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Zwo camera orientation without a rotator


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Hi all, 

This may seem a stupid question/conundrum.  Firstly I used to have a sw 72ed rotator fitted to the focus tube on my 72ed and the ovl FF attached, I was never overly happy with the connection between the two (yep I know on flos page for the rotator that it's only compatible with the short tube version, though mine is the long tube version but I could still achieve focus) as the threads were a slightly different pitch. I took off the bevel on the FF and connected this way. 

So now I found an M54-M48 adapter and screwed this onto my focus tube and then my Ovl FF and the rest of my imaging train. Now here's my thinking about orientation of my camera to the scope, it could be the ocd in me but I liked to have the sensor of my zwo asi294mc pro parallel and  (see attached images) the round bit on the 294mc pro tells me that the long side is facing me and lined up to the scope. 

I know there is no up or down, left and right in space but as I'm still tweaking my backspacing, so when adding or removing spacers the orientation of the camera moves so it's no longer as it was (long side of sensor facing me and the round bit moved) can I ask does this really matter? I hope I've made sense and not confuddled the bejeezus out of you and we'll done for getting to the end of my ramblings. 

Thank you for reading. 

Lee 

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The alignment should not matter. However, as you have all the parts screwed in place (if I read it correctly) you will need to rotate the scope in the rings for framing subjects.

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25 minutes ago, Clarkey said:

The alignment should not matter. However, as you have all the parts screwed in place (if I read it correctly) you will need to rotate the scope in the rings for framing subjects.

Thank you Clarkey, you did indeed read it correctly. Rotating my scope on the rings is do able so hopefully can solve any framing issues. I just needed some reassurance the the camera orientation in my screwed in place imaging train. 

Lee 

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Hello Lee, when you take an image the orientation is usually changed by the geometry of the mount, especially with a German equatorial mount. However, when you take the image you can post it to nova.astrometry.net. The result will give you the orientation, but in a form that is not in "plain English". The trick is learning to understand four numbers:

CD1_1   =   -0.000183421732869 / Transformation matrix                         

CD1_2   =    0.000492781214588 / no comment                                    

CD2_1   =    0.000492636225707 / no comment                                    

CD2_2   =    0.000182967937627 / no comment                                    

Those 4 numbers are a complete description of how the camera was rotated relative to the celestial sphere. I dont remember the exact equation, but the direction of the north celesial pole from the center of the image is something  like: North=atan(CD1_1/ CD1_2)  I regret its been a while since I needed that info and have forgotten the specifics. Its in the FITS specification pdf files. (Boring reading) But the angle is very very precise. So you might look into that and save the wear and tear on your hardware. The scale of the 4 values is the scale factors for X and Y in the image, so that is related to the image size of a single pixel.

The second 2 numbers are directly related to the first set, and indicate if the image is "direct" or "mirrored".

Another little detail: the SIP part of the FITS header describes any distortion found in your image, this can be from refraction, seeing, etc. If you dig into the math there is a ton of info in there. I can certainly understand if that seems like too much trouble tho. That can be a useful diagnostic source when you get the hang of what it means.

Hope that makes sense- and was useful!

 

 

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11 hours ago, AstroNebulee said:

I just needed some reassurance the the camera orientation in my screwed in place imaging train. 

Did you mean the orientation of the sensor. I like to set it up so that in parked position (pointing towards NCP) the sensor is oriented in landscape mode. That way in my head I know approx which way the FOV will be when scope rotates. And in the end I rely on platesolving to tell me the exact rotation angle that has been set up 🙂 I use Kstars and the view is clearly updated showing the FOV. I think NINA also has that feature.

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Posted (edited)
4 hours ago, AstroMuni said:

Did you mean the orientation of the sensor. I like to set it up so that in parked position (pointing towards NCP) the sensor is oriented in landscape mode. That way in my head I know approx which way the FOV will be when scope rotates. And in the end I rely on platesolving to tell me the exact rotation angle that has been set up 🙂 I use Kstars and the view is clearly updated showing the FOV. I think NINA also has that feature.

Yep exactly as you say, I like to do the same thing and have the sensor in landscape when parked. Sorry I didn't maje it clear, I got myself in a twiddle which isn't difficult. I've now managed to get hold of a rotator from RVO that I can attach between the m54-m48 adapter and field flattener, located by arrow in image, so when adding or removing the spacers or shims required to reach correct backfocus I can orientate the camera in landscape whern parked. 

Lee 

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Edited by AstroNebulee
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The rotator arrived from RVO today and so much better than the skywatcher one I was using, (there's no slop when all the grubscrews are loosened causing you to push the two surfaces together before tightening the thumbscrews) this one you just undo the grubscrews and turn and re tighten them. Solid piece and light too, really nice piece of kit. Definitely recommend over the skywatcher one. This is going to cure my said issue in original post. 

Lee

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Hi Lee,

I notice you have a filter draw between the field flattener and the camera. It is my (limited) understanding that different filters affect the back focus distance and different filter thicknesses affect the distance differently. You therefore need to be careful when determining flattener to camera sensor distance. You may of course already know this.

kind regards

Ian

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8 hours ago, IDM said:

Hi Lee,

I notice you have a filter draw between the field flattener and the camera. It is my (limited) understanding that different filters affect the back focus distance and different filter thicknesses affect the distance differently. You therefore need to be careful when determining flattener to camera sensor distance. You may of course already know this.

kind regards

Ian

Hi Ian 

Yep all understood and know the thickness of the filter affects the backfocus. The glass in the Astronomik L3 filter I use is 1mm and suggest add a third of that to the back focus. 

I've always had issues with backfocus hence stripping the imaging train back to basics and starting again. I've seen a few people with the ovl FF and older long tube version of the evostar use 60mm backfocus. On my last attempt before fitting the new rotator I was at 58.3mm and still needed a bit more. So that's where I am now and need clear skies to test it.

Lee 

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