Exposing Film + Lens Limitations & Variations?

Hi Everyone.

I think this warrants its own thread, as opposed to tagging this onto the "Box Speed" thread?

 

Anyway, I am wondering if a lens with a higher lowest aperture number (ie: f4.5, for example) would matter in choosing exposure settings? The lens is still wide open, but such a lens would be less than ideal for low light or night shots? Or would one just add more exposure time?

 

Let's say we have two lenses, one is f1.9 and the other f3.5.

How would each come into play when figuring exposure values?

Or is (available) light & film speed enough to calculate- and equipment variants do not matter or are insignificant?

 

Different lenses are going to have their individually optimum, or "sweet" spots, yes, for overall clarity, light dispersion & transmittal, distortion etc?

This too, factors in when calculating exposure settings? Or no?

 

Thanks, as always!

Tom

Edited February 12, 2020 by Ricochetrider

Film exposure values are a function of light intensity and color temperature. Lens' aperture, as it relates to exposure, merely quantifies the light passing thru the lens, and assuming each lens is clear and equivalent (ie for the same camera mounting), again from an exposure standpoint, there should be virtually no exposure differences. The aperture value, as a mathematical construct, is what it is regardless of its largest opening, and that is what relates to exposure. The "sweet" spots, are unrelated to exposure.

The difference is about 1.5 stops of light (f1.9 is close enough to a standard f2.0 aperture). So by slowing the shutter speed by about 1.5 stops, both lenses would provide the same quantity of light to film or sensor. Its really not that much more complex than this. I would expect the f1.9 if stopped down to f3.5 to be sharper than the f3.5 lens, but that may not be the case. An example is that if the f3.5 lens is a high quality macro lens, they are quite sharp at full aperture.

 

I have not found transmission or T factors to be much of a difference with still photography and distortion or lens sharpness is more of a choice of lenses, not exposure differences.

Lenses with different maximum apertures will transmit the same amount of light when set to the same taking aperture, allowing for sample variation. The F/1.9 lens would be better for low light not only because it could be used at F/1.9, but because even if stopped down, viewing and focusing (at maximum aperture) would be easier than with the F/4.5.

 

The biggest problem with shooting at fast aperture is the very limited depth of field.

Things seem to be in good hands here, so I'll just observe that some simple and "box" cameras like the Kodak Jiffy (LINK) had a tab with three waterhouse stops (LINK).

 

I think most of the users simply assumed that the tab was a pull-out camera stand.;)

We (or camera’s logic) set lens aperture diameter and shutter speed to obtain a “correct” exposure. These setting will be based on scene brightness and the ISO setting. However evaluating the amount of light that will traverse the lens is more complicated.

 

Image brightness as projected by the camera lens intertwines both the focal length and working diameter. This is because the working diameter dictates how much light energy the lens will gather however focal length dictates image size (magnification).

 

The greater focal lengths increase image size. However magnification comes with a price. The more the magnification, the dimmer will be the image. In other words, to gauge how much light will traverse the lens we must take into account both focal length and working lens diameter (aperture).

 

This is simple math. We divide the focal length by the working diameter and obtain what is called the “focal ratio”). We use the symbol “f/” or ”f-number” to abbreviate this ratio. The fact that this value is a ratio is import. A ratio is universal. Stated differently, any lens set to the same focal ratio, say f/4, delivers the same image brightness regardless of the diameters or focal lengths involved. A giant lens 8 meters in diameter with a focal length of 32 meters (think telescope), delivers the same image brightness (exposure) as a 10mm diameter lens with a focal length of 40mm. I can’t over emphasize that the f-number is a universal value.

 

Thus the truism, any lens set to the same f-number delivers the same exposure value. Minor variations exist. We are talking about the efficiency of the camera lens induced by the fact that the lens is not faithfully transparent, has multiple lens elements, and surfaces reflect thus light energy is lost. Professional movie cameras, use a “T” stop, a lens that has its f-numbers calibrated by photometric means. This maintains scene continuity when different lenses are mounted.

Thanks everyone, your information is great. I really appreciate your input.

