pixel trails and alignment

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BugEZ
Posts: 812
Joined: Sat Mar 26, 2011 7:15 pm
Location: Loves Park Illinois

pixel trails and alignment

Post by BugEZ »

There was some discussion in the Technical and Studio forum on pixel trails and alignment.
http://www.photomacrography.net/forum/v ... hp?t=17415

I thought I would add my two cents here in the equipment forum.

With my home built rig there is no guarantee that the camera axis and the actuator axis are aligned. I shoot with the camera stationary and the subject translating. I use a carpenter's bubble level to align the actuator and the camera with the horizontal plane.

Image
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Every time I attach or remove a lens the camera can rotate slightly at the tripod joint. I have found that it is "good enough" when I take a straight edge and extend it from the actuator parallel to the guide rails and align the axis of the lens with the straight edge. I do this by eye.

Image

The hot pixel trails and dust trails allow me to make sure everything is reasonably centered.

My actuator guide rails are approximately 1/8" in diameter and 3 inches long (from a CD tracking system) so they are not very stiff. When I used an acme screw to actuate the subject, the stick-slip friction at the screw joint tended vary as the screw rotated. The torque was reacted by the pins which deflected slightly. This caused the subject to deflect laterally and vertically forming corkscrew pixel trails. My actuator is currently driven by a rack and pinion. These plastic gears were part of the CD optical head drive mechanism. This rack and pinion driven by rubber band belts has reduced the wobble considerably and the trails are reasonably straight. I know I am in good alignment when all the trails point toward the center of the image.

Image

Even with a purpose built actuator such as a Stackshot, I would expect that the camera axis may not allways be perfectly parallel to the rail axis and the pixel trails are of value to help check alignment.

Kind regards,

Keith

canonian
Posts: 890
Joined: Tue Aug 31, 2010 4:00 am
Location: Rotterdam, Netherlands
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Post by canonian »

Thanks Keith for this well documented manual on aligning.
To be honest I never align with a level and do it 'by eye'.
I don't expect too much sag for my lenses. My setup is vertical, while yours is horizontal.
I have to clean my working space and what better time to get the bubble level out of the shed and dismantle, clean and re-align every part of the rig.

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