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# A reminder for some memebers as to what the F stop is all about.

Started Jan 26, 2014 | Discussions
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Almost.
2

boggis the cat wrote:

mapgraphs wrote:

I'll try and make it more understandable,

The f/ number is the Focal Length (FL) divided by the Diameter (D) of the entrance pupil.

so the equation is f/ = FL/D

You're defining f as focal length one moment and then defining f as aperture the next. It just doesn't work that way. So no they aren't the same.

Sorry.

Bob is saying that relative aperture (note relative) is defined as f/D, where f is the focal length and D is the entrance pupil diameter.

The trick is to make it clear whether you are talking about relative aperture (e.g. 'f/2') or physical aperture (e.g. '25 mm').

Not "physical aperture" but "virtual aperture" (entrance pupil). The virtual aperture is the image of the physical aperture through the FE (front element).

To get f/2 at f = 50 mm requires an aperture of 25 mm: 50/2 = 25. So, as an example:

• FourThirds: the ZD 50 mm f/2 lens has a maximum aperture of 50/2 = 25 mm
• 135: a 100 mm f/2 lens requires a maximum aperture of 100/2 = 50 mm.

Both the above lenses would have the same EFL of 100 mm (EFL means 'Equivalent Focal Length' in 135 terms).

Yes.

The 135 lens requires twice the physical aperture to achieve f/2 because the lens must cover a much larger sensor.

This isn't so.  A FF 100mm lens at f/4 (or a 100 / 4 lens) still has an image circle that covers the entire sensor.  In fact, a 100mm lens at f/4 on FF would project the exact same amount of light on the whole of the sensor as a 50mm lens at f/2 on 4/3 for a given scene luminance and shutter speed.

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Everything is relative in this world, so
1

When I say "the final word" it is what I think about my participation in this thread. Nothing else.

Your final word is up to you.

So never assume: because "when you assume, you make an ass of you and me" (a popular saying in the military).

best wishes.

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Sergei,
Calgary.
www.alberta-photo.com

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Let's say...

gsergei wrote:

Someone in Dave Gaines' thread exclaimed:

"convince me, that an Olympus 25mm F/2.8 produces the same light" as a FF lens at F/2.8"

then someone referred to a "guru" , saying" that bigger sensor "gathers" (I totally hate this) more light. This statements prompted me for my essay. That's all. Then the topic was highjacked by other people. I wasn't going to cut circles ad infinitum about DOF and FOV, which topics have already been beaten up to death.

...we take a pic of the same scene from the same position with the same shutter speed at 25mm f/2.8 on 4/3 and 50mm f/2.8 on FF. Then the amount of light per area falling on each sensor is the same (same exposure), but 4x (two stops more) light will fall on the FF sensor, resulting in half the noise for equally efficient sensors and half the DOF (this is the connection between DOF and noise that some did not understand).

best wishes.

Indeed!

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Re: Everything is relative in this world, so
1

gsergei wrote:

When I say "the final word" it is what I think about my participation in this thread. Nothing else.

Your final word is up to you.

So never assume: because "when you assume, you make an ass of you and me" (a popular saying in the military).

You do realize you've made two follow up posts after your "final word", right?

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Re: Please, refer to the original point of discussion:

gsergei wrote:

Someone in Dave Gaines' thread exclaimed:

"convince me, that an Olympus 25mm F/2.8 produces the same light" as a FF lens at F/2.8"

then someone referred to a "guru" , saying" that bigger sensor "gathers" (I totally hate this) more light. This statements prompted me for my essay. That's all. Then the topic was highjacked by other people. I wasn't going to cut circles ad infinitum about DOF and FOV, which topics have already been beaten up to death.

best wishes.

Well, I addressed your particular statement which I quoted. If all you try to discuss is the light meters and what they indicate, you are correct. You however in this thread entered the field of that dreaded equivalence, and that assumes equivalent images for cross-format comparison, whether you intended to "cut circles ad infinitum about DOF and FOV" or not. If you agree that with my additions your thesis does not hold anymore, I nod with satisfaction and retreat.

