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02-03-2019, 05:34 AM   #616
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QuoteOriginally posted by Kunzite Quote
@Mike:
Interesting story, and my bias towards books rather than Youtube tutorials is heavily due to my experience in computer programming.
However, I don't see where you're going. "Equivalence", after all, is just a formula to "convert" between formats - it brings no in depth understanding.
I don't think I'm going anywhere with that story, Alex... other than, perhaps, to illustrate how depth of understanding was / is important to me, but I got a long way initially without it (in this computer-related example). I felt compelled to gain that depth of understanding - I wasn't satisfied with simply knowing that high level statements in BASIC would give me certain results. I wanted to know why that happened, what was going on behind the scenes, to have fundamental understanding and control of what was going on.

I sometimes cringe when I look at web development activities these days, where some folks really only understand very high level programming related to very specific areas of functionality that relies on multiple frameworks and libraries of yet more high level code. So many of those people have no idea what's happening at the processor level. But that's mostly me being nostalgic for the way I learned. In reality, if they get the results they need without truly understanding the grass roots technology, it shouldn't matter to me.

I'm all for depth of understanding. But I think there's more than one route to get there. Learning formally by reading and practising is undoubtedly a great way. But sometimes folks will learn convenient tricks to help them achieve certain goals, and those can be useful until they develop a deeper understanding.

I do, however, accept the dangers and limitations therein, as I've previously noted

02-03-2019, 05:41 AM   #617
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This pertains to the subject but not about our subject. An article Ash put up got me investigating AOV and FOV because it contradicts what I had just learned and even the article contradicts itself.
This explores that contradiction. Might be of interest or not to you.
Angle of View Vs. Field of View. Is There Even a Difference?!
02-03-2019, 05:42 AM - 2 Likes   #618
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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.
02-03-2019, 05:53 AM   #619
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I think we've come to the place where we are arguing whether equivalence is about exact replication of image between formats or whether it is a general principle that simply relates different size sensors and the lenses mounted on them.

If you believe that it is only about the exact replication of individual images, then I agree, it has very little utility for most photographers.

If, on the other hand, you believe that for photographers who shoot multiple size sensors/film sizes it is something they often keep in the back of their mind as they are choosing settings, then there is benefit to understanding it. I still shoot APS-C and full frame and while I'm not constantly thinking about it, it does help me as I try to shoot images that achieve my vision of a particular scene.

02-03-2019, 05:55 AM   #620
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QuoteOriginally posted by BigMackCam Quote
There's an interesting parallel here - sort of - with my experiences in computer programming...

I got into programming as a young boy - I think I was 11 or 12 years old. My first computer was a Sinclair ZX-81 with 1K RAM. Initially, I learned to programme using the built-in BASIC interpreter, documented in the accompanying manual. Of course, I didn't really understand what the computer was doing, but BASIC gave me a means to an end, and I wrote some great little programmes. For a few months, I was able to achieve everything I wanted using just that limited knowledge of BASIC... but it was clear to me there was more going on behind the scenes, more I could do, things that I could achieve more efficiently if I understood the fundamentals. So I started reading up on microprocessors and instruction sets (my most-read book at the time was Rodnay Zaks' "Programming the Z80"), memory, I/O etc. And, indeed, I was able to do so much more... plus I then understood how the high level BASIC code I'd previously written was really working at the machine level.

Yet, for a time, I'd got by quite happily with just BASIC. It was enough to get me started

Years later, when I started working in IT, I realised most of the programmers I was working with had little detailed understanding of the computers they writing code for. They were developing in COBOL, FORTRAN, BASIC and PASCAL - often calling on huge libraries written by other people - and really didn't know the fundamentals of the processor or the inner workings of existing code packages; they didn't know what was going on under the hood, why certain things happened. Yet many of them were very good programmers, able to quickly design, write and test reliable code that matched requirements...
When I first taught CS, back in 1983, students with your type of background often had to unlearn much before they could learn anything; they had developed the bad practice of seeing what was wrong with their answers, then tweaking the code to get right answers, rather than thinking about what statements were causing the incorrect answers.

Over the years, CS practitioners have learned that the best way to implement a complex algorithm is to make a simple combination of subprocesses that have been established to be correct. The human mind can comprehend only so much at one time.


added: I had to go through "retraining" myself, because my introduction to programming was a FORTRAN course I took in 1965, before people like Nicolas Wirth had figured out how to organize it.

Last edited by reh321; 02-03-2019 at 06:26 AM.
02-03-2019, 06:15 AM - 2 Likes   #621
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QuoteOriginally posted by BigMackCam Quote
I got into programming as a young boy - I think I was 11 or 12 years old. My first computer was a Sinclair ZX-81 with 1K RAM. Initially, I learned to programme using the built-in BASIC interpreter, documented in the accompanying manual. Of course, I didn't really understand what the computer was doing, but BASIC gave me a means to an end, and I wrote some great little programmes. For a few months, I was able to achieve everything I wanted using just that limited knowledge of BASIC... but it was clear to me there was more going on behind the scenes, more I could do, things that I could achieve more efficiently if I understood the fundamentals. So I started reading up on microprocessors and instruction sets (my most-read book at the time was Rodnay Zaks' "Programming the Z80"), memory, I/O etc. And, indeed, I was able to do so much more... plus I then understood how the high level BASIC code I'd previously written was really working at the machine level.

