focal length and lenses

[ret]

I am interested in knowing abt the advantages and disadvantages of lenses with a fixed focal length [for e.g. f2.0] and with a range [for e.g. f2.8-f4.0]

the question popped up after looking at some of lenses, below:


http://www.four-thirds.org/en/products/img/img_sta14_35_01.gif


http://www.four-thirds.org/en/products/img/img_sta12_60_01.gif


source: http://www.four-thirds.org/en/products/standard.html

[Travis]

What you are talking about is the aperture rating of the lens and has nothing to do with focal length.

An aperture that remains at 2.8 throughout the zoom range is more advantageous to you. However, you do pay a price for it. 2.8 zooms are generally pro glass and companies designing these lenses often include there other fine elements of lens craftsmanship.

Variable aperture lenses stop down when zoom out (ie to f5) these allows less light to enter through the lens and forces you to compensate with shutter speed or ISO.

[ret]

thanks for the post @ travis

so can we say that a lens with a fixed aperture rating is usually better than the one with variable aperture rating

[tirediron]

thanks for the post @ travis

so can we say that a lens with a fixed aperture rating is usually better than the one with variable aperture rating

Not always; it will generally be more expensive because of the optical 'tricks' required to produce a fixed aperture in a zoom lens, but a 'Brand X' fixer aperture zoom may well be of poorer optical quality than it's name brand variable aperture cousin.

In the case of the example in your post however, yes, it would probably be safe to say that the fixed aperture version is a better lens overall than the variable one.

[scorpio_e]

Variable aperature do not always play nice with TTL flashes either.

[Marko]

Not always; it will generally be more expensive because of the optical 'tricks' required to produce a fixed aperture in a zoom lens, but a 'Brand X' fixer aperture zoom may well be of poorer optical quality than it's name brand variable aperture cousin.

In the case of the example in your post however, yes, it would probably be safe to say that the fixed aperture version is a better lens overall than the variable one.

Although what tirediron says is true, you'll notice that most pros (pros that make the majority of their income through photography) prefer fixed aperture lenses.

[tegan]

Yes, I must admit that I prefer 2.8 fixed lenses and have seldom bought anything slower. However when you get to 300mm and beyond size and weight of the lens becomes important for getting the shot or not. When it comes to hand holding a 4.5 versus needing a tripod for the weight of a 2.8, then the hand held 4.5 lens wins out for me.

Tegan

[PKMax]

although it was spam that brought this thread to my attention, I'm kinda glad it did heh. I wasn't aware of the fixed aperture zoom lenses.. it makes sense and now understand why them "pro" lenses are so frigging big lol.

I'd notice my lenses stopped down when zoomed in, and hadn't actually thought about it other than thinking, wow, that's annoying.. I'd not actually considered the fact that it would lose light as it was zoomed in more.