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Forum: General Photography
02-03-2019, 05:42 AM
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Let's do this: have levels of lessons in photographic "equivalence". Level 1 for the likes of me, who want to graduate with a working knowledge of equivalence between the formats. Level 2 for Mike and company, who want the working knowledge along with the theoretical application in real life examples to accurately recreate work with different formats. And finally, Level 3 for Kunzite and such scholars who wish to come out with a PhD in optical equivalence.
There, settled.
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Forum: General Photography
02-03-2019, 05:26 AM
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Yes, I agree with you.
AoV is usually what we care about in replicating a scene in a photograph. DoF is more to a personal taste rather than an intentional reproduction from another image, so I appreciate that the utility of equivalence seems to be more theoretical than practical. But the concept is still useful in that it makes the photographer consider the FL and aperture to get the intended effect that he/she has in mind with the gear he/she has. Of course, that means comparison with what is considered a standard format, let's say 35mm FF. But even without comparing, I know from knowing this theory that shooting with 4/3 format will mean I will need a wider lens with larger aperture if I am to create an image I would normally shoot in FF.
It all seems like blah, blah, blah after a while...
To me, once you appreciate the theory, the practice of it comes with mental calculations of FL and aperture to know what will work for the intended shot using different sensor formats.
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Forum: General Photography
02-03-2019, 02:58 AM
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Corollary situations:
The Hb-O2 dissociation curve: Understanding the Oxygen Dissociation Curve - Medical Exam Prep
cyclic adenine monophosphate and cellular second messenger systems: Cyclic AMP and Its Action
Cardiac Failure and the Frank-Starling Law: CV Physiology | Frank-Starling Mechanism
Obviously wrong forums for these topics but the point is: in medicine there are many, many concepts that are both simple and complex at the same time. Simple in that the phenomena can be explained and conceptualised in basic terms, and the learner can get a reasonable gist of how the body's physiology works. Complex in that there is an infinite amount of detail one can go into to explain the nuances of each bodily system and the physiological processes that occur within them.
We all start our knowledge base from somewhere, and these lecturers we had knew that we couldn't reach his level of knowledge unless he begins with the fundamentals of the physiology of the human body. His summarising statement at the end of his first lecture makes it sound easy: "Air goes in and out, blood goes round and round, and oxygen is good!"
Whilst that doesn't make intensive care specialists out of his students, it's meeting their needs at their level of expertise right where it should be.
So too can the approach to equivalence be. Steady steps towards a solid, workable understanding of the concept.
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Forum: General Photography
02-03-2019, 02:33 AM
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I believe it is up to the student to decide whether he/she is ready to delve into the topic, otherwise he/she should just shoot and leave the topic for when they are able to get their head around it.
Agreed. AoV and DoF together must be included in any discussion on what we're referring to as equivalence, or else it is not equivalence. That's fine. AoV alone is only concerned what what you can fit in the frame, which is only part of the picture.
Hear, hear. Although it may not be a major game changer, the AoV appreciated by my FA Ltds has (to me) breathed new life into these lenses.
Yes - either get a new teacher, or accept that the student is not ready for the topic and abort the lesson.
Once the concept is understood, it is no longer confusing.
That's a no-brainer there. You don't teach calculus to someone wanting to solve a linear equation.
If we're talking about photography class, then it's up to the teacher to "get it right". I don't think it's an overly difficult topic and the way I would teach it is by using scenarios married in with the images I have previously posted to illustrate the AoV and DoF interrelations.
Yes. The video was more for our benefit rather than for beginners. That is DEFINITELY not a video for beginners and this was made very clear at the beginning of the video.
You can elaborate on a simple concept to the nth degree, but the concept itself can be explained without all the complex mathematics.
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Forum: General Photography
02-03-2019, 12:51 AM
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I suggest its utility is not "very limited". It is a concept used all the time by photographers shooting with different formats. Only it is not thought of as being "used" because once the concept is grasped, it only involves basic mental calculations to obtain the information needed to get the result desired by the photographer. It becomes inherent, even second-nature, rather than a conscious application of a formula or calculation.
