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07-26-2014, 11:10 AM   #301
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A normal lens is defined as having a focal length of around the diagonal of the format. The same lens can behave as a wide angle, normal or long lens depending on which camera it is mounted.
This is part of the basic knowledge which is better applied without the shackles of "equivalence".

07-26-2014, 11:29 AM - 1 Like   #302
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QuoteOriginally posted by Kunzite Quote
A normal lens is defined as having a focal length of around the diagonal of the format. The same lens can behave as a wide angle, normal or long lens depending on which camera it is mounted.
This is part of the basic knowledge which is better applied without the shackles of "equivalence".

Comparing the diagonal of two sensors format and determining the corresponding normal focal length, is applying equivalence.
But you know that, you have mentioned that you are a software engineer, so I know you are smart.....therefore your reluctance to calling that applying "equivalence" leads me to believe that you are arguing just for the sake of arguing.
07-26-2014, 12:12 PM   #303
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Not exactly. I will remind you that "equivalence" means considering a set of parameters, not only the angle of view (as explained in JJ's article, and by many people here). You people are constantly shifting between different notions of "equivalence", to what's momentarily convenient.

Knowing what's a normal lens is not "equivalence"; it never was, in any of the books I've read It's just a simple definition, and a simple geometric relation. I can find out what's a normal lens on any format independently, without artificially using "crop factors". I do not have to multiply focal lengths, aperture openings and ISOs. I can afford to be imprecise about it by tens of millimeters.

So the only thing that you can cling onto is that I'll relate my experience to the new format, using lousy angle of view translations; I'll give you that. But then, I bought my 35 Limited for it's close-up capabilities (I'm not particularly fond of its angle of view), and the 21mm for its rendering.

By the way, if you supposedly can't choose without "equivalence" it means you can't choose at all; because "equivalence" needs a format to relate to, one on which you made some initial choices. That's obviously not the case, and one can choose without "equivalence".
And if you can do it once, you can do it again.
07-26-2014, 12:14 PM   #304
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QuoteOriginally posted by cali92rs Quote
When the people that reject equivalence switch from APS-C to FF, I hope they don't come back on these forums and maintain their dishonesty by saying that their 28mm is a normal lens and that their 50mm is a short telephoto.
Of course they can also claim that they didn't use equivalence when choosing their lenses, that they stuck a 28mm on their camera and found out that way that their 28mm is a wide angle with a FF camera.

The rest of the population with common sense can use equivalence and a seconds worth of math to figure out what a focal length looks like without taking the time to drive to a camera store which may or may not have your lens in stock.
But this has nothing to do with DOF wide open equivalence (which is optional; exposure equivalence - the industry and textbook standard isn't) but focal lenghts giving similar angle of view for their respective formats.
Nobody denies equivalent angle of view.

---------- Post added 07-26-14 at 10:10 PM ----------

There are three fundamental problems with DOF wide open equivalency:

1) It is used instead of exposure equivalency - the equivalency that state the indisputable and always relevant fact that F:4, 1/125s at 100ISO is the same exposure regardless of format. F:4 is F:4 regardless of format. Thats why it is printed on the lenses.
The wide open DOF equivalence isn't relevant to those who do not shoot wide open due to DOF, and/or shoot DOF insensitive images. Hence you cannot make universal laws from this. It is optional for those who cares. Exposure equivalency is not optional, it is mandatory - you can't escape it.
Ie if everything in the image is at or near infinity DOF is irrelevant as F:22 or F.1.2 give the same image. Hence, the law of DOF equivalence is irrelevant in this situation. However, conventional equivalence is not, as shooting at 1.2 or F:22 is very different regarding exposure.
One example are astrophotographers. Telling them that they have to compare lenses between format that are one stop faster is meaningless.
To sum up; you are replacing an always relevant law with a "law" that is only relevant sometimes and is indeed simply a choice.

2) The equalization of formats. This is pointless because it is the lack of equivalency in output that make people choose one format over the other. If the DOF wide open equivalency was indeed a law that was relevant why not compare the 645z with a cell phone? What useful information come out of this? That the excercise is pointless perhaps...

3) Insisting that DOF equivalency between format exists and lenses that do this exist. This is based on oversimplification of DOF and not taking into consideration the laws of optics.

DOF is dependent on focal lenght, aperture used, the image size obtained, and camera to subject distance.

- Whatever the focal lenght you use the DOF obtained varies with aperture.
- Regardless of the F:stop you use on any focal lenght lens, the closer the lens is to the subject, the thinner the DOF.
- When photographing from a fixed location, the longer the focal lenght is, the shallower the DOF at any focused distance.
- If image size and aperture is the same, all focal langht lenses give the same DOF.

