here's two screenshots 180 degrees rotation. Not sure that range I'm focused at here, need to play around a bit

 

Your biggest error sources likely to be tilt of the camera and lens assembly.  You will need to mount the camera/lens into a 1 1/4" tube. and then rotate it to see if the centre of the image stays still, if not adjust somehow.

[900SL]

Cheers Keith

My first newt so plenty to learn here

I fiddled with focus and gain and zoomed out the ROI video in ASIAir. 

Am I correct in assuming the various rings from outside in are:

1 Drawtube

2: Secondary

3 Primary with clips

4 Reflection of focus tube and camera , or is this the reflection of the secondary assembly in the primary? I'm focused on secondary only so the spider vanes are out of focus

5 Not sure about center donut, could this be reflection of allsky lens, or the center donut?

 

Edited Wednesday at 09:13 by 900SL

[CraigT82]

9 hours ago, 900SL said:

Cheers Keith

My first newt so plenty to learn here

I fiddled with focus and gain and zoomed out the ROI video in ASIAir. 

Am I correct in assuming the various rings from outside in are:

1 Drawtube

2: Secondary

3 Primary with clips

4 Reflection of focus tube and camera , or is this the reflection of the secondary assembly in the primary? I'm focused on secondary only so the spider vanes are out of focus

5 Not sure about center donut, could this be reflection of allsky lens, or the center donut?

 

Generally correct, but you wouldn’t want to try primary collimation like this, you need something with a peephole for primary collimation, this camera method is really for secondary collimation. Also useful for checking focuser tilt etc. looking at the images it seems you could do with adjusting the focuser tilt, have you tried with a Cheshire to confirm the off centre pointing? Looking at your earlier images where you rotated the camera 180, the is little offset between the two which is good, but points to focuser tilt, or the device being pushed out of perpendicular by the clamping mechanism, which amounts to the same thing 

Edited Wednesday at 18:24 by CraigT82

[CraigT82]

 

[900SL]

20 hours ago, CraigT82 said:

Generally correct, but you wouldn’t want to try primary collimation like this, you need something with a peephole for primary collimation, this camera method is really for secondary collimation. Also useful for checking focuser tilt etc. looking at the images it seems you could do with adjusting the focuser tilt, have you tried with a Cheshire to confirm the off centre pointing? Looking at your earlier images where you rotated the camera 180, the is little offset between the two which is good, but points to focuser tilt, or the device being pushed out of perpendicular by the clamping mechanism, which amounts to the same thing 

Many thanks Craig, much appreciated by this novice in the dark arts. I'm enjoying the Newt challenge

I've now got a cheshire collimator on order, and thinking of getting a Baader laser.

In the meantime, today I set up the two inch eyepiece and extension collar on a lightpad over a target where I had marked the geometrical center of the extension collar. On rotating the camera when viewing using ASIapp, the center reticule appears to orbit the center dot. The pencil dot remains centered on the screen and the reticule appears to orbit this point. I'm struggling to get my head round what this means, but think:

1: The camera/eyepiece holder/extension sleeve are all aligned

2: The sensor centerline/reticule/lens? is/are off center and rotating about the pencil mark

Some images

 

Edited Thursday at 14:54 by 900SL

[CraigT82]

Yes certainly seems to be something like sensor tilt there.  Or maybe the lens is cross threaded and tilted slightly?  Do you have another camera to try? 

If it was tilt induced by the clamping mechanism it wouldn’t orbit the dot, rather it would always be offset to the same side of the dot. 

Is this the F8 Bresser you’re collimating? I wouldn’t worry too much about the primary collimation of that to be honest, an F8 newt has a huge sweet spot.

For visual work the secondary collimation is not overlay important as long as it’s roughly there or thereabouts.

[CraigT82]

Just to give an idea of the size of the sweet spot of a parabolic mirror - AKA Diffraction limited field radius - the formula to calculate it is F³/90, so for an F8 scope it works out to be a whopping 11.4mm in diameter.  So if you imagine your primary mirror and the light reflecting from it as a long thinning cone of light, the centre of the tip of that cone only needs to be within 11mm of the centre of the eyepiece field lens (or centre of camera sensor) to be 'in collimation'.

In contrast an F4 scope only has a sweet spot of 1.4mm diameter, so the tip of that cone needs to be much more precisely placed. Hence why fast newts are harder to collimate than slow ones.

[900SL]

17 hours ago, CraigT82 said:

Yes certainly seems to be something like sensor tilt there.  Or maybe the lens is cross threaded and tilted slightly?  Do you have another camera to try? 

If it was tilt induced by the clamping mechanism it wouldn’t orbit the dot, rather it would always be offset to the same side of the dot. 

Is this the F8 Bresser you’re collimating? I wouldn’t worry too much about the primary collimation of that to be honest, an F8 newt has a huge sweet spot.

For visual work the secondary collimation is not overlay important as long as it’s roughly there or thereabouts.

Yes it is the f8 Bresser Craig. I've bought it as a 'galaxy imaging' and lunar scope. I'll pair it with a 533MM Pro and bin at 2x2, so it should be pretty fast even though f8

One other question if I may: Is the long cheshire collimator better suited to the f8 type newts? That seems to be the general recommendation from google. Nights are getting darker here now, so i might be able to do a star test soon

Edited yesterday at 12:01 by 900SL