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Do the math - focal length and Format demystified

Leigh

New member
I decided to split this out as a separate post...

Regarding ISO (supposed speed):

Any optical sensor system works by taking a sample of the sensor output. That occurs in an instant. The sensitivity of the system is what determines the "highest ISO" that can be achieved.

Lower ISO settings are done by summing the results of those instantaneous samples, with each "stop" being twice or half as many samples as its neighbors.

Noise (as being discussed here) is generally random. It won't appear at exactly the same location on multiple samples.

Thinking in terms of a single pixel on the sensor, when you add samples, the majority of them will not have noise at that pixel. If you sum a large number of samples, only one of which exhibits noise at that location, that noise averages out to nothing.

This is the ONLY reason that low-ISO exposures have less noise than high-ISO images.

- Leigh
 

Stefan Steib

Active member
Then the video is wrong.

I use exactly the same lens aperture for an exposure on 35mm and on 8x10".

That's about an 8x range of "sensor" sizes. Absolutely no difference in exposure.

The same is true on 35mm and MF digital.

- Leigh
You still don´t understand:
Nobody ever said- not me nor the guy in the video- that the exposure is varying.

The effective depth of field is varying. You mix that up !

Regards
Stefan
 

Godfrey

Well-known member
You still don´t understand:
Nobody ever said- not me nor the guy in the video- that the exposure is varying.

The effective depth of field is varying. You mix that up !
So why is this a revelation or a lie on the part of manufacturers? Depth of Field has always been linked to format, focal length, distance, lens opening, and acceptable circle of confusion. It's all somewhat arbitrary to begin with, as what is "acceptably sharp" rests on the qualitative judgement of the person looking at the photo.

Anyone who doesn't understand that when the format is reduced or enlarged in size, the coupling between an FoV and a DoF behavior will be different doesn't understand anything about photography. Never mind lots of other things about image characteristics resultant from format change...

The manufacturers' statement of "X focal length on mFT/APS-C formats is equivalent to 2x/1.5x that focal length on FF" is a simplistic, single parameter marker for people to estimate what they're going to get in the viewfinder. It says nothing about depth of field.

Sheesh, such a big fuss over such a simple concept. I still don't get what you're trying to say, Stephan, or why you're so up in arms about it.

G
 
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Stefan Steib

Active member
Is it really so difficult to remember posts from a day ago ?

how can it be put more clearly than this ?

http://www.getdpi.com/forum/584288-post56.html

And

"...Anyone who doesn't understand that when the format is reduced or enlarged in size, the coupling between an FoV and a DoF behavior will be different doesn't understand anything about photography...."

Thanks for stating this, yes I AGREE !!!! But as you have seen here, _SOME_ People do not understand !

And thus : again - why not telling people the truth from the beginning ?

Is this so difficult ?
 

Godfrey

Well-known member
Is it really so difficult to remember posts from a day ago ?

how can it be put more clearly than this ?

http://www.getdpi.com/forum/584288-post56.html

And

"...Anyone who doesn't understand that when the format is reduced or enlarged in size, the coupling between an FoV and a DoF behavior will be different doesn't understand anything about photography...."

Thanks for stating this, yes I AGREE !!!! But as you have seen here, _SOME_ People do not understand !

And thus : again - why not telling people the truth from the beginning ?

Is this so difficult ?
Why do you insist that "the truth" must include every possible detail about the characteristics of a whole imaging system? Do you expect every potential customer to read a dissertation on sensor size dynamics with respect to format, pixel density, Field of View, Depth of Field, sensitivity, dynamic range, resolution, CoC, et cetera ad nauseam?

All that the manufacturers have said is that the focal length of a lens on their sensor format is equivalent to such and such a focal length on a 24x36 format 35mm film camera. Which is absolutely true information. It's just not complete, nor does it need to be.

The fact that plenty of people don't understand that there are other considerations, or even if they do, what those considerations are is no surprise. Why is it the burden of a manufacturer to educate everyong to be an expert on this stuff? Their goal is to sell their product, and for the vast majority of users all they need to know is
"I have a Nikon 50mm lens from my old camera. Will they work on the new Nikon WhizzBang 456-25Ds model? What other lens should I buy?"
A masters degree in electrical engineering, optics, photography, etc, is uncalled for. The Nikon answer to the above question for the vast majority of people is

"Your old lens will work fine, but it will look like a 75mm lens because the new WhizzBang 456-25Ds has a DX sensor. You'll need the Nikon 35mm lens to get the same field of view. Of course, if you're interested in Even More Features and Better Quality Photos, you should buy the Nikon WhizzBang 456-25Fs body instead. This has a gawsh-all-mighty Full Frame sensor and only costs $1000 more! That's cheap for what you're getting ... And all your old lenses will work just as they always did on your film Nikons!

