Image size and “shooting to crop.”

(1) Image Size.

The amazing amount of resolution offered by the D800 has a significant downside. Each RAW file produced by the camera has a file size of about 40MB. This is, in turn, has two negative effects. Firstly, computers must have sufficient power to manipulate large amounts of information when processing images, and second, hard drive capacity gets used up very quickly.

To test download speeds, I shot 100 images and then used a USB 2 card reader to ingest them images Lightroom 4. In the first experiment, I was using a 2009 MacPro tower with a Lacie USB3 card connected to a Lexar USB3 reader and a Lexar 32GB 400 X UDMA compact Flash card. In the second, I was using the same tower and card with a USB2 card reader. Render times were (unsuprisingly) identical at 3.5 minutes. I also tested a 2009 MacBook Pro laptop with a firewire 800 card reader.

The results are as follows:

Download times for 100 images with Mac Pro tower.

Download times for 100 images with MacBook Pro laptop.

The same 100 images gave a total file size of 4.39 GB on disk. It should be noted that render time was significantly longer on the MacBook, which reflects its lesser power.

Whilst the above examples are interesting, it seems to me that they miss the true significance of this camera. Yes, file sizes are very big, and will clog a pipeline that does not have significant capacity (power or size). For those whose workflow involves shooting in RAW + JPEG modes, this will fill your drives even faster! Against that, computer power and hard drive space is improving significantly, and becoming more and more economical. I can see that drawback of trying to shoot a field assignment with many thousands of images when each file is around 40MB, and perhaps this is not the camera for that task, however, I feel that the advantages of the amount of information that this camera captures far outweigh the drawbacks.

Where it is significant is in the choice of memory that is used with the camera. Faster and bigger cards do affect buffer times and will allow more shots to be captured in bursts for fast action. Although rare, situation do exist underwater where being able to shoot a few more images may make a difference. Having said that, performance difference is minimal in shooting, with 1000 x cards adding perhaps a couple of extra images before the camera’s buffer fills.

There is no doubt that Compact Flash cards do write significantly faster than SD. This is definitely the case with the D800. I would suggest assigning a large capacity CF card as your primary memory. This needs to be 32GB or more in size.

Faster cards also decrease ingest times, so for people shooting large numbers of images, this may well be another factor to consider. In addition, fast firewire,USB 3 or Thunderbolt card readers are necessary accessories for use with this camera. Broadly speaking, buy the biggest capacity, fastest cards you can afford!

(2) Shooting to crop.

The large file sizes do have some advantages. One of these is the ability to deliberately discard significant amounts of image information and still be able to produce images with sufficient resolution to allow printing at a large size and with fine details.

This is further complicated by the camera’s ability to be used in DX mode, effectively a crop version, where only 16 megapixels of the available 36 are used. This allows the use of DX lenses, perhaps most interestingly the venerable Tokina 10-17mm fisheye zoom. It also potentially restores the 1.5 X magnification advantage for macro shots.

The relationship between resolution and image size is not linear, as it is an area (or pixel density) measure, rather than a straightforward proportional sum. The D800’s sensor measures 24 x 35.9mm with a resolution in FX mode of 7360 x 4912 pixels. In DX crop mode, the area of sensor used is 4800 x 3200 pixels. The actual pixel size and their performance is identical, so the advantages in high ISO and tonal range will carry through even when shooting in DX.

Practically, using the camera in DX mode causes a cropping boundary to appear in the viewfinder. In FX mode, the camera provides a 100% view in the viewfinder, in DX mode, all that is available is a proportion of this.

The above illustration does show a potential advantage of the DX image area mode. The whole image area is filled by the focus points, allowing a sharp image even if the subject is in the corners of the frame.

The use of the Tokina 10-17mm lens with the D800 does seem to test the lens’s performance. In ideal circumstances in DX mode, it can produce very pleasing image quality.

The D800’s fantastic tonal range is available even in DX mode.

But in more challenging conditions, it seems to lose sharpness a bit. On the forums are some interesting comparisons with this lens, and it would seem that the D800 can tend to out resolve it even in DX mode.

Beyond this, shooting in a cropped mode means that you are losing significant image data. Quantifiably, in DX mode the shooter is choosing to discard 20MP of available image information. Whilst available lens, port or housing choices may force the decision, I can see little advantage in shooting in DX mode, when you can shoot in FX and crop as appropriate later.

For macro photography, there is a feeling that DX is more suited as this “enhances” the magnification effect by 1.5 times. Effectively, this increases the focal length of your lens, so a 60mm becomes an effective 90mm, and a 105mm becomes a 150mm etc. I think that this may well have been the case when resolution was an issue. With 36MP, the shooter can crop his or her photographs by half and still retain 18 megapixels of information, Given that most publications are happy with files at 12MP, this should be more than enough. With DX, you would gain a 1/3 magnification advantage, but by cropping the 36MP FX image in half, you can still create tighter compositions with more resolution.

There will, of course, be instances like competitions that will not allow cropping, and DX will undoubtedly be better for macro in these, but outside of this, it is hard to conceive a situation where it would be advantageous not to use the camera’s full resolution.

1. Introduction.
2. The Nikon D800 body, controls and overview.
3. Resolution, ISO and tonal range.
4. Image size and “shooting to crop.”
5. Autofocus, teleconverters and built-in processing.
6. Conclusion.