Pre-exposure to increase the dynamic range of Instax film

A recent Stephen Schaub video ("Figital Revolution 2.0" blog) about doing pre-exposure with Polaroid material prompted me to try this with Instax. Pre-exposure, sometimes called pre-flashing is an old technique sometimes used, primarily with black and white large format negative material, to shift the exposure off the "toe" of the film's characteristic curve so as to get detail in the shadows without overexposing the highlights. I've never done it with negative film; the dynamic range is so good with modern film. But it got me thinking to try this with Instax, because the limited dynamic range is the main problem with this film.

I set up a low-key still life and used Instax wide in a Lomograflok back on a Graphic View II camera. I used a single flash in a small umbrella and metered with an incident flash meter. Here's the normal exposure.

Antique stereoscope by Howard Sandler, on Flickr

Then I repeated this, but first I took an out of focus exposure of white paper, with the flash adjusted 4 stops down. Since the paper is white, the overall pre-exposure is about 2.5 stops down from middle grey.

Antique stereoscope by Howard Sandler, on Flickr

This clearly lifted the shadows. You can see more detail in the inside corner of the box of cards and the handle of the stereoscope, but there is also a hot area in the lower right quadrant due to non-uniform exposure of the paper (I just held it at an angle to catch some of the light from the flash which was off to the side; not too precise a method.

Then I repeated a third time, this time with the flash 4 stops down and the camera aperture one stop down for the pre-exposure, so 5 stops in total, and the paper being white making this about 3.5 stops down from middle grey.

Antique stereoscope by Howard Sandler, on Flickr

It does seem to help a bit. I think a careful uniform exposure of a matte gray card 2.5-3 stops down would probably be ideal.

hsandler said:

It does seem to help a bit.

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I'm sorry, but I don't see shadow detail gain in this example. I do see a significant difference in color rendition. The first exposure looks severely crossed over from magenta (shadows) to green (lower midtones), while the last one has a more uniform green shift across the entire tonal range. It's possible this is due to the digitization of the print, though.

I'd be inclined to test a scene with an inherently higher brightness range; as you said, this is a low-key scene, which is esthetically pleasing, but IMO not the most suitable to test contrast control.

koraks said:

I'm sorry, but I don't see shadow detail gain in this example. I do see a significant difference in color rendition. The first exposure looks severely crossed over from magenta (shadows) to green (lower midtones), while the last one has a more uniform green shift across the entire tonal range. It's possible this is due to the digitization of the print, though.

I'd be inclined to test a scene with an inherently higher brightness range; as you said, this is a low-key scene, which is esthetically pleasing, but IMO not the most suitable to test contrast control.

Click to expand...

I see it, especially in the prints, but yes, I really need to repeat this with a high contrast scene like a sunlit garden with deep shadows, a wider range of colours in the scene, and a more controlled pre-exposure. The green shifting is probably more a result of me trying to fix the colour in the scans in a non-uniform way. I recall fighting the greenish cast to the wood.

Digitizing these kinds of prints with good color consistency can be a chore...I can relate. Whenever I need to do something like this, I either ensure that I scan all the comparison materials in one go with the same settings, or I use a color-profiled workflow. Both have their pros and cons.

I'd be very interested to see the results of a follow-up experiment; keep us posted!

It's really amazing how Instax has caught on.

OK, I finally got around to trying this again with a better test scene and more controlled conditions. First is the control case: a single exposure with a single flash into a small umbrella to camera left and up a bit, no fill flash or reflector. This was metered at f6.3, ISO 800, but I found an exposure of f9.5 gave the apples a better colour, and I wanted deep shadows to try to rescue, so went with that. Straight scan with no manipulation.

Control case: single exposure by Howard Sandler, on Flickr

I then repeated with another sheet from the same pack, same main exposure. I followed this up with a post-exposure of an "approximately" middle grey sheet of paper (same as the background sheet) at f16; i.e. 1.5 stops down from the main exposure, or 2.5 stops down from the metered exposure.

Post-exposure case: exposed scene, then grey sheet by Howard Sandler, on Flickr

I can see a bit more colour in the dark green leaf in the foreground that hangs over the grey card, and slightly more detail in the dark orchid petals, but overall, the black point is slightly lifted as well. I did try another post-exposure a bit less, at f20, but didn't see any effect, so I have not bothered to upload the scan.

I conclude that pre- or post-exposure (I haven't seen any evidence the order of which exposure comes first matters) exists as a phenomenon, but is too fiddly with Instax to bother in most cases. The range between no effect and muddying the shadows is too fine.

hsandler said:

OK, I finally got around to trying this again with a better test scene and more controlled conditions. First is the control case: a single exposure with a single flash into a small umbrella to camera left and up a bit, no fill flash or reflector. This was metered at f6.3, ISO 800, but I found an exposure of f9.5 gave the apples a better colour, and I wanted deep shadows to try to rescue, so went with that. Straight scan with no manipulation.

Control case: single exposure by Howard Sandler, on Flickr

I then repeated with another sheet from the same pack, same main exposure. I followed this up with a post-exposure of an "approximately" middle grey sheet of paper (same as the background sheet) at f16; i.e. 1.5 stops down from the main exposure, or 2.5 stops down from the metered exposure.

Post-exposure case: exposed scene, then grey sheet by Howard Sandler, on Flickr

I can see a bit more colour in the dark green leaf in the foreground that hangs over the grey card, and slightly more detail in the dark orchid petals, but overall, the black point is slightly lifted as well. I did try another post-exposure a bit less, at f20, but didn't see any effect, so I have not bothered to upload the scan.

I conclude that pre- or post-exposure (I haven't seen any evidence the order of which exposure comes first matters) exists as a phenomenon, but is too fiddly with Instax to bother in most cases. The range between no effect and muddying the shadows is too fine.

Click to expand...

Thought your first example looked really promising. The shadow underneath the stereoscope namely benefits a lot.