# 5d mkII vs 50D in terms of AF



## contrastny (Dec 15, 2011)

I am looking to upgrade from my 50D, especially with the price drop on the 5D mkII. I haven't used the 5D II, but one of the main complaints I have heard is the AF. Is it better or worse than the AF on my 50D?

I mainly shoot landscapes, but I occasionally use AF for other subjects. The 5D II will be a great upgrade and I'll get it with the Zeiss 18mm.


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## neuroanatomist (Dec 15, 2011)

The center point on the 5DII is just about as good as the center point on the 50D. The off-center points are not nearly as effective as those on the 50D.


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## Fab_Angilletta (Dec 15, 2011)

it's basically the same AF but your Zeiss will be MF only.
for occasional AF, 5D mark ii is more than capable, at least as good as your 50D.


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## MartinvH (Dec 15, 2011)

neuroanatomist said:


> The center point on the 5DII is just about as good as the center point on the 50D. The off-center points are not nearly as effective as those on the 50D.



How does the 5DII AF compare to the T2i/550d or similar T3i/600d ?
Similar centre point ,lousy off-centre points ?


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## contrastny (Dec 15, 2011)

Fab_Angilletta said:


> it's basically the same AF but your Zeiss will be MF only.
> for occasional AF, 5D mark ii is more than capable, at least as good as your 50D.



Yeah, I was just curious about the AF for my other lenses.


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## Mt Spokane Photography (Dec 15, 2011)

For landscapes, portraits , and general center point usage, I find it to be very good.

In terms of AF accuracy of the center point, its extremely accurate.

In low light, it matches or exceeds my 1D MK III and is better than the 1D MK IV

Outer points and subject tracking are its weak points.

The lens you use is a big part of AF speed, but tracking, low light, point selected, and accuracy vary by model.


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## neuroanatomist (Dec 15, 2011)

MartinvH said:


> How does the 5DII AF compare to the T2i/550d or similar T3i/600d ?
> Similar centre point ,lousy off-centre points ?



The individual points are similar in terms of performance between 5DII and the Rebel/xxxD cameras. The center is cross-type with one f/2.8 line and one f/5.6 line, outer points are single-orientation f/5.6 (vs. the 40D-60D cameras where the center point is a dual cross with f/5.6 orthogonal lines and f/2.8 diagonal lines, and the outer points are f/5.6 crosses). 

However, the relative spread of the 5DII AF points is worse - in fact, the 5DII has the least AF point spread of any current Canon camera (including the T3/1100D). All of the others manage to get an AF point at least somewhere in the approximate neighborhood of a rule-of-thirds intersection, but the 5DII doesn't come close.


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## wickidwombat (Dec 16, 2011)

Mt Spokane Photography said:


> For landscapes, portraits , and general center point usage, I find it to be very good.
> 
> In terms of AF accuracy of the center point, its extremely accurate.
> 
> ...



I agree the center point is accurate, I do think using an f2.8 or faster lens is essential on the 5d2

but i do find my 1d3 AF to be considerably better in every respect than the 5D2 especially using f4 lenses such as the 24-105 f4L or the 300 f4L


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## briansquibb (Dec 16, 2011)

I must be the only person that uses the centre point and FL recompose. Brillian method, especially in low light


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## wickidwombat (Dec 16, 2011)

briansquibb said:


> I must be the only person that uses the centre point and FL recompose. Brillian method, especially in low light



No I use this method too, works better using back button focus too


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## neuroanatomist (Dec 16, 2011)

wickidwombat said:


> briansquibb said:
> 
> 
> > I must be the only person that uses the centre point and FL recompose. Brillian method, especially in low light
> ...



Yes, I use it, too. It works just fine with a deep DoF, like f/4. But at f/2 and wider, it results in back-focused shots.


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## Mt Spokane Photography (Dec 16, 2011)

Focus and recompose works at smaller apertures where the error in AF accuracy that results is hidden in the depth of field, but get up close with a 35mm L at f/1.4, and it will give you fuzzy images due to focus errors..


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## wickidwombat (Dec 16, 2011)

does anyone use the EG-S focus screen on a 5DII with f1.4 lenses to MF? I'd be interested to hear their esperience with them


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## briansquibb (Dec 16, 2011)

Mt Spokane Photography said:


> Focus and recompose works at smaller apertures where the error in AF accuracy that results is hidden in the depth of field, but get up close with a 35mm L at f/1.4, and it will give you fuzzy images due to focus errors..



