Let's talk about Lenses!

[_Paz_]

There are several semi-pro camcorders out or coming out that can use interchangeable lenses via assorted mount adapters. Some of these adapters pass along some info and allow for things like auto focus on some of the lenses in a brand line, but not all. Sometimes almost everything is passed along except auto focus.

There are adapters for lenses I know little to nothing about, like 16mm, super 16, (may be the same thing), MFL (micro four thirds), EF, EF-s, PL, APS-C, E, F, CINE, and maybe more.

I know my Canon 7D has a smaller sensor than a 'full frame' camera and can use APS-C lenses, which give a more deeply zoomed in appearance based on the zoom designation. But I think it can also use lenses designed for full frame cameras. I expect it would still have a different 'apparent' size.

I don't think full frame Canon EDIT:[not -lenses] CAMERAS can use the APS-C lenses because they are designed for the smaller sensor. [Edit again - not that it would physically harm the camera but that the image would be a circle in the center of a black hole.]

It seems I remember reading about a movie that was filmed on 16mm film that could not be made into really high quality Hi definition.

Are most of these distinctions based on the camera body?

Does EF stand for Electronic Focus? If so, what does EF-s stand for?

I'm particularly curious about the Cine lenses. Are they especially good for making movies?

thanks,

Paz

[Bob]

It's complicated. There are really three factors at work. The type of mount, the size of the sensor (or film), and the design of the lens.

The mount is used to attach the lens to the body and provide electrical and, in some cases, mechanical connections to support lens functioning. In general, mounts are proprietary and different manufacturers use different mounting systems. In addition, it's not uncommon for a manufacturer to use different mounts for different cameras. A, E, F, and SL are all examples of mounting systems. A and E are from Sony, F is from Nikon, and SL is from Arri. In order to use a given lens with a given body, the two need to use the same mounting system and have compatible functionality.

In some cases, you can use an adaptor to mount a lens using one mounting system on a camera body using a different system. But, it's tricky and seldom recommended. Part of the problem is that the lens is designed to mount at a specific distance from the focal plane of the camera. But, different cameras use a different flange to focal plane distance. The Nikon F mount, for example, uses a 46.5mm distance while a Canon ES mount uses 44 mm. In this case, to use the Nikon lens on the Canon, you would need an adaptor that provides that missing 2.5mm thickness. On the other hand, you couldn't use the Canon lens on the Nikon because you would have to cut off 2.5mm. Some adaptors include an optical element to compensate somewhat, but introducing another optical element will greatly increase the cost and will introduce image degradation. Another problem is that it's unlikely that the electrical functionality will be maintained. In effect, you would need to use it as a fully manual lens.

I had a glitch and had to retype everything. I think I'm going to break this up into multiple posts just to be safe.

[Bob]

Part 2:

Let's consider the lens for a moment. The image projected by a lens onto the sensor is sharpest in the center and become less sharp as you move away from the center. At the same time, the light intensity falls off similarly introducing vignetting. Well designed lenses attempt to cover the area of the camera sensor without becoming either too soft or having too much vignetting. The larger the sensor the harder this is to do and the more expensive it becomes to design and manufacture the lens.

In still cameras, a camera with a sensor the same size as a frame of 35mm film (24mm x 36mm) is called a full frame or FX camera. A lens designed to be used with this kind of camera is called a full frame or FX lens.

APS-C is another popular sensor size. It is approximately 2/3rds the size of a full frame sensor. Because the area is smaller than full frame, the lens is easier to design and manufacture and will cost less. Both Canon and Nikon produce cameras with this size sensor using the same mounting system as their full frame cameras. This allows you to use FX lenses on either camera. If you own both a APS-C and a DX camera, you don't need to buy two sets of lenses. However, the same is not true of the APS-C lenses. Because they are designed to be used with a smaller sensor, they generally won't be satisfactory on a full frame camera. APS-C and DX are essentially the same thing. Canon uses the APS-C designation while Nikon prefers DX.

You can use a FX lens on a full frame or APS-C camera, but the images captured will not be identical. Because the APS-C sensor is smaller, it sees a smaller angle of view than a FX sensor would see with the same focal length lens. Compared to the FX image, it's like you cropped off the outer edges of the photo. Another way of thinking of this is the APS-C photo looks like it was taken with a longer focal length lens. Accordingly, the magnitude of this effect is referred to as either a crop factor or a focal length multiplier. If you multiply the focal length of a lens used on an APS-C camera by the crop factor of the camera sensor, you will get the focal length of a lens that when used on the full frame camera would result in the same size image. Canon and Nikon don't use exactly the same size sensor. Canon's sensor is a tiny bit smaller and has a crop factor of 1.6. Nikon's is a tiny bit larger and has a crop factor of 1.5. For example: On a full frame 35mm camera, a 50mm lens is considered a normal lens. Use that lens on a Canon APS-C camera and you would get about the same angle of view as using an 80mm lens on a FX camera (1.6 x 50). On a Nikon DX camera that would be equivalent to a 75mm lens. In other words, it would look like a mild telephoto or portrait lens. You would need about a 35mm lens with the APS-C sensor to match the angle of view of the 50mm normal lens on a full frame sensor.

[Bob]

Part 3:

With video and cinema cameras, the nominal sensor size relates back to the early days of Videocon tubes. The size of a video tube was the outside diameter of the tube that could hold the sensor expressed in inches. The actual sensitive area was about 2/3 of that. Video tubes are obsolete, but sensors for video are still expressed as the equivalent size of a camera tube. Known as the Optical Format, this size is the diagonal length of the sensor multiplied by 3/2 and usually expressed as fractional inches. In video cameras using the four thirds system, for example, the area of the sensor is approximately the same as the sensitive area of a 4/3 inch video tube.

