I often hear people say that they hope some day to upgrade to full frame. People talk about this upgrade in the same mystical fashion as finally getting to move up from the kids table on Thanksgiving. Some feel as though it will really improve the quality of their images. Possibly even take their photography to "the next level." Are they right? Over the next several weeks I'll be sharing my experience with this upgrade. Where it was magical and where it was just kinda ho hum. I assure you it was most certainly BOTH! I'd like to dispel some of the mystical speak and put it into comparative terms that most photographers should understand. If something is unclear, please drop me a line and I'll do my best to answer your questions.
Mystical quality number 1: Full frame cameras have way better low light performance.
There are a few factors that play into low light performance. ISO noise performance is one of the more important things you'll hear bandied about. If you're not sure what ISO Noise performance is, it's the ability for a camera to get a good clean, noise-free image when using high ISOs. Noise is something that people are familiar with from trying to take a picture of a darker scene with a cell phone camera. To be able to distinguish between light and dark areas, the camera sensor has to become more sensitive to light. This is similar to turning up the volume on a radio station that is fading out as you drive away from it. You get a lot of static and noise. When you look at a "noisy" image it looks about like you would expect that radio static situation to look if it was converted into image form.
It is generally true that full frame cameras have better ISO noise performance because the pixels are bigger. To help visualize this think about placing a 5 gallon bucket outside during a rain storm. In this example the bucket is like a pixel on your camera's sensor and the rain is light falling on that pixel. If you now set a kiddie pool next to this 5 gallon bucket which one is going to collect more rain (light) faster? Granted, they'll both have the same water depth but the container with the bigger opening will be able to collect a larger volume of rain given the same amount of time. It can also handle a larger volume of rain before overflowing.
When I talk about the pixels being bigger I mean the actual pixel down deep inside of your camera's sensor. On full frame cameras the bucket for collecting light is actually physically larger just like in the example above. These buckets are measured in micrometers (aka microns or uM) and their sizes are told to us by manufacturers in the camera specs.
Here are are the pixel sizes of a few popular cameras on the market today:
Canon 5D Mark III 6.25uM
Canon 6D 6.5uM
Canon T3i 5.3uM
Canon 1DX 6.95uM
Nikon D7000 4.78uM
Nikon D750 5.9uM
Nikon D800 4.88uM
Nikon D4 7.3uM
Nikon D3200 3.85uM
Nikon D5300 3.85uM
How important to you is this? Well lets look at a somewhat real world example. I have a crop sensor and a full frame camera at my disposal for doing a quick test. I have a Nikon D7000 and a Nikon D800. DXOMark specifies an ISO setting up to which a camera can capture "excellent quality images".
DXOMark Max ISO for Excellent Quality Images:
I took pictures of a brick wall using the same settings on both of these cameras. The images were taken with light appropriate to the camera settings, provided by a speedlight in TTL mode. Settings are 1/125sec ISO2500 f/5. Based on these settings we should be in an area were DXOMark says one camera can generate an "excellent quality image" and the other cannot. This is the type of situation a wedding shooter may end up in if they were to use small flashes to bring up the illumination in the room yet want to use a higher ISO to keep the the room feeling light in the final images.
Here are the results side by side. Both files have been sampled to the same size JPG from the camera RAW file.
Above Nikon D800, 1/125, f5, ISO2500, 200mm
Above D7000, 1/125, f5, ISO2500, 130mm
Above Nikon D800 Zoomed Crop
Above Nikon D7000 Zoomed Crop
The texture of the bricks tends to hide the noise. Much like the interest of a well taken shot will cover up noise. There are some interesting things going on here but so far I'm not so sure I've seen a justification for the $2000 price difference between these cameras. Granted these images were both properly lit and no post processing gain was needed. If you accidentally under exposed an image and had to brighten it in post, the ISO performance would show itself a bit more.
Next is a more direct comparison of the noise of the two sensors in these cameras. I took a picture of a door illuminated by a sun tube skylight. I purposefully underexposed these images and shot them at ISO3200. We're now above DXOMark's acceptable range for excellent quality images on both cameras. Camera settings are 1/200, f5, ISO3200. Then each image was bumped up by 2 stops from the original RAW file and then both images were exported to same size JPGs.
Nikon D800 - 1/200, f5, ISO3200, 200mm
Nikon D7000 - 1/200, f5, ISO3200, 135mm
Now for the pixel peepers:
Nikon D800 Crop
This is becoming more of a test just to show faults rather than a real world example but it gives you a better ability to see differences in noise performance at a fairly high ISO of 3200. I also noticed that seeing the differences in these pictures is a lot harder on my phone which I've always regarded to have quite an excellent full HD display.
All this being said if you REALLY have to push your camera to the limits on a regular basis shooting in low light; especially while shooting moving subjects. The Larger pixel sizes on most full frame cameras can really make a difference there. Here is a shot of a very dark corner inside where ISO 6400 was used to get the shutter speed up to 1/50. A 50mm f/1.4 prime lens was used wide open to get maximum light gathered. On previous images the shots were taken from the same location with equivalent focal lengths to compensate for the crop factor. Since this lens doesn't have a zoom capability to compensate for the crop factor, the full frame camera is a bit closer to get the same framing. There is a lot of difference here. If this is something you have to do frequently, you can look below and determine if it's worth the cost to you.
Note: Both of these images were shot with auto white balance.
I hope this gives you an idea of some of the subtle (and not so subtle) differences between a full frame and a cropped sensor camera. Next I'll be looking at one of two topics: Autofocus considerations for low light performance or depth of field equivalence and field of view differences. Both of these areas show much greater differences than what we explored today. If you would prefer to see one these topics first, please let me know in the comments below!