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Archive 2013 · Focal length reducer?
  
 
alfarmer
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p.1 #1 · p.1 #1 · Focal length reducer?


What the heck is a "focal length reducer"?

http://www.canonrumors.com/2013/07/the-next-eos-m-cameras-cr1/



Jul 08, 2013 at 04:04 AM
jctriguy
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p.1 #2 · p.1 #2 · Focal length reducer?


alfarmer wrote:
What the heck is a "focal length reducer"?

http://www.canonrumors.com/2013/07/the-next-eos-m-cameras-cr1/


I'd assume they are using the same idea as a Metabones Speedbooster. Instead of a teleconverter increasing focal length and reducing light, a reducer decreases focal length and increases light. The Speedbooster takes a lens designed for FF sensor and gives you the same angle of view on a crop sensor.

My guess is that they will offer two versions of an EF lens adapter. The basic one they have now and a new 'focal length reducer' that will give you the FF angle of view and the bonus of more light with full electronic control of the lens.

That combined with a viewfinder and the new AF on chip could make for a very compelling mirrorless package.



Jul 08, 2013 at 04:13 AM
dwweiche
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p.1 #3 · p.1 #3 · Focal length reducer?


I would assume they are referring to something like this:
http://www.lensrentals.com/blog/2013/01/metabones-magic



Jul 08, 2013 at 04:13 AM
johnctharp
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p.1 #4 · p.1 #4 · Focal length reducer?


The real question is whether or not they can control aberrations while still hitting a consumer-friendly (for Canon, at least) price point. There's some pretty complex optics involved, just as in a tele-converter, and we know what those go for.


Jul 08, 2013 at 05:54 AM
kalieaire
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p.1 #5 · p.1 #5 · Focal length reducer?


I'm going to be optimistic here.

I don't think cost conscious consumers are going to be the market here. There's already an EOS EF/EF-S to EOS M Mount adapter made by Canon for $149 and cheap ones for under $50. Cost conscious folks can go there. However, Canonrumors states that there'll be two models of the EOS M slated to be released. One for the kiddies and one for the big boys.

A focal length reducer would be one for the big boys, all the awesome of a 24-70 f2.8L lens including its perspective but sized down to 14-35 T2 or potentially even T1.4. However, we're still stuck with 2.8 aperture's lack of bokeh.

Primes will do much better though.



Jul 08, 2013 at 06:05 AM
jctriguy
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p.1 #6 · p.1 #6 · Focal length reducer?


kalieaire wrote:
I'm going to be optimistic here.

I don't think cost conscious consumers are going to be the market here. There's already an EOS EF/EF-S to EOS M Mount adapter made by Canon for $149 and cheap ones for under $50. Cost conscious folks can go there. However, Canonrumors states that there'll be two models of the EOS M slated to be released. One for the kiddies and one for the big boys.

A focal length reducer would be one for the big boys, all the awesome of a 24-70 f2.8L lens including its perspective but sized down to 14-35 T2 or
...Show more

I think the point is to keep the same angle of view as on full frame but using the crop sensor. So it would be a 24-70 f2 on the EOS-M. Basically correct the 1.6x factor of APS-C sensors and gain a stop of light in the process.



Jul 08, 2013 at 06:29 AM
KF
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p.1 #7 · p.1 #7 · Focal length reducer?


jctriguy wrote:
I think the point is to keep the same angle of view as on full frame but using the crop sensor. So it would be a 24-70 f2 on the EOS-M. Basically correct the 1.6x factor of APS-C sensors and gain a stop of light in the process.


Great news, I'll finally have the 800/4.0 I always wanted !!!



Koen.



Jul 08, 2013 at 10:13 AM
alundeb
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p.1 #8 · p.1 #8 · Focal length reducer?


The focal length reduction and the f-stop gain cannot be separated.

The focal length reduction will probably not be as much as 1.6, but I will use that number for the examples.

The 24-70 mm f/2.8 with a 1.6 focal length reducer becomes a real 15--44 mm f/1.8 lens
When mounted on a crop camera like the EOS M, it gets the equivalent FOV, DOF and photon noise characteristics as when mounting the 24-70 mm 2.8 on a FF camera

A 800mm f/5.6 lens with a 1.6 focal length reducer mounted on it becomes a real 500 mm f/3.5 lens. It is identical to an ordinary 500 mm f/3.5 lens.

