FS7: SpeedBooster Not...Boosting

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digitalinnovations

Well-known member
I just discovered an anomaly with my FS7 on the SBU; when I attach my Canon 24-105 it displays as f2.8 BUT when I attach my Zeiss Milvus lenses they do not display the boosted f-stop. For example: the Milvus 85mm f1.4 displays as f1.4 even on the SBU. Has anyone else noticed this? I'm asking more just out curiosity as I don't really need the extra stop for the type of work I do - especially when shooting primes.
 
It's just a mis-communication between lens, SBU and FS7. You will still be getting the extra stop of light because that is down to physics, not electronics.
 
I think I read somewhere on Metabones site that cameras wont report lower than F1.4 due to the cameras themselves not being programmed to handle that value. But you will still reach faster than F1.4.
 
Thank you both for the info.

I guess that means you can't be certain as to what f-stop you're actually at? But maybe, with these lenses, you run operate under the assumption that you're one stop faster than the display?
 
Actually the lenses that display an altered f stop with speed booster i.e. an f2 on an f2.8 zoom are actually the ones that are incorrect. F stop is a mechanical measure of the size of your iris. It is an f2.8 regardless of whether you use speed booster or not. However speed booster makes it function as if it were an f2. Likewise your 50mm lens is still a 50mm with speed booster but it functions like a 35mm on your camera.
Metabones communicates only with some lenses to display the functional f stop . It can be confusing.
 
LennyLevy said:
Actually the lenses that display an altered f stop with speed booster i.e. an f2 on an f2.8 zoom are actually the ones that are incorrect. F stop is a mechanical measure of the size of your iris. It is an f2.8 regardless of whether you use speed booster or not. However speed booster makes it function as if it were an f2. Likewise your 50mm lens is still a 50mm with speed booster but it functions like a 35mm on your camera.
Metabones communicates only with some lenses to display the functional f stop . It can be confusing.
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Agreed. The other misconception is people think because you get the extra stop of speed, via increased transmission, you get the corresponding change in DoF. You don't.
 
digitalinnovations said:
Thank you both for the info.

I guess that means you can't be certain as to what f-stop you're actually at? But maybe, with these lenses, you run operate under the assumption that you're one stop faster than the display?
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For exposure, forget the displayed f/stop. Look at your waveform.
 
You all are killing it today. Great answers and info with zero snark. Love it!

Liam: I totally agree with you on using the waveform for exposure. Just that one tool on the FS7 makes everything so much easier...at least for me.

I've heard a lot of people talking about false color being great on other cameras / monitors but I've never tried it. I may at some point though just to see if I like it / how it works for my particular style of shooting... It'd be an uphill battle against the waveform though.
 
LennyLevy said:
Actually the lenses that display an altered f stop with speed booster i.e. an f2 on an f2.8 zoom are actually the ones that are incorrect. F stop is a mechanical measure of the size of your iris. It is an f2.8 regardless of whether you use speed booster or not.
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I disagree.

A SpeedBooster is a type of Focal Reducer (aka Telecompressor), & f-stop is the ratio of the focal length to the diameter of the entrance pupil.

Since a SpeedBooster reduces the focal length of the lens this ratio changes, meaning the f-stop changes. The same math applies to Teleconverters.

Hopefully Brian Caldwell will chime in here.
 
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Hmm I'm not an expert in lens design. You might be right. I just think of it as getting full frame on super 35 size sensor, but what your saying is that it actually makes my 50mm f2.8 a true 35mm focal length lens and hence the same iris now measures as an f2. i'l buy that - thanks.
 
LennyLevy said:
...what your saying is that it actually makes my 50mm f2.8 a true 35mm focal length lens and hence the same iris now measures as an f2. i'l buy that - thanks.
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That's exactly how I think of it.

I'm not great at maths but pretty sure a 50mm @ f/2.8 on a FF35 sensor renders the same FOV & DOF as a 35mm @ f/2 on S35.
 