That is, unless you want the Super Duper Image Stabilization feature, then you need the new Nikon 50mm UltraExtraSpecial f/1.2 VR XdFt Z model lens. FAR better than your old Nikon 50mm and only $900 with the Nikon WhizzBang 456-25Fs body as a kit! Then you can go out on a starlit night and take perfectly sharp pictures of black cows under the New Moon that will be absolutely sharp on the Ultra-Shallow™ Depth of Field this new lens can provide!"
That's education, Stefan. Not all this FoV, DoF, pixel pitch, blah blah blah horsepucky. And it's all The Truth. ];-)

G
 

Annna T

Active member
Is it really so difficult to remember posts from a day ago ?

how can it be put more clearly than this ?

http://www.getdpi.com/forum/584288-post56.html

And

"...Anyone who doesn't understand that when the format is reduced or enlarged in size, the coupling between an FoV and a DoF behavior will be different doesn't understand anything about photography...."

Thanks for stating this, yes I AGREE !!!! But as you have seen here, _SOME_ People do not understand !

And thus : again - why not telling people the truth from the beginning ?

Is this so difficult ?
I don't understand the crusade you have undertaken here; I don't really see what the point is.

Most photographers visiting this list are experienced if not pro; most have used different formats and systems, whether analogue or digital and they know theoretically or by experience :


  • The different factors influencing DOF, including the sensor size and magnification level.
  • The fact that a smaller sensor with denser photosites is going to produce more noise (although it is difficult to link that directly and only to sensor sizes, because noise is the results of many different things and no two sensors are equal).
  • The fact that pictures taken on different formats will often have a different look.


I think there is only one point on which people are disagreeing with you : that the manufacturers are cheating and lying to customers when for the sake of easiness the manufacturers are speaking in terms of equivalent focal lengths.

So I have the feeling that you are undertaking a Don Quichote's fight, trying to blow out opened doors. That kind of equivalence fights are plaguing the DPreview forums, but what is your goal here among all the experienced photographers populating this friendly list ? What do you want to achieve ?
 
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Stefan Steib

Active member
You are really funny Godfrey.

First some guys demand that this video is too mainstream and doesn´t use the right terminology....I try to explain that it does summarize facts and is no BS..... people ask for this because they "don´t get the point ?"
And after the explanation you say : huh what about all this tec bubble, couldn´t you have said this easier ?

Boy...... :facesmack:

I wonder why I answered all this.
Seems to be useless.

I go ahead and build some new cameras and lenses now.

Greetings from Germany
Stefan
 

Godfrey

Well-known member
You are really funny Godfrey.

First some guys demand that this video is too mainstream and doesn´t use the right terminology....I try to explain that it does summarize facts and is no BS..... people ask for this because they "don´t get the point ?"
And after the explanation you say : huh what about all this tec bubble, couldn´t you have said this easier ?

Boy...... :facesmack:

I wonder why I answered all this.
Seems to be useless.

I go ahead and build some new cameras and lenses now.

Greetings from Germany
Stefan
As I said way back on post #27: "It's the same tired hogwash that I've read on DPR a thousand times, and 99% bullpucky."

Annna T is correct: Alleging that the manufacturers are "lying" to people is incorrect, it's a fool's errand too. They're just stating a simple focal length equivalence for people who want to know if their lenses will work.

Go build a camera and take pictures. Stop proselytizing this inanity. It's almost as bad as "film vs digital."

G
 

Stefan Steib

Active member
Well Godfrey

the first post was 3 days ago and it got 1709 views since then.
The bullpucky seems to be interesting for some.... people.
Maybe not you, but then: why are you posting here in this thread ?
You ARE the forum...... wow ?

:cool:
 

Shashin

Well-known member
Stefan, no one is doubting the relationships between format and DoF and FoV. There is nothing new in that regard.

What I am bothered with is attributing factors to things that are not true. He is basically using an equivalency scheme to make erroneous conclusions. Of course, he starts at some confusing places too with thinking that an f-number is a measure of DoF or focal length describes angle of view. His rant about ISO is silly--he states ISO should be somehow based on S/N, yet in all his claimed research he could not find that ISO is actually based on S/N. And the light gathering area of the sensor idea, well, lets just say that is another discussion.

I have taught photographic principles. For those that what to learn them, they can be a powerful tool. But when the ideas and concepts get muddled, I rarely find it is helpful. Someone questioned why I find this important--why I was wasting my time with this. I ask that of myself as well. But I believe the practitioners of a craft should understand the fundamentals of the craft--whether you want to do this logically or intuitively. Pernicious ideas do not help, and if you don't think these ideas make an impact, just look at the video you posted--he got that from somewhere. And learning what an f-number is is not exactly rocket science.

Now, to your point about crop factor being used to visualize difference in formats, both in FoV and DoF, yes, it works well. It worked just as well in the film era.
 

Stefan Steib

Active member
Will

Thanks for this clarification.