Love this story, Mike. I started out at a similar age with a TRS-80 CoCo 2 and got to the same point where I'd learned as much from interpreter BASIC as I was ever going to get. Like you, I bought a book on assembly code (for the Motorola 6809 in my case), but unlike you I realised pretty quickly that I didn't have the fundamental capacity to grasp it. The embarrassing thing is that my father designed processors for a living, and couldn't understand my inability to get what seemed like such simple concepts to him. I just accepted that I'd inherited my mother's art-farty genes instead.

What this forum needs is a "What was your first computer?" thread.
02-03-2019, 06:16 AM   #622
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My dad working at Honeywell on high level systems decided he needed to know how the computer was really working because to much was depending on it. Hence I
grew up starting around the Sphere.
History of Computers and Computing, Birth of the modern computer, Personal computer, Sphere 1
When he died we tried to donate it to a museum. If anyone knows of one that would want it his friend is showing it.
02-03-2019, 07:27 AM - 2 Likes   #623
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QuoteOriginally posted by reh321 Quote
When I first taught CS, back in 1983, students with your type of background often had to unlearn much before they could learn anything; they had developed the bad practice of seeing what was wrong with their answers, then tweaking the code to get right answers, rather than thinking about what statements were causing the incorrect answers.

Over the years, CS practitioners have learned that the best way to implement a complex algorithm is to make a simple combination of subprocesses that have been established to be correct. The human mind can comprehend only so much at one time.


added: I had to go through "retraining" myself, because my introduction to programming was a FORTRAN course I took in 1965, before people like Nicolas Wirth had figured out how to organize it.
I came across a few folks who had to un-learn things Me too, on a few occasions - but thankfully not many. I think I was just lucky... Without formal training, I tended to learn by reading, then trying out what I'd learned by writing small, isolated pieces of code. Only when I fully understood something at a fundamental level did I then use it.

That said, as a kid I had bad programming habits... I used to code "on the fly", with everything in my head, and I didn't add any in-line documentation. It was a culture shock for me when, in my first job, I found I had to first design any functionality without coding, then hand-write the resulting code on coder's paper sheets, and hand those to someone to have them input into a computer. And I had to book time on a computer to run, test and debug what I'd written. Debugging often meant noting down any problems, going back to my desk, modifying my coding sheets (or re-writing them!) and going back through the same cycle again That process made sure you got things absolutely correct on the first cycle as often as possible, if you didn't want to fall behind on delivery dates.

QuoteOriginally posted by Dartmoor Dave Quote
Love this story, Mike. I started out at a similar age with a TRS-80 CoCo 2 and got to the same point where I'd learned as much from interpreter BASIC as I was ever going to get. Like you, I bought a book on assembly code (for the Motorola 6809 in my case), but unlike you I realised pretty quickly that I didn't have the fundamental capacity to grasp it. The embarrassing thing is that my father designed processors for a living, and couldn't understand my inability to get what seemed like such simple concepts to him. I just accepted that I'd inherited my mother's art-farty genes instead.

What this forum needs is a "What was your first computer?" thread.
Thanks, Dave I remember the CoCo 2... I used to see them at my local Tandy store A friend of my Dad's had an earlier TRS-80 that I played around with for a while. Another friend, later on, had a Dragon 64, so I got to mess around with 6809 code a little when he was writing programmes for that.

I was crazy about computers - it consumed a huge amount of my time as a child, right the way through my teenage years, and it became my chosen career (at least to begin with). I had an awful lot of luck and good fortune along the way, though...

I started with the ZX-81, wrote some games and self-published a book of them... sold around a hundred copies of that through a local newsagents. That paid for my next computer, a Sharp MZ-80K, a year or two later. It was a fantastic machine... it had the benefit of loading the OS into RAM from tape deck at startup, so I had easy access to all sorts of development tools - compilers, assemblers, debuggers etc. I wrote mainly games for that too, one of which was sold commercially through Kuma Computers (looking back, it was quite simple and not very impressive, but it sold reasonably well). With the funds from that, I bought an old CP/M machine - a "Memory 2000" - with CP/M 2.2, and became more interested in the operating system, and controlling I/O systems and devices. Around that time (I think I was 15) I wrote some software for my Dad (at his request) to calculate financing schedules for his business clients when he was on site with them. He worked for Citibank Savings at the time. He showed it to his bosses, and soon after the company bought the code from me. With some of the money from that I bought a huge Westrex Pasca 640 machine with 2 x 8" drives and CP/M 2.2

A couple of years later, I dropped out of school and got my first job as a programmer in the real world. It was a big and very silly risk to take, skipping university as I did, but I was extremely lucky and very driven so it worked out fine.

