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Thread started 30 Oct 2012 (Tuesday) 23:10
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Cross-type focus points and other specs?

 
Naraly
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Oct 30, 2012 23:10 |  #1

I still don't fully understand some terms for DSLRs. How much of a difference does having several cross-type focus points make? Let's say, 9 vs 1 (comparing t4i to another DSLR). Also, can the human eye detect the screen resolution difference between 1,040k dots vs 920k dots? The website that I got that information from states the 1,040k dot screen resolution makes it easier to tell if an image is really in focus... Is it that big of a difference? Would the one with higher screen resolution win over the other one just for that?

And for the T4i users, is it true that although the T4i offers 12,800 ISO, the highest it can go to produce a good image quality without much noise is 722 ISO, so anything above that would create a lot of noise? (I'm comparing it to a different one that can go to 1,183 ISO and still produce a minimum noise).

Finally... I found these comparisons online between the 60D and the T3I. Are these images accurate for the capability of each camera, or was there some flaw? Because to my eye, in those images the T3i and Nikon D5100 really excel over the 60D, especially the shots of the water. I feel a little disappointed in the color and contrast quality of the 60D from those images...
http://www.cameralabs.​com …S_60D/sample_im​ages.shtml (external link)
http://www.cameralabs.​com …l_T3i/sample_im​ages.shtml (external link)



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Numenorean
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Oct 30, 2012 23:21 |  #2

Well for one whoever took those test shots isn't a very good photographer so I'd probably just toss out everything that's said.

Cross type focus points are more sensitive and can achieve focus lock in lower light much quicker and easier than non cross type. But usually this comes with the need for f/2.8 or faster lenses.

I don't really know about the T4i but I could use a 40D at ISO 800 without too much trouble so I'm sure the T4i could do at least 1600 if you get your exposure right.


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jhayesvw
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Oct 31, 2012 00:27 as a reply to  @ Numenorean's post |  #3

the cross type focus points are also better for catching action.
I thought they were good for f 5.6 though.


as for the screen resolution. when you zoom in you MIGHT be able to see the difference. I have a 60d withe the new screen and its nice.



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Oct 31, 2012 00:40 as a reply to  @ jhayesvw's post |  #4

Seems that the other points in your question have been adequately answered so I'll try the ISO part.

I think that YOUR acceptance of the level of noise at a particular ISO will mainly depend on what YOU consider to be a reasonable amount of noise.

However, modern cameras have made very nice improvements in high ISO performance, and provided that a shot is exposed correctly, I have seen excellent examples of photos shot at ISO 1600 and even higher...At least I find that the level of noise is acceptable.

Also, noise reduction software is getting better and better, so I think that ISO 722(where'd that come from?:confused:) is way too conservative an estimate.


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TSchrief
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Oct 31, 2012 00:47 |  #5
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Numenorean wrote in post #15189207 (external link)
Well for one whoever took those test shots isn't a very good photographer so I'd probably just toss out everything that's said.

Cross type focus points are more sensitive and can achieve focus lock in lower light much quicker and easier than non cross type. But usually this comes with the need for f/2.8 or faster lenses.

I don't really know about the T4i but I could use a 40D at ISO 800 without too much trouble so I'm sure the T4i could do at least 1600 if you get your exposure right.

I don't know about other bodies, but this is NOT how the 60D works. All 9 AF points on the 60D are cross-type. All 9 AF points are sensitive to f/5.6. The center point is dual-cross (think X on top of +) and is extra sensitive with f/2.8 or better glass.

I went from the 500D (T1i) to the 60D and the AF systems are spectacularly different. The 500D has 9 AF points, outer points are linear f/5.6, center is cross-type (not dual-cross) sensitive to f/2.8. I am not familiar with any of the newer Rebels, but suspect they are no better than the 500D.

I have shot my 60D at ISO 6400 (12,800 is pointless) and get decent results if shooting raw and working in LR4.x. I can shoot jpg to 3200 and get acceptable results. My 500D was noisy at 1600 and bad at 3200. Noise is highly subjective; you may love or hate what I thought was acceptable. But, comparatively, the 60D is easily one-stop better than the 500D as far as noise was compared.


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apersson850
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Oct 31, 2012 02:39 as a reply to  @ TSchrief's post |  #6

Normal cross type points are not more sensitive. They don't focus better in low light either. What they do is that they can measure both horizontal and vertical lines. Thus they have twice the probability to find a suitable contrast to focus on.

In some cameras, lenses with at least f/2.8 are required to get cross-type points, but not for the models mentioned in the original question here.

High-accuracy points are able to measure the focus distance more accurately. Depending on the camera model, they too may be cross-type or not, but they usually do require at least f/2.8 to work. It depends upon how much better accuracy they have.


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Oct 31, 2012 03:01 |  #7

apersson850 wrote in post #15189619 (external link)
Normal cross type points are not more sensitive. They don't focus better in low light either. What they do is that they can measure both horizontal and vertical lines. Thus they have twice the probability to find a suitable contrast to focus on.

Bingo, cross type strictly speaking has nothing to do with sensitivity in low light, with fast lenses, or speed or anything.

If you try to focus on a perfectly vertical line with a vertical sensor, it won't see it. A horizontal sensor won't see a horizontal line. A cross type sensor can focus on both (and everything in between).

It just so happens that in many focusing sensors, particularly lower end ones, there are a number of simple one directional focusing points and the best point is a cross type and is designed for higher accuracy and sensitivity. Even in top end current systems they fill in the gaps with one-directional focusing sensors.


