Basic slide vs print film question

[Farkle-Mpls]

Hello.

 

I've recently discovered this forum and ... wow! ... am I learning a lot. Thank you all for providing such a wealth of information. Your

opinions on which films to use and when to use them are valuable as I plan a trip to Thailand in two weeks.

 

I have what is probably a more basic question (although perhaps not a simple one). I've read a lot commentary stating the fact that print

film is much more forgiving in terms of +/- EV than slide film is (and forgive my lack of "transparency" vs. "reversal" nomenclature -- too

long to type and everyone knows what I mean).

 

Anyway ... I'm curious WHY there is such difference in the characteristics of the film? Why can't slide film provide me the +3/-3 stops of

exposure latitude which print film seems to allow? Is it the emulsion -- I assume so -- and why is that?

 

I love the color and contrast of many of the slide films discussed on this forum but I like the "forgiveness" implied by some of the print

films. Insights, explanations?

 

Thank you!

[peterblaise]

Earlier: "... Why can't slide film provide me the +3/-3 stops of exposure latitude which print film seems to

allow? Is it the emulsion -- I assume so -- and why is that? ..."

 

... plus chemistry and processing. Many scientists may explain what they understand of the inner workings of

each system, but you've got the gist - negative film for prints is more forgiving than positive film for slides.

If you're planning on a slide show, go with slide film. If you're planning to digitize, go with print film.

Places like http://www.sldes.com/ can convert digital image files into slides for you if you ever need to, and

you can crank the blacks and contrast up at that point.

[danield]

'I love the color and contrast of many of the slide films discussed on this forum but I like the "forgiveness" implied by some of the print films. Insights, explanations?'

 

The reality is that these two aspects go against eachother - high contrast means a narrower dynamic range and therefore less margin for error. I would not be surprised if it would be possible to manufacture a low-contrast high-dynamic range positive film - but there would be little market for it. Nobody would like it - low-contrast slides would look too dull compared with existing high-contrast ones. Remember, slides were made to be viewed on a projector, without any post-processing.

 

That being said, if you scan and post-process negative film, you can replicate the result of slide film to some extent by increasing the contrast.

[Ed_Ingold]

Negative color film has a much wider dynamic range - 8 to 10 stops - compared to 3-5 stops for reversal (slide) film. Latitude is somewhat of a misnomer, like depth of field. It's best to expose negative film correctly, but due to the wide dynamic range you can often get a useable print from an under or overexposed negative. Something has to give, however, so you tend to have distorted colors, excessive grain and loss of detail.

[Ed_Ingold]

Slide film is even less forgiving than its dynamic range would imply. With negative film you can compensate for the basic exposure in the printing process. With slide film, the negative/positive process is combined. As a result, the tolerance is about 1/2 stop in either direction. With some slide films you can push or pull the processing a stop or two if you were consistently high or low (e.g., low light work or using the wrong ISO setting).

[Farkle-Mpls]

Thank you for your replies. I have to admit never realizing the basic premise that slides, as a projected medium, needed

to be higher contrast than prints. Duh. Well, being self-taught (as most of us probably are), there are holes in my

knowledge big enough to drive a truck through.

 

A natural extension to my original question would be this: if print film has such great latitude, does that imply -- on a film

that could tolerate +3/-3 EV -- I can shoot a few frames +3 stops, the next few -2 stops, etc, have it processed as if it

were neither pushed nor pulled and expect the prints of all the images to come out good (implying either the film was

forgiving enough with the original exposure or that the correction was made on the printing step)? That sounds a little too

good to be true and a lot like the "auto ASA" setting on my DSLR.

 

Thank you.

[iliafarniev]

It is certanly too good to be true.

 

I would like to ask Mr Ingold to bring kindly his deffinition of dynamic range in f-stops to clarify this issue.

[Ed_Ingold]

Ilia said, "I would like to ask Mr Ingold to bring kindly his deffinition of dynamic range in f-stops to clarify this issue."

 

Please refer to an earlier thread in which I explained this parameter in detail. (http://www.photo.net/film-and-processing-forum/00QHJm) As I recall, Ilia confused latitude with dynamic range in that thread as well.

 

Latitude, like depth of field, is a practical fiction. You might get acceptible results if you were to overexpose or underexpose images, but you are better off with the correct exposure. One exception is if you were to combine under and over exposed images in order to synthesize a greater dynamic range.

[iliafarniev]

I do not understand this. Was going thoro the linked thread one time more but could not find any DEFFINITION OF DYNAMIC RANGE. All common technical documentation I could find on bw, color and chrom photo films do not make any mention of DYNAMIC RANGE as such. The DR first get mentioned in printing from color film on color paper optically and refer to its ability to reproduce given color more or less exactly. This DR usualy has value or 3+ for common color film such as, say Kodak Portra 160NC.

