Keeping the same camera orientation

[dannybgoode]

Another quick one hopefully this. It seems that most targets benefit from more than one night’s worth of data acquisition so how do folk that don’t have an obsy maintain camera orientation between sessions?

 Marital constraints mean a full tear down after each session so is there a way of making a temporary mark to note orientation or some other trick?

I could get close by just comparing an existing image to a test shot each session but are there other techniques I could use?

 Thanks all

[Davey-T]

Plate solving will give you the angle.

Dave

[dannybgoode]

23 minutes ago, Davey-T said:

Plate solving will give you the angle.

Dave

I only have a normal focuser and just use a 2” nose piece. How does the angle translate into camera position etc?

[michael8554]

I made a tippex mark on my camera T ring, and a corresponding mark on the focuser. 

Next session I align the marks, DSS copes with any slight difference in rotation with no problem. 

Michael 

Edited December 25, 2019 by michael8554

[vlaiv]

What scope are you using?

If it has secondary spider and tube rings you need to align two things rather than just camera between sessions.

Only thing that camera rotation with regards to previous session brings is reduction of field of view:

Software is capable of rotating subs to match each other, but resulting stack will have all subs present only in narrow central region (red rectangle above). Large rotation reduces surface considerably while small angles almost have no impact and only outer edges need to be cropped away.

You rotate your FOV by simply rotating camera in the focuser - you have 2" nosepiece? then just loosen it and just rotate camera and tighten it back again. Angle that you rotate it will correspond to angle that FOV rotates but direction is not easy to guess (depends on type of telescope - every mirror flips direction, etc ...).

Issue with secondary spider is that you need to orient OTA relative to RA/DEC the same way otherwise your diffraction spikes will not align and you will get multiple X patterns overlapped on stars - which looks bad. Something like this can happen:

Keeping OTA fixed in tube rings and just releasing dovetail from mount clamp and reattaching it next time will keep OTA orientation (don't take tube rings of the ota, nor loosen them and rotate ota inside rings between sessions).

[michael8554]

20 hours ago, michael8554 said:

I made a tippex mark on my camera T ring, and a corresponding mark on the focuser. 

Next session I align the marks, DSS copes with any slight difference in rotation with no problem. 

Michael 

I have a fork mounted Meade LX200GPS, so rotating in tube rings, and lining up the secondary spider, hadn't even occurred to me.......!! 

Michael 

[ollypenrice]

I'm a firm believer in leaving the camera aligned with RA and Dec, either in portrait (long side aligned with Dec) or landscape (long side aligned with RA.) It is dead easy to align the camera this way. Align the camera by eye with the dovetail first then just slew slowly in one axis during a shortish exposure of a few seconds and look at the angle of the star trails you produce. That's your camera angle. Rotate till the trails are horizontal or vertical as desired. If it's orthogonal you can add data years later because finding the RA/Dec angle is easy. Finding a random angle wastes vast amounts of time because there is no routine way of doing it.

Olly

[don4l]

CCDCiel has an option to display the image frame as part of its platesolving routine.  I suspect that other capture software has the same feature.

I platesolve a reference image from the first night's session, and then I have it as a background image in my Cartes du Ciel.  The next night, I platesolve and display the image frame in CdC.  I just rotate the camera until the frame lines up with the background image.  It usually takes no more that three attempts to be aligned to less than a degree.  The beauty is that you don't need to remember any rotation angles or numbers.  It takes about 2 minutes to be precisely aligned and rotated using 2 second exposures for the platesolving.

Here is a screenshot in which I would need to move the camera a bit to the left and rotate it a bit clockwise when I stand behind it.