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Problems? Probably very few.  When using a small-format chip, the off-axis distance is small enough that the in-focus imaging plane is basically flat with small spot image sizes. And deviating from the optimum distance isn’t as critical as for full-frame or large-format chips.

Here is a graph of the spot diameter in microns versus the imaging back focus distance in millimeters for the EdgeHD 11.

EdgeHD back focus vs spot size


The curve labeled 13.5mm off-axis is relevant here, as it corresponds to a 27mm diagonal, either nearly the same size or larger than the diagonal of these popular cameras and their chip sizes:

ST10 (14.7x10 millimeters, 18mm diagonal)

APS-C format camera like the Canon Digital Rebels, 20D through 60D (22.2mm x 14.8mm, 27mm diagonal)

Nikon DX (Nikon APS-C format 23.6mm x 15.7mm, 28mm diagonal)

As you can see, the spot size is less than twice the on-axis spot size even an inch (25mm) to either side of the optimum distance for this curve. Images at 13.5mm from the optical axis are only slightly larger than the diffraction pattern or Airy disk when the back focus distance is plus or minus 25mm from the 146mm optimum distance.

For a full-frame chip (so-called 35mm, actually 36mm x 24mm or 43mm diagonal), the curve labeled 21mm is relevant. Here the story is different. Images on the outer parts of this chip suffer from far more distortion if the back focus distance isn’t optimum.

At the other extreme, webcams like Celestron’s NexImage and products like the Mallincam have chips only 12mm or less across the diagonal. This means that the change in spot size with back focus distance is very small. Any distance within several inches either side of of 146mm optimum spacing will give essentially the same image quality.

NOTE: a regular 1-inch T-threaded photo extension tube screwed onto a regular #93633-A T-adapter is very close to the EdgeHD 8-inch T-adapter's (#93644) 5.25-inch optimum spacing size.