[ChristianRock]

A place like DXO Mark measures certain things -- SNR, dynamic range, etc. What they find is that for an equalized viewing/printing size and same generation sensor, full frame cameras have a little better than a stop better dynamic range and SNR compared to an APS-C sensor.

Ummm those are properties of the sensor, not the lens. Aperture has nothing to do with that.

I think technology can evolve to a point where these numbers are a non-issue at the APS-C size sensor, and it will start to look a lot like FF numbers (. People will still want FF because of the DOF, of course. We're seeing it already in dynamic range - K-5 IIs and D610 dynamic range are identical, and both kick the butt of any Canon FF sensor. SNR will follow.

[marcusBMG]

Good article addressing the topic with good examples:

What is equivalence and why should I care?: Digital Photography Review

[VisualDarkness]

I agree that it's stupid when the manufacturers write "equivalent focal length" on the lenses, only to confuse the potential consumers and lead them into a faulty way of thought.
On the other hand it's wrong to say that lenses that projects smaller image circles got less light gathering as that isn't how T-stops are measured.

---------- Post added 10-09-14 at 07:44 PM ----------

Good article addressing the topic with good examples:

What is equivalence and why should I care?: Digital Photography Review

Still, the DOF is only shallower with a bigger sensor if the subject is the same relative size in the composition and no cropping is done to skew things. In practice most people don't have to care about it. It's tough enough to get both eyes in focus in a portrait with my 55/1.4 at F1.4 so I would not need to take what FF would gain me in shallower DOF in account.

[Parallax]

Moved to the Full Frame forum to join the other threads on the same subject.

For my actual input as to the subject matter; see my sig line.

---

Last edited by Parallax; 10-09-2014 at 11:01 AM.

[rburgoss]

Well, the whole thing is pretty useless for most people shooting APS-c as they've never ever shot 135 film or digital FF. The best thing would be if people not in need of comparing "equivalence" just would stop doing it. There simply is no real need for it. If minimal depth of field is your biggest wish nothing will beat large format film cameras, so forget digital.

As an example of why the equivalence often is broken in practice is that the advantage of a bigger sensor gets completely diminished as soon as you start cropping pics to the equivalence of aps-c. So for me when shooting sports where I often end up cropping even at 200-300mm to get the right composition I would end up with the same result with FF, unless I get equally bright longer lenses.

---------- Post added 10-09-14 at 07:26 PM ----------

About the aperture equivalence the same thing applies, if you shoot with the lenses stopped down you don't have to care about lenses max aperture equivalence relative to sensor size at the same image composition.

You are all right in everything. The issue here is that the only thing that changes with sensor size, is MGNIFICATION. The rest stays the same. Aperture, focal length, shutter speed, ISO are all the same from one camera to the other. The only thing that changes is magnification, and or course, all its consequences. There is one very visible consequence of magnification change, which is depth of field. At higher magnification, less depth of field, no matter what format is used. Also the image noise, but this is more a technologial barrier in sensors than an applied light transmission law of physics. That's all to it.

As I stated in my first post about this subject, by being aware and keep track of whatever equivalence in magnification was obtained from certain focal length, is like a New Yorker living in California but still doing his stuff according to the eastern time zone. Its ridiculous.

Another trick question.... How do full frame digital photographers call this format after moving from medium format negatives? (crop????)

Another trick question: John, a pro photographer who uses large format (4x5 inch plates) for portrait shooting, has a hand held light meter (Gossen, Sekonic, whatever...). He always measures light, gets an EV value and adjusts his aperture and shutter speed accordingly. The only thing hi has to dial is the film speed (ISO). One day, he gets a nice digital camera, aps-c format DSLR, with a couple of lenses. Since John is a well educated photographer in light handling matters and the strict relation between aperture, shutter speed and ISO, he plans to use his trusty handheld meter to check the camera's accuracy... but wait, here comes Barney and tell him: "Hey John, that meter is no good because the light that falls in that little sensor is insignificant compared to your 4x5 inch plates... so aperture and shutter speeds are not the same!"

Did John threw away his light meter?

[Rondec]

Ummm those are properties of the sensor, not the lens. Aperture has nothing to do with that.

I think technology can evolve to a point where these numbers are a non-issue at the APS-C size sensor, and it will start to look a lot like FF numbers (. People will still want FF because of the DOF, of course. We're seeing it already in dynamic range - K-5 IIs and D610 dynamic range are identical, and both kick the butt of any Canon FF sensor. SNR will follow.

I guess the thing is that most full frame cameras (even Canon) hold on to SNR and dynamic range at high iso than APS-C cameras. Since iso, aperture and shutter speed are a triad that must be linked together, adjusting one will effect what you do with the other two. If you could shoot with a 55mm f1 lens, you would be able to have equivalent performance to what you see with a 85mm f1.4 lens on full frame. Such a lens doesn't exist, though.

[marcusBMG]

It takes a clear mind and pen to make points about technical issues without inadvertently muddying the waters. Looking back at my OP I was probably a bit careless in what I said in adressing the point of it being desireable to state an equivalent aperture along with an equivalent focal length when making a comparison between sensor formats. The analogy I suggested with tc's and extension tubes isn't quite right.

