it is said that full frame aperture equivalent of 2.8 to aps-c is 4.2. does it mean that shutter speed of aps-c is one stop slower that full frame on the same aperture? given the same focal length equivalent e.g. aps-c 23mm and ff 35mm.
No shutter speed is not affected by sensor size.
The crop factor is a relationship between aperture and focal length
it is said that full frame aperture equivalent of 2.8 to aps-c is 4.2.
Only in terms of depth of field, assuming you are matching field of view.
https://www.reddit.com/r/photography/wiki/technical#wiki_should_the_crop_factor_apply_to_aperture.3F
does it mean that shutter speed of aps-c is one stop slower that full frame on the same aperture?
No. Unless maybe you’re talking about comparing the same ISO noise level. But if so, it’s more complicated than that.
what confuses me is aperture diameter in aps-c 23mm f/1.4 is 16 while 35 in f/1.4 is 25. we all know that the bigger the aperture diameter, the more light comes inside the sensor, the more light, means faster shutter speed.
aperture diameter is a part of mechanical (size) that affects the light.
Aperture scales at the same scale as the sensor size so it’s a wash.
Yes, a larger entrance pupil diameter lets through more light than a smaller entrance pupil diameter.
But don’t forget that focal length also affects light transmission. A longer focal length gathers light from a smaller area of the scene and therefore less light than a shorter focal length.
That’s the whole reason the f-number is set up as a ratio between focal length and entrance pupil diameter, to normalize the effect of focal length so you don’t have to account for it separately when figuring exposure. So an f/1.4 aperture should be the same contribution to exposure no matter what the focal length. That’s why nobody needs to specify the focal length when communicating exposure settings. A 16mm entrance pupil diameter lets in less light while a 23mm focal length lets in more light, and that equals out to the same as a 25mm entrance pupil diameter letting in more light and paired with a 35mm focal length letting in less light.
And none of the above has anything to do with different format sizes. At 23mm and f/1.4 on full frame format you have the same brightness at 35mm and 1/1.4 on the same full frame format.
But don’t forget that focal length also affects light transmission. A longer focal length gathers light from a smaller area of the scene and therefore less light than a shorter focal length.
This is not the case in this context as it was specifically about APS-C vs FF. 23mm APS-C lens and 35mm FF lens have the same field of view, thus the same light reflects from the scene to the lens.
A 16mm entrance pupil diameter lets in less light while a 23mm focal length lets in more light, and that equals out to the same as a 25mm entrance pupil diameter letting in more light and paired with a 35mm focal length letting in less light.
A 16mm entrance pupil of 23mm f/1.4 on APS-C collects about 2.3 times less light than 35mm f/1.4 on FF with it’s 25mm entrance pupil - the same amount of light reflects from the scene to the lens, but the system with the larger entrance pupil collects more light.
For exposure purposes this is of course not relevant, but for image quality and DOF it is.
This is not the case in this context as it was specifically about APS-C vs FF.
Focal length affects transmission in any context. The f-number is calculated the same regardless of format size, incorporating the focal length. Exposure settings values, including the aperture as expressed as an f-number, work the same for every format size.
For exposure purposes this is of course not relevant
This discussion is about exposure purposes.
Focal length affects transmission in any context
It doesn’t, at least in principle.
The f-number is calculated the same regardless of format size, incorporating the focal length. Exposure settings values, including the aperture as expressed as an f-number, work the same for every format size.
Of course. Have I said anything else?
This discussion is about exposure purposes
Really? You went way beyond that for example when you wrote:
But don’t forget that focal length also affects light transmission. A longer focal length gathers light from a smaller area of the scene and therefore less light than a shorter focal length.
This has nothing to do with exposure purposes at all, but about how much light is collected. And as the context was FF vs APS-C and the size of aperture, what you wrote was hardly helpful.
It doesn’t, at least in principle.