When a 500 mm f/3.5 lens is mounted on a crop camera like the EOS M, it gets the equivalent FOV, DOF and photon noise characteristics as when mounting a 800mm f/5.6 lens on a FF camera.

If you believe that the 500 mm f/4 L IS is a 800 mm f/4 L IS on a crop camera, then I will step out of that discussion.



Jul 08, 2013 at 10:32 AM
BrianO
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p.1 #9 · p.1 #9 · Focal length reducer?


alfarmer wrote:
What the heck is a "focal length reducer"?


The simple way to think about it is that it is the opposite of a teleconverter.



Jul 08, 2013 at 11:43 PM
StarNut
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p.1 #10 · p.1 #10 · Focal length reducer?


BrianO wrote:
The simple way to think about it is that it is the opposite of a teleconverter.


I'd think about it slightly differently:

Teleconverters can come in two flavors, extenders and reducers. Extenders increase the focal length of the combined optic; Reducers reduce the focal length of the combined optic. Reducers also often are used as field flatteners in astronomical applications.

Mark



Jul 08, 2013 at 11:58 PM
 

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BrianO
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p.1 #11 · p.1 #11 · Focal length reducer?


StarNut wrote:
Teleconverters can come in two flavors, extenders and reducers.


I don't consider the latter to be a teleconverter. It's a focal-length converter, yes, but not a teleconverter. It is, in fact, exactly what the OP is asking about; a focal-length reducer.

(This is possibly a case where camera users and telescope users use the same terms in somewhat different ways.)


Edited on Jul 09, 2013 at 12:06 AM · View previous versions



Jul 09, 2013 at 12:02 AM
jcolwell
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p.1 #12 · p.1 #12 · Focal length reducer?


BrianO wrote:
The simple way to think about it is that it is the opposite of a teleconverter.


It's a "retrevnocelet".

\'ret-rev-noc-elet'\


Edited on Jul 09, 2013 at 12:10 AM · View previous versions



Jul 09, 2013 at 12:06 AM
BrianO
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p.1 #13 · p.1 #13 · Focal length reducer?


alfarmer wrote:
What the heck is a "focal length reducer"?


BrianO wrote:
The simple way to think about it is that it is the opposite of a teleconverter.


jcolwell wrote:
It's a "retrevnocelet".


Ynnuf yrev.



Jul 09, 2013 at 12:08 AM
DtEW
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p.1 #14 · p.1 #14 · Focal length reducer?


Brian Caldwell (celebrated optical designer responsible for the Speed Booster) mentioned in that product's white paper and his posts here that ~0.7x was a "cliff" of aberrations, which is why the final product was 0.71x and not the 0.67x that would be necessary to completely nullify the focal-length growth for a DX sensor.

Considering the even greater focal length reduction that would be necessary to reduce EF lenses to the correct FoV for the 1.6x Canon APS-C sensor... and then considering that Canon has the ability to do low-dispersion and aspherical elements (which I assume Caldwell does not, as there are no claims for these)... I think this will be quite the interesting thing to watch as it develops.



Jul 09, 2013 at 12:19 AM
jcolwell
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p.1 #15 · p.1 #15 · Focal length reducer?


BrianO wrote:

Ynnuf yrev.


Being a "noc", it would be especially useful in low light.



Jul 09, 2013 at 12:24 AM
kalieaire
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p.1 #16 · p.1 #16 · Focal length reducer?


alundeb wrote:
The focal length reduction and the f-stop gain cannot be separated.

The focal length reduction will probably not be as much as 1.6, but I will use that number for the examples.

The 24-70 mm f/2.8 with a 1.6 focal length reducer becomes a real 15--44 mm f/1.8 lens
When mounted on a crop camera like the EOS M, it gets the equivalent FOV, DOF and photon noise characteristics as when mounting the 24-70 mm 2.8 on a FF camera

A 800mm f/5.6 lens with a 1.6 focal length reducer mounted on it becomes a real 500 mm f/3.5 lens. It is identical to
...Show more


Actually, there is no f-stop gain. Aperture bokeh remains the same as whatever f-stop aperture it is set at regardless of whether or not there is a focal length reducer between the lens and the camera. However, the T-Stop changes, please tell me you know what a T-Stop is w/o having to google it.



