Debunking Tony Northrup.

[Meister]

I'm sorry, but I think this is where the analysis goes south. Yes, a 35mm sensor has more area and therefore can potentially collect more total light than a smaller (APS-C or M43) sensor, but the amount of light hitting the "crop" portion of the 35mm sensor is exactly the same (assuming all else is equal -- i.e., same lens, same settings, etc.).

I think it is easier to think about this portion of it by not getting into crop factors, effective fields of view, etc. If you shoot the same scene with the same lens (say 50mm 1.8G) at the same settings (say 1/250, f/2.8, ISO 100) on a D800 and D7000 and then crop the D800 image to 16.2MP, the exposure should be the same. Yes, the D800 sensor would have collected less total light than the D800 sensor, but the light that is relevant to the final image (i.e., the cropped center on the D800) is exactly the same.

That is a deception. ISO100 (on digital) is generic and not defined by a physical formula like the aperture is. Nikon adjusts the sensor so that ISO100 on the D7000 appears equally bright as ISO100 on a D800. The amounts of photons/light gathered is less by the crop factor.

In short: Your example settings "1/250, f/2.8, ISO 100" are not equal on the D7000 and D800. They merely appear equal because Nikon adjusted the ISO. All manufacturers do this and people seem not to know about this.

(I am starting to have a hard time explaining this because I learned maths and physics in german.)

 

[juanm]

What a rather hot and lively conversation here.

I'll just say that people ought to be using terms the same way or rather, have working definitions of terms such as

f/stop
t/stop
diaphragm
aperture
iris
impact of glass within a lens on measure of center of lens to back of lens etc.

I'll just add that back in the days of using view cameras, I could take a landscape scene with the bellows not drawn out too far then immediately take an image of a flower placed in the scene up close. The bellows draw would be considerably more and an adjustment made for the change of the amount of light hitting the film ("f/stop" or leaf shutter).

Then again, much of the challenges of potential shifts of light really don't matter because people use cameras with built in metering. I often think the exercise was more about having fixed ASA/ISO of films and trying to get consistency in exposure when lenses were switched.

Zoom lenses have come a long way and as glass moves within a zoom, there are changes made in the relative* size of the aperture in the diaphragm to represent an exposure value referenced as an f/stop.

Discussion like these are interesting and certainly food for thought.

I'm afraid we're still a long way from explaining T-stops and the like. I work in the movie industry, so I'm used to things like Iris, but since this is a photography forum, I try to keep things as simple as possible without shaving off anything important.

 

[Meister]

A cropped sensor with the same pixel size, pitch and technology on a hypothetical "Sony A7S DX" would have the same light sensitivity as the current A7S

This is actually correct

 

[MCH-1138]

That is a deception. ISO100 (on digital) is generic and not defined by a physical formula like the aperture is. Nikon adjusts the sensor so that ISO100 on the D7000 appears equally bright as ISO100 on a D800. The amounts of photons/light gathered is less by the crop factor.

In short: Your example settings "1/250, f/2.8, ISO 100" are not equal on the D7000 and D800. They merely appear equal because Nikon adjusted the ISO. All manufacturers do this and people seem not to know about this.

(I am starting to have a hard time explaining this because I learned maths and physics in german.)

Then make it even easier and consider my example using a D800 shot in FX mode and then cropped in post vs. a D800 shot in DX mode. So ISO isn't a factor. The amount of light hitting that portion of the sensor is the same.

 

[Meister]

Then make it even easier and consider my example using a D800 shot in FX mode and then cropped in post vs. a D800 shot in DX mode. So ISO isn't a factor. The amount of light hitting that portion of the sensor is the same.

This is correct. The photons per inch/pixel are equal.
This doesn't change the fact that with the same lens, less light is hitting a DX sensor than it would an FX sensor.

 

[simonsi]

You are wrong. The total light collected by a m4/3 is less than the total light collected by a 35mm sensor. This is why smaller sensors have worse low light performance. With the change of FOV also changes DOF and the total light gathering capability. And this change occurs exactly according to the equation ..

Alas total light captured by a sensor (or film), is totally irrelevant and nothing to do with exposure which is all about light intensity.

The light intensity (photons per sq mm say, and ignoring any light falloff in corners), is the same irrespective of film or sensor size assuming the image circle projected by the lens covers the area you are concerned with.

If you have an FX sensor and set your exposure, that gives you a certain light intensity, all things being equal your FX or DX sensor or film will then capture that exposure in the same way, the light intensity is the same across any of those sensor areas.

To test this, take a body with an FX sensor that can operate in crop mode. set the exposure of a scene in FX then switch to crop - does the camera light up with warnings? No, because the exposure per mm, or per pixel hasn't changed.

What makes small sensors generally operate differently isn't the total light captured but that typically small sensors have smaller photo sites than large sensors, consequently the light captured per pixel is less, so they need more amplification than an equivalent FX sensor so the ISO of the sensor effectively changes.

