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I recently bought a Nikon D90 camera body, which has a "DX" APS-C-sized sensor..

Within the same budget, should I go with DX lenses or should I get full frame lenses in case I upgrade to a full frame body in the future, when they become more prevalent?

50

The price you pay for using FX lenses on DX is bigger and heavier lenses and less appropriate focal lengths.

The core question you should be asking is: Why do you want to upgrade to full frame? Image quality in DX is superb and getting better. FX bodies have better low-light ability, but DX will be just as good; it just lags a few years. The higher resolution is a factor only if you have both great lenses and great tripod support - i.e., very few people. FX bodies will always be larger and heavier, and DX will be with us as long as F-mount is. Unless you can articulate a specific, good reason for an eventual FX upgrade path, stick with DX.

Finally, keep in mind that lenses retain their value very well. If you can sell a lens for 70-80% of what it cost you, why not just buy the most appropriate lenses and sell them if they become inappropriate?

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    Yeah, that last paragraph is the best advice. For example, don't hesitate on a 10-24 just because you might have a full-frame camera in 2 years. – Bobby Ketchum Jul 19 '10 at 2:55
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    @Jody, I think that's unlikely; DX cameras will always be smaller and cheaper to make than FX ones. And there's even a growing body of smaller sensors (4/3). Thus, IMO it's highly unlikely that DX will disappear. – Reid Aug 11 '10 at 2:20
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    Indeed, according to Wikipedia, a full frame sensor is 864 mm^2, while my D5000 has an area of 371.3 mm^2. Since the probability a defect is proportional to sensor area, that means a full frame sensor is more than twice as likely to be a reject as my D5000's DX sensor (assuming rejects are by total dead pixel count). Also, the manufacturing process should be able to put more than twice as many DX sensors on a single wafer. Both of these points are physical reasons why DX will always be cheaper than FX. – Benjamin Cutler Jan 27 '11 at 17:47
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    Hi Reid, can you please explain the implied negative impacts of your statement: less appropriate focal lengths ? Thank you. – Drew Jan 19 '12 at 1:41
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    The point there assumes that there are fields of view which are more desirable than others, and FX lenses are designed to deliver those fields of view on FX; on DX, the same lenses will give narrower fields of view. For an extreme example, you'd never put a 200mm lens on a compact camera: it would be far too long. The same effect happens with an FX lens on DX; it's just not so extreme. – Reid Jan 19 '12 at 15:44
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That depends on how likely it is that you will get a full frame camera, but also on what lens you buy. If you buy a cheap lens, it's likely that you want to upgrade the lens anyway if you get a better camera.

Another aspect is how the lenses work with the camera you have now. With a full frame lens you will get much less vignetting, and also better edge sharpness. Lenses are worst at the edges, so with a smaller sensor you use the best part of the lens.

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    The right question isn't "are you using the best part of the lens" but "is the lens good enough in relevant parts of the frame" - similar, but it's an important subtlety IMO. A little vignetting (which can be eliminated by stopping down) and edge softness are usually not a problem. – Reid Jul 19 '10 at 1:55
  • @Reid: I didn't write it so exactly that it can be taken out of it's context like that. The meaning is of course "you are avoiding the worst part of the lens", which should be obvious from the context. – Guffa Jul 19 '10 at 2:14
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    The point I was trying to make is: there's no reason to avoid the "worst" part of the lens if the worst parts are good enough. No reason to maximize - satisfice. I don't think I misinterpreted the context. – Reid Jul 19 '10 at 2:21
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With Nikon at least, recently I've been disappointed with the range of DX-specific lenses available. It seems Nikon are treating DX more as a second class citizen. When you look at the range of lenses available in DX and compare it to their FX range, the DX ones tend to be slower, more plasticky, and more zooms than primes - in other words, more targeted at amateurs. There are of course exceptions like the good (and expensive) 17-55, but there are no fast normal primes or wide primes in DX-only, apart from one 35mm which is not a particularly good performer for a prime.

