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07-14-2015, 06:39 PM - 1 Like   #91
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QuoteOriginally posted by lguckert79 Quote
Yeah I'm still here I just watched a video from Tony Northup and he had a good way of explaining the aperture when on a crop sensor so I'm good and I thank everyone's expanation's
Uh oh! Get ready, the "no-such-thing-as-equivalence" mob will be here soon to tell you that Tony is full of crap. Don't believe them, he's right, and has the images to prove it.

07-14-2015, 07:02 PM - 1 Like   #92
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QuoteOriginally posted by audiobomber Quote
Uh oh! Get ready, the "no-such-thing-as-equivalence" mob will be here soon to tell you that Tony is full of crap. Don't believe them, he's right, and has the images to prove it.
Except that his examples are seriously flawed!
I like his stuff, normally but he does not understand what he is talking about.
OK he probably understands it, but the explanation is missing important information and as a result is just plain wrong in the end and with the examples he gives.

Last edited by amoringello; 07-14-2015 at 07:17 PM.
07-14-2015, 07:12 PM - 1 Like   #93
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QuoteQuote:
You do not understand f-stop at all. It's very basic physics. F-stop controls the amount of light hitting the sensels. Sensor size is immaterial.
Now I'm going to say you need to watch Tony Northrup, and I never thought I'd say that to anyone. The ƒ-stop controls the intensity of the light hitting the sensor, not the amount of light collected. A twice as big sensor collects twice as much light, if and only if both sense are equally efficient at collecting light.


QuoteQuote:
The effect of increasing focal length is magnification. Longer focal lengths project larger images on the focal plane. If a subject is projected as a 1x1 square at 25mm it will be projected as a 2x2 square at 50mm. The same amount of light coming from the source is therefore spread more thinly over a wider area by the longer lens. This effectively reduces the amount of light PER UNIT AREA hitting the focal plane (sensor). Every sensel behind the longer lens will receive four times LESS the amount of light compared to the smaller sensor.
I guess you missed the part where the longer lens has a much bigger front element and gathers much more light than the shorter lens.

If you really know what an f-stop is, then you know its a ratio, a 200 mm lens has to have a much bigger opening than 50 mm lens to achieve the same f-stop.

QuoteOriginally posted by audiobomber Quote
Uh oh! Get ready, the "no-such-thing-as-equivalence" mob will be here soon to tell you that Tony is full of crap. Don't believe them, he's right, and has the images to prove it.
What about the "equivalence doesn't mean what you think it means crowd," can we come too?"

Last edited by normhead; 07-14-2015 at 07:18 PM.
07-14-2015, 07:23 PM - 2 Likes   #94
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Equivalent focal length with crop factor

QuoteOriginally posted by normhead Quote
Now I'm going to say you need to watch Tony Northrup, and I never thought I'd say that to anyone. The ƒ-stop controls the intensity of the light hitting the sensor, not the amount of light collected. A twice as big sensor collects twice as much light, if and only if both sense are equally efficient at collecting light.




I guess you missed the part where the longer lens has a much bigger front element and gathers much more light than the shorter lens.

If you really know what an f-stop is, then you know its a ratio, a 200 mm lens has to have a much bigger opening than 50 mm lens to achieve the same f-stop.



What about the "equivalence doesn't mean what you think it means crowd," can we come too?"

Total amount of light is totally missing the point. Photography is all about total amount of light OVER TOTAL IMAGING AREA (i.e. exposure). f-stop is f-stop regardless of focal length or aperture because it is a ratio. The ratio is all that matters.

Please reread items 1 and 2.

07-14-2015, 09:52 PM   #95
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QuoteOriginally posted by audiobomber Quote
Uh oh! Get ready, the "no-such-thing-as-equivalence" mob will be here soon to tell you that Tony is full of crap. .
Is this the 'cropped sensor camera manufacturers are cheating you because f2.8 isn't really f2.8' one?

Full of crap, as you say, Audiobomber.
07-14-2015, 09:54 PM   #96
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QuoteOriginally posted by boriscleto Quote
The 'C' stands for Classic. There were 3 APS formats.APS-H (High Definition, 30.2x16.7 mm, 16:9), APS-C (Classic, 25.1x16.7mm, 3:2) APS-P (Panoramic, 30.2x9.5mm, 3:1)

The C and P formats are made by cropping, so it could have been 'Cropped', but it wasn't...
Much obliged, Boriscleto (trademark applied).