It’s built into the aperture f-number because it does, just like entrance pupil diameter does. Thus, it answers OP’s real question about why exposure isn’t changing even when the entrance pupil diameter changes: because focal length is also changing and ultimately you’re arriving at the same f/1.4 f-number.
https://en.wikipedia.org/wiki/F-number
Have I said anything else?
Yes, you said: “This is not the case in this context”
You went way beyond that
I’m just talking about how focal length and entrance pupil diameter both go into the aperture f-number for the purposes of exposure. That’s literally how the f-number is mathematically defined.
This has nothing to do with exposure purposes at all, but about how much light is collected.
How much light is collected is not the same as exposure, indeed. But it’s a component of exposure that affects the exposure.
And as the context was FF vs APS-C and the size of aperture, what you wrote was hardly helpful.
What I wrote applies in the context of different format sizes. It also applies in the context of the same format size.
Well, I simply wanted to clarify what you presented in a way which seemed to me to be causing more confustion to OP in this context than necessary.
Basically this was the problem for me:
don’t forget that focal length also affects light transmission. A longer focal length gathers light from a smaller area of the scene and therefore less light than a shorter focal length.
In the context of format comparison, it can get confusing to the OP as in this context the focal lengths collect light from the same area of the scene, not different.
Thus, it answers OP’s real question about why exposure isn’t changing even when the entrance pupil diameter changes
We interpreted OP’s question differently. Not saying either interpretion is better or worse.
Crop factor equivalency for apeture is referring to the perceived depth of field with a different lens, not the brightness.
An f/2.8 lens will shoot as fast as f/2.8 does, no matter what you put it on.
An f/2.8 lens will shoot as fast as f/2.8 does, no matter what you put it on.
But what is this “speed” or “fastness”? The f-number is not just some abstract unit, but it’s tied to physical reality.
To answer to that one needs to understand that this “fastness” refers to an exposure time (or shutter speed) one can use to achieve desired image quality. Thus f/2.8 on one format does not equal f/2.8 on another.
In principle f/4.2 on FF, f/2.8 on APS-C do an identical job - they give the same image quality (noisewise) with the same exposure time, the depth of field is the same and the blur from diffraction will be the same.
do you mean that aps-c has an advantage over full frame on in terms of shutter speed?
for example, I am shooting at 35mm at 1.4 with 1/80s on full frame at the exact same light situation where I use an an APS-C sensor at 23mm at 1.4 will I get 1/80s?
if yes, 1/80s on APS-C will more less subject motion blur?
do you mean that aps-c has an advantage over full frame on in terms of shutter speed?
No, just the opposite. It won’t matter which body you put the lens on, it will operate the same way. The “equivalent” you’re chasing only pertains to FOV
100iso on full frame does not equal 100iso on aps-c. The numbers are the same but the actual amplification on iso is not transferable across cameras.
You can see this by looking at noise of the same ISO number on different size sensors, there would be more noise on smaller sensors.
https://photographylife.com/equivalence-also-includes-aperture-and-iso#iso-and-equivalence
You’ll get 1/80s with the same blur since you have the same field of view. Depth of field will be different though, the FF will be shallower.
If you stop down the FF to f2, then you’ll get similar depth of field, but then you’ll have to raise ISO to compensate.
There’s no such thing as aperture equivalent. The reason that people say things like that is because they fundamentally misunderstand what’s going on.
The people that do say things like that mean that if you are using a 50 mm lens at F2 to obtain a certain framing, you will be farther away from your subject with a crop sensor camera than you will, with the same exact lens on a full frame sensor camera. Because of the way that aperture affects the resulting boke. The crop sensor camera will appear to be similar to what you would have obtained using a larger aperture on the full frame camera at a closer distance to the subject. It has nothing to do with the amount of light physically let into the sensor, and if you were to take, the same picture of the same subject from the same position with both cameras, using the same lens and aperture and then crop the full frame image to match the framing of the crop sensor camera. The photos would be identical.
