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Strong rumours of Nikon Mirrorless by 2019   -   Page   16
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Posted: Tue Aug 21st, 2018 18:03
 
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jk



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Location: Carthew, Cornwall, United Kingdom
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 Eric wrote:
jk wrote:
With mirrorless it is more critical (depending on the AF method in the camera) to have the AF spot over the point of interest for sharpest focus.
That is a mirrorless learning. DSLRs potentially are the same but it 'seems' less critical.

In my testing if you use AF-S and single central point on a mirrorless and DSLR then the Mirrorless with AF point centred on point of interest yields a sharp picture 'every' time.
If you do central AF point and focus and recompose then your critical sharp images drops to 50-80%. Big difference!
DSLRs are different autofocus mechanism to mirrprless but even they are improved by this method of focusing from mirrorless.
Obviously it slows down your rate of working. Also it works best with static subjects. But that is why there are AF-C and AF-S modes and autofocus settings!

I don't understand that Jonathan.

In AF-S mode with the focus spot centre screen..... turning to position the subject under that spot centre screen, hitting the AF lock button at the back....fixes the focus point on that subject distance. Reframing without touching anything or moving, surely keeps the focus where you left it? Don't see why a mirrorless is any different to a DSLR in registering the correct focus point by this method?

I can understand it causing an issue if you use the shutter button to focus and do exposure AND if you remove your finger so it refocuses. I can also accept that if the subject requires AFC AND is off centre in the required framing, moving the sensor point could be beneficial.
But I don't understand how the camera having been focused using the focus and reframe method when locked can give differing results by moving the focus spot around the screen?

It is not intuitive but it is about lens physics.
The distance between the node point in the lens and subject and projected object (image plane) varies when you change the AF location point. Locking focus makes no difference. The effect is magnified in mirrorless as distance between lens node and image plane is less than DSLR, another effect is node to subject distance so any focus error is magnified whn taking portrais compared to lanscapes with subject close to infinity.
I feel the need for a drawing.



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Posted: Wed Aug 22nd, 2018 03:01
 
152nd Post
Eric



Joined: Wed Apr 18th, 2012
Location: United Kingdom
Posts: 4529
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 jk wrote:
Eric wrote:
jk wrote:
With mirrorless it is more critical (depending on the AF method in the camera) to have the AF spot over the point of interest for sharpest focus.
That is a mirrorless learning. DSLRs potentially are the same but it 'seems' less critical.

In my testing if you use AF-S and single central point on a mirrorless and DSLR then the Mirrorless with AF point centred on point of interest yields a sharp picture 'every' time.
If you do central AF point and focus and recompose then your critical sharp images drops to 50-80%. Big difference!
DSLRs are different autofocus mechanism to mirrprless but even they are improved by this method of focusing from mirrorless.
Obviously it slows down your rate of working. Also it works best with static subjects. But that is why there are AF-C and AF-S modes and autofocus settings!

I don't understand that Jonathan.

In AF-S mode with the focus spot centre screen..... turning to position the subject under that spot centre screen, hitting the AF lock button at the back....fixes the focus point on that subject distance. Reframing without touching anything or moving, surely keeps the focus where you left it? Don't see why a mirrorless is any different to a DSLR in registering the correct focus point by this method?

I can understand it causing an issue if you use the shutter button to focus and do exposure AND if you remove your finger so it refocuses. I can also accept that if the subject requires AFC AND is off centre in the required framing, moving the sensor point could be beneficial.
But I don't understand how the camera having been focused using the focus and reframe method when locked can give differing results by moving the focus spot around the screen?

It is not intuitive but it is about lens physics.
The distance between the node point in the lens and subject and projected object (image plane) varies when you change the AF location point. Locking focus makes no difference. The effect is magnified in mirrorless as distance between lens node and image plane is less than DSLR, another effect is node to subject distance so focus error is magnified whn taking portrais compared to lanscapes with subject close to onfinity.
I feel the need for a drawing.


:bowing:



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Eric
 




Posted: Wed Aug 22nd, 2018 03:02
 
153rd Post
Eric



Joined: Wed Apr 18th, 2012
Location: United Kingdom
Posts: 4529
Status: 
Offline
 jk wrote:
Eric wrote:
jk wrote:
With mirrorless it is more critical (depending on the AF method in the camera) to have the AF spot over the point of interest for sharpest focus.
That is a mirrorless learning. DSLRs potentially are the same but it 'seems' less critical.

In my testing if you use AF-S and single central point on a mirrorless and DSLR then the Mirrorless with AF point centred on point of interest yields a sharp picture 'every' time.
If you do central AF point and focus and recompose then your critical sharp images drops to 50-80%. Big difference!
DSLRs are different autofocus mechanism to mirrprless but even they are improved by this method of focusing from mirrorless.
Obviously it slows down your rate of working. Also it works best with static subjects. But that is why there are AF-C and AF-S modes and autofocus settings!

I don't understand that Jonathan.

In AF-S mode with the focus spot centre screen..... turning to position the subject under that spot centre screen, hitting the AF lock button at the back....fixes the focus point on that subject distance. Reframing without touching anything or moving, surely keeps the focus where you left it? Don't see why a mirrorless is any different to a DSLR in registering the correct focus point by this method?

I can understand it causing an issue if you use the shutter button to focus and do exposure AND if you remove your finger so it refocuses. I can also accept that if the subject requires AFC AND is off centre in the required framing, moving the sensor point could be beneficial.
But I don't understand how the camera having been focused using the focus and reframe method when locked can give differing results by moving the focus spot around the screen?

It is not intuitive but it is about lens physics.
The distance between the node point in the lens and subject and projected object (image plane) varies when you change the AF location point. Locking focus makes no difference. The effect is magnified in mirrorless as distance between lens node and image plane is less than DSLR, another effect is node to subject distance so focus error is magnified whn taking portrais compared to lanscapes with subject close to onfinity.
I feel the need for a drawing.

:rtfm:



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