Image quality equal at same focal length?

I often use my nifty fifty 50 mm 1.8 for portraits. But if I stop it down to f5.6 for sharpness, does it offer any advantage over my 18-55 mm kit lens at 50 mm with an aperture of f5.6? Or does the kit lens take the advantage because it has IS? Please offer your insight.
Thanks, Carter

I'm no pro but I would imagine the 50mm 1.8 would have superior IQ because as a prime, the construction of the lens is much simpler, thereby having fewer issues.

compare the test results in the reviews:
prime: http://www.dpreview.com/lensreviews/canon_50_1p8_ii_c16/page3.asp
zoom: http://www.dpreview.com/lensreviews/canon_18-55_3p5-5p6_is_c16/page3.asp
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-Will
- http://lifeinmegapixels.com

Oh, boy...

I haven't checked the actual measured resolution of the two lenses, so I'll make some assumptions and offer the following:

1. The difference between primes and zooms in terms of resolution (and corner sharpness) is typically greatest at the largest apertures. It diminishes as you stop down and with very good zooms the image quality can become so good that using a prime at those apertures is not so worthwhile in many cases.

2. Neither of these lenses starts out as being exactly a "great" lens, though both are certainly competent. If your use is not super-critical (e.g. - working from tripod, very careful focus, MLU, remote release, and producing very large prints), any difference between them as you stop down will very likely be insignificant.

3. If your use is not "super critical" (to quote myself...) then it probably doesn't matter which you choose in terms of image quality.

4. The IS on the zoom will diminish the effect of camera motion by the equivalent of at least a couple stops. (Some lenses have an effect equivalent to 2, 3, or 4 stops... supposedly.) So, in terms of camera shake IS will get you to at least f/2.8 as far as low light shooting goes. If someone knows more about the kit lens IS than I and can chime in, we might find that it is equivalent to shooting at perhaps f/2, which is essentially the same as f/1.8.

5. However, IS doesn't help at all when it comes to dealing with subject motion at low shutter speeds, so using the f/1.8 lens when moving subjects are the issue will be a better idea than using the kit lens if you are trying to keep the shutter speed high. (IS, it could be argued, is actually bad in this situation if it encourages you to use shutter speeds that are too low for the motion of your subject.)

Dan

cartercooper said:

I often use my nifty fifty 50 mm 1.8 for portraits. But if I stop it down to f5.6 for sharpness, does it offer any advantage over my 18-55 mm kit lens at 50 mm with an aperture of f5.6? Or does the kit lens take the advantage because it has IS? Please offer your insight.
Thanks, Carter

Click to expand...

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cartercooper said:

I often use my nifty fifty 50 mm 1.8 for portraits. But if I stop it down to f5.6 for sharpness, does it offer any advantage over my 18-55 mm kit lens at 50 mm with an aperture of f5.6? Or does the kit lens take the advantage because it has IS? Please offer your insight.

Click to expand...

...the answer is but a click away:

http://www.dpreview.com/lensreviews/widget/Fullscreen.ashx?reviews=26,1&fullscreen=true&av=5,5&fl=50,55&vis=VisualiserSharpnessMTF,VisualiserSharpnessMTF&stack=horizontal&lock=&config=/lensreviews/widget/LensReviewConfiguration.xml%3F4

Of course, it is possible that IS provides a advantage in some situations, but the main advantage of the 18-55 IS is that it zooms from 18mm to 55mm, as opposed to being "stuck" at 50mm. Then again, it can't get faster than f/5.6 at 50mm, either, and it's no where near as sharp.

Choose your poison.

Thanks for all your input! Here are sample images from a recent family photo session shot with both lenses: Flash used on both, EX430 with Sto-fen diffuser

Nifty Fifty 50 mm at 1/180, f5.6



Now this next shot is with the Kit Lens 18-55 IS, 39mm at 1/180, f9.5

Great Bustard said:

cartercooper said:

I often use my nifty fifty 50 mm 1.8 for portraits. But if I stop it down to f5.6 for sharpness, does it offer any advantage over my 18-55 mm kit lens at 50 mm with an aperture of f5.6? Or does the kit lens take the advantage because it has IS? Please offer your insight.

Click to expand...

...the answer is but a click away:

http://www.dpreview.com/lensreviews/widget/Fullscreen.ashx?reviews=26,1&fullscreen=true&av=5,5&fl=50,55&vis=VisualiserSharpnessMTF,VisualiserSharpnessMTF&stack=horizontal&lock=&config=/lensreviews/widget/LensReviewConfiguration.xml%3F4

Of course, it is possible that IS provides a advantage in some situations, but the main advantage of the 18-55 IS is that it zooms from 18mm to 55mm, as opposed to being "stuck" at 50mm. Then again, it can't get faster than f/5.6 at 50mm, either, and it's no where near as sharp.

Choose your poison.

Click to expand...

That is an AWESOME widget (assuming the data is accurate). Too bad they don't include all lenses.

However, the zoom has obvious advantages in stabilization and available focal lengths. As Great Bustard said, choose your poison: far better optical quality, or far better flexibility.

Wow that tool sure makes the 50mm 1.8 look like a great performing lens.

It is a great performing lens, at f/5.6 it is one of the sharpest EF lenses available. Only the really expensive super-tele lenses, macros and some L primes are better. Why is this so hard to believe. Maybe because a lens that cost 100 bucks just can't be that good.

I wonder how sharp a 50mm f/2 L could be, if Canon used all skills and design technology.

It depends on what - where and how you are shooting . Hand held or tripod ? moving object [ a baseball hitting bat / a flower in a vase ] what kind of light - bright sunlight - shade , a light in a bar ? What do you want out of pictures ? Who is looking at the shot ?
2 of any lens won't be same- there are good copies and bad .
good luck .
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