nickleback
Forum Pro
The entrance pupil show you the apparent image of the aperture stop, not the physical size of the aperture stop.
I'm a mathematician.
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The difference between "f-ratio" and "aperture"
- Thread starter joe mama
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Right - the aperture of the lens, the diameter of the entrance pupil.
Yes, but you and I (EE) are three sigma from the mean.
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Lee Jay
(see profile for equipment)
nickleback
Forum Pro
Diameter of the entrance pupil is the image of the aperture stop as seen through the front of the lens, it is not the physical size of the aperture stop or the physical size of the front element, or the physical size of anything. On long telephoto lenses (and telescopes), the front element tends to be the same size as the entrance pupil, so if you say "8 inch telescope", that's the front element and the aperture size. At least as far as I know. I'm not that much into telescopes. I could ask my boss, who is.
I wouldn't say we're that far. I've met plenty of nerdy photographers ;-)
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...standard deviations from the mean (I won't specify the direction), what, then is the "appropriate" term for the ratio of the focal length and the f-ratio, and what physical entity, if any, does it represent? I had thought it was merely "aperture" (as opposed to "apparent aperture" or "physical aperture") and represented the diameter of the element in the lens which contributed light to every point on the recording surface.
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--joe
http://www.josephjamesphotography.com
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I would say "aperture". I guess others would say "apparent" or "effective" aperture or some such thing. "Aperture", describing an optical device, should to me mean the optical size of the hole through which light can enter.
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Lee Jay
(see profile for equipment)
That's about right. On a scope, the aperture is the diameter of the entrance pupil. They tend to treat a central obstruction as a transmission loss like an ND filter, not as a reduction in aperture. This is because diffraction and resolving power are largely dictated by the diameter, and not the amount of light transmitted. So, f-stop matters more to astro-photographers than does t-stop.
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Lee Jay
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nickleback
Forum Pro
Where I went to school most of my profs said sd's. At least I think they did, my memory is a bit hazy.
aperture ratio
aperture
f-number
ratio
f
1 to x
I've heard at least these. Doesn't much matter to me, as long was whatever is said is understood.
And terminology varies quite a bit depending on even the subfield you are in. For instance, "order" has dozens different meanings in mathematics.
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nickleback
Forum Pro
Do scopes have aperture diaphragms? I'd guess not, as you want to shoot wide open. That could explain the difference in terminology.
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No they don't.
I'd be pretty much fine if my 85/1.8 didn't have one.
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Lee Jay
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nickleback:
Lee Jay:
Thus, combined with nickleback's next comment:
we can see that there is simply way, way, way too much confusion. Going back to the beginning of this thread, and the entire point of it, there is simply way too much confusion going on. Both the f-ratio and the ratio of the focal length and f-ratio (a term which I will argue "should" be called "aperture") are fundamentally important in photography, and need to be distinguished.
In other words, "f-ratio" is useful as a measure of the intensity of the light and for determining exposure, whereas "aperture" is useful as a measure for determining the total amount of light, and thus the "apparent exposure".
So, I argue that it is inappropriate to use the word "aperture" to refer to "f-ratio". If, however, you find "aperture" to be inappropriate to describe the ratio of the focal length to the f-ratio, then would you agree with the term "apparent aperture" since it relates to the total light and thus the apparent exposure?
Still, that seems contrived to me, and I think it's best to call the f-ratio "f-ratio" and to call the ratio of the focal length and f-ratio "aperture".
Arguments for or against?
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--joe
http://www.josephjamesphotography.com
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nickleback
Forum Pro
Sure, but I don't think you have a fix for it.
f-ratio is aperture, in the terminology of photography. Good luck changing it! And if you do, you'll only set off 20 more years of even worse confusion, as newer photographers use the term differently than old-timers.
Aperture ratio is most important to photographers, so it is called aperture. Aperture diameter is most important to astronomers, so it is called aperture.
I don't think aperture diameter is really important to photographers. You haven't sufficiently explained why it is. I know it makes a difference in hyperfocal distance and the related DOF, but that's why god invented calculators.
The difference between the light collected at the focal plane by small sensors and big sensors and the same aperture ratio has nothing to do with aperture diameter, and everything to do with sensor size. You don't need aperture diameter to explain this. Throwing in aperture diameter only adds to the confusion.
Only in the special case where you make assumptions that focal length is exactly adjusted so that angular view is the same. Use any other focal length and your aperture diameter argument falls apart. But use the sensor size and the argument doesn't change.
f-ratio has been called aperture by photographers since around the time dirt was invented. Trying to change this to something completely different only invites more confusion.
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Seriously? You don't think that the total amount of light that makes up an image and/or DOF are not only important to photographers, but central ? That's absolutely bizarre to me. I cannot fathom a photographer not thinking of these as critical considerations. A snapshooter, however, doesn't give a squat, no doubt.
