[figmental1978]

I shoot a lot in low light so yes, f/4 is unusable to me, even 2.8 can struggle in certain situations.

@ Digitalis...nice to see and Adelaide boy here.

[nobbsie]

It depends on what and how you shoot. If you shoot landscapes on a tripod then 1 stop isn't likely to make a difference but if you shoot moderate to low-light sports or anything else with lots of action 1 stop can easily be all the difference between getting the shot and packing up because you've run out of light.

In general a lens will be produce better sharpness and contrast stopped down. Fast lenses are usually still around f/2-2.8 when stopped down compared to consumer zooms which will be at f/8ish.

[Pentaxor]

a faster lens enables the use of faster shutter speeds, SR cannot compensate for subject motion but it can compensate for your motion.. also a faster lens allows you to stop down more an increase resolution a f/1.4 lens and a f/2 lens when both of them are stopped down to f/2.8 the f/1.4 lens is most likely to be superior in image quality.

or faster aperture speed is very useful because it negates the use of boosting up the ISO which could have adverse affect on the IQ.

[little laker]

I do a fair amount of shooting, with fast lenses almost wide open, just for the effect. Not for the speed.
I could never get the DOF I demand at f4.

On the other hand, a good friend of mine whom happens to be a good street photographer gets the job done with consumer grade lenses.
The way she appears to look at it, her pack is heavy enough. So why would she want to add heaver lenses.

[Arpe]

When I'm already shooting sport under lights at ISO4500, f2.8 and 1/350, then hell yes the 1 stop makes a difference.

[Digitalis]

or faster aperture speed is very useful because it negates the use of boosting up the ISO which could have adverse affect on the IQ.

that's why I love my Pentax K 50mm f/1.2

@ Digitalis...nice to see and Adelaide boy here.

not that adelaide has been treating me so well lately...

[Jodokast96]

I could be wrong, but the consumer 70-300 lenses are f/4 at 200mm.

[Spock]

I could be wrong, but the consumer 70-300 lenses are f/4 at 200mm.

Well you are half right. Most are F4 at the short end eg. 70mm, but would have a progressively smaller aperture as they were zoomed. Most are 5.6 or worse at the long end.

[Rondec]

It is definitely worth it to have a faster lens -- to a point. I shoot a lot at f2.8 -- great for isolating subjects from the background, great for cutting shutter speed in half. As mentioned above, SR is only good for camera shake -- it doesn't help with subject movement.

I said to a point, because I find it difficult to shoot at wider than f2.8 and keep my subject in good focus. I think the FA 50 is reasonably sharp, but at f2.0 the depth of field is so narrow that I feel like my photos are soft. Probably would be better with a sharper lens, but I tend to stay at f2.8.

[flash1100]

I look at it this way. When one buys a 2.8 or even f4 contant aperture lens you are not only getting an optically faster lens but in all likelihood (and particularly with longer zooms) you are also getting an optically superior lens. So even if you are using your lens at f5.6 @ 300mm comparing a consumer zoom say DA55-300 to a constant aperture zoom think Sigma 100-300 f4 for example the Sigma will produce a superior image.

[Edvinas]

Well, lenses usually are not very sharp wide open.

f/2.8 lens at f/4 will already be stopped down one stop and most likely will be much sharper than some f/4 lens wide open

Also shake reduction helps only for static scenes, for moving objects SR won't help.

[dadipentak]

There's also an advantage to fast lenses in terms of focusing, isn't there? That is, with A & AF lenses, focusing (AF or MF) is done with the aperture wide open and the lens stops down to the selected aperture only when the shutter is triggered. Thus, there is some value to having a f/2.8 lens even where--as with my [cough, cough] Sigma 70-200mm]--resolution is marginal wide open.

Have I got that right?

[Pentaxor]

It is definitely worth it to have a faster lens -- to a point. I shoot a lot at f2.8 -- great for isolating subjects from the background, great for cutting shutter speed in half. As mentioned above, SR is only good for camera shake -- it doesn't help with subject movement.

I said to a point, because I find it difficult to shoot at wider than f2.8 and keep my subject in good focus. I think the FA 50 is reasonably sharp, but at f2.0 the depth of field is so narrow that I feel like my photos are soft. Probably would be better with a sharper lens, but I tend to stay at f2.8.

the 1.7 would be your best bet.

[melander]

I would never consider buying a lens slower than 2.8. (oh well, i got the voigtlander 180/4 but thats a ok ^^ )
I shoot alot of low light, concerts etc and my da*55 works perfectly at 1.7.

[MikePerham]

In this day and age of camera body SR, does one stop faster really make such a difference? I mean is it really worth paying much more $$$ to get a F2.8 lens over a F4?

Discuss.

Well, there is more to the issue than just the aperture. The faster lens is also the top of the line in terms of build and optical quality. In the case of Pentax, they make some really good mid range glass (ie: the 17-70 or 16-45 constant f4 lenses) that optically may equal, or come close to the top of the line f2.8 zooms such as the DA* series in IQ but are still a notch below overall.

For my money, I would go with the top of the line because you buy cameras but invest in lenses.