A Confusion with Lenses and Focal Length

[Derrel]

TLDR,TLDR,TLDR.*

























*Twin-lens damned reflex, twin lens damned reflex, twin lens damned reflex.

 

[Jim Walczak]

The conclusion I have reached is, for good or bad, digital imaging software has lessened the final product differences between cameras and lenses in today's market.

Much of what a lower priced camera lacks when compared to a much more sophisticated piece of equipment can be digitally altered (in post production) to give a reasonable appearance of quality. It won't fool the dedicated pixel peeper but it will be more than good enough for the average consumer.

In fact I did get most of your point...I was simply explaining, perhaps in my own long winded way, why I happen to disagree with it. My own opinion is that while quality has certainly improved on all fronts, that lower ground and upper ground territory still exists with the prevalent mid ground being ever so dominating, just as it always has. The difference between a disk camera, Polaroid or an Instamatic and 35mm for example was significant to a trained eye, however such cameras still produced images that were "good enough for the average consumer", just as camera phones and digital compacts do today. I would also point out that what's considered "good enough for the average consumer" is equally subjective...just as it has always been. Today we call them pixel peepers, in the old days people used to use a loupe...same concept...and as such, that degree of quality between products has always been rather subjective in terms of perception regarding the "average consumer" vs. "professional"...and in my mind at least, that's a rather significant distinction.

Likewise, I do strongly believe that most things I do in Photoshop today, I could have done in a darkroom...however in this case I would clarify that I never said it was "easy" to do in a dark room. Yes...PS is certainly easier...MUCH easier...and you're right in that many people probably don't understand what goes on "under the hood" there, as apposed to the days of dark room processing (although I would suggest that one must know what things like chromatic aberration means and be able to recognize it BEFORE they can learn to correct it). Photoshop does make such tools available and easier to use to a wider range of people...one or two mouse clicks and many problems can be easily fixed. Trust me...even with my background, I'll NEVER go back to film, LOL! That said however, such techniques have again been around long before the advent of digital. My father worked for a major Cleveland newspaper for most of my life, so yes, I even got to witness things like advanced composite images long before computers were around...back when the term "cut & paste" actually involved the use of scissors and glue, LOL! What's more is that even though software is in fact easier to use, there -IS- a learning curve there as well...just as there was in learning the tools of a dark room. Perhaps the difference there is simply availability...after all, you couldn't just download a pirated copy of darkroom supplies back in the 70's (LOL). More people today have grown up with the likes of Photoshop (or Coral, Gimp, etc), so there's A LOT more people today who are at least somewhat familiar with such tools, HOWEVER...most people don't just download a copy of a new software package such as Photoshop and say "Today I will be a great photographer". Even with the likes of Lightroom, there are many novices who struggle with the learning curve regarding post processing. While I've been a Photoshop user since the mid 90's, having gone back to college in 2009, I did in fact get to watch people struggle with learning such software...it's just not as easy as your comment insinuates.

In any case, again...I do very much get your point(s), however again - I happen to disagree with them.

 

[soufiej]

" ... however in this case I would clarify that I never said it was "easy" to do in a dark room."


And my point has been, it is incredibly easy to do in the digital domain.

In-camera, it's all being done for us.

In post production, it is a matter of seconds not hours and days and cut and paste and separating layers and adding this or removing that.

We can straighten lines, horizons and building tilt with the greatest of ease. We can add/remove filters and adjust color imbalances and boost/cut saturation levels.

We can sharpen and change the contrast by globally or ever so discretely changing whites and blacks.

We can even add a touch of film "grain" if we prefer.

A simple mouse click and it's done for us.

Most would even consider it cheap when compared to the cost of the actual lenses and hardware and time which would have been required in past decades.

On that point, do we not agree?

 

[andytakeone]

Haha wow, what an interesting discussion.
Don't worry about hijacking my thread, it was a pleasant surprise and an interesting read.