As for if it has to be confusing, no. But the learner has to be at a stage where the concept can be imparted with understanding for it to be useful. The trick is to discern whether the learner is indeed ready for the lesson. If not, it is indeed a waste of time trying to get them to the finish line. If so, then the concept can be perpetually beneficial to them picking up a camera, any camera, and be able to choose the lens (and aperture) they need for the job at hand.
As for it is being forced, I don't understand who is forcing who to learn equivalence here. Kunzite has been immensely valuable in the discussion, despite any small difference of opinion in the approach of this topic. I respect that, but I see no evidence being dismissed. I have already stated previously how topics can be confused, but that should not mean they cannot be learned. Right place at the right time. That's all.
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Forum: General Photography
02-03-2019, 12:37 AM
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:lol:
We worked out "equivalence"
Now, how to explain it without causing confusion...
Perhaps this might help:
Youtu.be
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src="https://www.youtube.com/embed/6XMk9jFcnlA?controls=1" allowfullscreen>
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Forum: General Photography
02-03-2019, 12:15 AM
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See it this way: I did advanced mathematics in high school. Absolutely loved the subject. Devoted way too much time to it to the detriment of other subjects. But it required a lot of work to master. Advanced calculus is a topic that is quite complex looking at the typical questions being asked, because they often require multiple concepts to be used in order to break down the problem into workable "bite-size" pieces of the puzzle to decipher and get to the final answer. Many of my schoolmates faltered and either dropped down to the less advanced level, or just ignored the concepts. The teacher was very good at demonstrating the concepts required to work the complex problems out. We don't consider calculus a useless topic with no value just because the excellent teacher did not succeed at getting all the students to fully understand the concepts in the subject. It is used extensively in engineering and construction. We just have to accept that not all will understand it adequately to be able to use it (so maybe rethink their desire to be high-rise building engineers).
The topic is sound, rooted in observational science, demonstrable and repeatable. The fact that it is difficult for some to comprehend only means that either the teacher is not getting the message across well enough, or it is simply too complex for the student to appreciate the concept.
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Forum: General Photography
02-02-2019, 11:59 PM
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Um, I'm not denying that the topic is being confused. Nor should you insinuate that I don't get that it can be confused. What I am saying is that a topic that is difficult to grasp by some does not denigrate its practicality. If a beginner doesn't understand it, yet wants to understand why different FLs produce different FoVs on different formats, then the *same concept* has to be explained in a way in which he/she can understand it. Such as: here's a 50mm lens. Here's it on a K-1. See the FoV on that? Now here is it on a K-3. See the FoV on that? They are different right? So now here's a 31mm lens on the K-3. See the FoV on that? Looks the same as the 50mm on the K-1, right?
So now shoot a close-up portrait with both cameras and their respective lenses at f/5.6. They look different right? That's because the wider FLs will have greater DoF at the same aperture. Now to get a similar result with the K-3 + 31 as you do on the K-1 + 50, you would have to set the aperture wider on the K-3 + 31 to achieve a similar result. It won't be the same because the OOF areas will be rendered differently on the 31 as it will on the 50, but you get the general idea.
If somewhere along the line a beginner is lost, the step would need to be demonstrated differently again, preferably using examples. Or call it a day and just practice shooting, because the subject is probably beyond them. That's okay. But that doesn't mean the topic being confused has no practical value.
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Forum: General Photography
02-02-2019, 11:19 PM
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Mike has been saying this from the beginning, just the other way around (confusion is in the teaching, not the concept), and his original post actually does the subject quite a lot of justice. It's all the other baggage attached to it that makes it more problematic than it really is (or needs to be).
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Forum: General Photography
02-02-2019, 09:44 PM
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I do believe the science of it is bogging down the practicality of the basic concept. We know that what a lens sees is "snooted" by the camera sensor depending on its size, and this determines your field of view, but there isn't much more to equivalence than getting a similar field of view and depth of field in the different format. Everything else is superfluous. Yet another way of depicting the concept:
 "Normal" Lens Field of View Equivalents of 645 Medium Format
And seeing the concept from outside the sensor: Equivalent Focal Length and Field of View |
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Forum: General Photography
02-01-2019, 05:25 PM
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Now, now. Let’s settle down with the personal undertones. This topic has well and truly burnt itself out, so let’s not try and make it into a “why I won’t use equivalence” satire thread.
