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!

[TTMartin]

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@ebiggs1 wrote:

Instead of thinking of it as the total light that hits the sensor, think of it as the intensity of light that hits the sensor. That remains unchanged regardless of the crop factor, assuming an evenly lighted subject. This is what the exposure meter uses to determine the correct exposure.  You don't need a projector to see this.  Put a white piece of paper in the center of a round table.  Look at it.  Fold it in half.  Did it get brighter?  Darker?  No it stayed the same. 

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If you have even constant light and you place your piece of paper on a table it will get hit by a certain number of photons per minute. When you fold the paper in half, now half of those photons now hit the table which is no longer covered by the paper and half hit the folded paper. The full piece of paper receives twice the total number of photons per minute or light than the folded paper does. The same is true of a crop sensor and a full frame sensor.

So what does this mean to us as photographers. If we have a full frame camera with an EF 85mm f/1.8 lens set at f/1.8, ISO 100, 1/100 and a crop camera with a 50mm f/1.8 lens set at f/1.8, ISO 100, 1/100 both will have approximately the same angle of view and the same exposure, but, since the full frame camera sensor is larger it has gathered more TOTAL light. As you increase ISO this difference in total light gathered becomes apparent in noise. This is why full frame cameras have approximately a one stop noise advantage at high ISOs. This is because Canon and every other camera manufacturer compensates for the differences in total light received by sensors, by changing the amplification of signal. So as photographers we don't have to worry about it, except that it is the reason that smaller sensors seem noisier than larger sensors. The smaller the sensor the more amplification that is needed to simulate the same ISO..

Now lets look that crop camera with the 50mm f/1.8 lens set at f/1.8, ISO 100, 1/100 and the full frame camera with the 50mm  f/1.8 lens and a 1.4X TC wide open, ISO 100, 1/100. Now you again have approximately the same angle of view, but, the image area that fell on the crop sensor is now spread out over the entire full frame sensor. The photons that would have hit the crop sensor are now spread over the full frame sensor. Both sensors are now receiving the same TOTAL light, but, since the full frame camera isn't automatically compensating for the fact that it is receiving less light, due to the TC, you will be one stop underexposed. 

[jrhoffman75]

Question for TTMartin.

APS-C crop sensor cameras are called that because the sensor size is close to the APS negative size in the film days.

If what you says holds true about light and area was ISO 100 APS film ISO 200 35mm film cut down in size and rebranded as ISO 100?

[TTMartin]

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@jrhoffman75 wrote:
Question for TTMartin.

APS-C crop sensor cameras are called that because the sensor size is close to the APS negative size in the film days.

If what you says holds true about light and area was ISO 100 APS film ISO 200 35mm film cut down in size and rebranded as ISO 100?

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See Tim's post about how the enlargement process comes into play when you are talking about a completely analog film process. To make the same size print when you are using smaller pieces of film the enlarger head has to be further away, when the enlarger head is further away, you have to increase the exposure time. So while the difference in film size didn't impact the exposure while you were taking the photo, it did impact the exposure when you were making the print.

edit: Were prints from APS film just as good as prints from 35mm film with the same ISO? Are prints from 35mm film just as good as prints form medium format film with the same ISO? 

[jrhoffman75]

Don't bring enlarging into it. A properly exposed negative is a properly exposed negative.

If the APS-C digital sensor needs more amplification to expose properly at a given ISO, f/stop and shutter speed compared to full frame how did APS-C film accomplish that?

[TTMartin]

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@jrhoffman75 wrote:
Don't bring enlarging into it. A properly exposed negative is a properly exposed negative.

If theAPS-C digital sensor needs more amplification to expose properly at a given ISO, f/stop and shutter speed compared to full frame how didAPS-C film accomplish that?

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You have to bring enlarging or scanning into it, because getting a negative is only half of the processing. It would be like exposing the sensor on a digital camera and never having it process and write it to the memory card. You have to take the complete film process from the time the photo is taken, till the time you have usable output, or it isn't an analogous comparison. 

[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]

Bob from Boston,

"Who are those "others" on Tom's side of the argument?"

This is an old concept.  I guess there might be a smidgen of sense here but not what Mr. Martin is claiming.  As I understand him anyway. I have had this debate before (several times) almost as soon as the term "crop camera" was created.  I have discussed it extensively with my buddy Tom Martinez, who was also a Hallmark photographer.  He is an optical expert and gives many lectures.

[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.