Digic III vs Digic IV AF speed in entry level dslr's

[nas_z]

<p>I've been comparing the two in recent days and one aspect of the camera performance i can find very little about is the AF speed and accuracy. I've read a lot of different posts on many different sites and forums and there seems to be quite a few people who own the 450d who complain about the AF being slow or inaccurate. I'd like to know if there are any improvements in AF speed/accuracy on the 500d over the 450d? I think the AF systems are pretty much the same but does the new Digic IV processor make the 500d any quicker at focusing?</p>

[wayne_woodruff]

<p>"quite a few people who own the 450d who complain about the AF being slow or inaccurate" is a rather vague statement. What lens? What were the shooting conditions? What exposure mode?<br>

This article sums up the variables nicely. <br>

http://www.learnslr.com/slr-beginner-guide/16-xsi-auto-focus-issue</p>

<p> </p>

[phule]

<p>The only relationship Digic IV has with AF is during Live View, when the normal AF processor is out of the loop.</p>

[nathangardner]

<p>A good lens will make a bigger difference in AF speed than the Digic IV. Take a 70-300mm and a 70-200mmL side by side and see which focuses first.</p>

[PuppyDigs]

<p>The improvements of one digic processor to the next makes little difference in AF speed. Heck, the AF of my 1990s EOS 5 and 3 isn't much different from the latest and greatest. I think most of the CPU power goes to image processing. Besides, the overhead for each generation of digic processor increases greatly with the extra MP, NR, and other image processing chores, so the faster CPU doesn't seem much faster in actual use.</p>

[kou_lee]

<p>Yeah, I think AF is going to depend more on the lens than the processor of your camera body. Take a 50mm/1.8 lens put it on a T2i body then move it to a XSi body and it will still be slow.</p>

[tien_pham]

<p>1. AF is dependent on the lens it uses, eg., faster lens AFes faster than slower lens, especially in a low-light environment.<br>

2. Lenses with bigger front element generally and theoretically AF faster than the similar lenses with smaller front element.<br>

3. AF depends also on the type of AF sensor used, eg., crossed or horizontal, or vertical.<br>

4. According to the image recording sequence, an image goes to the uP (Digic engines) after it achieves focusing and shutter has been pressed. It also relates to the format of the image, eg., JPEG or RAW/NEF. If shooting w/ the RAW/NEF format, the Digics will not be invollved!</p>