So Tony is totally right, as you are above, total light captured does change. But it is also totally irrelevant to an exposure calculation.

 

[Meister]

Alas total light captured by a sensor (or film), is totally irrelevant and nothing to do with exposure which is all about light intensity.

The light intensity (photons per sq mm say, and ignoring any light falloff in corners), is the same irrespective of film or sensor size assuming the image circle projected by the lens covers the area you are concerned with.

If you have an FX sensor and set your exposure, that gives you a certain light intensity, all things being equal your FX or DX sensor or film will then capture that exposure in the same way, the light intensity is the same across any of those sensor areas.

To test this, take a body with an FX sensor that can operate in crop mode. set the exposure of a scene in FX then switch to crop - does the camera light up with warnings? No, because the exposure per mm, or per pixel hasn't changed.

What makes small sensors generally operate differently isn't the total light captured but that typically small sensors have smaller photo sites than large sensors, consequently the light captured per pixel is less, so they need more amplification than an equivalent FX sensor so the ISO of the sensor effectively changes.

So Tony is totally right, as you are above, total light captured does change. But it is also totally irrelevant to an exposure calculation.

Well explained!
Its really just about me and junam bickering about crop factors and f-stops.

 

[JBunkers]

What does this have to do with Macs?

If a Goddess marries a man, what does that make him?
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Tony Northrup!!

 

[juanm]

That is a deception. ISO100 (on digital) is generic and not defined by a physical formula like the aperture is. Nikon adjusts the sensor so that ISO100 on the D7000 appears equally bright as ISO100 on a D800. The amounts of photons/light gathered is less by the crop factor.

In short: Your example settings "1/250, f/2.8, ISO 100" are not equal on the D7000 and D800. They merely appear equal because Nikon adjusted the ISO. All manufacturers do this and people seem not to know about this.

(I am starting to have a hard time explaining this because I learned maths and physics in german.)

In reality it's noise, and signal amplification, so it's counted in decibels, but photographers are used to ISO.

 

[simonsi]

Well explained!
Its really just about me and junam bickering about crop factors and f-stops.

LOL, just woke up, glad to see this thread sorted out the issue without a lot of technical discussion.

Oh wait, I just found something else wrong on the internet....charge!

Learning physics in German - respect!

 

[juanm]

Well explained!
Its really just about me and junam bickering about crop factors and f-stops.

And you still believe a 2.8 lens Nikon DX lens is like a 5.6 full frame lens, right?

 

[leighonigar]

Meister is spot on.

A very educational discussion.

 

[juanm]

Meister is spot on.

A very educational discussion.

Care to explain in what universe a lens loses two stops of light when you use it with a smaller sensor?

 

[Meister]

And you still believe a 2.8 lens Nikon DX lens is like a 5.6 full frame lens, right?

Are you surprised that your well thought out arguments:

"Tony Northrup is your white haired guru."
"The definition of aperture doesn't apply."
"I have lots of experience as a videographer."

Haven't changed my opinions on the laws of physics.

----------

Care to explain in what universe a lens loses two stops of light when you use it with a smaller sensor?

I don't think you are able to follow my (and the white hair guru's ) line of argument.

 

[leighonigar]

Care to explain in what universe a lens loses two stops of light when you use it with a smaller sensor?

The one in which I produce images. It is the images that matter, and that is it as far as photography goes. I cannot actually comment on the physics, except to say that clearly it is the focal ratio or 'aperture' that affects the amount of light falling on a particular area of light-gathering surface. Obviously I am not disagreeing with you on this (I don't think anyone else is either). What follows is a reflection of my experience of image making.

As far as equipment goes only the aperture (and here I mean the size of the physical opening) really affects the depth of field. What the focal length and sensor size define is how close you stand to your subject for a certain composition, and obviously the closer you get the narrower your depth of field becomes. So you stand further away with a given focal length as your sensor size decreases and therefore you have more depth of field. You get closer as you reduce focal length and maintain sensor size, so again you gain depth of field.

Because of the effect I have just described, you need a larger physical aperture (smaller f number) to achieve the same look with a smaller sensor. I've not even glanced at these Tony videos, but I can only imagine this is the effect he describes.

Because the amount of light (total) hitting the sensor is also reduced with sensor size it is not just the rendering/depth of field which changes if you choose an equivalent focal length but neglect to choose a smaller f-number. You get more noise too.

Photographically there is no respect, with the exception of exposure for a given sensitivity, in which f-stops are equivalent with 'equivalent focal lengths' as sensor size changes.

 

[leighonigar]

Anyway. So I'd never seen any of this chap's videos, but I googled and found this http://petapixel.com/2014/03/28/concise-explanation-crop-factor-affects-focal-length-aperture/

I agree 100% with every single word he says except at one point he uses the word 'bokeh' in a slightly colloquial way, yes, we all know that it's the aesthetic quality and not the sheer blurriness. I can forgive him this slip.