I think you will find that the accuracy depends on the radius, the distance moved and the contour of the subject.

Like everything else - know your tool and you can use it in the right way. With the 5D2 you can take a step back to get the focus points to cover the right point and use MP for the crop. 

There are always exceptions - I am sure that we could find something that the D3X and 1DX cant do as well.


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## The Bad Duck (Dec 16, 2011)

wickidwombat said:


> does anyone use the EG-S focus screen on a 5DII with f1.4 lenses to MF? I'd be interested to hear their esperience with them




I do (5D mkII + 35/1.4; 50 /1.4 and 85 /1.8). With the EG-S you have an easier time telling when your focus is off. But it really does not help that much when it comes to telling if focus is spot on @ f/1.4. Live view @ 5x or 10x is the only way to really know you got it right at those apertures. Of course, that might not be possible to do in actual shooting.

Also your viewfinder gets darker and that makes it harder to handle f/4 zooms in low light.

A way to get higher odds of getting your focus right is to have a flash to help with infra red AF-assist and use the focuspoint where you want your picture sharp - even if it is not the centre point. You donÂ´t have to fire the flash, but the AF-assist really helps out. I canÂ´t figure out why there is no AF-assist in the body. I would love that for low light, no flash situations since an external flash makes the camera heavier and it also makes the camera bigger and more intimidating to some subjects. Finaly its harder to keep your camera haning over your shoulder at a party with a flash attached. 

Also, something Im still trying to get used to, is that the slightest movement from you or your subjekt might mean you loose focus. FF and fast lenses is demanding in a way I did not understand when I upgraded from my 30D and f/4 zooms.

So - go ahead and use the EG-S, it does help but does not do wonders.


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## te4o (Dec 16, 2011)

contrastny said:


> I mainly shoot landscapes, but I occasionally use AF for other subjects. The 5D II will be a great upgrade and I'll get it with the Zeiss 18mm.


Get the 21/2.8 or the 25/2. Better IQ and colours

does anyone use the EG-S focus screen on a 5DII with f1.4 lenses to MF? I'd be interested to hear their esperience with them
I use the CZ 35/1.4 with an EgS - it's better than nothing but there are many more costly and better alternatives like brightscreen.com 
35 is wide enough to be usable as MF even at 1.4 - and the CZ has a smooth focusing ring. Don't know about Canon MF, it's so wobbly that an EgS won't make a big difference...


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## sawsedge (Dec 16, 2011)

The AF factor has kept me out of the lower end FF market.

When both of these cameras came out, I had the choice to buy either. I picked the 50D for the improved AF. The AF system on the 5D2 is the same as the 5D, which is the same as the 20D. I had issues with my 20D at times. I have fewer problems with the 50D. Ironic that the 7D came a year later with much better AF. ;-) 

For my uses, I felt the IQ differences are minimal. Check this out: http://wyofoto.com/EOS_IQ_shootout_2008/EOS_shootout_2008.html The only flaw with his comparison is using the same post processing. The cameras have different sensors... different signal processing... and require different settings in post. I took his sample files and did a little different sharpening on the 50D file... and got it to look as good at low ISO. I generally don't need high ISO, but with good NR I get clean images up to ISO 1600 easily, and I've found I can do a good job with 3200 as well... on the 50D. I haven't experimented a lot with 3200 yet. 

Until you really push the print size and ISO together, I can't see any major differences in print.

For my uses, which does not *usually* include poster-sized prints, I have zero qualms with my prints from the 50D. I'm talking up to 13"x19". I came from 35mm film, and even the 20D blew my K64 and F100 slides away, so I just don't worry about it much. 

Having said all that... their is one factor that would get me to buy a full-frame model... that is the desire to use certain lenses at the wide side, like the Zeiss 21mm. If you have a specific lens or set of lenses in mind, then FF might be the right choice for you.


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## briansquibb (Dec 16, 2011)

The Bad Duck said:


> Finaly its harder to keep your camera haning over your shoulder at a party with a flash attached.
> 
> Also, something Im still trying to get used to, is that the slightest movement from you or your subjekt might mean you loose focus. FF and fast lenses is demanding in a way I did not understand when I upgraded from my 30D and f/4 zooms.



