# C70 Speedbooster for EF glass. Does this mean RF glass has smaller image circle? How does this all work?



## cayenne (Sep 25, 2020)

Hi all,

I'm hoping someone can explain this to me.
on the new C70, it takes RF lenses naturally.

For using EF glass it takes and adapter, but it is also a focal reducer/speed booster.

Why does EF glass require a focal reducer on this camera but the RF glass does not?

Does this mean that the EF glass has a larger image circle than RF glass? 

If this is the case, how is this working on say, the R5? My understanding was that the EF - > RF adapter for the EOS stills cameras was not a focal reducer.

If this is the case, how does the RF lens work on FF camera along side of the EF lenses without a focal reducer there?

Clear as mud?

Thanks in advance,

cayenne


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## koenkooi (Sep 25, 2020)

The C70 has a crop sensor ("super 35"), not an FF sensor. If you use the RF-EF-FR adapter on an R5 you'll a roughtly APS-C sized image on your sensor with black borders due to the baffles in the adapter.


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## H. Jones (Sep 25, 2020)

Like Koenkooi said, the C70 is a crop sensor camera.

You can use any EF glass you want on any other RF adapter you want, but you will see the 1.6x crop magnification, so your 200mm becomes effectively 320mm.

But when using the speedbooster, it reverses the 1.6x crop of the sensor by shrinking the image circle of your full frame glass down to a crop sensor image circle. So now your 200mm F/2.8 becomes a 125mm F/2, as shrinking the image circle condenses more light onto a smaller area, so you gain a stop of light. 

When that 125mm is seen through the C70's crop sensor, the 1.6x crop factor turns that 125mm back into 200mm, making you able to use full frame lenses with the same effective focal length as if they were on a full frame sensor.

Now, if you were to put the speedbooster on a full frame camera, you would see a tiny circular image in the center of the frame with large black borders, as the speedbooster only covers a crop sensor area of the sensor. So on the R5, you would have to use the 17 megapixel crop mode to use a speedbooster, defeating the purpose.


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## cayenne (Sep 25, 2020)

koenkooi said:


> The C70 has a crop sensor ("super 35"), not an FF sensor. If you use the RF-EF-FR adapter on an R5 you'll a roughtly APS-C sized image on your sensor with black borders due to the baffles in the adapter.




I get that the C70 is a smaller sensor.

But here's my confusion.

ON R5 - FF sensor...you have RF lenses, work natively. You have EF lenses, with an adapter that is NON-focal reducer, that work for the same FF sensor.

Now, we have the C780. 
Apparently, with this smaller sensor, you have the RF lens on there natively. 
HOWEVER, for some reason, the EF lens adapter requires a focal reducer.....

So, what's the difference?

Why on C70, does EF require a focal reducer and RF does not?

Hoping that clarifies a bit more what's confusing me.

TIA,

cayenne


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## H. Jones (Sep 25, 2020)

cayenne said:


> Why on C70, does EF require a focal reducer and RF does not?



It does not require it. The speedbooster exists only for people who want to avoid the 1.6x crop factor of the C70.

All RF glass on the c70 will be impacted by the 1.6 crop factor, but the speedbooster gives the C70 the ability to look "full frame"-ish when you use EF glass and the speedbooster.


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## cayenne (Sep 25, 2020)

H. Jones said:


> It does not require it. The speedbooster exists only for people who want to avoid the 1.6x crop factor of the C70.
> 
> All RF glass on the c70 will be impacted by the 1.6 crop factor, but the speedbooster gives the C70 the ability to look "full frame"-ish when you use EF glass and the speedbooster.




Thanks for the info.

So, in this case, it seems a disadvantage to actually shoot the C70 with RF glass, since you're not using the whole image circle?

I wonder why they didn't come up with a speed booster to use on the RF lenses...so that you could enjoy the full image circle from the very $$$ RF glass?

Am I wrong in seeing this as EF is a better choice of lens for the C70 with the focal reducer adapter than using RF lenses natively on there?

Am I missing something?

Thank you!!

C


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## padam (Sep 25, 2020)

It is a 1.43x crop on the EOS C70 sensor.
So with the focal reducer adapter attached to an EF lens, it is effectively a 1.02x crop compared to FF with a Cinema 4K aspect ratio.
Almost exactly the same as the EOS R5 or EOS 1DX III in FF mode.


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## padam (Sep 25, 2020)

cayenne said:


> Thanks for the info.
> 
> So, in this case, it seems a disadvantage to actually shoot the C70 with RF glass, since you're not using the whole image circle?
> 
> ...


