Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon Lenses

Reply
 
Thread Tools Search this Thread
Old Feb 27, 2008, 2:28 AM   #1
Senior Member
 
Join Date: Oct 2004
Posts: 278
Default

I just bought the 70-200 L f/2.8 non IS version. Lens not very sharp at higher f/stops at f/2.8 seems fine. I ran some test on the lens. I also used 2 other lens the sigma 70-300 non apo and the nifty fifty lens. Both these lens seem better. I tested using "AV" mode. On both zoom lens I shot my subject at 13 ft and the 50mm I shot the subject around 5ft. Pics Im posting are at 100% value. Basing on my observations should I bring my lens in for calibration? Thanks
BTW. the top 2 is the sigma 70-300, next 3, 50mm and the last 5 pics is canon 2.8 L.
Attached Images
 
garman is offline   Reply With Quote
Sponsored Links
Old Feb 27, 2008, 3:12 AM   #2
Super Moderator
 
peripatetic's Avatar
 
Join Date: Nov 2004
Posts: 3,599
Default

You were using a tripod and cable release right? Otherwise the shutter speeds are ridiculously low for trying to test lens sharpness.

Also try to give the camera some decent light for the AF if you are testing for sharpness.

From your current tests it's more or less impossible to tell if you have a problem or not.
peripatetic is offline   Reply With Quote
Old Feb 27, 2008, 9:00 AM   #3
Senior Member
 
surfnron's Avatar
 
Join Date: Jun 2003
Posts: 578
Default

I'd redo the test outdoors in bright light where you can remove vibration caused by low shutter speed as a possible reason for the blur.
Ron
surfnron is offline   Reply With Quote
Old Feb 27, 2008, 9:56 AM   #4
Senior Member
 
Join Date: Oct 2005
Posts: 1,105
Default

if its a sunpack tripod i would still see some blur because of the tripod itself. My 500 when mounted on a relatively steady bogen tripod, vibrates like hell before it comes to rest like after 5-10seconds. Thats one reason why i stopped using the tripod with the 500.

So if ur not having a relatively sturdy tripod, i would suggest putting the lens on a table or something thats really sturdy.
nymphetamine is offline   Reply With Quote
Old Feb 27, 2008, 10:28 AM   #5
Senior Member
 
Join Date: Oct 2004
Posts: 278
Default

it was on a tripod, using the timer settings. the question is why is it fairly sharp at f/2.8 and when shooting at higher f/stops the blur is more pronouced. I shot some more photos with very high f/stops. It seemed to become sharper from f15 and beyond.
Also if you look at the top 5 photos the sigma and the 50mm look like what I'd expect them to be using a tripod, but the L lens seems odd when changing f/stops. thanks
garman is offline   Reply With Quote
Old Feb 27, 2008, 10:34 AM   #6
Senior Member
 
Join Date: Oct 2005
Posts: 1,105
Default

if the orientation of the images are exactly the same as u took it, it does feel like vertical shake of the camera. The tripod could be the culprit here mainly because as peripatetic said, ur shutter speed is way too low to test this condition.



Place ur subject under a study lamp or something to remove slow shutter speed out of the equation.



As i said previously, if u have a 40D u can actually see the shake in the live mode due to the tripod. Focus the subject and zoom it to 100% in live mode. U can easilly track the tripod movement and can elimate one more factor with a much sturdy holder(like a table or something)
nymphetamine is offline   Reply With Quote
Old Feb 27, 2008, 10:55 AM   #7
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

garman wrote:
Quote:
it was on a tripod, using the timer settings. the question is why is it fairly sharp at f/2.8 and when shooting at higher f/stops the blur is more pronouced.
Because you're using faster shutter speeds at f/2.8 ;-)

Your problem is almost certainly your shutter speeds. Any vibration from camera shake or mirror slap is going to be magnified as focal lengths get longer (hence, why you're seeing more of a problem shooting with it at 200mm).

Quote:
I shot some more photos with very high f/stops. It seemed to become sharper from f15 and beyond.
Probably because your shutter speeds became slow enough so that the effect of vibration from mirror slap wasn't as obvious (the vibration is not occuring for as much of the exposure time at slower shutter speeds).

Mirror related vibration is typically going to be more of a problem using shutter speeds between about 1/2 second and 1/30 second. Blur will be worse as focal lengths get longer.

Were you using Mirror Lockup (Custom Function 7 in your XT)? At those shutter speeds, I'd use Mirror Lockup with a Cable release with a longer lens.

Quote:
Also if you look at the top 5 photos the sigma and the 50mm look like what I'd expect them to be using a tripod, but the L lens seems odd when changing f/stops. thanks
Again, blur from camera vibration is going to be amplifed as focal lengths get longer.

Use faster shutter speeds in better light to test the lens. It's probably fine.

JimC is offline   Reply With Quote
Old Feb 27, 2008, 11:23 AM   #8
Senior Member
 
Join Date: Oct 2004
Posts: 278
Default

Brothers.... you hit the nail right on the head. it was the shutter slap. I changed some settings jacked the iso up and lite the subject, shutter speeds increased and help out the sharpness.
Attached Images
 
garman is offline   Reply With Quote
Old Feb 27, 2008, 11:29 AM   #9
Senior Member
 
Join Date: Oct 2004
Posts: 278
Default

One other question. What is the longest shutter speed you can have when mirror slap starts to become a problem and how do you prevent this problem occuring when shooting long exposures ie astrophotography, night photography.

question answered I just noticed JimC response. Being a newbie is tough. thanks
garman is offline   Reply With Quote
Old Feb 28, 2008, 3:12 AM   #10
Super Moderator
 
peripatetic's Avatar
 
Join Date: Nov 2004
Posts: 3,599
Default

You learned something about photography and discovered that your lens is fine.

The rule-of-thumb for shutter speeds is 1/equivalent focal length.

So for 20mm * 1.6 = 320mm you should probably be looking at around 1/500 for hand-hold shutter speed.

I would guess from the results you had with your tripod that it's simply not strong/stable enough to cope with the camera + 70-200. You could try hanging a weight underneath (like your camera bag) it to make it more stable.

With a fully stable tripod (no wind or people walking nearby etc) + mirror lock-up and cable release (or timer) you should be able to go almost as long as you like.

How much vibration is introduced by mirror-slap depends on many things, the specific camera, how much vibration is dampened by the tripod head and body, and probably a bunch of other factors too.

But vibration can be introduced by lots of other things too, even walking on the ground nearby can do it. Wind. Loud noises. + ????

As a wild guess I'd expect even a relatively poor tripod to give you a couple of stops better than the hand-hold rule-of-thumb. So 1/125 should be OK, even 1/60.

You'll just have to experiment to see what works for you.

P.S. Just lighting the subject better might have helped a lot because the AF had much better data to work with.
peripatetic is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 4:41 PM.