Posted by: David Vernon | May 26, 2010

Sensor Size Debating

Matthiessen Lake Falls FinallyCamera sensors come in many flavors, for many costs, and with many inherent talents. And before I say anything else, let me talk for a moment about the “megapixel myth” and pixel quality – two very important factors that help you, as a camera buyer, decide what kind of sensor you need. First of all, I want to throw out the idea that more pixels are simply better. It’s really the pixel quality that goes a long way – more so to me – then pixel quantity.

What do a lot of pixels get you? To me they get you two things: 1) the ability to print larger and 2) the ability to crop as part of post-processing while still being able to support the ability to print larger. I don’t really feel that more pixels buys you more than that.

How much larger? My old Nikon D70 has 3,008 pixels on its long side and 2,000 pixels on its short side.Multiply 3,008 x 2,000 and you get right around 6,000.000 pixels – or 6 megapixels. By comparison, my current Nikon D300 is 4,288 on its long side and 2,848 on its short side. That’s 12,212,224 pixels or 12.2 megapixels. Seems like a large jump, doesn’t it? In reality however it isn’t much of a jump at all.

Most folks consider 300 pixels per inch the entry-level gold standard for high print quality. This is considered “high-resolution” (I even consider anything above 240 pixels per inch to be quality high-resolution). So if you divide the number of pixels by 300, you get the approximate size of the printed image at high-resolution. My D70 therefore would print natively 6 2/3 inches by 10 inches. My D300 only prints a bit bigger. It’s native high-resolution output is 9 1/2 inches by 14 1/4 inches. Want to go a step further? Nikon’s flagship camera, the “full-frame” D3s, with its 4,256 x 2,832 pixel depth is actually a bit smaller than my D300. Wait. What? How does that work?

It’s all about sensor size and therefore pixel size. Here are some more numbers (sorry). The sensor in my D70 and in my D300 are the same basic size. About 23.6 mm x 15.8mm (about 375 mm²). Obviously to pack 12.2 million pixels on my D300’s sensor, things are going to be packed a lot tighter then on my relatively roomy D70. Tighter – or smaller. Want six million more pixels than the D70? Make ’em all smaller so they fit. And there’s a sort of universal truth to the notion that, with everything else being equal, more pixels actually degrades image quality. At what point does the trade-off between quality and quantity cause trouble?

Fortunately camera manufacturers have gotten better at processing images in-camera. They’ve been able to grow pixel counts and still make beautiful images because of advances in technology when it comes to the manipulation of those pixels.So all other things being equal… well the heck with that. They aren’t equal. So how does the D3s, with roughly the same number of pixels as my D300, make such amazing images? Well – the pixels sit on a larger sensor and are therefore can be much larger themselves. A D3s is a full frame sensor. It’s the same size as piece of 35mm film, which means its 36mm x 24mm (about 865 mm²). That’s quite a bit larger than the non full-frame (or cropped) sensors. Since the pixels are so much larger, their ability to handle noise and create impressive images is unparalleled in the 35mm format.

So what do you really gain besides an improvement in the general quality of the image? You gain an impressive ability to shoot in low light at very high ISOs. I’m comfortable going to ISO 1,000 on my D300. After that I feel like image quality really starts to degrade. I shot with a Nikon D700 last week – which is the entry-level full frame camera from Nikon. I was shooting some images at ISO 3,200 and didn’t feel like I was sacrificing image quality at all. What a difference. Couple that with a fast f/2.8 lens – and you can achieve amazingly fast shutter speeds in low light. That is a huge advantage. Period.

So why doesn’t everyone just shoot full frame? Why doesn’t everyone want the best image quality they can get? Well – the main deterrent to the bigger sensor? A much bigger cost – for camera bodies and proper lenses. You can pick up a D300s (the replacement for the D300 – but very similar) for under $2,000. Most DX lens – lens optimized for the crop sensors – run under $1,000 – and some much less. The D3s will cost you close to $5,000. Want Nikon’s highest quality glass for that body? It’s at least $2,000 per for the 14-24 f/2,8, 24-70 f/2.8, or the 70-200 f/.8 lenses. And that’s just in the 35mm format. Go medium format and you’re looking at costs of between $10,000 and $40,000.

I made a basic decision the other day that will both save me a lot of money and – eventually – cost me a lot of money. As a landscape photographer I have very little need for full-frame. My D300 with a few decent but not over-the-top lenses (the 10.5 f/2.8 fisheye,10-24 f/4 and 18-200 f/3.5-5.6) will suffice. On the quality continuum I’m still in pretty good shape since I shoot everything at ISO 200 from a landscape perspective. I don’t need the low-light magic of full-frame; I can just take longer exposures.

But in the long-term, for my other work doing commercial or event photography, where I need shutter speed – then full-frame is what’s best. And I’d be quite content with a D700 class camera along with 2-3 fast lenses. I can get by with the D300, but I’ll do better with the full-frame. So someday…

So consider what it is you need to shoot and then ask if the cropped sensor camera get it done? If so – you’ll save a boatload of money going that route. On the other hand – it never hurts to buy the good glass. It will work very well on both types of sensors where the cropped-sensor lenses struggle to move up to full frame. Good glass and any body works. Good glass and a good body works really well – if you have deep pockets. If you don’t – and you like shooting from a tripod – the cropped sensor will still take you far.

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Responses

  1. I find my D700 with a 24x36mm sensor to be ideal (12MP). Excellent results up to ISO6400. Great for landscapes also at ISO200.

    I also still use my D2h, a fast focusing machine gun (4MP), but it can only go up to ISO1600. But noise reduction software helps it along a little, Noiseware Pro is great.

    But I hardly ever crop after capture. Sometimes a DX is better such as the D300s as it gives extra reach when birding.

  2. A lot of this depends on your final output and what you customer accepts. I shoot with a D80 and have done a bit of cropping and blowing up – not without fear and trepidation. But more often than not I am pleasantly surprised that the quality is still there. It is very easy to get caught up in the math but in the end does the customer buy the picture and/or are we happy with the results.


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