WHY does slide film have a narrower exposure latitude?

RPC · Nov 27, 2017

keenmaster486 said:
Ah, but you're not looking at the negative when you view your T-Max or Portra. You're looking at a print or a scan which has been adjusted to compensate for the over or under exposure.

You don't have this luxury with slides. They have to look perfect with no adjustments whatsoever.

The point is that the overexposed negative film would have recorded highlight information much better than the slide film, which at four stops over would be blown out in the slide. Therefore the information could very well be brought out in a print from a negative, either in a straight print or with some manipulation, but not in a print from the overexposed slide, no matter how it is manipulated, since it wasn't recorded to begin with, due to its limited dynamic range compared to negative film.

markbarendt · Nov 27, 2017

RPC said:
The point is that the overexposed negative film would have recorded highlight information much better than the slide film, which at four stops over would be blown out in the slide. Therefore the information could very well be brought out in a print from a negative, either in a straight print or with some manipulation, but not in a print from the overexposed slide, no matter how it is manipulated, since it wasn't recorded to begin with, due to its limited dynamic range compared to negative film.

One thing that bears mentioning here is that over exposing a slide results in clear film, no silver or color at all, there is nothing recoverable on an overexposed slide.

A negative works exactly the opposite way, extra exposure generally just gives you more usable data (density).

tomfrh · Dec 4, 2017

markbarendt said:
One thing that bears mentioning here is that over exposing a slide results in clear film, no silver or color at all, there is nothing recoverable on an overexposed slide.

Isn't this the essence of the original question? Why does slide film crash into white when neg film keeps yielding?

MattKing · Dec 4, 2017

tomfrh said:
Isn't this the essence of the original question? Why does slide film crash into white when neg film keeps yielding?

Because while slide film develops clear when too much light hits it, negative film develops clear when too little light hits it.
For negative film, if too much light hits it in any particular area, you can still recover details from that area by putting more light through that area during the printing stage - the film is designed with a corrective printing stage in mind.
For slide film, no printing stage is available. If too little light hits it in any particular area, that area develops too dark. If slide film was designed like negative film to permit recovery of details in the dark areas (on the slide), when you projected a slide the shadows in the scene wouldn't look on the projection screen like shadows - they would look muddy and soft instead.
It is the two stage process - expose and develop negative + print and develop positive - that allows you to design in exposure latitude. Single stage processes don't offer exposure latitude.

RPC · Dec 4, 2017

Since negatives are not viewed directly, but printed, they can be designed with low contrast, which increases dynamic range. Slides, to look good when projected, are high contrast and have lower dynamic range.

The high slide contrast means the slide approaches maximum and minimum densities at a much faster rate upon exposure and development than a negative does, with its lower contrast, meaning the slide loses detail faster than a negative upon overexposure.

Steve Smith · Dec 4, 2017

It doesn't. But negative film has an extra stage where it is turned positive and compensation can be made for differences in exposure.

Think of exposure latitude as the amount you can get it wrong then correct it!

Steve.

tomfrh · Dec 4, 2017

MattKing said:
Because while slide film develops clear when too much light hits it, negative film develops clear when too little light hits it.

Yes, but again that’s just a restatement of the question. Neg film is hard to exhaust, whereas slide film clips easily.

Are you guys saying it’s entirely deliberate? I assumed it was some sort of limitation of producing positives directly, as opposed to a design decision. I’m sure many people would have enjoyed lower contrast slides with greater shadow detail and less clipping of skies, even if it had a little less pop.

michr · Dec 4, 2017

tomfrh said:
Yes, but again that’s just a restatement of the question. Neg film is hard to exhaust, whereas slide film clips easily.

Are you guys saying it’s entirely deliberate? I assumed it was some sort of limitation of producing positives directly, as opposed to a design decision. I’m sure many people would have enjoyed lower contrast slides with greater shadow detail and less clipping of skies, even if it had a little less pop.

I know from experience that contact printing a negative onto another negative yields a positive with a great deal of latitude. There must be something about the process of bleaching out the negative which takes out more silver than would be left in an internegative. I've had a little recent experience with transferring 35mm slides to digital using a digital camera (Nikon D7000). What I discovered, to my surprise is a slide where the camera couldn't capture the entire dynamic range in one shot. It was a photo of a white train and rail platform, the sunlight hit the front of the train and detail was clearly visible in that region. The platform was shaded with an awning, and while detail was visible in that area it was very dark. Slide projectors were limited in light output by the heat of the bulbs, since all of the ones I've ever seen used halogen bulbs. When I digitized this slide I used a series of long and longer exposures and created an HDR file. There was significant detail in the shadows that was not visually apparent. I wonder how the slide would look projected with a very strong cold light source.

Photo Engineer · Dec 4, 2017

The eye is linear! It interprets things with an effective contrast of 1.0 by definition, and it has a high latitude due to the iris in the eye and the photoreceptors, as if the diaphragm and the film speed could change constantly. Film has a toe and shoulder and so does a digital image. These can be shown in a D logE curve and a V Log E curve respectively. They eye interprets the toe and shoulder as part of the image and this lowers contrast. So, to get the eye to see an image correctly, one which has a toe and shoulder, the image must have a contrast greater than 1. Thus, reversal images that are viewed have a contrast of about 1.5 - 1.7 by definition to make the integrated image look right. For technical (chemical) reasons, the Dmax is limited in most all films to about 3.0 and thus the latitude is defined.

In negatives, this is not the case. The image is most all on a straight line but when printed by any means, the rules above hold true.

PE

RPC · Dec 4, 2017

Steve Smith said:
It doesn't. But negative film has an extra stage where it is turned positive and compensation can be made for differences in exposure.

Think of exposure latitude as the amount you can get it wrong then correct it!

Steve.

The extra step has nothing to do with what happens in the films, though. Negative film has lower contrast, so it will build density slower with additional exposure than a slide film loses density, and will lose density slower with less exposure than a slide builds density. Therefore a negative takes more change in exposure to reach minimum or maximum density limits than a slide.

keenmaster486 · Dec 4, 2017

So PE, to get this straight, what you are saying is that the very nature of the human eye limits how we can design materials which are supposed to be directly viewed, while for intermediary stages we can pull out all the stops?

Photo Engineer · Dec 4, 2017

Basically, yes!

tomfrh · Dec 5, 2017

Photo Engineer said:
an effective contrast of 1.0

What units are these?

bvy · Dec 5, 2017

tomfrh said:
What units are these?

No units. It's the slope value of the straight line portion of the characteristic curve. Rise over run from algebra class.

removed account4 · Dec 5, 2017

tomfrh said:
Isn't this the essence of the original question? Why does slide film crash into white when neg film keeps yielding?

its because it is a reversal process. too much is too little and too little is too much
its the opposite of b/w film ... BUT
you can develop slide film in black and white chemistry if you want.
over expose the hell out of it and develop it in dektol or ansco130 (1:time ) for time ( minutes )
and while you won't get a color diapositive, you will get an over exposed black and white negative
and if you process it in caffenolC the tonality from the coffee will mask over the yellow mask of the b/w negative.
its a reversal thing. and while i suggested it was similar to paper negatives, glass plates/wet or dry &c
the non color emulsion still seems to maybe have a longer range, unless exposing in high contrast situations
and then like with diapositive film you are SOL.

WHY does slide film have a narrower exposure latitude?

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