Any camera with interchangeable backs would already have dark slides on the backs for sure, but in principle lens changes could be quicker if they didn't have to be used. I'm curious about Hasselblads in this regard. I have run aground on that reef several times. You can just dismount the lens any time you want to, including when you have forgotten to insert the dark slide :-D. On my Mamiya Universal, however, there is no such interlock. And as you said, it's designed so that you can't take the lens off before you deploy the film cover. The internal cover had to be deployed before the bail that clamps the lens board could be released. This was sometimes handled via a secondary 'shutter', really just a blanking panel, which covered the film gate when lenses were changed. It ruins not only the frame in the film gate, but the one after it, too.) (I have one such camera from the 1960s and have exposed the film by changing lenses without the dark slide inserted. User don't change lenses while shooting, but having the ability to configure the same camera for different uses, or gain access to the lenses in a particular system, has some value.Д«ut just for the OP's information, if he or she ever buys an interchangeable-lens camera that uses in-lens leaf shutters some of those, especially older ones, can indeed expose the film when you change lenses, if you don't do the procedure right. There are some industrial and scientific use cases where a similar kind of calculus applies. The lens interchangeability is still useful, however, because it allows the same camera to be configured for different kinds of shots before any individual dive (wide vistas of a coral reef vs. There are interchangeable-lens underwater cameras, and, of course, you can't change their lenses while shooting with them underwater. It ruins not only the frame in the film gate, but the one after it, too.)ДЄgain, true for all normal and practical purposes, but there are some weird exceptions. But just for the OP's information, if he or she ever buys an interchangeable-lens camera that uses in-lens leaf shutters some of those, especially older ones, can indeed expose the film when you change lenses, if you don't do the procedure right. You're quite right, of course, for the OP's cameras. Have a look through an unmounted lens and see what you see, you might experiment to see if you can find the lever which actuate the diaphragm.ДЄnd further, an interchangeable lens camera wouldn't be very useful if you couldn't interchange the lenses in the middle of shooting.ДЄlso, it's not the lens which is stopping light getting to the film, the lens is designed to let light in, so whether you have it attached or not, is not what's stopping the film getting exposed. You can usually see that better from the back, when there's no film in the camera.ДЄlso, it's not the lens which is stopping light getting to the film, the lens is designed to let light in, so whether you have it attached or not, is not what's stopping the film getting exposed. When you wind the film on, you'll see (if the mirror isn't in the way) both curtains moving back, while tightly closed against each other, and not letting in light. The curtains go one opens, and then the second closes. You should see the mirror flapping up and down, and the shutter curtains opening and closing. You might do well to take the lens off and look at what's happening behind the lens when you shoot a frame. To expand on that, the shutter is closed, so no light gets to the film.

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