Looking to get into full-frame...

neil_g · 12 Sep 2011 at 14:20

jonneymendoza said:
if u don print larger then A4/A3 and don shoot high ISO, why u using a 5dmk2?

rofl. youre funny.

jonneymendoza · 12 Sep 2011 at 14:26

Ejizz said:
^^^
You kind of have a point, but they will argue they bought the camera to take advantage of other features other than AF, such as ISO or MP's, which is fair enough I guess.

well thats why i said how if someone doesnt shoot high ISO and doesnt print large pints, again, why use a 5dmk2.

This is not just about AF. my whole point is the advanced features a camera body has and a scenario where a person doesnt USE most/none of the key features.

Rojin · 12 Sep 2011 at 14:28

A lot of people buy a FF camera for that simple fact, they like a FF sensor. Everything else is just a bonus, and lets be honest the sensor in the 5D2 is rather nice!

D.P. · 12 Sep 2011 at 14:47

To be straight to the point, the reason not to focus and recompose is because the focus plane is exhibits a lot of field curvature, especially on most of the fast lenses that we all like to use, and it is even wore at short focus distances. The plane is not a plane at all but a 3D manifold. Unless you are shooting at f/8 with your fancy 24-70mm, 85mm f/1.4 type lenses then you will reduce IQ and suffer out of focus images. A second problem is the mere trigonometry of the situation will further push the focal point away from where you inetnd it to be when you recompose.

It ahs nothign to do with using the functionality of the camera. Presumably one buys a FF camera because they care about IQ or shoot shallow DoF scenes.
If you care about IQ, then you care about getting the focus and DoF correct. The focus and recompose technique does not allow you to achieve this.

BusError · 12 Sep 2011 at 14:54

jonneymendoza said:
a car and a camere is completetly different. a car u judge by comfy inside, leg room at the back? engine? reliability, build quality etc etc.

for camera's u usualy judge by IQ, ISO quality and AF. maybe a couple more but point is that u cant compare a car to a camera and my points still stand i.e if u don print larger then A4/A3 and don shoot high ISO, why u using a 5dmk2?

You should downgrade your keyboard, you obviously don't need one with "y" or "o" keys that much.

Tooks · 12 Sep 2011 at 15:05

D.P. said:
To be straight to the point, the reason not to focus and recompose is because the focus plane is exhibits a lot of field curvature, especially on most of the fast lenses that we all like to use, and it is even wore at short focus distances. The plane is not a plane at all but a 3D manifold. Unless you are shooting at f/8 with your fancy 24-70mm, 85mm f/1.4 type lenses then you will reduce IQ and suffer out of focus images. A second problem is the mere trigonometry of the situation will further push the focal point away from where you inetnd it to be when you recompose.

It ahs nothign to do with using the functionality of the camera. Presumably one buys a FF camera because they care about IQ or shoot shallow DoF scenes.
If you care about IQ, then you care about getting the focus and DoF correct. The focus and recompose technique does not allow you to achieve this.

I'll be honest, and say I don't really understand what you're going on about...

But, I'll play along. I think you're saying if I focus on something, lock that focus, and then move the camera to recompose so that the subject I focussed on is to the left edge of my frame for instance, then the plane of the sensor/lens will have moved, and that will likely mess up my focusing?

So, if using focus and recompose doesn't allow you to achieve correct focus and DoF, you're suggesting that I should compose the shot, then choose my focus point via the selector? I can see how in some circumstances, the latter might be more 'correct', but it depends on what you're shooting doesn't it? If the end results look good though, does it matter whatever method you use?

Tooks · 12 Sep 2011 at 15:14

Rojin said:
A lot of people buy a FF camera for that simple fact, they like a FF sensor. Everything else is just a bonus, and lets be honest the sensor in the 5D2 is rather nice!

