What type of lens would I need for this?

[harmonica44]

I want a deep focus lens for my Canon T2i. But it seems all lenses for it are shallow. I would want to get the a lens that can be snapped onto it with an adapter, I am guessing, but the camera stores were not of much help for adapters. I looked it up on the net, but not finding anything that can go on the T2i with an adapter for it specifically. Is there any?

[PaulGriffith]

1. Why an adapter?

2. There's no such thing a a "deep focus lens." Many have explained it on here, one more time:

• The wider the lens, the more deep the DOF.

• The slower you run the lens (high aperture), the deeper the DOF.

• The smaller the sensor, the deeper the DOF.

Now, the sensor size is the one thing you can't really change on your camera. So, get a wide lens. If you're buying then the Rokinon 14mm 2.8 is pretty killer. If not, your 17mm kit lens is pretty stinking wide.

Second, close the aperture. Try running at 17mm at f/8 or go nuts and do f/20 (disclaimer: for best image try not to go past f/8 on most lenses. But for the sake of this, try it). At 17mm f/20 absolutely everything more than a couple of feet in front of the lens will be in focus.

If that is too dark, try setting your ISO higher. If you ISO won't go higher or is making too much noise, light the *%#! out of the scene. Find some 2K's or something.

[harmonica44]

Okay thanks, but, I was on set and the camera man was able to follow move the camera back and forth towards the actor, about literally 20 feet back, and forth, without having to focus pull. He just kept pushing back and forth, take after take. I asked him and he said he had a lens that could do the job. Plus I thought I was told before that certain video camera lenses have deeper, unless I misunderstood. I also acted in another shoot, and the guy was handholding a video camera, and moving it all around without focus pulling. I saw the end result and it managed to have deep focus the whole time.

Okay so it's all about aperture in all cases then, I was told by some there were lenses that could help with that. Thanks.

[Ernest Worthing]

Originally Posted by PaulGriffith

• The wider the lens, the more deep the DOF.

• The slower you run the lens (high aperture), the deeper the DOF.

• The smaller the sensor, the deeper the DOF.

^ This and:

You can utilize camera to subject to background distances to get everything in focus as well.

[that1guyy]

It seems you want everything in focus and not a shallow depth of field? If so, like Paul said, just close your aperture (the higher the number means the smaller the hole).

[jax_rox]

Cameras with smaller sensors - ie Consumer, Prosumer and Broadcast cameras that have 1/5", 1/4", 1/3" and even 2/3" sensors are going to have deeper DOF than a S35 sensor. Period. A wider lens will get you deeper DOF, as will closing down your aperture. Note that the more you close down the aperture, the more light you need to add to expose it properly.

Also note that most (if not all) prosumer and consumer cameras have autofocus, so you're probably seeing the combination of a smaller sensor allowing deeper depth of field, and auto focus allowing for no need to pull focus constantly.

[TheArtist]

By deep focus do you mean everything in focus ?

[harmonica44]

Originally Posted by jax_rox

Cameras with smaller sensors - ie Consumer, Prosumer and Broadcast cameras that have 1/5", 1/4", 1/3" and even 2/3" sensors are going to have deeper DOF than a S35 sensor. Period. A wider lens will get you deeper DOF, as will closing down your aperture. Note that the more you close down the aperture, the more light you need to add to expose it properly.

Also note that most (if not all) prosumer and consumer cameras have autofocus, so you're probably seeing the combination of a smaller sensor allowing deeper depth of field, and auto focus allowing for no need to pull focus constantly.

Oh okay, but I was told that with autofocus you constantly see the camera go in and out of focus, as it keeps adjusting. I can't see it though, so maybe autofocus just isn't noticeable to a lot of people.

Originally Posted by TheArtist

By deep focus do you mean everything in focus ?

Yes.

I read that a lot of filmmakers don't like to work with deep focus, because it means closing the aperture, and therefore, having to use a lot more light. But if this is the case then why don't they just use autofocus instead?

[jax_rox]

Originally Posted by harmonica44

Oh okay, but I was told that with autofocus you constantly see the camera go in and out of focus, as it keeps adjusting. I can't see it though, so maybe autofocus just isn't noticeable to a lot of people.

This is true of DSLRs and any interchangeable lens digital camera that features auto focus. This is because to autofocus instantly, the camera sends out a beam to find what should be in focus, and then sets the focus ring/focal point to that distance. This works on fixed lens cameras, as the lenses essentially talk to the camera and tell them where the focus ring should be set for what distance. Most interchangeable lenses don't 'talk' to the camera in that way, and most cameras that have interchangeable lenses don't have autofocus features anyway.
The reason you see DSLRs and the like go in and out of focus is because the camera is essentially 'guessing' where the focus ring should be set, assessing the picture to check the focus and then taking another guess to get closer to the mark. Also, those cameras with fixed lenses that do have pretty instant autofocus often go in and out of focus because the camera doesn't know whta it's meant to be focussing on. When you have two things in frame that seem to be of equal importance but are two different distances away, the camera doesn't know which one it should be focussing on, and so it moves between the two.