Jul 09, 2013 at 01:13 AM
cameron12x
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p.1 #17 · p.1 #17 · Focal length reducer?


alundeb wrote:
If you believe that the 500 mm f/4 L IS is a 800 mm f/4 L IS on a crop camera, then I will step out of that discussion.

Isn't it possibly even better than a 800mm f/4 L IS in some regards?

The reasoning being that the crop sensor picks off the "sweet spot" of the MTF function for a given lens (e.g. the cropped corners are now much closer to the center of the lens; edge-to-edge resolution is improved).

As far as aperture goes, is it 800mm f/4 or f/6.4 or other?



Jul 09, 2013 at 02:44 AM
johnctharp
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p.1 #18 · p.1 #18 · Focal length reducer?


cameron12x wrote:
Isn't it possibly even better than a 800mm f/4 L IS in some regards?

The reasoning being that the crop sensor picks off the "sweet spot" of the MTF function for a given lens (e.g. the cropped corners are now much closer to the center of the lens; edge-to-edge resolution is improved).

As far as aperture goes, is it 800mm f/4 or f/6.4 or other?


I'm not sure I fully understand what happens with these 'speed boosters' or 'focal length reducers' or 'light concentrators' (my description to break from techno-marketing speak). Smarter people than me will have to answer the question, as I keep running into corners working the math. But here goes:

Wouldn't a 'focal length reducer' widen the effective FOV while shrinking the DOF? And if so, wouldn't it also increase the effective F-stop, thus increasing the actual exposure?

And then, given that it's being mounted to a crop sensor, wouldn't it just be making up for most of the light lost from the smaller sensor? So easy to get confused.

Aside from that, the question that sticks in my head, is just exactly what is this 'focal length reducer' actually doing. If we consider that the image circle of an EF lens with the ~44mm flange distance has to be ~44mm in diameter to clear the corners of an FF sensor, does the 'FLR' now take that full image circle and focus it onto the crop sensor with an image circle around 30mm in diameter? Or is it something different or in between?



Jul 09, 2013 at 03:11 AM
alundeb
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p.1 #19 · p.1 #19 · Focal length reducer?


alundeb wrote:
The focal length reduction and the f-stop gain cannot be separated.

The focal length reduction will probably not be as much as 1.6, but I will use that number for the examples.

The 24-70 mm f/2.8 with a 1.6 focal length reducer becomes a real 15--44 mm f/1.8 lens
When mounted on a crop camera like the EOS M, it gets the equivalent FOV, DOF and photon noise characteristics as when mounting the 24-70 mm 2.8 on a FF camera

A 800mm f/5.6 lens with a 1.6 focal length reducer mounted on it becomes a real 500 mm f/3.5 lens. It is identical to
...Show more
kalieaire wrote:
Actually, there is no f-stop gain. Aperture bokeh remains the same as whatever f-stop aperture it is set at regardless of whether or not there is a focal length reducer between the lens and the camera. However, the T-Stop changes, please tell me you know what a T-Stop is w/o having to google it.


FYI

I Own Sony NEX cameras, a regular EF-NEX adapter and a Metabones EF-NEX SpeedBooster. When I mount the EF 35 mm 1.4 L on the SpeedBooster, the camera reports maximum aperture 1.0 and used wide open I get 1 stop brighter exposure than when using the lens on the regular adapter.



Jul 09, 2013 at 04:44 AM
alundeb
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p.1 #20 · p.1 #20 · Focal length reducer?


alundeb wrote:
If you believe that the 500 mm f/4 L IS is a 800 mm f/4 L IS on a crop camera, then I will step out of that discussion.

cameron12x wrote:
Isn't it possibly even better than a 800mm f/4 L IS in some regards?

The reasoning being that the crop sensor picks off the "sweet spot" of the MTF function for a given lens (e.g. the cropped corners are now much closer to the center of the lens; edge-to-edge resolution is improved).

As far as aperture goes, is it 800mm f/4 or f/6.4 or other?


As far as aperture goes, it is 500 mm f/4.



Jul 09, 2013 at 04:46 AM
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