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Step One is to confess that you’re a retired engineer ... so far, so good ;-)

R.G. Loc: Scotland

Yep, that definitely has advantages over the "dismantle" approach .

R.G. Loc: Scotland

Still here? I thought you found this thread unworthy of the effort required to actually read the contents.

Delderby Loc: Derby UK

With both my PZ lenses, I look in the viewfinder - when i flick the zoom switch on the lens barrel (with my left thumb) the f no. shows on a scale at the bottom of the live display - which disappears when I release the switch. This gives me an instantaneous view and a deep understanding of how focal length affects not only magnification but also perspective.

Delderby Loc: Derby UK

Yes - we see this all the time on TV - especially in crowd scenes. The camera man can make a thin crowd look dense, as if they were breaking covid distancing rules, by angling his camera and adjusting focal length. It's about DOF as well as the angle of the dangle.

R.G. Loc: Scotland

If there's anybody still following this thread and still not sure of its purpose and content, I included the following pointers (which should have been enough to keep things clear):-

1) The thread's title - Focal Length and Perspective.

2) The opening sentence - "Part of the problem with this subject is the undefined use of the term "perspective".

3) The two subheadings in the opening post - PERSPECTIVE and PERCEPTION.

It should have been obvious (to anybody that's actually bothered to read the opening post) what the main purpose of the thread is. The usual misunderstandings and misuse of the term "perspective" are associated with the technical aspects of its meaning, and that is what I attempted to clarify. It should be obvious (to anybody that's bothered to read the intro) that I was referring specifically to the technical, geometric aspects of perspective.

R.G. Loc: Scotland

Since the problem referred to in the opening post relates to the use (and misuse) of terminology, I have some suggestions of my own to make.

1) When discussing the effect that focal length has on what we see through a lens, instead of referring to perspective (in the geometric sense) we should refer to depth perception because that is what focal length affects - not perspective.

2) When referring to the effect that focal length has on depth perception, instead of using the expression "natural perspective" to describe what a FF focal length of 43mm (or thereabouts) gives us we should use the expression neutral* depth perception (*IMO "neutral" is more specific than "natural").

Since the effect that focal length has on our perception of distance changes from compression to extension (two very vivid and real phenomena), there has to be a crossover point between the two, which indicates that there is a point of neutrality. I would say that anybody who takes photography seriously would benefit from understanding that point. Compression and extension can both be used for effect, and in addition to that, there will be times when neutral depth perception is the preferred option. That option is provided by a full frame focal length of approximately 43mm (or close to it).

The crossover from compression to extension happens gradually, so the value doesn't have to be precise. 50mm is often seen as providing a neutral depth perception (I would advise against calling that a neutral perspective - which would be potentially misleading ).

Another point worth bearing in mind is that cropping affects depth perception in exactly the same way that optical zooming does. The focal length provides us with a starting point but cropping (if any) will determine the final result.

larryepage Loc: North Texas area

This mostly makes sense to me. The only thing I am struggling with is your last two sentences. I've played with it a little bit using the ability to quickly switch between FX and DX formats on my D850. I can't see a change in depth perception when doing that. It may be that it isn't happening, it may be that my brain just doesn't perceive it for some reason, or it may just be too early in the morning. I'll keep working on it.

R.G. Loc: Scotland

The effect starts to become vivid only when it starts to become extreme. There are demonstrations out there somewhere that show the effect when you take a wide angle shot and crop it to give the same framing as a telephoto shot taken from the same spot. For that to work there has to be something in the bit you crop down to that shows depth compression - something moderately close and something not quite so close behind it. As in real life, the effect doesn't jump out at you unless it's being emphasised in some way.

That same test can be used to demonstrate that focal length doesn't affect perspective. Provided that the wide angle shot and the telephoto shot were taken from exactly the same spot, the only thing that changes (geometrically speaking) is the angle of view. However, the changing field of view does affect our perception of depth, and that's true whether the change was due to optical zooming or cropping. It just won't be obvious in every situation. It takes something like a long corridor or objects that nearly line up to emphasise the effect. Having said that, our perceptions can work in very subtle ways and it's possible that we may register depth perception subconsciously without being consciously aware that we're doing it.

Picture Taker Loc: Michigan Thumb

Understand I majored in Physics. Worked with a bunch for the Palo-alto Labs and a bunch from the Ukraine.

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Saw “larrypage” in the main index. LP is real. So what’s your excuse ? It’s “your thread” ? Not any more it ain’t. All UHH “author’s rights” always dissolve at page three. Welcome to page four, and to the Great Beyond. Snug up your waders.

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Modern SLR screens don’t show 3-D qualities very well. Were you just viewing or did you actually record and view on a screen ?

R.G. Loc: Scotland

Making a string of negative (and erroneous) comments on a thread you haven't even read properly isn't exactly to be commended. If your background is in the least bit technical you should know that you need to be in possession of the facts before you can have any kind of informed opinion or make any kind of relevant comment.

larryepage Loc: North Texas area

Time was limited. So just relied on the back screen this morning. I'll look more carefully later when I have more time. It wasn't obvious in the masked viewfinder either.

larryepage Loc: North Texas area

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