Note: I discovered weeks after this test that the filter drawer of this lens actually contained a Nikon UV filter. That might have influenced the result, so further testing required.
And these are the results of some testing with this setup are a bit disappointing! actually it seems that the sharpness of this particular lens cannot compare with ‘real’ telescopes, and that’s maybe not a great surprise. To be comparing apples with apples: the APO image was taken with a F/7 Esprit 120mm with a focal reducer/flattener to F/5,5 resulting focal length 663mm. Second point: the total imaging time of the reference image was 150 minutes, compared to only 7,5 minutes for the F2.8 image, and 50 minutes for the F4 image. .
- the images from the Nikkor are blown up to match the size of the reference image
- the Nikkor images are clearly less sharp, with notable halos on the brighter stars in the F2.8 image
- the star shape seems to be a bit irregular, that is not necessary a lesn issue it might be related to guiding issues.
The real strength of this lens is probably more in the area of wide-filed DSLR imaging?
And these are the images taken with the Nikkor 300mm F2.8 and the ASI183mm, using a Baader contrast booster 1 1/4″ filter to avoid blue/purple fringes and IR. The F/4 image can be recognised easily due to the 18-pointed stars, caused by the 9 iris blades in the lens. The F/4 image is clearly sharper, however the F2.8 image obviously got the image faster but with less sharpness.