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photo question 9-Dec-2004 At 3:35:59 PM bapak

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Some topical items below :-

(a) Key physics of "Photographic Resolution" :-

* The industry standard is "Line Pairs Per Millimetre".
* Generic 100 ASA Film = Resolves around 80-100 Line Pairs per mm.
* Most Camera lenses stopped down to "optimum" (F8 for 35mm) = around 100 LP/mm
* Most enlarger Lenses at optimum = around 100LP/mm
* Most Colour Photographic paper = around 80 -100 LP/mm
* Thus the "sum of the errors" = Around 20 LP/mm Max onto the Printed Image.

(b) Key "Psycho-optical" considerations" :-

* The limit of Human Optical Resolution is around 20 LP/mm.
* This is @ 250mm from the flat plane of the image = around an 8" x 12" Print.
* This means that any prints > 8" x12" from 35mm Film lose resolution @ 250mm.
* Thus an 8"x12" Print = Optimum Size for 35 mm Film any bigger and you lose
from the lack of detail from Film/Lenses & Smaller = lose through the paper size.
* Medium Format & Large Format Camers/Film produce less resolution on the Film
* They more than make up for it by having larger Film Area = x 4 for MF x 10 for LF.
* A High Contrast Image for a given amount of LP/mm will always look sharper.
* A "back lit/projected" image (Slides/VGA Screen) will always look sharper.

(c) Digital vs Analogue :-

* Digital Resolution is measured in "Pixels" (ILO LP/mm) and it's not feasible/fair to
compare one with the other as each Pixel can turn itself into any colour vs the Film
emulsion is limited to the "randomly spread grains" on the various layers.
* Thus some Scenes (for a given resolution) will look better captured on a Digital
Camera CCD vs a Film Camera.
* Also (on average - for a given resolution) a Digital Images look around "Twice as good as
they should". (there are more complex reasons involving > contrast on edges)
* The final "perceived" resolution always depends on the "presentation" and thus with
Digital Prints we are limited to the Printer/Paper or the PC/VGA Screen.
* To compare Say 100LP/mm with Pixels = 200 Pixels/mm. (5,080 Dots/Inch)
* Thus (in theory) 35 mm Film (24 x 36 mm) = 34 Megapixels (It ain't really !!)
* After going through Lens #1 & Lens #2 & on to paper = "Sort of" Around 10 Megapixels.
* "Sort of" due to all of the variables mentioned above as in most cases as long as you
aren't printing @ 12" x 18" or greater "apparent" resolution will be comparable "most"
5 to 6 Megapixel Digital Cameras.
* If you really want "maximum resolution" from Digital = 200 Megapixel Camera Backs
are available (For $60K inc Storage Hard Drive/software/Power Pack = > 10kg)

(d) HDTV & TV Resolution.

* We Australians are so lucky having the PAL System vs the horrid American NTSC.
* TV Res is measured as Line Per Inch = for the PAL System @ Studio Quality =
500 Lines, around 400 by the time you see it @ home & 250 Lines off your VCR
for 1st recording and it goes down hill for each generation. MPEG2 encoding
(digital) knocks it around a bit too but prevents ghosts/noise/smear.
DVD is still only around 400 to 500 Lines & depends on the source. HDTV is 1200
Lines/Inch @ "Studio Quality".
* Believe it or not the only "bulk stock" of HTDV 70 mm Telecine Film was "I Love Lucy"
= luckily we have much more (inc Imax 90mm/CSI etc)
* Although It's not possible to display more than 1 Meg on a VGA Screen photos taken
with Digital Cameras of "higher resolution" (and/or 35 mm Film Drum Scanned)
will always look better.
* Images scanned @ 1,200 DPI from a good 8" x 12" Sized Print will generally look better
than one scanned from the Original Neg/Tranny as there is more data in the print scan
even through it has been through an enlarger lens/printing process.
* Drum Scanning @ 2,400 DPI or greater will provide maximum file size.
* I have a few hundred Scans of 6cm x 7cm & 4"x5" Negs/Trans each = 75 Mbyte files !

Apologies for length/detail;

Steve.M.

PS : Have all of Ansell Adams theory Books/Photographic Portfolio Books, Biography
= great/inspirational stuff !! (have a look at Amazon.com re Ansell Adams books
= great shots of Half Dome & other Yosemite monuments)

Digital vs Analogue resolution comparisons.

* Not really apples for apples