Basic Lens and Aperture Question

[MiKaLa119]

I was reading this book "Photography"by John Freeman and he says: "...An alternative might be to purchase a single zoom lens that went from 28 to 200mm. However, this type of lens will probably be quite slow, with a maximum aperture of f3.5-f4.5 depending on the focal length you adjust it to, and the optical quality quite poor."

After readig this, I figured if I'm going to buy a lens it should have an aperture of at least 2.8. However, from the posts that I've been reading in here and other forums, people hardly shoot with this setting and generally use f/8. I'm still trying to distinguish the main difference, and "think" I understand the general idea of aperture settings.... but where am I going wrong here? What do you usually look for in a lens (besides the range)? And what is your aperture "generally" set to in the different scenarios?

 

[Dave_D]

I have some general use lenses like 28mm-105mm f/3.8 , a 100mm-300mm and so on. I have specific lenses for specific photography for example: Micro Nikkor 55mm prime f/2.8. Very flat focal range I use for photogaphing single dimension macro in low light without a flash (hence the f/2.8). If you shoot mostly landscapes then wide aperature is not a concern as you would want every thing in focus so higher f/ stops.
Here in modern times even the cheapest of lenses have laser ground glass and many would be hard pressed to tell the difference between an econo lens and a "pro" lens based on image quality. Zoom lenses are also hard to differentiate from primes by image quality as technology has come a long way. I have "econo" models and "pro" models and either way I have found lenses with a wide zoom range say 28-200mm will start to have abberations when fully zoomed so, I would avoid them.
Now there are some die-hards out there that will swear by prime lenses and pro glass, but your best bet is to decide how you will use your camera the most, then select a lens type best suited for said use and start reading reviews on those lens types. I have Sigma lenses that I would use over my "pro" glass and some that I would throw away. When you find a few reviews that all agree then it's probably a safe buy.....Good Luck!

 

[Big Mike]

Well...aperture is important to know about. It controls the DOF or Depth of field. That is the field of distance from the camera...in which objects will appear to be in focus. The wider the aperture (smaller number) the more shallow the DOF will be. Alternatively, a smaller aperture (large number) will give you a deeper DOF.

So...a wide aperture like F1.8 or F2.8 will allow you to get a short DOF...which will allow you to blur out a distracting background. (makes for nice portraits)

Besides DOF, a wider aperture allows you to shoot hand held in lower light situations because a wider opening allows more light to get into the camera. The more light that gets it...the faster a shutter speed you can use. When shooting hand held, you want to keep a fast enough shutter speed to prevent blur do to camera shake. The rule is this...for a 200mm lens, keep the shutter speed at about 1/200 or faster. For a 100mm lens use 1/100 or faster.

So if you are inside and don't want to use a flash, a lens that has a maximum aperture of 2.8 will let in 4 times as much light as a lens with a maximum aperture of 5.6. That could make a big difference in the shutter speed that would give proper exposure. This is why we like wide apertures...it gives us the option to use the lens wide open when we need to.

Yes you are right, a lot of the time, F8 is a good aperture to shoot at...lenses are usually sharper in the middle of the range...or at least a few stops from the max & min settings. I wouldn't say it's a setting to use for general photography...but it's a nice average.

Now when buying lenses, you will see that the bigger the maximum aperture...the more expensive the lens...they will also be bigger and heavier with wider apertures. If you want a zoom lens that can open up to F2.8 you will have to shell out some serious money.

 

[selmerdave]

Larger maximum aperature also provides a brighter image in the viewfinder which (combined with the shallower depth of view) makes it much easier to focus. My 200/f4 is quite difficult to focus when light levels are lower than an overcast day. Not impossible but difficult.

One thing to keep in mind though is that you pay a lot for the larger aperature and it often requires more complicated manufacturing, so sometimes the larger-aperature lenses are ultimately poorer optically than their smaller-aperature counterparts. Of course with the higher price comes higher expectations from the customer so I wouldn't say it's a rule of thumb, but I'll go on a limb and suggest that in most cases with two otherwise identical lenses from the same manufacturer the one with the smaller maximum aperature will likely perform optically at least as well as the one with the larger maximum aperature. I guess keep that in mind when checking out the price of that 85/1.4

Dave

 

[AlmightyWa]

Basically, you change the aperture to suit your situation and the results from the picture you want. You would use a large aperture (such as your 2.8 ) in low light conditions and when you want a shallow depth of field. You will use a small aperture when you have lots of light and want a large depth of field.

Don't worry about buying a lens because it has a massive aperture as the situations that you use this in will be relatively limited (I'm presuming you're still taking photos for fun). Try and find a lens thats a happy medium between a small(ish) aperture and the amount of money you want to pay.

And if you meet a salesperson don't let them convince you that you really need a f1.4 800mm lens.