I got a FF sensor camera for its noise/low light performance (owl photography where the light is always getting worse!), simple as that. I couldn't care less that it has a narrower depth of field etc, it's horses for courses isn't it.

bigredshark · 12 Sep 2011 at 15:16

Tooks said:
I'll be honest, and say I don't really understand what you're going on about...

But, I'll play along.

So, if using focus and recompose doesn't allow you to achieve correct focus and DoF (although I'd have thought focusing on what you want to focus on using a single point, recomposing the shot, and ensuring you're using the aperture you want would do exactly that), what do you suggest we should all be doing instead?

His point is good, the focus plane isn't perfectly flat, or in some cases anywhere close, so if you focus then recompose with a wide aperture then there's a decent chance your subject won't be in focus anymore because it's in a different part of the frame and hence out of the focal plane for that location.

The answer is, don't autofocus and recompose wide open. How you resolve that is up to you, either outer AF points or manual focus would be the obvious.

D.P. · 12 Sep 2011 at 15:21

F
Here is a link explaining the simple trigonometry problem:
http://www.digital-photography-school.com/the-problem-with-the-focus-recompose-method

Bascially the hypotenuse of a triangle is longer than the oposite edge. This is one small problem which recieves most of the attention, but is not the biggest culprit. However, it is clear that from this alone you can find your focus distance incorrect by a distance larger than your DoF!

Secondly, one expects when focusing say parallel at a brick wall that the focus is a flat plane and everything to the edge would be sharp. With fast glass the focus is not a plane at all, it is very curved. So if you stand 2m away from a wall and focus in the centre you expect a focus plane at 2m, but away from the centre of the frame the focus actully curves away.

Have a look in this link, at the section discussing Field Curvature.
http://www.photozone.de/canon_eos_ff/528-canon2470f28ff?start=1

See how the focus plane is not a flat plane but curved. It is actually curved in 3D, so both sideways and vertically, this is called a manifold. Anyway, From that diagram you can clearly see that focusing the camera at one distance, then recomposing will mean the subject may not be close to the focus plane intended.

Fast lenses exhibit this more, the affect is worse at shroter distacnes, and worse with wider apertures. It is entirely possible to get a focus error of 20-30cm even altjough your DoF is only 5-10cm, thus an entire human head goes out of critical focus during the recomposition.

BusError · 12 Sep 2011 at 15:24

Focus and recompose is a skill, it's not as simple as "just move your head". there is a bit of camera twisting involved to make sure the focal plane rotates more around the subject and not around the camera. It is a very subtle knack to get, but is in fact very easy.
Also, with a Eg-S screen, you can very easily control where the focus actually is and adjust as necessary.

I much, much prefer to focus and recompose, especially when I have to turn the camera landscape/portrait, otherwise you spend your time faffing around with the focus point instead of looking at the subject.

D.P. · 12 Sep 2011 at 15:29

The solutions are to stop down the lens, manual focus, or selct the focus poitn closest to your intended subject, i.e. the outer focus points.

Sorry if I sounded insulting when explaining that I was shocked that people still do the old focus and recompose technique. To me it is just basic rule, i.e. use a fast enough shutter speed, properly expose, use a tripod if possible, etc.

D.P. · 12 Sep 2011 at 15:33

BusError said:
Focus and recompose is a skill, it's not as simple as "just move your head". there is a bit of camera twisting involved to make sure the focal plane rotates more around the subject and not around the camera. It is a very subtle knack to get, but is in fact very easy.
Also, with a Eg-S screen, you can very easily control where the focus actually is and adjust as necessary.

I much, much prefer to focus and recompose, especially when I have to turn the camera landscape/portrait, otherwise you spend your time faffing around with the focus point instead of looking at the subject.

It si nto easy because field curvature is different on every lens, at eevery aperture at every focus distance, and is a non-linear function of of distance form the centre of the frame. To make matetrs worse all these variable act in a somewhat non-linear way. There is no easy way around it, it is a physical phenomenon. You can try to minimise it by selecting the focus point closest to your subject.

