1D1d Mark4 single-line sensitive with 400 5.6 prime

[john leigh]

hi
i am new here, just a quick question which i also posted in other forums

can anyone tell me if the single line sensors that would be used
with the above combo, would be inferior to the 7d's cross type-
sensors and the same lens?( the centre point i think is also single-line
sensitive with the mark 4 and 400 5.6).

i am thinking for servo and bif shots

i can get the 1d mark 4 but if the 7d focuses better with an 5.6 lense
i will go for that instead.(just thought that the 1d being the 1d might still
do better with single-line sensors that the 7d's cross type one's.

does anyone have the 1d and 400 5.6 for bif

thanks jon :)

[arash_hazeghi]

1DMKIV AF is miles ahead of 7D IMO despite single line sensor, with all the lens/TC combo that I have tried I have 500 and 400 f/5.6, while none of which will activate the cross type sensors off center but it is still consistent for flight shots.

[John Chardine]

This is an extract from Canon's White Paper on the mark IV. Page 17. The white paper can be downloaded at:

http://www.usa.canon.com/uploadedima...20IV%20WP1.pdf

"During manual AF point selection,38 (or 18 during automatic AF point selection) cross-type
AF points (excluding the center AF point) provide high-precision,cross-type performance
with lenses whose maximum apertures are f/2.8 or faster.Their horizontal line sensors (sensitive
to vertical detail) provide up to 3 times the precision of the vertical sensors,providing added
focusing accuracy with wide-aperture lenses where it’s needed most.When lenses with slower
maximum apertures are used (with some notable exceptions — see below), the vertical line
sensor becomes the only component used, allowing AF with lenses or lens/extender
combinations that are f/5.6 or faster.The center AF point,as mentioned above,can perform
AF with lenses as slow as f/8 (such as an f/4 lens with a Canon EF Extender 2X or 2X II
attached).Whenever lenses slower than f/4 are used,the center point reverts to a single vertical
AF line sensor,which is sensitive to horizontal detail."

[john leigh]

thanks guys

white paper says " Their horizontal line sensors (sensitive
to vertical detail) provide up to 3 times the precision of the vertical sensors "
if this is so what is it in the mark4's vertical lines that makes the focus better than the 7d's cross types?
are they bigger or more sensitive?

also if i am reading it right does this mean a 500 f4 with 1.4t/c becomes none cross type in the centre also?

thanks jon

[arash_hazeghi]

thanks guys

white paper says " Their horizontal line sensors (sensitive
to vertical detail) provide up to 3 times the precision of the vertical sensors "
if this is so what is it in the mark4's vertical lines that makes the focus better than the 7d's cross types?
are they bigger or more sensitive?

also if i am reading it right does this mean a 500 f4 with 1.4t/c becomes none cross type in the centre also?

thanks jon

-Canon does not specify technical details (i.e. size, number of pixels, sensitivity, SNR etc.) of the AF sensors so you can't compare 7D and MKIV line sensors, 7D sensors are cross type but they might be smaller, less dense in terms of pixels or have lower SNR. The bottom line is that they are not as good.

-That is correct, with 500 naked only center point is cross type and with 500 + TC there are no horizontal sensors active, but IME, MKIV has way better consistency. IMO, given my standards and for flight shots against varied BGs I would rate both 1DMKIV and 5DMKII above 7D, regardless of paper specs. Of course, when used by competent photographers with correct settings :)

You should rent both of these cameras and test them in the field.

hope this helps.

[Roger Clark]

Regardless of cross type sensors, the 1D series cameras have a smaller circle of confusion (CoC) defined in the AF algorithm compared to consumer cameras (xxD, xxxD series). So when a camera does its AF, if AF is within that circle of confusion, it is "good enough" and will not try and do better, e.g. in AI servo. There was a white paper years ago describing this--if I find it, I'll post a link. I'm not sure what the CoC is for the 7D, but could be larger than the 1D. It is the combination of processor speed and coC definition that makes for generally better AF in the 1D cameras. (kind of like 1D will Af at f/8--just a tighter algorithm) It may be the AF sensors in the 1D have smaller pixels, but I have not seen anything on that.

Roger

[john leigh]

see the thing is, i have a 5d classic but i am getting more into
the wildlife side of things now but the 5d mk1 is too slow.
so i need a new camera first, but also will get the 500 f4 at some point.
so basically if i get the 1d to go with the 400 5.6 that is the lens
i will be using for at least 12 months, so i needed to be certain about
the single line sensors with that combo - or go with the 7d
good idea arash i need to try before i buy, thanks;)
jon

[Peter Hawrylyshyn]

roger -
i always wondered how the cross-type AF sensors on the 50D or 7D could be less accurate than the 1D series
thanks for the explanation
peter

[Robert Hardy]

i think Canon should have made it clear about why the mk4 does not have or need cross type focus, most times we are told it is better than single line .
Rob.