First off, you really need to understand why you need it…and I will try and explain in English rather than overload you with technobabble (although there will, inevitably, be a bit!)
Let’s start with “Depth of field”, this basically refers to how much of the image you film/ photograph is in focus and how much is out of focus. A deep depth of field means almost everything is in focus in the frame, from far away to close up. A shallow depth of field is the opposite where a selective part of the frame is chosen to be in focus This is used to draw your attention to something in particular. It also makes the image more three dimensional, less flat. It’s a very useful tool in film-making and photography. Generally this is achievable with full size cameras by shooting wide open, getting far away from object as you can and zooming in to the bit you want in focus.
With the advent of smaller cameras came smaller image sensors. This causes problems with narrow depth of field. Basically the smaller the sensor the harder it is to get that shallow depth of field. Full size cameras normally have 2/3 inch sensors, cameras like the F350 and EX1/ EX3 have 1/2 inch sensors then cameras like the HVX200, Z1, Z7, Canon A1 etc have 1/3 inch sensors. Sony’s V1 camera has a 1/4 inch sensor, tiny!
So what is the solution? There is only so far back you can go and so much you can zoom in so that is where 35mm adaptors come in.
35mm film and digital cameras are capable of incredible shallow depth of field, way more than even 2/3” cameras as their equivalent sensors are so much bigger, so clever boffins created ways to give the same shallow DOF characteristics of these cameras. They did this by creating the Depth Of Field adaptor, otherwise known as the 35mm adaptor. Here is wikipedia explaining it in a more coherent way than me!
A DOF adapter looks to take the place of the camera’s sensor and use a focusing plate to display an image through the external lens attached to the adapter. Since this image is focused onto a translucent screen (similar to how one would look at a focused image through a system camera’s viewfinder), the camcorder is able to frame this intermediate screen and record it. The principle of one of these adapters is similar to pointing a video camera at a movie screen. The lens attached to the adapter now takes the job of the camcorder’s focusing and aperture mechanisms, as the camcorder’s only responsibility at this point is to record what is being projected onto the focusing screen (called backfocus).
Simple idea, but hard to get right. There are number of good adaptors out there, the M2, Brevis 35, SGPro and the Letus.
These use various focusing plates (or ground glass, called that as it is literally finely ground piece of glass). The all vibrate and spin, the reason they do this is to get rid of the pattern created by making it translucent. A vibrating one shakes the rectangular glass on 4 axis, the spinning one spins a circular one to do it.
The advantage of spinning versus vibrating is simple. If you get dust of the vibrating one you will see it, even if it vibrates, but the spinner hides dust. Also, generally spinners let you stop down more letting you get a deep depth of field and use higher shutter speeds before you start to see the glass pattern.
There are a number of downsides to these adaptors. They lose light, some more than others and require more glass on top of the lens you are already using. Some cameras with removable lenses can use adaptors with relay lenses instead of normal video lenses. These are fixed focal length lenses designed to be the perfect length to focus in on the ground glass. Making the camera shorter and improving low light sensitivity. As long as the glass is fast enough!
Good lenses cost money. Prime lenses (fixed focal length) are normally faster than zooms, but are inconvenient due to the inability to zoom (although you can zoom into the ground glass more with some adaptors to change the frame size). Zooms are convenient and are generally way slower. There are constant f2.8 aperture zooms available but they are expensive. Also compare this to the speeds of most of my primes, which are f1.4. Cheap zooms often start at f3.5 and go to f5.6 on the long end. These are not good enough for 35mm adaptors. For more information on lenses please visit my lenses page on my forum…
Which one is best? Well they all do the same job with varying degrees of success. I own them all except the SGPro and the one I use all the time is the quite wonderful Letus Ultimate which is my work shows really deserves it’s name, although people are getting amazing success with the others…
One thing you need to be aware of is a DOF adaptor will flip the image upside down, this is because a lens always projects an image this way round. It’s physics! Now the camera lens is flipped right way round by the camera, but by putting another piece of glass in front of it means your image will be upside down both in camera and recording. The solution is either have a camera that can invert the image, basically the JVC HD200 and 250 or get a flip attachment for your adaptor. The Letus only comes in one form and that is with a built in flip. All the others are modular and I cannot recommend enough you getting one for your adaptor.
When it comes to critical focus this is when things get difficult. With a shallow DOF focus is hyper critical and every cameras bar one has a sub par LCD for focusing. Only the EX1 and EX3 have usable LCD, the other cameras really all need external monitors.
With cameras like the EX3, Canon XL and JVC HD which have removable lenses, sticking a 35mm lens onto body will not affect the DOF at all as the sensor hasn’t changed size, all you are doing is projecting a very large image onto a very small sensor which means most of the image is lost and lens’ true length is multiplied 7 or 8 times. so a 100mm lens becomes a 700mm lens. Great for wildlife, crap for anything else. You need that 35mm sensor or a fake 35mm sensor like you get in these adaptors.
Follow focuses are essential if you plan to do rack focus mid shot, touching the lens barrel will cause wobble. Redrock and Zacuto both maker terrific follow focuses and I thoroughly recommend them both.
Don’t forget to watch the Letus Extreme demo video to really see the difference in action!
Also don’t forget the have the ability to get a shallow depth of field doesn’t mean EVERYTHING should be crazy shallow. Use that to enhance your storytelling, also don’t shy away from big wide, sure most will be in focus but it’s all about getting that lovely filmic, organic look and that is not to do with shallow DOF.
There is one main thing I forgot to mention about 35mm adaptors. Getting one will not make you shoot beautiful pictures. You can shoot beautiful pictures without one very easily. It’s how you use your camera that is more important. If you are not getting great results without one don’t think this is the answer to all your problems. It most likely isn’t. They are expensive when you buy fast glass, they are hard to use and get consistently good results from, but when you do they are mind blowing, but it takes a lot of time and practice. See how good you can get without one first, then when your normal pics are wonderful, jump in. You won’t regret it!
There never has been a more exciting time in Indie film making than right now. The 35mm market is as Will Ferrell’s Mugatu might say “SO hot right now”. Letus have the Ultimate out, an amazing attack on the pro market dominated by P&S and Movietube, capable of incredible images. Cinevate have all sorts of innovations with their Brevis and SGPro have announced the astonishingly good looking Blade. Redrock meanwhile are concentrating on superb accessories but who know what is around the corner!? All I know is the more these guys work harder the better it is for us.
Now if you have any other topics you think I should cover in the FAQ section please let me know.