Bern has it right - the same reasoning can be found in the Q&A section of Metabones webpages.

Piotr
 
Yep, Bern is right in the engineering/physics sense. It's the exact same effect - reversed - as a teleconverter.

I think confusion arises because some people think of it as a focal reducer, and others think of it as 'increasing their sensor size'. So there are a mixture of FF and S35 equivalency numbers thrown around that are not always consistent. Treat it as a focal reducer = effective focal length and aperture change. Treat it as giving you a FF sensor, = lens specs stay exactly the same.

In response to OP's question, my Canon 50 1.4 does the same thing - does not ever go higher than 1.4. I've never been bothered by it as I know the lens elements are still there doing exactly what I expect of them, regardless of how the electronics register it.
 
For my needs I've always viewed at as focal reducer; in combination with the standard adaptor it gives me additional focal lengths. The speed boost is just a pleasant bonus when necessary.

Thanks to everyone.
 
LennyLevy said:
Actually the lenses that display an altered f stop with speed booster i.e. an f2 on an f2.8 zoom are actually the ones that are incorrect. F stop is a mechanical measure of the size of your iris. It is an f2.8 regardless of whether you use speed booster or not. However speed booster makes it function as if it were an f2.
Click to expand...

Incorrect. I'm surprised that a camera person does not understand basic principles of optics. Speed booster is a focal length reducer. F-stop is a the ratio of the system's focal length to the diameter of the entrance pupil. Since you are reducing the focal length but not the diameter of entrance pupil you are changing the ratio - which is the f-stop.

LennyLevy said:
Likewise your 50mm lens is still a 50mm with speed booster but it functions like a 35mm on your camera.
Click to expand...

Again, incorrect. Speed booster reduces focal length "physically", the resulting lens which is a combination of the prime and the focal reducer should be consider a new lens of a new focal length. In fact many prime and zoom lenses which we use everyday have an integrated focal reducing group, focal length is calculated using all the groups.
 
broughtonfilm said:
Incorrect. I'm surprised that a camera person does not understand basic principles of optics. Speed booster is a focal length reducer. F-stop is a the ratio of the system's focal length to the diameter of the entrance pupil. Since you are reducing the focal length but not the diameter of entrance pupil you are changing the ratio - which is the f-stop.



Again, incorrect. Speed booster reduces focal length "physically", the resulting lens which is a combination of the prime and the focal reducer should be consider a new lens of a new focal length. In fact many prime and zoom lenses which we use everyday have an integrated focal reducing group, focal length is calculated using all the groups.
Click to expand...

Ahh...sorry. Was viewing the forum on a phone, did not notice that this was already corrected. They say don't kick a man when he's down... Sorry Lenny.
 
Ouch!#%$^&(*T^0

Actually I understood the basic principal all the time but didn't think of the lens and speed booster as a single unit but that does make more sense.
 
I remember back in the days of shooting in 4:3 mode on 16:9 sensors on full size 2/3 chip cameras, thinking that I was working on a disadvantage trying to get shallow depth of field. Nobody ever talked about it, but it was a disadvantage using just a part of the sensor. You were using a smaller (part) of the sensor than if you had a native 4:3 sensor version of the same camera. I had both and if I was going to shoot 4:3 would always use the 4:3 native sensor camera if possible to use a larger sensor. It was the first time I'd experienced lenses having different fields of view depending on which camera I took out that day. Lens manufacturers made lenses that had a 4:3 / 16:9 switch built in them so as to retain the widest field of view when used on 4:3 sensors. The lens manufacturers inferred you HAD to use a switchable lens if shooting on a switchable camera which was not true! I'm sure they sold a lot of new lenses to folks that didn't need them that way.
 
Har. I still have one of those sitting in the office. (22x Fuji 4:3/16/9 zoom) But it was a mighty fine lens for many years, and would still have life today...if I had anything equipped with a B4 converter.
 
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