converting slides to B&W

[Kendrick Pereira]

Marko, My comment was not very well worded. It is only the greater fineness of resolution of slides that I am not convinced of. I agree that negatives afford more flexibility than slides.

The slides and colour negatives I refer to were taken 10 to 35 years ago. They are the records we have of that period, when we were bringing up our children. Of course we use digital for the equivalent of those snapshots now.

My impression that slides are no sharper than negatives is not based only on 4"x6" prints but also on larger prints of selected photos up to A4 from scan files from both slides and negatives as well as impressions formed by conventional projection of the slides [using a Leitz Prado with tungsten lamp and 120mm f/2.5 Hektor].

[darr]

Magnus: I shoot strictly color slide film with my walk-around medium and small format cameras for convenience. I will not get into all of my personal choices that led me to this over 30+ years of shooting, but I have them. Post processing to black & white via the digital darkroom is not terribly difficult if you have the proper software and went through the necessary learning curves on scanning and Photoshop. It can also be a personal taste issue.

When I shoot large format it is a different story. I pre select my composition and select the best film for the job. If I know that I want a black & white negative only, I will use black & white film, if I want more options, I'll shoot color slide film. I also shoot Polaroid 55 P/N for its own characteristics.

My job experience lies mainly in the composition of the thing photographed so someone that is a professional black & white printer may have a totally different take on the film from the start. For the work that I have produced, my technique has always worked and I guess that is why it is what it is. I will continue to shoot color slide film and post process to black & white if the composition looks better and my equipment at the time of shooting required a quick zoom lens or quiet rangefinder.

Here is a snapshot of a recent quick zoom shot I post processed to black & white because what I imagined at the time of shooting was more on the black & white look. Hope this post has been helpful in some way.

Attachment 413 Attachment 412

[Kendrick Pereira]

Magnus, you may have found the thread in this forum titled “Re: Shadow detail & flatbeds”. If not, what follows indicates some of the material in posts on it which I think might interest you.

In what follows the more widely spaced sequences of dots indicate passages of text omitted. The more closely spaced sequences of dots are as in the original post. Square brackets indicate an addition or emendation of my own which the author might not own - I suggest accessing the thread and reading the whole post.

Abstracted from a post by Tim Atherton: “The "d" means density. . . . and when measuring density that film records (as in contains valid image data), there is a minimum value (dMin), and a maximum value (dMax) . . . . Positive (transparency) film has a clear base...so the dMin for it is going to be quite low...as compared to negative film, which has a cloudy base...so the dMin for negative film will be quite a bit higher than positive film. Both films will pretty much have the same max density, black is still black, whether it's positive or negative film . . . . It's purely the film base "offset" that creates the difference in density range.. . . .(and so you don't need the same density range to get the info out of a negative film as you do from a transparency film) . . . . the same range . .[of subject brightness] . . could be recorded on either film...just that negative film would have the range compressed, film density wise that is, compared to positive film”

You might also find the contents of a post by Helen Bach on the same thread illuminating. Citing an example of a negative film “with a very wide dynamic range” Helen tells us it “can record about twelve stops of scene brightness range” and then gives some estimates of the density range on the film itselfwhich would result from this scene brightness range. She goes on to remark that if, when the film has been scanned, the full density range of the film is printed on paper (paper with a density range which she specifies), then twelve stops of scene brightness range will have been compressed to five and a bit stops of film density range and then expanded to about seven and a half stops of print density range.

I am not concerned with the specific figures Helen gives, though I have no reason to doubt them. My point is simply that this sort of compression and expansion does occur when transfers are made from one medium to another (O.K., the original subject is not a medium but I am sure you see what I’m driving at). The degree of compression from subject to film varies from one negative film emulsion to another and from one positive film emulsion to another depending on the chemical formulation. The exposure latitude of a film is intimately tied up with the subject to film compression of that particular emulsion. It is not the only factor involved but other things being equal or indifferent the greater the degree of compression the greater the exposure latitude i.e. the "softer" = less contrasty the film the greater the latitude.

We have therefore to put forward a third* consideration bearing on your original enquiry. Recognising that some negative films are more contrasty than others and the same with positive films the question arises whether, taking one film with another in each category, the chemists at Kodak &al tend to formulate positive film emulsions to be more contrasty than negative film emulsions.

The impression certainly used to be widespread in the amateur photographic fraternity that this is in fact the case. I have not heard it mentioned recently so I hesitated to put it forward in my first post.

The safest bet would be to expose colour negative film, choosing a soft film which can record a wide subject brightness range. Scan it. Adjust the contrast in the digitized image using your photo-editing software and print the desired density range# on the paper of choice.

This cautious policy should yield good or better than good quality almost all the time: but it is inherent in this practice of greater compression with consequent subsequent greater expansion that there could be very subtle low-contrast detail which is so thoroughly suppressed in the compression phase that it is no longer separable from the “surface noise” arising from the inefficiency of the equipment and so is not recoverable in the expansion phase. If you must have the best, the very best, quality there is nothing for it but to live dangerously on the edge.

*1) The possibility of correcting at printing stage affords the photographer using negative film a little extra latitude. I raised this when I was not quite sure what you were asking. I doubt if in the end it is of relevance to you. 2) By raising the density threshold without raising the density ceiling the relative opacity of the support reduces the density range of colour negative film. So what? Such compression of the density range as arises from this factor does not increase the exposure latitude of the film. If anything, it would tend to marginally impair it inasmuch as the density that your scanner cannot penetrate will be reached a little sooner due to the augmentation of the emulsion density by the relative opacity of the support. 3) A "softer" = less contrasty emulsion could give you a real increase in exposure latitude, other factors being indifferent (and why should they not be?).

#Helen Bach writes, “In most cases . . [the full density range of the film] . . would look rather dull. However, there is no need to print the full density range of the film. Typical colour wet print systems are designed to produce a print from the equivalent of seven stops of scene brightness range (depends on the film contrast and the paper contrast).”

[Magnus W]

Kendrick,

Thanks for the informative reply, I will re-read a couple of times to let it all sink in. Thanks also for pointing to previous threads, which I will dig out of the archives.

/Magnus

[Kendrick Pereira]

Magnus,
The thread “Re: Shadow detail & flatbeds” is a pretty current thread. In fact I wonder if Bruce Watson's post of 28th instant doesn't address your question head-on. I hadn't seen that post when I typed in mine.