You can only use a lens that has empty space behind it that is normally "filled" with an EF - EOS R adapter, it just extends the lens to match the flange distance and the optics go into that same exact space to focus the light onto the smaller sensor.
The RF lenses are designed with optics in already in place at that space, you can't add a focal reducer to that. (only a teleconverter for compatible lenses, which has the opposite effect but if you are switching between adapters, you can change the field-of-view with the EF lenses)

RF lenses still offer other types of advantages, such as:
-less distortion, less aberrations
-less focus breathing, more silent AF
-some newer f/2.8 lenses have IS, while EF lenses don't
-newer, better lens IS
-quicker communication, a wider AF area coverage

It is important to point out that with an EF lens and any kind of EF adapter (whether normal or the 0.71x) in place, the Dual-Pixel AF area on the sensor gets reduced to 60% from 80%


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## H. Jones (Sep 25, 2020)

cayenne said:


> Thanks for the info.
> 
> So, in this case, it seems a disadvantage to actually shoot the C70 with RF glass, since you're not using the whole image circle?
> 
> ...



Speed boosters have to be "focal reducers," they cannot extend the overall length of the distance between the image sensor and the front of the lens, because that would instead extend the focal length, like a teleconverter, and reduce the amount of light.

Speedboosters are only created as adapters for other mounts for this reason, as you can only reduce the focal length by placing optical elements within the existing path that light travels, not by adding something that would extend the path that the light travels.

As others have said, speedboosters also reduce image quality and will limit the amount of autofocus areas. It is a huge advantage for those who want the full frame look for wide angle glass, but in most scenarios RF glass will work ideally as long as you don't need a super wide shot. The speedbooster is a great idea when using lenses like the 11-24 and 16-35, but is kinda defeating the purpose when using a 70-200 or most of the range of a 24-70.


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## AJ (Sep 25, 2020)

Question:
There are some rumours floating around about an R-mount stills camera with an APSC sensor, to be developed.
Suppose this comes to market. Could I use the speedbooster with my Sigma 150-600/ 5-6.3 to get f/3.5-4.5? That would be nice to have.


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## Frodo (Sep 25, 2020)

Would this adapter work on the R on the cropped 4K video mode so thst wide lenses remain wide?
I note that the info above specifies particular lenses so may not be of more general application.


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## Joules (Sep 25, 2020)

AJ said:


> Question:
> There are some rumours floating around about an R-mount stills camera with an APSC sensor, to be developed.
> Suppose this comes to market. Could I use the speedbooster with my Sigma 150-600/ 5-6.3 to get f/3.5-4.5? That would be nice to have.


Would it though? A speedbooster trades focal length against light density (f/number). The whole point of using the 150-600 mm is to get as much reach as possible for a decent price. If you use a speedbooster, you loose reach and pay more. As I see it, a speed booster makes sense to avoid developing crop sensor lenses that match the equivalent FF ones. So you don't have to provide a 31 mm 0.75 if you can instead just use a speedbooster and 50 mm 1.2.


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## cayenne (Sep 25, 2020)

H. Jones said:


> <snip>
> 
> As others have said, speedboosters also reduce image quality and will limit the amount of autofocus areas. It is a huge advantage for those who want the full frame look for wide angle glass
> <snip>



I don't think I saw where anyone commented that the speed booster *would reduce image quality*...?

I do understand that it would reduce the amount of autofocus area....but for me, ANY autofocus on a video camera would be new and novel idea, so that would be fun still for me.

But if the speed booster optics are of good quality, I can't imagine that it would degrade the image coming out of the lens?

C


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## Joules (Sep 25, 2020)

cayenne said:


> I don't think I saw where anyone commented that the speed booster *would reduce image quality*...?
> 
> I do understand that it would reduce the amount of autofocus area....but for me, ANY autofocus on a video camera would be new and novel idea, so that would be fun still for me.
> 
> ...


Well, a speedbooster that is designed to work with any lens has to be some form of compromise. Using a FF lens on a native FF body vs with a speedbooster on a crop body. The speedbooster variant can't exceed the performance of the bare lens on a FF sensor. And the odds of exactly matching it are fairly low, so that leaves less quality as the most likely option. I doubt such differences will be noticeable with a measly 8 MP (4K) of detail. Maybe in situations with bright light there may be lower contrast and more flare with the speedbooster compared to the lens being used natively on a FF sensor.


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## AJ (Sep 25, 2020)

Joules said:


> Would it though? A speedbooster trades focal length against light density (f/number). The whole point of using the 150-600 mm is to get as much reach as possible for a decent price. If you use a speedbooster, you loose reach and pay more. As I see it, a speed booster makes sense to avoid developing crop sensor lenses that match the equivalent FF ones. So you don't have to provide a 31 mm 0.75 if you can instead just use a speedbooster and 50 mm 1.2.


True, I'm often at 600 mm, but not always.
Suppose there is a subject that frames well at 400 mm on crop. With the speedbooster I could shoot it at 600 mm, get more selective focus, and a faster shutterspeed or lower iso.
I do get the point about avoiding primes with crop imaging circles. My old 50/1.8 would become a 30/1.2 which sounds way more exciting than 50/1.8. Again the speedbooster would allow more selective focus and a higher shutterspeed.


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## H. Jones (Sep 25, 2020)

cayenne said:


> I don't think I saw where anyone commented that the speed booster *would reduce image quality*...?
> 
> I do understand that it would reduce the amount of autofocus area....but for me, ANY autofocus on a video camera would be new and novel idea, so that would be fun still for me.
> 
> ...




