Thursday, February 24, 2011

Comparing Digital with Film: Dynamic Range

You may have noticed in my previous post that the photo looked a little different even though I didn't apply any post-processing, and that's because I used a film camera, in an experiment to gain better appreciation for the difference between digital and film.

Details after the jump.



I took the film shots here with a Nikon N90 and a Nikon 28-105 f/3.5-4.5D lens.  I was planning to use flash as fill light for some photos but for some reason my SB-800 wasn't working correctly with the camera so I just turned it off altogether (I found out later that I just needed to clean the TTL contacts).  I used a fairly inexpensive film: Kodak Ultramax 400 (color negative film), which I got from Target for $2 ($8 for 4 rolls).  The film was developed, scanned, and burned to CD at Costco.

I compared the film shots with shots that I took with a D70 and a Sigma 50-150 2.8.

I took the shots under the same lighting conditions (same weather, same time of the day, same location).  But it's not exactly a very scientific comparison for at least a few reasons:
- The film scanning resolution is rather low.  Nominally, the files were JPEG with a resolution of 3087 x 2048, however when I zoom in, it looks like it was up-rezzed from a lower resolution, perhaps only 1/2 or 1/4 of the supposed resolution.
- The Sigma 50-150 was equipped with a lens hood while the Nikon 28-105 was not.  Given that many of these shots were backlit (plus the film shots used wide angle), this creates a significant disadvantage in the film camera's image quality.
- On the digital side, I only used a D70, a 7-year old camera, which is not representative of the abilities of current cameras.
- I used fill flash for the D70, which helped add a little extra shadow detail, and also caused the white balance to appear warmer (because Nikon's i-TTL shifts the white balance to a warmer tone to compensate for the bluish light from the flash).

In the future, I plan to do a more scientific test by having both the digital and film cameras with me, using more similar effective focal lengths, similar composition, and using identical exposures and flash technique.  Next time, I'll use the D300 with the Tamron 17-50 VC.  And yes, I have the Nikon 28-105's lens hood on order. 

For what it's worth, I saw for myself the significant dynamic range advantage of negative film (at least in comparison to an older sensor).  I had read about the dynamic range of negative film but had assumed that such dynamic range was accessible only through processing techniques.  I thought that the range of tones that could be visibly represented was about the same, regardless of format, while the rest of the tones would be just latent information in the image.  What I found instead was it appears that the entire dynamic range of negative film (around 10 stops) can in fact be represented in the image.  And unlike HDR images, the wide range of tones represented in film somehow look natural.

In this pair, the first shot is digital while the second shot is film.  Both shots were taken under similar lighting conditions (indeed, the digital shot got a little help from a bit of fill flash).  While the digital shot captured most of the midtones and shadows, the brightest highlights (clouds and pavement) were blown out.  The film shot, on the other hand, manages to corral the very wide range of tones in the scene -- nothing is blown out.



I took a look at the images in Lightroom to confirm this.  In Lightroom, blown out parts of the image can be made to show up as red, while blocked shadows can be made to show up as blue.  Here we see that the clouds (behind the top of the trees), plus the brighter parts of the pavement were blown out.
In the film shot, there's nothing blown out at all, and while the shadows are quite deep, the only blocked shadows are tiny specks from the ground toward the lower right hand side of the image (you'll have to zoom in to see them).

In this pair of shots, the backlight effect is even stronger, further increasing the dynamic range of the scene.  In the digital shot, we can see the subject just fine, but the camera just gives up on the sky in the background.  In the film shot, the subject looks underexposed, almost becoming a silhouette, but the sky is preserved:


Comparing the histograms and blinkies, we see that in the digital shot, the entire sky and parts of the pavement are blown.

Surprisingly, the film manages not to blow out anything except the middle of the sun.

Here are a couple more comparisons:


Histograms and blinkies showing the digital shot with blown out pavement. The film shot has no blown highlights and only has specks of blocked shadows on the ground (showing up as blue).







One more set.  The film shot captures the entire dynamic range of the scene (including all the highlights in the clouds, which are blown out in the digital shot):
Histograms and blinkies:


I'm stoked about these results and will continue to pursue shooting with film.  In my next comparison between digital and film I plan to add some shots to compare the tonality of film with digital.

Meanwhile, here's a link to the web album of scanned film shots:
Film vs Digital 1

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