File :-(, x, )
Apertures and cheap fast lenses Anon
has anyone taken their cheapest (preferably broken) lens apart before? If so, where did you find the aperture blades? in the middle? at the back?

Also, why cant the aperture sit in the front of the lens elements, so that you have more space for f/0.012 ish apertures?

pic somehow related
>> Anonymous
PHYSICS DO NOT WORK THAT WAY
>> Anonymous
lol wut
>> Anonymous
why
>> Anonymous
oh fuck

this is like the guy the other night that wanted to argue that a 500mm lens on a crop body magically becomes a 750mm.
>> Anonymous
>>205246
He wasn't arguing that. He was saying they should be labeled like that, which is a hey-let's-cater-to-the-LCD error of judgement, not a hey-the-Earth-is-flat error of knowledge.
>> Anonymous
>>205248


but not all crop cameras have the same crop.


Why not just stick to the 35mm standard?

it works, it's standardized, and APS-c will be phased out as FF DSLR sensors get better.
>> Anonymous
>>205251
I doubt that. Entry level compacts will stick with APS-C sensors. Full frame will become cheaper and more widespread but APS-C sensors still have their place.
>> Anonymous
>>205251
>Why not just stick to the physical focal length?

Fixed.
>> Anonymous
>>205251
Tell the medium and large format people to stick to the so called 35mm standard then. 80mm? Bullshit, it's a "40mm". As many film formats as there are sensor crops.

A focal length is a physical property.


>>205106
As for the OP, the aperture blades in a common lens nowadays will usually be found in the middle of the lens, often at the central intersection.

The f number designates the size of the light ray that is let into the camera through the lens. Lenses are spherical, allowing a beam of light of the f-number's diameter to enter at the lens' angle of view, forming an image of said f-number throughout the image.

If you were to put an aperture at the front, you'd be closing the field of view by a fuckton, and only the center would be useful. Your lens of said aperture is no longer giving you the field of view you were going for.

Additionally, about the f/0.012 thing, ignoring the fact that it's theoretically impossible, have you also realized how big a lens of any focal length would be? Here's something to think about: because of what I just said about the angle of the beam of light entering the front element, front elements generally have to be wider than their supposed focal length.

I could go on, but believe me, as I have learned myself, there is -way- more into optical design than one would think.
>> Anonymous
Imagine a massive aperture for a lens with a small image circle for a tiny sensor.
>> Anonymous
>>205260
>>205258
Elaborating on this, let's calculate the approximate size of a 50mm F/0.012 lens, which isn't possible.

50/0.012 = 4166mm. Your light beam is over 4 meters wide.

Now, a good lens doesnt just gather light in the center, right? Let's calculate that a 50mm lens has an angle of view of around 45 degrees. That blows the lens' size up quite a bit, to around say.... 7 meters wide? 8 meters?

It's not even possible but... lolwut

Realize what you're saying?
>> Anonymous
>>205263
Sorry, I forgot to add this.

That's 8m wide for a front element. How thick is your glass going to be? What material? What's the price on that? Additionally, it needs to focus light approximately 50mm behind it.

I rest my case.
>> Anonymous
>>205263
Now calculate the DoF for lulz.
>> Anonymous
>>205265
lol That would certainly be interesting. Brb, getting the calc.

0m 2.87cm, focusing at an object 10 meters away.

1 meter away? (oh lawd) 0.03cm.

Source on the DOF calculations:
http://www.tawbaware.com/maxlyons/calc.htm
>> Anonymous
And I hadn't even thought about it... what kind of shutter speed for that?
>> Anonymous
>>205269
Depends completely on the light you're shooting in as any reasonably intelligent person would know.
>> Anonymous
>>205272
Obviously. Let's assume F16 for a sunny day, with iso 100 film, wide open. Someone else care to do the calculation? I'm busy. : P
>> Anonymous
>>205275
At constant illumination: (F-number)^2 * (1/shutter speed) * (ISO speed) = const

Using Sunny 16, we get: 16^2 * (1/(1/100)) * 100 = 2560000

Now open the aperture to f/0.012:
0.012^2 * (1/x) * 100 = 2560000

Solving this, we get x = 1/177777777 s
>> Anonymous
1/(1.7*10^8) s

Light would only travel about 3*(1/1.7) ~= 1.76 m in that time, right? what a lens.
>> Anonymous
oh, actually more like ~1.6875 m, sorry.
>> Anonymouuuss
>>205308
So even then at that large aperture the light is still too slow to reach the sensor? is that what it means?
>> okto
>>205332
If the lens were more than 1.76m long, yes, but our hypothetical monster lens is a 50.

Another consideration is image quality. The faster you go, the worse your image gets, and the more elements you have to put in for things like chromatic aberration, comae, and field distortion.

For example, Canon's 50/1.0L is their worst-performing normal lens. Costs $5000, but even stopped down just about any other lens can beat it for IQ. The 1.2L is a little better, the 1.4 is pretty great, and the 1.8 is nearly perfect—even though it's a piece of shit mechanically.

Your f/0.012 lens would be like taking a picture with the lens off, except for the half a millimeter plane that would be in focus, and that would be distorted to shit. Basically, you'd have a lens for making fabulous bokeh with no sharp areas. :P
>> Anonymous
And that is why there is no chance in hell that, lets say a zoom lens of 200 / 300mm prime reaches f/1.2 without being ridiculously large (telescopic, even), not to mention ridiculously expensive (see sigma's 1200mm f4.. at f4 its still friggen large)