Pro video blog…Produced by Philip Johnston DoP/Editor

It’s all about “CROP” and this topic is very confusing, people who market Nikon DX cameras will have you believe you are getting more magnification using a full frame FX lens onto a DX camera but in fact what you are witnessing is nothing more than the middle of the lens being used by the smaller sensor so it looks like you are getting a 1.6x magnification when you are actually getting the same picture as a full frame camera but a cropped version.

You would swear P2 was indeed 2x bigger than P1 but in reality you are getting the same picture but the smaller sensor in the micro Four Thirds camera is only using the centre of the lens if I were to now crop P1 I could make it look the same as P2.

A 10mm lens on a 35mm camera will have a field of view 1.6 times greater than it does on a camera with an APS-C sensor.  The reason the Nikon DX lenses offer good value is because it will only give full sensor coverage on a APS-C sized sensor (F3 users beware!!!), so on a 35mm senor you would have a solid vignette around the outside of the image. Nikon do not adjust the focal length stated on the lens to suit different sensors, in the just the same way as Sony don’t. So at the end of the day a 10mm DX lens will have the same FOV as a 10mm lens from any other product line.

The crop factor is exactly the same. What happens is the smaller sensor CROPS you image and creates an image that would be the same as if you used that lens on a full frame but since you lose the edges of the picture it makes an image that appears to be magnified.. The magic word is cropping, the rest of the image spills over the sides. The image size on the sensor is the SAME for either sensor. This is why these new small sensor lenses dont do well on full frame since the lens design does not have to support the increased area of the large sensor.

We are all looking for the perfect fast lens to use with the AF101 and yesterday I thought the 17-55mm f2.8 was indeed that lens but alas we are just going to have to wait for the camera to arrive and do some hands on tests to determine a good all round f2.8 lens for the Panasonic AF101. I must thank a few of my readers for pointing me in the right direction.


Having been working in the video business since 1988 I have amassed a great amount of knowledge of both the kit and production values over the last 30 years.

5 thoughts on “The “CROP CONFUSION” of micro Four Thirds

  1. No.
    He does have a clue, it’s just that the concept is tricky to explain.

    Using a 35mm format lens on a smaller sensor gives a crop factor which is easily calculated if you know what you are doing.
    Of course the lens is not longer, but the angle of view is equivalent to a longer lens.
    However, seeing as everyone has “in 35mm terms” on the brain, it’s easier to describe the effect this way.

  2. Everyone seems to have 35mm stills frame on their brain… Those of us who have worked our entire lives with 35mm Cinema / academy frame won’t see a huge difference from the framing we are used to.

  3. You obviously know what you are talking about Phil, but I reckon this explanation makes it sound more confusing. I think the problem is the way you have used those two pictures. To be honest I still don’t understand what they are meant to represent. They are two different sensor sizes but you have represented them as the same size. If they were both shot with a 50mm lens the image would be the same size if you compared them relatively. You would just see more of the image on the larger sensor, because of its larger area. You also add in the different aspect ratio which confuses more. I think if you want to do comparisons you need to show the sensors the correct size relative to each other. I also think mentioning the fact Nikon or Sony don’t change the focal length printed on their lenses adds a confusion that shouldn’t be there. A 50mm lens is always a 50mm lens no matter what sensor you use it with, so they can’t print anything different on the lens otherwise they would be printing the wrong focal length on the lens. I know you know this, but just feel the explanation above might confuse people more than help them.

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