As for calculators, do you really need one to use the same multiplier that you use to get the same AOV to set the f-ratio for the same DOF? That is, no one seems to balk at halving the FLs for 4/3 to get the same AOV, so why can't they be bothered to halve the f-ratios to get the same DOF? Why is it "calculator work" for f-ratio, but not AOV?
The point is not to say that the difference in total light is due to the sensor size. The point is to say that the total light (and DOF) is the same with the same aperture.
Whoa, whoa, whoa! Are you saying that the same perspective and AOV are "special cases"?! In other words, someone with a 5D does not usually frame the same way as someone with a 20D or E3?!
Why would you use any other FL other than that which gives the same AOV for the same perspective? That is totally bizarre to me!
I understand the battle. But "aperture" is a perfectly good word that has a more meaningful use than "f-ratio". In the days of old, photographers did not compare systems with different formats. In modern days, they do. And they do so inappropriately because they do not compare equivalent images. Because people compare systems at the same f-ratio rather than the same aperture, they incorrectly conclude, for example, that larger sensors have horrible edges, more vignetting, and even suffer diffraction softening earlier -- all of which are false.
There is no reason to redefine a term unless there is a need. Well, there is a need.
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--joe
http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
JulesJ
Forum Pro
joe mama wrote:
Only two points I'd like to comment on from your appraisel of my post
Jules
Why can't you blow bubbles with chewing gum?
Only two points I'd like to comment on from your appraisel of my post
Part of running a successful business includes choosing the right equipment. The business is not initially successful because of it.
See my previous point.
Jules
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sherwoodpete
Veteran Member
Which is why it is necessary to use a specific technical term, such as "Relative Aperture" or "Effective Aperture" or "Physical Aperture" when that is what is meant.
As I said previously "aperture" on its own is a vague term. It is not possible to assign a single technical definition to such a vague word.
Regards,
Peter
nickleback
Forum Pro
DOF is calculated with aperture ratio, and a bunch of other factors including focal length. Because focal length is in there and aperture ratio is the ratio of aperture diameter to focal length, you can easily substitute aperture diameter for aperture ratio, but you really don't need to. Aperture ratio is quite sufficient.
Aperture diameter doesn't affect either the intensity of or total light that makes it to the focal plane. Aperture ratio affects the intensity, sensor size affects the total light gathered.
Throwing aperture diameter into either one of these discussions only adds to the confusion.
No, not at all. It's useful for comparing systems, to see what the performance envelope is of one vs. the other.
But you don't need one if you are shooting with the system you have in hand.
If I'm shooting 35mm and want to figure out the DOF I'll get at a certain focus distance and aperture, I could whip out tables, a DOF wheel, my Treo, or even use the DOF preview function on the camera. But I'm not going to take this result and think "gee, if I had a 4/3 camera I'd need (focal length * 2) and (aperture ratio / 2), or if I had a 4x5 camera I'd need (focal length / 3.5) and (aperture ratio * 3.5)". There's no point. You use the camera you've got.
Because it doesn't look good to marketing, whose job it is to point out the advantages and ignore the disadvantages? Because it's not blindingly obvious, like focal length is?
I don't know.
But it is!
And again, aperture diameter has little meaning to photographers and there's a good reason for that. I already explained it above.
If you'd like to say the focal length needs to be adjusted by a certain factor, and aperture ratio by the inverse of this factor, I'll completely agree with you. There is no need to drag in aperture diameter. You are only going to cause more confusion.
Yes.
I'd certainly say somebody with a 5D or 20D does not frame (as in fill the frame, perhaps not imagine how they'll crop later) the same way as somebody with an E3. They can't! They have different aspect ratios!
The "focal length factor" is based on comparing diagonals. It's one (but not only!) way to compare focal lengths between different camera with different aspect ratios. But I've yet to meet a photographer who frames diagonally. I'm sure one exists.
See above. Different aspect ratios. If I want to shoot something with the same horizontal field of view, and I've got a 5D and a E3 in hand, the focal length on the E3 is going to be not half, but less than half the 5D's focal length. And of course I could figure out the ratio of focal lengths in this situation, and then apply the same ratio (but inverted) to aperture ratio, or even go the extra unnecessary step of converting aperture ratios to aperture diameters and comparing those.
But really, is this going to happen? Maybe, if I am in a store trying to pick one or another, but that's it. If I'm shooting, I'm shooting with the camera I've got. All this comparing focal lengths and aperture ratios and aperture diameters aren't going to matter. I can't change the camera I have in hand, I just have to shoot with the damn thing.
They most certainly did. But if you just hung around people who shot 35mm exclusively, which was 98% of all "serious" (I hate that term) photographers since the '60s, you'd never hear it.