Yes, I do see your point Jim on concerning oneself more on the implications and results of different mm lenses rather than the mathematical underpinnings of what define them. This is something that I'm currently in the process of training myself to do (I currently have a 28-105mm 3.5-4.5 kit lens) so I'm slowly becoming familiar with when to use a wide angle, a 50mm, or close in. The main reason for my question is merely that I don't do well with arbitrary numbers. It tends to confuse me. As in, I accept that 28mm is a "shorter" length than 105mm which results in a wider angle of light coming into the lens and thus a wider shot. But the disconnect that a 28mm "length" is not 28mm "long" really gets under my skin because I begin to worry "Why did they call it 28mm then?". It does alleviate some frustration to know that this is a more mathematical and complicated problem that I thought (my thinking that I was misunderstanding something very simple and under my nose) and so, now that I at least know that the length has something rather to do with the measurement of converging light, I can accept that and go on my merry way and use the lenses more practically.

As far as the discussion between you and soufiej, I can see where both of you are coming from.
If I'm not mistaken, soufiej is saying that digital processing has allowed low end lenses to in a way "make-up" for their deficiencies by fixing things like chromatic aberration, vignetting & distortion in Photoshop/Lightroom, thus narrowing the gap between low and high and lenses.
And that Jim is saying that this gap between low and high end has always kind of been the same (with things like Polaroids)--it's just now there's a different coat of paint on it. That although the objective quality of being able to fix lens deficiencies has become more advanced, the subjective qualitative differences between low and high end equipment remains the same: people are just as wow'd by Instagram filters and amateur Photoshop adjustments as people were wow'd by the instantly gratifying look of Polaroids.

Again, thanks all for the comprehensive and detailed replies.

 

[Solarflare]

But the disconnect that a 28mm "length" is not 28mm "long" really gets under my skin because I begin to worry "Why did they call it 28mm then?".

Because that defines the viewing angle ?

As the most simple and easiest example, assuming we want to make a camera obscura, so thats the most simple of cameras, a camera with simply a small hole instead of any optics, then the distance between the hole and the sensor area is exactly the focal length of that camera obscura, and one could have a camera obscura with a zoom simply by allowing to change the distance between the hole and the sensor.


Its is still the same for large format cameras. Large format cameras have two "planes", one at the front for the lens and one at the back for the sensor area, and a cloth protection between so light doesnt enter the camera except through the lens. They are focused by moving these two planes (which, as mentioned in the Wikipedia article, allows additional trickery of shifting and tilting).

That means large format lenses (as well as some medium format and small format lenses) are of a single group, i.e. the lens elements stay fixed towards each other, and the lens is focused by moving this single group, i.e. the whole lens, instead of moving lens element groups individually.

And many of these lenses arent telephoto (and for large format I have yet to see one thats retrofocus). Obviously if they are, they will no longer behave like a camera obscura.

If you focus such a lens at infinity, the distance between the "hole" (the aperture) and the sensor will be indeed exactly the focal length of that optics. And for the record, if you want to use the same lens for macro, for 1:1 macro, the distance between sensor and optics will be exactly twice the focal length.

It should be added that such lenses also have extreme focus breathing. I.e. the focal length of your lens changes if you change focus. So your 150mm "normal" lens on a 4x5 camera (about the equivalent of a 50mm on small format), when focused at 1:1 magnification, will be 300mm from the sensor area (again this is the distance between the sensor of the APERTURE HOLE and not between front element of the lens) and will indeed have the focal length of 300mm.


With more complex lens designs, i.e. lenses that can stay in a fixed position towards the sensors, lens element groups are moved individually, which is of course more error phrone, but medium and small format cameras dont archieve the insane resolutions of large format anyway, so thats tolerated. There are some medium and small format cameras that also use focusing by moving the lens as a whole, though.

Either way such constructions allow all kinds of trickery, including for example zooms, and allow to focus without moving the front element of the lens at all (avoids sucking in air, which means that lens is much less phrone to dust).