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10-10-2014, 08:36 AM - 1 Like   #121
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QuoteOriginally posted by ChristianRock Quote
No, because you expose like a 1.8 lens, not like a 2.8 lens.

So, like it was said earlier, equivalence is for DOF and FL, not for exposure.
Equivalence will help describe Total Light, and that's more than DOF and FL - it also determines image noise and DR.

Thus a K-5 with the Sigma 18-35 f/1.8 will completely match a D800 with a 24-70 2.8 in the 28-52mm range - the D800 would have no noise/DR-related IQ advantage there - because the Total Light would be the same (which affects photon shot noise) and the sensor efficiency happens to be about the same (which affects read noise.)

I'm impressed that the Sigma has those specs while being a very sharp and not-too-expensive lens - I thought something was going to have to give when I heard the advance specs. Sigma has done well there.

If Pentax could come out with a series of similar very fast/good lenses, there would be less (or no) reason for a Pentax FF body.

---------- Post added 10-10-14 at 09:48 AM ----------

QuoteOriginally posted by Kunzite Quote

FTR, you did that "pushing assumptions" yourself, several times. Others did it too, should I remember (again!) the recent moon shooting example?
What 'moon shooting', did I miss something?


QuoteQuote:

P.S. I'd really like to know what makes anyone think that, when switching formats:
- the shutter speed should stay constant
- aperture will be selected exclusively to obtain a specific DOF
- there are no other reasons which might dwarf wide-aperture DOF in importance
Equivalence doesn't require you to keep everything constant when shooting - it uses constant parameters simply to describe differences between formats. (I'm getting carpal tunnel typing that.)

Q: Isn't Equivalence all about DOF?

A: No, Equivalence is not "all about DOF", but it is very much about understanding that both DOF and noise are intimately connected to the aperture. That said, DOF, by itself, is still a critical consideration to the captured detail in the photo, since portions of the scene outside the DOF, by definition, will not be sharp, and all systems suffer diffraction softening equally at the same DOF.


Q: Doesn't Equivalence say that we should shoot different formats at the same DOF?

A: Not at all, and, in fact, quite the opposite. That is, one does not choose one format over another to get photos Equivalent to what one would get on another format. Rather, one chooses one format over another to get photos they could not get on another format, or get better photos than they could get on another format, assuming, of course, that differences in operation, size, weight, and cost are not significant enough to be the primary consideration.


Last edited by jsherman999; 10-10-2014 at 09:08 AM.
10-10-2014, 09:00 AM   #122
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QuoteOriginally posted by redrockcoulee Quote
People do, especially when they first start out and do not have a light meter. I have a light meter in my MF bag and another in my LF bag but one of the reasons I use a K-r and small primes is the ease of taking them with me if a am going off with one of the larger formats they add neither much bulk or weight. The light meters in an iPod or iPhone would be more convient than a dslr as well. I also read of some one claiming to backpack with a Fuji GX680 so anything is possible.

There is also the sunny 16 rule and now I need to get an app to translate it between the various formats I have.
Point your K-r at a scene with shadows and bright light and around a 85mm lens. Now do the same with a 18mm lens. Your DSLR will give you different readings, no? Are you going to carry a big zoom to cover all the equivalent focal lengths you will use on your medium and large format?

Sure, use a DSLR and phone app if that works for you. But if you head over to the Large Format Forum and say, "hey guys, I know most of you use a DSLR to meter your scenes, which one works best for your..." I think you'll get a bunch of WTF responses.

A Pentax digital one-degree spot meter fits in your pocket, is more accurate than using a DSLR, you can meter from a distance and is not fooled by high or low contrast scenes because it uses a human brain to select your middle gray exposure. I strongly encourage using one.
10-10-2014, 09:22 AM   #123
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QuoteOriginally posted by jsherman999 Quote
Equivalence will help describe Total Light, and that's more than DOF and FL - it also determines image noise and DR.
That's the part where we will just have to agree to disagree... image noise and DR are determined by the technology in the sensor, not by equivalence.