Now add different formats into this soup, which is changing focal lenght for the same angle of view, the magnification factor that inevitable show up when compaing formats of different sizes plus the fact that at certain distances DOF is endless anyway. It should be apparent that DOF equivalency between formats is a futile goal that in reality will never be fully achieved.

EG: A 50mm lens on APS has about the same angle of view as a 75mm lens on FF. We have a 77mm FF lens which is close enough and plenty of Pentax 50mm lenses. If you compare the focus scale and the DOF scale on the 77 Limited and the 50/1.8 you'll see that they are different. In fact, and this may come as a surprise - a 50mm at 1.8 on APS will give thinner minimum DOF than can be obtained a 77mm at 1.8 on FF - in fact about 60% thinner! In addition the 50mm will have the ability to give larger maximum magnification and different perspective. Of course, if you insist that the APS lens should be a lens that is one stop faster than the FF lens, the APS lens will also show a larger range of DOF.
These lenses are simply not equivalent except for angle of view on their respective formats and speed..

If you are going to insist on comparing DOF you have to state at which focusing distance. Else it has no meaning. You then have to make exceptions to the law when the image is DOF insensitive or the "crop factor" to come in. In other words, the thinnest DOF and where the DOF is thinnest or the same (at any aperture!) is dependent on focusing distance.
They say there are holes in every law but the holes in the law of equivalence can be seen from space!


Last edited by Pål Jensen; 07-26-2014 at 02:12 PM.
07-26-2014, 01:40 PM   #305
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QuoteOriginally posted by eyeswideshut Quote
Equivalists argue that not only will the farmer with more acres receive more rain, but his crops will be better for it.
That's actually not at all what they argue.

Equivalence says that 2 acres receiving 1" of rain will have the same amount of water as 1 acre receiving 2" of rain.

It also says that the pictures will be the same. Not that bigger is better; not that smaller is better. Equivalence just tells you which settings will result in the same picture.
07-26-2014, 01:48 PM - 1 Like   #306
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QuoteOriginally posted by ElJamoquio Quote
It also says that the pictures will be the same. Not that bigger is better; not that smaller is better. Equivalence just tells you which settings will result in the same picture.
And why would you want the same picture (ignoring the fact that the same picture isn't strictly true anyway)?
I'm not buying a 645z in order to get the same picture as a smaller format let alone a P&S.


All you need to know is that formats are not DOF equivalent and that you have to shoot at one stop slower shutterpeed on FF than on APS for the same DOF all else equal. Of course all else doesn't have to be equal but what you prefer is not a law or a principle but a choice....
07-26-2014, 03:07 PM   #307
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QuoteQuote:
QuoteQuote:
Car A goes the same speed at the same RPM as Car B. Car A just does it in 4th gear, while Car B does it in 5th gear.
Why would you want to go the same speed in two different cars?
Sometimes I drive the same speed even if I'm in a different car.
07-26-2014, 03:14 PM   #308
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False analogy. To be used when real arguments are lacking.

07-26-2014, 04:33 PM   #309
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You guys may argue all you want about how useless it is...but the fact of the matter is that plenty of people do use it because they want their FF lenses to look how they looked on their 35mm cameras, hence Lens Turbos and Metabones. The existence of those products proove that there are MANY people that care enough about getting equivalent pictures across different formats that they are willing to pay hundreds of dollars. So you can stick your fingers in your ears and say "its useless its useless its useless", but the money changing hands prove otherwise.
07-26-2014, 04:44 PM   #310
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Equivalence is your Pal, Pål.

QuoteOriginally posted by Pål Jensen Quote
But this has nothing to do with DOF wide open equivalence...
What is 'wide-open equivalence?' Equivalence is true at any aperture.

.
QuoteQuote:
2) The equalization of formats. This is pointless because it is the lack of equivalency in output that make people choose one format over the other.
Assuming I'm able to parse your point, this isn't true. Almost all aps-c shooters who chose that format for example didn;t choose it because they wanted a specific DOF, or FOV, or wanted less noise capability than FF, they chose it because it was a good deal (to them) - a largish sensor in a nice package, not too expensive, with a lot of lenses available.

When/if they consider the addition of or migration to another format like m43 or FF - especially FF, which can share lenses with aps-c if it's a body from the same manufacturer - they do themselves a favor by understanding equivalence.

