Query about the 40Dfocus points - expert advice needed.

Hi,

I read that the outside sensors of the 40D are only capable of F5.6 - so does this mean that using a 300mm at F2.8 on one of the side sensors is ineffective and may not focus correctly?

I cant get my head around this.

Likewise, the centre AF point is F2.8 - so again, does this render at 1.8 or 1.4 next to useless?

Any advice greatly rec'd.

Thanks in advance.

Pete.

Read this. I haven't read too much about the 40D, but what I think it is is the cross type sensors will activate with lenses F5.6 and faster (ie F4 and F2.8 are fine, F8 not so much). That pretty much means the cross type sensors will work with most lenses, even the kit lens. Remember this is the maximum aperture, as the lens is wide open until the shutter button's pushed.

Thanks a lot, I could not work it out, but clearly it is capable with fast glass.

Nice one dude.

Pete.

Also, the center point will work the same as the outer points with f/5.6, f/4, or f/3.5 lenses and with added accuracy with f/2.8 or faster.

bristolpete wrote in post #4009638
I read that the outside sensors of the 40D are only capable of F5.6 - so does this mean that using a 300mm at F2.8 on one of the side sensors is ineffective and may not focus correctly?

I am not an expert but I play one on the internet...

Facts:
1.
Canon has four terms its marketing department uses to describe its AF sensors. High precision, Cross Type, Sensitive (vertical or horizontal), and Regular Precision.

2.
A sensor that will work up to f5.6 also works all the way to f2.8. One that works up to f2.8 is BETTER than one that STARTS at f5.6 for its sensitivity. Some people want f8 sensitive. I would not want it.

Ok now that you are familiar with Canon's terms let look at what the cameras offer.

350D = No cross type or High precision sensors.

30D = Only the center point is Cross type & High Precision. That is two things. The others are just like the 350D.

40D = Only the center point is Cross type & High Precision. The others are Cross Type with their sensitivity beginning at f5.6. In other words they are not Canon's best but better than before.

1D Mark III = 19 Cross Type & High Precision AF points beginning their sensitivity at f2.8! Now that is a Camera!!!


Please STUDY these:

20D
http://www.canon.com/c​amera-museum/tech/report/200​409/report.html

5D
http://www.canon.com/c​amera-museum/tech/report/200​509/200509.html

30D
http://www.canon.com/c​amera-museum/tech/report/200​603/report.html

XTi
http://www.canon.com/c​amera-museum/tech/report/200​609/200609.html

1D Mark III
http://www.canon.com/c​amera-museum/tech/report/200​703/200703.html

wow.... can we say troll....

anyway, to answer the OP, you are looking at the numbers backwards, they are saying that the cross type AF will work on any lens 5.6 or smaller, which is pretty much every AF lens anyway. the center one also has cross type at 5.6 or smaller, but has a high precision sensor that kicks in and focus even better with lenses f2.8 and faster.

pcunite wrote in post #4013501
[1D Mark III = 19 Cross Type & High Precision AF points beginning their sensitivity at f2.8! Now that is a Camera!!! To bad it does not work

What do you mean by they don't work?

DNFTT...

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sunnythepsychocat wrote in post #4015682
What do you mean by they don't work?

I was being humorous with my post. Those who are calling me a troll have apparently not taken the time to read the technical links to Canon's site I posted. I have two 40Ds, 6 EF lenses and 4 580EX flashes so I am VERY familiar with Canon equipment. The 40D focus very well for its center point. I am just tired of Canon making its AF a $4,000 feature like what is found on the 1D series hence my statement about peanuts.

number six wrote in post #4015737
DNFTT...

DNCSAT
Do not call someone a troll

It is rude. I am here to be a respectful member of these forums. A humor post about Canon's AF is not troll worthy.

while i agree the non cross type points on the 20/30D blew for just about anything other than one shot in perfect lighting. i myself, and i think most everyone else would agree that adding cross type to all of the focus points was one of if not the largest technical improvement the 40D had.

Billginthekeys wrote in post #4017927
while i agree the non cross type points on the 20/30D blew for just about anything other than one shot in perfect lighting. i myself, and i think most everyone else would agree that adding cross type to all of the focus points was one of if not the largest technical improvement the 40D had.

Yes it really does help. But just so that you know they are not High Precision. What this means in the field I do not know yet.

pcunite wrote in post #4017877
I was being humorous with my post. Those who are calling me a troll have apparently not taken the time to read the technical links to Canon's site I posted. I have two 40Ds, 6 EF lenses and 4 580EX flashes so I am VERY familiar with Canon equipment. The 40D focus very well for its center point. I am just tired of Canon making its AF a $4,000 feature like what is found on the 1D series hence my statement about peanuts.

TANSTAAFL

tzalman wrote in post #4018026
TANSTAAFL

I know I know but my wife can not hold the 3lb 1D Mark III with the 3lb 24-70 attached. I don't need all of it functions either. Just give me a 40D with 1D AF and charge more for it. I think Canon may be forced to do this after a few years.

pcunite wrote in post #4017877
I was being humorous with my post. Those who are calling me a troll have apparently not taken the time to read the technical links to Canon's site I posted. I have two 40Ds, 6 EF lenses and 4 580EX flashes so I am VERY familiar with Canon equipment. The 40D focus very well for its center point. I am just tired of Canon making its AF a $4,000 feature like what is found on the 1D series hence my statement about peanuts.

You think all the peanuts were handed out with the 1D series cameras? Try using a f/5.6 lens (i.e. f/4 + 1.4x TC) on any 1D series camera and count how many cross-type sensors you end up with compared to a 40D or even a 30D. Zip. Nill. Nada.

I have a Mark II and a Mark III and I'm still waiting for my peanuts to arrive.