625 replies to this topic

[rms40]

Gaston, How will Skywave handle sensor tilt? It seems like that could cause a sensor alignment issue that might affect results of collimation. Could it also change results when I rotate the camera?

 

I have never spent time adjusting tilt with my CDK14 or FSQ106 imaging trains. There may be some but it is not obvious in my images. Both scopes have much larger image circles than even my full-frame ASI6200mm. So, would any tilt matter with SKYW?

 

Randall

Edited by rms40, 12 July 2021 - 08:53 AM.

[rockstarbill]

How is this coming along? I have a 12.5" iDK I would love to give this a run on once it's ready. In either a beta or released capacity.

Edited by rockstarbill, 26 July 2021 - 09:23 PM.

[Corsica]

Gaston, How will Skywave handle sensor tilt? It seems like that could cause a sensor alignment issue that might affect results of collimation. Could it also change results when I rotate the camera?

 

I have never spent time adjusting tilt with my CDK14 or FSQ106 imaging trains. There may be some but it is not obvious in my images. Both scopes have much larger image circles than even my full-frame ASI6200mm. So, would any tilt matter with SKYW?

 

Randall

Sensor tilt, unless very large, creates a defocus gradient.  In the context of scope collimation we are mainly interested by asymmetric aberrations such as astigmatism and coma.
SKG provides aberrations by type, one can ignore defocus/field curvature and only consider coma and astigmatism.

This is possible because SKW acts as a wavefront analyzer, like a Shack Hartmann.

SKG advanced version will provide field dependent aberration processing multi-stars, hence multi wavefront data on and off axis. This will be useful for creating aberration maps, such as field curvature, by processing this information we can provide sensor tilt/tip information but also the direction of corrections for the mirrors (miss alignment angles).

[Corsica]

How is this coming along? I have a 12.5" iDK I would love to give this a run on once it's ready. In either a beta or released capacity.

Still working on the documentation and tutorials, but you can still be part of beta test, just contact me by email at gaston@innovationsforesight.com

[rms40]

Gaston, Thanks for clearing up the sensor tilt effect on collimation.

 

Will SKW be included with SKG when available?

 

I will be glad to help test this on my CDK14 if you want. I am finally semi-retired and have time to test at my dark site. I have Maxim DL, SKYX, SGP and Voyager along with Teamviewer. I am still using Focuslock but would like to get SKG working - especially for maintaining focus.

 

Randall

[rms40]

One more question: What is the effect of sampling with SKW for collimation? Is sampling corresponding to seeing best? Any benefit from over-sampling? I bin my ASI6200mm at 3x3 for .91 arc secs/pixel on my CDK. Of course, I could bin 1x1 and spread the light over more sample points.

 

Randall

Edited by rms40, 28 July 2021 - 09:20 AM.

[Corsica]

One more question: What is the effect of sampling with SKW for collimation? Is sampling corresponding to seeing best? Any benefit from over-sampling? I bin my ASI6200mm at 3x3 for .91 arc secs/pixel on my CDK. Of course, I could bin 1x1 and spread the light over more sample points.

 

Randall

Since miss collimation (optical surface alignment) leads to low order aberrations the sampling is not critical for those. We recommend having at least 50 or more pixels across the defocused star profile.

This would be a different story when looking at higher order aberrations for testing optical surface quality for instance, at least for zonal defects.

Edited by Corsica, 04 August 2021 - 03:35 AM.

[rockstarbill]

All set to test this software out tonight on a 12.5" iDK from AGO. The only collimation work I have done so far on it was to bench collimate it with the usual tools - Tak Collimation scope and a Sight Tube. Very interested in seeing what the software thinks of the current state of the scope, and how it can improve that. 

[FredOS]

I have tested it on my Planewave CDK 12.5. Very positive experience and resulted with perfect stars. I’m not good at collimation so the tool was great. I look forward to the final release.

[Peteram]

Great guys,

 

keep us posted!

[rockstarbill]

I have tested it on my Planewave CDK 12.5. Very positive experience and resulted with perfect stars. I’m not good at collimation so the tool was great. I look forward to the final release.