Not the best approach to learning, and one I'd not recommend to anyone else... but it sure was fun

Ah, happy days...

Apologies for drifting off-topic. I think you're right, Dave... a thread on "first computers" might be fun


Last edited by BigMackCam; 02-03-2019 at 07:36 AM.
02-03-2019, 09:05 AM - 1 Like   #624
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QuoteOriginally posted by Kunzite Quote
@Mike:
Interesting story, and my bias towards books rather than Youtube tutorials is heavily due to my experience in computer programming.
However, I don't see where you're going. "Equivalence", after all, is just a formula to "convert" between formats - it brings no in depth understanding.
Although "equivalence" does have a simple numerical formula for conversion between formats, it is much more than that. Behind that simple formula is all the geometric reasoning and algebraic manipulations that prove the truth of the simple "equivalence" formula. If you want, you can trace "equivalence" all the way back to the thin-lens formula and Snell's law of refraction. But none of that is necessary in order to tell the beginner some answers about focal length and aperture if they are deciding among systems different formats, are trying to apply advice that was meant for a different format (e.g., 85 mm = "portrait lens"), or trying to understand what they are seeing when they use different formats (e.g. discrepancies between their smartphone and their new camera). The simple formula will answer those questions. If they don't believe the formula or want to understand why the formula works, then they'll need some prerequisite understanding of geometry and algebra to get a deeper understanding of equivalence. And if the beginner finds geometry and algebra to be confusing, then they'll be forced to to stay at a surface level of knowledge of just using the rote formula.

Deep understanding is only needed under the most limited conditions because deep understanding isn't really needed for most applications. For example, no beginner needs a deep understanding of semiconductor physics to use a digital camera. It's only if the beginner wants to understand why there are no modern digital cameras with a base ISO of 25 or why their MILC images are noisier after the camera has been running for a while that the beginner needs to delve deeply into sensor technology. The same is true of "equivalence" -- as with semiconductor physics or gravity, it works whether you understand it or not.
02-03-2019, 10:05 AM - 1 Like   #625
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QuoteOriginally posted by Ash Quote
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.
Of all the people I know shooting multiple formats, including myself, absolutely nobody use equivalence all the time. When shooting, no half decent photographer thinks "If I had a FF, I would use a FL of x and aperture y, but since I'm with another format I must use a equivalent settings of a and b". It never happens! They just take what they have on hand, frame the picture with the perspective they want, adjust DOF with the aperture and press the shutter. They couldn't care less about equivalence and what would be the settings with another camera and lens combination...

Exactly as BigMackCam describes in another post:
QuoteOriginally posted by BigMackCam Quote
I'd agree that, having used it a few times or for a short while, most folks that have used equivalence would likely use it much less over time. You either become familiar with the lenses you're using or, without thinking, translate between those lenses when switching systems. Or both.

I continue to shoot both APS-C and full frame (albeit in different brands), and I switch quickly and seamlessly between each format. Sub-consciously, I probably do a quick lookup in my head between my lenses on each format rather than calculating anything. Or maybe I'm doing the AoV equivalence calculation without even realising it. Either way, I don't think about equivalence now, or very rarely at least.

I guess the last time I used AoV and DoF equivalence together, and it was in an extremely rough and ready way, was when I bought my Sigma 30mm f/1.4 Art. I knew that I liked the subject isolation I could achieve at 50mm f/2.8 on full frame (with my 24-70 f/2.8 zoom). So I was looking at APS-C lenses in the 30 - 35mm range, and - without any precise calculations - knew that a 30mm f/1.4 lens would cover my needs...
Even for people using multiple formats, equivalence has very little practical use...
02-03-2019, 10:17 AM - 1 Like   #626
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QuoteOriginally posted by CarlJF Quote
Even for people using multiple formats, equivalence has very little practical use...
It has been useful for me, Carl... I can only speak as I find
02-03-2019, 10:18 AM   #627
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QuoteOriginally posted by photoptimist Quote
Although "equivalence" does have a simple numerical formula for conversion between formats, it is much more than that. Behind that simple formula is all the geometric reasoning and algebraic manipulations that prove the truth of the simple "equivalence" formula. If you want, you can trace "equivalence" all the way back to the thin-lens formula and Snell's law of refraction.
No, no, no - you won't get away with that, with the including of mathematics and everything into "equivalence".
Remember, this sort of thinking is often used by "equivalence" advocates to reach the absurd conclusion, "you either accept the glory of "equivalence" or you're rejecting mathematics". I've seen some of that nasty stuff even on this forum
But the "geometric reasoning and algebraic manipulation" tools, it's something we have outside "equivalence", and not a part of it. And to include even refraction? Absurd.
02-03-2019, 10:21 AM - 3 Likes   #628
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Folks, I think we're probably just going to bounce back and forth with the same arguments, so I'll close the thread here, I think.

Thank you once again for your participation. It hasn't been dull, that's for sure
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