Red Vs Viper

[Adrian T.]

I think we're all agreeing... we just don't know how to say it.

Stop, subject distance and focal length. Change any single factor and DOF will change. Change multiple factors in a complimentary fashion and DOF will not change.

Well said. Case closed. :biggrin:

 

[Brook Willard]

OK, I learned something after reading that link. The dof doesn't technically change. However the illusion of dof most certainly does therefore I'll change my statement . A 100 mm lens at any f stop will have the ILLUSION of more dof on a 1/3' sensor than on a 35mm sensor at the same f stop.
-A

I suppose that depends on who's looking...

 

[Stephen Williams]

That's right. But now you're changing two variables at the same time: subject distance and focal length. In the field you don't know about any magnification factor (subject distance divided by focal length) but you know exactly what subject distance and focal length you have.
.

Hi,

Changing the lens and the image magnification are also 2 variables! L.O.L

To increase the DOF stop down the lens or make the image smaller. There are 2 ways to make the image smaller!

Stephen

 

[Stephen Williams]

OK, I learned something after reading that link. The dof doesn't technically change. However the illusion of dof most certainly does therefore I'll change my statement . A 100 mm lens at any f stop will have the ILLUSION of more dof on a 1/3' sensor than on a 35mm sensor at the same f stop.
-A

Hi,

I think you have that backwards! A 100mm lens on a 1/3 inch sensor is one hell of a long lens!

Stephen

 

[Poi Boy]

I'd say most anyone looking, that is why the myth persists.
-A

 

[Paris Remillard]

>Point being, in the real world, we use longer lenses or different focal lengths to alter DOF properties as that's often the most practical solution.<

But technically speaking, you could get the same shallow depth of field by moving in closer with a wider lens to achieve the same image size. The problem with that, though, as I stated before, is that the image characteristics, or perspective, change. The compression of longer lenses makes the out of focus objects in the background larger and harder to distinguish making them look more out of focus than they would with a wider angle lens even though the DOF would be exactly the same given the same image size.
Also, things like peoples noses looking huge and clownish, and perspective on buildings, etc. But technically speaking, DOF is not affected by focal length. Perspective is.

 

[Brook Willard]

But technically speaking, DOF is not affected by focal length. Perspective is.

This is only true if you are moving the camera to maintain the same frame. As mentioned before, if you keep the camera at 10' from your subject and swap out the 18mm for an 85mm, the 85mm lens [at the same stop] will have shallower DOF.

This is just to prevent confusion.

 

[zak forrest]

I suppose that depends on who's looking...

smart ass :clown2:

 

[Chris Kenny]

Regarding DOF, read this:

http://www.bluesky-web.com/dofmyth.htm

Focal length IS NOT a factor. It's determined f-stop and subject distance or focus distance (which is where the image size issue comes into play).

The stretching of wide angle lenses and compression of long lenses will give the images different characteristics which can also lend to the impression of more or less DOF.

Format size has to do with FOV ONLY.

So, Stephen is correct on this issue.

Um... Stephen was saying DOF was determined by the resolution of the lens and the imaging system, which it's mostly not. (This does have some marginal impact, as it determines what counts as acceptable focus.)

As to the argument that varying focal length while maintaining subject size doesn't impact DOF, I've presented it here (or, actually, I think over at DVXUser) previously. I've thought about it since then, and decided that whether or not it's true is largely semantics.

Using a wider lens exaggerates perspective, which causes background objects to look smaller. Because they look smaller, they also look sharper. This results in them appearing to be more in focus.

 

[Tom Lowe]

So how does sensor size play into all of this?

 

[Brook Willard]

It doesn't. DOF does not change depending on format size. What changes is FOV.

For example:

Here is a scale diagram of a 50mm lens on S16mm and S35mm. You can see that they have different FOV. But DOF? It's not accounted for on this diagram, but the DOF would be the same.

So why do smaller formats appear to have deeper DOF? It's simple.

To match the FOV of S35mm on a 50mm lens, you'd put a 25mm lens on S16mm. While the FOVs will match, the focal length itself has changed. Different focal length = different DOF. The 50mm lens on the S35mm camera will have a shallower DOF than the 25mm lens on the S16mm camera [with nothing else changed].

So the format itself does not change the DOF, it merely changes the FOV. If you match FOV between formats, that's when the DOF changes [because the only way to match FOV between formats is to modify focal length].

Make sense?

 

[Ace]

One of my favourite past times on reduser is reading up on all the theories regarding depth of field. Every post presents a whole new version of it!

Its almost like that Airplane on a conveyor belt physics question that floated around the web a couple of years back.

 

[Anders Holck]

Using a wider lens exaggerates perspective, which causes background objects to look smaller. Because they look smaller, they also look sharper. This results in them appearing to be more in focus.

Yes the funny thing here is that there is actually only one exact distance that is 100% in focus, DOF is only an illusion of objects "appearing to be in focus" based on the Circle of confusion.

Now back to the subject "Red vs. Viper"

 

[Chris Kenny]

This is only true if you are moving the camera to maintain the same frame. As mentioned before, if you keep the camera at 10' from your subject and swap out the 18mm for an 85mm, the 85mm lens [at the same stop] will have shallower DOF.

Right. And if you stand in the same place and replace your 18mm lens with an 85mm lens, and then switch to a larger format camera, you get both the shallower DOF and the same field of view. As I said before, this is why we say larger format cameras have shallower DOF. Basically, because you can use a longer lens from the same distance (which lowers DOF) without having an unacceptably narrow field of view.

Edit: Oops, you already beat me to it with this explanation.

 

[Brook Willard]

Bingo. Semantics.

 

[Brook Willard]

Its almost like that Airplane on a conveyor belt physics question that floated around the web a couple of years back.

The plane could take off, dammit! Thrust is independent of the wheels and the wheels are independent of airspeed!

 

[Ace]

The plane could take off, dammit! Thrust is independent of the wheels and the wheels are independent of airspeed!

Absoloutely! Thats what I said. Einsteins third law.

 

[Ace]

Sorry NEWTONS third law.

 

[Poi Boy]

I think it was copernicus.
-A

 

[Brainstorm]

i agree with haakon completely. but boy am i sick of hearing that, either here on the red boards, or on CML, and in real life. the next time i hear anyone talk about how "its more than just the camera" to make a good film it will be TOO SOON. this is the most obvious thing in the world, and even if you think its not, its been said probably more times than anything else, ever, on these boards. the boys over at cml really love to say that one too... "just because you have a red doesnt mean you have talent, or good lighting, blablablablablabla

OH MY

am i the only one who seriously gets driven crazy when they read stuff like that? its just so obvious, and the most overplayed comment in the history of these boards, it drives me nuts. "you have a red camera but you will still have to breathe air on the set..."

Zak... :cold:

The ONLY point I was trying to make was that audiences don't give a toss what any film is shot on, as long as it looks good. Does anybody (other than people like you, me and other filmmakers) watch Zodiac to see what the Viper's images looked like? Probably not. Do they care what it's shot on? Probably not. Do they know if it's digital video of celluloid? Probably not. Do they care or know if it's 4K, 2K or 1080P? Probably not. Do they care if it's entertaining? Well, the answer to that is obvious.

I'm so sorry if my earlier comment bored you. It won't happen again. Maybe I'll take to posting images of my dog instead of mentioning "storyline" in relation to film at any time in the future.:nuke: