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Metabones and DOF

Brian Wengrofsky
 

If Metabones E-EF Speed Booster makes a 70mm T2.8 into a 50mm T2, is the resulting Depth Of Field calculated as 50mm T2?

Brian Wengrofsky

Director of Photography

New York City

Jay Holben
 

On 9/24/2018 4:05 PM, Brian Wengrofsky via Cml.News wrote:

If Metabones E-EF Speed Booster makes a 70mm T2.8 into a 50mm T2, is the resulting Depth Of Field calculated as 50mm T2?

Brian Wengrofsky

Director of Photography

New York City


Brian -

No. It's still a 70mm, you're just squeezing the image circle that was intended for a larger sensor onto the smaller sensor. That changes your angle of view, but the depth of field is still calculated as a 70mm. The Metabones doesn't change the 70 to a 50, it only shrinks the image circle; the 70mm is still a 70mm. Calculate your depth of field for the 70mm and the stop set on the lens - not the additional stop of light you get.

Keep in mind, however, if Metabones' claim of increased sharpness/resolution/MTF from their Booster is correct (I've not tested), that could diminish your DOF from what the calculator presents because the sharper image will make it easier to discern what is or is not in focus.

All the best,

Jay Holben
Director/Producer
Co-Chair, Lens Committee, ASC Motion Imaging Technology Council
Contributing Editor, American Cinematographer Magazine
Adakin Productions
Los Angeles, CA
www.jayholben.com
Instagram @jayholben

On 9/24/2018 4:05 PM, Brian Wengrofsky via Cml.News wrote:

If Metabones E-EF Speed Booster makes a 70mm T2.8 into a 50mm T2, is the resulting Depth Of Field calculated as 50mm T2?

Brian Wengrofsky

Director of Photography

New York City

Leonard Levy
 

You will be calculating for a 70mm f2.8 on a full frame sensor though. 
If I’m not mistaken that should be quite similar to a 50mm f2 on an APS-C sensor. 
I’ve never looked it up on DOF tables though. 

Leonard Levy, DP
San Rafael, CA







Timur Civan
 

Calculated as original lens. It's a focal reducer, so it's the same FOV. 

On Mon, Sep 24, 2018 at 7:34 PM Leonard Levy <nsll@...> wrote:
You will be calculating for a 70mm f2.8 on a full frame sensor though. 
If I’m not mistaken that should be quite similar to a 50mm f2 on an APS-C sensor. 
I’ve never looked it up on DOF tables though. 

Leonard Levy, DP
San Rafael, CA







--
Timur Civan
Director of Photography 
www.timurcivan.com
917-589-4424

Philip Holland
 

Just to add a bit more to this conversation.


Speedboosters/Focal Reducers are an empowering tool that allows for larger format glass to cover smaller format sensors with the benefit added light gathering ability.


However, there's been a great deal of misinformation regarding things like "it makes your glass better".  While on one perspective a reducer can improve your MTF due to magnification, you are still indeed adding glass into the optical chain.


Things to look out for are added distortion, chromatic aberrations, subtle bokeh character differences, a different look to the flare, and increased vignetting in comparison to the lens on a larger format sensor at maximum aperture.


They are very cool and useful, but not the cure all for all things.  You're still tampering a bit with the look of your glass and for the discerning DP you see that pretty damn quickly.


There's also a few funky things they can do one a few systems to look out for that might even enhance potential aliasing in some situations, so be on the lookout.


As always stopping down 1-2 stops helps combat a few of the tells.


Phil


-----------------
Phil Holland - Cinematographer
http://www.phfx.com
http://www.imdb.com/name/nm0390802/
818 470 0623


From: cml-glass@... <cml-glass@...> on behalf of Timur Civan <timurcivan@...>
Sent: Monday, September 24, 2018 4:48:15 PM
To: cml-glass@...
Subject: Re: [cml-glass] Metabones and DOF
 
Calculated as original lens. It's a focal reducer, so it's the same FOV. 

On Mon, Sep 24, 2018 at 7:34 PM Leonard Levy <nsll@...> wrote:
You will be calculating for a 70mm f2.8 on a full frame sensor though. 
If I’m not mistaken that should be quite similar to a 50mm f2 on an APS-C sensor. 
I’ve never looked it up on DOF tables though. 

