lens question

[AdamsCanon]

I noticed in an amateur p magazine that someone had used a 24 - 70 lens on one picture and on another used something like a 17 - 100. Either way the first lens fit in the focal length of the second lens. what can the smaller focal length lens acheive that the other cant when it is in its range? just wonderd why someone would use that lens if the other one can get the same shot but with more choice of focal length

 

[Russ77]

I would say the focal length range of the lenses is irrelevant here, what would be more important is the performance of each lens, i.e. IQ and maximum aperture.

Most people will choose a lens that fits their requirements/budget.

For instance, a portrait photographer using a full frame body might choose an 85mm prime whereas a landscape photographer using a crop body would probably go for a zoom lens with a range somewhere between 10mm-100mm.

Using a longer focal length flattens perspective so that could also be a factor to consider.

 

[Alastair]

A Volvo estate and a Ferrari will both do 30mph, but only one will carry a piano while doing it.

There's a lot more than just focal length when it comes to lenses..

 

[Craft]

I would agree aperture would be a consideration, as Russ hints at this could allow more flexibility with regards to depth of field.

 

[Tricky01]

A Volvo estate and a Ferrari will both do 30mph, but only one will carry a piano while doing it.

There's a lot more than just focal length when it comes to lenses..

A brilliant post; the point being different things do different things.



In answer to the OP, this was something that confused me at the beginning of my DSLR journey - why buy a 70-200 lens when I can have a 70-300 or a 18-200?

The answer is that typically the trade off in increased focal range is a decrease in optical quality. A lens designer who is making a lens for only 50mm length (a fixed focal length is referred to as a prime lens) can invest all their time in designing and testing the optical performance at one focal length.

If they then were asked to design a 50-51mm zoom lens, then that's two focal lengths to design and test to. then designing an 18-200, there are many things to test and consider which pull resource away from optimising IQ.

As mentioned above, another consideration is that the largest aperture (smallest f number) is likely to be smaller (larger f number) when the focal range is greater; which means it isn't very good in low light situations amongst other disadvantages (but aperture is another topic completely, best saved for another day!)

The 17-100 lens was likely used because the situation either made changing lenses difficult or they couldn't carry two or more lenses to cover the range they wanted.

 

[Oggy]

A Volvo estate and a Ferrari will both do 30mph, but only one will carry a piano while doing it.

There's a lot more than just focal length when it comes to lenses..

Take the legs off, lay them between the turbos and get a Halfords universal universal roof rack for the rest.

Simples.

 

[AdamsCanon]

A brilliant post; the point being different things do different things.



In answer to the OP, this was something that confused me at the beginning of my DSLR journey - why buy a 70-200 lens when I can have a 70-300 or a 18-200?

The answer is that typically the trade off in increased focal range is a decrease in optical quality. A lens designer who is making a lens for only 50mm length (a fixed focal length is referred to as a prime lens) can invest all their time in designing and testing the optical performance at one focal length.

If they then were asked to design a 50-51mm zoom lens, then that's two focal lengths to design and test to. then designing an 18-200, there are many things to test and consider which pull resource away from optimising IQ.

As mentioned above, another consideration is that the largest aperture (smallest f number) is likely to be smaller (larger f number) when the focal range is greater; which means it isn't very good in low light situations amongst other disadvantages (but aperture is another topic completely, best saved for another day!)

The 17-100 lens was likely used because the situation either made changing lenses difficult or they couldn't carry two or more lenses to cover the range they wanted.

ahh i see! thanks for explaining. learn something new everyday