Reading this article might save you some money. No, I’m not sponsored to write this, so you may safely proceed. All you’ll get is technical insight and honest opinion.
Perhaps like many photographers, you’ve thought about going for a full frame camera. Perhaps you’ve heard about shallow depth of field, low light shooting and noise. Maybe you’ve heard that full frame is “one stop faster” or “one stop brighter”.
In this article, I’ll cover one of the reasons for going full frame – more light, and how much sense it makes, especially for your bank balance.
By going from APS-C to full frame – probably the most common move – you gain approximately one stop of light, i.e. because the sensor is twice as large, you can capture twice as much light, all else being equal. It would be approximately true to say that shooting ISO 200 on full frame, you get the same noise if you look at the entire image (equally framed and shot at the same aperture) as shooting ISO 80 on APS-C. So you can shoot faster shutter speeds and, looking at the sensor as a whole, get the same noise. However, if you shoot 16 megapixels on APS-C, then shooting 36 megapixels full frame, you will get the same PER PIXEL noise, at the same ISO. So far, so good.
So if we shoot the same apertures, we gain a stop of light. So we can ask the question, how much does it cost to gain a stop of light?
If you upgrade from an 18-55/3.5-5.6 APS-C kit lens to a 17-50/2.8 APS-C premium zoom, you gain 1-2 stops of light, and it might cost you 150 Eurodollars if you buy used. Or for about the same price, you could upgrade to a 17-70/2.8-4.5, which gives you almost exactly one stop advantage over the kit lens, and a bit of extra range.
If you further upgrade to an 18-35/1.8 zoom, you might pay about 600 Eurodollars used or a good offer new, and you would gain a stop over the 17-50/2.8 or over two stops vs. an 18-55/3.5-5.6 kit lens. But you shorten your range by about one stop of teleconversion. Don’t worry if that sounds technical – just remember that 35mm is 35mm and not 50, 55 or 70mm.
If low light shooting, reduced noise or faster shutter speeds are what you’re after, and you’re still shooting with an APS-C camera and kit lens, you owe it to yourself to first invest the 150 to see if the extra light is worth it. This will put you in a much better position to judge whether you want to invest about ten times that amount (or more) to get to a full frame camera and appropriate lens. (Note that a full frame camera with an f/4 lens offers no light advantage over an APS-C camera with an f/2.8 lens!)
There are other points to consider, of course, some of which I’ll touch on briefly. A full frame camera generally offers greater sharpness due to both an increase in resolution and easier manufacture and assembly of appropriate glass. The full frame format is more resistant to diffraction, typically tolerating f/11 rather than f/8 (APS-C) or f/5.6 (Micro Four Thirds) – note that these assumptions only hold for certain pixel pitch, i.e. a 36 megapixel full frame camera is just as sensitive to diffraction at the pixel level as a 16 megapixel APS-C camera. (Other assumptions apply, such as having comparable filter stacks in front of the sensor.) However, over the entire frame, the full frame camera is more tolerant. The flip side is that you need to shoot at those smaller stops to reach the same depth of field, meaning that in landscape shooting, there is no full frame advantage in available light, for the same positioning and framing.
Furthermore, full frame has greater limitations when it comes to designing zoom lenses – you may notice that a common superzoom lens specification for full frame is the 28-300mm lens, whereas on APS-C, the limit has been pushed to 16-300mm – the same versatility in focal length as a 24-450mm on full frame!
Similarly, compare the Sigma 18-35/1.8 to its full frame sibling, the 24-35/2. The smaller lens is both faster and, depending on your point of view, slightly more versatile. (The comparison is hampered by the full frame lens being the equivalent of a 16-24mm on APS-C – not an easy comparison!)
So a full frame camera is best suited to the shooter who knows what situations they want to cover and what their preferred focal lengths are. If you prefer spontaneous shooting and versatility, it is likely that a full frame camera will not make you happy.
Arguments about achieving shallow depth of field more easily on a full frame camera deserve a separate article.
Update 2/2/2017: Also check out my newer article, Low light photography? Affordable? Look no further! for the latest development, or check out a sample image.