Why are fixed aperture lens so expensive?

dinneenp

Hi,
(no such thing as a stupid question)...
but why are fixed aperture lens so expensive? Do they cost a lot more to produce, need special materials etc?
I'm sure there's an obvious answer.
cheers,
Pa.

magicbastarder

do you mean fixed focal length (i.e. primes?)
fixed aperture would imply no aperture control.

assuming so, i'd say it's partly down to volume - there's a lot more standard zooms made than prime lenses.

NothingMan

I reckon he means the likes of the 24-105 f4. No matter what focal length your max aperture doesn't change.

I think it's so expensive because the aperture value is the focal length divided by the number ie, 2.8, 4 etc... so basically the aperture can stay the same diameter along different focal lengths but the f number changes, because it's a ratio. To keep the f number the same requires some technical wizardry to allow the f value to stay the same across all focal lengths, hence making it more difficult, rare and hence more expensive.

I could be way off, but that's how I figured it.

magicbastarder

yeah, that makes more sense than how i read it.

dinneenp

NothingMan wrote: »

I reckon he means the likes of the 24-105 f4. No matter what focal length your max aperture doesn't change.

That's what I mean.
I know it takes some 'wizardy' but just wondering what and why it makes it so expensive....(and I'd love one)

magicbastarder

as NothingMan mentioned, more technically complex. which drives up the price, and as a result, drives down the demand - so lower volumes drive up the price too, as a result of fewer economies of scale.

Morrisseeee

I'd imagine they're more costly to produce/manufacture, they're larger, and the quality of the material (especially glass) is better (bit like you were presuming in your OP).

pixbyjohn

To have a larger aperture you have a bigger lenses. So that means more glass and internal parts. Those lenses also, typically are made with better and more precise optics which all raises the price.

the_monkey

Speaking of prices of lenses, what do you think the production costs for Canon are of a 400mm f2.8 L IS ?? compared to a 70-200 f2.8L IS

the 400mm is about €5,000-€6,000 ... the 70-200 is around €1300 ..

you think the production costs for the 400mm are 4 times more expensive ?

Ciaran500

the_monkey wrote: »

you think the production costs for the 400mm are 4 times more expensive ?

Lens quality glass is extremely expensive and the 400mm has alot of glass in it.

EDIT: 400mm is ~5.5kg, the 70-200mm is ~1.5kg

Slidinginfinity

the_monkey wrote: »

Speaking of prices of lenses, what do you think the production costs for Canon are of a 400mm f2.8 L IS ?? compared to a 70-200 f2.8L IS

the 400mm is about €5,000-€6,000 ... the 70-200 is around €1300 ..

you think the production costs for the 400mm are 4 times more expensive ?

Ciaran500 wrote: »

Lens quality glass is extremely expensive and the 400mm has alot of glass in it.

That plus the 400mm is in less demand.

pixbyjohn

I wouldn't think that but its all about market forces. As long as people pay huge prices there will always be huge prices asked.

pixbyjohn

the_monkey wrote: »

Speaking of prices of lenses, what do you think the production costs for Canon are of a 400mm f2.8 L IS ?? compared to a 70-200 f2.8L IS

the 400mm is about €5,000-€6,000 ... the 70-200 is around €1300 ..

you think the production costs for the 400mm are 4 times more expensive ?

Its all about market forces, I don't think the cost of manufacture really comes into it.

magicbastarder

the_monkey wrote: »

the 400mm is about €5,000-€6,000 ... the 70-200 is around €1300 ..

you think the production costs for the 400mm are 4 times more expensive ?

just in terms of the amount of glass - the surface area of glass required for a 2.8 aperture in a 400mm piece of glass is four times the surface area required in a 200mm lens. that doesn't take glass thickness into account.

kelly1

I believe the term is "constant aperture"

Barname

The Glass baby, the glass

Burnt

To have a constant f ratio through out the range of focal lenghts,
your clear aperature has to effectively get bigger as you zoom.

This means bigger (more material) complicated (more time)optics.
The further you move from the optic axis the harder it is to correct
the aberations in the system, this is the real source of expense.

f/4 at 50mm is a clear aperature of diameter 12.5mm

f/4 at 200mm is a clear aperature of diameter 50mm

which works out as an area X16 bigger to correct aberration across