Mark Sturtevant wrote:
I have no opinion about the Opteka diopters, as I've not used them.
I neglected to mention that you would have less vignetting with diopters if you go with a crop sensor body. I had used the R150 on my olde 300mm lens, and it worked great. But the body was a crop sensor.
I purchased the Opteka screw-on Diopters to use on my 18-140MM at 75MM or great on my C-Crop Nikon D-7100. I am hopeful for a success and a nice in-the-field quick solution for swapping out. Thanks to all for your input !! More to report soon I hope.