DOF and Cropping take 2

Started 5 months ago | Discussions thread
awaldram
Forum ProPosts: 10,691Gear list
Like?
Re: Awaldram
In reply to moving_comfort, 5 months ago

moving_comfort wrote:

Great Bustard wrote:

Here we are:

http://www.josephjamesphotography.com/equivalence/#quick

Neither the focal length nor the f-ratio of a lens change as a function of sensor (for example, a 50mm f/1.4 lens is a 50mm f/1.4 lens, regardless of the sensor behind the lens). However, the effect of both the focal length and the f-ratio on the visual properties of the photo very much depend on the sensor, and scale in direct proportion to the size of the sensor:

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 diagonal angle of view (25mm x 2 = 31mm x 1.6 = 33mm x 1.5 = 50mm) and aperture diameter (25mm / 1.4 = 31mm / 1.8 = 33mm / 1.9 = 50mm / 2.8 = 18mm).
  • The photos all have the same perspective when taken from the same position.
  • The photos all have the same DOF (as well as diffraction softening) when they are taken from the same position with the same focal point and have the same display size.
  • The photos all have the same motion blur for the same shutter speed (regardless of pixel count).
  • The same total amount of light falls on the sensor for the same DOF and shutter speed.
  • The same total light falling on the larger sensor will result in a lower exposure than the smaller sensor (the same total light over a larger area results in a lower density of light on the sensor).
  • The larger sensor system will use a concomitantly higher ISO setting for a given brightness of the LCD playback and/or OOC (out-of-the-camera) jpg due to the lower exposure.
  • The same total light will result in the same noise for equally efficient sensors (regardless of pixel count and regardless of the ISO setting).
  • If the 25mm lens at f/1.4 has twice the resolution as the 50mm lens at f/2.8 on FF, 1.33x the resolution of the 33mm lens at f/1.8 on 1.5x, and 1.25x the resolution of the 31mm at f/1.8 on 1.6x, the sensors have the same pixel count and same AA filter strength, then all systems will also resolve the same detail.
  • Other elements of IQ, such as bokeh, color, distortion, 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".

.

So Awaldram, you've called Falk's paper a 'fallacy', although I doubt you'd really think the whole thing could be a fallacy. I'm left with not knowing what parts of it you agree with or not. So let's move to the above - what do you think is false or 'crackpot' to use your word, in the above?

You seem to not agree with:

  • The larger sensor system will use a concomitantly higher ISO setting for a given brightness of the LCD playback and/or OOC (out-of-the-camera) jpg due to the lower exposure.

Based on what you said here (in reference to Ian stating a correct equivalent relationship he layed out which would have required the FF image to use ISO 225 to match the aps-c ISO 100 with the same total amount of light) :

...Ian/MC said FF required iso225 to match iso100 aps-c - wrong

...On another subject you keep saying iso100 on aps-c = iso 225 on FF

...Again your doing some kind of weird 'equivalence' to push some FF agenda

And you seem to disagree with the following: "...However, the effect of both the focal length and the f-ratio on the visual properties of the photo very much depend on the sensor, and scale in direct proportion to the size of the sensor"

Based on what you said here:

...Ian/MC said DoF is a function of sensor size - wrong

...I said an f2.8 lens is an f2.8 lens on any sensor - Check Proved

...Ian/MC stated a lens alters it behaviour and f2.8 is not the same but depends on sensor size - yet again wrong.

So, anything else you disagree with in the above (or can you be more specific about what you disgaree with in Falk's paper? )

Do you read what you quote??

Neither the focal length nor the f-ratio of a lens change as a function of sensor (for example, a 50mm f/1.4 lens is a 50mm f/1.4 lens, regardless of the sensor behind the lens).

Yet another source agrees with me !

You see what you miss is the qualifiers which then leads you to make assumptions based on insufficient data.

In your quote iso100- iso225

the premise Ian is taking is that to match DoF you need to shut the aperture down this intern means you need to up iso to maintain the exposure solution.

Now it seems good stuff ? ....But you could also crop the same image from the same lens across format and achieve the exact same result but without altering exposure, (because an f2.8 lens is always an f2.8 lens !!!!)

Yet you alter multiple factors and then use them singularly to 'prove' your fallacy.

As to Falconeyes white paper I said it was unproven and thefore made up, It's his view and like most things has stuff I agree with and stuff I don't but if unproven its all conjecture.

Nothing wrong with that , but you then are using it as 'the bible on equivalents' is just funny ... an unproven source is your mantra .

Given the evidence above it obvious to all  the 'Equivalent ' model your pushing as some kind of new photography rule is wrong and broken.

It only works for a very small subset of conditions and only if you assume FF is superior to anything else.

Something we all know all those proposing it are indeed FF Zealots.

.

-- hide signature --

Here are a few of my favorite things...
---> http://www.flickr.com/photos/95095968@N00/sets/72157626171532197/

 awaldram's gear list:awaldram's gear list
Pentax Q Pentax K-3 Pentax smc DA* 55mm F1.4 SDM Pentax smc DA* 16-50mm F2.8 ED AL (IF) SDM Pentax smc DA* 50-135mm F2.8 ED (IF) SDM +11 more
Reply   Reply with quote   Complain
Post (hide subjects)Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark post MMy threads
Color scheme? Blue / Yellow