EDIT: also see the later post with outdoor shots and opposite results. You know, sometimes you have a little doubt running around in your head so you say: "ok, let's do a couple of test shots". After three hours you wake up, have lunch 2 hours late, and here I am with the results. The 75-300 is much better at 200 then at 300 so the question was: what if I shoot at 200 and upscale? TL;DR: shoot at 200mm/f8 and upscale. Here's what I found out. 0. About the test. Shot on tripod, self timer, etc. All at close focus distance indoor. Raw develped with Darktable with the same minimal processing (no denoise, little sharpening). 1. For these tests I took three or four shots for each setting. Then I selected the best one of each set. It was quite impressive to see the difference between shots supposed to be identical. Maybe AF differences, maybe a little shutter shock, whatever was was clearly visible (at 100%). See best/worst samples on Flickr. 2. The 75-300 resolution drops sharply after 200 and regains a little close to 300. So yes, upscaling by 160% gives much better results (in pixel-peeper terms) then a straight 300mm shot both at f8. 300mm View attachment 443364 200mm upscale only (160%) View attachment 443365 3. At 200mm the best aperture is f8. From 6.1 to 7.1 there is almost no difference then there is a little jump a f8. The difference is small, much smaller then the 6.7-8 difference at 300mm, so it's not a big loss going wide open. 4. For upscale I simply used GIMP with "Sinc(Lanczos3)" algorithm (the one that worked best). After upscale I think that the sharpening is mainly lost so, on a different version, I also reapplied a light unsharp mask. The 200mm upscaled with no sharpening is already better then the original 300mm. In the comparison crop below I used the first version. 5. unless you need to print big there is no need to upscale: just crop and be happy. 6. To see the impact of the upscale I reopened from scratch an upscaled file (saved as jpeg 100% quality) and downscaled back to the original size. I could see no difference at all switching back and forth between the two files at 100%. 7. I also tried upscaling other focal lenghts: best one was 200mm. First set: 75, 150, 200, 300 (left to right order, center crop (resized by flickr to insert it here)) Second set (A): 200, 228, 256, 300 8. I asked myself if the drop in IQ was due to the tripod too small for those focal lengths, especially considering the slow shutter speed. Maybe. At the same time all reviews I've seen report the same drop in IQ. Even if it is some problem with the tripod, shutter shock, etc. I think I'm going to encounter it even in real life so I consider it part of what I'm testing. Anyway I'm going to repeat a limited test next time I'm outdoor with fast shutter speed (testing distant focus too). 9. On flicker there are 15 huge uncompressed jpegs. There are two sets, the first one (75, 150, 200, 300) and the "A" set (200, 228, 256, 300). See the file name for details. Flickr quick zoom is not 100% but good enough to see the difference. Download the files if really interested. I'm quite happy with the results. First, now I have a sharper lens . Second, it's a little faster and shorter so it needs less stabilization making it even more fast. Third, I have one more reason to get closer to the subject that is probably the thing that matters most anyway. Fourth, I can now resist a few more months before getting an E-M1 and the Oly 150/2 or the 300/4.