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I've read upon many online resources that the dynamic range of film is usually between 9 and 11 stops. However, it is frequently mentioned that 17 stops can be achieved with additional tricks in the development and scanning process.

From the point of view of development, what would be those tricks about? I just started with film and I'm interested about this because I do mostly architecture and long exposure, and always looking for the best dynamic range.

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17 stops sounds...wishful. A film's characteristic curve is, for the most part, set. One can change the slope (contrast) by adjusting development or purposefully expose to the left or right of the curve and then bring it back in development (push/pull)...but there really isn't a way to extend the curve to where base+fog moves further left or blocked highlights moves further right.

If one has a super contrasty scene, you can use a compensating developer to keep the highlights from blocking up...but again, this isn't really moving the curve, simply finding a way to compress your scene into the given curve. Hence the adage, expose for the shadows & develop for the highlights.

The next compression comes at print time...where you have to decide which values in the tonal range to keep, because no print can match film's range.

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It's been decades since I've developed film, however for B&W film using a two step developer like "Diafine" can extend the apparent dynamic range considerably.

Standard one step developers have activators as part of the mix. How much the film is developed is a function of time and temperature.

Two step developers like "Diafine" have the activators as the second step. The first step allows the film to soak up the unactivated developer. After the film is fully saturated, it's moved to the activator only second step. The parts that have high light exposure rapidly exhaust the developer absorbed and self limit to a short cycle. The low light parts develop slower and longer to bring out low exposure image portions.

Good Luck!

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    Techniques like this, and stand development, and compensating developers in general, are there to rescue highlight detail that might otherwise be blocked. This isn’t extending the range of the film - this is bringing the captured image within the film’s range. The latitude hasn’t changed. If the film curve says you get 10 stops - then you get 10 stops. This technique doesn’t extend range to, say, 13 stops. It halts development at highlights so as not to block them (hopefully at 10 stops). So, again, range isn’t extended - you’ve compressed the capture into the curve. – Hueco Jan 13 at 16:22
  • Yes, this why I said "apparent" range. The same concept applies to High Dynamic Range (HDR) digital. The range is compressed to accommodate the media. Ultimately it boils down to whether you derive useful results from the techniques. – user10216038 Jan 13 at 17:02

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