SURVEY - Do FT / mFT users know the difference from "full frame"? Replies wanted!!

Started Apr 26, 2013 | Discussions thread
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Great Bustard Forum Pro • Posts: 33,065
Re: SURVEY - Do FT / mFT users know the difference from "full frame"? Replies wanted!!

JosephScha wrote:

Thank you for a much more useful answer.  I read the article on ISO and I understand it.  I don't think I disagreed with it ever but I was not using the terminology it suggests.  I will from now on.  So, exposure is what happens at the sensor, in-camera ISO or brightness as adjusted in a raw converter is called brightening. Good term.  Intuitive.  Let me say in my defense that as the article points out even much of the literature (and in fact the slider in Adobe Camera Raw that affects brightening) still uses the word "Exposure" where it should be "Brightening" (or perhaps for ACR's slider it could be "ISO adjust").

I've also read the "FAQ" on Equivalence that Great Bustard posted on the Oly forum under a previous user name.   I understand now that this has nothing to do with equivalent brightness but it does have to do with equivalent exposure (light on the sensor).

Here's a good summary of Equivalance:

A 50mm f/1.4 lens is a 50mm f/1.4 lens regardless of the sensor that sits behind it.  However, the effect of 50mm f/1.4, in terms of the visual properties of the recorded photo, depend very much on the sensor that sits behind the lens:

25mm f/1.4 on mFT (4/3) is equivalent to 31mm f/1.8 on 1.6x (Canon APS-C), 33mm f/1.9 on 1.5x (APS-C for everyone else), and 50mm f/2.8 on FF (FX), where "equivalent to" means:

  • The photos all have the same AOV (diagonal angle of view) and aperture (entrance pupil) diameter: 25mm / 1.4 = 31mm / 1.8 = 33mm / 1.9 = 50mm / 2.8 = 18mm.

  • The photos all have the same DOF (as well as diffraction softening) when they have same perspective (subject-camera distance), AOV, aperture diameter, and display size.

  • The photos all have the same motion blur and the same total amount of light falls on the sensor when the aperture diameter and shutter speed are the same. which means the larger the sensor, the lower the exposure (same total light over a larger area) and thus a higher ISO setting for a given brightness).

  • The photos all have the same same noise when the same total amount of light falls on the sensor if the sensors are equally efficient (less noise if the sensor is more efficient, more noise if the sensor is less efficient).

  • Other elements of IQ, such as resolution, bokeh, flare resistance, etc., as well as elements of operation, such as AF speed/accuracy, size, weight, etc., are not covered in this use of the term "equivalent".

Note the fourth bullet where total light, exposure, brightness, and ISO are discussed.

I am not yet sure that "Equivalence" as defined in the faq is worth my effort to consider, but I do understand what it is - he spells it out clearly.  I'll read the FAQ again in the morning.

I recommend the full monty:

or, at least, this post in this forum:

BTW: Even that article on ISO spoke about light intensity (light per unit area) on the sensor.

Yes -- that's what exposure is.

Made good sense to me.  Talking about total light on different sized sensors ...

Total Light = Exposure x Sensor Area.  Kinda intuitive, once you understand that the exposure is the density of the light falling on the sensor.

again, I'll have to reread the FAQ in the morning.

Enjoy!  But keep in mind that Equivalence is mainly useful for comparing different formats, although there's plenty of other "good stuff" in the essay.

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