Opinions on Extenders, please?

[PajamaGuy]

Extender EF 2x III - or the EF 1.4x III.  Same price.  Other than the obvious, why one over the other?  Are the optics equal?

Thanks!

[RobertTheFat]

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@ebiggs1 wrote:

"The concept is NOT wrong and you are very confused."

Well Mr./Ms. Martin, you are right about one part. I am usually “very confused”. I have gotten used it it over the years. However on this concept I am not.

No sensor uses all the light a lens provides. Some is always out of the image circle that any lens makes since no lens makes a square image. Where you go wrong in your theory and the others that think like you is there are many conditions that make a photograph. Sensor size is simply one. Signal to noise, dynamic range, signal amplification along with pixel size and pixel placement. How close, tightly packed, to one another pixels are and so on, etc.

When we construct a lens it is fixed. It can not change its parameters, ever. It does not care what sensor you choose to put behind it.

If said lens is set to f4, every pixel in that sensor is going to get f4. No matter what size the sensor is, they all get f4. If this were not true, hand held light meters would not work. Because there would have to be a different one for every sensor made.

You can prove it to yourself. Put a lens on your cropper and take a photo. A nice daylight outdoor scene. Put the same lens on your FF take the same photo. The settings will be the same if you did both exactly the same way.

Another point where you and the others go wrong is forgetting the AOV. If your photo, from above, eliminated much of a brighter area you may get a different reading and as such you will mistakenly assume the smaller sensor got less light. It didn't. AOV is just another factor in this myriad of exposure settings in a complicated world of photography.

And this brings us to the topic of DOF. You are correct in assuming DOF increases by about one stop. When identical lenses are compared on a crop vs FF. This changes the AOV so a resulting increase in f-ratio. This changes the scene or subject also. It does NOT change the lens or the sensor. They remain exactly the same. f4 remains f4. Each pixel is still getting f4 no matter how much light is wasted out side the sensor's physical dimensions.

All you need to remember is, no difference in f-stop because the exposure rules are the same. You do know the “triangle of exposure”? It matters not what the sensor size is. Does it?

If both cameras have the same shutter speed and ISO settings, the aperture will be the same as well. It does not matter what size the sensor is.

My advice. Instead of setting behind your keyboard, explaining how confused I am, go outside and use your camera. Play with it. Learn it. Learn all its idiosyncrasies. Get it off the green square and P. It's fun. It's great.

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Who are those "others" on Tom's side of the argument? I'm under the impression that the rest of us are all on your side.

[TTMartin]

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@RobertTheFat wrote:

Who are those "others" on Tom's side of the argument? I'm under the impression that the rest of us are all on your side.

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It is a good thing for me that facts don't need to be popular to be true.

[ebiggs1]

"It is a good thing for me that facts don't need to be popular to be true."

Or even correct?

I guess we have switch to “noise” now?

Crop factor can only impact the aperture in the sense of DOF, not the exposure. 

One big problem is the very term Crop Sensor.  Crop factor as a concept, or term, exists only to allow photographers to get similar results with lenses used on different size sensors.  It is such a misleading term.  I wish it had never been created.  We never had it in the film days and we had several different formats of film size.  People knew if you used a 50mm lens on a 35mm film camera it gave a certain AOV.  If you use it on a Medium Format the AOV was different.  They didn't need to say, oh let's see it is 1.6x or no a 1.5x or ..........

So here we are.  Why does the full frame camera (seem to) have a cleaner signal? The photosites on the full frame sensor can be twice as large as the ones on a crop sensor. Photosites on a sensor are like buckets that collect photons. The more photons you can collect in your bucket the stronger the signal will be that is sent to the D/A converter.  This will require less amplification.  And of course will introduce less noise. Agreed?

But the exposure is related to the density of light collected and not the total amount of light collected. Noise is related to how much of the total light is collected.

And signal to noise ratio is based on the size of the pixels, not the sensor size. The light the sensor sees is the same, but bigger sensors generally have bigger pixels.  Right?

 The mistake Mr. Martin makes is he states that the f-number changes according to sensor size. That is not true.
Two images with the same f-stop, the same shutter speed, and the same ISO, will have the same exposure.  Period!

Signal to noise ratio is not determined by total light hitting the sensor, but by the light-per-area, which is identical given identical lenses and apertures. The cropped sensor receives no less light per area than a Full Frame. The signal-to-noise ratio is measured at that point not across the entire sensor.  But the image from a crop sensor has to be magnified more so it can be displayed at the same size as the FF. This means greater apparent noise in the final image.

[TTMartin]

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@ebiggs1 wrote:

 
Two images with the same f-stop, the same shutter speed, and the same ISO, will have the same exposure.  Period!

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In never said that it wasn't. When you use the proper definition of exposure, which is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance

What I said was that the reason they have the same ISO is because that is how the manufacturers design the camera to behave. This is despite the fact that smaller sensors receive less total light for any given exposure due to the fact that they have less surface area to capture the light, so the camera manufacturers use more amplification so it is mostly transparent  to the user of the camera.

