Richard Butler: It's been suggested to me that people would be happier if we used the term 'Equivalent F-number' rather than 'Equivalent Aperture.' Is this the case?
@mostlyboringphotog - I don't own the DPR and I'm trying not to enforce my own opinion on everyone, that's why I'm asking. The problem is that there are multiple opinions on the matter.
I realise you don't like the term equivalent F-number, since you're not comfortably with describing it in terms of F-numbers. However, while I understand the semantic concerns, I think suddenly trying to use a different metric to describe almost all of the behaviour associated with the aperture would be perverse (personally).
I was under the impression that 'equivalent aperture' was less objectionable than 'equivalent F-number' on that basis, but other people are telling me otherwise.
That's why I'm checking.
beavertown: Best 1' sensor in the Market:
What makes you think there are that many 1"-type sensors on the market?
We know that Sony and Aptina make them. Who else does?
kociasek: The caption under the photograph of the four lenses seems to be wrong. It says:"These four lenses are all 85mm equivalent F1.2s. However, this does not mean they're all 85mm F1.2 equivalent."Unless I'm mistaken, "equivalent" should be dropped from the first sentence.
The intent of the article is to provide the information to assess any two pieces of equipment (neither of which are necessarily full frame).
It doesn't presuppose one starting point or one end point.
For instance, compare the Olympus XZ-2 and Sony RX100 II:
Olympus has a 1/1.7" sensor, a 6-24mm (28-112mm equiv) F1.8-2.5 lens
Sony has a 1" sensor, 10.4-37.1mm lens (28-100mm equiv) F1.8-4.9 lens
Which offers shallower depth-of-field at wide angle? How about at the long end? How different/similar are they?
At which point, saying:
Olympus, 6-24mm F1.8-2.5 lens (28-112mm F8.4-11.7 equiv)
Sony, 10.4-37.1mm F1.8-4.9 lens (28-100mm F4.8-13.2 equiv)
Tells you something useful, doesn't it? (Being able to see [how they progress]( http://www.dpreview.com/files/p/E~articles/6489685206/EnthusiastAperture0314.png) is arguably even more useful.
Hi Kociasek. No problem.
I agree a hyphen would help, but enough places on the web (including us, from time-to-time, embarrassingly), forget to even include the word 'equiv.' let alone a hyphen, so I'm just expressing it the way it's most commonly encountered.
It's been suggested to me that people would be happier if we used the term 'Equivalent F-number' rather than 'Equivalent Aperture.' Is this the case?
Personally, when I shoot, I try to compose the final image I want (regardless of format). As such, it's useful to understand to which extent what equipment in another system would allow me to take a similar photo (if I was choosing between systems, which is what this is primarily useful for).
It seems much more likely that I'd use an 85mm on FF and a 32mm on 1"-type, shooting at the same distance (since they offer the same field-of-view), and it's easier for me to imagine than it is to try to think about shooting a 32mm lens on FF but standing at portrait-shooting distance, then trying to think of where the crop would be.
Cropping an image also *does* change the per-image noise performance, if you view/print both images at the same size.
wansai: while applaud dpreview for doing this article, i have the distinct impression all it is doing is confusing more ppl than it is helping.
camera settings for any exposure of a scene is done for your respective sensor/camera. it's not useful to consider its equivalence, only what focal length/reach do you want, how are you framing it and what settings on THIS camera do i need to get the exposure.
equivalence is purely academic and is being used almost entirely by fanbois to support either of their cases for superiority.
when taking a shot, what does it matter what the Ff ewuivalence is? here, now, my camera, i need my f stopped to x to get a certain amount of dof. i need the iso and shutter to be set at xx. i expose.
that's all that matters.
Isn't that almost exactly [what the article says](http://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care/4#why)?
You are mistaken. It's the word order that's important. For example, the Nikon 1 lens could quite accurately be described as:
1) 32mm f/1.22) 87mm equivalent f/1.23) 87mm f/3.2 equivalent
The second description is the most common currently used and is accepted by industry body CIPA.
