What is the resolution of a professional film ? Ecktachrome 100 plus 4x5 inches for example ? (i have post the question at Kodak but get no answer by now). Can it be express in DPI ?

Best Regards Luc M.

-- Luc M. Comolli (Lucamax@bigfoot.com), December 21, 1998

Answers

Film resolution is a tricky area, due to issues like grain size, emulsion thickness, etc.

If you wanted a ballpark idea though, the 35 mm film scanners that top-out at around 2700 dots per inch are at that point starting to really show film grain on most films - go any higher in scanning resolution, and all you're going to see are bigger film grains. Since Ektachrome is the same, whether 35 or 4x5, I'd say that 2700 dpi is a reasonable upper limit for scanning it. Note though, that this is the limit on scanning resolution,and the actual ability of the film to resolve detail may be a good bit less, maybe as low as 1000 dpi.

-- Dave Etchells (web@imaging-resource.com), December 21, 1998.

Luc,

Dave's answer was real good. Here at my work, we scan 35mm at 2700dpi and it provides beautiful 8 x 10's. We can send that 20+ Meg file to our 4k film recorder and it then RIP's the file up to about 80Meg and makes a beautiful 2 1/4 neg that will then make a very good wall size portrait.

The bottom line is if you start with a PROPERLY exposed image that's been shot on a tripod, you can do some incredible stuff in Photoshop and then repurpose back to an inkjet print, a new negative, or a file.

We used to have a drum scanner and could scan at 4000 dpi and we found that at much above 1000 dpi, we'd get big files that were extremely grainy and that wouldn't produce good prints. It kind of boils down to the fact that you can also take a 35mm neg and theoretically blow it up in a traditional photo to 48" x 96". It will also look very grainy and fuzzy, so resolution is really complicated and depends on so many factors, it's hard to specifically pin down a resolution.

Boy, I wasn't much help, huh?

Phil Pool

-- Phil Pool (pep44@excite.com), December 22, 1998.

The best fine-grained Kodak color negative film (ISO 64) is said to resolve 100 line/mm or 2540 line/inch. Since a pair of lines (or dots) means a dark/light/dark that amounts to 5080 pixels/inch. I think to get the same imaging capability as say 35mm format (36X24mm)would therefore require a 7200X4800 image array.

-- Rick Griffen (rgriffen@vabch.com), December 22, 1998.

I would like to say also that film resolution is just a part of "system definition". I mean that best lens in reflex camera does not reach 100lines/mm. Perhaps some of them could reach this resolution but at a price over 5000$. So if you want to retreive a good focused picture don't forget the couple film/lens. for a sample a 200mm 2.8 aperture lens form canon at 2000$ does you less than 75 lines/mm. I hope that this little contribution help you. sorry for my english but i am french:=)

-- patrick pusel (patrick.pusel@wanadoo.fr), January 14, 1999.