It's fine if you only want kit lenses or inexpensive superzooms but this got me thinking about how with Nikon, I'd have to move up at least to FX lenses, if not FX all together (since FX lenses don't have appropriate focal lengths on DX bodies) if I really wanted to go further with my photography. And I doubt that real photographers would want to pay good money for my DX lenses for that reason.

Which ended up in me switching to Olympus/Panasonic, who don't treat their cropped sensor size (4/3) as a second class citizen and already have a number of high quality normal/wide primes for their sensor size, but that's another story.

I guess my point is that the DX/FX issue is more an effect of who Nikon and Canon target these devices at rather than the techical merits of the sensor size. DX (indeed, any APS-C or even 4/3) sensors themselves are technically excellent, it's just that Nikon/Canon target them to a lesser-experienced audience.

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There's no "right" answer to this question. Other than the fact that DX only works on the APS-C (crop factor) bodies, there really aren't any global differences between the DX lenses and any other.

If you think you'll be getting a full-frame body in the future, I'd definitely skip the DX lenses. If you don't have that in your plans, get the DX lenses if they meet your needs.

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I'd say it depends on budget and which end of the spectrum you are talking about. On the wide angle side, you're going to pay a lot more for a full frame lens that gives you an ultra-wide experience on the D90, so if you really want something megawide, I'd say a DX lens 10-17mm is going to be a more useful thing to you that something way down there in FX world.

For prime lenses, 100% absolutely go for full frame lenses unless you have a really good reason not to.

For zooms:

In the middle, and on longer lenses I'd say if you can go for full frame. The D90 is an EXCELLENT choice because it has a built in focus motor, and that opens up a whole world of great low cost lenses to you.

You can do a lot worse than the 35-70 f2.8 D zoom that is a tank and is a standard to short tele on the D90, but only around $250 used. On the zoom end, I'd highly suggest avoiding the consumer telephotos and going with something more solid like the twin ring 80-200 f2.8 or on a budget the surprisingly good 70-210 f4 lens from film era. They are about $100 and will work well with your D90 and give way better results than the newer consumer 55-200 or 300 type lens.

Those are all full frame lenses, and really a good pairing with your D90. I'm assuming you bought a D90 because you're somewhat on a budget, so these lenses fit right in.

On a budget I always recommend steering clear of the D5xxx and D3xxx ranges for the reason that these lenses don't work, and recommend the D90, the D7100 or the D700 if you want to get into full frame on a budget.

K

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I think it depends on the lens, and how you plan to use it on both DX and FX in the future, as well as how imminent your move to FX is.

If FX is just a farflung dream, and you're hoping to get there someday, then FX is probably not a great purchase for you. The lenses are bigger, heavier, more expensive, and not always suited for DX use. If, however, you plan to move to FX within a few months, and DX is merely a temporary stopgap, then minimizing DX lens purchases may make sense.

The main issue however, is how crop factor works. What is ultrawide on FX is merely walkaround on DX. What is telephoto on FX is supertelephoto on DX. Whatever the lens, once you switch formats, the FoV and basic usage of that lens will change on the other format.

If you are using a set of portrait primes, this may not be an issue. 50 on DX is like 85 on FX; 85 on DX is like 135 on FX, etc. Your lenses may be able to cover for each other on FX. But if you rely on a supertelephoto zoom for sports or wildlife, prepare to take a bit of a hit on "reach" when you go FX. For example, the 80-400 on FX has the same angle of view/equivalency as a 53-267mm on DX does. In other words, prepare to do the crop math backwards and watch all your lenses get 1.5x shorter on FX than on DX.

And the sole exception to lenses you should get on DX while you're shooting DX would undoubtedly be ultrawide zooms. Because the lenses that cover an FX sensor that would still be considered ultrawide on DX are rare and expensive, and a 10-20 would probably serve you far better (and much more cheaply) until the move, when you can sell it to fund part of an FX ultrawide zoom lens.

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