I agree. But adjusting focal length and aperture ratio are sufficient. There is no need to drag in aperture diameter. It doesn't change the result, it just adds a step and causes even more confusion.
I disagree.
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In days of old, people certainly did compare systems of different formats, but I don't remember nor have I read that equivalent images were of much concern. Format comparisons seemed to center around things like available viewing systems (ground glass back, reversed reflex, unreversed reflex, simple optical, etc), negative size (larger negatives are easier to retouch and can make contact prints suitable for albums; larger negatives require less enlargement for a given print size for potentially sharper, more grain-free images), economy/flexibility/convenience (roll film is cheaper per frame and easier to carry, but cut film allows individual processing of each image; miniature and medium formats can allow successful hand-held photography under many conditions; roll film was more readily available than cut film or 35mm cassettes).
In modern days, it's still appropriate to compare formats using factors other than equivalence in image-making, but we've also reached a point where commonly-used formats are no longer capable of being equivalent. With 35mm and medium format, either can give limited depth of field or extended depth of field (the 35mm camera might need an f/1.7 lens to match the isolation properties of medium format at f/2.8, but it can be done), but the small sensor cameras (e.g., the 1/2.5" sensor) simply can't be opened up wide enough to throw a background as far out of focus with a normal focal length lens--you get extended depth of field all the time (which might be great, but needs to be a considered choice).
It has only been in the digital age that I've found a use for aperture diameter. With the absence of usable distance and depth of field scales on the lenses, I've been turning more to Harold Merklinger's approach to achieving the needed depth of field in an image, and his system is based on aperture diameter. http://www.trenholm.org/hmmerk/DOFR.html
JulesJ
Forum Pro
...aren't i lucky to have got through fifty years of photography without having to worry about all this stuff.
jules
(Enjoying photography without the pseudo content.)
Why can't you blow bubbles with chewing gum?
jules
(Enjoying photography without the pseudo content.)
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Why can't you blow bubbles with chewing gum?
This is the source of all the confusion! I'm talking about comparing systems, you're talking about using a particular system. That's why we disagree on the importance of "aperture" vs "f-ratio".
Now that is the exact point I was trying to imply! : )
In the context of comparing systems, do you still think that?
For sure, the aspect ratio plays a critical role in framing. But I would argue that even then, people would frame with the same, or nearly the same, AOV, regardless of the system they used.
One exception is that with the higher IQ of the 5D, I notcie that I now frame wider than I did with the 20D. However, were I comparing the 5D to the 20D, I'd compare at the same FOV.
Actually, it's more minor of a correction than you might think. Scroll down to the 5th paragraph of the FOV / AOV section here:
http://www.josephjamesphotography.com/equivalence/#equivalence
I stand corrected (per the jrtrent's reply on this issue).
For sure, as it's not as important when staying within a single format. I like to compare the distinction between f-ratio and aperture as being similar to that of mass and weight. So long as you remain in a uniform acceleration field, they are often (but not always) interchangable. But when you are comparing motion in different acceleration fields, the distinction is key.
Yes, but the concept of "aperture" explains why the f-ratio changes. Many people feel, as this thread began, that "f/2 = f/2 = f/2" regardless of format, and do not fully understand, or understand at all, what effects the f-ratio has on sensors of differnent sizes. By thinking instead in terms of "aperture", all becomes clear.
The reason I feel that way is that I am coming from the perspective of comparing systems, where you are coming from the perspective of using a particular system.
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--joe
http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
I should temper my opinion as I've no "real" business experience. I base my opinion on the times I have seen photos (magazines, such as National Geographic), the newspaper, school photos, and one portrait I had made.
In no case do I see images that any modern DSLR could not "get the job done" in terms of IQ (operation, yes -- IQ, no).
For example, the single portrait photo I've ever purchased is this:
Fuji S2 pro, 38mm, f/8 (61mm, f/13 35mm FF equivalent), 1/125, ISO 100:
http://www.pbase.com/joemama/image/76745231
Would it have been better with a 5D? For sure. Did the equipment they were using affect my buying decision? Not in the least.
So, I wish to temper my earlier opinion by saying that there are a great number of businesses where they would be aptly suited with any modern DSLR, but not necessarly all businesses.
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--joe
http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
Much in the same way that a person can happily drive a car for fifty years without ever knowing how it works. A person doesn't "need" to know how it all works to be an excellent, or even outstanding, photographer. But for some people, a knowledge of how and why things are the way they are is interesting on an intellectual level.
And not a thing wrong with that, either. If you don't enjoy the technical, there's no reason you should be encumbered by it.
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--joe
http://www.josephjamesphotography.com
http://www.pbase.com/joemama/
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