Hang your camera from a harness

If you are able to AF then use SERVO mode to hold focus whenever possible


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## awinphoto (Dec 16, 2011)

The center point of the 5d2 and the 6 invisible "assist" points are nice, but the rest of the focus points are not cross points like the 50D... In the center point the 5d is as good if not a slight edge but if you like composing WITHOUT recomposing after you locked focus and using your outside points, the 50D wins... kinda takes you back to the 30D days.... Reminds me of DigitalRev's video comparison of the 7d vs 5d2... they said the 7d's AF was kinda a smart-ass, always knowing where you want to focus on, and the 5d2 is kinda depressing.


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## Caps18 (Dec 16, 2011)

I use a 50D at work, but I have a 5Dm2 at home.

Price is a consideration, and if you are using longer telephotos to take astro photography, the 50D is probably better.

But, I have a 16-35mm, and it creates great pictures on the 5Dm2.

I am a basic focus guy, so I don't do very much in the AF arena that is demanding. I even focus in live view with the AF-On button...


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## contrastny (Dec 16, 2011)

te4o said:


> contrastny said:
> 
> 
> > I mainly shoot landscapes, but I occasionally use AF for other subjects. The 5D II will be a great upgrade and I'll get it with the Zeiss 18mm.
> ...



I'll look into those as well, but I really want something wider than 21mm and has threads for filters. I know I can stitch, but I don't want to do that to tons of images.


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## contrastny (Dec 16, 2011)

sawsedge said:


> The AF factor has kept me out of the lower end FF market.
> 
> When both of these cameras came out, I had the choice to buy either. I picked the 50D for the improved AF. The AF system on the 5D2 is the same as the 5D, which is the same as the 20D. I had issues with my 20D at times. I have fewer problems with the 50D. Ironic that the 7D came a year later with much better AF. ;-)
> 
> ...



I'm mainly looking to get a FF for less diffraction with smaller apertures. The Zeiss 18mm seems like a great lens, but I'm also open to other suggestions for ultra wide lenses that will accept filters. And eventually the Canon TS-E 24mm f/3.5.


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## MartinvH (Dec 16, 2011)

neuroanatomist said:


> MartinvH said:
> 
> 
> > How does the 5DII AF compare to the T2i/550d or similar T3i/600d ?
> ...



Thanks for this info, I could not find this detailed AF comparison information on The-digital-picture.com or any other site.
This info keeps me on the side of the ones waiting for what is coming (and saving money for that occasion) instead of buying now a discounted nice but 2008 technology 5D Mark II with a focus system even older.


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## sawsedge (Dec 20, 2011)

contrastny said:


> I'm mainly looking to get a FF for less diffraction with smaller apertures. The Zeiss 18mm seems like a great lens, but I'm also open to other suggestions for ultra wide lenses that will accept filters. And eventually the Canon TS-E 24mm f/3.5.



I've also done some testing of diffraction. I tested it on 35mm years ago, and found going down to f/16 was OK. I read that diffraction was a bigger issue with crop, and tested it on both my 20D and 50D... and again found acceptable results down to f/16. I don't see any noticeable real-world difference. f/22 is too soft for my taste with all systems, but f/16 is OK. Even the-digital-picture notes that the DLA is more of a calculation than real issue. If you compare images side-by-side, you can see some image quality loss as you stop down, but as a picture on its own, no issue. Other factors such as motion, lens quality, DOF, and precise focus are more important.

Again, if you want a superwide, you have more choices with FF.

The best wides I'm aware of are the Zeiss 21mm, Canon 24 f/1.4L, Canon 24mm TS-E. I've also read that the Olympus OM 21mm lenses are little gems, not quite as nice as the Zeiss, but an excellent value, and easily adapted to EOS.


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## dtaylor (Dec 20, 2011)

contrastny said:


> I'm mainly looking to get a FF for less diffraction with smaller apertures. The Zeiss 18mm seems like a great lens, but I'm also open to other suggestions for ultra wide lenses that will accept filters. And eventually the Canon TS-E 24mm f/3.5.



Diffraction doesn't impact any format more than any other for the same FoV and DoF. This is true from 4/3rds through large format.

