Daa 1.8 FE has no OSS, therefore cheaper 

One is for full format and the other for APS-C, whereby full format can also be operated on APS-C. 

Hi, in wide-angle lens if on the most darkness stop , suggesting focus length is 20-24 for avoiding vignetting. 

1. Adapting APS-frame lens to full-frame camera, it may generate vignetting, some cameras could correct it by adjust APSC, please contact us and provide your lens&camera model to check the way to correct it.
2. Adapting full-frame lens to APS-frame camera (i.e: large format to medium format, medium format to 35mm, 35mm to micro 4/3) provides excellent edge-to-edge sharpness. The smaller image field helps minimize the effects of lens distortion and aberration by using the 'sweet spot' or center of the larger lens image circle. and it will magnify the focal length by 1.6 on Canon, 1.5 on Nikon and Sony，2.0 on M4/3 camera.

 

The size is important because they are made to be used with a single swipe The sensor is not the issue it is the oils in the lens chamber and if you touch that with the swab you have ruined it and can mess your sensor up badly... if you use a smaller size one it can work but I would want a sensor loupe to see what I am cleaning up and also to make sure my swab is clean and I am not taking particles that I picked up on the 1st swipe and running that into another part of my sensor... The sensor is the eyes of your camera... Hope this is helpful.