What cause the 20D to not AF at a max fstop smaller than 5.6 where the models above can? Is this something a firmware release can fix? If so, why don't we have one?
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John MuellerRegistered UsersPosts: 2,555Major grins
Logic would assume that if you had enough light, like a beach scene with high reflections in the middle of the day, you ought to be fine with AF at f/8 on the 20D. Think about it. I would think EV would come into play here.
Maybe the 20D could AF at f/8 in bright sun, but Canon things that it is not worth trying and then having the user upset that it cannot perform, so they simply set the limit at 5.6 with no regard to the intensity of the light entering the lens.
Maybe the 20D could AF at f/8 in bright sun, but Canon things that it is not worth trying and then having the user upset that it cannot perform, so they simply set the limit at 5.6 with no regard to the intensity of the light entering the lens.
Under most circumstances the consumer models won't AF at apertures above 5.6. Sure, some situations will exist where it can. They are likely to be not the norm. On the other side of things, if the scene is dark enough even my 1.4 lens won't autofocus. But the spec needs to be put somewhere.
In engineering there exists a lot of specs that are somewhat fuzzy in this regard. They are sometimes labeled as "typical" values. This is a common pratice, and often there is no better alternative.
What cause the 20D to not AF at a max fstop smaller than 5.6 where the models above can? Is this something a firmware release can fix? If so, why don't we have one?
It costs more to make a sensor sensitive enough to do AF at f8 and smaller. Ergo, the cheaper bodies can't.
Keep in mind that f/8 is a REALLY slow lens. If you shot at f/8 with a 2.8 lens, you'd still have AF, as AF occurs before the lens aperture closes to take the picture.
You have a slow lens that you make even slower by putting an extender on it.
f/8 is the MAX aperture of that lens/converter combo....leaving you to MF on the 20d.
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Cincinnati Smug Leader
Cincinnati Smug Leader
Thinking one thing while typing sometimes has me reading everything into it when I left something out.
Yes, when an extender makes the maximum aperture f/8 or lower, why can't the 20D autofocus when the higher models can?
The higher models have more sensitive auto-focus sensors. This is why the auto-focus with less light. Those sensors cost more money.
A former sports shooter
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Maybe the 20D could AF at f/8 in bright sun, but Canon things that it is not worth trying and then having the user upset that it cannot perform, so they simply set the limit at 5.6 with no regard to the intensity of the light entering the lens.
Under most circumstances the consumer models won't AF at apertures above 5.6. Sure, some situations will exist where it can. They are likely to be not the norm. On the other side of things, if the scene is dark enough even my 1.4 lens won't autofocus. But the spec needs to be put somewhere.
In engineering there exists a lot of specs that are somewhat fuzzy in this regard. They are sometimes labeled as "typical" values. This is a common pratice, and often there is no better alternative.
A former sports shooter
Follow me at: https://www.flickr.com/photos/bjurasz/
My Etsy store: https://www.etsy.com/shop/mercphoto?ref=hdr_shop_menu
Keep in mind that f/8 is a REALLY slow lens. If you shot at f/8 with a 2.8 lens, you'd still have AF, as AF occurs before the lens aperture closes to take the picture.
You have a slow lens that you make even slower by putting an extender on it.
f/8 is the MAX aperture of that lens/converter combo....leaving you to MF on the 20d.
Lee