I just learned about f-stop equivalency...

[nerwin]

I was watching a photography video this morning and learned about this. I had no idea there was such thing as f-stop equivalency.

So a Sony RX100 M3 24-70 or Nikon DL 24-85 have 35mm equivalency of focal length but not aperture. Their 35mm aperture equivalent is actually f/4.9-7.6.

Samething applies to a 50 1.8 on a Nikon DX body. While the lens is a 50mm with a maximum aperture of f/1.8 on full frame but when its on a 1.5x DX crop body, its equivalent of a 75mm at f/2.8 on full frame. However, would this apply to dedicated DX lenses?

I could be completely wrong. But it kind of makes sense because not all the light coming through the lens will hit the smaller sensor. But because the 35mm full sensor uses the whole image circle of the lens, it collects most of the right? I'm slightly confused haha.

 

[Ysarex]

Slightly confused. The f/stop equivalence that you're talking about pertains to DOF not exposure. Exposure with an f/2.8 f-stop on a crop sensor is the same exposure as with an f/2.8 f-stop on a full frame camera. As far as exposure f/2.8 is f/2.8 regardless of the camera sensor or film size.

The issue comes up when trying to compare DOF between cameras of different sensor size. The smaller the recording media whether film or sensor the greater the DOF in general. You get more DOF from small sensors and small film and less DOF from large sensors and large film. So the f/stop equivalence factors you're seeing are used by people who want to compare DOF between different sensor size cameras.

Joe

 

[Solarflare]

Why yes, for depth of field that true.


Exposure though is light per sensor area. Thus the size of the sensor doesnt change it. And its depends upon T-stops, not f-stops.

T standing for Translucence - how much light is actually channeled through the lens

While f is standing for focal length. Thats because the aperture is defined as k = f / D. K being the aperture, f being the focal length, and D being the diameter of the pupil. So if you have for example a 50mm f1.0 lens, it has a pupil of 50mm diameter. If you stop it down, aperture blades are forming an increasingly smaller hole, so at f2 it would be for example only 25mm now, and only allow 1/4 of the light through that it allowed before.

F-stops are only related to T-stops in that the f-stop is are always lower than the T-stop. The only way to make them equal would be to have an optics without any light loss at all, and well thats not possible.


And as always, optical features like aperture are part of the lens, not the sensor. The lens doesnt care what kind of sensor you use with it. It will always operate at the focal length, f-stop and T-stop thats typical for the lens, and it will also have the depth of field that corresponds to that focal length and f-stop.

Thus if you use a 50mm f1.8 lens on an APS-C sensor, its focal length stays 50mm, its f-stop stays 1.8, and its T-stop stays whereever the heck it is at f1.8, hopefully something close like T1.9 or T2.0.

The only thing thats changed is the viewing angle. And yes, if you recompute the depth of field, you would have to have a different dof - aperture. Its much easier to remember though that the 75mm equivalent you use on the APS-C sensor will have the exact same depth of field as a 50mm f1.8 on a small format sensor. Because depth of field only depends upon optics, not the sensor.



P.s.: Ooops, of course exposure isnt specified in T-stops ... it only depends upon the T-stop of the lens plus the current luminence of the scene.

 

[JustJazzie]

I've gotta agree with the comments above. When I bought my hand held light meter, the didn't offer a FF version.

I too, think they were referring to the DOF rendering between the two.

 

[Ysarex]

Because depth of field only depends upon optics, not the sensor.

This is incorrect and a common misconception. The size of the sensor (film) is a DOF determinant. DOF changes with the size of the recording medium. To calculate DOF requires a value for the variable CoC (circle of confusion) and that value is determined by sensor size: Online Depth of Field Calculator

Joe

 

[Braineack]

So a Sony RX100 M3 24-70 or Nikon DL 24-85 have 35mm equivalency of focal length but not aperture. Their 35mm aperture equivalent is actually f/4.9-7.6.

in regards to DOF, not exposure.

 

[Solarflare]

This is incorrect and a common misconception. The size of the sensor (film) is a DOF determinant.

Uh-hu.

Well, you are obviously wrong with that assumption, and your link doesnt prove it either.

DoF is exclusively a function of the optics. Which is logically extremely obvious. What can the sensor do about the light falling on it ? Absolutely nothing, except recording it. Thus DoF happends in the optics, nowhere else.

The only reason larger sensors offer more DoF is because for a larger sensor, longer focal lengths are required. Thus a MFT sensor uses a 25mm, an APS-C sensor a 33mm and a FF sensor a 50mm optics for the same field of view. Which means the FF sensor gets a lot less DoF. But not because its larger. If you use the FF sensor with a 25mm optics, it sees the same DoF as the MFT sensor with it, except it gets a whole different viewing angle.

The only influence of the sensor is the pixel size, which indeed changes the DoF a bit. Because mathematically no matter which focal length and which aperture - only the focus plane is in focus.