There’s no such thing as aperture equivalent.
Of course there is. If one compares different formats, then f/2 on APS-C and f/3 on FF do identical job - in principle it would be impossible to know which system was used. Thus the apertures are equivalent.
Not in the least, in your example, the pictures would absolutely be able to be differentiated between
If you put a 50 mm lens at f3 on a full frame sensor and take a picture from 10feet away from your subject with the background 10 feet behind your subject. And then take the same photo with the same lens, but now set at F2, on a crump sensor, and you want the same framing you will have to step back to about 15 feet, which means that the ratio of Camara to subject compared to subject to background has gone from one: one to 1.5: one but you have made the aperture small smaller you get the same apparent bokeh however, because of the difference in your physical position, when you took the photo, you introduced different parallax and differences between the apparent size of the subject and the background
However, If you use a 50 mm F2 on a crop sensor and take a photograph 15 feet away from your subject with the background 10 feet behind them then you switch that exact same lens to a full frame camera and use the exact same settings and take the picture from the exact same spot with the exact same background, the full frame picture will have wider framing, (the subject will take up less of the frame) but once you crop it down to the same framing as the crop sensor camera it will be identical. But, if you were to do this, but utilize a larger aperture on the crop sensor camera, then once both pictures are cropped to the same framing, the crop sensor will have less bokeh of the aperture
As I said, a lot of people think a lot of things because they don’t actually understand what’s going on
> If you put a 50 mm lens at f3 on a full frame sensor and take a picture from 10feet away from your subject with the background 10 feet behind your subject. And then take the same photo with the same lens, but now set at F2, on a crump sensor, and you want the same framing you will have to
I only commented on your " There’s no such thing as aperture equivalent. " as being false as it is.
Thus the context is 50/3 on FF and 33/2 on APS-C. In this context the apertures are equivalent, thus your statement was false.
A 50mm lens at F2.8 on a crop sensor camera will give you exactly the same depth of field and light as a 50mm lens at F2.8 on a full frame.
The difference is that the crop sensor uses less of the image circle so appears to be a narrower lens. This is where the crop factor comes into effect. The crop factor was invented in the early days of professional digital cameras, when there were no sensors that covered the full frame at the time.
It is a concept invented so that professional photographers who had years experience using 35mm film cameras could compare the field of view on the new digital cameras and select the correct lens.
After years of using the 35mm lenses they could look at a scene and know which lens they needed, but with the new smaller sensor digital cameras this would result in to cropped an image so the crop factor was used to make it easier to work out that they needed a 25mm lens when their eye’s told them a 50mm full frame lens was needed.
So now that 25mm lens gives them the field of view of the 50mm, but it’s still a 25mm and as the short focal length you use the deeper the depth of field you get for a given aperture, you would still have the depth of field of a 25mm at f2.8.
This is when they realised that the crop factor would also work in the description of the depth of field. So this meant that they would say that a 25mm f2.8 is the equivalent of a full frame 50mm f5.8 – but this only equated to the depth of field and not the light gathering capabilities of the lens.
All of these are parameters of the lens, they don’t affect the shutter speed so the shutter speed stays the same. It also only relates to the physical size of the sensors and does not take into account the resolutions of the sensors being compared.
A 50mm lens at F2.8 on a crop sensor camera will give you exactly the same depth of field and light as a 50mm lens at F2.8 on a full frame.
Different light actually. Cropping throws away light.
And diffent DOF as you enlarge the images from image plane by different amounts to the viewing size, though as the field of views are also diffent, comparing DOFs isn’t IMHO too meaningful.
So this meant that they would say that a 25mm f2.8 is the equivalent of a full frame 50mm f5.8 – but this only equated to the depth of field and not the light gathering capabilities of the lens.
The light collecting is a function of several parameters: scene luminance, field of view, exposure time and aperture size.
