22nd July 2005, 03:08 PM
I alway carry a touch light. If the subject is not afraid of a touch light shine at it, then your camera should able to lock on the focus. I find this out way back in the days of EOS 630, where autofocus system can't focus **** in low light if not for my trusty energizer pocket touch light. D.I.Y. AF assit device
22nd July 2005, 05:02 PM
7D AF compares to several Pro level bodies
That's what I read in a few reviews by Pros. They claim 7D AF performance rivals several Pro level bodies.
Originally Posted by Zerstorer
22nd July 2005, 06:37 PM
Just to note: You are comparing a f/3.5-4.5 lens to a f/1.8. The 20/1.8 has almost 2 f-stops advantage...
Originally Posted by wind30
It is like comparing the focussing between a f/4 lens with a f/8 lens
22nd July 2005, 06:42 PM
yup, a 20/1.8 on D70 should be able to get you decent shots at the same locale.
22nd July 2005, 09:33 PM
Auto focus accuracy is based on the ev (or light that is entering the lens). This also attributes the the faster focusing speed.
All auto focus engines depend on the amount of light that is reaching the focus sensor through the lens. This is why an f/1.8 lens focuses somewhat faster then and f/3.5.
Remember that even if you set your aperture at f/22 during the focusing it is irrelevant to the focus engine, as all new autofocus lenses use an automatic diaphram. Which means at all time during the focusing and metering the lens' aperture blades are opened to its max. f/3.5 for the 18-70 and f/1.8 possible for the prime.
This alone would suggest that the conclusion drawned by the original poster is inaccurate.
Here is another example.
Why do all manufaturers tell you that when using a 2x tele-convertor with a lens that has a maximum aperture of 5.6 and less should be focused manually?
This is because, when using a 2x tele-convertor on a f/5.6 lens, the f/5.6 become f/11. It makes it nearly impossible for the autofocus engine to focus, unless in extremely bright situations.
for example.. a 70-300 f/4-5.6 AF-D ED with a 2x convertor, would be one example that would prove this point.
23rd October 2005, 01:49 PM
Re: DSLR low light focusing accuracy...
That is why they have AF assist beams. Lets face it even our eyes have difficulty seeing the the dark. Every camera and lens have their limit when it comes to low light or AF speed.