Arguably stating both 1 and 3 is the most useful information to provide.
lumigraphics: Sorry but you guys botched a bunch of this. :sigh:
"Total light" is completely unimportant. Yes, there is less light hitting a smaller sensor, but it doesn't matter because its a smaller total area. Light PER SENSEL is the same.
And lenses don't matter at all. Given a frame-filling grey card (as an example) a 50mm f/4 and 100mm f/4 will give exactly the same 18% grey image on any sensor size. If lenses didn't work that way, you couldn't have external light meters.
Larger digital formats aren't less noisy because they are larger so they collect more light, its because they can have a lower sensel density. In the film days, it was because you didn't have to enlarge so much with a bigger negative.
smdh...and I'm only on page 2.
You'll notice there's almost no mention of pixels in the article. This isn't unintentional.
There will be an article about noise in the coming weeks. I'm afraid it's likely to say some things that you disagree with.
xtoph: Where this article stumbles is in not clearly addressing at the start the fact that the two systems compared have different aspect ratios, and thus the 'equivalent' shots will not look at all the same (different things will be included and excluded in each; they will decidedly not "have the same framing"). This maybe should be obvious, but i doubt it actually is obvious to many of the people who might actually benefit from reading this (people just geting started choosing a camera).
Also, xtoph, this isn't about two systems, it's about *all* systems.
I really didn't want to use Four Thirds as the example, since I know that's the format about which there's been most argument. Equally, I went out of my way to stress that Full Frame is used as a reference point because it was well understood in the film era and has therefore become the reference point for focal lengths, not because it is an optimal or idealised standard.
However, it's much easier for most people to do mental arithmetic with multiples of 2, so it's easier for people to spot something doubling or halving, relative to another.
This is information is relevant for comparing between 1/1.7"-type, 1"-type, Four Thirds, APS-C, Full Frame and medium formats.
Bodhi Dharma Zen: To put it in other words. MARKETING people are (professional) liars. They would push a lens as being "2.8" when, in reality, their light sensitivity is a lot less (depending of course of the relative size between sensor and lenses)... There should be LAWS to guarantee that marketing people should be limited to stating FACTS in RELATION to an approved standard.
They behave comparably in terms not just of depth of field but also how much light in total is projected onto the whole sensor area during any given exposure time. (ie: change ISO, not shutter speed).
However, we are not advocating the use of equivalent aperture for exposure.
Ultimately, if they two behave so comparably, what else would you propose we use, rather than F-number?
@Fygaren - it's not totally wrong.
By *definition* F1.2=F1.2=F1.2. We're not disputing that.
However, F1.2 does not give the same results across different formats. The combination of the way F-numbers and ISO rating work mean that they give the same JPEG brightness. Again, the article explains that.
An F1.2 aperture on a 2.7x crop camera behaves comparably (from a physics perspective), to an F3.2 lens of the same field-of-view on a full frame sensor. This is demonstrably true (and I've done my best to demonstrate it).
We've not suggested that anyone should completely give up on the ISO way of looking at exposure or do away with F-numbers.
However, we have explained a rigorous means of understanding how formats compare to one another, which can help understand the trade-offs inherent in *all* camera systems.
Autoxave: The specs of of this lens is 25-400 mm/2,8-4. In terms of a FF sensor this will translate (equivalence) into 9-148 mm/5.6-10,8?
In simple terms: F-numbers dictate how *intense* the light is - how many photons land on each square mm of sensor. Sensor size dictates how many square mm you have, collecting the light.
As a result, a 25mm F7.6 lens on full frame would project 1/7.4th the light onto each square mm of the sensor than the 9.1mm f2.8 lens would onto the FZ1000's sensor.
However, the full frame sensor is 7.4 times larger, so the total light available to make up the image would be the same.
Ruy Penalva: Butler. My question. It is told that f/8 is the optimum limit to diffraction in digital sensor. My question to you is: The shift in aperture equivalence is followed by a decrease in diffraction too? In other words. Take a Panasonic lens with an upper f/5.6 aperture. The equivalent aperture of that lens would be f/11.2. How that real aperture of f/5.6 (or 11.2 equivalent) behaves in regard to diffraction? Is diffraction related to amount or to intensity of light?