 

The exp. latitude is not a practical fiction but one of basic technical characteristics of photo film and I have not confused it with dynamic range.

[thomas_wilson1]

Carl, I understand your confusion so lets try to leave the semantics on the back shelf for a bit. Your question

is a good one. If I may paraphrase, Will the wide exposure latitude of color negative print film compensate for

significant errors in exposure? eg. +3 ev followed by -2 ev (on the same roll) The short answer is no. Try to

look at wide exposure latitude as the film's ability to render good detail in the highlights and shadows while

maintaining mid-tones as mid-tones (grey as grey in B&W). This is where the processed film's density come in to

play. As film is under exposed, it becomes increasingly thin. As film is over exposed, it becomes increasingly

thick. An excessively thin or thick negative becomes difficult to print, albeit thick is better than thin. As a

negative's density decreases, so does any usable shadow detail. Any attempt to bring out shadow detail from an

excessively thin negative usually results in milky or muddy shadows with a complete lack of contrast. I tend to

expose 160 ASA (box speed) at 100 ASA (my speed) for good overall density. A thicker negative will require more

time on the clock when printing and typically will yield

a snappier print, to a point. Adjusting the development times can control excessive contrast. I digress. In

short, try to meter for the mid-tones, take two exposures as indicated, and bracket your exposures at least 1 EV

in each direction. The extra frame in the middle is some insurance against potential dust, scratches, or future

damage to

the "Keeper" from the trip of a lifetime. Good luck

[Farkle-Mpls]

Everyone (especially Thomas) ... thanks for an amazing amount of technical detail. I understand enough of the

concepts put forth to make meaningful decisions about what speed to shoot my print film at (and why it may be a good

idea to override the "box ASA" to make it appear slower to the camera to force 1/2 stop overexposure). I agree that

bracketing is a good idea, particularly since this is a bit of experimentation for me and that buys some security.

 

Ilia: Thanks for mentioning an interesting topic. For completeness sake, I'll see if I can find a good explanation of Dynamic Range and

Exposure Latitude as well. I've heard mention of them on several forums and it's worth me spending some time getting familiar with the

concepts.

 

Again ... thank you!

[Ed_Ingold]

The dynamic range of film can be estimated from the characteristic curve, exposure vs density, which is given by most manufacturers in the technical data sheet. In essence, the dynamic range is the range of exposures which results in a significant change in density. In other word, dynamic range is the range of light in the subject which can be captured on film. This is different from contrast, which is the output or density range of the film. It is also different from latitude.

 

Characteristic curves usually have a long toe region in which there is little change in density for a considerable change in exposure. There may be a shoulder region which gives similar behavior at high exposures or the curve can be fairly straight. I prefer to graphically determine the intersection of the asymptotes of the toe and "S" shaped region for the lower end and similarly for the higher end. The dynamic range is the difference between these intersections along the absissa (horizontal axis). The exposure is a logarithmic scale (base 10), from which you divide by 0.301 (log 2) to obtain the equivalent range in f/stops.

 

Most subjects have a range of light intensities of interest. Latitude is the variation of exposure, up or down, over which the range of the subject lies within the dynamic range - the "box", so to speak. The wider the range of the subject, the less the latitude of the film. Any time the negative is thinner or denser than necessary, the quality suffers. The range itself is a subjective judgement. Hence latitude is a "fiction", borrowing a term from the law - useful but ill-defined.

[Ed_Ingold]

Bracketing is a process more often discussed than executed. At best, you use two or three times as much film to accomplish what you should do the first time, once you learn to measure and set exposures. Even with digital, the only time I "bracket" is where the range of the subject clearly exceeds that of the medium, like a lighted stage and dark audience. I then combine the images in Photoshop, usually by masking and compositing.

[Farkle-Mpls]

Thanks Edward. Again, your technical commentary makes overall sense (thankfully I have a strong math background) but

there are specific aspects of your reply I will need to research in greater detail, since I find this topic rather interesting. Do

you have a good online or book source which explains characteristic curves, their interpretation and ultimate impact on the

mechanics of photography? (For instance, I find your correlation between the log10 scale of exposure to f/stop very

interesting -- I'm always very interested in taking the defined and measurable elements of the physical medium and relating

it back to light/shutter/fstop settings.)

[Ed_Ingold]

You will find a good explanation of characteristic curves in "The Negative", Ansel Adams (p. 85-88). Characteristic curves exist for a wide variety of stimulus vs response measurements, including digital cameras. Photoshop "Curves" allows manipulation of the characteristic curve of an image. In general, a long toe region is an indication of extended shadow detail. The steeper the center section, the higher the contrast (gamma). A long shoulder region indicates good highlight detail.