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Re: To all who continue to accuse me of all kinds of photographic sins...

windsprite wrote:

gsergei wrote:

Or why the light meter doesn't care.

Hello, again.

Let me repeat my point:

Given the same light source conditions and ISO setting the illumination, measured in lumens, received by any size of sensor is equal across all formats (no Ifs , no buts) , when cameras are set to the same A , S, ISO values. So, in practical terms this means, that the illumination received by my tiny c7070 at 125/5.6 and ISO 100 is exactly the same as on the so called FF sensor camera set to the same values. This will result in the same picture brightness/darkness , subject to DR and noise differences.

Please, do not feed me things like "amount of light", "sensor area", "light power" , "bigger lens opening" etc. and try to operate , using known physical terms and concepts.

Here is the final word.

Sorry, but you do not get to decide what the "final word" is.

Please, do me a favor:

get hold of ANY light meter (be it a 40 year old analogue one, or a modern Sekonic) and look at it carefully and then tell me , where do you see "Canon FF" or "Olympus c2020" or Fujifilm X100s ??? And then prove me wrong.

One might say the same of a ruler. Why, then, is it acceptable to say 300mm on FT is equivalent to 600mm on FF?

Julie

And one might also ask why it is that  nation states, universities and mega-dollar consortia build huge telescopes with enormous imaging sensors.
Each of the two Keck telescopes is FL=17,500mm f/1.75 . . .they know that the huge 10 metre aperture captures more photons.

Peter

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Re: To all who continue to accuse me of all kinds of photographic sins...

Messier Object wrote:

And one might also ask why it is that nation states, universities and mega-dollar consortia build huge telescopes with enormous imaging sensors.
Each of the two Keck telescopes is FL=17,500mm f/1.75 . . .they know that the huge 10 metre aperture captures more photons.

Peter

Yes indeedy!

Speaking of astronomy, I always get a kick out of your user name!

Julie

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Camera obscura

This thread just gives me a headache but I will say one thing, windsprite has the best AV by far.

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Re: Everything is relative in this world, so
1

gsergei wrote:

When I say "the final word" it is what I think about my participation in this thread. Nothing else.

Your final word is up to you.

Usually when we say "the" final word, we mean the final word on the topic for everybody, ie. the only correct answer. I would have understood your meaning if you had said something like "my final word." I understand that not everybody here is a native speaker of English, though, and not even native speakers read everything exactly the same way. Thanks for clearing it up.

So never assume: because "when you assume, you make an ass of you and me" (a popular saying in the military).

I know this saying well. It is the basis for my favorite scene from the TV comedy "The Odd Couple"!

It's funny that you mention it, because it was exactly the phrase that came to mind when I read your original post, which seems to assume (incorrectly) that the people you're arguing against don't understand the meaning of an f/ stop or exposure.

Julie

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Re: Camera obscura

Braxton7 wrote:

This thread just gives me a headache but I will say one thing, windsprite has the best AV by far.

windsprite thinks so too.

I guess you know where it came from, then?

Anyway, thanks for noticing!

Julie

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Re: Glad that you had such big aperture
1

philosomatographer wrote:

Anybody still participating in the "equivalence" debate have a serious dead-horse-beating fetish - they should get out and take some photos, possibly with a "full-frame" system. Just remember to stop down those lenses to f/8 for a nice and even performance across the frame!

I've taken a few.  Would you like to see some?

I use four thirds, 35mm "full-frame" (Leica), 6x7cm Medium Format (Mamiya), and 4x5in (Linhof) all on a regular basis. There are no optically better lenses than the Olympus SHGs when looking across all optical parameters.

Are you talking about lp/mm (line pairs per millimeter on the sensor) or the photographically more meaningful measure of lw/ph (line widths per picture height)?  Or are you talking about some other measures or combinations of measures (e.g. flare, bokeh, AF, etc.)?