Thus the truism, any lens set to the same f-number delivers the same exposure value. Minor variations exist. We are talking about the efficiency of the camera lens induced by the fact that the lens is not faithfully transparent, has multiple lens elements, and surfaces reflect thus light energy is lost

 

Your post is very educational Alan, thanks

 

One question: Given that minor variations exist, do you know of a lens that gets closer to maximum theoretical efficiency than all other lenses ?

Your post is very educational Alan, thanks

 

One question: Given that minor variations exist, do you know of a lens that gets closer to maximum theoretical efficiency than all other lenses ?

A simple single element lens fills this bill. Sorry to report, all lenses suffer from 7 major aberrations. These are always present but can be mitigated by building the lens using multiple lens elements, each a different shape, some different density glass. In theory, it takes 7 elements to correct the 7 major aberrations. Light loss is high about 4% per lens surface. This is reduced to about 1 1/2% by proper lens coating. A modern lens can have as many as 10 or 12 coats. Each must be 1/4 wave length in thickness for a specific color of light. The purpose of the coat is to reduce reflections from the polished surface of the lens.

It's great learning from you Alan

 

I'll treat all "f" stops as theoretical approximations from now on

The f-number -- traditional number set 1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 45 - 64

This number set -- each number going right is its neighbor on the left multiplied by the square root of 2 and rounded = 1.4. Each number going left is its neighbor on its right divided by 1.4. The lens is generally a circular figure. The aperture opening is generally also a circle. It the area of the lens that we are talking about making changes too. The f-number set is based on adjusting the lens surface area by doubling or halving its area. Multiply or divide the diameter of a circle by the square root of 2 does this deed. Square root of 2 is 1.414, more accuracy than we need. Due to gear lash and other mechanical limitations we can only set the f-numbers to an accuracy of about 1/3 f-stop (some exceptions apply). This 1/3 f-stop increment applies to shutter speed as the mechanical shutter is based on a pocket watch type gear movement.

Since nearly all modern - and not-so-modern - cameras have TTL (Through-The-Lens) exposure metering, the light loss through a lens is automatically compensated for. Therefore the transmission properties of a lens are fairly irrelevant, and as long as the aperture mechanism operates properly, the quantity of light admitted will halve or double with each marked stop.

 

In cinema use, where knowing the transmission of a lens is important, lenses are often marked in 'T' stops. T stops take the transmission of a lens into account and give the effective f-number at which a perfect lens would pass the same amount of light. However, as far as depth-of-field and aberrations are concerned, the f-number still dictates those parameters, no matter how much light is lost through transmission.

 

For example; a lens with a geometric stop of f/2 may have a T-stop of 2.2, but will still give the same depth-of-field as a 'perfect' lens of f/2 aperture.

 

You also have to bear in mind that maximum light transmission only takes place at the very centre of the the image circle. There's always some light falloff - called vignetting - as you move away from the centre of the image.

 

So lenses aren't perfect. Do not worry about this. Modern lenses are about as close to optically perfect as makes no difference. Take those marked f-numbers at face value. It will make no significant difference to the exposures you get using separate metering, and no difference whatsoever if you use TTL metering.

 

Stop wasting time and brain-power worrying about irrelevant small details and get your head around the bigger picture - pun intended. Grasp the relationship between the light admitted by the lens and the time it's admitted for. That's what's called the exposure, and is usually thought about in doubling or halving steps - or stops.

 

1 second @ f/32

1/2 second @ f/22

1/4 second @ f/16

1/8 second @ f/11

1/15 second @ f/8

1/30 second @ f/5.6

Etc.

They all give the same exposure, as near as makes no difference. Notice that the marked shutter times don't exactly follow a precise doubling or halving pattern either. That's because it doesn't matter. The exposure tolerances allowed in photography are huge - compared to almost any other discipline.

 

Worry more about what your pictures actually look like (important), and less about the technical nitty-gritty (unimportant).

Not mentioned yet, zoom lenses tend to have smaller maximum aperture (larger number),

partly because of the complications of making one.

 

For most outdoors shots, you won't be more than the f/4.5 or so that you mentioned.

Also, zoom lenses are very convenient when situations change fast.

 

For low light situations, such as indoors without flash, you want the

prime (non-zoom) lens with larger aperture (smaller number).

