Why choose a f2.8 lens over f4?

[rhino123]

Excuse me, but it IS common knowledge, so why should you suggest that I don't know what it is?
Isn't that presumptuous on your part?

I'm sorry, it is not common knowledge that bokeh or its quality is determine by whether you are using a prime or a zoom.

http://en.wikipedia.org/wiki/Bokeh
http://www.kenrockwell.com/tech/bokeh.htm

The above are two references that actually explain what the heck is bokeh and none of them mentioned that zoom lens or prime lens produce excellent or better bokeh as compared to the others.

 

[Cowseye]

Let's not argue for the sake of arguing..

My logic is very simple. You can do F/4 on a F/2.8 lens while you can't do the reverse.

If the extra cost is of value to u, just take the F/2.8. The value(s) includes, but not limited to:

- thinner DoF
- more light for faster shutterspeed
- less weight (if u take the F/4 lens)
- lens element glass quality

 

[ZerocoolAstra]

I see,,, need to save more $$$ for F2.8 instead F4 with VR

You may come to dislike the weight 'penalty' that the f/2.8 zoom lens forces you to incur, compared with the variable-aperture or smaller-aperture alternative

 

[Kenneth67C]

I'm sorry, it is not common knowledge that bokeh or its quality is determine by whether you are using a prime or a zoom.

http://en.wikipedia.org/wiki/Bokeh
http://www.kenrockwell.com/tech/bokeh.htm

The above are two references that actually explain what the heck is bokeh and none of them mentioned that zoom lens or prime lens produce excellent or better bokeh as compared to the others.

You have misquoted me as I was referring to what bokeh means, not in relation to whether it was produced by a prime or a zoom.

True both (primes and zooms) can produce good bokeh, I'm not disputing that.
What I was suggesting is that given a zoom of f2.8 vs a prime of say f1.4, you would probably get better bokeh from the prime than the zoom.
I'm not saying that all primes are good for producing bokeh, but if you are looking for a typical portrait lens, say like the Sigma 85 f1.4, its bokeh would be [subjectively] better than even the best f2.8 zoom.

 

[Rashkae]

You have misquoted me as I was referring to what bokeh means, not in relation to whether it was produced by a prime or a zoom.

True both (primes and zooms) can produce good bokeh, I'm not disputing that.
What I was suggesting is that given a zoom of f2.8 vs a prime of say f1.4, you would probably get better bokeh from the prime than the zoom.
I'm not saying that all primes are good for producing bokeh, but if you are looking for a typical portrait lens, say like the Sigma 85 f1.4, its bokeh would be [subjectively] better than even the best f2.8 zoom.

Nope and Nope. Again, you are making assumptions about bokeh based on a large-aperture prime having better bokeh than an f/2.8 zoom. This is a folly and not true. You will get *more blur*/Thinner DOF shooting at larger apertures, but this does NOT in any way mean you will get better bokeh.

 

[Rashkae]

Excuse me, but it IS common knowledge, so why should you suggest that I don't know what it is?
Isn't that presumptuous on your part?

No, it is purely based on your statements. It's not presumptious, it's pretty obvious from what you said.

 

[ZerocoolAstra]

You have misquoted me as I was referring to what bokeh means, not in relation to whether it was produced by a prime or a zoom.

True both (primes and zooms) can produce good bokeh, I'm not disputing that.
What I was suggesting is that given a zoom of f2.8 vs a prime of say f1.4, you would probably get better bokeh from the prime than the zoom.
I'm not saying that all primes are good for producing bokeh, but if you are looking for a typical portrait lens, say like the Sigma 85 f1.4, its bokeh would be [subjectively] better than even the best f2.8 zoom.

This is a totally debatable point, so it is of little value to make it.
That was the whole reason for the rebuttal.
The "you probably got a bad prime lens" remark was uncalled for and served no purpose.

 

[Rashkae]

This is a totally debatable point, so it is of little value to make it.
That was the whole reason for the rebuttal.
The "you probably got a bad copy" remark was uncalled for.

Correct, ZerocoolAstra understands it perfectly. Those sort of sweeping statements with no real link are a folly.

 

[rhino123]

You have misquoted me as I was referring to what bokeh means, not in relation to whether it was produced by a prime or a zoom.

True both (primes and zooms) can produce good bokeh, I'm not disputing that.
What I was suggesting is that given a zoom of f2.8 vs a prime of say f1.4, you would probably get better bokeh from the prime than the zoom.
I'm not saying that all primes are good for producing bokeh, but if you are looking for a typical portrait lens, say like the Sigma 85 f1.4, its bokeh would be [subjectively] better than even the best f2.8 zoom.

What I am saying is that you got it wrong on what cause bokeh... technically, bokeh is caused by the aperture blades (number and shape of the blades)... and being prime or zoom had absolutely no effect on what the bokeh would look like and that is the science behind bokeh.

So now, your claim is theoretically wrong to say that in comparism prime would produce better bokeh as compared to zoom. However it might that a f1.4 lens might have better bokeh as compare to a f2.8 because of the DOF of the lens.

So in essence, a f2.8 might yield better result as compared to a f4 and that is taken into assumption that the number of blades and shape of the aperture is the same.

So if you compared a zoom to a prime, both with the same number of aperture blades and shape of the blades, and both shooting at f2.8, they might generally yield same bokeh effect.

The only difference that zoom might lose up to prime is the sharpness of the pics taken because zoom is much more complicated and had more elements, optics, etc in it, but prime do not have.

True a 85mm f1.4 will surely produce better bokeh as compared to say a zoom lens of 17-55 or 17-50mm f2.8 lens. But the science behind this was not because prime can generally do that but because of the aperture blade design and shape.