A speedbooster introduces glass into the optical pathway. Any time you add glass, the optics and quality of that lens changes. The same as a teleconverter, adding that glass can reduce quality slightly or increase flaring/distortion. As these have to work with all EF lenses, there has to be sacrifices somewhere, its not special designed per lens to ensure the same quality, same as a teleconverter. 

Same concept even as UV filters, which add a lot of flare even if they don't decrease image quality by much, because it adds glass.


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## Mt Spokane Photography (Sep 26, 2020)

cayenne said:


> I don't think I saw where anyone commented that the speed booster *would reduce image quality*...?
> 
> I do understand that it would reduce the amount of autofocus area....but for me, ANY autofocus on a video camera would be new and novel idea, so that would be fun still for me.
> 
> ...


Any lens is imperfect, and introduces aberrations. Normally. additional elements must be added to reduce CA and they are also imperfect. A Speed Booster is merely a TC that reduces rather than magnifies the image and while they can be very good, when you put several glass elements in the image path, optical performance decreases.


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## padam (Sep 26, 2020)

When the lens is attached to a FF sensor, it will have the best peak sharpness, lowest pixel density, no additional optics.

But compared to using a FF lens with a simple adapter on a crop sensor, a Speed Booster might be better, because it is not punching on the image.
Same pixel count on a bigger effective sensor area, effectively reducing the pixel density, so the lens does not have to resolve as much.

Of course there may be minor distortion added to the image, softness at the extreme corners (probably outside the 17:9 video crop area) etc. but Canon will work on supporting more lenses and correcting it with the camera's software.

So yes even at 8K resolution (or even 12K in case of the Blackmagic), the Speed Booster will work well enough, with a FF lens it could be sharper than using a similar FF lens with a bare adapter on the same 8K crop sensor. (assuming they give same FOV, etc.)


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## dcm (Sep 26, 2020)

I’m intrigued by the flat foot On the bottom of the Mount Adapter EF-EOS R 0.71x with what appears to be two holes. No mention of it anywhere.


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## koenkooi (Sep 26, 2020)

dcm said:


> I’m intrigued by the flat foot On the bottom of the Mount Adapter EF-EOS R 0.71x with what appears to be two holes. No mention of it anywhere.
> 
> View attachment 192999
> 
> View attachment 192998



I suspect that's for lens support. Smallrig sells something similar to but the weight of the lens+rigging on the cage instead of the RF mount.


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## Mt Spokane Photography (Sep 26, 2020)

padam said:


> When the lens is attached to a FF sensor, it will have the best peak sharpness, lowest pixel density, no additional optics.
> 
> But compared to using a FF lens with a simple adapter on a crop sensor, a Speed Booster might be better, because it is not punching on the image.


Do you also believe in perpetual motion? Lenses curve different colors of light different amounts. You add more elements to try and neutralize it, at least in the center. Each lens is ground imperfectly and the glass has flaws too. You keep adding them, usually 5 or 7 elements to the point where there are diminishing returns. It will never produce a better image than the bare lens.


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## dcm (Sep 26, 2020)

koenkooi said:


> I suspect that's for lens support. Smallrig sells something similar to but the weight of the lens+rigging on the cage instead of the RF mount.



That was my first thought since the EF-EFM adapter has a detachable lens support. I found it strange that there was no mention or attachment included. Always interesting when there is a visible feature that is ignored. It's like having an extra, undocumented button on a camera.


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## Joules (Sep 26, 2020)

Mt Spokane Photography said:


> Do you also believe in perpetual motion? Lenses curve different colors of light different amounts. You add more elements to try and neutralize it, at least in the center. Each lens is ground imperfectly and the glass has flaws too. You keep adding them, usually 5 or 7 elements to the point where there are diminishing returns. It will never produce a better image than the bare lens.


The point was that aspects like poor resolution or CA are usually more prominent on APS-C Tham FF because of the greater magnification. So by compressing the image circle those are also reduced. So it becomes a question of how much aberration is added through the speedbooster vs. how much the lenses own aberrations are hidden.

If the lens already outperforms the crop sensor or the speedbooster isn't all that great optically a bare lens will of course perform better.


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## padam (Sep 26, 2020)

Mt Spokane Photography said:


> Do you also believe in perpetual motion? Lenses curve different colors of light different amounts. You add more elements to try and neutralize it, at least in the center. Each lens is ground imperfectly and the glass has flaws too. You keep adding them, usually 5 or 7 elements to the point where there are diminishing returns. It will never produce a better image than the bare lens.


Again, it depends on what you are comparing and I explained the *specific case* where adding this adapter will lead to *sharper *results with potentially *slightly less chromatic aberrations* than without it. Will the flare become worse with the extra elements? Will the bokeh rendering change? Possible.
There are quite a few comparisons regarding the Metabones Speed Booster which you can look up if you want.
With the Canon adapter there are no side-by-side examples as of yet, but on the first look video, it looks to be even a bit better than the Metabones (maybe because it is even more optmised for the Canon sensor size)


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