LOG IN    OR   REGISTER TO FORUMS


Focus variations

FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses
Thread started 30 Oct 2006 (Monday) 14:13   
LIST NEARBY THREADS
 
curiousgeorge
Goldmember
curiousgeorge's Avatar
Joined Feb 2006
3,802 posts
London
[MORE/SHARE]

Have anyone noticed how, when you autofocus on a particular point in the frame, if you repeatedly press the shutter button half way, the focus will jump around ever so slightly backwards and forwards? Even if you keep the camera still.

The lens is therefore unsure as to the distance to focus on and it follows that the image is unlikely to be correclty focused.

This may explain how, when I take two shots of the same image, one is better focused than the other.

Post #1, Oct 30, 2006 14:13:38


Photos from Icelandexternal link | Lake Districtexternal link | Isle of Lewisexternal link | Japanexternal link | Macrosexternal link
Canon EOS 40D | Canon 17-55mm f/2.8 IS | Canon 100mm f/2.8L Macro IS | Canon 70-200mm f/4L | Speedlite 430EX II | Canon Powershot G9

LOG IN TO REPLY
sponsored links
(this ad will go away when you log in as registered member)
Jon
Moderator

Cocker Spaniel Mod

Jon's Avatar
Joined Jun 2004
68,170 posts
Bethesda, MD USA
[MORE/SHARE]

Remember, the AF sensor area's actually somewhat larger than the area delimited on your screen. It's quite possible for the AF point you use at any given time to be picking up something outside the area you were expecting. AlsoAF isn't designed to nail the exact same spot every time; it's considered within spec if it's within somthinge like 1/3 the DoF when focussed.

Post #2, Oct 30, 2006 14:17:26


Jon
----------
Cocker Spaniels
Maryland and Virginia activities
Image Posting Rules and Image Posting FAQ
Report SPAM, Don't Answer It! (link)
PERSONAL MESSAGING REGARDING SELLING OR BUYING ITEMS WITH MEMBERS WHO HAVE NO POSTS IN FORUMS AND/OR WHO YOU DO NOT KNOW FROM FORUMS IS HEREBY DECLARED STRICTLY STUPID AND YOU WILL GET BURNED.
PAYPAL GIFT NO LONGER ALLOWED HERE

LOG IN TO REPLY
curiousgeorge
THREAD ­ STARTER
Goldmember
curiousgeorge's Avatar
Joined Feb 2006
3,802 posts
London
[MORE/SHARE]

It happens when the entire frame is in the same focal plane though, eg the cover of a book.

I wouldn't expect it to vary at all in this situation.

Post #3, Oct 30, 2006 14:37:56


Photos from Icelandexternal link | Lake Districtexternal link | Isle of Lewisexternal link | Japanexternal link | Macrosexternal link
Canon EOS 40D | Canon 17-55mm f/2.8 IS | Canon 100mm f/2.8L Macro IS | Canon 70-200mm f/4L | Speedlite 430EX II | Canon Powershot G9

LOG IN TO REPLY
gasrocks
Cream of the Crop
gasrocks's Avatar
Joined Mar 2005
13,431 posts
Portage, Wisconsin USA
[MORE/SHARE]

Are you swaying back and forth?

Post #4, Oct 30, 2006 14:39:08


GEAR LIST
_______________

LOG IN TO REPLY
philbyuk
Senior Member
philbyuk's Avatar
Joined Nov 2005
753 posts
manchester uk
[MORE/SHARE]

maybe its just rechecking the focus !!!

Post #5, Oct 30, 2006 14:43:43


My Gear

My Galleryexternal link

LOG IN TO REPLY
sponsored links
(this ad will go away when you log in as registered member)
Jon
Moderator

Cocker Spaniel Mod

Jon's Avatar
Joined Jun 2004
68,170 posts
Bethesda, MD USA
[MORE/SHARE]

curiousgeorge wrote in post #2191361external link
It happens when the entire frame is in the same focal plane though, eg the cover of a book.

I wouldn't expect it to vary at all in this situation.

Read point 2 of my post. Also, your subject needs to be sufficiently high contrast for it to get a good read. The lower the contrast, the more likely you'll have variations. Also the smaller the aperture.

Post #6, Oct 30, 2006 14:52:03


Jon
----------
Cocker Spaniels
Maryland and Virginia activities
Image Posting Rules and Image Posting FAQ
Report SPAM, Don't Answer It! (link)
PERSONAL MESSAGING REGARDING SELLING OR BUYING ITEMS WITH MEMBERS WHO HAVE NO POSTS IN FORUMS AND/OR WHO YOU DO NOT KNOW FROM FORUMS IS HEREBY DECLARED STRICTLY STUPID AND YOU WILL GET BURNED.
PAYPAL GIFT NO LONGER ALLOWED HERE

LOG IN TO REPLY
curiousgeorge
THREAD ­ STARTER
Goldmember
curiousgeorge's Avatar
Joined Feb 2006
3,802 posts
London
[MORE/SHARE]

OK, so it's normal behaviour, but in real life shots this happens every time and it's frustrating when you don't know when it has the best focus reading.
I thought someone else would have noticed it.
I would use MF if I could rely on my eyesight.

Post #7, Oct 30, 2006 16:15:29 as a reply to Jon's post 1 hour earlier.


Photos from Icelandexternal link | Lake Districtexternal link | Isle of Lewisexternal link | Japanexternal link | Macrosexternal link
Canon EOS 40D | Canon 17-55mm f/2.8 IS | Canon 100mm f/2.8L Macro IS | Canon 70-200mm f/4L | Speedlite 430EX II | Canon Powershot G9

LOG IN TO REPLY


LIST NEARBY THREADS
862 views & 0 likes for this thread
Focus variations
FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses



NOT A MEMBER YET? CLICK HERE TO REGISTER TO FORUMS

CHANGE BODY TEXT SIZE FOR ALL THREAD PAGES
POWERED BY AMASS 1.0version 1.0
made in Finland
by Pekka Saarinen
for photography-on-the.net


SEND FEEDBACK TO STAFF  |  JUMP TO FORUM...  |  FORUM RULES


Spent 0.00071 for 4 database queries.
PAGE COMPLETED IN 0.01s
1033 guests, 814 members online
Simultaneous users record so far is 3341, that happened on Dec 11, 2014
Latest registered member is Madden5D3

COOKIES DISCLAIMER: By using this site you agree that some cookies will be stored on your browser. For unlogged users we store one session id cookie. For registered members we store (in addition to login session cookie) only cookies that are essential for required functionality, we do not store any personal tracking data in cookies or other browser's data storage methods.