Nikon DX lenses

October 23, 2005 at 11:41 am · Filed under Hobbies and leisure, Ramblings

Wow. This was totally a shock to me. I had an email thread at work with some photo enthusiasts, and eventually chatted with Michael a bit about how we could prove one way or the other.

The claim was that the Nikon DX-style lenses take into account the 1.5x Focal View Crop that the D70 camera sensor creates… Well, Nikon covers this in a bunch of detail in their knowledge database. But even after reading this, and reading a bunch of the forum comments (like this one), I was TOTALLY CONFUSED.

For me (and probably for most of the folks on the forums, etc) the question was very simple: Does 70mm on my D70 with a DX lens equal 70mm on my D70 with a non-DX (“135″-format) lens.

The reason there’s so much confusion around this is probably because there’s two answers, they’re different, and they’re both true.

The first answer is: Absolutely yes. 70mm is 70mm. Duh.

The second answer is: No. Because the DX lens “knows” it is working against a non-full-frame sensor. The DX lens is specially designed to only cover the crop of the dSLR sensor, so it “takes into account” this difference and provides a “true” focal length.

I fall more inline with the second camp. I mean, really… who cares if it’s actually 70mm specified on the lens if it’s EFFECTIVELY 105mm on the sensor.

So, thanks to Michael for “proving” the second answer for me by taking the same exact picture at the same exact focal length (70mm) with two different lenses just to show how different “70mm” can look if the lens does (or doesn’t) take into account the 1.5x crop:

18-70mm ED DX @ 70mm

 70mmWithDX

70-300mm ED @70mm

70mmWithNonDX

 

So, that about proves it for me, and here are my takeways:

  • A DX lens on my D70 can be taken to provide exactly the effective focal length it quotes (ie – my 18–70mm lens will work just like an 18–70mm lens)
  • A non-DX lens on my D70 will provide the 1.5x focal length multiplier effectively (ie – the 70–300mm lens works like a 105–450mm lens)

Now I get to rethink my 70–300mm lens strategy so I don’t end up with a big gap in focal-length coverage with my 18–70mm (kit) lens… drat.

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