Perfect DPI for film

Discussion in 'Film Discussion and Q & A' started by zamanakhan, Sep 9, 2010.

  1. zamanakhan

    zamanakhan TPF Noob!

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    i just got into film photography recently and purchased a v300 epson to scan my film, what my question is what dpi should i be scanning at? when do the diminishing returns occur? like when is the dpi so much that its just taking too long and not useful? iam most likely going to be only printing 5x7's but may print a 8x10 here and there, but i dont mind rescanning a single negative for 8x10 alone
     
  2. Early

    Early TPF Noob!

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    I would think you should scan at the highest optical res the scanner allows you... just in case.
     
  3. Josh66

    Josh66 Been spending a lot of time on here!

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    I usually scan at 6000x9000, which is not quite the maximum my scanner can do (that would be around 6796x10200), but there seems to be a significant increase in file size at higher resolutions than that.

    I guess the file size/resolution relationship would depend a lot on the scanner & software you're using - it might be different for you.

    As far as how long it takes to scan, I guess smaller sizes would be faster, but it hasn't really bothered me much...
     
  4. zamanakhan

    zamanakhan TPF Noob!

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    well this is the thing, iam not printing 8x10's and if i feel the need to print one or 2 i can just scan those negatives seperately, but just for cataloging i wanted a resolution thats perfect for 5x7's, as this is what i print most often. this way i don't have to spend an hour near the scanner just to go through one roll.
     
  5. flea77

    flea77 TPF Noob!

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    What film are you using? What lens? What camera? It all matters.

    Lets take an example.....

    Ilford Delta 100 is rated at 160l/mm. Assuming you can actually resolve that (nice rangefinder with Zeiss glass gets close), that is 4064 l/inch. A 35mm frame is 0.94488189 inches by 1.41732283 which means about 3840x5443 pixels. Scanning at 3600dpi gets you 3402x5102 which is dang close. Anything more and you are wasting your time and hard drive space. Anything less and you are not getting the maximum out of this film/camera/lens combination.

    Every film has a different lines per millimeter resolution. Every lens has different l/mm resolving power. Different cameras decrease the resolving power differently (rangefinders tend to be better because the lens is closer to the film plane, some SLRs use vacuum to hold the film perfectly flat, etc etc etc).

    If you want to play it safe, Delta 100 has one of the highest l/mm out there so just scan everything at 3600dpi and be done with it. That results in about 17mp or so on 35mm, 72mp for 6x6 medium format, and 260mp for 4x5 large format.

    Allan

    PS. Of course this all assumes you scanner can actually resolve 3600 dpi well, heh.
     
  6. zamanakhan

    zamanakhan TPF Noob!

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    this is exactly what i needed to know, thnx!!!
     
  7. Helen B

    Helen B TPF Noob!

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    Just remember that it takes two pixels to resolve a 'line' (it's really a line pair - line pairs per mm, usually shortened to lines/mm because the 'pairs' is understood).

    You can go higher - it isn't only about resolution, but also about the characteristic graininess of the film.

    Your scanner may not be able to give a true resolution anywhere near 3000 spi - so do practical tests. Find out by scanning the film at different resolutions.

    Best,
    Helen
     
  8. Helen B

    Helen B TPF Noob!

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    When the final print size is known, a general rule-of-thumb is to scan at a resolution that results in somewhere between 200 and 720 ppi on the print, 300 ppi being the default number if no other number is known (for example RGB laser and LED printers have 200 ppi, 300 ppi or 400 ppi native settings mostly; Epson inkjets work their best at 288 ppi, 360 ppi or 720 ppi in general).

    A 5 x 7 is about a 5X enlargement of a 35 mm negative (it's about 1 inch wide on the short side). Therefore the rule-of-thumb suggests a scanning resolution of 300 x 5 = 1500 spi. My suggestion would be to try 1800 spi and 2400 spi as realistic resolutions your scanner should be capable of (just because the specification says that it has an 'optical resolution' of 4800 ppi doesn't mean that it can actually resolve 4800 ppi).

    Best,
    Helen
     
  9. djacobox372

    djacobox372 No longer a newbie, moving up!

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    3200dpi is what I scan at, 2400dpi for high-grain films.
     

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