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Posts: 11,674
Registered: ‎12-07-2012

Re: T7i Focusing Issues?

[ Edited ]

"I do not recommend “focus and recompose” techniques ..."

 

I totally disagree with this. I use focus and recompose all the time.  Almost every shoot I go on will have a focus and recompose situation. Focus and recompose is not focusing on a distant mountain and then fixing on a close up tree.

It involves the subject, in perfect focus, and then simply moving the frame.  The subject is just in a different place in the frame not further or closer.

One shot and single center focus point is your most accurate AF.  It should be your priority mode.  Employing the others as situations occur.

 

As for SS, 1/250 should capture any toddlers movements.  Even fast toddlers!

 

Your T7i has 25% more resolution than the T5i.  That is good but focus errors will be 25% easier to see vs the T3i.

EOS 1DX and 1D Mk IV and several lenses!
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Posts: 11,674
Registered: ‎12-07-2012

Re: T7i Focusing Issues?

Since you have two cameras using the same lens, one works and one doesn't, you may have a defective camera.

Call Canon support 1 (800) 652-2666

EOS 1DX and 1D Mk IV and several lenses!
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Occasional Contributor
Posts: 10
Registered: ‎01-18-2018

Re: T7i Focusing Issues?


@ebiggs1 wrote:

"I do not recommend “focus and recompose” techniques ..."

 

I totally disagree with this. I use focus and recompose all the time.  Almost every shoot I go on will have a focus and recompose situation. Focus and recompose is not focusing on a distant mountain and then fixing on a close up tree.

It involves the subject, in perfect focus, and then simply moving the frame.  The subject is just in a different place in the frame not further or closer.

One shot and single center focus point is your most accurate AF.  It should be your priority mode.  Employing the others as situations occur.

 

As for SS, 1/250 should capture any toddlers movements.  Even fast toddlers!

 

Your T7i has 25% more resolution than the T5i.  That is good but focus errors will be 25% easier to see vs the T3i.


With most lenses this seems to work, but with the 24-105 it seems that the image will be soft. I'm not sure why, but seems to have to do with angles and triganometry. I watched some videos on the subject, and its better to use a different focusing point in camera than focus and recompose.

VIP
Posts: 11,674
Registered: ‎12-07-2012

Re: T7i Focusing Issues?

"... but with the 24-105 it seems that the image will be soft."

 

I used the ef 24-105mm f4L for years and years.  Two of them as a matter of fact.  Neither exhibited that behavior.  I used them both on Rebels and 1 series and 7 & 5Dxxx cameras.  Focus and recompose is a fact of life if you are in business to sell your work.

 

The ef 24-105mm f4 isn't the sharpest tack in the drawer but it is plenty sharp.

EOS 1DX and 1D Mk IV and several lenses!
VIP
Posts: 8,641
Registered: ‎08-13-2015

Re: T7i Focusing Issues?

"As for SS, 1/250 should capture any toddlers movements.  Even fast toddlers!"

 

Eh, I do not know about that claim of "any" movement.

 

The rule of thumb says use a minimum shutter speed of 1/FL, FL equals focal length.  On a crop body, I like to go with with 1/(2*FL), because the math is easier than using 1.6.  That works out to roughly 1/200 to 1/250 as a minimum speed.  

So, that 1/250 is really near the bottom end of the range of recommened minimum shutter speeds.  And, the OP asked if 160-250 shutter is fast enough.  The 1/160 speed is not fast enough, at all.  The correct answer is no, using a 160-250 SS is not quite fast enough for an APS-C sensor camera body and that lens combination.

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Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: T7i Focusing Issues?


@ebiggs1 wrote:

"I do not recommend “focus and recompose” techniques ..."

 

I totally disagree with this. I use focus and recompose all the time.  Almost every shoot I go on will have a focus and recompose situation. Focus and recompose is not focusing on a distant mountain and then fixing on a close up tree.

It involves the subject, in perfect focus, and then simply moving the frame.  The subject is just in a different place in the frame not further or closer.

 


Ernie, it depends on the depth of field (which is why I said I wouldn't do this unless I had a broad depth of field).  But this is a well-understood issue.  Focus & recompose with a shallow depth of field is a good way to get a lot of out-of-focus shots.

 

Here's a diagram that will hopefully clear things up.

 

Focus & Recompose.png

 

This is a perfect circle with a camera located at the center.  The camer is focused to the radius of the circle such that everything on the blue circle would be in perfect focus.

 

I've drawn a subject on the circle toward the right and indicated the position of the subject's eyes.  I've also drawn a depth of field box ... green is in focus, red is out of focus.   There are two of these boxes.  The one over the subject is used to establish "focus".  The one in the top center of the circle is used for "composition" (e.g. rule of thirds).

 

Notice when you look at this, that the subject's eyes are no longer on the focus plane.

 

This is why you really need to be careful when doing focus & recompose if using a shallow depth of field (which often is used for portraiture.)

 

Do not just rely on the center AF point for everything.  There's a good reason the camera has more than one AF point.

Tim Campbell
5D III, 5D IV, 60Da
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Posts: 11,674
Registered: ‎12-07-2012

Re: T7i Focusing Issues?

Tim that might work in the lab or on a pretty graph but it doesn't hold true in the real world shooting.  I use it constantly.  I used it last week on yearbook photos.  No one said darn you recomposed didn't you?

You of all of us should know graphs and charts don't tell the whole tail.

EOS 1DX and 1D Mk IV and several lenses!
VIP
Posts: 11,674
Registered: ‎12-07-2012

Re: T7i Focusing Issues?

"The rule of thumb says use a minimum shutter speed of 1/FL, FL equals focal length.  On a crop body, I like to go with with 1/(2*FL), because the math is easier than using 1.6.  That works out to roughly 1/200 to 1/250 as a minimum speed."

 

One big problem is, "the rule of thumb" is a suggestion.  It is not a law.  Not only do you need to know what camera, you need to know what lens and most importantly what subject you are shooting.  Even the individual photographer will effect "the rule of thumb".

 

That is one fast toddler if he can move quicker than 1/250th of a second.  I typically avoid shooting babies and toddlers, I leave that to my niece, but when I do, super fast SS is not needed.  But you do as you see fit.

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

Re: T7i Focusing Issues?

Physics is physics.  The laws of physics are true everywhere, for everyone, and for everywhen.  There are no exceptions.

 

 

True, charts & graphs don't tell us everything about a lens.   They don't tell us how well image stabilization works or how fast the auto-focus motors can achieve focus.  They don't tell us what sort of character we can expect in the out-of-focus background blur.    BUT... when we care about in-focus areas... charts and graphs DO tell us that.

 

BTW, I did qualify that whether or not you can trust "focus & recompose" depends on depth of field.  Don't use it when using shallow DoF.  If using a broad DoF ... use it all you want.

 

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

 

Tim Campbell
5D III, 5D IV, 60Da
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Posts: 8,641
Registered: ‎08-13-2015

Re: T7i Focusing Issues?

"That is one fast toddler if he can move quicker than 1/250th of a second.  I typically avoid shooting babies and toddlers, I leave that to my niece, but when I do, super fast SS is not needed.  But you do as you see fit."

I see.  Once again, you have totally missed the point.  It is not about how fast the toddler can move.  The point is having a fast enough shutter speed for the focal length that you are using, which in this case means using a 24-105mm lens, or 105mm.

BTW, a 1/400 shutter speed is not super fast, but it is the minimum that I would use with that lens photographing toddlers.  With a T7i, you might want to drop that to 1/320, to keep ISO as low as possible.

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