Plus, even now, saying an ISO 6400 on a D810 will look *exactly* the same as ISO 3200 on a K-5 IIs (or ISO 2800, or whatever the 1/3 down from 3200 is) sounds very far fetched to me. Noise isn't even linear like the in regards to sensor performance. Take a CCD vs CMOS sensor, or even a Sony vs a Canon sensor, and their noise increase will differ slightly.
10-10-2014, 09:27 AM   #124
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I'm not going to argue with anyone arguing using a spot meter, with film in the studio it's indispensable, and possibly for sunsets and other high DR situations... on the other hand, I'm not going to say I use one. It's too easy and cheap to bracket theses days. My histogram is just as effective. I'm sure one could learn to use their DSLR to calculate exposures, after all, it does have exposure tools built into it. But I'm also certain the learning curve would be just as steep as learning to properly use a light meter, and probably a bit less precise, but who knows? You might be able to make it functional. But it's not going to be a simple matter of taking a reading with your camera and transferring it to your film camera, anymore than taking an incident reading with a light meter is going to help you determine what the brightest and darkest area of a scene are.

Without understanding the limitations of each process, either method is going to be less than productive. With light meters, there is lots of accepted practice to draw on. Using digital cameras to be light meters, not so much.


Last edited by normhead; 10-10-2014 at 09:37 AM.
10-10-2014, 09:39 AM   #125
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QuoteOriginally posted by normhead Quote
I'm not going to argue with anyone arguing using a spot meter, with film in the studio it's indispensable....
Not if you use strobes in your studio A one-degree is not going to measure that light. And actually a DSLR to set exposure on film when using strobes is good use for one.
10-10-2014, 09:44 AM   #126
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QuoteOriginally posted by jsherman999 Quote
What 'moon shooting', did I miss something?
No, it wasn't anything important, just your average equivalentionist jumping to say that 645z can't possibly be better than FF for moon shots, because you can shoot at f/1.4 instead of 2.8

QuoteOriginally posted by jsherman999 Quote
Equivalence doesn't require you to keep everything constant when shooting - it uses constant parameters simply to describe differences between formats. (I'm getting carpal tunnel typing that.)
And here's the rigid thinking: some constant parameters are assumed constant, others are assumed important while others are simply ignored. The photographic purpose is completely ignored. What if I'm using a tripod? What if DOF really isn't a factor? What if I'm using a technical camera and have control over the plane of focus? What if I'm going medium format (I wish I had the money!) for its amazing detail and nothing else? What if I crop?
Oh, no, I must be wrong and I must apply this formula, look, a FF with a fast lens is what I need!
QuoteOriginally posted by jsherman999 Quote
Q: Isn't Equivalence all about DOF?

A: No, Equivalence is not "all about DOF", but it is very much about understanding that both DOF and noise are intimately connected to the aperture. That said, DOF, by itself, is still a critical consideration to the captured detail in the photo, since portions of the scene outside the DOF, by definition, will not be sharp, and all systems suffer diffraction softening equally at the same DOF.
Wow. You really wrote something like that.
Looking for detail outside of DOF? Wait, looking for critical detail outside of the plane of focus? How desperate to make everything depend on DOF? (and at the same time, claiming it's not "all about DOF")

Take a look at e.g. Photozone.de - diffraction isn't really a factor until you stop down quite a bit. I can safely use my Limiteds at f/4-f/11 without worrying. With FF, I'd probably want to have only one eye in focus anyway

QuoteOriginally posted by jsherman999 Quote
Q: Doesn't Equivalence say that we should shoot different formats at the same DOF?

A: Not at all, and, in fact, quite the opposite. That is, one does not choose one format over another to get photos Equivalent to what one would get on another format. Rather, one chooses one format over another to get photos they could not get on another format, or get better photos than they could get on another format, assuming, of course, that differences in operation, size, weight, and cost are not significant enough to be the primary consideration.
Wrong question leading to irrelevant answer. Your "equivalence" is forcing you to choose based on DOF, without caring for your opinion. Your "equivalence" tells that 645z cannot best FF for moon shots, nor landscapes, nor any other photographic genre.
10-10-2014, 09:49 AM   #127
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QuoteOriginally posted by marcusBMG Quote
Thanks for the post jshermann999 - clarity

However I should apologise for my OP - it was carelessly thrown in and I didn't understand the distinction between total light and light density (intensity) This is now clear to me. My analogy with eg TC's is incorrect.