Cine lenses are basically lenses designed for professional cinema use. These are usually made to fit an Arri PL mount as most professional cinema camera makers have standardized on that. However, Panasonic is also a big player in this arena and makes cine lenses using their own proprietary mount. Cine lenses are built tough to withstand the rigors of producing professional cinema. They also need to be built to a high degree of precision and uniformity. These lenses are very expensive and it's not unusually for a production company to rent them rather than buy. If they have to go back months later and shoot additional footage or redo a scene, the footage has to match even if it's taken with a completely different lens. They are also consistent with regards to operation, range of aperture stops, follow focus, etc..

Almost forgot. EF does stand for Electronic Focus. EF-s is also Electronic Focus, but the "s" stands for "Small image circle" meaning it was designed for the smaller APS-C sensor and cannot be used on full frame cameras. Some say it also means "short back focus" meaning that it's designed to project further into the camera body. But, not all EF-s lenses use short back focus.

[AllieB]

Thank you Bob. A very clear and understandable text.

[Ron Hunter]

Wow Bob, thanks for the super helpful info. You never cease to amaze me!

[_Paz_]

Thanks, Bob. You are indeed amazing. One of your gifts is the ability to take an 'it's complicated' subject and explain it so well.



I've been looking specifically at video cameras that can use interchangeable lenses. Found some I really like - except it seems that Continuous Auto Focus goes out the window as soon as an interchangeable lens is added.

[Chuck Engels]

We need to keep that in our Smiley collection for daily use, Paz can we borrow that please????

[Bob]

Which video cameras are you looking at?

[_Paz_]

We need to keep that in our Smiley collection for daily use, Paz can we borrow that please????

Absolutely, Chuck! How can I get it to you? Can you simply right click on it and add it to the MuviPix smilies?

[Chuck Engels]

Yes, Ron can take care of it just wanted your approval first
Thanks !!

[_Paz_]

My pleasure, Chuck.

One thing's for sure... Bob has saved my bacon many times! And I definitely appreciate it!

[_Paz_]

Which video cameras are you looking at?

I've looked at so many I can't remember them all, Bob. I'm still looking. Have not found a perfect one yet.

Many of them use Metabones adapters to attach other brands of lenses.

I liked a lot of things about the Sony NEX -FS-700, but it is huge and weighs in at 10 pounds.

http://www.bhphotovideo.com/c/product/1 ... _35mm.html


I originally looked at the JVC brand to see if they had a camcorder with higher image quality than mine (a cheap one) that would offer the ability to touch the screen to select an object to focus on, set exposure for, and track across the screen if it moves. So far I have not found any pro or semi pro camcorder that can do this.

Even in the movies with the highest level pro cameras, it seems there is a job called the 'focus puller' and that means a person who is constantly changing the focus as the characters move around.

Anyway, here's the JVC I like... especially because it is small at around 3.5 pounds (without lens) and because it has a way to sort of zoom into the image on the view screen to select focus with peaking, and because the photographer doesn't have to go through lots of menus to make changes to the camera:

http://www.bhphotovideo.com/c/search?Nt ... yes&sts=ps

This one does not have lenses. It uses adapters to attach lenses. I don't see it listed now, but earlier B&H offered the body with the choice of a Canon to M4/3 Metabones adapter, or it seems a Nikon G or Nikon6? adapter, or either of two Rokinon Cine lenses.

I could see using the Canon glass I'm already invested in with this one, and perhaps the Schneider lens that came with my view camera, or my first 35mm lenses, Olympus- Zuiko. As I'm sure you know, there are certain highly respected lenses out there from many brands, such as the Canon 70 - 200 'stove pipe.' It looks like a great idea to have a body that could accept anything and be able to carefully add (probably used, but good quality) lenses over time.


Now that I've seen the footage of the hummers from the Panasonic Lumix GH4 (posted in the Humdinger thread, here), I'm agape. That photographer says he was using the GH4 with a 400mm macro lens, a Sigma. So I guess the GH4, which I have not looked into yet, can use something like the Metabones adapters to use different lenses.

I probably said it wrong - I know there are some camcorders, video DSLR cameras that can do autofocus while videoing, like Canon's 70D. Or D70. But I believe they are all using their own brand of lenses, and from what I've read, the focusing isn't always very reliable.

I'm just surprised that 'Hollywood' movie cameras don't auto focus like my little camcorders do. Perhaps it is something about the Cine lenses, or maybe the bodies they use haven't been given the newer technology because 'they've always done it that way.'

[Chris B]

I found an article on why autofocus (especially on dslr cameras) is bad in cinema cameras. http://www.theblackandblue.com/2012/05/ ... ed-epic-5/

From what I understand most "proper" movie shots are fixed focus or have a limited range. I once saw it said "If you don't know what you're focussing on why are you filming?". So the inclination is to compose and focus the shot with the right depth of field, lighting etc. and then start filming. Much easier when you have a bunch of actors to direct. It's the same school of thought that tells you to tape over the zoom button as well.

I see you have a reply to your question on his video. He says the lens was manual focus and exposure and because it's a fixed focal length would have had to reposition to the right distance for every shot. Probably noted where birds tended to settle - set up the camera and waited....

[_Paz_]

"If you don't know what you're focusing on why are you filming?"

Ha! Because it is an adventure! As Forrest's mama said, "You never know what you're going to get!"

Thanks for that link. Now I understand. The movie companies' needs are simply different. And I can see why they'd be really aggravated with still lenses on their movie cameras.

I'm afraid I can't afford to hire a focus puller. I'd have a hard time putting him into my pocket and carrying him around anyway. I have to figure out a way to be able to do it myself - and I need as much technical help as I can possibly get from the camera and lenses.