Several years ago, I purchased the Canon EOS 60Da to be used mainly for Astrophotography. I have several Canon lenses; two are EFS types; 55-250mm & 18-135mm and neither have manual f/stop settings on the lens. The only other lens I have is a Canon 50mm that is rated f/1.8.
I am assuming that the camera can set the f/stop for the two EFS zoom lenses using the camera’s menu, which I have never done. I was using the camera most of the time attached to my telescope and the telescope was the camera lens. That way no f/stop setting was needed since I could just use the shutter speed for exposure and focus was using the telescope.
One question: Can I select the f/stop for the EFS lens using the camera and still achieve focus for astrophotography? The reason I ask is, I have a 70-300mm Sigma zoom lens that I was hoping to use on a ZWO adapter for the lens where a ZWO deep sky cooled camera could be used. I found out that the old Sigma lens (that was on a Nikon D70 SLR film camera) f/stop settings will not focus unless the f/stop is set to f/22. I tried different zoom settings and different f/stop settings and nothing would focus unless f/22 was used on that lens. Oh, I tried using an adapter to attach the Sigma lens to my Canon camera, but it produced elongated stars at the perimeter of the picture.
Second question: If I get a ZWO adapter for the Canon EFS lenses, will I have the same issue on f/stop setting or not even have the ability to set the f/stop?