That said, there are some lens options which call for FF. If you buy a 17mm T/S or a 24 f/1.4L, you probably want the stated focal length, not the cropped focal length. And T/S lenses don't work well with the flash housing on the crop bodies. (FF bodies don't have a built in flash.)

There are of course excellent UWA zoom options available now for crop if the goal is simply to go wide. Tokina 11-16 f/2.8, Canon 10-22, Sigma 8-16, etc.


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## neuroanatomist (Dec 20, 2011)

dtaylor said:


> Diffraction doesn't impact any format more than any other for the same FoV and DoF. This is true from 4/3rds through large format.



True in regards to sensor size, in that APS-C sensors do not have inherently greater diffraction than FF for a given DoF, which is a common misperception. But...doesn't pixel density play a role? So, contrastny has a 50D with 4.7Âµm pixels and a diffraction-limited aperture (DLA) of f/7.5, whereas the 5DII has 6.4Âµm pixels and a DLA of f/10.2. With the 50D at f/7.5, the same DoF would be achieved (assuming a change in focal length to compensate for FoV) at f/12 on a the 5DII. That suggests that for a given DoF, the 5DII is actually _more_ diffraction limited than the 50D, which is the opposite of the prevailing viewpoint.


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## skitron (Dec 20, 2011)

Concerning the original topic, I got my 5D2 in last night and the initial impression is the center focus point is better on it than the center focus point on my 50D. 

However, I quickly discovered that I much prefer the DOF characteristics of the crop body so far. Maybe the ridiculously thin DOF possible on FF has some uses at longer distances, but for anything shot inside a house it is not for me. I was rather surprised at that finding. 

I like nice bokeh as much as the next person, but I like it to be in the realm of the natural. It seems f1.4 on a FF goes way, way beyond what is even remotely natural and as of now I see no use for it. Please share experiences and uses if you have them!

So it will be interesting to see how stopping down a FF to get some DOF vs being able to open up on a crop plays out with respect to ISO performance. It almost looks like it's a wash if I want the kinds of DOF I get on a crop. 

For example for DOF = 1' on the 50D I set f2 for subject distance of 10' (using a true 48mm lens). For 5D2 I have to stop down to 3.2 with same lens and move subject distance 6.25' to get the equivalent shot in terms of framing and DOF. 

The 1.2 difference in aperture requires higher ISO for same result, assuming same shutter. So did I really gain anything in terms of ISO performance for equivalent shots? Is the 5D2 more than 1.2 stops better than 50D in terms of ISO/noise? Or is the only real difference perspective and resolution, given same lens / equivalent shot?


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## neuroanatomist (Dec 20, 2011)

skitron said:


> So it will be interesting to see how stopping down a FF to get some DOF vs being able to open up on a crop plays out with respect to ISO performance. It almost looks like it's a wash if I want the kinds of DOF I get on a crop.
> 
> Or is the only real difference perspective and resolution, given same lens / equivalent shot?



Practically speaking, it's pretty much a wash. Putting the same lens on FF, you have to get 1.6x closer for the same framing, and thus you get 1.6x shallower DoF (=1.3 stops). The FF sensor gathers more total light, such that ISO noise is 1.6x (same 1.3 stops) better. So, you stop down by 1.3 stops to get the DoF you want, bump the ISO by 1.3 stops to maintain the shutter speed. Wash.

If you downsample the 21 MP output of the 5DII to the 15 MP of the 50D, you'll have a little less noise because of that. 

As you state, the perspective is different, since that's determined only by subject distance - maybe that's a good change, maybe not. You could fix that (i.e. match perspective) by using a 1.6x longer focal length on the FF body.

An f/1.4 lens on APS-C gives you the DoF of f/2.2 on FF. The thing is, you can set the lens to f/2.2 on FF if you prefer, but you can't get the DoF of f/1.4 on FF using an APS-C camera (at least, not conveniently, since you'd need an f/0.9 lens). However, if you have no use for the thinner DoF then FF isn't an advantage in that area.


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## koolman (Dec 20, 2011)

neuroanatomist said:


> MartinvH said:
> 
> 
> > How does the 5DII AF compare to the T2i/550d or similar T3i/600d ?
> ...



neuroanatomist: Does what your explaining above mean - that even using the CENTER focusing point for focus, the 60d for example is more advanced then the 550d - as its center point has "duel cross" ? I was thinking to upgrade to the 60d - soley for the purpose of more accurate AF . Would I feel a diffrence?


