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M43 Crop Factors to Nikon DX
#1
Here is an interesting question that I can't find the answer for anywhere online. Maybe one of you wizz-kids out there can either confirm my reasoning or tell me where I am wrong.

The Nikon DX sensor has a 1.5 crop factor when compared to full frame. This is because the sensor is smaller: 28.4mm diagnol for DX compared to 43.3mm diagnol for full frame. Likewise, my m43 camera has a 2x crop factor because it has a 22.5mm diagnol sensor. (2 x 22.5 is approximately the full frame 43.3).

This means when I use a full frame lens on my m43 camera, the *apparent* focal length is 2 times the stated one: 24mm becomes 48mm etc.

So...here is my question: I have 2 DX format leneses, my Nikon 12-24 and my trusty Nikon 18-200. The m43 sensor is 22.5mm diagnol and the DX sensor is 28.4mm. Does this mean that when I put a DX lens on my m43 body that the apparent crop factor is approx 1.25? (1.25 x 22.5 = 28.125)

Does this mean that my 12-24 on the GF-1 becomes a 15-30 equivalent and the 18-200 becomes a 22.5-250 equivalent?

I have never seen this discussed online - but I am sure that many inquiring minds want to know. Those would be 2 killer lens ranges if I am right. I accept that I may be wrong though - so feel free to educate me.

Thanks people.

BTW - I am patiently awaiting delivery of my Nikon G to M43 adapter.
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#2
Focal length is focal length - all that changes with the format is the angle of view. A DX lens is just designed to cover a smaller image circle, just like a 4/3 lens is designed to cover an even smaller image circle than that. Whatever the focal length is, double it on your GF1 to get its 135/35mm film equivalent, no matter what the lens is. If you somehow macguyver a 4x5's 'normal' lens - 150mm - onto a m4/3 body, it will give you a 8° 15' field of view, even though it can cast an image that's bigger than the camera. The 12-24 becomes 24-48, and 18-200 becomes 36-400.

Now, not to rain on any parades here - there's been plenty of that in Toronto this past weekend - but what adapter are you awaiting? I see that you mentioned 'Nikon G', so I'm thinking that you already know this, but if you have an adapter without an aperture control built-in - like the Voigtländer that I use - then you'll be restricted to only using the smallest aperture opening, which I think is f/22 for both.
matthewpiers.com • @matthewpiers | robertsonphoto.blogspot.com | @thewsreviews • thewsreviews.com
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#3
Interesting question Rob... I look at it this way - focal length is the same regardless of what kind of lens it is (MFT, DX, etc.). The sensor (or body I guess) determines the "crop factor" to produce a 35mm equivalent focal length.

So the MFT 14-42 kit lens gets a 2x crop factor on a MFT body = 28-84mm (35mm equivalent)
And your 12-24 DX lens also gets a 2x crop factor on a MFT body = 24-48mm (35mm equivalent)

Toad Wrote:So...here is my question: I have 2 DX format leneses, my Nikon 12-24 and my trusty Nikon 18-200. The m43 sensor is 22.5mm diagnol and the DX sensor is 28.4mm. Does this mean that when I put a DX lens on my m43 body that the apparent crop factor is approx 1.25? (1.25 x 22.5 = 28.125)
I had a closer look at the logic (gets quite confusing doesn't it) and you need to bring it back to 35mm equivalent to compare. What you are trying to do is compare the MFT to DX, and yes there is an increase of 1.25x but only relatively, and not in 35mm terms.

- DX sensor size = 28.4mm diagonal x 1.5 crop factor = 42.6mm diagonal
- MFT sensor size = 22.5mm diagonal x 2 crop factor = 45mm diagonal (roughly equivalent given the 4:3 aspect ratio)
- Full frame is actually 43.3mm diagonal - 35mm refers to the long side of the sensor

Anyway, I better sit down now, head is swimming with too much math.
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#4
By the way, there's a nice reference table towards the bottom of the article here on wikipedia:
http://en.wikipedia.org/wiki/Image_sensor_format
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#5
OK - thanks for the clarifications - if it seems to good to be true, it likely is... I still have some problems with the concept, and I guess I will have to run some experiments to prove it to myself.

I am getting an adapter with a built-in aperture control - but not so pricy as the Voigtlander. There is a fellow in Singapore (jinfinance) who sells them for about $40 on ebay. They get good reviews online and cost maybe 1/6 as much. I gather the early models back a year or 2 had issues with infinity focus, but everything I read says the new models are totally satisfactory.
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