f2.8 vs f4 lenses Question

[will_kim1]

Hi,

 

 

I was just curious what the these two types of lenses were primarily used for? I mean some lenses come

with a constant f2.8 while some have a constant f4. What would the f2.8 on zoom lenses be good for? I

am sure the pictures would come out really well on both type of lenses. I am just wondering "what

situations" would they be good for? Also, would you be able to raise your ISO on a f4 lens to compensate

for the lack of f2.8? I am a new to all this and was just curious. I hope the question I ask is not

understandable. Thank you in advance for all your help.

 

 

 

Will

[will_kim1]

I didn't mean "not understandable" I mean understandable.

 

Thank you

[tdigi]

If your interested you should get a book called understanding exposure by Bryan Peterson.

F2.8 F4 F 5.6 refer to the aperture of the lens. The smaller the number the larger the opening

the shorter the depth of field. Each stop doubles the amount of light that hits the sensor. You

use this in combination with shutter speed and ISO to get proper exposure.

[davebell]

For low light work F2.8 lenses are better, ignoring IS. F4 IS lenses are good for low light stationary subjects, but for stopping motion (or at least more so than smaller max aperture lenses) in low light with a zoom lens, F2.8 is the only way to go. That's why most wedding photographers swear by them, whilst others claim F4 IS is sufficient. I have a 24-105 F4 IS and it is a great lens, but I will soon be adding the 24-70mm F2.8 as it serves a slightly different purpose. I recently photographed a wedding in a very dark venue, at night, with a 5D/24-105F4IS with 75% of the shots at 3200 ISO, exposed correctly and run through noiseware (mild dose) - they looked fine!

[ronald_moravec1]

Keep in mind slower lenses are for an amateur market and that means the wide open stops

will not be as sharp as pro lens wide open. So not only do you have a slower lens, you have

to stop it down to get a sharp image. Where as the pro lens can be used full open. So

there are really two stops difference, perhaps more.

 

Then consider consumer grade zoom lenses are not constant aperture, ie they will go to 5.6

as you use the tele position. More losses.

[tibz]

one stop

[mark u]

A faster aperture allows a higher shutter speed to freeze action (this becomes critical e.g. in indoor sport, where often even f/2.8 isn't fast enough), and it also allows distracting backgrounds to be blurred away much more effectively. To get an equivalent image including blurring effect as with say a 300mm f/2.8 on a full frame camera you need a 200mm f/1.8 on a camera with a 1.5 crop factor, so fast aperture becomes more important with a crop sensor camera. If your photography depends on nicely blurred backgrounds what you may save by buying shorter focal lengths will probably disappear in the cost of faster aperture lenses.

[mr. sullen]

"...what the these two types of lenses were primarily used for?" They have no primary use.

 

"What would the f2.8 on zoom lenses be good for?" Lower light situations. Most lenses that I am aware of are either a constant, let's say, 2.8 or go from 4.5 to 5.6 or whatever depending on focal length. So constant can be a good thing.

 

"I am sure the pictures would come out really well on both type of lenses." Yes they would.

 

"I am just wondering "what situations" would they be good for?" Many situations

 

"...raise your ISO on a f4 lens to compensate for the lack of f2.8?" Yes but with more noise.

[craig_gillette]

Besides the difference in aperture/amount of light when it comes to shutter speeds, aperture also controls the "depth of field." The smaller the aperture (higher f numbers) the greater the sphere that appears to be in adequately sharp focus. The greater the aperture/smaller the f number, the smaller that sphere is. This can allow the photographer to control foregrounds and backgrounds. So an f2.8 lens will have a smaller area of focus at f2.8 than the f4 lens, at the same focal length. So depending on the focal lengths and subject matter, the f2.8 user can get some additional separation of the subject, more softening of foreground or background elements.

[david_m]

You need to read a basic book on photography.

[jim_k6]

thank you for your help, your answers kinda already backed up what I was thinking.

 

thanks!

[machts gut]

2.8 also brings a brighter image in the viewfinder, i.e. 100% more light!

[studor13]

Most lenses need to be stopped down a bit to get the best performance, so an f4 lens is probably not going to be great at f4 whereas the f2.8 lens is going to be excellent by then.

 

Also, generally speaking an f2.8 lens - particularly for zooms - are pro grade in many other aspects. For example, built quality, resistance to flaring and ghosting, and distortions.

 

There are also a host of other factors such as design complexity and cost of a super tele f2.8 lens vs the equivalent focal length at f4.

 

What Stefan said is also very much underestimate. When there is a lot of light it's not a problem, but as soon as the light drops that one stop can make a big difference in the view finder.

[edgreene]

Ronald Moravec: <p><b>Keep in mind slower lenses are for an amateur market</b><p>Not always true, else Canon would not have two 70-200 ``L`` lenses in f/2.8 and f/4.0.<p><b>The major difference in f/2.8 constant aperture lenses and f/4.0 constant lenses is build quality</b>.<p>Back when most manufacturers made constant aperture lenses, the major consideration was cost, not build quality. <p><b>...that means the wide open stops will not be as sharp as pro lens wide open. </b><p> Again, not always, not even <i>usually</i> true, the more obvious differences being quality of ``Bokeh`` and DOF. <p><b>So not only do you have a slower lens, you have to stop it down to get a sharp image</b>. <p>Almost without exception, any modern lens is acceptably ``sharp``, even wide open. Stopped down, an f/4.0 constant easily rival many ``pro`` lenses (<i>in the same focal length</i>). <br> What some (some) f/4.0 lenses can do is shoot stop for stop with f/2.8 lenses of the same focal length when both are stopped down. <p><b>Where as the pro lens can be used full open. So there are really two stops difference, perhaps more. </b><p>There is only <i><b>ONE STOP</b></i> difference between f/2.8 and f/4.0 <i>at all times</i>.