If you couldn't understand the simple concept that a whole piece of paper is hit by more light than half a sheet of paper then it is useless to discuss this further.

[ebiggs1]

"If you couldn't understand the simple concept that a whole piece of paper is hit by more light than half a sheet of paper then it is useless to discuss this further."

I am sorry I disappointed you.  But the piece of paper got and has the same exposure. Right?  The rest of the light is nothing.

BTW, I already said further discussion was futile. Neither of us is going to be swayed and that's OK.  We just don't happen to agree on this subject.  Perhaps someone better versed than I will do a better job.

[TTMartin]

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@ebiggs1 wrote:

"If you couldn't understand the simple concept that a whole piece of paper is hit by more light than half a sheet of paper then it is useless to discuss this further."

I am sorry I disappointed you.  But the piece of paper got and has the same exposure. Right?  The rest of the light is nothing.

BTW, I already said further discussion was futile. Neither of us is going to be swayed and that's OK.  We just don't happen to agree on this subject.  Perhaps someone better versed than I will do a better job.

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Yes, they got the same exposure. The same amount of light PER UNIT AREA. The whole piece of paper has more UNITS OF AREA, than the half sheet of paper so the whole sheet of paper received more TOTAL LIGHT.

[ebiggs1]

"Yes, they got the same exposure."

See we agree!  You are beginning to see "the light". Until we get into electronics, this is all that matters.  Total light is meaningless.  As is all the light that falls out side of the piece of paper.

[TTMartin]

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@ebiggs1 wrote:

Total light is meaningless.  As is all the light that falls out side of the piece of paper.

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Total light is not meaningless, because it is the total light that the camera has to process to make a complete picture. 

The light that falls outside of the paper or sensor is meaningless, but, the light that falls on the sensor isn't meaningless. The sensor with more surface area receives the same exposure or same amount of light PER UNIT AREA, but, has more UNITS OF AREA so it receives more TOTAL LIGHT. So the camera has more signal due to the fact that the sensor got more TOTAL LIGHT for any given exposure. And more signal results in less amplification, and less noise.

[ebiggs1]

Mr Martin did you fail to read this long explanation?  I believe we are actually saying the same thing. Or at least in the same ballpark.  Here it is again if you just glossed over it.

I guess we have switch to “noise” now?

Crop factor can only impact the aperture in the sense of DOF, not the exposure. 

One big problem is the very term Crop Sensor.  Crop factor as a concept, or term, exists only to allow photographers to get similar results with lenses used on different size sensors.  It is such a misleading term.  I wish it had never been created.  We never had it in the film days and we had several different formats of film size.  People knew if you used a 50mm lens on a 35mm film camera it gave a certain AOV.  If you use it on a Medium Format the AOV was different.  They didn't need to say, oh let's see it is 1.6x or no a 1.5x or ..........

So here we are.  Why does the full frame camera (seem to) have a cleaner signal? The photosites on the full frame sensor can be twice as large as the ones on a crop sensor. Photosites on a sensor are like buckets that collect photons. The more photons you can collect in your bucket the stronger the signal will be that is sent to the D/A converter.  This will require less amplification.  And of course will introduce less noise. Agreed?

But the exposure is related to the density of light collected and not the total amount of light collected. Noise is related to how much of the total light is collected.

And signal to noise ratio is based on the size of the pixels, not the sensor size. The light the sensor sees is the same, but bigger sensors generally have bigger pixels.  Right?

 The mistake Mr. Martin makes is he states that the f-number changes according to sensor size. That is not true.
Two images with the same f-stop, the same shutter speed, and the same ISO, will have the same exposure.  Period!

Signal to noise ratio is not determined by total light hitting the sensor, but by the light-per-area, which is identical given identical lenses and apertures. The cropped sensor receives no less light per area than a Full Frame. The signal-to-noise ratio is measured at that point not across the entire sensor.  But the image from a crop sensor has to be magnified more so it can be displayed at the same size as the FF. This means greater apparent noise in the final image.

[TTMartin]

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@ebiggs1 wrote:

But the exposure is related to the density of light collected and not the total amount of light collected. Noise is related to how much of the total light is collected.

And signal to noise ratio is based on the size of the pixels, not the sensor size. The light the sensor sees is the same, but bigger sensors generally have bigger pixels.  Right?

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Except it has nothing to do with pixel size, the 5DS has the same pixel size as a crop cameras do, but, has less noise for the entire picture than an APS-C camera because its sensor has MORE UNITS OF AREA. Not because it's pixels are bigger, they aren't. but because the sensor is bigger.  

So on a per pixel basis (per unit area) the 7D Mk II and the 5DS have the same amount of noise, because their pixel sizes are the same and they are receiving the same exposure. What DXO calls their screen measurement.

But, because the 5DS has more UNITS OF AREA (a bigger sensor) and it received more TOTAL LIGHT.  It has a higher signal to noise ratio for the entire photo. What DXO calls their print measurement.