They can answer the question, for example: "Should I get a FF body and a 28-75 2.8, or stick with my aps-c body and buy a Sigma 18-35 f/1.8? Which would perform better for me and be better bang/buck, knowing what I know about my shooting needs, usual FLs used, etc? If I buy a FF body, what lenses would I want to keep, or sell, based on my most-used FLs on aps-c? Will I even see an advantage in DOF for my FOVs, if I move to FF? Or is there an m43 alternative that would work even better, for me? What exactly would I lose IQ-wise by going m43, or gain?"

Isn't that a valid and possibly common set of questions? Equivalence is your Pal, Pål.

.
QuoteQuote:
If the DOF wide open equivalency was indeed a law that was relevant why not compare the 645z with a cell phone?
You're choosing two radically different sensor sizes and tools, but you certainly could make the comparison if you wanted, using equivalence.

Usually the comparisons are more pragmatic - they describe a set of tools you may actually be choosing as alternatives to each other; aps-c vs m43, m43 vs FF, FF vs. aps-c, 1'' sensors vs. other stuff, etc.

.
QuoteQuote:

... a 50mm at 1.8 on APS will give thinner minimum DOF than can be obtained a 77mm at 1.8 on FF - in fact about 60% thinner! I
Only if you move forward with the 50mm/aps-c shot resulting in a completely differently-framed image. I honestly wish you'd do your homework on this issue before posting... but why should anything change now.

QuoteQuote:
If you are going to insist on comparing DOF you have to state at which focusing distance. Else it has no meaning.
Of course. This is why equivalence lays the groundwork for these particular comparisons by assuming the same FOV and distance to subject.

.

Last edited by jsherman999; 07-26-2014 at 04:55 PM.
07-26-2014, 05:15 PM   #311
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QuoteOriginally posted by Kunzite Quote
A normal lens is defined as having a focal length of around the diagonal of the format. The same lens can behave as a wide angle, normal or long lens depending on which camera it is mounted. This is part of the basic knowledge which is better applied without the shackles of "equivalence".
I'm sorry to jump in on a discussion that's way above my head but please stop quoting this! I am a noob and say so without any reservations but, I have never measured the size of a sensor or a piece of film. I do accept that someone might have done that and I accpet that 50mm in FF is normal, that someone else measured an APS-C and said 30mm is normal I have to accept that too. I think however that they just did the math based on one measurement. I don't even know where to find the documented diagonal for a 1/2.3 sensor, or who measured it so I don't even know what's normal there.

Also if we are going to be so sensitive about definitions, I somehow recalled being told in math that there is a difference between something being equal and equivalent. Can someone correct me if I'm wrong. As a noob I choose a DSLR not because I want the shot, my cell phone could have gotten it, I choose a DSLR because I wanted a certain look that was roughly equivalent to what the "pros" got, shallow DoF, bokeh (yes that's what us noobs talk about), isolation etc. A little reading would suggest that I needed a large aperture (try figuring that one out by yourself). So when my PnS with it's fairly large aperture was still give me a cellphone look, the question became why?. I think Tony's videos help to explain that in a big way.

So some people don't need to use crop factor, fine, for those of us who do (and see it in ads for gear) really appreciate because it puts our photos into perspective. Videos like those aren't meant for practicing professionals, they're made for noobs and upgraders. These videos can definitely relieve the frustrations of not getting "the look". They can't help with the shot, but they'll help with the frustration.

Anyway, I do love the debate and the fact that it hasn't fallen to pieces.

Last edited by wilton; 07-26-2014 at 05:24 PM.
07-26-2014, 05:16 PM   #312
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I guess I would say that I have a couple of problems with equivalence. First of all, there are few equivalent lenses to the lenses that Pentax currently offers. Where is the 15mm f4 or, the 70mm f2.4 equivalent? And bear in mind, that I don't want a faster lens, as that is going to increase the size of my kit. I want an equivalent aperture in order to control flare and keep the kit small. But it isn't there -- and if it were, the odds are that the cost of such a lens would still be similar in the Pentax universe.

I don't particularly like the use of equivalence as a bludgeon, either, to force every to appreciate what a deal full frame is. Comparisons are always done between third party lenses (full frame) and brand name lenses (APS-C) and top end APS-C models and bottom end full frame cameras, in order to demonstrate how expensive APS-C is compared to full frame. Pentax is quite expensive right now, but that is because it is a small company and not because its lenses are APS-C. The FA limiteds are even more expensive.

Finally, I am bothered by the focus on extreme situations. High iso has gotten very good on both APS-C and full frame. Some people need this, but the reality is that in the majority of situations, you are not going to see a difference between APS-C and full frame, unless you print very large, or shoot wide open all of the time (I don't do either).
07-26-2014, 05:51 PM   #313
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Do you have a problem with equivalence, or FF choices?