Also it is not absolute that large aperture would give you better bokeh effect.

you reckon what lens was used to produce that image... EF 70-200mm f4L IS. and yes that is a zoom lens.

 

[Rashkae]

Quite frankly, if you want to get better bokeh, go for a prime with >f2.

That was folly #1. I've used many high-end Leica, CZ prime lenses and even though they are wonderfully sharp, their bokeh is not nice.

Then you probably got a bad prime lens. :bsmilie:

Folly #2, assuming that I only tested/referred to a single prime lens.

What I was suggesting is that given a zoom of f2.8 vs a prime of say f1.4, you would probably get better bokeh from the prime than the zoom.
I'm not saying that all primes are good for producing bokeh, but if you are looking for a typical portrait lens, say like the Sigma 85 f1.4, its bokeh would be [subjectively] better than even the best f2.8 zoom.

Folly #3: Backtracking on your own statements. From the first statement, you try to say it was only a "suggestion"

And even then, the suggestion and explanation has the same incorrect sweeping statement as your first statement.

 

[ZerocoolAstra]

rhino123, your post is a bit of a red herring, coz it's focusing the attention on the aperture blades and the shape of those blades solely, but there's more to it than that.
Case in point: the Nikon DC (defocus control) lenses that can alter the way the bokeh is rendered by moving some lens elements around. I doubt that by turning a ring, the design of the aperture blades can be altered.

The point "... a 85 f/1.4 will surely produce better bokeh as compared to a 17-55/2.8 lens..." is not necessarily true. It could be debated till the cows come home.
You can do a side-by-side comparison of 2 particular lenses and compare the bokeh to see which is preferred, but to make such a statement is generalizing it too much.

 

[Rashkae]

However it might that a f1.4 lens might have better bokeh as compare to a f2.8 because of the DOF of the lens.

Then it just has thinner DOF/more blur, but NOT necessarily better bokeh.

So if you compared a zoom to a prime, both with the same number of aperture blades and shape of the blades, and both shooting at f2.8, they might generally yield same bokeh effect.

Similar maybe, but not necessarily. The lens elements and design play a big part too. If I take 2 50mm lenses, both with a 9-blade aperture, but with different lens designs, the bokeh *might* be similar, but it could also just as easily be poor. Sure, both may have nice round specular highlights, but this does not mean the highlights are nicely blurred or have the harsh, ni-sen bokeh edges. That comes down to lens design.

True a 85mm f1.4 will surely produce better bokeh as compared to say a zoom lens of 17-55 or 17-50mm f2.8 lens.

Now you are making the same mistake.

 

[rhino123]

Then it just has thinner DOF/more blur, but NOT necessarily better bokeh.



Similar maybe, but not necessarily. The lens elements and design play a big part too. If I take 2 50mm lenses, both with a 9-blade aperture, but with different lens designs, the bokeh *might* be similar, but it could also just as easily be poor. Sure, both may have nice round specular highlights, but this does not mean the highlights are nicely blurred or have the harsh, ni-sen bokeh edges. That comes down to lens design.



Now you are making the same mistake.

Ahh... understood now... thanks for the clarification. Still learning... and I am a slow learner... sorry about that. Hope I have not cause more confusion to TS.

 

[daredevil123]

Actually to be fair, bokeh is just the quality of the blur. Prime lenses do not necessarily mean it gives better bokeh, but most modern day mid priced primes gives relatively good bokeh. For example, the bokeh from the low priced canon 50/1.8 or Nikon 50/1.8 are actually less pleasing than the Nikon 70-200. The 50/1.8s gives donut bokeh while the 70-200's is much smoother.

The other point about DoF is also very dependent on other factor like focal length and subject to camera distance. At the same subject distance, a 70-200 at 200mm @f/2.8 gives a much thinner dof than a 35mm prime at f/1.8.

And IMHO a 300/2.8 gives much nicer bokeh than a 85/1.4. And a thinner dof too. So have to consider many factors. Even though one is 2.8 and the other is 1.4.

 

[GSiGuy]

imho, for this discussion to have any meaning at all, you guys may have to come up with an agreement on what "better bokeh" means... (which by itself may be argued til death)...

 

[Cowseye]

imho, for this discussion to have any meaning at all, you guys may have to come up with an agreement on what "better bokeh" means... (which by itself may be argued til death)...

Or simply leave quality of bokeh out of discussion because it varies with different lenses. I thought it started out to be a discussion betw. why F/2.8 over F/4?

 

[daredevil123]

imho, for this discussion to have any meaning at all, you guys may have to come up with an agreement on what "better bokeh" means... (which by itself may be argued til death)...

The simple Definition is:

The quality of the blur has come to be known as "bokeh".

From this site, with examples of good and bad bokeh too...
http://www.bobatkins.com/photography/technical/bokeh.html

Here is the complicated definition
http://www.luminous-landscape.com/essays/bokeh.shtml

 

[GSiGuy]

Or simply leave quality of bokeh out of discussion because it varies with different lenses. I thought it started out to be a discussion betw. why F/2.8 over F/4?

yeah seems like a slight bit off the subject of the thread to do so... or perhaps a related corollary but only a small part of the whole

 

[gohjialong]

Hi guys, i posted the question, went for lunch and came back with so many replies and debates! anyway thanks to those who let me uds more between these 2 apertures. will read up more and think about it.

 

[gohjialong]

Another thing is , if f2.8 is sharper at like f4 , then what is f4 sharpest at?

If my situation would most likely be casual portraits on the streets or in restaurants, would 2.8 be a better choice given its ability to go for faster shutter speed at low lit areas?