M81+M82 + NGC3077 - Camera rotation question...

[Aramcheck]

From the evening of 3rd into the morning of the 4th April. 89 x 180s subs (4 hours 27mins  total) with SW130dps, Canon 600d (astromodified), IDAS D2 LP filter & EQ6 mount & Bortle 7 skies. Would have gotten more, but meridian flip & precarious camera battery change ate into available time...

Question is how does the Camera angle in Stellarium's Occular plug-in relate to the physical camera angle on the newtonian scope? I was faffing around trying to get the the camera at 120 deg. (according to the Stellarium image) in order to get a god framing of the 3 galaxies. After a few attempts & then knocking the focus & I settled on just getting them in the frame, even though not perfect. Looking at Stellarium this turned out to be about -120 deg, so should I have mounted the camera upside down?

Many thanks!
Ivor

 

[vlaiv]

34 minutes ago, Aramcheck said:

Question is how does the Camera angle in Stellarium's Occular plug-in relate to the physical camera angle on the newtonian scope? I was faffing around trying to get the the camera at 120 deg. (according to the Stellarium image) in order to get a god framing of the 3 galaxies. After a few attempts & then knocking the focus & I settled on just getting them in the frame, even though not perfect. Looking at Stellarium this turned out to be about -120 deg, so should I have mounted the camera upside down?

There is no connection really.

I think that easiest way to establish rotation is to do test shot on bright star and slew scope while taking a shot. This will create a trail on sensor that you can examine. Say you slew in RA - then star will make a line that is RA line in the sky. That can be your reference and you can rotate camera with respect to that.

I know how to orient sensor in "straight thru" designs - like refractor or RC/MCT/SCT  (where camera comes at the end of the scope and faces the same way as aperture) - as you can easily orient sensor with RA or DEC - by just looking at the mount.

With newtonian - you have more reflections and things are perpendicular. There is also OTA/focuser rotation with respect to mount / rings that can change - and that rotates FOV, so I'm not sure if there is a easy way to determine sensor orientation by just looking at it.

Most people make focuser either "horizontal" or "vertical" with respect to the mount (when scope is in home position) - I guess that makes things easier, but I'm still not sure if I could figure out which way camera is oriented without piece of paper to trace the light.

 

 

 

Edited April 5, 2021 by vlaiv

[CloudMagnet]

With my camera, the image sensor matches the Stellerium view when the text on the back of the camera is upright and this text also lines up parallel to the focuser knobs (if that makes sense). So the camera in this position is what I count as "0" degrees. Rotating the camera 90 degrees clockwise also matches with  adding 90 degrees to the camera angle on Stellerium as well. Make sure you use the equatorial mount otherwise the image angle will be all wrong.

Handy tip to remember if you ever use APT to control your camera is to invert the image preview horizontal and vertical when you image in the western hemisphere as it will be back to front otherwise.

[vlaiv]

2 minutes ago, CloudMagnet said:

With my camera, the image sensor matches the Stellerium view when the text on the back of the camera is upright and this text also lines up parallel to the focuser knobs (if that makes sense). So the camera in this position is what I count as "0" degrees. Rotating the camera 90 degrees clockwise also matches with  adding 90 degrees to the camera angle on Stellerium as well. Make sure you use the equatorial mount otherwise the image angle will be all wrong.

Handy tip to remember if you ever use APT to control your camera is to invert the image preview horizontal and vertical when you image in the western hemisphere as it will be back to front otherwise.

Does it matter how the tube is rotated or not?

Do you have your camera in up/down or left/right position - or maybe at arbitrary angle?

[CloudMagnet]

Just now, vlaiv said:

Does it matter how the tube is rotated or not?

Do you have your camera in up/down or left/right position - or maybe at arbitrary angle?

No tube position doesnt matter (i think), as long as the camera is attached with the text the right way up and parallel to the focuser knobs as in the picture below, then it is always lined up to match stellerium.

I rotate the tube itself so that the camera forms a near straight line through to the counterweight shaft. That means that I can balance the scope in declination as otherwise the camera weight pulls the scope down on one side.

[vlaiv]

3 minutes ago, CloudMagnet said:

No tube position doesnt matter (i think), as long as the camera is attached with the text the right way up and parallel to the focuser knobs as in the picture below, then it is always lined up to match stellerium.

 

I rotate the tube itself so that the camera forms a near straight line through to the counterweight shaft. That means that I can balance the scope in declination as otherwise the camera weight pulls the scope down on one side.

Ah, ok.

So you have your camera in "up/down" position - indeed that is easier to balance in DEC as camera is "parallel" to CW shaft.

However - I do believe that rotating OTA rotates the view as well and if you mount scope so that focuser is at 90° to CW shaft - camera FOV will also rotate by 90°

[CloudMagnet]

Just now, vlaiv said:

Ah, ok.

So you have your camera in "up/down" position - indeed that is easier to balance in DEC as camera is "parallel" to CW shaft.

However - I do believe that rotating OTA rotates the view as well and if you mount scope so that focuser is at 90° to CW shaft - camera FOV will also rotate by 90°

hmm, might have a try at that and see if it makes a difference with the tube rotated. I always set it up at the exact same angle just for keeping the center of mass in balance, so the only variable is the rotation of the camera itself.

OP might just need to experiment to find how the camera needs to be rotated to produce a matching view with Stellerium. First deciding on the angle the OTA should be rotated (keeping balance in mind) and then sticking with it. Only afterwards then finding the angle of the camera required to keep consistancy between different nights.

[vlaiv]

13 minutes ago, CloudMagnet said:

hmm, might have a try at that and see if it makes a difference with the tube rotated. I always set it up at the exact same angle just for keeping the center of mass in balance, so the only variable is the rotation of the camera itself.

OP might just need to experiment to find how the camera needs to be rotated to produce a matching view with Stellerium. First deciding on the angle the OTA should be rotated (keeping balance in mind) and then sticking with it. Only afterwards then finding the angle of the camera required to keep consistancy between different nights.

Indeed. I think it is good idea to always put focuser in the same position - like you do. That way you take one variable out of the equation (and also helps with DEC balance).

[Stu Wilson]

Nice image 🙂

[fortytwo]

By a strange coincidence I'm sitting readin this while imaging the same target having had the exact same probelm earlier, only with a refractor.

The target for some reason wasn't central despite a good polar and two star alignment, (Betelgeuse and Dubhe) but it was tracking well for 60 sec exposure so I have left it alone.

I'm not sure if I should use the slew to align the target more centrally after I've polar and two star aligned, will that mess up the tracking at all?

Fabulous image, I'm certain mine won't be as good especially with only 60 sec.

Cheers,

Jeff