ChrisR
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To recap, the tests at filmscanner.ino suggest that the Plustek as a maximum resolution of 3500 dpi, though you might need to scan at higher resolutions to get that.
The test frame is from a roll of Precisa with some fine detail near the centre of the frame, shot on a Pentax MX last autumn. I didn't remember until after going through all the scans that the lens was the Tokina SZ-X 80-200 zoom. This is a very nice lens for general use, perfect for a day doing autumn colours at the arboretum, but not the sharpest tool to choose for comparisons! Here is the shot:
1611BPMXCS33 by Chris R, on FlickrI then scanned it at 1200, 1800, 2400, 3600, 4800 and 7200 dpi. The 4800 scan was a “custom” choice in Vuescan Plus; I guess this means it is not automatically offered by the hardware, and may involve some sort of interpolation. Vuescan also offers a pixel reduction option, so I ended up with 3 1800 dpi scans (straight, 3600 reduced by two, and 7200 reduced by 4), 2 2400 dpi scans (straight and 4800 reduced by 2) and 2 3600 dpi scans (straight and 7200 reduced by 2). The files were saved as 16-bit TIFFs, which was a somewhat daft choice as colour depth was not an issue; 8-bit TIFFs would have been fine. Each scan was a single pass, no multi-exposure or dust removal.
It’s worth noting the times and file sizes for the various scan options (not affected by saving at reduced size:
1200 0:18 mins 11.3 MB
1800 0:24 mins 25.2 MB
2400 0:29 mins 44.9 MB
3600 1:10 mins 100.9 MB
4800 3:07 mins 179.4 MB
7200 3:20 mins 403.6 MB
Presumably the 8-bit TIFFs would be half those sizes. By way of comparison, the JPEG of the 2400 dpi scan I made originally when scanning this frame is 1.7 MB (but note, I don't save at particularly high JPEG quality; a Filmdev JPEG scanned at 2000 dpi but saved at high quality is typically 5-6 MB)!
After scanning each frame I took an approximately 800 pixel (across) 100% crop near the centre of each. I have not tried to adjust these crops to match the magnification, but I did look at the lower resolution crops with the loupe at greater than 100% (I couldn’t see an easy way to share the results of the loupe).
The shot was taken in afternoon light with a Pentax MX using (I think) the Tokina SZ-X 80-200 zoom lens at the wider end. https://www.pentaxforums.com/userreviews/tokina-80-200-sz-x-f1-4-5-5-6.html. It is a pretty good zoom lens, especially for its weight, but it does show the problems of trying to draw conclusions from everyday shots like this. I suspect the lens is one of the limitations here, with obvious aberrations at edges.
Since this thread is about print sizes, I also printed all the crops except the 1200 dpi version, side by side (3 rows of 3) on a single sheet of A4 at what would have been approximately 300 dpi for the printed file. I could print to JPEG and include that here but reduced to 1024 pixels across I don’t think it would tell us much!
My conclusions? I didn’t really see any advantage in the 4800 and 7200 dpi versions; the 100% crops of both look very mushy. The 2400 dpi versions look best to me, but the 3600 dpi shots are OK. In the 1800 dpi and 2400 dpi scans I thought the shot reduced from a higher dpi scan was better than the straight scan, but it’s pretty marginal. For the 3600 dpi scan I thought the straight scan was a smidge better than the 7200 dpi scan halved. I normally scan at 2400 dpi with at least two passes and a multi-exposure pass, plus possibly an infra-red pass, but I did not do that comparison this time.
Overall, I’m happy with the way I scan, and happy to go to 3600 dpi for a shot I want to print bigger. Above that, I don’t think I’ll bother.
So, here are the crops:
EDIT: hmmm not working the way I planned, says image too large to upload to TP (800 KB ish). Will need to think again. Check back later!
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