Thanks for the correction.
07-14-2015, 10:01 PM - 1 Like   #97
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QuoteOriginally posted by Class A Quote
By cropping, you reduce the signal (after all, you crop out a lot of signal).
And the noise, by exactly the same proportion! (rolls eyes).

SNR is the ratio of signal to noise.

QuoteOriginally posted by Class A Quote
how downsampling (using many pixels to calculate the values for fewer pixels) increases the SNR of the image (i.e., reduces its noise). The formula on the last page tells you exactly how much noise advantage you can expect from downsampling.
Class A, downsampling has nothing to do with sensor size.

It has to do with numbers of pixels.

A 24Mp APS-C K3 will downsample better than a 16Mp FF Canon 1D.

QuoteOriginally posted by Class A Quote
The fact that there is less DOF is caused by the additional light gathered. The fact that less light is gathered causes more DOF.
OMG!


Last edited by clackers; 07-14-2015 at 10:10 PM.
07-14-2015, 10:21 PM   #98
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Nice to know I'm not alone here Clackers
07-14-2015, 10:37 PM   #99
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QuoteOriginally posted by dtmateojr Quote
You do not understand f-stop at all. It's very basic physics. F-stop controls the amount of light hitting the sensels. Sensor size is immaterial.

---------- Post added 07-15-15 at 09:30 ----------

For the sake of everyone, allow me to explain the very basic concept of f-stop. This is the sort of explanation that even kids should be able to understand. After this, I will stop responding to this thread. Buckle up...

Assume that you are shooting a uniform light source and comparing m43 and FF sensors. To get the same angle of view, we need to use 25mm and 50mm lenses respectively. Assume for now that the lens openings are the same for both.
You mix a lot of thing trying to prove you point.

QuoteQuote:
The effect of increasing focal length is magnification. Longer focal lengths project larger images on the focal plane. If a subject is projected as a 1x1 square at 25mm it will be projected as a 2x2 square at 50mm.
The projected size of the image is not affected by focal length, it depends on the image circle of the lens. a 50mm lens for m43 is projected on a smaller area at the focal plane than a 25mm for FF. If the light source is uniform, focal length do not affect exposure, only f-stop does.

QuoteQuote:
The same amount of light coming from the source is therefore spread more thinly over a wider area by the longer lens. This effectively reduces the amount of light PER UNIT AREA hitting the focal plane (sensor). Every sensel behind the longer lens will receive four times LESS the amount of light compared to the smaller sensor. This results in underexposure of the larger sensor. It's like spreading a spoonful of peanut butter on different sizes of loaves. The smaller loaf will have more peanut butter per bite.
If using the same source of light for different sensor sizes (same f-stop) the illumination will be the same on both and the larger sensor will capture more total amount of light.

Using different focal length with same aperture size (different f-stop) as in your example is not using the same source of light.
Fi using 25mm f/2 for m43 has the same aperture size as 50mm f/4 on FF.

QuoteQuote:
To compensate for the unfair spread of incoming light, we need to
1) increase the opening of the longer lens, or,
2) reduce the opening of the shorter lens
What is usually done is to increase ISO with two stops on FF compared to m43 in you example,

On m43 - 25mm f/2 @ 1/100s @ ISO100
On FF - 50mm f/4 @ 1/100s @ ISO400

QuoteQuote:
The ratio between the focal length and lens opening is your f-stop. That's why for the same f-stop, each sensel receives exactly the same amount of light. Sensor size is immaterial. This is the physics of photography in its entirety.
Only true if assuming that the sensel size is the same of different sensor size. If sensor size was immaterial, then why are not everyone using smartphones?

Last edited by Fogel70; 07-14-2015 at 10:45 PM.
07-15-2015, 12:09 AM   #100
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Equivalent focal length with crop factor

QuoteOriginally posted by Fogel70 Quote
You mix a lot of thing trying to prove you point.

The projected size of the image is not affected by focal length, it depends on the image circle of the lens. a 50mm lens for m43 is projected on a smaller area at the focal plane than a 25mm for FF. If the light source is uniform, focal length do not affect exposure, only f-stop does.