Any feedback on the experience while using the tool? What workflow did you follow? How was the feedback from the software as you worked through it? Any details would be great to know as I set up for tonight's test. 

[xthestreams]

I can only speak for my RC but it’s generally pretty straightforward, about the most difficult part is getting it looking in the right place for files - the process can be a little confusing when using something like Voyager and then ensuring any variable parameters are entered correctly. 
 

the initial process of collimating is in some respects just as frustrating as ever, determining what screws do what to the final outcome (ie: calibrating the human) but once you get started, it’s pretty clear when you’re making things worse or better with the added value of solid (ie: not CCD Inspector) data to back it up

 

there is/was? A lot of detail on the screens that can be intimidating, but even without instructions after an hour or so with the tool you’re pretty much an expert

 

highly recommended 

[Corsica]

Any feedback on the experience while using the tool? What workflow did you follow? How was the feedback from the software as you worked through it? Any details would be great to know as I set up for tonight's test. 

Here are my recommendations.

I would suggest to focus on the collimation tool with the setting below:

 

Sensitivity to normal, Optical axes to normal, mirror spacing disabled (unchecked).

Set the seeing FWHM to your normal value.

When possible use a red filter and aim for a signal level on the defocused star around 1/2 to 2/3 of the full ADU scale, do not clip.
Use a star near the center of the imager chip, on axis, You will have to recenter it most likely between collimation adjustments.
The wavefront processing time is only few seconds, most of the time is related to frame download (do not bin) and detection of suitable stars in the FOV. You could speed up the process by cropping the frame, for the file that SKW will load, around the on axis star, say 300x300 pixels or so.

[rockstarbill]

Here are my recommendations.

I would suggest to focus on the collimation tool with the setting below:

SKWCol.jpg

 

Sensitivity to normal, Optical axes to normal, mirror spacing disabled (unchecked).

Set the seeing FWHM to your normal value.

When possible use a red filter and aim for a signal level on the defocused star around 1/2 to 2/3 of the full ADU scale, do not clip.
Use a star near the center of the imager chip, on axis, You will have to recenter it most likely between collimation adjustments.
The wavefront processing time is only few seconds, most of the time is related to frame download (do not bin) and detection of suitable stars in the FOV. You could speed up the process by cropping the frame, for the file that SKW will load, around the on axis star, say 300x300 pixels or so.

Thanks Gaston!

 

When using the Red filter, should the Lambda be changed to 650nm? 

[rockstarbill]

I can only speak for my RC but it’s generally pretty straightforward, about the most difficult part is getting it looking in the right place for files - the process can be a little confusing when using something like Voyager and then ensuring any variable parameters are entered correctly. 
 

the initial process of collimating is in some respects just as frustrating as ever, determining what screws do what to the final outcome (ie: calibrating the human) but once you get started, it’s pretty clear when you’re making things worse or better with the added value of solid (ie: not CCD Inspector) data to back it up

 

there is/was? A lot of detail on the screens that can be intimidating, but even without instructions after an hour or so with the tool you’re pretty much an expert

 

highly recommended 

Thanks. 

 

I am not concerned about setting the folders up to look for the data, that I can do fairly well. I plan to use a DragScript to take a series of shots once I have it manually dialed in with test shots. Then the software can look at 5 or so images and I can see if there is any variation in the results it is giving. 

 

How much defocus is needed to get a reading, and how differing levels of defocus impacts the results is something I am interested in seeing as well.

 

As for which screw does what, the DK's typically are only concerned with the secondary, and I just stick my hand in front of the scope and take an out of focus image to determine which screw is lined up to which part of the OOF donut. That usually gets me what I need.

Edited by rockstarbill, 12 August 2021 - 05:22 PM.

[Corsica]

Thanks Gaston!

 

When using the Red filter, should the Lambda be changed to 650nm? 

Yes, 650nm is a good value for most red filters. It does not need to be super precise anyway.

[Corsica]

Thanks. 