From the bottom of page 2:
*Although diffraction depends on F-number, its impact on the image is proportional to sensor size. This means diffraction will have the same impact on two images shot at equivalent apertures.*
Consequently, if you've decided that f/8 on full frame is as far as you're willing to push the depth-of-field/diffraction balance, then yes, that would be f/4 on Micro Four Thirds.
Fygaren: Richard:"But F1.2 is not equivalent to F1.2 across different formats"F-number is a relative dimensionless number that is a quantitative measure of lens speed, so there cant be an "equivalent" across different formats. Its already "the equivalent" so to speak. When you use f-number and DOF toghether things get messed up, as its only distance and aperture diameter that determins DOF. The f-number free it self from aperture diameter (f2 can be any diameter) and only say something about intensity.You can use the f-number to calculate the aperture diameter and compare it to other aperture diameters, but "equivalent f-number"...nah, its a relative number for light intensity per square area. Anyway, a clumsy mix when used together.F2=F2=F2 and the same aperture diameter gives the same DOF.Nothing wrong in your article, just that so many speak of f-number as if it was aperture diameter. I think a clear use of f-number with exposure and aperture diameter with DOF would help
It is, but, given a 50mm f/2 lens on a Four Thirds sensor and 100mm f/4 lens on a full frame camera (at the same shutter speed) give the same field-of-view, project the same amount of light over their imaging circles, give the same depth-of-field and the same diffraction, it would seem perverse to try to invent a new way of describing the aperture, just for this usage.
Equally, you could argue that focal length is focal length, so why do people keep saying a 9.6mm lens can be equivalent to a 28mm lens?
No aspect of the 9.6mm lens has suddenly become 28mm.
JABB66: Some special considerations in case of Foveon sensors?
@JAB66 - You don't have to make any other considerations of sensor area, though the very different sensor performance of Foveon chips (which I can't sensibly address in the space available), is an extreme example of why I'm wary of drawing absolute conclusions from the effect of total light.
I didn't mean to suggest total light isn't *a* metric - just that it isn't the metric of image performance, since equally efficient sensors isn't a perfect real-world assumption.
And yes, we fully plan to write an article looking at sources of noise (and the fact that shot noise is your biggest enemy in most circumstances).
quezra: This article goes to show that people will believe what they want to believe, and all the detailed evidence and careful explanation in the world won't change that. The enormous number of posters jumping in to flatly assert the article is wrong (or make claims that clearly show zero understanding of the article) is getting into the double figures now. Fun to watch actually :D
4) Are we asking lens manufactures to include markings in equivalent F-stops?
No. Or, at least, I'm not. That wouldn't be helpful. Maybe list it in marketing materials, but don't mark it on the camera/lens.
5) By this process a lens can be described by any equivalent FL/F-stop which is contrary to the lens specification as we know today.
Given how poorly understood they are, maybe we should change them. CIPA currently allows the inclusion of FL, F-stop and equivalent FL. Rather than mixing and matching (and getting the '25-400mm F2.8-4' confusion), why not state FL + F-number then eFL + eF-number?
6) You do say that 50/2 lens on a m43 will have equivalent DOF of 100/4 lens on FF and I say full stop(pun intended) here and don't add then therefore 50/2 lens have equivalent F/4.
I'm not saying it will have equivalent F/4. I'm saying its behaviour on that sensor is equivalent to the behaviour of an 100mm F/4 on full frame (which it is, in almost every respect).
Reason 1) Equivalency of a dimensionless number seems counter intuitive.
I agree, it's not ideal. But, since you've got the equivalent focal length, you know what it's referring to.
2) will be confused with "equivalent exposure", IMHO.
I'm not sure what we can do about that (it's not my terminology).
3) The equivalency is on DOF and not F-stop, IMHO.
I'm open to suggestions of better terminology.
In which case, I don't understand your concerns. I can't see what you're taking issue with in the article, just that you don't like it.
I'm also not sure what makes you think any posters have any connection with me or reason to wish to defend me.