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Anonymous
Hello /p/.

I recently bought this Sigma 28-300mm f/3.5-6.3 DG Macro for my Sony DSLR-A200 with it's magical Minolta fitting.

I'm a bit of a photonoob but I'm assuming f/3.5-6.3 is the min/max aperture the lens will go to. This makes me a bit concerned since my camera happily auto-exposes/let's me set the apeture all the way from f/3-f/40.

Is the camera just dicking around, having no idea what apeture the lens can go to, or am I doing it wrong?

tl;dr: Camera lets me set apeture higher and lower than the lens says it can go to. What gives?
>> Anonymous
why did yo make this again?
>> Anonymous
>>240058
Again?
>> Anonymous
>>239961

i didnt read any of your shit because i only noticed the lens
>> Anonymous
the 3.5-6.3 is the change in maximum aperature throughout the zoom range, example, at 28mm the maximum aperature is f/3.5, while at 300mm it is f/6.3

the lens minimum aperatures also change, from f/22 at 28mm to f/32 at 300mm
>> Anonymous
and if your camera lets you set aperatures above/below the lenses min/max, it wont do anything. the min/max aperture is controlled by the mechanical parts within the lens, not the camera
>> Anonymous
>>240076
Oh okay. That makes sense, I think.

>>240077
Ah. I was looking at the lens itself while taking photos at the odd apertures to see what the fuck was going on, and the size of it seemed to change still, beyond the min/max still, thougj.
>> Anonymous
>>240088

at the wide (short) end, it can only open to a MAXIMUM of f/3.5, that doesn't stop you from closing it down to anything larger than f/3.5, like f/4.. f/8.. f/11 but you can't make it go any lower than f/3.5, like f/2.. f/1.8

it's physically impossible to do it

at the long end, it can only open to a MAXIMUM of f/6.3, that doesn't stop you from closing it down to anything larger than f/6.3, like f/7.. f/8.. f/11 but you can't make it go any lower than f/6.3, like f/5.6.. f/4

it's physically impossible to do it
>> Anonymous
>>240093
I ment the actual physical aperture bit was still changing. As in, if I set it to f/6.3, which should be the max, and then put it up to f/22, the physical apeture would be smaller than what it is before.

I am so confused ;_;
>> Anonymous
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>>240097

small number = big hole
larger number = small hole

http://en.wikipedia.org/wiki/Fstop

see picture
>> Anonymous
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>>240098
Yeah I know.

This is what happens. I am so sorry for being terrible ;_;
>> ac !!VPzQAxYPAMA
>>240097
The f/stop is ratio of the focal length to the actual diameter of the lens. So a 50mm f/2.0 lens would have a 25mm diameter and a 100mm f/2.0 lens would have a 50mm diameter. The clever thing is that they both let in the same amount of light, so you don't have to remember that a 50mm diameter gives you the same amount of light on a 100mm lens as a 25mm diameter aperture does on a 50mm lens, you just have to know "f/2.0".

And now that you know that, the "f/whatever" notation should make sense: f/2.0 means "Focal length divided by 2.0". And that's why the number in f/number gets larger when the physical aperture gets wider and lets in more light. Focal length divided by 22 is going to be a lot smaller than focal length divided by 5.6.
>> ac !!VPzQAxYPAMA
>>240101
...and so when someone says the *maximum* aperture, they mean the widest physical aperture possible, which is a lower f/number.
>> Anonymous
>>240105
The fact that a higher number means a smaller diameter is not what I'm confused about though. It's the fact that my camera seems to be going out of the range of what the lens says it should go to, but still works fine.

Thanks for your explanation though.
>> ac !!VPzQAxYPAMA
>>240108
The "range" on the lens is just the maximum apertures at each end of the zoom. Look at my previous explanation: Focal length over "f-number" gives you the actual diameter of the hole. When you zoom in, your focal length changes, but the lens doesn't get wider.

So imagine you have a 50-100 f/2.0-4.0, which nobody makes but it makes the math easier. That range is giving the *maximum* aperture at each end of the zoom range. 50mm f/2.0 means a 25mm aperture diameter. 100mm f/4.0 means a 25mm aperture diameter. The aperture diameter doesn't change, just the maximum aperture at the given focal length of the zoom.

Nobody really cares about the *minimum* aperture. It's also a property of the lens, but it's not one most people give a damn about.

(And it also changes when you zoom)
>> ac !!VPzQAxYPAMA
So to sum up:
>I'm assuming f/3.5-6.3 is the min/max aperture the lens will go to.
That is where you made your mistake. It's not the min/max, it's the max/max. Max at the wide end, max at the tele end. The minimum apertures are unspecified.
>> Anonymous
>>240111
I think I get it now. So at 300mm focal length, the biggest diameter the aperture could be open would be around 50mm, right? And the smallest diameter the aperture could be open is unspecified, right?

Thank you so much. ;_;
>> ac !!VPzQAxYPAMA
>>240115
Exactly
>> Anonymous
>>240118
It all makes sense now. Thank you! <3