Question about lenses

[Funboy]

Hi everyone,

I’m in the middle of deciding what camera and lenses to get as a hobbiest. I understand that there are zoom lenses and prime lenses, but I don’t understand lenses that have variable apertures. My friend has a 20mm F2 lense that has adjustable aperture on it. Is this just a prime lens that allows for manual aperture adjustment?

 

[petrochemist]

Variable aperture is usually used to describe zoom lenses that have different maximum apertures at different focal lengths.

If the actual opening remains the same (as seen from the front of the lens) the lens might be f4 at the wide end but only f5.6 when zoomed in.
One on my 'lenses' doesn't have an aperture control at all, it's a slow f16 at 1000mm and zooms to a quite useless 4000mm f64

 

[Rickbb]

The only lens that don’t have variable F-stops are cell phone cameras, old point and shoots like Kodak Instamatics, Polaroids, etc.

Almost all variable F-stop lens can be automatically or manually adjusted, depending on the camera body, model, price, etc.

 

[wfooshee]

When a lens is marked as f:3.5-f:5.6, that means it's maximum aperture is f:3.5 at its shortest zoom setting and f:5.6 at its longest. That's what "variable aperture" means, and it only exists on zoom lenses. Not all zoom lenses are variable aperture. If the lens is pricey enough, the maximum aperture applies no matter what focal length is used, for example a 70-200 f:2.8 will have f:2.8 as its maximum aperture at any focal length.

The term variable aperture does not apply to prime (fixed-focal-length) lenses, and "variable aperture" does not mean "adjustable aperture," as the aperture is always adjustable except as stated above, for a really cheap point-and-shoot that actually has no adjustments or settings.

 

[RAZKY]

Hi everyone,

I’m in the middle of deciding what camera and lenses to get as a hobbiest. I understand that there are zoom lenses and prime lenses, but I don’t understand lenses that have variable apertures. My friend has a 20mm F2 lense that has adjustable aperture on it. Is this just a prime lens that allows for manual aperture adjustment?

Your friend's lens is merely a prime lens with adjustable apertures. It most likely has an automatic diaphragm, meaning it's wide open for focusing and composing and the camera closes it down automatically when making the exposure. With a manual diaphragm lens, you have to manually set the desired aperture - the camera does not control it.
A variable aperture lens is a zoom whose aperture values change when you change focal lengths. The better class of zooms, where the aperture value remains constant at any focal length setting, are properly called constant-aperture zoom lenses.
Try Googling "Automatic vs. Manual Diaphragm Lenses" and "Variable-Aperture vs. Constant-Aperture Zoom Lenses" for a better explanation.

 

[Funboy]

Your friend's lens is merely a prime lens with adjustable apertures. It most likely has an automatic diaphragm, meaning it's wide open for focusing and composing and the camera closes it down automatically when making the exposure. With a manual diaphragm lens, you have to manually set the desired aperture - the camera does not control it.
A variable aperture lens is a zoom whose aperture values change when you change focal lengths. The better class of zooms, where the aperture value remains constant at any focal length setting, are properly called constant-aperture zoom lenses.
Try Googling "Automatic vs. Manual Diaphragm Lenses" and "Variable-Aperture vs. Constant-Aperture Zoom Lenses" for a better explanation.

Thank you so much, this explained exactly what I was confused about

 

[petrochemist]

The only lens that don’t have variable F-stops are cell phone cameras, old point and shoots like Kodak Instamatics, Polaroids, etc.

Not true, unless you use 'etc.' to just mean any other lens without an iris.
Look at Catadioptric (mirror) lenses, these hardly ever have an adjustable aperture.
Then there are telescopes, microscopes, projector lenses, all of which get used for photography...

Despite being able to adjust the aperture to smaller values many zooms are called constant aperture types if the fastest f-number remains the same throughout the zoom range

 

[RAZKY]

Thank you so much, this explained exactly what I was confused about

Thank you for the feed-back!