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Registered: ‎12-07-2012

Re: T7i Focusing Issues?

"BTW, a 1/400 shutter speed is not super fast, but it is the minimum that I would use with that lens photographing toddlers."

 

Have at it, there is no law or 'rule' against it.  Smiley Very Happy  It just isn't necessary.

EOS 1DX and 1D Mk IV and several lenses!
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Registered: ‎12-07-2012

Re: T7i Focusing Issues?

Tim said,

"This news shouldn't be a surprise to anyone.   Most experienced photographers know this.  I didn't invent the idea."

 

WOW, perhaps I need to go live my life all over again.  Smiley Surprised

Most experienced photographers know what works and what doesn't.  But than again most experienced photographers don't have the time to read pretty graphs and book learn about physics. They do what works.  If they are out making money that is.

 

"There are no exceptions."

 

Oh, yes, there is.  There are the hobbyists, the book learners, and those infatuated with the physics of photography. Then there are the rest of us that just do the work.  Just like my little test images of the best lens vs a much less good lens. No reliable guesses but the charts tell us you should see the difference quite readily.

EOS 1DX and 1D Mk IV and several lenses!
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Posts: 3,816
Registered: ‎06-11-2013

Re: T7i Focusing Issues?


@ebiggs1 wrote:

Tim said,

"This news shouldn't be a surprise to anyone.   Most experienced photographers know this.  I didn't invent the idea."

 

WOW, perhaps I need to go live my life all over again.  Smiley Surprised

Most experienced photographers know what works and what doesn't.  But than again most experienced photographers don't have the time to read pretty graphs and book learn about physics. They do what works.  If they are out making money that is.

 

"There are no exceptions."

 

Oh, yes, there is.  There are the hobbyists, the book learners, and those infatuated with the physics of photography. Then there are the rest of us that just do the work.  Just like my little test images of the best lens vs a much less good lens. No reliable guesses but the charts tell us you should see the difference quite readily.


Ernie... I don't know why you're trying to defend this.  

 

The diagram helps people see how when a subject distance has not changed, and only the camera composition changes, something that had critical focus will no longer be in critical focus after re-composing.  

 

Technically lenses do not have perfectly flat focus fields, but they do endeavor to try to be flat.  

 

So here's an example using actual photographs.  This was taken using an 85mm f/1.4 lens.  The camera is on a tripod.  The focus card is on another tripod.  This guarantees that the distance never actually changed, nothing moved, there was only a rotation of the tripod head to recompose for the 2nd shot.  This is "straight out of the camera" (other than converting RAW to JPEG and sizing it for the message forum.)

 

In photo 1, I've centered my focus test target, used the center AF point, and I've put it on the center of the high-contrast test target.  Check the diagonal scale to the right of the focus point and you can see that the "0" point is nicely focused.

 

2W0A1331.jpg

 

Photo 2 was also focused using the same center AF point and using the same position on the target (the high-contrast target just left of the "0" position on the scale) BUT THIS TIME after the camera locked focus, I recomposed so that this position would be on the right side of the frame.  Notice what happens to focus here:

 

2W0A1332.jpg

 

Since these are uncropped images, but the size had to be reduced to fit on the forums, you might not be able to read the focus card very easily.  So I've supplied the same images, but cropped in on the area of interest.

 

Here's the first image (cropped) where the target is at the center.

 

2W0A1331-2.jpg

 

You can see in the image above that the camera did a pretty good job with the focus.

 

But here's the crop of image #2 where we re-composed.

 

2W0A1332-2.jpg

 

The focus target is no longer in optimal focus.  We have at least 1 full centimeter of back-focus and the detail we can view around the "0" position (which is blurry) is what we could expect if this were a subject's eye and we focused and recomposed with a shallow depth of field.

 

Now I did say that the laws of physics are the same everywhere, for everyone, and for everywhen ... and that there are no exceptions.

 

Ernie, you took issue with that statement.  Are you suggesting that if we replace a focus test target with a human face and eye that, for some reason, the laws of physics will change?

 

I would have thought the diagram would have been enough for most people to visualize why this happens. 

 

 

 

Tim Campbell
5D III, 5D IV, 60Da
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Posts: 11,666
Registered: ‎12-07-2012

Re: T7i Focusing Issues?