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Forum: General Photography
01-31-2019, 04:46 AM
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Given the exact same subject, the images between these examples will be similar but not exactly the same. This shouldn't be in dispute, but the similarity is enough to give the phenomenon a name. Whether equivalence or parity, it really shouldn't matter. It is recognised that results won't be "equivalent" but can approach equivalence with close observation of the parameters. That should be the limit to how much equivalence we attribute to "equivalence". And let's get on choosing the right lens and aperture for the shot being taken...
I'm not sure when this ever became a doubt, but of course you cannot have "equivalence" without recreating the depth of field formulated by the alternate aperture for the alternate focal length.
It must be time to get out and shoot already.
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Forum: General Photography
01-30-2019, 02:17 AM
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In the current climate, we can wrap this thread up by calling equivalence “fake news”. :lol:
But as with all fake news, there is an element of truth mixed with embellishments and/or untruths that this topic seems to fit into much the same.
Nevertheless, there are practical examples where an almost-equivalent photo (because let’s be frank, in replicating an image it doesn’t have to be exactly the same) can be achieved with an alternate format using basic formulae to calculate the FL and aperture required on the new format compared to the “base” (comparator) format.
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Forum: General Photography
01-30-2019, 01:31 AM
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A fair point. I don’t believe there is a situation where a photographer has the aperture, shutter speed and depth of field in mind before considering what subject will be photographed. Invariably the thought process is the corollary. See an interesting subject, measure out the settings required to create the desired effect in the photo, then shoot. Equivalence doesn’t come into play unless another format is on hand with the right lens for the job.
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Forum: General Photography
01-29-2019, 08:29 PM
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Yes! This ^^
And Alex, I’m certainly not ignoring your comprehensive responses, just appreciate that not everyone approaches the challenge as scientifically as you and want to look for a simple answer to the simple question of how to recreate an image in a different format. I must admit, I don’t personally find equivalence a pragmatic endeavour, because there is no question in my mind as to what FL is needed for the task ahead of me, no matter whether I pick up the K-1 or the K-5. Even as an academic exercise, it should be less of a purist and more of an applicative consideration.
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Forum: General Photography
01-29-2019, 01:16 PM
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The notion that equivalence “breaks” at the slightest variance of factors doesn’t mean its utility is limited to perfect circumstances only. Approaching equivalence with those factors kept as close to constant as possible is still helpful to explain how one format obtains an image and how with a change of FL and aperture you can obtain a similar image on another format.
One has to appreciate what FL is “normal” or “wide” or “telephoto” on a given format for it to be useful to compare with another format.
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Forum: General Photography
01-29-2019, 02:47 AM
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Yes, thank you also Dave. I appreciate your answer in the same vain. Informative and not at all demeaning.
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Forum: General Photography
01-28-2019, 08:29 PM
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The debate is seemingly about whether format affects depth-of-field.
The proof that it does is seen in photographs, but the photographs must be taken under certain conditions, assuming only one variable, which is often not the case as I alluded to above with regards to image projection. Images printed the same size between formats already introduces another variable which "breaks" the equivalence formula.
When comparing the amount of depth-of-field of two formats, the photographs must have the same field-of-view or magnification (focal length ÷ object distance).
If the field-of-view is the same, then you're comparing apples to apples.
A 35mm-film photograph taken with a 50mm lens, has a wider field-of-view, than does a photograph taken using a 50mm lens.
So, if a comparison is made between a 35mm-film camera with a 50mm lens, the focal length of the DSLR must be 33mm (1.5 lens factor).
Because equivalent focal lengths are used, giving the same field-of-view, the only variable is format size.
Besides having the same field-of-view (magnification), these factors also apply to the discussion.
• The subject is the same distance from both cameras.
• The lens opening number is the same for both cameras.
• The circle-of-confusion used to determine depth-of-field for each format is the same fraction of the camera's format sizes.
So the out-of-focus blur that is considered to acceptably sharp, the depth-of-field, is judged using prints of the same size, and viewed from the same distance.
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Forum: General Photography
01-28-2019, 08:22 PM
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What gets confusing is how the images are projected onto a screen.
