Teleconverters v Pixels

A key advantage of smaller sensors like APS-C and Micro FourThirds is that of reach – specifically being able to work at long distances with small lenses. Sports photographers working in large arenas may favour APS-C over 35mm sensors for exactly this reason. Of course, larger sensors offer better low-light performance – specifically lower noise. How equivalent then is a smaller sensor to a teleconverter?

Let’s assume for a moment that you have a Canon EF 200mm lens mountable on a number of different camera bodies, and you require an image of at least 6000 pixels in width. Your M43 body has a 2x crop; your Canon RF body 1.6x and your GFX 0.79x. You might think of the 200mm becoming a 400mm lens on the M43 camera, but the G9 II has an extra 5MP to play with – which enables you more easily to reach your 6000 pixel target. But what about the difference in image ratio? And what if you mount that lens on the GFX? Assuming the image circle covers the sensor, the focal length is much reduced, but the large file size allows you to crop in more heavily – also effectively using the big sensor as a teleconverter.

The following table shots the ‘teleconversion effect’ of different sensors on a lens with a 200mm focal length. The shot-grabbing potential of the lens is unchanged (ie, the shutter speed remains identical), but the depth of field will be different on each sensor, and there is a global image-noise penalty when using a smaller part of a larger sensor (ie, cropping). 

  Pixel Pitch Equivalent Focal Length  Pixel Width Teleconverter 
effect of sensor (HFoV)
Micro FourThirds 20MP   400mm 5184px 343mm
Micro FourThirds 25MP   400mm 5776px 382mm
M43 Pixel-Shifted (20MP)   400mm 10368px 685mm
M43 Pixel-Shifted (25MP)   400mm


APS-C 24MP (1.6x)   320mm 6048px 320mm
APS-C 33MP (1.6x)   320mm 6960px 368mm
Full Frame 24MP   200mm 6048px 200mm
Full Frame 42MP   200mm 7952px 263mm
Full Frame 61MP   200mm 9504px 314mm
Fuji GFX 100MP   158mm 11648px 304mm
Fuji GFX (Pixel Shifted)   158mm 23269px 608mm

The difference between a 24mm full frame camera and a 24mm APS-C camera is a predictable 1.6x increase in reach, at the expense of some global image noise: the denser pixel pitch of the small sensor typically results in higher per-pixel noise.

However, relative to a 24MP capture using a 200mm lens, simply using a higher resolution camera behaves like a teleconverter: the jump from a 24MP to a 61MP camera is like using a 1.6x teleconverter, if cropped to 6048px. And in the case of cameras with pixel-shift – temporarily setting aside considerable technical issues obtaining comparably sharp, artefact-free images to make a like-for-like comparison with a single capture – the effective reach is multiplied hugely.

If you’re looking to shoot relatively static subjects (stars, buildings, landscapes, etc) and you’re shopping for a monster lens, you might want to look instead at a different camera, because pixels are reach.

Granted, the advantages of an f2.8 lens are somewhat reduced if you have to gather and combine four, six, eight or even sixteen captures, but on the other hand what teleconverter can turn a 200mm lens into a 764mm one without optical penalties?

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