I have a question about using my ASI1600MM, or any other non-DSLR camera, with some of my Canon lenses. When using the camera with an automatic lens, one where you have to adjust the aperture in camera, does the aperture default to the widest value? I.e. I have a Sigma Art 18-35 f/1.8 so would the aperture always be f/1.8 when used with my ASI? I also have a manual Samyang 135mm where you can adjust the aperture on the lens itself but I just want sure how it worked with a non-manual lens.
CCD/CMOS with a DSLR lens
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Yes. For automatic lens, here is one trick to adjust the aperture. First you need a DSLR camera, then connect your DSLR camera and your lens. Next, adjust the aperture and push the "depth of field preview" button and remove the lens at the same time. After that, it will be OK! 
Liu Zhuokai:
Yes. For automatic lens, here is one trick to adjust the aperture. First you need a DSLR camera, then connect your DSLR camera and your lens. Next, adjust the aperture and push the "depth of field preview" button and remove the lens at the same time. After that, it will be OK! 8)
Does this mean that a Canon lens would be at the last aperture used on the Canon camera?
i did not know this I thought they would go wide open, thanks
BJ Jones:
Does this mean that a Canon lens would be at the last aperture used on the Canon camera?i did not know this I thought they would go wide open, thanks
Yes, if you use the depth of field button trick that Liu mentioned the Canon lens will stay locked at that aperture. Otherwise it will revert to wide open once removed from the Canon camera. I have used this trick many times with my Canon glass, and can confirm that it does work. Some people still prefer to use aperture masks in front of the glass because they don't like the diffraction pattern from the aperture blades.
One other thing, I've heard online that this trick does NOT work for Nikon.
Cheers, Nico
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Thanks everyone!
Another method widely used is adaptors meant for reducing thread size. Then you don't see diffraction artifacts from the aperture blades..