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## neuroanatomist (Dec 20, 2011)

koolman said:


> neuroanatomist: Does what your explaining above mean - that even using the CENTER focusing point for focus, the 60d for example is more advanced then the 550d - as its center point has "duel cross" ? I was thinking to upgrade to the 60d - soley for the purpose of more accurate AF . Would I feel a diffrence?



Yes, the 60D has a more accurate center AF point than the 550D, in addition to having better (cross-type) off-center points. In some situations, you'd notice a difference, while in others (good light, high-contrast subject) probably not.


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## koolman (Dec 20, 2011)

neuroanatomist said:


> koolman said:
> 
> 
> > neuroanatomist: Does what your explaining above mean - that even using the CENTER focusing point for focus, the 60d for example is more advanced then the 550d - as its center point has "duel cross" ? I was thinking to upgrade to the 60d - soley for the purpose of more accurate AF . Would I feel a diffrence?
> ...



Do you think new rebels like the 650d - will have better AF like the 60d - or they will continue to employ the lower AF of the 550d?


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## neuroanatomist (Dec 20, 2011)

koolman said:


> Do you think new rebels like the 650d - will have better AF like the 60d - or they will continue to employ the lower AF of the 550d?



Probably not the 650D. I think that if the 70D gets improved AF, the 40/50/60D system will trickle down to the Rebel/xxxD line. But, that might require a better AF in the 7DII first, or the 70D might get a slight bump. Historically, Canon has used the AF system as a significant differentiator between the lines.


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## RonQ (Dec 21, 2011)

WOW!! 
You guys have me all confused about the 5DII, I'm this close to pulling the trigger on purchasing this body and now I'm not so sure. I shoot events and weddings; AF accuracy is extremely important to me. If the AF is that bad then why do I see so many wedding photographers using the 5DII? I should just stick with the 7D then if this is the case, sure I lose out of the FF but AF accuracy is very important. I also understand that noise is much better on a FF body, but that's what Lightroom is for.....


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## skitron (Dec 21, 2011)

After a second session with my new 5D2 here are comments I have. 

First after getting a handle on the shallow DOF I really like it at longer distances and learned to just stop down at short distance unless I want the "emerging from fog" effect. 

Second, (probably should be first since it is the subject of the thread), the AF center point is a little better than my 50D. I messed with the peripheral points in pretty low light and at least with my Sigma 50 1.4 they actually worked pretty good. I was expecting total disaster after reading here and was pleasantly surprised.

Third, the empirical IQ/noise/ISO performance is very good, it's easy to get great looking shots with this camera. Everybody and their dog shoots this camera for weddings so RonQ I'd say give it a whirl and I think you'll like it (unless maybe it's a couple of 100 meter sprinters getting hitched  )


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## neuroanatomist (Dec 21, 2011)

FF offers a substantial benefit at high ISO, and church interiors where flash isn't permitted mean you need high ISO. For static and slow-moving subjects, the 5DII's AF is fine (well, the center point is, and the outer ones in decent light). Personally, my issues with the 5DII are the poor servo tracking for somewhat faster and unpredictably moving targets. Brides and wedding guests don't usually fall into that category (if the bride is running, things have gone terribly wrong...). The center point will do well in dim light (better than the 7D, in my experience), and at the reception and other events you can mount a flash (if only for the AF assist). 

For weddings and events, portraits, etc., I think the 5DII's AF will be just fine. Running kids, agility dog competitions, etc., not so much - there, if you want sufficiently capable AF and the ISO benefits of FF (indoor sports, dance recitals, etc.), a 1DsIII or 1D X is a better option. But they're expensive, and if personal or business budgets don't support that, compromises are necessary.