I have been scrutinising the Northrup videos. At ~8mins in the long one he says (discussing ISO, SNR)

" ISO basically amplifies the amount of light to achieve a particular level of brightness"

Then at ~ 10mins he says:

"..ISO has a co-dependent relationship with the sensor size. The small sensor is not gathering enough light so ISO over there is, like, 'don't worry I'll just crank it up I'll amplify everything'. And that does allow us to use the same settings, but not to take the same pictures."

All very muddy with hindsight. I just want to say that it is at this point IMO he should be clear and say.:

"of course I am not saying this affects the exposure, exposure doesn't depend on this but on the light intensity, which depends upon the real aperture not any equivalent/calculated aperture..."

Like it does in the dpreview article.

He does not do so, and in fact he does not say this at any point in any of his videos. He is cognisant of this point, he mentions it in responses to comments. I do not know whether this is merely careless on his part, or perhaps an unfortunate consequence of trying to keep things simple.
One other thing he does that drives me crazy is he says "bokeh" when he means "DOF".

Bokeh is a very different thing than DOF, and the same DOF from two different combos can have much different bokeh. Also bokeh quality is in no way described using equivalence, so him using the terms interchangeably is really the wrong thing to do.

But yes, I think he did it to try to keep things simple - I would have made a few different choices though.

Last edited by jsherman999; 10-10-2014 at 10:06 AM.
10-10-2014, 09:56 AM   #128
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QuoteQuote:
Equivalence will help describe Total Light, and that's more than DOF and FL - it also determines image noise and DR.
It helps explain why a Full Frame image might have less noise or Dynamic range than a smaller image. It does nothing to explain why a K-5 had as much effective Dynamic Range as any sensor of it's time...
It's only part of the equation. Perhaps even not the most important part.

Total light in itself is a pretty meaningless measurement, given the images many cameras produce with very small sensors.

10-10-2014, 09:58 AM   #129
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QuoteOriginally posted by ChristianRock Quote
No, because you expose like a 1.8 lens, not like a 2.8 lens.
No I don't. I shoot for DOF and SNR. Not some 'exposure'. When I display a picture I don't put a little blurb at the bottom telling people what the ISO was.
10-10-2014, 10:01 AM   #130
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QuoteOriginally posted by ElJamoquio Quote
No I don't. I shoot for DOF and SNR. Not some 'exposure'. When I display a picture I don't put a little blurb at the bottom telling people what the ISO was.
You shoot pictures? Just kidding
10-10-2014, 10:15 AM   #131
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I shoot for exposure and in general, to maximize depth of field. SNR and noise are secondary.
10-10-2014, 10:19 AM   #132
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QuoteOriginally posted by Kunzite Quote
And here's the rigid thinking: some constant parameters are assumed constant, others are assumed important while others are simply ignored. The photographic purpose is completely ignored.
This is absolutely not true, and it's an example of the 'straw man' argument I talk about - getting mad at equivalence for what it's not, for what it doesn't ever claim to be.

Equivalence is a tool used to determine some important differences between formats that would affect Total Light. It can't and has never claimed to describe every difference between a given combo and another. The photographer or potential buyer still has to do some legwork if they want to fill that in.

It's most useful when determining, for example, how that "28-600mm f/2.8" superzoom will really probably perform compared to a "24-105 2.8" on a 1.5'' sensor for example. And when comparing various lens/body combos between FF and aps-c or m43 when sensor technology is close to same-gen.

But it's not the soul source of truth, it can't be, and it's never laid claim to that. Don't construct straw-man arguments in which you imagine people are saying that.

.
QuoteQuote:
Wow. You really wrote something like that.
Actually that Q/A snippet was a cut n' paste from here.

.

---------- Post added 10-10-14 at 11:22 AM ----------

QuoteOriginally posted by Rondec Quote
SNR and noise are secondary.
For me, SNR/noise are probably more important than DOF control. For me the less-DOF I get with FF is a by-product of what I'm really after - noise control and more DR up from base ISO - and usually, I find that by-product (less DOF) more pleasing anyway.
10-10-2014, 10:24 AM   #133
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QuoteOriginally posted by marcusBMG Quote
It's obvious when you think about it.

