To jog my memory- AI-Focus AF,Al- Servo AF & shutter speed.

[Nathaniel]

The instructions manual states that (i) AI focus is to be used when the subject is "still or about to move". Does this mean that one can set AI focus when shooting birds and moving subjects without using Al- Servo? It seems to me that one can use this more or less permanently when shooting whether it be for one shot AF or Al-Servo AF. Am I right?
(ii) If one can use Al-focus AF for still and moving subjects, is there any need for Al Servo AF to be selected for moving subjects?
(iii) Irrespective of the selected AF mode, one should always use a faster shutter speed that is greater than the focal length of the lens to prevent camera shake i.e if it is a 55mm-250mm lens,a shutter speed of 1/250 or higher is advisable?

[codachrome]

Re: To jog my memory- AI-Focus AF,Al- Servo AF & shutter speed.

WHAT?

[stalker]

Re: To jog my memory- AI-Focus AF,Al- Servo AF & shutter speed.

As far as i recall, AI Focus starts off expecting a fixed subject, but if it then moves more than a certain amount AI servo kicks in...
so if you were photographing something you know is moving, you would be better to put it in AI servo mode as it will react to focus change quicker..

[Rasputin]

Re: To jog my memory- AI-Focus AF,Al- Servo AF & shutter speed.

Hi Nathaniel

I always use AI Servo for wildlife of any kind.

Regarding the shutter speed, I have seen 2 explanations. If your 55 - 250 was on a full frame then yes you need 1/250; but on a crop you have to factor that in, so it would be 1/400 to eleiminate camera shake. However, the 55 - 250 has IS so you can shoot at slower shutter speeds without camera shake. But, to freeze movement you will need higher speeds, potentially over 1/1000 depending on what you are shooting.

Regards

[Nathaniel]

Re: To jog my memory- AI-Focus AF,Al- Servo AF & shutter speed.

Thanks Stalker/Rasputin. That explains quite a lot.I did try some flying birds shots on holiday and set the focus on Al-servo AF but I clean forgot the crop factor in respect of the shutter speed i.e 1.6 x 250mm= 400!!! I am posting 3 images- two where I got it wrong with the shutter speed (zoomed out to 250mm & shutter speed 1/250) & one I got it right more by chance (the Mallard duck "taking off" when I zoomed in to around 140mm (shutter speed 1/250). Pictures taken in Lake Como