Sensor Orientation for imaging

[Nikolas74]

I was always wondering what is the best way to orientate the camera for most uses.... Sensor to be orientated on its Height? or Width? Does it play any role on how much sky you can fit in the image? 

 

[Seelive]

Depends upon what you're imaging and how big the target is relative to the overall image size, but it's best to orient the camera so as to get as much of the chosen target as possible.  Although an image can always be rotated during post processing, you can loose a lot of the available imaging area when you subsequently crop.

[Nikolas74]

I see, thank you very much for your answer. 

[rickwayne]

A secondary consideration, if you're imaging on an equatorial mount, is aligning with the mount axes. If you know that e.g. horizontal in the image is right ascension and vertical is declination, it's a lot easier to diagnose problems.

[vlaiv]

If you don't have issue with framing and you can fit whole target in the frame with many orientations - choose either landscape or portrait orientation.

There are several reasons why orienting camera sensor with respect to RA/DEC axis is beneficial.

- if you have slight issue with guiding / tracking and you get your stars somewhat elongated - direction of elongation will tell you where the issue is and also - if you have star elongation in horizontal or vertical - eye does not notice it as much as in the case it is at an angle

- it is much easier to repeat such orientation than is arbitrary angle. When you want to align your sensor to RA or DEC - you can check your orientation with a single exposure. Just start exposure with bright star in frame and slew telescope in either RA or DEC. You will get star trail in the frame. Is it horizontal or vertical (depending if you've chosen landscape or portrait)? You are properly aligned. Is at an angle? you need to turn your camera more.

- when doing mosaics - it is easier to calculate RA/DEC of each panel center (although decent mosaic planing software will handle any orientation).

[david_taurus83]

If the camera is 'upright' in the home position then the top and bottom of the sensor will be parallel with right ascension lines, no matter what target you choose. The same applies to declination if you rotate the camera so the 'sides' of the sensor are facing up and down in the home position.

Example of sensor 'upright'

 

Sensor rotated 90° or on its 'side'. Bottom and top are now parallel to declination.

 

You can use this to pre-frame a target to get you close to the desired framing. I tend to stick to either upright or sideways though as they are easier to replicate.

[vlaiv]

4 minutes ago, david_taurus83 said:

If the camera is 'upright' in the home position then the top and bottom of the sensor will be parallel with right ascension lines, no matter what target you choose. The same applies to declination if you rotate the camera so the 'sides' of the sensor are facing up and down in the home position.

This is true for refractors and SCTs/MCTs/RCs - but not necessarily so for newtonians and hyperbolic astrographs that mount camera to the side.

With such scopes orientation depends both on camera orientation with respect to OTA but also with rotation of OTA with respect to rings - and it is much harder to figure out orientation before you take test image.

You can only be certain that you'll align sensor with RA/DEC if you align it to OTA and put it in one of four positions with respect to dovetail bar - top, bottom, left, right. Even then it is really tough to figure out if you have your sensor longer side aligned with RA or DEC.

[Nikolas74]

Many thanks to all of you.. Got it.. I always use to have the camera sensor oriented "upright" as it is easier for me to understand the movement of the mount... When I press North the stars move up, when I press West the stars move left... So I guess I will continue do the same and unless the target doesn't fit maybe I will rotate the camera.. 

The only thing that I was thinking is that when the sensor is upright there is less of a sky in the image on the "left" and "right" sides. 

Anyway I am not going to make it more complicated.... 😁

Many thanks! 

Edited December 23, 2020 by Nikolas74

[vlaiv]

4 minutes ago, Nikolas74 said:

The only thing that I was thinking is that when the sensor is upright there is less of a sky in the image on the "left" and "right" sides. 

Exactly - so you rotate it 90° and you get more space left/right - if that suits your target better. First try those orientations and only use "diagonal" if you can't fit your target in up/down or left/right orientations.