QuoteOriginally posted by Rondec Quote
I guess I would say that I have a couple of problems with equivalence. First of all, there are few equivalent lenses to the lenses that Pentax currently offers. Where is the 15mm f4 or, the 70mm f2.4 equivalent?
Keep in mind that you don't need to try to find exactly-equivalent lenses using equivalence - you can use it to determine if the lenses that are available would show you any advantage or disadvantage, for a given format, and you can use that information to determine if it makes sense to migrate to that other format.

For example, your 15 f/4 would be the equivalent of about a 23mm f/6 on FF - so if you wewre to pick up a used $200 M20mm f/4 (a great little lens, by the way) you'd get a lens that's just as small, a bit wider and faster - but MF. Or you could get an autofocus Sigma 24mm f/2.8, which is small and extremely sharp, and around $100 used. If Pentax came out with an FA 20mm f/2.8, you'd be a few mm of equivalent FL and gaining a lot in terms of speed, but it would probably be larger. These would be the real choices you have avaliable, and equivalence would take you a long way toward knowing how these choices would look/behave compared to your current kit.

Your 70mm f/2.4 would be equivalent to about a 105mm f/4, so a FF-capable 100mm f2.8 macro for example would get you about the same FOV, with about a stop more DOF control and that capability of gaining that extra stop of noise control. Plus, most macros are very sharp with nice bokeh and can be used as very nice portrait glass - a worthy replacement for your DA 70.

QuoteQuote:
And bear in mind, that I don't want a faster lens, as that is going to increase the size of my kit. I want an equivalent aperture in order to control flare and keep the kit small. But it isn't there -- and if it were, the odds are that the cost of such a lens would still be similar in the Pentax universe.
But the fact that your choice isn't there isn't the fault of equivalence, is it? In fact, you used equivalence to tell you your first choice wasn't there. Didn't the application of equivalence just save you some money, maybe?




.

Last edited by jsherman999; 07-26-2014 at 05:56 PM.
07-26-2014, 06:24 PM   #314
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QuoteOriginally posted by jsherman999 Quote
Keep in mind that you don't need to try to find exactly-equivalent lenses using equivalence - you can use it to determine if the lenses that are available would show you any advantage or disadvantage, for a given format, and you can use that information to determine if it makes sense to migrate to that other format.

For example, your 15 f/4 would be the equivalent of about a 23mm f/6 on FF - so if you wewre to pick up a used $200 M20mm f/4 (a great little lens, by the way) you'd get a lens that's just as small, a bit wider and faster - but MF. Or you could get an autofocus Sigma 24mm f/2.8, which is small and extremely sharp, and around $100 used. If Pentax came out with an FA 20mm f/2.8, you'd be a few mm of equivalent FL and gaining a lot in terms of speed, but it would probably be larger. These would be the real choices you have avaliable, and equivalence would take you a long way toward knowing how these choices would look/behave compared to your current kit.

Your 70mm f/2.4 would be equivalent to about a 105mm f/4, so a FF-capable 100mm f2.8 macro for example would get you about the same FOV, with about a stop more DOF control and that capability of gaining that extra stop of noise control. Plus, most macros are very sharp with nice bokeh and can be used as very nice portrait glass - a worthy replacement for your DA 70.



But the fact that your choice isn't there isn't the fault of equivalence, is it? In fact, you used equivalence to tell you your first choice wasn't there. Didn't the application of equivalence just save you some money, maybe?




.
Your examples would have none of the flare resistance of the Da 15 or 70. Less glass combined with good coatings is the key and equivalence tells you nothing about that.

I probably will get a full frame camera if Pentax releases one, but not because of equivalence or, because it will be smaller or, because it will be cheaper than a K 3 and all the lenses I currently own , even though I have heard all those reasons bandied about .

When I get full frame , it will be because I want it , nothing more or less and I won't need to rationalize that decision to myself or , my wife .
07-26-2014, 06:51 PM   #315
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QuoteOriginally posted by Rondec Quote
Your examples would have none of the flare resistance of the Da 15 or 70. Less glass combined with good coatings is the key and equivalence tells you nothing about that.
Of course not, equivalence can't answer everything about everything, it's simply acts like a calculator solving arithmetic problems - it provides a strong, accurate starting point for you, the decision maker to embark from. You have to decide what matters after you reach the point equivalence brings you to. And again it's not the fault of equivalence if the answers it brings are not to your liking, it's the fault of a manufacturer, or format.

QuoteQuote:

When I get full frame , it will be because I want it , nothing more or less and I won't need to rationalize that decision to myself or , my wife .
OK. It's not a rationalization thing, either, but I suppose some could use it that way. However it's master is best served.
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