I use a lot of different lenses on my large sensor video cameras. Over the years I’ve collected quite a collection of Nikon and Canon mount lenses. I like Nikon mount lenses because they still have an iris that can be controlled manually. I don’t like Nikon lenses because most of them focus back-to-front compared to broadcast, PL and Canon lenses. The exception to this is Sigma lenses. The vast majority of Sigma lenses with Nikon mounts focus the right way – anti clockwise for infinity. If you go back just a few years you’ll find a lot of Sigma, Nikon mount lenses that focus the right way and have a manual iris ring. These are a good choice for use on video cameras. You don’t need any fancy adapters with electronics or extra mechanical devices to use these lenses and you know exactly what your aperture is.
But…. Canon lenses have some advantages too. First is the massive range of lenses out there. Then there is the ability to have working optical image stabilisation if you have an electronic mount and the possibility to remotely control the iris and focus. The down side is you need some kind of electronic mount adapter to make most of them work. But as I do own a couple of Canon DSLR’s it is useful to have a few Canon lenses.
So for my F3, initially I used Nikon lenses. Then along came the FS100 and FS700 cameras plus the Metabones adapter for Canon, so I got some Canon lenses. Then came the MTF Effect control box for Canon lenses on the F5 and now I have my micro Canon controller with integrated speed booster for the F5 and F55. This all came to a head when on an overseas shoot I got out one of my favourite lenses to put on my F5, but, the lens was a Nikon lens and I only had my Canon mounts (shame on me for not taking both mounts). Continually swapping mounts is a pain. So I decided to permanently fit all of my Nikon lenses with Nikon to Canon adapters and then only use Canon mounts on the cameras. You can even get Nikon to Canon adapters that will control the manual iris pin on a lens with no iris ring.
Now a problem with a lot of these adapters is that they are a little bit too thin. This is done to guarantee that the lens will reach infinity focus. If the adapter is too thick you won’t be able to focus on distant objects. This means that the focus marks on the lens and the distances your focussing at don’t line up. Typically you’ll be focussed on something 3m/9ft away but the lens markings will be at 1m/3ft. It can mean that the lens won’t focus on close objects when really it should. If your using a zoom lens this will also mean that as you zoom in and out you will see much bigger focus swings than you should. When the lens flange back (distance from the back of the lens to the sensor) is correctly set any focus shifts will be minimised. If the flange back distance is wrong then the focus shifts can be huge.
So what’s the answer? Well it’s actually quite simple and easy. All you need to do is to split the front and rear halves of the adapter and insert a thin shim or spacer. Most of the lower cost adapters are made from two parts. Removing 4 small screws allows you to separate the two halves. Make sure you don’t loose the little locking tab and it’s tiny spring!
Split the two halves apart. Then use the smaller inner part as a template for a thin card spacer that will go in between the two parts when you put the adapter back together. The thickness of the card you need will depend on the specific adapter you have, but in general I have found card that is about the same thickness as a typical business card or cereal packet to work well. I use a scalpel to cut around the smaller part of the adapter. Note that you will also need to cut a small slot in the card ring to allow for the locking tab. Also note that when you look at the face of the larger half of the adapter you will see a small lip or ridge that the smaller part sits in. Your spacer needs to fit just inside this lip/ridge.
With the spacer in place offer up the two halves of the adapter. Then use a fine scalpel to “drill” out the screw holes in the card, a fine drill bit would also work. Then screw the adapter back together. Don’t forget to put the locking tab back in place before you screw the two halves together.
Before putting the adapter on the lens use a very fine blade screw driver to gently prise apart the lens locating tabs indicated in the picture. This will ensure the adapter is a nice tight fit on the lens. Finally attach the adapter to the lens and then on to your Canon mount and check that you can still reach infinity focus. It might be right at the end of the lenses focus travel, but hopefully it will line up with the infinity focus mark on the lens. If you can’t reach infinity focus then your shim is too thick. If Infinity focus is short of your focus mark then your shim is not thick enough. It’s worth getting this right, especially on zoom lenses as you’ll get much better focus tracking from infinity to close up. Make up one adapter for each lens and keep the adapters on the lenses. You’ll also need to get some Canon end caps to protect you now Canon mount lenses.