Leonard Levy, DP
San Rafael, CA







--
Timur Civan
Director of Photography 
www.timurcivan.com
917-589-4424

J. Brian Caldwell
 

Yes.  A 70mm T2.8 plus a 0.71x Speed Booster *is* a 50mm T2.  This is misunderstood by many people, but I can take that combination, put it on my optical bench, and measure the focal length to be 50mm.  The image circle is smaller than the original 70mm lens, but that doesn't matter if the combination covers the format size of your camera.
If Metabones E-EF Speed Booster makes a 70mm T2.8 into a 50mm T2, is the resulting Depth Of Field calculated as 50mm T2?


J. Brian Caldwell
Caldwell Photographic Inc.
 


From: Brian Wengrofsky via Cml.News <rooster=bway.net@...>
To: cml-glass <cml-glass@...>
Sent: Mon, Sep 24, 2018 4:05 pm
Subject: [cml-glass] Metabones and DOF

If Metabones E-EF Speed Booster makes a 70mm T2.8 into a 50mm T2, is the resulting Depth Of Field calculated as 50mm T2?
Brian Wengrofsky
Director of Photography
New York City

Argyris_Theos_cml
 

If Metabones E-EF Speed Booster makes a 70mm T2.8 into a 50mm T2, is the resulting Depth Of Field calculated as 50mm T2?



Exactly. Well put. 
The only part that could better put is that, no matter what the T stop is, the depth of field is calculated from the f stop. 
Example: One lens might be 25mm f2, T2,2 while another one (different model) might be 25mm f1,9 T2,2.  A slight difference should be calculated,   Being more important at wide apertures
Best

Argyris Theos, gsc 
DoP, Athens Greece,
+306944725315
Skype Argyris.Theos
via iPhone


Jay Holben
 

On 9/24/2018 9:27 PM, J. Brian Caldwell via Cml.News wrote:
Yes.  A 70mm T2.8 plus a 0.71x Speed Booster *is* a 50mm T2.  This is misunderstood by many people, but I can take that combination, put it on my optical bench, and measure the focal length to be 50mm.  The image circle is smaller than the original 70mm lens, but that doesn't matter if the combination covers the format size of your camera.
If Metabones E-EF Speed Booster makes a 70mm T2.8 into a 50mm T2, is the resulting Depth Of Field calculated as 50mm T2?


Brian -

You're saying that the Speed Booster changes the actual focal length of the lens? Or, rather, that it takes the image circle from the existing lens and compresses it equally in all directions to fit a smaller sensor. There's a significant difference.

You built this thing - so if my understanding of the design and function is wrong - I'll defer to you, obviously - but just to make sure we're on the same page - it's basically acting as a reverse expander and the lens/adapter combo has a new actual focal length?

All the best,

Jay Holben
Director/Producer
Co-Chair, Lens Committee, ASC Motion Imaging Technology Council
Contributing Editor, American Cinematographer Magazine
Adakin Productions
Los Angeles, CA
www.jayholben.com
Instagram @jayholben


J. Brian Caldwell
 

Hi Jay:
Its a matter of accurately defining what the "lens" is.  Think of a "lens" as all of the optical elements attached to the front of a camera.  When you attach a Speed Booster to a "lens", you have created a new "lens".  If the original lens has six elements, and the Speed Booster has five elements, then your new lens has eleven elements.  The new lens has a different focal length and f/#, and the magnification of the Speed Booster tells you how to calculate exactly what the new values are.  In the case of a one-stop Speed Booster, which has a magnification of 0.71x, you simply multiply the focal length and f/# of the original lens by 0.71 to figure out the new focal length and f/#.

Of course, the original lens still exists within the combined lens in its unaltered state, but it is now just a component of a different and more complex lens system.  Its just like any multi-component lens system:  what counts are the characteristics of the system as a whole, not the characteristics of individual components within the system.  

J. Brian Caldwell
Caldwell Photographic Inc.
 


From: Jay Holben <jay@...>
To: cml-glass <cml-glass@...>
Sent: Mon, Sep 24, 2018 10:43 pm
Subject: Re: [cml-glass] Metabones and DOF



Brian -

You're saying that the Speed Booster changes the actual focal length of the lens? Or, rather, that it takes the image circle from the existing lens and compresses it equally in all directions to fit a smaller sensor. There's a significant difference.

You built this thing - so if my understanding of the design and function is wrong - I'll defer to you, obviously - but just to make sure we're on the same page - it's basically acting as a reverse expander and the lens/adapter combo has a new actual focal length?

All the best,

Jay Holben
Director/Producer
Co-Chair, Lens Committee, ASC Motion Imaging Technology Council
Contributing Editor, American Cinematographer Magazine
Adakin Productions
Los Angeles, CA
www.jayholben.com
Instagram @jayholben