(Many museums that allow photography don't allow flash.)

Not yet mentioned is the total lack of perfection in any subject matter. Once that has been sorted out, then is the time to worry about lens variation.

Get to know your lenses. Reading up about them online might be cheaper than taking a lot of shots wondering and testing things out, for exact answers. (<- Especially on film!)

On negative film 2/3 of an f-stop (vignetting / whatever) shouldn't matter much.

You probably have to shoot stuff side by side on BW (same stock same processing tank) to notice a difference between 2 lenses. And even as a darkroom rookie you should be able to print each result acceptably (on it's own). I believe lenses I have or had used were maybe 1.5 to 2 Ilford Multigrade grades apart, contrast wise. If your primary goal is to print on the same fixed grade of paper you might have to adjust film processing for some cameras accordingly., which might demand exposure correction since push processing is one way to gain more contrast, isn't it?

No clue to what an uncoated lens would lead within the Zone system besides capturing a higher contrast subject.

___________________

Low light: when we let the hope that tearing our aperture wide open would gain us great images go we are down to shooting at reasonable aperture for an appropriately extended shutterspeed from a tripod. Fast glass might make TTL focusing (your view camera, T-/SLR, MILC...) easier. But for real low light rangefinders or Rangemeter & auxiliary finder combos work best.

 

Lenses varied a lot over the decades & price ranges, so it seems wrong to associate something globaly to their speed. If you are after sharpness an aspherical Apo Summicron 50 should make you perfectly happy, even wide open, while something else might need stopping down quite badly, to deliver some sharpness over its entire image circle in use.

The responses to this conversation and the advice, actual and implied, contained in those responses might easily be classified into two families. Those being:

 

> Theory, for the sake of Theory Family

> It Matters Zip, in the Real World Family

 

My view is, it’s good that both families’ views are harmoniously represented here, especially in the Beginner Forum. This allows the OP (and others) a broad range of input, often not available in structured learning, from which they, themselves, can choose what is interesting and relevant.

 

This conversation is yet another example of Photo.net's talented and experienced Membership, working well.

 

It's worthwhile mentioning this, as a fact.

 

WW

Worry more about what your pictures actually look like (important), and less about the technical nitty-gritty (unimportant).

 

Aren't theory and practice inextricably intertwined? How do you get pictures that look 'good' without having some command of the 'nitty-gritty'?

 

Of course, the answer to that is having a camera that has all technical functions controlled by the camera, I guess :p

Aren't theory and practice inextricably intertwined? How do you get pictures that look 'good' without having some command of the 'nitty-gritty'?

There's knowing enough to get a good picture.... and then there's making an entire hobby or obsession out of knowing arcane and ultimately useless (and doubtless soon to be redundant) details about the process.

Unfortunately, the lumpen bourgeois assumption that some modern "art" is simply passing off whatever mess results from not "knowing enough to get a good picture" by calling it "art" is sometimes justified.

On the other hand, I've watched film of Jackson Pollock painting, and I, at least, am firmly convinced that he was strongly in technical control. His imitators, not so much.

 

I'm also pretty firmly convinced that Robert Frank was in control of his technique as well.

 

So I would be reluctant to set too low a bar on technical expertise, as I think some do.

Aren't theory and practice inextricably intertwined? How do you get pictures that look 'good' without having some command of the 'nitty-gritty'?

 

Quite a good question, one of the best I've seen on Photo.net

On the other hand, I've watched film of Jackson Pollock painting, and I, at least, am firmly convinced that he was strongly in technical control.

But Pollock used tins of commercially made paint. He didn't grind Lapis-lazuli, ochre or vermilion and mix it with oil or egg-white. So he wasn't exactly that devoted to the 'nitty gritty' technicalities of painting. Didn't even shave a squirrel to make his own brushes AFAIK.

 

There are degrees of knowledge needed for various aspects of any craft. A good wildlife photographer needs a knowledge of and passion for their 'prey', and to hone their stalking skills. As does a good street photographer. Not the same skillset as needed by a still-life photographer, or a sports shooter. In all cases I'd place knowing what goes on inside a camera or lens as a very secondary and low-level mechanistic knowledge, and one that improves the final image by very little.