But this actually fights the DoF "advantage" of the larger sensor, since the larger sensor has larger pixels and thus is more tolerant. This influence however is nonlinear - meaning to get twice the DoF, you would need 4 times as large pixels. Also recently larger sensors tend to have more and more the same pixel size as smaller sensors, so I prefer to just ignore this issue altogether.



P.s.: The best way to quickly disprove your claim is to go to the link you provided yourself and scroll to the end of the "camera" list. Instead of any camera, there is a list of CoC values. How could there be CoC values without any sensor size ? Thats because sensor size isnt part of any of the formulas to compute DoF. Only focal length, aperture, distance and CoC are.

 

[gsgary]

As they say a little knowledge is very dangerous

 

[KmH]

Transmission stop - T-stop
f-number - Wikipedia, the free encyclopedia

 

[Braineack]

P.s.: The best way to quickly disprove your claim is to go to the link you provided yourself and scroll to the end of the "camera" list. Instead of any camera, there is a list of CoC values. How could there be CoC values without any sensor size ? Thats because sensor size isnt part of any of the formulas to compute DoF. Only focal length, aperture, distance and CoC are.

That website uses this formula:

Zeiss formula - Wikipedia, the free encyclopedia

In photographicoptics, the Zeiss formula is a supposed formula for computing a circle of confusion (CoC) criterion for depth of field (DoF) calculations. The formula is

, where

is the diagonal measure of a camera format, film, sensor, or print, and

the maximum acceptable diameter of the circle of confusion.

 

[Ysarex]

This is incorrect and a common misconception. The size of the sensor (film) is a DOF determinant.

Uh-hu.

Well, you are obviously wrong with that assumption, and your link doesnt prove it either.

DoF is exclusively a function of the optics. Which is logically extremely obvious. What can the sensor do about the light falling on it ? Absolutely nothing, except recording it. Thus DoF happends in the optics, nowhere else.

The only reason larger sensors offer more DoF is because for a larger sensor, longer focal lengths are required. Thus a MFT sensor uses a 25mm, an APS-C sensor a 33mm and a FF sensor a 50mm optics for the same field of view. Which means the FF sensor gets a lot less DoF. But not because its larger. If you use the FF sensor with a 25mm optics, it sees the same DoF as the MFT sensor with it, except it gets a whole different viewing angle.

The only influence of the sensor is the pixel size, which indeed changes the DoF a bit. Because mathematically no matter which focal length and which aperture - only the focus plane is in focus.

But this actually fights the DoF "advantage" of the larger sensor, since the larger sensor has larger pixels and thus is more tolerant. This influence however is nonlinear - meaning to get twice the DoF, you would need 4 times as large pixels. Also recently larger sensors tend to have more and more the same pixel size as smaller sensors, so I prefer to just ignore this issue altogether.



P.s.: The best way to quickly disprove your claim is to go to the link you provided yourself and scroll to the end of the "camera" list. Instead of any camera, there is a list of CoC values. How could there be CoC values without any sensor size ? Thats because sensor size isnt part of any of the formulas to compute DoF. Only focal length, aperture, distance and CoC are.

Joe

 

[table1349]

As they say a little knowledge is very dangerous

 

[Braineack]

View attachment 116607

Joe

in other words, if you took the above shot, and cropped the FX photo to match the DX, the FX shot would have less DOF even though everything else was equal.

 

[Derrel]

I consider this 2012 dPreview article with photographic examples, and actual, specific cameras and sensor-size classes, to be a simply fantastic example of how SENSOR SIZE actually plays a significant role in the degree of background blur that can be achieved, and also a fantastic article for giving a good sensor of how degrees of blur are graphed out, across a spectrum of common, modern types of digital cameras, from the iPhone 5 at one end, to the Canon 6D with the 85mm/1.8 Canon EF lens at the other end.

Background blur and its relationship to sensor size

As a sort of related comment, I'll just say that in matters of depth of field, blur, hyperfocal distance, and other technical details of classic photographic knowledge, there exists on the interwebs a TON of fertilizer-grade "wisdom". At one end are those selling unadulterated 100% pure bullsh**, some are selling 50-50 Fact & Bulls** Mix, and there are also those who sell some pretty high-grade, made-in-USA of Imitation Butter Flavored Bullsh**, and then there is on the other end, Actual Factual Knowledge, free From Internet-Era Adulterations, Made with No Bullsh** Added.

Ysarex consistently has in stock only the last product category. It's a slow-seller, but in the end, the tomatoes are bigger, riper, and sweeter.

 

[jcdeboever]

I'm still trying to wrap my arms around specular highlights and how to work a flippin tri-pod.

F-stop equivalency? I'm banging my head against the wall.... Hedgecoe, Hedgecoe, ....oh boy

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