focus questions

[crockny]

Hello -- I have focusing issues -- trying to get pictures of wildlife/birds -- I had some success using continuous shooting and AI Servo but the focus is not sharp enough. I have read the only way to get really sharp focus is to do it manually - but birds rarely hold still for this ... what's the secret???? Also I wear my glasses to manually focus and I'm slightly nearsighted with astigmatism -- do I need to get some kind of adaptor for my viewfinder? Sometimes it's hard for me to tell if something's in focus - especially an animal's eyes ... thanks in advance for any advice!




Canon EOS Digital Rebel XSi
Tamron 18-270 lens
Exposure: 0.01 sec (1/100)
Aperture: f/6.3
Focal Length: 270 mm
ISO Speed: 200
Exposure Bias: 0 EV
Flash: Off, Did not fire

[Sterling]

Part of the issue could be camera shake due to too low of a shutter speed. The old rule of thumb is to consider 1/focal length as a safe minimum handheld shutter speed. In this case that would mean 1/270 second. I also read an article that said that rule of thumb was based on the 35mm format and that for crop sensor cameras the 35mm equivalent focal length should be used. In your case that would mean using a minimum speed of 1/432.

[WVCoalMiner]

At 270mm without IS it is almost impossible to get sharp focus without using a tripod and remote shutter release. and f6.3 is awfully slow is that as wide open as your aperture will go at 270mm?
At 270mm camera shake is multiplied immmensly which makes it VERY VERY hard to get sharp focus. You are probably going to have to go with a faster lens or tripod/remote shutter release.

[crockny]

Hmmm -- well the Tamron lens has VC -- I thought that was supposed to help with camera shake. But you're right, the lens was at its limit. I could have experimented more with apeture and shutter speed but didn't want to miss the birds. I haven't a clue how to use a tripod with birds -- they're flying all over the place!

And the crop factor thing I don't understand yet at all ...

As far as using continuous shooting and AI Servo - is that the way to go?

[RichardTaylor]

What focus point are you using?

I photograph birds and agree with the above comments re the slow shutter speed.

Don't be afraid to bump up the ISO - Take it to 800 at least.
Much better to have a grainy shot than one spoilt by subject motion or camera motion.
As other have said consider using a tripod or mono pod, I use a mono pod


Also keep in mind if light levels are low your camera may have problems focussing especially if your maximum aperture is F6.3 (at the focal length you are shooting)

Edit: I shoot AI servo & centre focus point only active.

[WVCoalMiner]

The only thing I have found about your dilemma is FAST SHUTTER SPEED!!!!!!
I also found this explanation of AI Servo

" it should be fine to use One Shot because the subject is still in the same position. if you use AI servo and something else in the frame moves, it may track that object instead."

That may be what you are experiencing.

The Tamron's VC is Vibration Control NOT movement control it can "fix" camera shake but not camera movement such as following a moving bird.
I suggest getting your shutter speed as FAST as you can and your blur problems may fix itself.
This was handheld, OneShot, 300mm NO IS or VC
See my settings:
Camera: Canon EOS Digital Rebel XSi
Exposure: 0.02 sec (1/50)
Aperture: f/5.6
Focal Length: 300 mm
ISO Speed: 100
Exposure Bias: 0 EV
Flash: Off, Did not fire

[crockny]

I'm trying to focus on the bird's face which is not always easy since I'm not that close and the little critters are very active ... but I will up my ISO next time to see if I can triple my shutter speed ... I guess I thought 1/100 was pretty good but forgot about the focal length -- there's so much to pay attention to ....

Thanks everyone for all the good tips! Here's another shot from the same day ... guess I should have experimented with more settings ...



Camera: Canon EOS Digital Rebel XSi
Exposure: 0.01 sec (1/100)
Aperture: f/6.3
Focal Length: 270 mm
ISO Speed: 200
Exposure Bias: 0 EV
Flash: Off, Did not fire

[RichardTaylor]

This is what I mean.
Canon 40D (a 1.6 crop camera)
Exposure: 0.002 sec (1/500)
Aperture: f/14.0
Focal Length: 400 mm
ISO Speed: 800
Exposure Bias: -1/3 EV
Flash: Off, Did not fire

I may have been hand holding if I had to shoot up at the bird. If so the IS (VC,VR) would have been on.

[crockny]

Yes, I see the eye is much sharper on yours ... nice pic! I can't wait to go out again and up the shutter speed ...

[PSPhotos]

I would say the 1/100 shutter speed played into it but also, how far cropped are these shots? How close were you? Notice that the shot posted by richard had much more light available and as such he was able to close down the aperture and increase his DOF too.