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## RonQ (Dec 21, 2011)

neuroanatomist said:


> FF offers a substantial benefit at high ISO, and church interiors where flash isn't permitted mean you need high ISO. For static and slow-moving subjects, the 5DII's AF is fine (well, the center point is, and the outer ones in decent light). Personally, my issues with the 5DII are the poor servo tracking for somewhat faster and unpredictably moving targets. Brides and wedding guests don't usually fall into that category (if the bride is running, things have gone terribly wrong...). The center point will do well in dim light (better than the 7D, in my experience), and at the reception and other events you can mount a flash (if only for the AF assist).
> 
> For weddings and events, portraits, etc., I think the 5DII's AF will be just fine. Running kids, agility dog competitions, etc., not so much - there, if you want sufficiently capable AF and the ISO benefits of FF (indoor sports, dance recitals, etc.), a 1DsIII or 1D X is a better option. But they're expensive, and if personal or business budgets don't support that, compromises are necessary.


Now I'm leaning back to the 5DII, thanks!! 
The lens arsnal I'll be using on the 5D2 is a 24-70, 70-200 2.8 (non IS), and a 50 1.4. I see mostly shooting with a 24-70 and for indoor reception hall switching to my 50 1.4 with a 580EXII attached. I'm hoping that this line up will do it's job... What do you think?


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## neuroanatomist (Dec 21, 2011)

@RonQ - sounds like a plan. I'd consider a double strap with the 70-200 on a crop body, for longer shots without the need to change lenses, and so you always have a backup camera at hand, just in case.


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## RonQ (Dec 21, 2011)

Sounds good, thanks for the info/feedback neuroanatomist.


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## briansquibb (Dec 21, 2011)

Mt Spokane Photography said:


> For landscapes, portraits , and general center point usage, I find it to be very good.
> 
> In terms of AF accuracy of the center point, its extremely accurate.
> 
> ...



+1

Plus the viewfinder is good

At weddings I always compose inside the viewfinder - ie leave a little extra as this avoids cutting little bits off which you dont seen when taking shots.

I find the 70-200 the tool to take outdoors pictures when getting head and shoulders images. I think you will find the 50mm too long indoors - if you are using flash then a lens such as the 17-40 more useful as the f/4 is not an issue as probably the aperture you will be shooting will be f4/f5.6 at as it avoids missing images though OOF from lack of DOF. You may find that even the 24-70 is too long indoors for couples/groups.

Remember that a wedding shoot is as much a reportage project as an artistic exercise. There are some shots that you MUST get - keep taking them until no one is pulling a face/blinking. Artistic shots are a bonus.

If you can get to the venue a vew days before at the same time as the wedding you will be able to checkout the lighting. Take the camera and take some images - if you can, take the future bride and groom to see how their heights affects the shots. Just think of the wedding pictures of Kris Humphries and Kim Kardashian - very difficult due to the difference in height - that would very much affect your lens choice and possibly where you take pictures - there is nothing worse than seeing a picture rail at ear height


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## RonQ (Dec 21, 2011)

@briansquibb 
So in terms of the 17-40, I would assume then you use center AF point to shoot? If that's the case then how can you insure that all subjects will be in focus? Like short & tall subjects as you indicated, given that the AF is not that advanced.....


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## briansquibb (Dec 21, 2011)

RonQ said:


> @briansquibb
> So in terms of the 17-40, I would assume then you use center AF point to shoot? If that's the case then how can you insure that all subjects will be in focus? Like short & tall subjects as you indicated, given that the AF is not that advanced.....



Not sure what context you are talking about here - most images have OOF subjects, it is only the one which you are interested in which are important.

If you are talking about a wedding group - focus on the ground in front of the nearest person and then have sufficient DOF dialled in.

Tall and short people are all in the same plane so will be in focus


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## wickidwombat (Dec 21, 2011)

RonQ said:


> WOW!!
> You guys have me all confused about the 5DII, I'm this close to pulling the trigger on purchasing this body and now I'm not so sure. I shoot events and weddings; AF accuracy is extremely important to me. If the AF is that bad then why do I see so many wedding photographers using the 5DII? I should just stick with the 7D then if this is the case, sure I lose out of the FF but AF accuracy is very important. I also understand that noise is much better on a FF body, but that's what Lightroom is for.....



just use the center point and f2.8 lenses or faster and you'll be fine


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## briansquibb (Dec 21, 2011)

wickidwombat said:


> RonQ said:
> 
> 
> > WOW!!
> ...



I think F/4 as well?