I read that a lot of filmmakers don't like to work with deep focus, because it means closing the aperture, and therefore, having to use a lot more light. But if this is the case then why don't they just use autofocus instead?

Autofocus is not equivalent to deep focus. Opening the aperture will still give you shallow depth of field whether autofocus is turned on or off. To get deep focus, you need to close the aperture and use a wider lens. That's the only way. A smaller sensor will also give you deeper depth of field, as the smaller sensor essentially acts as a 'widener' to a lens. Smaller sensors and closed apertures need lots of light to expose properly.

Also, filmmakers don't use autofocus because a camera isn't as good at making decisions as a human. Aside from the fact that you effectively can't pull focus if it's set on auto, the moment we take it off auto, we can get a lot more control about what we want in focus.

[TheArtist]

I've got ONE WORD for you and I'm suprised noone mentionned it before.

HYPERFOCAL.

You can achieve deep focus with any lens and with any aperture as long as you focus on the hyperfocal.

[knightly]

Who is this camera friend... he either doesn't know much about the physics of photography, or can't communicate it to you well.

Having shallow focus is the choice of the director in discussion with the DP. It's meant to focus the viewer's attention and support the story by doing so. When doing a moving shallow focus shot, you'll need a second person attached to the camera to perform the follow focus. Focus isn't a sharp image, it's a specific point in space at at specific distance form the capture plane of the camera (the chip/cmos/ccd)... it is the single point at which the light from that point converge on the capture plane. Everything in front or behind it are out of focus... period.

When you turn the focus ring on the lens to infinity, it is the farthest out you can focus away from the capture plane. there are chunks of space before and after the singular point that are in "acceptable focus"

3 things make up the Depth of Field (DoF) of a shot:
- The f-stop or aperture (ratio of the the size of the hole light is coming through;iris to the length of the lens)
- The focal length (the mm rating of the lens -- like 18mm-55mm on a short zoom lens)
- The size of the capture plane (full frame DSLR = 35mm, my canon XL1s ~ 8mm)

if you make the aperture smaller, you need to increase the amount of light coming in... however, you lengthen the "acceptable focus" range... also known as a deeper DoF. It is easier to make your focus adjustments if you have more fudge room than if you have less, the drawback is that there is more stuff in focus... and if you need the background to be out of focus for a shot, the movement of the camera may have to change, or the production will need a 1st AC (follow focus operator) to do nothing but monitor and adjust the distance from the camera to the subject. IMHO, this is the hardest technical skill in the camera department, there's no close enough, it's right or out of focus!

The focal length magnifies the background and compresses space as it gets longer. An 18mm lens (or zoom set at 18mm) will seem to have a much deeper DoF than an 85mm lens. I say seem, because it's really doing this:

A) Camera ---------- 8' ---------- Subject ---------- 8' ---------- Background
then magnifying it (not actually moving the stuff, just zooming in) to appear closer to the camera:
B) Camera ----- 4' ----- Subject ----- 4' ----- Background

The distances now look like half each, but if you look at it thusly:

A) CS = 8'; CB = 16'
B) CS = 4'; CB = 8'

you'll see that the subject has moved 4' closer to the camera whereas the background has moved 8' closer. So the slightly out of focus background becomes larger and you can see it as more out of focus than it seemed before (google: Circles of Confusion).

the bottom line here is that changing the lens doesn't undo the physics of getting the shot you want... if you want a shallower DoF for a shot, he'll need to have a 1st AC to pull focus, or work really hard to keep the distance from the camera to the subject constant to keep them in focus so he doesn't have to pull focus on the shot... or you'll have to use a deeper DoF.

[harmonica44]

Okay thanks. I did some tests with the aperture at the lowest, at 22. I tested with the background, and an object in the foreground. The background was in focus but the foreground object was still not. I adjusted and got it in focus, but the background was then out of focus. So what I am doing wrong?

[jax_rox]

What lens were you using? Also, the other factor to consider with depth of field is distance between the two objects. If you have one object 5 feet in front of the lens, and a second object 50 feet behind them, you'd need to set your aperture to f/8 on a 24mm lens (35mm sensor). If the second object is only 10 feet behind, you'd only have to set it at f/4.
On a 50mm lens (35mm sensor) to get something 5 feet in front of camera in focus, as well as something 50 feet behind them, you'd need to set your aperture to f/32. Get your subjects/objects closer together.

[harmonica44]

Okay thanks. I am using an 18-55 lens, and a Canon T2i. Okay so it is the lens as well and not just the aperture being set to 22. It's good to know cause there are all sorts of variables. Should I use a different lens to get more?

[PaulGriffith]

At 18mm f/22 everything past about two feet in front of your camera should be in focus.