f-stop: lens versus camera puzzlement

Superape

Superape

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OK, let me preface this by saying that I totally get what an f-stop is, and how depth of field works.

What gets my head spinning is why I can set my camera (which is supposed to be really clever and knows more about these things than I do) so that it has an f-stop beyond what the lens will do. Or does it? Who's telling who what do do?

What gives?

Ta :)
 
A lens will only have a certain range of apertures, for example F4 - F22, you can set it to any (in stops) of the range inbetween, but it wouldn't go above F22 or below F4 :)
 
The camera wont let you select an aperture the lens is not capable of using, so i'm not sure how you did, or maybe you are confused about what apertures it can use at which focal lengths.

(the variable aperture range of a zoom lens could be a source of confusion)
 
If you have a camera that is allowing you to select apertures beyond what the atteached lens is capable of delivering, I'd be interested to know the make and model of the camera so that I can avoid it. ;)
 
Scarecrow said:
If you have a camera that is allowing you to select apertures beyond what the atteached lens is capable of delivering, I'd be interested to know the make and model of the camera so that I can avoid it. ;)
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On the other side of the coin, if it turns an f4 into an f2.8 then i want one. :lol:
 
Blue Eagle said:
The camera wont let you select an aperture the lens is not capable of using, so i'm not sure how you did, or maybe you are confused about what apertures it can use at which focal lengths.

(the variable aperture range of a zoom lens could be a source of confusion)
Click to expand...

Probably this :D

I have two lenses that were part of a 450D bundle - the standard kit lens (18-55) and a Tamron 70-300mm f4/5.6 DI LD Macro.

Enlighten a noob!
 
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I was using the Tamron and was trying to set the camera at F16 (as an experiment) and it quite happily let me do that..

I usually shoot in full manual mode, if that helps.
 
Superape said:
I was using the Tamron and was trying to set the camera at F16 (as an experiment) and it quite happily let me do that..

I usually shoot in full manual mode, if that helps.
Click to expand...

That lens will go all the way to f32
 
According to the specifications, the mnimum aperture is F32 - 45...

SpecificationsModel A005
Lens Construction (Groups/Elements) 12/17
Angle of View 34°21'-8°15'
Diaphragm Blade Number 9
Minimum Aperture F/32-45
 
Curse my slow copy/paste skills :D
 
Superape said:
I was using the Tamron and was trying to set the camera at F16 (as an experiment) and it quite happily let me do that..

I usually shoot in full manual mode, if that helps.
Click to expand...

So why do you think f16 is out of range?
 
Dogfish_magnet said:
That lens will go all the way to f32
Click to expand...

Aaaah, so what I'm doing is misunderstanding what the lens can do!

I was looking at the numbers on the lens and in its product description and assuming that was the limit of its operation. I had noticed that the kit lens and the Tamron will go to different lower f-stops.

The other thing that was confusing me while trying the shot was that it was still giving a relatively narrow depth of field - is that because of the 70-300-ness of the lens? Am I better switching to manual focus for long exposure landscape shots? Had I not gone far enough in narrowing the aperture?

Thanks for the help so far :)
 
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You say that you are OK with f stops & apertures so you should know that the smaller the f stop number the larger the size of the aperture.

With a zoom lens, such as the Tamron 70-300mm f4/5.6, the f stop figures quoted are the largest aperture that the lens has. It can open up as far as f4 at 70mm but only as far as f5.6 at 300mm.
It will however close down (or stop down) to a very small aperture.

Some zoom lenses have a constant aperture at all focal lengths although they are expensive.

In the good old days we used to call lenses with constant apertures zoom lenses and ones where the aperture changed variable focal length lenses.
 
Thank you all for your help, it's cleared up a few mysteries.

When I said I understood DOF & F-stop, it was as far as 'small f-stop = wider aperture = faster shutter = less in focus' & vice-versa. The nitty gritty of how lens & camera & focal length interact with each other was obviously the sticking point (and how lenses are described) & something I obviously need to read more about!

Thanks for the link too :)
 
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