 

I am not concerned about setting the folders up to look for the data, that I can do fairly well. I plan to use a DragScript to take a series of shots once I have it manually dialed in with test shots. Then the software can look at 5 or so images and I can see if there is any variation in the results it is giving. 

 

How much defocus is needed to get a reading, and how differing levels of defocus impacts the results is something I am interested in seeing as well.

 

As for which screw does what, the DK's typically are only concerned with the secondary, and I just stick my hand in front of the scope and take an out of focus image to determine which screw is lined up to which part of the OOF donut. That usually gets me what I need.

The defocused is automatically computed by SKW for a given model and expressed in term of defocused distance (in microns) to be applied to an external focuser.

 

There is a tolerance to this value, depending of the scope f/#, usually around +/-100 microns or so.

This is not a black and white situation though, working outside this tolerance range, for a given model, leads to a progressive reduction in the aberration calculation accuracy, this is not very sensitive for collimation, it is more a concern in the context of a precise measurement of aberration values, say to retrieve mirror figures or quantify an optical system performance (SR).

Current standard models are made with a defocus value (4.5 waves rms) which provide a good trade off between the size, in pixel, of the defocused star and the aberration measurement accuracy. However we can make custom models for any defocus value we may like.

 

SKW will tell you how close you are to the required defocus value for your model.

 

The DK scope design features a spherical secondary mirror. Therefore you should need to only adjust the secondary tilt/tip screws to reach collimation (both mirror alignment), like with a SCT, this is one of the nice property of DK scopes.

Edited by Corsica, 12 August 2021 - 07:55 PM.

[rockstarbill]

Okay, so I am fresh off of using the software, and the number one thing I want people to take away from my post is....

 

This is software of the decade level good

 

This is the innovation we needed so badly. Something that could help us make sense of out of focus donuts, and arbitrary takes on them. This solves that for you. It does have some quirks to it, which I will not go into tonight.

 

I will share my graph (which has plots on it for my corrections) and I want everyone to know that I completely cranked its judgment all the way down to Chile levels (0.5") and holy cow is this software incredible.

 

I will post more later, but I will share this picture of the data analysis taken with my last frame, with the seeing cranked far better than I could ever hope to have here.

 

 

We all need this software, and we need it now.  

[rockstarbill]

Secondary to this, holy crap does Dave make incredible scopes. 

[xthestreams]

I’d be interested see what you get when you switch sensitivity to high!

[rockstarbill]

I’d be interested see what you get when you switch sensitivity to high!

What does that do and mean?

[Corsica]

What does that do and mean?

High sensitivity is used for lab work with an artificial star and without any seeing effect.

[rockstarbill]

High sensitivity is used for lab work with an artificial star and without any seeing effect.

Ahh so not something to be concerned about for this use case.

 

EDIT: Turning this all the way up had no effect on the results. They were the same.

Edited by rockstarbill, 13 August 2021 - 03:19 PM.

[rockstarbill]

Here is the out of focus star after the final adjustments were made.

 

 

Similar to the CDK example Gaston provided, in the sense that the shadow is not perfectly centered, yet the Wave Front Analysis shows excellent collimation. 

Edited by rockstarbill, 13 August 2021 - 02:47 PM.

[Corsica]

Here is the out of focus star after the final adjustments were made.

 

SkyWave-OOFStar.JPG

 

Similar to the CDK example Gaston provided, in the sense that the shadow is not perfectly centered, yet the Wave Front Analysis shows excellent collimation. 

Thank you for sharing.

This is a very common situation.

A slight mechanical de-center error of the secondary mirror or its mount/baffle leads to a non concentric shadow on the defocused star even though the collimation is perfect (mirrors optically aligned), especially with spherical secondary mirrors.
SKW can tell the difference between this situation and the one where the shadow is offset because aberrations indeed, such as coma, coming from miss-collimation.
As mentioned before most of us have been told that a centered shadow means a good collimation, this is not always the case nor an accurate indication of the collimation state unless the scope mechanics is near perfect.

Edited by Corsica, 13 August 2021 - 03:10 PM.