Silly Lens Question Time

[Dylanlewis2000]

But... with all the super Zooms on the market having lenses ranging from 28-500mm and SLR lenses from Tamron that have a 18-270 range, why is it that the super zooms start at f2.8 whereas the superzooms start at f3.5.

Is it something to do with quality?

 

[acs]

Size, weight and cost of fixed aperture lenses would be some, here's a 200-500/2.8

http://www.sigma-imaging-uk.com/lenses/telezoom/200-500mm.htm

Dimensions Diameter 236.5mm X Length 726mm
Weight 15,700g
SRP £23,999.99

Even you you made them variable aperture you'd still hit these problems to some degree. Though there have been a number of 2.8-4 lenses.

 

[towershot]

Size, weight and cost of fixed aperture lenses would be some, here's a 200-500/2.8

http://www.sigma-imaging-uk.com/lenses/telezoom/200-500mm.htm

Dimensions Diameter 236.5mm X Length 726mm
Weight 15,700g
SRP £23,999.99

Even you you made them variable aperture you'd still hit these problems to some degree. Though there have been a number of 2.8-4 lenses.

Got one on order from W Express.........................No date yet...........

 

[Dylanlewis2000]

yeah but what im saying is that a super zoom has a small lens and small element on the front end, and at 500mm they are f5.6 why are SLR lenses much more

 

[susie]

It is quality plus if the maximum aperture is f5.6 they will let less light in than if they are at f2.8. If you need to use the lens in dark places without flash (perhaps a church for a wedding or in my case an indoor arena with bad light) f5.6 will get you a very dark picture that is prety much unusable, whereas f2.8 will do the job. The slower f5.6 lens will have a smaller diameter as it does notneed to get as much light and will need less glass inside so will be a lot cheaper and lighter.
The f/3.5 will only apply to the wide end of the lens, at the long end you will not get less than f5.6
It will still be a good lens for outdoors or if you can use flash - it all depends on your use, if you are always at for example f/8 to f/16 you are not going to get full use of the more expensive lens.
If you have a friend who has one at f/2.8 or even f/4 that you can borrow give one a try against your normal lens and see the difference, just beware as it could be detrimental to your bank balance!!

 

[The Matt]

Are you talking about the fixed lens bridge cameras?

The reason they can have such a massive zoom range is because of their small sensor size. The actual focal length of the lens will be something like 5mm to probably no more than 70mm and the massive multiplication factor makes it equivalent to 28-500. Since your f number is relative to you actual focal length (i.e. f2.8 on a 50mm lens is a much larger hole than 2.8 on a 28mm lens) the superzoom bridge cameras still have a pretty tiny aperture because it's relative to a ~5mm lens. For the dslr zooms to be f2.8 this would involve much more glass and get really costly.

I'm sure there's also issues with image quality but I don't know anything about these.

 

[feeb]

well simply the smaller the sensor the less quality of image - which is why these cameras that bleat on about Pixels are silly, it doesnt matter if your phone camera has 14MP its still rubbish because they are fitting loads of pixels onto something half the size of a stamp!

Sensor size, and quailty, is far more important

 

[HoppyUK]

But... with all the super Zooms on the market having lenses ranging from 28-500mm and SLR lenses from Tamron that have a 18-270 range, why is it that the super zooms start at f2.8 whereas the superzooms start at f3.5.

Is it something to do with quality?

You are not comparing like with like - that is 28-500mm eqivalent. And come to that, 18-27mm is approx 28-430mm equivalent, depending on format. That is to say, equivalent to those focal lengths on full frame format.

Compacts can get that range because of their tiny sensors. But that is where the benefits end. Yes, it's a quality issue.