So I was looking at my 28-70mm f/3.5 lens, and I realized that the maximum was literally not physically wide open, as you can see in the picture compared to my f/1.4 lens. I know that f-stop does not necessarily describe the quantity of light that hits the sensor, but why can't my f/3.5 lens open even wider? What would happen if the aperture was removed all together?(not that I'm planning on doing that). General aperture discussion thread?
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>>2786714
because the aperture blades have width that doesn't magically disappear when they're retracted.
It's constrained by the size of some smaller elements than the front. Try looking at it from the back.
>>2786716
No.
The aperture is literally the ratio of the opening of the aperture blades to the focal length.
>>2786719
The blades are incidental. The actual constraint is the minimum element diameter. If the iris assembly didn't exist, this wouldn't change.
>>2786716
OP here, these are taken from the back...
>>2786721
No, the blades are not incidental. It's literally the opening of the aperture blades to the focal length.
>minimum element diameter
If you think this is the case you literally have no clue how optical elements work.
![Nam_RAY_aiming_21[1].gif](https://i.imgur.com/kElXEPZ.gif "Nam_RAY_aiming_21[1].gif")
>>2786726
Okay
try zooming the lens all the way out and looking again
>>2786953
this wouldn't change anything lol
>>2786955
Actually, it might. Some variable-aperture zoom lenses automatically open and close their aperture to whatever the max is for the given focal length.
this is either one hell of an elaborate troll or...whatever i'm tired and bitey
>>2786726
yeah and the maximum aperture is literally the opening of the smallest lens element to the focal length (that's why wide open is a circle and not a polygon!)
>>2786958
this lens is probably something like 28-70 f/3.5-4.5. the blades don't contract as it zooms wide open is just relative to the focal length of the lens. as a lens gets longer wide open ain't so wide open anymore.
>>2786967
Ugh yeah, it's late and I dunno what I was thinking.
On that note, it just occurred to me to wonder how the fuck a fixed aperture zoom works, so I just pulled out my 70-200 to see if the blades open and close depending on zoom. They don't.
It actually kinda makes me think, if they can make like a 4-5.6 or whatever, I wonder why our 70-200s aren't some crazy shit like f/2-2.8.
>>2786714
It doesn't open more because it wasn't designed to. If you were to remove the aperture blades or open them up somehow I bed you'd see all sorts of unpredicted changes in distortion and maybe focal points/area.
>>2786955
this.
>>2786958
>>2786969
>>2786953
All of my manual lens are open all the way no matter what because the little protruding rod controls the aperture. when using viewfinder the lens is completely open, when you press shutter release a bar moves the rod and aperture moves to correct position.
The AF lens are different. Some couple and set it but most new G and canon retain last setting. I might be a little off on this, I don't sperg out on my aperature when it's not connected to the camera
>>2786969
yeah i misspoke actually the aperture value is related to the physical length of the lens not the focal length. zoom is achieved in constant aperture lenses internally so the physical length doesn't change except when focusing probably.
>>2786969
Limitations of the optics, especially the smallest element. Otherwise the lens would have to be particularly fat. Particularly fat can be done though, Samsung has a 16-50 2-2.8 and there's a 14-35 f/2 zoom lens out there
And f/1.4 zoom lens for compact cameras
But again, as your focal lengths get larger, so do your lenses. There's limitations beyond focal length/diameter if you want to keep it in a small package - you still have to retain the focal length otherwise
Holy retardation, Batman!
None of you understand lens design. Please, read a Photo 101 book, or at least stop spreading bullshit.
Max aperture is found by formula:
Focal length (in mm) divided by diaphragm opening (in mm).
Thus, a 200mm lens with a diaphragm of 50mm gives an f/stop of 4, meaning a 200mm f/4 lens.
Variable aperture zooms use diaphragms that either don't open or close at all, or open or close only slightly during zooming. Continuing from above, if a 70mm lens has a diaphragm of 50mm, it equals 70mm f/1.4.
Combined, it would be 70-200mm f/1.4-4 lens (which, technically possible as it may be, isn't likely to sell, so they don't make it.)
Constant aperture zooms using diaphragms that open or close during zoom.
70mm lens with 25mm diaphragm equals 70mm f/2.8. 200mm with 71mm diaphragm equals 200mm f/2.8
So, as a 70-200mm zooms, the diaphragm opens or closes in direct relation to the focal length of the lens.
>>2786714
probably because they want it to be constant f/3.5 rather than some weird shit like f/3.2 - f/3.5
Why can't we make a zoom which is slower on the wide end than the long end?
An f4-2.8 25-90mm zoom would make so much more sense than a f2.8-4 25-90mm
>>2786969
>wonder why our 70-200s aren't some crazy shit like f/2-2.8.
Are you being serious? I get the feeling that you said that seriously.
Let's take a minute to look at a 135mm f1.4.
Now, feel free to look at a 200mm f2 lens. Now take a look at the length of your average zoom compared to a prime.
Right there. That's why.
>>2787057
>why can't we make a pipe with a thinner diameter when it's short and a wider diameter when we stretch it out?
Because physics, anon, the same reason we get more of your brand of questions as more millenials discover *chans.
