Approve the Cookies
This website uses cookies to improve your user experience. By using this site, you agree to our use of cookies. Read More.
OK
Index  •   • New posts  •   • RTAT  •   • 'Best of'  •   • Gallery  •   • Gear  •   • Reviews
New posts  •   • RTAT  •   • 'Best of'  •   • Gallery  •   • Gear  •   • Reviews
Register to forums    Log in

 
FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses
Thread started 30 Oct 2006 (Monday) 14:13
Prev/next
sponsored links
(this ad will go away when you log in as registered member)

Focus variations

 
curiousgeorge
Goldmember
curiousgeorge's Avatar
3,802 posts
Joined Feb 2006
London
Oct 30, 2006 14:13 |  #1

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.


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
Cream of the Crop
Jon's Avatar
69,628 posts
Joined Jun 2004
Bethesda, MD USA
Oct 30, 2006 14:17 |  #2

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.


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
3,802 posts
Joined Feb 2006
London
Oct 30, 2006 14:37 |  #3

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.


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
13,431 posts
Joined Mar 2005
Portage, Wisconsin USA
Oct 30, 2006 14:39 |  #4

Are you swaying back and forth?


GEAR LIST
_______________

LOG IN TO REPLY
philbyuk
Senior Member
philbyuk's Avatar
753 posts
Joined Nov 2005
manchester uk
Oct 30, 2006 14:43 |  #5

maybe its just rechecking the focus !!!


My Gear

My Galleryexternal link

LOG IN TO REPLY
Jon
Cream of the Crop
Jon's Avatar
69,628 posts
Joined Jun 2004
Bethesda, MD USA
Oct 30, 2006 14:52 |  #6

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.


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
3,802 posts
Joined Feb 2006
London
Oct 30, 2006 16:15 as a reply to Jon's post |  #7

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.


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)

1,066 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 the forums.
Registered members get all the features: search, following threads, own gear list and ratings, likes, more forums, private messaging, thread follow, notifications, own gallery, settings, view hosted photos, own reviews and more...


AAA

Send feedback to staff    •   Jump to forum...    •   Rules    •   Index    •   New posts    •   RTAT    •   'Best of'    •   Gallery    •   Gear    •   Reviews    •   Polls

COOKIES DISCLAIMER: This website uses cookies to improve your user experience. By using this site, you agree to our use of cookies. Privacy policy and cookie usage info.

POWERED BY AMASS 1.4version 1.4
made in Finland
by Pekka Saarinen
for photography-on-the.net
Spent 0.00074 for 4 database queries.
PAGE COMPLETED IN 0.02s
Latest registered member is Akhil1968
647 guests, 510 members online
Simultaneous users record so far is 5577, that happened on Mar 02, 2016