Keeping all sensors equal in terms of pixel pitch and *proportional* resolving capability, you have 1.5x the pixels on a FF vs an APS-C image, and then what happens is that it is projected to "fill the screen" on the monitor when editing/viewing the image. This gives the lower resolution APS-C image the impression of lesser depth of field when there is strictly no change to these factors.
People who understand equivalence will appreciate this and not attribute the different results as being an advantage of APS-C over FF.
The following article addresses this quite well: Sensor Size, Perspective and Depth of Field - Photography Life |
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Forum: General Photography
01-28-2019, 08:09 PM
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Aside from the terminology discrepancies, which are bound to happen, the concept itself is sound IMO.
What has been confused a number of times in this thread is that it is not the FL of a lens that has to be "recalculated" for equivalence between formats, because that is a fixed optical quality for any given lens.
The crop factor alters the FoV, which then requires an alternate FL to achieve the equivalent FoV seen through the VF of the FF camera.
How much does this help a beginner? Only as far as what they see through the VF. That would be the extent of its practicality for the early stage photog.
For the more advanced photog, it is a more intuitive phenomenon that can be calculated mathematically, but pragmatically is more instinctive, since in the field, when carrying multiple cameras of different sensor formats, switching from a FF to an APS-C for a particular shot will be an easy mental exercise to determine the FL required to get the job done.
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Forum: General Photography
01-27-2019, 03:24 PM
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Okay, thanks for that. Nevertheless I acknowledge my own error and edited my post to reflect this to perhaps help to avert confusion that is inevitable in the topic.
The optical properties of a lens are fixed. I'd like to see what others think of the two scenarios I posed, both from seasoned photographers and those who consider themselves a rookie in optical theory and less experienced (I find myself straddled between the two groups).
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Forum: General Photography
01-27-2019, 03:14 PM
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As another example, there is the scenario of using a single lens, let's say 50mm f/1.4, on a FF shooting at 2m from the subject at f/2.8 compared with the same subject shot on APS-C from 3m away at f/2.4 (or thereabouts). If all else is equal, does this produce equivalence like the example I gave previously (post #271)?
It's a loaded question, the results are not going to be identical, but is a newbie going to tell the difference?
Perhaps we're alluding to the concept of equivalence being too involved for a beginner to get their head around for it to be meaningful, yet they are the very target for explaining the differences between sensor formats. Sure, this concept is not vital for a customer to know whether they are buying into the right system for them, but if all beginners had a complete grasp of this theory, would it have made them purchase an APS-C over a FF or vice versa? Hard to know.
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Forum: General Photography
01-27-2019, 02:59 PM
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You might be referring to mine, but it was a genuine mistake, rather than a misunderstanding. So let's revisit the scenario then: A photo with FF at 50mm f/2.8 compared with the same subject shot with APS-C at 35mm f/2.4 with the same subject to camera distance for both shots. All else being equal (including lens qualities, pixel pitch, ISO and lighting), is it the same result? A beginner will say yes. What do all of us say here? Is it going to be a meaningful difference?
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Forum: General Photography
01-27-2019, 02:13 PM
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There would be little point in trying to completely explain equivalence to a newbie with no understanding of FL and aperture, but the basics of equivalence (i.e. not the finer details and nuances) can be introduced and the caveats of the “similar results” comparisons between sensor formats be pointed out for clarity. What it takes is someone knowledgeable in the field to explain this right. How many people in the position of explaining this to those who are in most demand of this knowledge actually fit this description?
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Forum: General Photography
01-27-2019, 02:07 PM
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Equivalence is neutral in this discussion, just like any branch of science it can be misunderstood or misused to be more of a hindrance than a help. But just like in my own field, there is no point in decrying and seeking the abolishment of Dr Google when people implement incorrect guidance from it when they were none the wiser, and wanted a DIY fix. When people get it wrong, they often seek professional help (hopefully what they’ve done doesn’t kill them before they’ve sought assistance).
Here, equivalence is certainly no Swiss Army knife, but it’s also not totally useless. Beginners do want to understand what the differences are between sensor formats and equivalence is one of those methods of explaining them. Whatever other explanation there is for a beginner, it still has to incorporate what it would take to make the viewfinder look similar between the two formats. We know here that the FL and aperture of lenses can be “changed” to render similar but not strictly the same results, but a beginner will not appreciate the differences.
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