Photography is FUN!! I've been reading all about F numbers, focal length, etc!

[snapsnap1973]

I'm new to photography and learning the "math" side of it and some of the terms so I maybe can operate my camera a little better instead of being an ignoramus! Anyways, I was reading about "f-stops" and "f-numbers" and it said that to determine the f-number you divide the focal length by the aperture (entrance pupil) diameter. So a 10mm (focal length?) lens divided by a 5mm (aperture) would give you an f-number of 2. Pretty cool! I hope I'm doing it right.

I'm also learning that the closer the lens is to the (sensor?) the "wider" the shot will be and of course vise-versa. So technically a 28mm lens is 28mm from the sensor? Can anyone recommend any good beginning photography books that are cheap? Something that explains it all!!


Thanks

 

[KmH]

The lens mount of a DSLR is a fixed distance from the image sensor plane and is known as the Flange Focal Distance - Flange focal distance - Wikipedia, the free encyclopedia

That's why a 20 mm lens is physically shorter than a 200 mm lens. Note that some optics have a 'folded' light path that allows for a shorter overall lens length. Cassegrain reflector - Wikipedia, the free encyclopedia.

Angle of view - Wikipedia, the free encyclopedia

Short focal lengths are categorized as Ultra Wide Angle or wide angle.
In general the angle of view a 50 mm delivers is considered the focal length that is closest the angle of view the human eye delivers.

 

[KmH]

Moving on to lens aperture and the concept of a 'stop'.

A stop is a doubling (2x) or a halving (0.5x).
The concept of a stop also applies to shutter speed and ISO.

Changing the shutter speed from 1/100 to 1/200 halves the length of time the shutter is open. Going from 1/200 to 1/100 doubles the amount of time the shutter is open.
The same works for ISO. ISO 100 is half as sensitive to light as ISO 200 is, and ISO 1600 is half as sensitive to light as ISO 3200 is.

It's a bit difference for lens aperture because it's the area of the lens opening, and not the diameter of the opening that matters.
A further consideration is that the lens opening area at f/2 for a 50 mm lens, is different than the lens opening area at f/2 for any other focal length lens.

Note the the little f in f/whatever represents the variable that is the lens focal length.

So, since area of the lens aperture is involved we have to use the square root of 2 - 1.4142 - instead.

One stop less than f/1 is f/1.4, or 1 x 1.4142 = 1.4
One stop less than f/1.4 is 1.4 x 1.4142 = 1.98 which gets rounded to f/2.
One stop less than f/2 is 2 x 1.4142 = 2.8 or f/2.8

Those are full stop steps, but most DSLRs are set by default to adjust in 1/3 stop steps to give finer control over exposure.
Note that all 3 - lens aperture, shutter speed, ISO - are usually adjustable in 1/3 stop steps.

 

[snapsnap1973]

Wow, that's a lot to absorb right now! I guess I've got a lot of reading to do LOL! Isn't ISO a form factor? Did it not used to do with "film" speed?

 

[Helen B]

The distance from the front lens element to the rear lens element determines lens focal length.

...

Shorter focal length lenses deliver a wider field/angle-of-view, Angle of view - Wikipedia, the free encyclopedia, because the front and rear lens elements are closer to each other.

Er, no.

The simple explanation of focal length is where a simple, thin, single element lens would be that gave the same image (when focused at infinity). It has absolutely nothing to do with the distance between the front and rear elements. A 28 mm lens behaves like a thin, single element lens that is 28 mm from the sensor.

A multi-element 28 mm lens can be further from the image plane than 28 mm (at infinity focus). That would be a retrofocus lens. A multi-element 200 mm lens can be less than 200 mm from the image plane: that would be called a telephoto lens ("telephoto" is also used for lenses with a longer-than-normal focal length.

 

[Tuffythepug]

snapsnap1973, you are beginning to see that when you go beyond "point and shoot" automatic settings there is a lot to learn. Those of us who grew up with manual film cameras that had no light meters were in the same boat. The learning curve discouraged a lot of folks. It is confusing at first but you will gradually learn how all of these elements fit together and it will make sense to you. Then you will be able to create the images you want to create by using all these tools. Stick with it. It gets easier as you go

 

[tirediron]

snapsnap1973, you are beginning to see that when you go beyond "point and shoot" automatic settings there is a lot to learn. Those of us who grew up with manual film cameras that had no light meters were in the same boat. The learning curve discouraged a lot of folks. It is confusing at first but you will gradually learn how all of these elements fit together and it will make sense to you. Then you will be able to create the images you want to create by using all these tools. Stick with it. It gets easier as you go

Or, you could do what I do: Know that each stop equals twice (or half) the amount of light of the one before it, not really give a damn about why, and when Helen explains it, nod wisely and reach for the aspirn bottle!

 

[bsinmich]

The way a normal lens is determined is by taking the diagonal of the film or chip size. For a 35mm negative of 24X36 mm that figures out to around 58mm. We just use the 50mm as normal because it is close and a convenient number. If you shoot medium such as format 6X6 a normal lens comes to around 80mm. 105mm for a 6X9 format.

 

[JamesSomerset]

The question I feel you have to ask yourself is - do you want to be a great practical photographer or do you want to be able to have people walk away from you at photographic meetings while you go off on one about how the automatic mode on flash guns means nobody understands the inverse square law anymore.

When I first started in photography I really wanted to know all the technical stuff. I delighted at always getting the highest mark in college for my knowledge of the physics and chemistry of photography. Six months in and I noticed all the kids who never gave a damn about that stuff were getting higher marks with their photography and producing much better images.

The time you spend learning the physics could be spent carrying your camera and taking photographs.

Although there is a place for understanding the physics there is a point at which it doesn't help you produce better shots.

Learn enough to be able to make vital choices about depth of field and exposure at the taking stage. It is absolutely essential you know how to bring in to focus everything you want to be in focus. With Photoshop, reducing the apparent depth of field in an image that is too sharp is relatively easy.

Learn enough about fill-in flash, aperture choice and the use of filters on camera to get by - then get out there snapping everything that interests you - and plenty of things that don't. Once you have the basics, an hour taking photographs is far more valuable to your development as a photographer (please forgive the pun) than an hour puzzling about why the reciprocity law fails at long exposures.

My opinion - for what it's worth!

 

[Patrice]

The way a normal lens is determined is by taking the diagonal of the film or chip size. For a 35mm negative of 24X36 mm that figures out to around 58mm.

A bit of a miscalculation there, the diagonal of a 24 mm x 36 mm rectangle is 43.3 mm and not 58 mm.

 

[cynicaster]

The time you spend learning the physics could be spent carrying your camera and taking photographs.

Although there is a place for understanding the physics there is a point at which it doesn't help you produce better shots.

I agree completely. I'd consider myself to be a prime example of somebody whose grasp of the theory far overreaches his ability to leverage that knowledge to make appealing art.

The moral of the story:

Great results are still possible without encyclopedic knowledge of the textbook principles, but great results are nigh on impossible without practice.