[Class A]

For the question of usefulness: equivalence reduces four parameters (focal length, fstop, iso, sensor size) into three parameters (field of view, aperture, noiselevel)

Nice!

Also, there is not only a reduction in number of parameters, but the three remaining parameters are more closely aligned with that a photographer should really care about:

field of view -> framing
aperture -> DOF
noiselevel -> Image IQ

In contrast, the traditional parameters have a more technical orientation:

focal length -> optical power of the lens (allows inferring framing, if the sensor size is constant)
fstop -> exposure [in combination with shutter speed] (allows inferring noise-level, if the sensor size is kept constant; and DOF if, in addition, focal length is kept constant as well)
iso -> exposure compensation (may indicate level of under- or over-exposure, if the sensor size is kept constant)
sensor size -> influences the photographic relevance of all of the above.

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Last edited by Class A; 07-23-2015 at 06:47 AM.

[Parallax]

Like it is irrelevant if one knows that fstop means focal length divided by aperture diameter?

Yes, essentially.

[monochrome]

Actually, the easiest way is for a person to to learn how each of his/her lenses renders on his/her camera(s), regardless of sensor size, and think of "equivalence" as just another word in the dictionary.

We're all assuming the subject and photographer are cemented to spots on the ground. Just move your subject farther from the background and move yourself proportionally farther from the subject (or both closer, as the format may be) and DoF pretty much looks the same.

[jsherman999]

We're all assuming the subject and photographer are cemented to spots on the ground. Just move your subject farther from the background and move yourself proportionally farther from the subject (or both closer, as the format may be) and DoF pretty much looks the same.

If you're willing to achieve a certain DOF at the expense of maintaining a certain perspective.

And if you can hover in the air sometimes. Or change your body matter density so that you can sink into the ground, or move through a wall, or turn invisible so the subject doesn't notice you walked right up to and became part of the scene. (Come to think of it, The Avengers are probably DOF masters with any lens combo! )

[Ian Stuart Forsyth]

With wildlife photography you will use the longest/fastest lens that you can afford and wield. End of story. Has nothing to do with equivalence.

As to whether or not you should use a full frame camera, probably not, because you'll probably be cropping your D800 past APS-C levels. Once again, not an equivalence thing, just common sense. If you aren't using the outer one half of your sensor, why pay for it?

I bet you more wildlife photographs just as any other photographers select their lenses based on what FOV DOF and the perspective they are looking to capture. If I selected my lenses on the greatest reach most of my shots would be framed to tight for my liking and would be of no use to me. I bet more photographers buy the best lens to fill the greatest gap for their needs because of the cost of such lenses. How does this pan out for FF shooters ( if their style of photography ) they are not FL limited gives them a greater range with a single lens.

If I am looking at the $7500 300 F2.8 for my aspc I would go FF and go for $7500 get a 400mm F4 to get the best out of that $7500 lens.With the higher pixel counts of the newer FF bodies you are left with greater versatility with that FOV. One could ( with a 36mp) camera use a 1.22 crop and still hold a 24mp image with the FOV 490mm F4.9 lens and that lens would only have to resolve for a pixel no smaller than that found in the K5.

[osv]

We're all assuming the subject and photographer are cemented to spots on the ground. Just move your subject farther from the background and move yourself proportionally farther from the subject (or both closer, as the format may be) and DoF pretty much looks the same.

changing perspective is not equivalence.

claiming that equivalence only entails three parameters is not equivalence either, because it ignores perspective and all the rest of the essential parameters.

this discussion just keeps going downhill

[calsan]

When I really want to know the depth of field in my photo before I take it, I just push the dial around the shutter button clockwise, and I can SEE the DOF in the viewfinder. I don't require a tape measure and pocket calculator.

[Rondec]

Your question is wrong, of course, but even if you had asked 'is the SNR better at 100 or 400', of course, the answer depends on the amount of cropping and is thus quickly determined by equivalence.

If you don't mind the moose running away while you're taking your shot, you can just haul an extra lens and swap lenses of course.

Really. My understanding would be that you are cropping the same. Is that not the point of equivalence, that you need the same final image? My question was facetious and assumed that I was comparing iso 100 and 400 on the same camera. My point being that your goal when shooting (whatever size sensor, however much you will need to crop) is to use the lowest possible iso while maintaining shutter speed adequate to capture the scene/action before you. And yes, even on the D800, I believe that iso 100 is better than 400 (for resolution, dynamic range and SNR -- just "better) the difference may not be huge, but it is certainly measurable.

