what are the advantages and disadvantages to having a zoom camera lens with a fixed f stop?

Question

I currently have a canon digital rebel xt and am searching for a new set of ZOOM lenses and i was wondering what the advantages and disadvantages of having a fixed f stop were, any information would be helpful thanks!

Answer 1

I'm not totally sure what you mean by "fixed f-stop," but I will assume that you mean a "constant aperture" zoom. Such a lens would be specified as the Canon Zoom Super Wide Angle EF-S 17-55mm f/2.8 IS USM Autofocus Lens ($1,000), rather than the Canon Zoom Super Wide Angle EF-S 17-85mm f/4-5.6 IS USM Autofocus Lens ($500).

The main advantage is that you do not "lose light" as you zoom out. With the cheaper lens above, you see that the maximum aperture at full zoom is f/5.6. This is the reason why point and shoot cameras have such terrible flash range as you zoom in closer, but you don't need to worry about that so much with your Rebel XT. You can get nicer depth-of-field effects if you don't automatically stop down just by zooming.

The disadvantage is that the glass is bigger, so the lens costs more money - lots of it - and the lens is heavier. You will also have to buy larger diameter filters, which cost more money.

Personally, my favorite lens is my 17-55mm f/2.8 lens. I'm a Nikon guy, so my lens is not even image stablized like the Canon lens, although I don't think you need too much help at "only" 55 mm.

Answer 2

Constant f/2.8 zooms or (cheaper) constant f/4 zooms offer relatively fast shutter times throughout the zoom range. This is a very good thing in low light situations.
Fast zooms are generally also top of the line lenses in terms of image quality. Most of them will produce great pictures wide open, whereas consumer grade lenses should be stopped down to f/5.6 or f/8 for decent results.
The large aperture opening also offers shallow depth of field when you need it.
And finally, most of Canon's fast zooms are 'L' lenses, which offer fantastic build quality.
In short, these are professional grade lenses... with pro prices to match.

Answer 3

nicely, the digital camera would not care. Will it extra wholesome? specific! Will it paintings nicely with the digital camera? easily! Will it extra wholesome your purpose? i don't know, considering which you probably did no longer let us know what you desire to shoot with it. oftentimes however, this is an rather good 2nd lens for this sort of digital camera. this is between the Nikon's maximum time-honored selections between funds minded shooters, who want the attain of 200mm. for many persons this is not ok for the only lens, because of the fact this is a telephoto. For some uncommon situations, once you purchase the whole gadget in specific for the telephoto paintings, it ought to fare, yet for ninety 9% of human beings, this is huge area of 55mm can't cut back it. At 55mm you will in all probability have the skill to get a single face or a single individual right into a shot once you're the two interior a similar room (in keeping with room length). this is good for products extra suitable away, or small issues. to have the skill to shoot oftentimes in close variety, you will additionally want the time-honored equipment 18-55mm lens. Then the two will make an rather good starter set to cover an rather good variety and to no longer destroy your funds, like the very costly 18-200mm lens, it quite is large yet costly. LEM.