18-85mm lens

[Rogelio Salinas]

This may be a dumb question because I am not as familiar with lenses, but will the 18-85mm RED lens provide the 35mm cinema look shooting in 4K or 2K with the options to get a shallow DOF or be able to switch to get everything in focus from the background to the foreground? Thanks.

 

[Dominic Jones]

OK - I may have completely misunderstood your question here, so apologies if I have...

Is what you're asking "can I get a deep and shallow DoF with this lens"??

If so then essentially the answer is yes - DoF is affected by a range of factors, but most importantly lens length and aperture (sometimes, in fact often, referred to as the "stop").

A longer lens produces a shallower DoF at the same stop. *

A larger aperture produces a shallower DoF at the same length of lens. *

* = All other things being equal.


So stopped down a little at 18mm (even at 35mm-sized 4k acquisition), you will get a very deep DoF. Wide open at 85mm you will get a fairly shallow DoF (easily enough to separate an actor from the BG at a close-up shooting distance of around 6'-10').

People often misunderstand the issue of different size formats vs DoF, but essentially the important thing to remember is this - the DoF is a characteristic of the lens, not the recording format (or gate size etc) - so switching to windowed 2k mode *will not* affect the DoF, assuming you do not change any of the lens settings.

What it will do is make all of the shots a lot tighter in terms of field of view, allowing you to use a wider lens for the same look in terms of spatial compression, thus allowing a deeper DoF *for the same FoV as you would have had on a 35mm gate*.

But with just the 18-85mm, windowing will not affect your range of available DoF's, only your range of FoV's.

Make any sense??!

 

[Rogelio Salinas]

Yes, the exact way you worded the question is correct, and your post has answered it. Thank you for the quick response.

 

[Emmanuel Cambier]

People often misunderstand the issue of different size formats vs DoF, but essentially the important thing to remember is this - the DoF is a characteristic of the lens, not the recording format (or gate size etc) - so switching to windowed 2k mode *will not* affect the DoF, assuming you do not change any of the lens settings.

Well I am afraid this isn't true.
No matter what lens you use, you'll never get 35mm Dof with 1/3 or 2/3 or 16mm camera.
The size of recording media is very important.
I'm no expert in those things, and find all this matter very confusing indeed, so if any expert want to shine in, all the better.

Yours Emmanuel

 

[chuck colburn]

Dof

Dof

There is lots of info on DOF. This one I found to be concise and understandable to my aging brain.

http://www.vanwalree.com/optics/dof.html

Chuck

 

[Brook Willard]

Well, technically DOF does not change on the same focal length between different formats. If you have 2' DOF on a 50mm, you'll have that same DOF on 16mm or 35mm. That said, the 35mm will have a wider FOV. If we were comparing FOVs [instead of lens focal lengths], then yes, 35mm would have a shallower DOF for the same FOV. The lens would have to be a different focal length in order to make this possible, though.

 

[Emmanuel Cambier]

What I meant to say is:
shooting 35mm format with a 35mm format lens of 50mm focal lenght
gives a different Dof than
shooting 16mm format with a 16mm format lens of 50mm focal lenght.

I guess we'd better come out with better terminology soon, or there will be trouble.

Emmanuel

 

[Brook Willard]

Wrong: you will have exactly the same DOF on a 50mm on 16mm or 35mm. The FOV is what will change.

If you wanted the same FOV, you'd need a 100mm on the 35mm and a 50mm on the 16mm. Then you would have shallower DOF on the 35mm camera with the same FOV.

If you kept the 50mm on the 35mm camera and put a 25mm on the 16mm camera [once again equating the FOV], the 35mm camera would have a shallower DOF.

This is why format-independant DOF charts are possible.

 

[Dominic Jones]

People often misunderstand the issue of different size formats vs DoF, but essentially the important thing to remember is this - the DoF is a characteristic of the lens, not the recording format (or gate size etc) - so switching to windowed 2k mode *will not* affect the DoF, assuming you do not change any of the lens settings.

What it will do is make all of the shots a lot tighter in terms of field of view, allowing you to use a wider lens for the same look in terms of spatial compression, thus allowing a deeper DoF *for the same FoV as you would have had on a 35mm gate*.

What I meant to say is:
shooting 35mm format with a 35mm format lens of 50mm focal lenght
gives a different Dof than
shooting 16mm format with a 16mm format lens of 50mm focal lenght.

Wrong: you will have exactly the same DOF on a 50mm on 16mm or 35mm. The FOV is what will change.

Quite, exactly my point - much misunderstood!

Brook is completely correct - a 50mm lens is a 50mm lens - the format changes the FoV only...