 

[NayborAxi]

Tony northrup have haters? wow this is like a new low. You can feel his passion about photography and he shares tons of free info on his youtube channel and people still find a flaw to hate the guy? He might not be 100% accurate on all his claims but god making a "Debunking tony northrup" is really lame.

 

[d4rkc4sm]

his wife is hot

 

[leighonigar]

Chipping in with comments about his wife seems a bit naff. It's not quite catcalling but it's on the spectrum.

 

[juanm]

Anyway. So I'd never seen any of this chap's videos, but I googled and found this http://petapixel.com/2014/03/28/concise-explanation-crop-factor-affects-focal-length-aperture/

I agree 100% with every single word he says except at one point he uses the word 'bokeh' in a slightly colloquial way, yes, we all know that it's the aesthetic quality and not the sheer blurriness. I can forgive him this slip.

Yes, in this case he actually explains it rather correctly. Apparently he got a lot of flak in an earlier video (the one I watched, I guess) where it was apparent he didn't know what he was talking about, and he went back to wikipedia and made this video to concentrate on the one case where yes, his point applies exactly: trying to match exactly a picture made with a cropped sensor to an image made with a FF sensor, you'll need a smaller aperture.

But it's still worth noting that a lens and its aperture won't change depending on what you put it on. A 1.8 DX lens will still be 1.8 on a full frame, only with black corners, and a 1.8 FX lens will still be a 1.8 lens when mounted on a cropped sensor camera, only with a lot of light wasted. And that's something our friend Meister still doesn't get.

 

[Meister]

But it's still worth noting that a lens and its aperture won't change depending on what you put it on. A 1.8 DX lens will still be 1.8 on a full frame, only with black corners, and a 1.8 FX lens will still be a 1.8 lens when mounted on a cropped sensor camera, only with a lot of light wasted. And that's something our friend Meister still doesn't get.

I never said that and you know this. Since you have no arguments except for personal attacks you are resorting to misrepresent what I wrote. The focal length and f-stop is a fixed quality of a lens. Neither change. Ever. Everyone knows this and nobody is claiming otherwise. You are starting to lead everybody on a tangent about something that was clear from the beginning. And I am starting to hear a song by Eduard Khil in my head.

 

[v3rlon]

ok, imagine an FF sensor with 1 "pixel" per square mm.

That is 864 pixels for 35*24. These pixels each require 4 photons to give proper exposure. That is 3456 photons for a good shot.

Now there is an APSC Senor (ish) at 24*16 =384. That is 1536 photons.

Because pixels = area in this case, we can see that the crop factor is the square root (864/384) or 1.5 exactly.

If you do not believe me, use actual Nikon numbers 864 for FF, and 23.7*15.5=367.35*1.53*1.53 (1.53 squared) = 860.

ok, our fictional crop sensor receives 44.4% of the light of the FF sensor all things being equal, but it only NEEDS 44.4% of the light because it is lighting fewer pixels. The other 66% of the light bounces around inside the camera and does nothing.

If we tried to throw all 3456 photons at those 384 pixels, each would get 9 photons, or more than double a good exposure worth.

If we tried to light the FF sensor with 1536 photons, each sensor would get an average of 1.8 (so most would get 2 and some would get 1). This would be slightly less than half the light needed.

Now do you see?

Yes, a crop sensor gets less light than a FF sensor. It NEEDs less light because it has less area. Think about it, if the Aperture thing applied to LIGHTING, Medium format guys would need different light meters than 35mm guys, and that predate digital by decades.

Now for DoF, you DO multiply, and this is exactly what the Tony Nothrup video shows. That has nothing to do with the amount of light needed or the aperture setting needed to achieve a good exposure.

 

[Dsching]

I'd never heard of him until yesterday, but he appears to have invented a conspiracy theory of sorts in a parallel universe where aperture changes with focal length, ...

That conspiracy theory would be the formula that defines the aperture as Meister has quoted above. The aperture changes with focal length. That is a fact and I am not sure what you are trying to disprove.

 

[FWRLCK]

Tony northrup have haters? wow this is like a new low. You can feel his passion about photography and he shares tons of free info on his youtube channel and people still find a flaw to hate the guy? He might not be 100% accurate on all his claims but god making a "Debunking tony northrup" is really lame.

It's just shameless self-promotion with the odd intentional click-bait video thrown in to boost his view count. Even when his content isn't wrong, it's not as if he's sharing new ideas or teaching exceptionally well. His channel is just about building his personal brand. Which is fine. I suspect there are a lot of working photographers (Matt Granger, etc) who release these videos to build their brands. In this case though, I tend to think of him as someone who's building his brand by pushing videos of little to no value.

 

[juanm]

That is a fact and I am not sure what you are trying to disprove.

That focal length (and thus the aperture) change with the sensor mounted on them, which is Meister's assertion.

Basically what he says is that a 2.8 lens is not really a 2.8 lens.