Using Lenses Designed for Camera With Different Sensor Size

PetaPixel has an interesting post on using a lens on one camera when it was designed to be used on one that had a sensor that was a different size (or a Leica).

The article was originally posted at Lens Rentals.

This is the second time Lens Rentals has be the subject of one of my blog posts.  The first was when they got a new, custom-made lens testing/calibrating machine. 


The article is a bit technical in parts, especially when it comes to the graphs used.  To me, those are just a bunch of pretty lines.


I'll try and boil it down to what a photographer needs to know.

First, some digital cameras have a sensor stack located in front of the senor.  This is a piece of optical glass that varies in thickness depending on camera manufacturer and the size of the sensor.  Micro 4/3 cameras tend to have sensor stacks that are thicker than those in APS-C or full frame cameras.  The manufacturer also matters, Leica for example uses thinner sensor stacks than other manufacturers.

The sensor stack does serve a purpose: it filters infrared and ultraviolet light, preventing it from reaching the sensor.  These wavelengths can have an impact on an image's colors if there are not filtered. 


This piece of glass needs to be taken into account when designing lenses for the camera in order to ensure that light hits the sensor correctly. 


What this means: using a lens designed with a camera that uses a sensor stack with a particular thickness on a camera that uses a stack with a different thickness will result in light not hitting the sensor in the way designed by the manufacturer.

In other words, using a lens designed for a a full frame camera on an APS-C or micro 4/3 (or vice versa) camera will result in the lens not working as intended.  It will still be useable, but the image quality may not be as good as if used with the correct sized sensor.


As a side note, removing the sensor stack is a hack that will enable a camera to take IR images.  This can have an impact on the camera's ability to focus properly in AF mode.