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## Meh (Dec 21, 2011)

RonQ said:


> @briansquibb
> So in terms of the 17-40, I would assume then you use center AF point to shoot? If that's the case then how can you insure that all subjects will be in focus? Like short & tall subjects as you indicated, given that the AF is not that advanced.....



@RonQ I recall you asked a similar question the other day in another thread. It might just be your choice of words but your question about short/tall subjects being in focus if only using a center AF point suggests that you might think that by using multiple focus points that the camera can independently achieve focus at each point but that is not the case (I apologize if I'm just misunderstanding your comment). The camera can only focus at one distance at a time and every object that is at that distance from the camera will be in focus. A tall person standing vertically (assuming the camera is held perpendicular to the ground) will be in focus from head to toe (more or less) because their whole body is aligned on the focal plane. It doesn't matter whether you only used the center AF point, an off center point, or many points.


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## RonQ (Dec 21, 2011)

Meh said:


> RonQ said:
> 
> 
> > @briansquibb
> ...


It's OK Meh, I'm just trying to learn from others.... I recently had a similar experience where my lens was wide open 2.8 shooting in AP and only the foreground subject was in full focus, all others were not. I was so upset that I kicked myself several times trying to figure out what, if anything, I did wrong..... Once I changed to A-DEP the next day trying to take a similar shot with different subjects, everyone was in focus. However, the only difference between the two were one was shot at sunset and the other (test subjects) were shot in full sunlight. 
Yehh, I'm aware it could have also been my camera and that's a possibility, I took it into the Canon Service center (about 2 blocks) from me and they swore nothing was wrong... However, 2 days later, I shot a family for portraits and I had a similar issue..... I was so frustrated that I went to manual focus and finished the job. I took it back to Canon and told them that this was unacceptable, it took them 8 days to get the camera back to me indicating that they had to change out the FA and that it was causing inaccurate focus, they changed it out and did some electrical adjustments and since I have not had any clients to shoot, I'm assuming it's back to normal but still curious as to how other photographers are shooting.


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## QNeX (Dec 21, 2011)

briansquibb said:


> wickidwombat said:
> 
> 
> > just use the center point and f2.8 lenses or faster and you'll be fine
> ...



Well, with f/4 you get only horizontal sensitivity, vertical line has
sensitivity with f/2.8 or brighter lenses only.

In other words, with f/4 lens you won't have a cross center focus point,
you'll get plain old horizontal f/5.6 point.


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## skitron (Dec 22, 2011)

QNeX said:


> briansquibb said:
> 
> 
> > wickidwombat said:
> ...



Now that is a fly in the ointment for my plan to buy a 70-200 f4 IS...


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## neuroanatomist (Dec 22, 2011)

QNeX said:


> briansquibb said:
> 
> 
> > wickidwombat said:
> ...



Briansquibb is correct. The 5DII's center AF point is an f/5.6-sensitive cross-type point, with additional f/2.8 sensitivity in a single orientation.


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## QNeX (Dec 22, 2011)

neuroanatomist said:


> Briansquibb is correct. The 5DII's center AF point is an f/5.6-sensitive cross-type point, with additional f/2.8 sensitivity in a single orientation.



I've had an impression that a single line can be either higher precision (f/2.8), but will only work with f/2.8 or faster lesnes, and that is the reason why xxD bodies (IIRC starting with 40D) have center point that is composed of horizontal and vertical lines sensitive to f/5.6 and additional diagonal lines sensitive to f/2.8.

I did look for more authoritative source and found this:
http://cpn.canon-europe.com/content/education/infobank/autofocus/autofocus.do



> *EOS 5D Mark II AF system*
> (...)
> The centre AF point has a special hybrid design. With f/2.8 or faster lenses, focusing is a two-step process. First, the f/5.6-sensitive cross-type sensor components are used to focus. When focus is almost achieved, a switch is made to the f/2.8-sensitive vertical line-sensitive sensors for high-precision focusing.
> 
> ...



So, I stand corrected. Thanks for pointing this out!


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## neuroanatomist (Dec 22, 2011)

QNeX said:


> xxD bodies (IIRC starting with 40D) have center point that is composed of horizontal and vertical lines sensitive to f/5.6 and additional diagonal lines sensitive to f/2.8.



I think the reason for that arrangement is so that the center AP point is acting as cross type with _all_ lenses for the entire focusing process.


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