OK so reading the dpreview article has clarified a few points for me.

F stop depends on light intensity, which is defined by the aperture. ie photons per unit area. So what Rob rbrgoss says about exposure is right.

However what I was hinting inexpertly at in pointing out the total light isn't wrong, it's relevant.

As the dpreview article explains

But surely F1.2=F1.2=F1.2?
Yes, it is. But F1.2 is not equivalent to F1.2 across different formats.
The equivalent aperture not only tells you how much depth-of-field you get, on a different system, it also tells you how much total light you'll get. And, because the more light you capture, the less noisy your image, this is key to why large sensors generally give better image quality than small ones.

So anyway, happy to have been of service in provoking an enthusiastic response, and to have improved my understanding of things .. at least a bit...

I think I'll sign off now.

[Rondec]

Moved to the Full Frame forum to join the other threads on the same subject.

For my actual input as to the subject matter; see my sig line.

Could we rename this the "One Eye in Focus Forum?"

[Parallax]

(no)

[ChristianRock]

Quote:
But surely F1.2=F1.2=F1.2?
Yes, it is. But F1.2 is not equivalent to F1.2 across different formats.
The equivalent aperture not only tells you how much depth-of-field you get, on a different system, it also tells you how much total light you'll get. And, because the more light you capture, the less noisy your image, this is key to why large sensors generally give better image quality than small ones.

See, I have to disagree with that. I could be wrong, but I have to disagree.

The lens is projecting a certain amount of light at its back, regardless of what size sensor is capturing it - the sensor doesn't change the T-stop of the lens. The image outside of the sensor is wasted if you are using a smaller sensor, but it still helps maintain the overall qualities of the image. The image projected on the sensor is always the same brightness (or as they like to say, the same amount of light is 'sucked in'). You don't 'suck in' less light because the sensor is smaller.

The reason why the sensor sizes give different numbers is pixel density, not size. As I pointed out above, dynamic range is already similar for APS-C and FF. SNR will follow and DP's point will be proven wrong, in fact I think it's already being proven wrong...

[VisualDarkness]

It takes a clear mind and pen to make points about technical issues without inadvertently muddying the waters. Looking back at my OP I was probably a bit careless in what I said in adressing the point of it being desireable to state an equivalent aperture along with an equivalent focal length when making a comparison between sensor formats. The analogy I suggested with tc's and extension tubes isn't quite right.

OK so reading the dpreview article has clarified a few points for me.

F stop depends on light intensity, which is defined by the aperture. ie photons per unit area. So what Rob rbrgoss says about exposure is right.

However what I was hinting inexpertly at in pointing out the total light isn't wrong, it's relevant.

As the dpreview article explains


So anyway, happy to have been of service in provoking an enthusiastic response, and to have improved my understanding of things .. at least a bit...

I think I'll sign off now.

F-stop is a function of focal length and the optically most narrow point, nothing less and nothing more. This is why equivalent F-stops becomes useless unless you are really stuck in 35mm sensor thinking and need to translate. The same thing applies for focal length equivalents, it's useless on its own.
T-stops that is actual light transmission is not a subject to equivalence at all.

[rburgoss]

F-stop is a function of focal length and the optically most narrow point, nothing less and nothing more. This is why equivalent F-stops becomes useless unless you are really stuck in 35mm sensor thinking and need to translate. The same thing applies for focal length equivalents, it's useless on its own.
T-stops that is actual light transmission is not a subject to equivalence at all.

My God, I would dare to say it almost hurts when someone is so stubborn as to only read and "cherry pick" out of context whatever statement may find anywhere, just to keep claiming truth in a total bogus statement.

The above said by VisualDarkness is total true. There is nothing more to add to it. Just someone who want to scramble things may try to do so. There are certain laws of physics that prevail over whatever statement anyone here can say, even if they get the Pope, Mother Teresa, Obama or the Dalai Lama to back up such statements.

Light is light. It has no nationality nor political agenda. Light only has color and intensity. That's it.

Photo lenses handle light by MAGNIFICATION and f/stop (aperture). Prime lenses offer fixed magnification. Zoom lenses offer variable magnification. Aperture is the same for every lens. f/2.8 transmits the SAME AMOUNT OF LIGHT with any focal length.

Sensors (as film) is a light capturing device, but since what is intended to capture is AN IMAGE and not a total sum of photons, then what matters is its capacity to receive that projected light over a certain area. The sensor size (or film) makes no difference.

Depth of field is a product that comes from the magnification of any given image, projected into any given area, then enlarged to a FIXED viewing size and being analyzed at a specific viewing distance. Its a bit complicated but the thing that matters, is that the sensor size has nothing to do here. Is the total magnification what matters.

F/Stops (aperture) is identical from one lens to another, no matter the film or sensor format. That is if your intended measurement is LIGHT. If you intend to measure "depth of field" (luck on that one) and since depth of field has to do with MAGNIFICATION, then in order to get the same magnification over the sensor format, it means that the focal length should be changed. As a consequence, the aperture should be changed too because you are changing MAGNIFICATION..... That is why sometimes there is a reference of "equivalent aperture", which relates to equivalent depth of field over the equivalent magnification of any given image, but this equivalence has nothing to do with LIGHT TRANSMISSION.

