Difference between 18-70mm and 18-250mm lens, apart from the obvious?

[iSamurai]

I'm wondering what's the difference between a standard lens and a lens that can zoom from close to far...

But let's not discuss the obvious: zoom, price, weight.

Is there any picture quality difference between the lenses? Will the 18-250mm lens have slightly "dark edges" and straight lines distorted (like bulbing/curving) when not zoomed afar?

 

[gatepc]

It depends on the lens's, in general the more focal range a lens covers the more likely it is to have lower IQ and so forth.

 

[HBOC]

well, apertures will vary as well, at the same focal length. Let's say the said 18-70mm is a 2.8 fixed through the whole range, and the 18-250 is probably atleast a 3.5-5.6, which varies through different focal lengths.

 

[clams]

One thing about all-around zooms like the 18-250mm is the fact that it is not completely sharp throughout the entire range. This is because it is very difficult to design a lens to be able to adapt to so many different focal lengths and remain sharp. Usually this problem would occur at the highest focal lengths of the lens.

 

[HBOC]

One thing about all-around zooms like the 18-250mm is the fact that it is not completely sharp throughout the entire range. This is because it is very difficult to design a lens to be able to adapt to so many different focal lengths and remain sharp. Usually this problem would occur at the highest focal lengths of the lens.

well, this is true generally of consumer grade lenses. Most manufacturers' offer higher end glass (Canon L) that will have close to the same focal range, that will be much sharper than their consumer grade counterparts..

 

[cube]

well, apertures will vary as well, at the same focal length. Let's say the said 18-70mm is a 2.8 fixed through the whole range, and the 18-250 is probably atleast a 3.5-5.6, which varies through different focal lengths.

Just for the record, there is no 18-70 or whereabouts fixed f/2.8

 

[HBOC]

Just for the record, there is no 18-70 or whereabouts fixed f/2.8

Well, I know that is not a focal length in Canons' lineup. It sounds like a Nikon or something... I know that Canon makes a 17-55 2.8 and a 24-70 2.8.

Lets just say that the 18-70 is 3.5-5.6 and the 18-200 (whatever the other example was) is f3.5-6.3 (most likely would be f3.5-5.6) At the same focal length on both lenses, I am assuming that the longer zoom would be a bit slower wide open.

Currently, i dont really have any lenses that overlap focal lengths to test this with. i have an 18-55 and a 55-250.. in this case, the 55-250 is faster wide open than the 18-55..

 

[cube]

Well, I know that is not a focal length in Canons' lineup. It sounds like a Nikon or something... I know that Canon makes a 17-55 2.8 and a 24-70 2.8.

Lets just say that the 18-70 is 3.5-5.6 and the 18-200 (whatever the other example was) is f3.5-6.3 (most likely would be f3.5-5.6) At the same focal length on both lenses, I am assuming that the longer zoom would be a bit slower wide open.

Currently, i dont really have any lenses that overlap focal lengths to test this with. i have an 18-55 and a 55-250.. in this case, the 55-250 is faster wide open than the 18-55..

Those canon lenses are not whereabouts of a 18-70. A 17-70 would be, as well as a 16-85 (but not the reverse).

It's more likely that a 18-200 will end in 6.3. Only Nikon and Canon offer 5.6

If you compare 18-70 and a 18-200 both f3.5-5.6, there's a good chance the 18-200 will be faster at 70mm.

 

[clams]

well, this is true generally of consumer grade lenses. Most manufacturers' offer higher end glass (Canon L) that will have close to the same focal range, that will be much sharper than their consumer grade counterparts..

Definitely true. But if you look carefully. I don't think there are any Ls that cover a focal range as wide as 18-250mm. For good reason too.

 

[HBOC]

Definitely true. But if you look carefully. I don't think there are any Ls that cover a focal range as wide as 18-250mm. For good reason too.

they make a 28-300L, but that is the widest they have (to my knowledge) with this much variation in focal length..

 

[clams]

they make a 28-300L, but that is the widest they have (to my knowledge) with this much variation in focal length..

Oh true. I forgot about that one. I hear good things about it. Then again, it is a solid 3.7lbs of glass

 

[El Cabong]

I'm wondering what's the difference between a standard lens and a lens that can zoom from close to far...

But let's not discuss the obvious: zoom, price, weight.

Is there any picture quality difference between the lenses? Will the 18-250mm lens have slightly "dark edges" and straight lines distorted (like bulbing/curving) when not zoomed afar?

Listing brands, at the very least the brand of your camera, is useful.

In any case, here are links to some reviews that pick out the less-than-obvious features of 18-70 and 18-250mm lenses:

Nikon 18-70mm
Photozone
SLRGear

Sony 18-70mm
DPReview
Photozone
SLRGear

Tamron 18-250mm
Photozone
SLRGear

Sigma 18-250mm
SLRGear

In a nutshell, the Nikkor is a solid performer, the Sony is not (corner softness and high CA throughout range), the Tamron superzoom is surprisingly good considering its range but still has the limits of a superzoom, and the Sigma's sharpness suffers significantly in its telephoto focal lengths.

Compared to the Nikkor (not so much the Sony, though it's still better optically than the superzooms), you'll compromise focus speed and max aperture (i.e. max at 70mm on the Nikkor is f/4.5 whereas it's about f/5 for the others) when using the superzooms, not to mention optical quality (sharpness, CAs, distortion, etc). Also, the superzooms are prone to lens creep.

In general, the superzooms trade off optical quality and aperture for their wide range, although there isn't a *huge* difference in quality until you compare them to primes or f/2.8 lenses.

Note that Canon does not make lenses in these specific ranges.