Many astrophotographers know the problem: after accurate focusing, in one or two corners the stars are not pinpoints. Often, the sharpness of the image is compromise to a level that the image has to be cropped.
Some possible causes of this problem are:
- a tilted camera sensor (fraction of a millimetre are enough)
- a tilted focuser
- a tilted focal plane of the telescope (common in Newtonian telescopes)
- tilted optical accessories by imprecise clamping
As solution, a tilter can re-establish the parallelism between elements and therefore the details on the corners of your photo will return sharp.
The best way is to calibrate it is using test images:
- Identify the corner of your photo which has unsharp / aberrated stars.
- Loosen the 3 pull screws (the smaller one).
- Slightly turn the push screws in correspondence of for the corner of the photo that is unsharp.
- Take a second image. If the sharpness has deteriorated, turn the adjustment screw in the other direction until all 4 corners of your photos has the same sharpness.
- Tighten the pull screws.
