TL APO804, Telenegative improving corner sharpness (1 Viewer)

The TLAPO804 is a great little scope but suffers from softness in the corners. I believe Fernando explained in a post quite some time ago it is caused by not using field flattener. I does not matter in practice for bird photography, so I have not bothered about it.

When testing the other day I happened to find out that using a telenegative (~1.45x, from a stripped Zuiko 100-200 zoom lens) seems to improve the corner sharpness. Is that positive side effect possible? Or is it an illusion?

Attaching two photos of same res chart photographed at 8 meters with same light conditions.

Hard to say from that test because the TN is going to give you a boost in sharpness anyway. You would have to do it so that the test chart is about 1/3 the hight of the frame and placed in the corner of the frame on both shots, which means you would have to be closer with the scope without the TN. Then crop and balance the exposure and WB.

The TN's act like a barlow so I'd guess you get a different shaped light cone. The light cone with a TN will be a bigger diameter than without it and so the soft part of the image will now fall outside of the cameras sensor.

Paul.

Exactly.