We’re only interested in the aperture size here. 50mm/5.6 and 25mm/2.8 both have about 9mm aperture diameter, or area of 63mm^2 or so. Thus the same amount of light goes through.
The practical implication of this is that the pictures from these systems would look identical to each other.
If we were to increase the light collecting of either system via making the aperture larger, we’d improve the image quality (noisewise) but also decrease the depth of field.
what confuses me is aperture diameter in aps-c 23mm f/1.4 is 16 while 35 in f/1.4 is 25. we all know that the bigger the aperture diameter, the more light comes inside the sensor, the more light, means faster shutter speed.
For the same lens?
The f stop is the relationship to the apparent aperture opening (as looked at through the front of the lens) and the focal length of the lens. This doesn’t matter if it is on a crop sensor, full frame sensor, medium format sensor or just sitting on your desk not connected to a camera as looking through the front will always give you the same size for the same fstop.
what confuses me is aperture diameter in aps-c 23mm f/1.4 is 16 while 35 in f/1.4 is 25. we all know that the bigger the aperture diameter, the more light comes inside the sensor, the more light, means faster shutter speed.
is this true?
Larger aperture diameter (with the same field of view, as in this case) will collect more light over the same amount of time (and also the depth of field, DOF, will be more shallow). Thus with equal exposure time the larger format will have better image quality (due to more light being collected).
The density of light will be the same though as the light is spread over different areas (FF is 2.3 times larger than APS-C). This is relevant for the exposure calcualtion of the cameras exposure meter. Thus if you use an automatic exposure program, then same f-number on different formats gives you the same exposure time. That’s kind of the point of the whole f-number system.
it is said that full frame aperture equivalent of 2.8 to aps-c is 4.2
Assuming same field of view, in principle f/4.2 on FF and f/2.8 on APS-C will create create identical results: DOF, noise, diffraction blur all will be the same.
In practise there may be some differences:
- FF can usually capture more light before burning, thus one may be able to use a longer exposure time to get better image quality.
- FF image is enlarged less for the final output, thus the lens can be somewhat worse to get the same resolution
- The smaller f-number requirement for APS-C may mean more complex and/or inferior optics
For most shooters it’s quite irrelevant if one uses FF or APS-C - not that much difference usually.
does it mean that shutter speed of aps-c is one stop slower that full frame on the same aperture?
Shutter speed can be what ever the user wants. If one let’s the camera to decide it instead, then an autoexposure program of the camera would likely use a different exposure time in each case, assuming the same ISO and light levels.
No and this is why I don’t like folks trying to use the term equivalence. Confuses folks. In exposure calculation, f/X.X is always f/X.X
There is so much misinformed nonsense in this thread that it would be utterly impossible (and likely pointless) to even try to address it.
It makes me sad that with so many “photographers” and amazing gear, this is where we are in understanding it. Not talking about the OP who asked a simple question that should have been answered and not created the pile of dung in evidence here.
Ok, against my better judgment…
Exposure is the same with every camera and lens. If a scene needs 1/100th @ f4 for correct exposure, it will need that setting (or it’s equivalent, like 1/200 @ f2.8) on every camera and every lens. Exposure is independent of sensor size. Exposure is independent of the camera or the lens. It works this way because everybody agreed that makes the most sense over 100 years ago. That way, you can pick up any camera and the exposure will be the same for any given lens.
However, a smaller or larger sensor (or film) size will have other effects: depth of field will be different at the same f-stop with a FF versus an APS-C sensor. Field of view will also vary with the same lens on two cameras with different sensor sizes.
There can be other less important effects, which are being argued about here pointlessly, but ignore them for now. What is important that that exposure is always the same, no matter the sensor size, but a different sensor size will effect depth of field and field of view.
Just learn that. Ignore all the other nonsense in this thread for now. None of it is the important part. Once you completely understand what I have told you, then you can start looking at things like noise, etc.
This is the simple correct answer to your question. No doubt someone will argue with it. Ignore it like I will.
