Lower Rez for zoom lenses?

[droosan]

When I take a picture with my 50/1.4, 100/2, or 200/2.8 I can zoom in to the maximum scale on the LCD of my 10D and the picture is still sharp. When I take a picture with my EF28-105 zoom and zoom in to maximum scale, it is fuzzy.

First, do you think this is a result of the difference in optical quality between well-known high-quality primes, and a middling zoom? Or does my zoom suffer from the 10D's fabled poor focusing on some lenses?

Second, if my zoom's quality is simply not as good as the primes, should I simply go ahead and set my camera to 2.8MP when I have that zoom on, since 6.3MP of fuzz is kind of pointless. Does anyone else do this?

[robertwgross]

No, there is no change in resolution in a Raw image. You always get 6MP.

Of course, some lenses are sharper than others. Prime lenses tend to be somewhat sharper then zooms, especially in some areas.

Why don't you check out your camera and lens on a focus-check ruler test?

Then also, you will find that the sharpness or lack thereof is not really detectable with the rear display on most cameras. The proof is more what you see on the computer screen at 100%.

---Bob Gross---

[Jesper]

When you review photos on your 10D, the LCD screen only shows the low-res thumbnail image. If you zoom in on the thumbnail, you'll see that it will become a bit blurry - the camera just blows up the thumbnail. If you download the RAW image to the computer, convert it and zoom in on it, you'll see that it's much sharper than what you see on your 10D.

You can't use the LCD screen of the camera to accurately judge the sharpness of your image, just as you can't use it to accurately judge exposure (use the histogram instead), color, etc. - the LCD is only meant for quick review.

If you really want to do a sharpness test, you must take as many precautions as possible to rule out any sources of blur other than the lens - put the camera on a good tripod, use mirror lock-up and a remote shutter release.

If you stop down your zoom lens to around f/8 or so, I don't think you'll see much difference in sharpness between your zoom lens and better lenses. My 28-135 is just as sharp as my 17-40L if I stop it down.

[ron chappel]

Basically it's hard to say if you have a dud 28-105 or not without comparing it to a known good example.

I've had several pass through my hands.The worst were definitely fuzzy compared to the primes (50/1.8 and 85/1.8).The best one i had ,it was really quite difficult to tell them apart without blowing the test pics up to at least 50% actual pixels on the computer.It really was close :)

[nosquare2003]

There are several versions of 28-105, the better one is EF28-105/3.5-4.5 (compared to the EF28-105/4-5.6). Which 28-105 lens do you have?

Is it easy to judge it by the camera's LCD :?:

[Jim_T]

I've got the EF 28-105 f/3.5-4.5 II USM.. I think it's a great lens. Very under rated... It's a bit soft at the edges. It shows when using it with a full frame 35mm camera, but the 1.6 sensor crop takes care of this :)