What is better about 400D autofocus?

Started Sep 20, 2006 | Discussions thread
Glenn W. Veteran Member • Posts: 6,428
Re: Here is what's better...

I don't know how much this may help anyone trying to understand all this... however this is possibly the best description I've seen so far of how the more advanced focus system first introduced on the 20D...

"Compared with the Canon EOS 10D, the 20D features greater AF detection precision, improved focusing performance in low light and an improved focusing point layout. The 20D has a totally new 9-point, CMOS, AF sensor. This new design, seen for the first time in the 20D, provides full cross-type performance with maximum apertures as small as f/5.6, yet it achieves up to 3 times the standard focusing precision when used with EF Lenses featuring maximum apertures larger than or equal to f/2.8. This is made possible by a new AF sensor design that features two sets of vertical line-sensitive linear pixel arrays for the central cross-type focusing point. When an f/2.8 or faster lens is used, the camera automatically switches to a wider baselength measurement system to maximize autofocusing precision."

I found that in the following document...

http://www.robgalbraith.com/public_files/Canon_EOS_20D_White_Paper.pdf#search=%22%20TTL-CT-SIR%20dual%20precision%22

It's my understanding that this same focus system is in the 30D and now in the 400D... Based on the above, it would seem that precsion with f2.8 or greater you should see 3 times the focus precsion with the 400D vs the 350D... (I'd say that's pretty significant)

I also found some other information that indicates the 350D has a cross sensor center focus point, however it's not able to make better use of f2.8 lenses like the 20D, 30D, and 400D can... I get this from the following document...

http://www.usa.canon.com/app/pdf/slr/EOS_System_Bro2006.pdf#search=%22%20TTL-CT-SIR%20dual%20precision%22

Apparently the older 300D does not even have the center cross point focus that the 350D has, so presumably the 300D's focus is not even as good as that of the 350D's is, but I can not find any document that covers this differance...

At the very minimum it should be clear that if you have a f2.8 or faster lens, then you should get much better focus with it on a 400D then you did on any of the previous entry level EOS DSLR cameras...

Snareman wrote:

I've tried searching through old threads, but can't seem to find
the answer to this. I have the 350 and am considering whether the
upgrade is worth it.

There is talk about the autofocus being better on the 400D. What
exactly is better about it and is it significant?

Thanks.

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