Zeiss is the only manufacturer to have "caught on" with having to produce retrofocus, oversized lenses for ultimate performance on digital (the Otus 55/1.4). Manual focus, no weather sealing, single focal length, \$3.5K

It'll be a while before somebody applies those ideas to an ultimate-performance f/4.0 (for "equivalence"), fast-focusing, fully weather-sealed zoom lens for 35mm sensors. Then we'll talk about cost and size, compared to the ZD 14-35mm f/2.0!

You mean like the Canon 70-200 / 4L IS?

As it stands, we have junk like the Nikon 16-35mm f/4.0 that is not only huge like a telephoto lens, but distorts like a fisheye. See - only if they severely compromise on one parameter (distortion) do they manage a good showing with the others.

Truly uncompromising lenses are very rare in the 35mm world, yet we have them in the form of four zooms covering 7mm to 250mm in the four-thirds system. Of course, due to abandoned development, we are stuck with a "compromised" sensor, but such is life.

Compromises always exist.

So - what were we debating in this thread again?

I think it was about the relationship between relative aperture (f-ratio) and virtual aperture (entrance pupil), the difference between the amount of light per area that falls on the sensor (exposure) and the total amount of light recorded by the sensor, and how these relate to the visual properties of the captured photo.

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Re: Both sides are sort of right
1

Do you guys actually get out and take photos?

Or maybe it is winter and this is the equivalent of whitiling.

: )

My experience is that I can get an excellent image from any camera but when I need to pull more from the image in Photoshop the Full frame gives more. eg I have tried a 60 and 50D for Real Estate work but the need to have clean shadows means I have to use a 5D. No doubt the sensor tech is continually improving and this has allowed photographers to down size. As for the whole tech debate  - Who cares as long as the camera does what you want.

Current cameras. SX40, X100, 7D and 5D.

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Re: Both sides are sort of right
1

Dougbm_2 wrote:

Do you guys actually get out and take photos?

I've taken one or two that, in my opinion, were decent.

Or maybe it is winter and this is the equivalent of whitiling.

: )

My experience is that I can get an excellent image from any camera but when I need to pull more from the image in Photoshop the Full frame gives more. eg I have tried a 60 and 50D for Real Estate work but the need to have clean shadows means I have to use a 5D. No doubt the sensor tech is continually improving and this has allowed photographers to down size. As for the whole tech debate - Who cares as long as the camera does what you want.

Current cameras. SX40, X100, 7D and 5D.

In my personal opinion, pretty much any DSLR is "good enough" for the vast majority in the vast majority of situations in terms of IQ and DOF options. It's differences in operation that matter more, by far.

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So what is your answer to this?

Great Bustard wrote:

Wow. Just wow. Everything you wrote is entirely incorrect, and I will prove it wrong with a single example that you can all do at home.

Let's take a photo of a scene with an E5 + 35-100 / 2 at 50mm f/2 1/200 ISO 3200 and 100mm f/2 1/200 ISO 3200 (note that we have used the same lens, same f-ratio, same shutter speed, same ISO, same sensor, and thus same sensor efficiency and pixel size).

We now crop the 50mm photo to the same framing as the 100mm photo and display both photos at the same size. Which photo is more noisy and why?

(Hint: while the sensors are the same size, the cropped photo uses only 1/4 the area of the sensor, and thus only 1/4 as much light makes up the cropped photo as the uncropped photo.)

We have a 300mm f/2.8 on a Canon 1Dx and a 300mm f/2.8 on a Olympus E-M1. Same ISO. Both cameras are 16 MP. Now crop the shot from the 1Dx to fit the FOV of the E-M1. What image has less noise? What image has less detail?

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And the answer is:
2

DonSC wrote:

Great Bustard wrote:

Wow. Just wow. Everything you wrote is entirely incorrect, and I will prove it wrong with a single example that you can all do at home.

Let's take a photo of a scene with an E5 + 35-100 / 2 at 50mm f/2 1/200 ISO 3200 and 100mm f/2 1/200 ISO 3200 (note that we have used the same lens, same f-ratio, same shutter speed, same ISO, same sensor, and thus same sensor efficiency and pixel size).

