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Old March 19th, 2009, 12:52 PM   #1
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Focus/Grid questions on XHA1

Can anybody point me in the right direction regarding how the grid pattern might work (if at all) in relation to maintaining auto focus? I am trying to understand a few things regarding AF on fast moving targets such as birds and birds in flight.
In still Photography, the AF can be set to AF on certain points of the frame, it can also be set in AI servo mode which maintains focus automatically at all times when the subject is moving.
The issues I am having are maintaining a constant and crisp focus while my subject is moving. Any AF tips would be highly appreciated.
Thanks in advance,

Tim
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Old March 19th, 2009, 04:39 PM   #2
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Hi Tim............

It's been my experience with the auto focus that unless the target occupies the vast majority of the central box when the grid lines are turned on, the camera will not hold focus and will tend to "take to the hills" or whatever the backdrop is.

This can work both for you and against you.

When I say "vast majority", you really need to experiment yourself using something like a cardboard box on a pole with a backdrop some considerable distance behind.

Use the zoom to change the object size in the central grid and see at what point the "Push AF" button will accurately and consistantly aquire it instead of the background. Use the focus ring to throw it out after each test.

This should give you a pretty good idea how your particular camera behaves, as I think from similar conversations here before, all A1's are not created equal in this respect.


CS
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Old March 19th, 2009, 06:20 PM   #3
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Thanks Chris

Quote:
Originally Posted by Chris Soucy View Post
It's been my experience with the auto focus that unless the target occupies the vast majority of the central box when the grid lines are turned on, the camera will not hold focus and will tend to "take to the hills" or whatever the backdrop is.

This can work both for you and against you.

When I say "vast majority", you really need to experiment yourself using something like a cardboard box on a pole with a backdrop some considerable distance behind.

Use the zoom to change the object size in the central grid and see at what point the "Push AF" button will accurately and consistantly aquire it instead of the background. Use the focus ring to throw it out after each test.

This should give you a pretty good idea how your particular camera behaves, as I think from similar conversations here before, all A1's are not created equal in this respect.


CS
Thanks Chris, Am understanding this correctly? I can adjust the grid size and control which grid will hold auto focus? I realize the results may vary but am I grasping the concept correctly? And will you need to hit the instant AF each time say for instance when shooting a bird in flight?
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Old March 19th, 2009, 06:57 PM   #4
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No, not quite.....

When you set the grid lines to "on" in the A1's menu (Display Setup - Markers - [Grid]), you'll find the lines make a central box on the LCD screen (this box size is fixed and cannot be altered, nor can you assign a focus zone to any other area of the grid, unfortunately)

It's been my experience that a subject that does not occupy the best part of this box will not kick the AF into action, and it will instead focus on the background wherever that happens to be.

What you need to test is just how much is "the best part".

Having established that percentage, you then need to apply that knowledge to keeping a potential target "in the zone" to keep the AF's attention.

It's not easy, especially with something the size and speed of a bird where long zooms are the norm.

Sorry if I wasn't clear in my first post.


CS
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Old March 19th, 2009, 08:52 PM   #5
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Thanks once again Chris

Yes Chris, you were clear I just wanted make sure I had it right. So basically having the grid on does nothing for focus other then marks the central focus zone where the camera seems to focus anyway without the grids activated? Kinda like a visual reminder to keep your target in the center?
What I have been doing thus far is keeping the target in or as close to the center as possible as that is where the A1 seems to want to focus in AF mode, (so much for the rule of thirds) . I just wanted to know if the grids acted as focus points like with a DSLR telling the camera where you want it to focus.
Thanks again Chris for your help,
Tim
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