Note, it is not as simple as simply keeping the distance to subject the same, That wont work.

An Exception · 12 Sep 2011 at 15:33

BusError said:
Focus and recompose is a skill, it's not as simple as "just move your head". there is a bit of camera twisting involved to make sure the focal plane rotates more around the subject and not around the camera. It is a very subtle knack to get, but is in fact very easy.
Also, with a Eg-S screen, you can very easily control where the focus actually is and adjust as necessary.

I much, much prefer to focus and recompose, especially when I have to turn the camera landscape/portrait, otherwise you spend your time faffing around with the focus point instead of looking at the subject.

Doesn't solve the trigonometry problem. Focus recompose is useless when shooting something like a portrait wide open, as the eyes won't be sharp.

D.P. · 12 Sep 2011 at 15:37

Ejizz said:
Doesn't solve the trigonometry problem. Focus recompose is useless when shooting something like a portrait wide open, as the eyes won't be sharp.

This is a clasic case of focus and recompose failure, wehn you need mm focusing accuracy.

Raymond Lin · 12 Sep 2011 at 15:40

D.P. said:
This is a clasic case of focus and recompose failure, wehn you need mm focusing accuracy.

FF at 1.2.

I often get the eye lashes in focus but not the eyeball...it is a very fine line.

An Exception · 12 Sep 2011 at 15:40

D.P. said:
This is a clasic case of focus and recompose failure, wehn you need mm focusing accuracy.

Or if you get lucky the wrong eye is sharp...

An Exception · 12 Sep 2011 at 15:42

Raymond Lin said:
FF at 1.2.

I often get the eye lashes in focus but not the eyeball...it is a very fine line.

I mostly try to aim for the bottom eyelid.

Rojin · 12 Sep 2011 at 16:00

What you want is the "Tracking Focus" or whatever it is called on the new Sony A77, you focus on the subject in the centre then recompose your frame and the camera keeps the focus on target for you. Nice

(If it all works of course!

)

Raymond Lin · 12 Sep 2011 at 16:21

Or bring back eye control back from the 90's, implement it with cross points focus all round.

Compose, look at your subject and shoot.

Tooks · 12 Sep 2011 at 16:29

D.P. said:
F
Here is a link explaining the simple trigonometry problem:
http://www.digital-photography-school.com/the-problem-with-the-focus-recompose-method

Bascially the hypotenuse of a triangle is longer than the oposite edge. This is one small problem which recieves most of the attention, but is not the biggest culprit. However, it is clear that from this alone you can find your focus distance incorrect by a distance larger than your DoF!

Secondly, one expects when focusing say parallel at a brick wall that the focus is a flat plane and everything to the edge would be sharp. With fast glass the focus is not a plane at all, it is very curved. So if you stand 2m away from a wall and focus in the centre you expect a focus plane at 2m, but away from the centre of the frame the focus actully curves away.

Have a look in this link, at the section discussing Field Curvature.
http://www.photozone.de/canon_eos_ff/528-canon2470f28ff?start=1

See how the focus plane is not a flat plane but curved. It is actually curved in 3D, so both sideways and vertically, this is called a manifold. Anyway, From that diagram you can clearly see that focusing the camera at one distance, then recomposing will mean the subject may not be close to the focus plane intended.

Fast lenses exhibit this more, the affect is worse at shroter distacnes, and worse with wider apertures. It is entirely possible to get a focus error of 20-30cm even altjough your DoF is only 5-10cm, thus an entire human head goes out of critical focus during the recomposition.

Ok, thanks, I understand more what was being said with the links etc.

Thankfully, with my photographic subjects, using the point and recompose method isn't something I've noticed making a mess of my intended focus point, I guess my situations mean it isn't that critical. Having said that, it could have course explain why occassionally I get a shot that isn't in focus, even though I know I focused there!

I shall consider this a bit more next time I'm shooting some portraits.