We now crop the 50mm photo to the same framing as the 100mm photo and display both photos at the same size. Which photo is more noisy and why?

(Hint: while the sensors are the same size, the cropped photo uses only 1/4 the area of the sensor, and thus only 1/4 as much light makes up the cropped photo as the uncropped photo.)

We have a 300mm f/2.8 on a Canon 1Dx and a 300mm f/2.8 on a Olympus E-M1. Same ISO. Both cameras are 16 MP. Now crop the shot from the 1Dx to fit the FOV of the E-M1. What image has less noise? What image has less detail?

Instead of "same ISO", how about we say, "same f-ratio and shutter speed", as the ISO setting isn't particularly relevant to the matter at hand, and the cameras may not meter the scene the same at the same ISO setting.

Then the EM1 photo will have less noise since it has a more efficient sensor. The EM1 photo will be more detailed since it has 4x as many pixels on the subject.

Now let's assume we had a FF sensor made with the exact same pixels as the EM1 sensor.  Then the photos would be all but identical.

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Re: Please, refer to the original point of discussion:
1

gsergei wrote:

Someone in Dave Gaines' thread exclaimed:

"convince me, that an Olympus 25mm F/2.8 produces the same light" as a FF lens at F/2.8"

then someone referred to a "guru" , saying" that bigger sensor "gathers" (I totally hate this) more light. This statements prompted me for my essay. That's all. Then the topic was highjacked by other people. I wasn't going to cut circles ad infinitum about DOF and FOV, which topics have already been beaten up to death.

Now there was I, convinced you were an 'equivalence' plant because your 'essay' was so completely ludicrous and your reaction to any criticism was to accuse the other party of not knowing what they were talking about, while including more than enough elementary gaffes to show you hadn't a clue. Now you're trying to convince us you were for real. You're going to have to work harder on that one...

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Bob

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Re: Question:
1

Great Bustard wrote:

Close Encounter

Would the "success" of that photo suffered if it had been instead taken at 83mm, 1/2000, f/2.8, ISO 200 with a 50-200 / 2.8-3.5 instead of the 83mm, 1/4000, f/2, ISO 200 with the 35-100 / 2 that you used?

If so, then that's why some choose larger formats. If not, why not use the smaller, lighter, and less expensive zoom that has a much greater focal range? Is it for the 35-50mm end of the zoom?

That's a fair question indeed. You know what? I don't think the success of the photo has much to do with the gear at all - I'd like to take most of the credit. Could i have made this exact photo with a 70-200mm f/4 on a 5D MkIII? Sure. It would not be as sharp and contrasty across the frame - it really wouldn't - but that doesn't matter. We're talking minor differences here that don't impact the content of a photo.

The 50-200 is not in the same class as the 35-100 - and I think the frustration of being limited to a rather deep field of focus would outweigh any optical signature, unlike with the 35-100. The 50-200 is a "practical, budget-friendly" lens, the 35-100 is an uncompromising showpiece of a lens.

I'd like to think - and this is borne out of my experience using many systems - that there is something utterly special about the flawless rendering, insane microcontrast, out-of-focus transition etc of the ZD 35-100mm at f/2.0. I have yet to see it matched by another 70-200mm lens at f/4.0, but we're talking about the very edge of the performance envelope here, and it's only visible when you pixel-peep or look at large prints.

I have to add that you really don't have to tell me about "that's why some use larger formats" - I use much larger formats than what you do on an almost daily basis. It's purely a matter of liking this range of lenses, because they are optically special for the kind of work that I like to produce.

They harmonise nicely with the look I get from my Leica M lenses on film. The grain of the E-5 sensor even helps

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You think so?

Great Bustard wrote:

Of course, 4/3 lenses are sharper than FF lenses, which offsets that advantage for FF somewhat. That is, if a 4/3 lens is twice as sharp as a FF lens, it will resolve as well as a FF lens for sensors with the same pixel count and AA filter.

