Do you loose a stop of light when using 35 mm lens adapted for the gh4?

C

canada John

Member
Never thought of it till now but was wondeing....

If a Metabones Speedbooster increases the 35 mm lens' light by a full stop, while also removing the 2X crop, does that mean that any 35 mm lens adapted to the GH4 automatically looses a stop?

John
 
Your question doesn't really clearly mention lose a stop compared to what... Compared to other lenses of the same focal length and aperture? Then no, the format the lens was designed for does not matter as long as it covers the sensor size you are using.

However, if you are asking compared to using the same lens on a 1.4x wider sensor, yes and no. Technically you are throwing out half of the light designed to hit the sensor since you are cropping further into the image circle, but an f-stop is a mathematical calculation relating to the focal length and entrance pupil of a lens design so it is independent of the sensor placed behind it. It is a common misconception that fstops measure light but they are only correlated it light measurement for a given ISO and a sensor's ISO is going to be partly determined by its format/size and design since a smaller sensor will 'see' less light for the same f-number as a larger sensor.

So yes you lose photons in a quantity similar to closing down your aperture by a stop, but technically you won't ever see a higher f-number, more likely just a less sensitive sensor. Of course you also increase your depth of field in an an amount equal to one stop.
 
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There is no light loss or increase in DOF. Format is irrelevant.

Try this experiment. Shoot some full frame footage/stills with your GH. Try the same in a crop mode. Result...the image does not get darker & the DOF is identical.

A 50 is a 50 is a 50!
 
I edited my response above because I originally assumed the OP asked comparing the same lens on a GH4 to S35 but now, after reading Bern's response, see it is a somewhat unclear question and he may have meant compared to lenses designed for the smaller format which is a much simpler answer.
 
Bern Caughey said:
There is no light loss or increase in DOF. Format is irrelevant.

Try this experiment. Shoot some full frame footage/stills with your GH. Try the same in a crop mode. Result...the image does not get darker & the DOF is identical.

A 50 is a 50 is a 50!
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Yes but when cropping you are losing light, throwing away photons, just not darkening the image or changing your f-stop, but those are not actual measurements of light quantity. And the DOF is the same but the FOV is much smaller and the DOF would be greater if you compensated for FOV with a shorter focal length which is a much more practical comparison.

A 50 is 50 but you should not expect the same image quality and attributes at 50mm on 35mm m43 and 16mm even if a manufacturer says the ISO is the same...
 
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Bern Caughey said:
Cropping does not effect exposure. Better lenses deliver the exact (or close to it) same exposure over their entire coverage.

With your premise the center of an image would be darker then the edges, but if anything the opposite is true.

https://matthewduclos.wordpress.com/2009/11/03/a-50-is-a-50-is-a-50/
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Sounds like you are measuring light by photons per square area which is independent of the sensor whereas I'm talking about the number of photons reaching the sensor and comprising the image. So yes cropping doesn't affect exposure but it does affect the amount of photons used to create the image. Exposure will be the same but the image will certainly not be.

I completely agree with that Duclos article but you seem to be misunderstanding me. Perhaps my post was too complicated in that I was trying to answer two different questions because it seemed unclear which question the OP posed.
 
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I've personally tested this myself and found that exposure does not change. You loose FOV, but every part of the lens that is visible to the sensor will be equally as bringht, thus at the equivalent F-stop marking of the lens.
 
nyvz said:
a smaller sensor will 'see' less light for the same f-number as a larger sensor
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The image a lens produces is not dependent on the sensor it falls upon, so the actual brightness of the image is the SAME if you are using the whole image from the lens or only a tiny portion of the image. Nobody cares about how many photons are hitting a sensor, but rather can I obtain correct exposure for the light sensitivity of the film/sensor that I am using.

f/2.0 at 1/48th of a second represents the SAME exposure whether I use the whole image from a lens or only a tiny portion of it.
 
No, seems like everyone agrees on this one. Though I'm still not totally clear on the intent of the question.

TheDingo said:
Nobody cares about how many photons are hitting a sensor, but rather can I obtain correct exposure for the light sensitivity of the film/sensor that I am using.
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Well it depends on the question, some may care...
 
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nyvz said:
No, seems like everyone agrees on this one. Though I'm still not totally clear on the intent of the question.



Well it depends on the question, some may care...
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I don't.

I deal with "practicalities", I work with "what is" in a practical sense. Exposure for the image falling on the sensor is not affected (in a practical sense) by photons not being used.

The only thing that might affect exposure might be the reflective brightness of the FOV being used as compared to the overall brightness of the lens circle of confusion. Some adjustment may be needed but has nothing to do with "thrown away" or "lost" photons. More like "photographic judgement".
 
Bruce Foreman said:
I don't.

I deal with "practicalities", I work with "what is" in a practical sense. Exposure for the image falling on the sensor is not affected (in a practical sense) by photons not being used.

The only thing that might affect exposure might be the reflective brightness of the FOV being used as compared to the overall brightness of the lens circle of confusion. Some adjustment may be needed but has nothing to do with "thrown away" or "lost" photons. More like "photographic judgement".
Click to expand...

Yes, if it's a question of comparing a S35 lens to an m43 lens of the same focal length and aperture. But I was questioning if the OP was asking about that or comparing a S35 lens on m43 compared to the same lens on S35. It sounds like everyone else has a consensus the question refers to the former but is not understanding that I was answering both that and the latter. And some people seem to be mistaking photographic exposure for a direct measurement of light when exposure is dependent on ISO which is usually correlated with sensor size. You can talk about the luminous flux or the illuminance and both measure light and both are important so don't tell me luminous flux isnt worth caring about even if your light meter won't measure it. I get that as an operator you may only care about the dials on your lens and readings on your meter but you'll never convince me it's useless to understand and talk about light more deeply than that...

The OP's phrasing asked about light which I read as luminous flux, not exposure which relates more to illuminance. Though I do agree he may have meant exposure and wanted to compare to an m43 lens since that is a more trivial question with a more simple answer.

I apologize if my preoccupation with the ambiguities of the question has confused anyone but it just seemed like a much more interesting question that way, so sorry no one seems to know what I'm talking about :P
 
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nyvz said:
I was questioning if the OP was asking about that or comparing a S35 lens on m43 compared to the same lens on S35.
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Lenses are optimized for a specific imaging format, so it's true that a lens optimized for S35 may perform better with S35 cameras than m43 cameras. The reverse may be true too, especially when looking at the resolved lp/mm of m43 lenses against FF 35mm lenses when used with m43 cameras.

nyvz said:
when exposure is dependent on ISO which is usually correlated with sensor size
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Sensor technology is still evolving, and I would consider it a serious mistake to assume that ALL sensors behave the same way given a specific size.
 
TheDingo said:
Sensor technology is still evolving, and I would consider it a serious mistake to assume that ALL sensors behave the same way given a specific size.
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Well despite any evolution or new technologies, the correlation exists because larger sensors are actually capturing more light at the same "exposure" as I mentioned earlier.
 
nyvz said:
Well despite any evolution or new technologies, the correlation exists because larger sensors are actually capturing more light at the same "exposure" as I mentioned earlier.
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Hey, write a paper on this and present it to a scientific forum. Nobel prizes are given out for new discoveries in the properties of light.
 
I'm not sure I get what you're saying, this is a fairly simple concept, not something to write a paper on.

It's like how solar power tech is always improving but a larger solar cell will always have an easier time collecting more light/power.
 
Are we confusing pixel size with sensor size? Yes, a larger pixel can absorb more light and a larger sensor has more real-estate to accommodate larger pixels. But the size of sensor itself does not influence the light gathering.
 
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