Please, someone put this in simpler words. English is not my native language and I am struggling here.

[Kunzite]

I'm with Northrup, pacerr, I blame the marketing departments and their hired minions, they have a vested interest in confusion and misunderstanding...

When it's actually the likes of Northrup who should be blamed, for making simple things complicated and pointless. All to appear as "experts".

Aperture is not defined by DoF. Read the wiki definition, I posted it in the last thread where this was posted. DoF is about DoF, and it's not measured in stops, it's measured in measures of linear units, anyone who wants to measure DoF in stops is trying to do a con job on you.

ISO is not about total light collected. The man in the video is simply lying. There was more difference in the amount of light collected by the "sensor" in film days when there were 8x10 film cameras and milota minoxs that were completely tiny, yet the ISO standard was adopted.. ISO hasn't been made obsolete by digital. The total amount of light captured by the film was never part of ISO. Again read the wiki entry. SO once again the author claims a term is irrelevant, that is still completely irrelevant. The brainwashing continues with his diagram where FF is the biggest sensor. What happened to MF? Oh, well that doesn't fit with the Full Frame superiority mindset so, it's conveniently left off.

This man is lying through his teeth. I just hope no one gets sucked in by this nonsense.

Add another blatant lie: focal length is not angle of view. He's amazed that the same FL does not give the same angle of view on different formats, which is downright stupid.
FL is precisely defined, the most basic optics notion, and it doesn't even care if the lens is mounted on a camera or another device.

Anyway, even in its most scientifically-sound form "equivalence" is a fraud, a misapplication of existing notions which doesn't really makes sense outside heated forums discussions. The good old system - which "equivalence" seeks to modify - appeared with purpose, it's elegant and universal, instead of that silly mess. Focal length is what it is; basic geometry will allow you to get the angle of view. f-number appeared as FL/aperture - guess why - and together with ISO and shutter speed it works nicely as the exposure triangle. ISO can be seen as "standard sensitivity per square mm", and that worked perfectly in an era where multiple film formats existed - all cut down from the same large film roll. And DOF was a bit subjective - based on a convention regarding print size and viewing distance, not all manufacturers agreeing about the CoC (IIRC Zeiss used tighter values).

Breaking news: digital didn't obsolete optics. You don't have to keep your shutter speed constant and vary the aperture to get the "same" DOF (reasons you're using a certain f-stop might not be those assumed by "equivalence"). You don't increase ISO to get the "same" noise as for a smaller format. You cannot forget about details. And last - but not least - you will crop. This means changing the effective "total light", effective DOF, angle of view.

However... the discussion is pointless. "Equivalence" fans will always assume they're right, and everyone who don't agree with them lacks knowledge and is unable to understand - they don't even care what arguments we might present. Wait, here it is:

I would like to respond to what you are saying Normhead but you are not making any sense at all. if you want to enage with the discussion then dicuss the points raised. I don't know why you are calling Northrup a liar, I suspect you haven't seen the video or don't understand it.

P.S. Apologies for repeating what was already said. Well, we're constantly hit with this "equivalence" religion, even when it obviously cannot be applied (see the recent moon example), perhaps it doesn't hurt to put it to its place.

[redrockcoulee]

Another trick question: John, a pro photographer who uses large format (4x5 inch plates) for portrait shooting, has a hand held light meter (Gossen, Sekonic, whatever...). He always measures light, gets an EV value and adjusts his aperture and shutter speed accordingly. The only thing hi has to dial is the film speed (ISO). One day, he gets a nice digital camera, aps-c format DSLR, with a couple of lenses. Since John is a well educated photographer in light handling matters and the strict relation between aperture, shutter speed and ISO, he plans to use his trusty handheld meter to check the camera's accuracy... but wait, here comes Barney and tell him: "Hey John, that meter is no good because the light that falls in that little sensor is insignificant compared to your 4x5 inch plates... so aperture and shutter speeds are not the same!"

Did John threw away his light meter?

Many people who move into MF or LF cameras use their dslr for a light meter or use an app for their smart phone. We use the latter for our pinhole cameras. The lens settings do not change when I put a roll film back on my 4X5

If you mostly used a certain lens like a 28mm in 35mm film days then equivalence is a good starting point when moving onto another format even if the aspect ratio is different but oft times one uses different formats in slightly different ways so even that is not always a fool proof method of choosing lenses. As far as the so called f-stop equivalencies I have no idea what my LF lens on 4X5/5X7 or whole plate would be in 35mm terms no any of my Hasselblad lenses compared to 35mm or LF.

[ChristianRock]

Yeah I wouldn't say equivalence is a fraud or is useless. But it's nothing more than a reference point, and even as that, it's not as broad a concept as some people put it. There are some aspects where equivalence makes sense (comparing DOF or FOV) but others where it doesn't (everything concerning exposure). It is what it is.