What would be the difference between a, say, 85mm lens and 70-300mm lens set at 85mm?

[gauz09]

Hi,

I am completely new to SLR/DSLR world and have no experience at all in real photography. I just had baby and, like few of the people do, would like to make some good pictures of my baby. So bought a Nikon D7000 and have been reading lot of books on of exposure, aperture, shutter, lighting, portrait, etc. Also trying to apply what I read. More often than not it doesn't work but I am learning.

However, I have a basic question. Lot of books/articles that I have read talks about a single focal length lens of 50mm or 85mm for portrait or closeup photography. I have a 70-300mm lens with AF-S, VR. Would highly appreciate if somebody can help me understand how is a single focal length 85mm lens different than a 70-300mm lens that is set at 85mm. Will there be a difference when making photographs with both set at 85mm?

Thanks much for your kind help.


- Gauzy

 

[brush]

The lenses with a single focal length are called prime lenses. A prime lens gives you a sharper image because it doesn't need all the extra elements & ability to zoom through a range of focal lengths, it's sort of the "do one thing, do it well" mentality. Also, prime lenses usually have much lower apertures than zoom lenses. Your 70-300 is probably like a f4-5.6 variable aperture but a prime 85 may be as wide as f1.8 or even f1.4 which lets tons more light in and gives you more control over the depth of field. The portraits you see with the subject in crisp focus & the background blurred with a nice bokeh are usually shot with a prime lens at a wide open aperture like 1.4. You can't do that with a zoom lens.

 

[naptime]

a few things i read:

prime lenses:
faster
smaller
sometimes better quality glass
less expensive

zoom lenses:
slower
more convenient
fewer lenses changes


here is a great read on comparing the two types.... Zoom vs. Fixed Focal Length (Prime) Lenses - Which to choose?

 

[gauz09]

The lenses with a single focal length are called prime lenses. A prime lens gives you a sharper image because it doesn't need all the extra elements & ability to zoom through a range of focal lengths, it's sort of the "do one thing, do it well" mentality. Also, prime lenses usually have much lower apertures than zoom lenses. Your 70-300 is probably like a f4-5.6 variable aperture but a prime 85 may be as wide as f1.8 or even f1.4 which lets tons more light in and gives you more control over the depth of field. The portraits you see with the subject in crisp focus & the background blurred with a nice bokeh are usually shot with a prime lens at a wide open aperture like 1.4. You can't do that with a zoom lens.

Thanks brush, appreciated your quick response.

Sorry, but have another question now. I read in one of the article, kind of an interview with a photographer who is into micro photography. She said she likes to use 85mm for most of the time like while taking closeups of flowers, bugs, etc.

I was wondering why doesn't she use a 50mm than 85mm as that would give her more close composition which she could achieve since her 85mm is not a zoom lens.

I am sorry if that's a stupid question but I want to understand things correctly and the only way to get things right is this forum and all you gurus.

Thanks.

 

[gauz09]

a few things i read:

prime lenses:
faster
smaller
sometimes better quality glass
less expensive

zoom lenses:
slower
more convenient
fewer lenses changes

here is a great read on comparing the two types.... Zoom vs. Fixed Focal Length (Prime) Lenses - Which to choose?

Thanks naptime for replying quickly and providing the link. I am going to that link now.