Put a 1.5x tc on a lens and you take it for granted that you are going to lose slightly more than a stop. Put extension tubes on to magnify another 1.5x - same. Crop factor is no different - there is no free lunch. If you think your classic 70-200 f2.8 is giving you 105-300mm and f2.8, you too have been successfully ...... what word should I use here, brainwashed? gulled? confused? led astray... you decide! by camera and lens marketings smoke and mirrors. You can't multiply the focal length by the crop factor and NOT multiply the aperture by the crop factor . As Tony Northrup says in his video "it breaks the math".
Your 70-200 f2.8 equates to 105-300 f4.2!!!

Sorry.
since post become a mess, and guys just messing who got a longer dick, its impossible to write a normal answer

if you look the last two minutes of the video you posted, probably you will understand whats wrong with Tony´s "definition" of crap-factor.
He explaining by himself that he used on the FF camera much higher ISO than on the Aps-C and <mFT. So to expose same DOF FF camera needs much more light.

1,5x Crop factor is applied to the DOF and not to the exposure. Thats why Lenses with "big" aperture as 2.8, 1.4, 1.2 etc are called FAST lenses.
that means that buying yourself a 70-200 2.8 you are getting and advantage of faster shooting or shooting with lower ISO, which improves quality.
So just saying that the lense is eqvivalent to a 70-200 f4 isn´t right.

elsewise you would saying that applying the same lense on aps-c and FF will just give FF more light, it would mystically create one only because its a FF.
listen the last two minutes. he says it twice and then although showing you the data with ISO 800 FF and iso 200 µFT. if you flip it it means you can shoot 4 times faster with same ISO. Thats simple math.

and flipp it one more time - Getting 1.5x DOF or shoot at the SAME exposure - if thats a disadvantage its up to you. many macro photographers will stick with µFT instead of Focus stacking with FF

The whole story is only about definition, Tony is wrong to say that Aperture is only DOF, and has with the Exposure nothing to do so you get any advantages getting FAST lenses.

You have chosen your format by picking sensor Size and you should be smart enough to calculate your DOF, so changing the number how Fast lense can go, or how many light the lense actually gather isn´t right.
10-10-2014, 10:29 AM   #134
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jsherman999:
That is absolutely true, I'm afraid.

You like going in circles and repeat yourself over and over again, don't you? If it's just that, if you really admit its limits you wouldn't promote it so much And you wouldn't use Capital letters - just sayin'.
"Equivalence" is a fraud precisely because it's hyped so much, so aggressively.

The sad thing is, you didn't even tried to answer my questions, you just copy/pasted from your dear article.

Last edited by Kunzite; 10-10-2014 at 10:41 AM.
10-10-2014, 10:32 AM   #135
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QuoteQuote:
It's most useful when determining, for example, how that "28-600mm f/2.8" superzoom will really probably perform compared to a "24-105 2.8" on a 1.5'' sensor for example. And when comparing various lens/body combos between FF and aps-c or m43 when sensor technology is close to same-gen.
Empirical knowledge is always superior to theoretical constructs. IN fact, you can't even assume theoretical constructs to be true, unless supported by empirical examples.

QuoteQuote:
28-600mm f/2.8" superzoom will really probably perform compared to a "24-105 2.8" on a 1.5'' sensor for example.
A perfect example. Equivalence actually tells you almost nothing about that performance, because, it says nothing about how those images will appear to the human eye, what other factors might affect those image, what role different technologies play etc. The judged performance of a lens is a combination of all those things. I'm not sure why anyone would want to compare a couple of theoretically simple lenses, in theoretically similar technologies, when no such circumstances ever exist in the real world. Picking out one set of parameters and ignoring all the others is pretty useless. People are interested in real world performance, and real world performance is images.

People can argue equivalency all day... but what's the pay off? It doesn't mean anything. It doesn't make a great picture taken with an APS-c camera less than a great picture taken with an FF camera. Don't even try and go down that road. IN the major camera brands, there is not a shred of evidence that pictures judged to be excellent pictures are determined by anything more than the market share of the manufacturer. It would appear, that the limitations of APS-c and even 4/3 are not so great as to stop people from taking great pictures with them. My guess, looking at images is that while format makes a difference to some types of image... for many images, it makes no difference at all. For many images a bridge camera or point and shoot would have been good enough. Until this notion of equivalence is expanded to take that into account, it's just nonsense.

All folks need to know are the parameters around which they might need to go to a larger or smaller format. Equivalency, doesn't address that. it's pretty much meaningless information, taken on it's own.

Last edited by normhead; 10-10-2014 at 10:46 AM.
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