Yet Another Lens Question

[NateNLogansDad]

If you're out shooting during the day would you get a better picture from a 2.8 lens than you would using something like a kit lens if you stopped them both to something like F/16? Is there a difference in the glass itself or would you pretty much expect the same results?

 

[VVFF]

If you're out shooting during the day would you get a better picture from a 2.8 lens than you would using something like a kit lens if you stopped them both to something like F/16? Is there a difference in the glass itself or would you pretty much expect the same results?

The results will depend on the lens. Generally speaking, the higher quality the lens, the better results you'll get at a equivalent F-stop for similar lenses. This is very general though.

F/16 is pretty far stopped down though, no lens will perform its best there.

 

[disneyboy2003]

I'm no expert at lenses, but I believe that higher-priced lenses (ie. the ones with f/2.8) are better built than cheaper lenses. So even at smaller apertures (bigger f-numbers), you should still get better image quality with the higher-priced lenses.

For example, according to the-digital-picture.com, the kit lens suffers from lower contrast, chromatic aberrations in the corners, and mild vignetting. There are also times where the cheaper lenses aren't as sharp as the more expensive lenses, too. Here's the review: http://www.the-digital-picture.com/Reviews/Canon-EF-S-18-55mm-f-3.5-5.6-IS-Lens-Review.aspx

(the above link also provides a mouse-over comparison of photos taken from different lenses at the same aperture, so you can compare the quality of photos yourself)

One other thing about lower-priced lenses. Usually, they have variable maximum apertures (ex. f/3.5-5.6). So when you're at 55mm on the kit lens, for example, your maximum aperture is f/5.6. The autofocus (AF) systems in most DSLRs require a minimum aperture of f/5.6 to work. The larger your maximum aperture, the better your AF system will perform. So, I would expect the f/2.8 lens to have a better AF performance at the same 55mm focal length. (Note: this is regardless of what aperture you're using for exposure. It's the maximum aperture of the lens that affects AF performance)

Plus, the viewfinder will be 4 times brighter (2 stops brighter) with the f/2.8 lens than the cheaper lens at f/5.6. (the viewfinder brightness depends on the maximum aperture) This becomes important if you need to manually focus or if you're using Live View.

One final thought. Typically, the "sweet spot" for any lens is about 1-2 stops below its maximum aperture. The "sweet spot" is the aperture at which your lens produces the best, sharpest images. This varies depending on the lens, but I believe it's a general rule-of-thumb.

Also, because of a concept called diffraction (for more info, see here and here), your sharpest pictures will be at around f/8 to f/11. Any smaller than that (ex. f/16, f/22, etc), and your pictures will show some softness due to diffraction. Diffraction depends on the sensor of your camera, not on the lens.

Well, this was a much longer reply than I had anticipated. Like I said, I'm no expert at lenses, so I'm sure I've made some mistakes above, so please correct me if I'm wrong.


BTW, I guess my answer to your question is: yes, higher-priced lenses (f/2.8 lenses) will give you better quality images than kit lenses, even at smaller apertures.

 

[ukcatfan]

You can use these sites to compare lenses to know for sure.

http://www.photozone.de/reviews

http://www.photodo.com/products.html

 

[jann1033]

agree with the above but you might need to check out your particular lens copy as well...ie my 50mm f1.8 is great at smaller aps( ie above 18), where it is "supposed" to stink and not as good at larger aps. where it is reviewed as sharp. generally though, i would think most 2.8 lenses would be sharper than a kit lens since you are usually talking about a lot more money for 2.8 than kit so probably better all around lens.

very generally speaking, i've found with lenses, usually money does equate to "better glass" although that is of course relative to the brand . ie a $700 tamron ,heading toward "an expensive" lens for that line might be close to "equal" to a $1200 canon for glass quality although the build might not be as good. there is a reason why they cost more, i mean other than price gouging


another good site is slrgear.com http://www.slrgear.com/reviews/index.php i like their test chart where you can see results for different aps and focal lengths

 

[NateNLogansDad]

I'm speechless. You guys never cease to amaze me Thanks for putting up with questions from new guys like me. I'm hoping one day I'll be able to chime in with some advise that will help someone else as much as you guys do for me. Thank you

 

[Groucho]

It really depends on what your idea of "better" is. Even the cheapest kit lens can usually produce a fairly sharp photo once you get to F8 or so, but is more likely to have geometric distortion (straight lines not straight), inconsistent sharpness across the frame, flatter color, and less pleasing bokeh. You will also usually see a difference if taking night shots with bright lights - the cheap lenses will usually have 6 aperture blades, which means you'll get hexagonal highlights and six-pointed stars around bright lights. The higher-line lenses usually have 8 or 9 blades, which means 8 or 18-pointed stars (the odd-number ones give you double)... and if shooting in bright light, a higher-line lens should have a lens hood on it and possibly better coatings, both of which should reduce flare and increase contrast over some cheap lenses that don't have hoods and maybe cheaper coatings.

 

[boBQuincy]

At wider apertures than the sweet spot, usually around f/8, lenses are limited by aberrations. Past f/8 diffraction takes over. There are other lens issues that can affect image quality such as distortion, coloring, flare, and transmission, that are not as affected by aperture settings.
Kit lenses are not all the same quality, Canon's original 18-55 was barely worth the low price while the newer 18-55 with IS is optically quite good.

Some f/2.8 lenses are designed with priority on the large aperture, smaller maximum aperture lenses are easier to design and may give better image quality if built to the same quality level. An example is Canon's 70-200, where the f/4 version is at least as good in most regards as the f/2.8 model. Their 17-40 and 16-35 show this characteristic also.

Looking at DPReview's tests of Canon's 70-200 f/2.8 and Canon's 18-200 f/3.5-5.6 shows small differences in sharpness and chromatic aberration at 100mm and f/16. At 200mm and f/16 the 18-200 actually has better sharpness in some areas of the frame but *much* worse chromatic aberration. It seems a good lens is good (if not great) everywhere while a not so good lens may be good somewhere but pretty bad somewhere else. The MTF charts can reveal some of these issues, a smooth curve is a good indicator while wild peaks and valleys might indicate some problems.

So, to answer your original question, a f/2.8 lens will probably give a better photo than a kit lens although in good lighting conditions the difference may be small. Also, f/2.8 by itself is no guarantee of a good lens and some f/4 (or other apertures) lenses are top quality.