 

[Emmanuel Cambier]

well, how come it's nearly impossible to get a really shallow DOF on my DVX100 then, if it's not dependent of sensor size ?

Emmanuel

 

[Charles Papert]

If you set your DVX lens to 50mm, you will get the same DOF as on a 35mm camera (or with equivalent sized sensor, i.e. RED)--just realize that this is the equivalent field of view as using a 220mm lens on the 35mm camera, so it's hard to compare.

An easy way to think of this is to imagine a 35mm slide (we do remember these, don't we?!!); now place a tiny little 1/3 size chip on top of that slide, and the part of the image that is underneath that chip is the framing that you would get with that exact same focal length setting on your DVX100.

 

[Emmanuel Cambier]

Hey guys I very much apreciate your knowledgable input on this,believe it, but I do hope you realize what a strech all this is from common sens, including my own input of course.
I guess my trouble comes mainly because I insist on keeping the FOV as my main reference point, because this is what matters most for me when I pick up a lens to compose a shoot.
I mean, would you pick up a 14mm to shoot your everyday close up?
Would you pick up a 300mm to shoot a wide landscape establishing shot?
I believe for the sake of clarity it would be urgent to decide what we want our reference point to be, and STICK WITH IT.
Then we can start comparing apples and oranges again but with a common ground this time.

Now I have two "simple" and "honest" questions, i would love you guys to answer to clear my mind.
1) You can buy a 50mm lens that was made for 35mm cameras, or you could buy a 50mm lens that was made for 16mm cameras.
2) Do both of those lenses have the same FOV when put on their respective format camera

Yours emmanuel

 

[Brook Willard]

Yes, they would have the same FOV on the 16mm format. They would NOT have the same FOV on the 35mm format because the 16mm lens will be incapable of rendering an image much outside of its designed 16mm frame. There will be extreme vignetting. That said, inside of the vignette, the FOV would be the same.

Was that clear?

 

[Emmanuel Cambier]

Yes, they would have the same FOV on the 16mm format.

Was that clear?

I am afraid it's not that clear.
Could someone confirm that both lens would have the same FOV on a 16mm camera?

Also my question 2) is still to be answered, mind you
In case I wasn't clear enough, by "respective format" I meant :
putting the 16mm lens on the 16mm camera
putting the 35mm lens on the 35mm camera
Now… do they have the same FOV or not?
That is the question…

Yours "at any FOV" Emmanuel

 

[chuck colburn]

apreture, focale length, working distance, circle of confusion (like this thread), viewing distances, projected size of image, and what demension you currently reside in! LOL

But seriously it's some combo of the above.

 

[Emmanuel Cambier]

sure!

 

[Zane Roach]

I'll choose 18mm for example. Same depth of field regardless of the format, but...

18mm lens on 35mm format = wide lens
18mm lens on 16mm format = normal lens
18mm lens on a DVX = telephoto

Now, if you were shooting 35mm and wanted nice shallow depth of field you would not choose 18mm, you would go for maybe 50mm or 85mm. On a DVX these focal lengths would be the equivalant to a super telephoto shots (Can the DVX even zoom that far?). This is why you can't get that 35mm depth of field feeling with the DVX lens.

So FOV changes DOF doesn't.

 

[Anders Holck]

Here you can see the difference between a 105mm lens made to cover 35mm and a lens made to cover s16mm:

Here you see a 105mm lens made to cover the 35mm format.
The green box is the 35mm gate, the red is the s16mm gate.
The circular image is how the lens projects it's image onto a non confined image plane.
The lens covers both formats as the circular projection of the lens is larger than both formats
As you can see the FOV chages because the s16mm frame is smaller, but DOF will stay the same because both originates from the exact same image, it's just cropped by the two gate sizes.

Here we got a 105mm lens made to cover s16mm.
As you can see the 35mm gate and the 16mmm gate recieves the same image with the same magnification and FOV as on the lens made to cover the 35mm gate , but because the Lens projection is made only cover the s16mm gate the 35mm gate vignettes badly.
The smaller image circle makes the lens smaller, lighter and cheaper.
As the s16mm gate recieves the same image with both lenses, it's a also good idea to do so. Why use a heavy, expensive lens when you can get the lighter one, cheaper?

 

[S. Um]

The picture above also answers your depth of field questions. This was mentioned above by Charles, but the picture shows it well. Look at the first picture, and let's say that the green box is the size of a 35mm sensor, and the red box is the size of a 1/3" sensor. You can see that it's the same picture so the DOF does not change. However, with the smaller sensor, you get the effect of zooming in on the subject.

 

[ericyoung]

Nice one Anders.