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FrayAdjacent
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Oct 31, 2012 06:06 |  #8

apersson850 wrote in post #15189619 (external link)
Normal cross type points are not more sensitive. They don't focus better in low light either. What they do is that they can measure both horizontal and vertical lines. Thus they have twice the probability to find a suitable contrast to focus on.

In some cameras, lenses with at least f/2.8 are required to get cross-type points, but not for the models mentioned in the original question here.

High-accuracy points are able to measure the focus distance more accurately. Depending on the camera model, they too may be cross-type or not, but they usually do require at least f/2.8 to work. It depends upon how much better accuracy they have.

Most people would count doubling the probability of getting something correct as 'more accurate'.


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apersson850
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Oct 31, 2012 06:19 as a reply to  @ FrayAdjacent's post |  #9

No, neither do I. But I've seen many referring to high-accuracy AF points as "more sensitive". Now I'm not a native English speaker, but shouldn't that rather be "more accurate"? To me, an AF point that's more sensitive is perhaps better at measuring focus in low light, or better at figuring out the correct focus even if the lens is extremely defocused (imagine a long telephoto, set at the closest distance but aimed at infinity).

TSchreif wrote:
The center point is dual-cross (think X on top of +) and is extra sensitive with f/2.8 or better glass.

Personally, I would have written this as: The center point is dual-cross (think X on top of +) and provides higher accuracy with f/2.8 or better glass.

What do you English speakers say?

Anyway, as stated above, a cross-type point is able to find lines in all rotations. When they get to 45° compared to the sensor element, the other element takes over.

High accuracy points have their two segments further apart (longer baseline), but that also requires a larger opening for the light rays entering into the camera. Hence the requirement for f/2.8 (usually) for these points to be active.

Some cameras have cross-type points with normal accuracy. The 7D is one example, where all 19 points are cross-type with normal accuracy from f/5.6. Then the center point has an additional cross-type point, which wakes up at f/2.8. This additional point has higher accuracy, since the elements are further apart. Thus this camera has a center point which provides higher accuracy in both directions, from f/2.8.

A camera like the 1D Mark IV has linear points only at f/5.6. At f/2.8, several of them become cross-type, because the other sensor pair at each point is of high accuracy (longer baseline). Thus it gets AF points that are cross-type and of hybrid accuracy, better in one direction than the other. But it doesn't have any point at all that supports high accuracy in both directions. No 1D-series camera had that until the introduction of the 1DX. Across other models it was first introduced with the 40D.


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Oct 31, 2012 06:53 |  #10

i wouldn't put too much stock into those sample images as they dont even use the same lens, so you wont get the images, and even the 60D and the t3i have the same sensor they wont produce identical images, especially jpegs since the firmware is different and may be applying settings differently.

if it were me i ignore the minor differences in AF and focus points and look at the other features of the camera, (it not like you are comparing a 7D and t3i) i would opt for the 60D over the t3i simply becuase it has a better control layout, if you really get into photography you'll be happy you aren't digging though a menu to set something when you have a dedicated button for it.


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apersson850
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Oct 31, 2012 07:12 as a reply to  @ mike_311's post |  #11

You don't know if the ambient conditions were identical either. The 600D images look a bit artificial to me. Probably higher saturation setting, maybe contrast too. Lesser cameras in Canon's model range often have that by default, since at Canon they don't expect the users of these models to be equally adept at doing the setup themselves. I think may users of cameras like the 600D use it with the Standard picture style set at the default settings all the time.


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Yogi ­ Bear
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Oct 31, 2012 15:25 |  #12

mike_311 wrote in post #15189972 (external link)
if it were me i ignore the minor differences in AF and focus points and look at the other features of the camera, (it not like you are comparing a 7D and t3i) i would opt for the 60D over the t3i simply becuase it has a better control layout, if you really get into photography you'll be happy you aren't digging though a menu to set something when you have a dedicated button for it.

Last time that I checked, the T3i had a pretty good array of buttons to choose from to make adjustments, not like a Nikon D3100 for example. What function is it that you are concerned about "digging through a menu" on the T3i?


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Oct 31, 2012 15:33 as a reply to  @ Yogi Bear's post |  #13

It's mainly the dual dials and the buttons for immediate changes of certain settings in front of the top display that differs. The top display by itself is also a difference.


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Oct 31, 2012 15:44 |  #14

Yogi Bear wrote in post #15191712 (external link)
Last time that I checked, the T3i had a pretty good array of buttons to choose from to make adjustments, not like a Nikon D3100 for example. What function is it that you are concerned about "digging through a menu" on the T3i?

apersson850 wrote in post #15191744 (external link)
It's mainly the dual dials and the buttons for immediate changes of certain settings in front of the top display that differs. The top display by itself is also a difference.

Granted, the second control dial is a major difference, but as far as buttons go, I contend that the T3i has all of the major functions covered, just as a 60D.


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apersson850
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Oct 31, 2012 15:59 as a reply to  @ Yogi Bear's post |  #15

I'm not sure about what they've changed in the more recent models in that range, but the 400D I once used had no rear dial, no rear joystick, no separate buttons for setting things like WB, drive mode, FEC, metering mode, AF mode and ISO. Those buttons for such things it did have were combined with the arrow keys, so when using them for immediate AF points selection, you had to watch your timing vs. the last use of the trigger button, or you changed the wrong thing.

There's a substantial difference compared to my 7D, for example, which has more different buttons, dedicated to different things. But the 7D is more modern, so it should of course be compared to a camera like the 600D or so, not the old 400D, to make it fair. The 60D is a bit less equipped than the 7D in this case.


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