Solution to Controlling Aperture on an AF SLR Lens - Pertinent to 35mm Adaptor owners
 

This post provides a solution to use your Canon EF Auto focus lenses with the Letus, while having control of the aperture setting.

When using a 35mm adaptor such as the Letus one typically needs manual focus lenses so as to have control over the aperture, primarily stopping down, since the lens is normally wide open.

Now that the Letus supports the Canon EF mount I can use my Canon SLR lenses with the Letus. However, since all my lenses are auto focus fast prime lenses I was concerned with a very narrow DOF if I were to use these lenses, and so I was playing with the Depth Of Field Preview button on my Canon 40D trying to figure out if I could build an electronic circuit to do what it does.

Here is what I found, if you set the aperture to the desired number and press the DOF preview button and while keeping it pressed dismount the lens the aperture remains stopped down!

So essentially, you can use your Canon EF SLR lenses with the Letus and still have control over the aperture provided your DSLR has a DOF preview button!

Disclaimer: Use at your own risk.

Shiv

Hi Shiv. Sounds like a good workaround if it is not going to damage anything. Does this work if you switch off the camera before dismounting the lens?

Richard

No unfortunately.

FWIW, I've dismounted and remounted the lens in this fashion over a hundered times, without turning off the camera in between. Everything works just fine. But of course once again, use at your own risk :)

that is why the nikon mounts are popular. You don't need to keep taking the lens out and fitting to a SLR to change the aperture. Hence carry a SLR camera lesser and also keeping the dust out.

David,

Sure, but what if you have a huge investment in Canon lenses? Further, typically, it's not like (for most shoots anyway) you're constantly changing the f stop.

For example, I've got a few f/1.2 and f/1.4 lenses and the DOF is very shallow (about an inch) at these f stops rendering these great lenses virtually impossible to use for normal video stuff. So one could stop down the lenses before getting to location. For me at least, these lenses are in the same bag as my SLR so I'll have the bag with me anyway. Plus I need my SLR for my shoots too!

It's a solution for those of us who need it.

Shiv.

I will add to this, for years I have changed lenses with out turning the power off, I have done this with 10D, 20D, 5D and the 1D Mk III and have never had a problem with lens, body or image due to this.

Thanks for coming up with a solution.

Denny