"I don't know why you're trying to defend this."

 

I am not trying to defend this, I am telling it like it is.  You can show all the test graphs and charts you want.  In reality it makes no difference in the finished work.  That is the important part that all graph and chart readers don't realize.

 

Would you like for me to show you several thousand photos and have you tell me which were recomposed?  This makes for a good coffee table discussion or perhaps a college lecture hall but that's about it.  You see the big difference is in our background.  You are a hobbyist and this stuff is important to you.  To working photographers like me it doesn't.  Why?  Because it doesn't effect our work like it does your lab tests.

 

If you believe MTF charts you would think some lenses were so bad to be nearly useless.  But in fact that couldn't be more untrue.  It is the same thing.

 

Tim if you a worried this will ruin your photographs, make sure you follow the rules.  I'll continue to shoot the same way as I always have until somebody complains about recomposing focus issues.   Perhaps you would like to explain to this young lady her shot is ruined because it is recomposed?

 

_DS32719.jpg

 

It is all about how you use it.  It is all about how you use your gear.  It is not about charts and graphs that don't tell the true story.  Tim I am done because we are too far apart.  I am not a chart reader, you are.  We are both happy so there is an end to it.

 

EOS 1DX and 1D Mk IV and several lenses!
Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: T7i Focusing Issues?


@ebiggs1 wrote:

"I don't know why you're trying to defend this."

 

I am not trying to defend this, I am telling it like it is.  You can show all the test graphs and charts you want.  In reality it makes no difference in the finished work.  That is the important part that all graph and chart readers don't realize.

 

Would you like for me to show you several thousand photos and have you tell me which were recomposed?  This makes for a good coffee table discussion or perhaps a college lecture hall but that's about it.  You see the big difference is in our background.  You are a hobbyist and this stuff is important to you.  To working photographers like me it doesn't.  Why?  Because it doesn't effect our work like it does your lab tests.

 

If you believe MTF charts you would think some lenses were so bad to be nearly useless.  But in fact that couldn't be more untrue.  It is the same thing.

 

Tim if you a worried this will ruin your photographs, make sure you follow the rules.  I'll continue to shoot the same way as I always have until somebody complains about recomposing focus issues.   Perhaps you would like to explain to this young lady her shot is ruined because it is recomposed?

 

_DS32719.jpg

 

It is all about how you use it.  It is all about how you use your gear.  It is not about charts and graphs that don't tell the true story.  Tim I am done because we are too far apart.  I am not a chart reader, you are.  We are both happy so there is an end to it.

 


 

You're right.  In that photo, with a depth of field so broad that we can read the name of the school on the building in the background, a short focal length (with wide-angle distortion and the vertials leaning apart due to an unlevel camera), shot in mid-day sun with no fill-lighting,  and a subject placed so far apart and so small, we can't even see the subjects eyes... much less count the eye-lashes -- the focus & recompose just doesn't matter.

 

Tim Campbell
5D III, 5D IV, 60Da
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Posts: 10
Registered: ‎01-18-2018

Re: T7i Focusing Issues?

Oook... anyway, got the 6D Mk 2 today... some preliminary results show that it focuses quite well with that lens. Will have to try more.

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Re: T7i Focusing Issues?

[ Edited ]

@rgfoto wrote:

Oook... anyway, got the 6D Mk 2 today... some preliminary results show that it focuses quite well with that lens. Will have to try more.


It focuses very well with it. With 27 f/8 AF points, it tracks very well with an 1.4x extender with telephoto lens. Set Image Priority to Focus Priority.

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Posts: 11,666
Registered: ‎12-07-2012

Re: T7i Focusing Issues?

"...the focus & recompose just doesn't matter."

 

Now you know the difference between real world situations and your theoretical chart world.

EOS 1DX and 1D Mk IV and several lenses!
Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: T7i Focusing Issues?

That camera supports the "auto focus micro-adjustment" feature.  If you focus an AF point on a subject, but the result consistently focuses a touch closer or a touch farther, the AFMA feature will let you tweak the camera's focus behavior.  

 

AFMA can track independent focus adjustments based on lens model.  So if one lens slightly front focuses, but another slightly back-focuses, it's still able to be adjusted to accommodate both lenses.

 

Tim Campbell
5D III, 5D IV, 60Da
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