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DX Lenses Becoming Obsolete


A 35mm camera has, interestingly enough, a data collection mechanism (film) that is 35mm. Most of the digital SLR cameras (from Nikon or otherwise) on the market today have a sensor that is smaller than 35mm. The net result is that if you use a 35mm lens on a digital SLR the lens focal length is increased, and in some cases the image quality is sharpened at the same time. [1] For many lenses this is a positive result as a 400mm film lens becomes a 600mm lens when used with the smaller sensor. For wide angle lenses (anything below 50mm for a film lens is considered wide angle) this is not such a good thing. [2]

As a result Nikon came out with a line of DX lenses that were designed for the size of the sensor used in their digital SLR bodies. These lenses were smaller and less expensive and made it easier for new folks to get involved with digital SLR photography. But the problem is they’re already becoming obsolete.

Not too long ago Nikon released their first “full frame” digital SLR: the Nikon D3. This camera is about $5,000 just for the body itself :shock: so I don’t plan to immediately purchase one. But one of the advantages of this camera is that the digital sensor has the same geometry as the 35mm film that it’s replacing. This means that a 400mm lens is now exactly a 400mm lens, and even better a 20mm lens is exactly a 20mm lens again.

Is this a good thing? In my opinion, yes. But it means that all of those cheaper DX lenses are now obsolete. Well, perhaps “now” is too strong of a term, but “now becoming obsolete” is probably not too far off of the mark. You can only use a DX lens on a DX-compatible camera body. I expect that digital camera bodies are updated much more frequently than lenses. My general expectation is that a camera will be used for 3-5 years and then retired as new technology comes out. Lenses should have an expected life-span of 10-15 years or more, depending on the whims of the camera company, of course. I can take a 25 year-old Nikon lens and mount it on a new camera body and some of the functions will quite probably work. Not all of them will, of course, but the fact is that Nikon has not changed the physical structure of their lens mount in decades.

Update: It has been pointed out to me that DX lenses will, in fact, work on an full-frame digital sensor or even film. They just won’t correctly. :) A DX lens mounted on an FX sensor camera body will function just like it did on a DX camera, which is to say the outer parts of the image will be missing and you won’t get the advantage of the full capacity of the sensor. So in a strict sense: yes, a DX lens will still work. But given the way it works, I submit that it’s not working well enough to be considered a viable option.

But in this case, DX lenses will have to be retired as DX bodies are replaced. I am glad that I have only purchased one DX lens, and that was for a special purpose fisheye lens. This wasn’t a recent decision; as soon as the DX lenses started coming out I realized the potential issue and stayed away from the very beginning.

Buy Now?

You can still get DX lenses, and they’re still less expensive than their full-frame equivalent. If I were buying a digital body today, would I get a DX lens? For me, no. :) I want my lenses to be able to work on all of my camera bodies including those that shoot film. But what if this was going to be your only camera?

You can get a 10-12MP image sensor in a digital SLR and a couple of decent DX lenses for under $1,000 from mail / web-order companies. If this is your first SLR then you are probably less concerned that the DX lenses won’t work on another camera that you already have… since you don’t have one. :lol: You can get a nice point-and-shoot for several hundred dollars, or you can get a digital SLR kit with a couple of decent lenses and probably be quite happy.

Years ago when people would find out that I am interested in photography I would get asked, “Which digital camera should I buy?” My standard answer that (as it is now) is to buy the best camera you can get for $350 or less. That way you won’t be discouraged when you want something new in 2 years. If I take that dollar amount and extrapolate to 5 years instead of 2, that gives me a budget of about $1,000, which oddly enough does match the price point I mentioned in the prior paragraph.

What’s Next?

What about the future? Will there be a “bigger-than-full-frame” sensor released? It’s certainly a technological possibility, but I wonder if Nikon will really do that. Instead of increasing the size they might increase the density of the sensor, making it possible to take extremely high resolution images with a standard-sized sensor. This would preserve the tremendous investment that many folks have in their glass.

If you have a DX body, look for lens prices to drop dramatically and also check out eBay as I expect the number of DX lenses for sale to increase quite a bit over the next two years.

Notes
1. Can a digital body sharpen a film lens? No, not really, but it can appear to do so. Since the digital sensor is smaller it is only going to use the “sweet spot” in the middle of the lens and ignore the corners. Since some lenses have light falloff or lower image quality at the corners the net result is an apparently sharper image. It’s just because of the geometry of the sensor, nothing more.

2. Why is it a problem that a 20mm lens becomes 30mm, but not a problem for a 400mm to become a 600mm? It’s not too hard to comprehend, really. People typically spend big bucks on big lenses in order to be able to capture birds or other wildlife. The bigger and faster the lens is, the more it costs. So getting a 50% boost in apparent zoom factor is a nice bonus when using a 400mm lens on a digital body. It makes the zoom “zoomier” as a result.

However, for landscapes you don’t want to get close, you want to extend your vision. A wide angle lens is used to capture more, not less, of the scenery. The digital multiplication factor that works to an advantage for telephoto lenses is a disadvantage for wideangle because unfortunately it doesn’t make a wide wider, it’s still “zoomier”, and that defeats the purpose of getting a wide angle lens.


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