I always try to get to points by new ways of thinking. For me this video was kind of a nice attempt to make people understand a bit more of what is happening there. Probably this could be done better.

So why don´t you do it ? I always ask people who criticise work of others:
could you have done it better ? And if someone says: yes of course !
Then: why don´t you do it ?

I am sure this would be really helpfull for many and as you have seen the concept is NOT clear for a bunch of people.

Greetings from Germany
Stefan
 

Godfrey

Well-known member
Well Godfrey

the first post was 3 days ago and it got 1709 views since then.
The bullpucky seems to be interesting for some.... people.
Maybe not you, but then: why are you posting here in this thread ?
You ARE the forum...... wow ?

:cool:
Please, let's not change the discussion into an ad hominem rant. I'll ask the moderators to remove it if you push it that way.

Obviously, the topic is of some interest to me, for reasons that are quite similar to what Shashin posted. And in response to your question of why I don't do something better, well, I have when I was teaching photography and image processing, but I don't have the time today.

Too much mysticism and obfuscation in this video. It's a bunch of muddled ideas that do not represent what is going on at the right (consistent and conformant) level, coupled with silly assertions that "They are Lying to Me!", which are untrue and inflammatory at the same time. Typical internet horsepucky in my opinion.

G
 

philip_pj

New member
„ The rules of optics are complex and nasty! “

"Nevertheless I am going to show you on the following pages, that things are not that bad, and that you can understand the basic relationships without an excursion into higher mathematics of Fourier-optics.

And those who see too many numbers and curves may be assured that these are not really necessary for good photography, since photography is mainly based on
experience. But it is great fun to understand your tools in a better way.."

This is part of the intro to Hubert Nasse's revealing foray into explaining MTF, it seems to encapsulate some things of relevance here. i actually don't mind some passion in discussions, people feeling strongly about things is far better than disinterest, and we can, all things considered, learn from each other. So thanks all.
 

Leigh

New member
You still don´t understand:
Nobody ever said- not me nor the guy in the video- that the exposure is varying.
Sadly, it appears your memory is seriously flawed.

Going back to post #5 in this thread, you said:
the sensitivity of newer sensors may have been improved , but not by a square of 2 ? The number of Photons caught is still the measurement of quality.
Sensor sensitivity has absolutely nothing to do with Depth of Field in any image acquisition system.

It ONLY impacts exposure calculations.

- Leigh
 

Guy Mancuso

Administrator, Instructor
Folks Im in the middle of a big shooting job. You want this moderated please use report to mods button. But to be honest I am not moderating this myself.
 

Stefan Steib

Active member
Sadly, it appears your memory is seriously flawed.

Going back to post #5 in this thread, you said:

Sensor sensitivity has absolutely nothing to do with Depth of Field in any image acquisition system.

It ONLY impacts exposure calculations.

- Leigh
??? - Sorry to spoil Guys nerves , but it seems your understanding of the english language is seriously flawed. THIS is totally out of context, doesn´t even use the word exposure and has not even the slightest connection to the claim you make here.

?????
 

Leigh

New member
Sorry to burst your photon, Stefan...

But I have an excellent command of English, thank you.

Sorry you can't say the same.

- Leigh
 

Jorgen Udvang

Subscriber Member
Godfrey, finally I understand why my photography sucks! I will walk, no run, to the nearest Camera Temple and acquire the Nikon WhizzBang 456-25Fs with the Nikon 50mm UltraExtraSpecial f/1.2 VR XdFt Z right away, or at least as soon as the Camera Priests unlock the door to their Holy Vault.

For decades, I have wandered around on the surface of the earth believing that the photos I take, the end result of my humble work, is what decides if I'm a worthy member of the World Wide Photographic Congregation. I now understand that things look differently, and that without a Nikon WhizzBang 456-25Fs (or an equivalent sacred relic from another temple), I'm just an annoying nobody, sticking worthless, black boxes up unto the noses of respectable citizens, unable to satisfy the spiritual requirements of our Great Spiritual Leader, The Holy 35mm.
 

Georg Baumann

Subscriber Member
Well, one thing I feel strongly about is credibility:

1. The link to the video states already:

http blah blah
/sony-olympus-panasonic-cheat-customers
So, because his claim has not been proven that get's a solid :thumbdown:

2. This ain't a 100% educational video, on the contrary, this is a sales pitch from a guy selling his own and other peoples stuff. It is camouflaged as tech expert blah, stirring the **** but not putting meat to the bone at all.

This too get's a super solid :thumbdown:

3. His video adds zero, and I mean that, zero news or revelations to the world of photography knowledge, not a sausage. On the contrary, it leads, and in my opinion he does that deliberately in deed, to even more confusion with people who are not too versed in the technical department.

Need I say this get's a :thumbdown:

There is more but that is enough for me, as a self proclaimed tech expert, he lost all credibility in my book.
 
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