---------- Post added 07-23-15 at 06:09 AM ----------

I bet you more wildlife photographs just as any other photographers select their lenses based on what FOV DOF and the perspective they are looking to capture. If I selected my lenses on the greatest reach most of my shots would be framed to tight for my liking and would be of no use to me. I bet more photographers buy the best lens to fill the greatest gap for their needs because of the cost of such lenses. How does this pan out for FF shooters ( if their style of photography ) they are not FL limited gives them a greater range with a single lens.

If I am looking at the $7500 300 F2.8 for my aspc I would go FF and go for $7500 get a 400mm F4 to get the best out of that $7500 lens.With the higher pixel counts of the newer FF bodies you are left with greater versatility with that FOV. One could ( with a 36mp) camera use a 1.22 crop and still hold a 24mp image with the FOV 490mm F4.9 lens and that lens would only have to resolve for a pixel no smaller than that found in the K5.

I included the word "afford," because the number of folks who are spending 7500 dollars on a single lens is pretty small. El J's example had to do with capturing a distant moose and he was comparing a 200mm lens with a TC to a 400mm lens. Now, I do find it odd when people throw TCs into the mix, because TCs are such a mixed bag. Equivalence may tell you about framing and depth of field with a lens/TC combination, but it won't tell you about performance -- either auto focus or resolution and most TCs do not perform at the level of a dedicated lens in a given focal length. Putting a 1.5x TC on a 200mm f2.8 lens will not really give you a 300mm f4 lens. If it is a good enough TC, it might be close, but if you can afford it, you should go for the 300mm lens.

I am not a wildlife photographer. My experience in listening in on birders talking is that they always want a little more length, but I wouldn't know from personal experience.

[falconeye]

The depth of field at the same focal length never changes, regardless of sensor format.

It is good that you did not bother to argue because you would have incorrectly opposed to a correct assertion.

I didn't make the comment for Adam's post because I didn't want to disturb a thread this early in evolution. But in essence, Adam made the same incorrect statement now corrected by Class A.

It may first come as a surprise that cropping a photo does indeed change a photo's depth of field (doesn't matter if done later in post or earlier by a sensor crop). BTW, it does change noise at the image level too.

That's the kind of understanding I meant above when I insisted that by now, equivalence is part of useful photography knowledge.

Among others, it helps understanding and planning the effect of cropping or the Brenizer method (which can be thought of to be the opposite of cropping).

---------- Post added 23-07-15 at 13:02 ----------

I can SEE the DOF in the viewfinder.

You are aware that what you see is dependend on the viewfinder magnification?

[BrianR]

When I really want to know the depth of field in my photo before I take it, I just push the dial around the shutter button clockwise, and I can SEE the DOF in the viewfinder. I don't require a tape measure and pocket calculator.

I though that was the "make everything go dark" switch.

[mohb]

It may first come as a surprise that cropping a photo does indeed change a photo's depth of field

Doesn't it just alter the viewer's perception of it?

[BrianR]

Doesn't it just alter the viewer's perception of it?

Not by the definition of DoF that I'm used to, but people like to argue the semantics. Consider an 8x12 print that's 2 feet away.

-Crop it to 4x6 using scissors. View it from 2 feet away. DoF hasn't changed.
-View this 4x6 print from 1 ft away. DoF has now changed.
-Crop your photo in photoshop to match the view of this 4x6. Print the resulting file at 8x12 and view from 2 feet away. DoF is now different from the original 8x12.

Here's calculator to play with, crop via selecting the sensor size, hit 'advanced' to access viewing distance and print size controls: A Flexible Depth of Field Calculator

[kh1234567890]

Not by the definition of DoF that I'm used to, but people like to argue the semantics. Consider an 8x12 print that's 2 feet away.

-Crop it to 4x6 using scissors. View it from 2 feet away. DoF hasn't changed.
-View this 4x6 print from 1 ft away. DoF has now changed.
-Crop your photo in photoshop to match the view of this 4x6. Print the resulting file at 8x12 and view from 2 feet away. DoF is now different from the original 8x12.

Hmm... No matter how much cropping and chair wheeling I do, a shot like this (apologies for the bad composition) looks the same to this tired old brain and eyeballs. The man behind the coat and sunglasses girl refuses to pop into focus.

[mohb]

Hmm... No matter how much cropping and chair wheeling I do, a shot like this (apologies for the bad composition) looks the same to this tired old brain and eyeballs. The man behind the coat and sunglasses girl refuses to pop into focus.

All that cropping and resizing does is alter the visual signals we use to measure depth, the actual DOF will still remain what t was when the photo was taken.

[Not a Number]

Then we get someone who posts something and it turns into a 15 page thread...

Up to 11 or 12 already