I don't believe this is necessarily true. They are told to be sharper because they resolve more lines per mm, but that is only because those lenses are tested with the sensors that have the highest pixel density. Third party lenses that are ported and adapted to different formats show that twice as sharp Olympus lenses are nothing but the myth.

Take Sigmas for example, many on this very same forum will agree that Sigma 17-50/2.8 will indeed deliver more detail than the celebrated Zuiko 14-54 (Bootstrap made several comments on it, even Ray agreed and echoed it), whereas the same Sigma is not necessarily the best or better lens than many Nikon equivalents when used on APS-C cameras. Or Sigma 150 macro, whenever there is a mention of it on this very same forum you will hear nothing but a praise. Yet again, Nikon 105 and Nikon 200 are at least as good if not better alternatives. I tried Tamron sp90 in the past, it was very much the same story - excellent lens on FT, good but not the best on APS-C.

And of course, how many times do we hear how good 50-200 is, some will not even change to the system that does not have such a lens, yet it is not really that great when you spend time and really compare it.

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- sergey

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Re: And the answer is:
1

Great Bustard wrote:

Instead of "same ISO"

Here's an interesting question (not for you, you already know the answer) - when people say 'same ISO' what is it that is the same? Put it another way, take two cameras set to 100 ISO, what are you getting 100 of on each camera?

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Bob

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Re: Question:
2

philosomatographer wrote:

Great Bustard wrote:

Close Encounter

Would the "success" of that photo suffered if it had been instead taken at 83mm, 1/2000, f/2.8, ISO 200 with a 50-200 / 2.8-3.5 instead of the 83mm, 1/4000, f/2, ISO 200 with the 35-100 / 2 that you used?

If so, then that's why some choose larger formats. If not, why not use the smaller, lighter, and less expensive zoom that has a much greater focal range? Is it for the 35-50mm end of the zoom?

That's a fair question indeed. You know what? I don't think the success of the photo has much to do with the gear at all - I'd like to take most of the credit.

And yet, the title of your post was:

*THIS* is what f/2.0 is all about...

Could i have made this exact photo with a 70-200mm f/4 on a 5D MkIII? Sure. It would not be as sharp and contrasty across the frame - it really wouldn't...

Well, until we see the photos, we only have your "good word" on that.

...but that doesn't matter. We're talking minor differences here that don't impact the content of a photo.

On that point, I most certainly agree.

The 50-200 is not in the same class as the 35-100 - and I think the frustration of being limited to a rather deep field of focus would outweigh any optical signature, unlike with the 35-100. The 50-200 is a "practical, budget-friendly" lens, the 35-100 is an uncompromising showpiece of a lens.

The same can be said of FF vs smaller formats.

I'd like to think - and this is borne out of my experience using many systems - that there is something utterly special about the flawless rendering, insane microcontrast, out-of-focus transition etc of the ZD 35-100mm at f/2.0. I have yet to see it matched by another 70-200mm lens at f/4.0, but we're talking about the very edge of the performance envelope here, and it's only visible when you pixel-peep or look at large prints.

I am always amused by those who claim that you have to see the prints to see the differences that would be invisible on a computer monitor.

I have to add that you really don't have to tell me about "that's why some use larger formats" - I use much larger formats than what you do on an almost daily basis. It's purely a matter of liking this range of lenses, because they are optically special for the kind of work that I like to produce.

Anyone can claim that the lenses they are using are "optically special".  Indeed, I've heard people say that about compacts, even.

They harmonise nicely with the look I get from my Leica M lenses on film. The grain of the E-5 sensor even helps

If you want to say that you enjoy using your E5 and SHG lenses, and are pleased with the photos they produce, I would never argue against it.  If you want to go further and say that you prefer the output of the E5 and your SHG lenses to any other system, I would never argue against it.  Indeed, I've heard people make the same types of comments about the original 5D vs its successors.

It's when you imply that the E5 and SHG lenses are "better than" any other system out there as a blanket statement that I take exception.

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