Ahahahaha!!! Gold!

Focal length does not affect projected image size?! Really? How do zoom lenses work then? Certainly not by changing the image circle.

I happen to have a degree in physics and I majored in optics. I won't even try to correct you. You might learn something from me. ROFL!
07-15-2015, 01:13 AM   #101
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QuoteOriginally posted by clackers Quote
Class A, downsampling has nothing to do with sensor size.

It has to do with numbers of pixels.
How can you not see that if you keep pixel size constant that a larger sensor will have more pixels?

Please excuse me that I'll give up at this point.

QuoteOriginally posted by clackers Quote
OMG!
OK, so you are challenging the idea that additional light gathered will reduce DOF.

Why is it then, may I ask, that no manufacturer offers a very bright lens with lots of DOF?
Why can I not buy a lens with "f/1.0 light gathering ability" but "f/8 DOF"?
Why is it that I have to pay a price (shallower DOF) each time I want to increase the exposure by opening up the aperture?

Answer: Because there is no separation between "light gathering ability" and "DOF" and statements like "It has the light gathering ability of an f/2.8 lens but the DOF of an f/4 lens" are complete and utter nonsense.

However, again, I think it is time for me to leave this thread.
07-15-2015, 01:35 AM   #102
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QuoteOriginally posted by Class A Quote

OK, so you are challenging the idea that additional light gathered will reduce DOF.

Why is it then, may I ask, that no manufacturer offers a very bright lens with lots of DOF?
Why can I not buy a lens with "f/1.0 light gathering ability" but "f/8 DOF"?
Why is it that I have to pay a price (shallower DOF) each time I want to increase the exposure by opening up the aperture?

Answer: Because there is no separation between "light gathering ability" and "DOF" and statements like "It has the light gathering ability of an f/2.8 lens but the DOF of an f/4 lens" are complete and utter nonsense.

However, again, I think it is time for me to leave this thread.

DoF of f/8 can be achieved at f/1 if you go very very very wide or if you focus farther away. DoF is not just affected by aperture but focal length and subject distance as well.

But let's not go there. I just want to laugh
07-15-2015, 02:34 AM   #103
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QuoteOriginally posted by dtmateojr Quote
Ahahahaha!!! Gold!

Focal length does not affect projected image size?! Really? How do zoom lenses work then? Certainly not by changing the image circle.

I happen to have a degree in physics and I majored in optics. I won't even try to correct you. You might learn something from me. ROFL!
A zoom lens for a camera changes focal length by moving lens groups inside the lens, but the projected image size is constant. (At some focal lengths the image circle might be a bit oversize to simplify lens design).

As a lens for a camera has a fixed distance to the sensor, it is designed to give a constant projected image size. There is not much point in projecting the light on a area much larger than the sensor, as with a larger image circle the lens elements inside the lens has to be made larger.

Telephoto Zoom Lenses with Donders-type Afocal System, by P. Toscani
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07-15-2015, 02:54 AM   #104
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QuoteOriginally posted by clackers Quote
Smaller distance to the sensor, Bossa?


In the words of another famous Australian, 'Please explain!'


The 'C' stands for cropped - the sensor is in the same position - where you'd also put film, it's just smaller.
Forget I mentioned it. For some unknown reason I was thinking the registration distance was different for FF and APS-C. I've been thinking a lot about MF lately and I have been preparing to mount an exhibition of my late mother's artwork. Lots of stress.
07-15-2015, 05:53 AM - 1 Like   #105
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QuoteOriginally posted by clackers Quote
OMG!
Within the context of additional light from a larger aperture, he's correct.

It's not just this extra light on it's own that's important, it's where it ends up landing on the sensor that's reducing the DoF. A key point since you've quoted just a snippet that's easy to misinterpret and dismiss as nonsense - this additional light from opening the aperture is not going to exactly the same place as the extra light you'd get from a longer exposure time.

Any point not in focus gets projected to a little blurred disc on the sensor. As you open the aperture to let more light in, these blurred disc gets larger and as a result stuff gets a little less in focus. Larger blur discs means less of them fall within your acceptable circle of confusion, this means less DoF.
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