# F8 AUTOFOCUS



## liongate (Aug 26, 2014)

I'm probably rehashing a subject already beat dead, and you'll probably think I'm an idiot, but can somebody explain briefly what all this talk about F/8 Autofocus is? Is there some reason a camera wouldn't AF at F/8? What am I missing here? Is this why I can't get clear focus from my 20D? lol.


----------



## rs (Aug 26, 2014)

Almost all DSLR's autofocus only functions when the lenses aperture wide open is f5.6 or brighter. It's for the same reason that slow lenses make the split prism focus screens on old manual focus SLR's go black.

Being able to AF, even with limited AF functionality with lens combos as slow as f8 was the preserve of the 1 series for canon shooters until the 5D3. Think of a 600/4 with a 2x TC, or a 100-400 with a 1.4x TC. 

Your 20D focus issues will be unrelated. It will only attempt to AF with f5.6 lenses (or brighter). If it consistently misses, that's likely down to a problem (calibration or otherwise) with your lens or body.


----------



## liongate (Aug 26, 2014)

rs said:


> Almost all DSLR's autofocus only functions when the lenses aperture wide open is f5.6 or brighter. It's for the same reason that slow lenses make the split prism focus screens on old manual focus SLR's go black.
> 
> Being able to AF, even with limited AF functionality with lens combos as slow as f8 was the preserve of the 1 series for canon shooters until the 5D3. Think of a 600/4 with a 2x TC, or a 100-400 with a 1.4x TC.
> 
> Your 20D focus issues will be unrelated. It will only attempt to AF with f5.6 lenses (or brighter). If it consistently misses, that's likely down to a problem (calibration or otherwise) with your lens or body.



I'm still confused. Are you saying that my lens would autofocus at f5.6 or f6.3 but not at f8 or f11 and that I should be using manual focus at any aperture smaller than f5.6?


----------



## preppyak (Aug 26, 2014)

liongate said:


> I'm still confused. Are you saying that my lens would autofocus at f5.6 or f6.3 but not at f8 or f11 and that I should be using manual focus at any aperture smaller than f5.6?


No, in this case, its referring to the maximum aperture a lens has. For example, a 100-400 has a max aperture of f/5.6 at 400mm, and so it will auto-focus on all Canon cameras. If you stop it down to f/8 or f/11, it will still autofocus. However, if you put a 1.4x converter on it, you've turned it into a 560mm f/8 lens, and it will no longer autofocus on most Canon bodies (1D series and 5dIII aside). The autofocus system relies on light and contrast to focus, and you've made it too dark a lens for the auto-focus system to work reliably.

Now, technically, it will auto-focus at f/8 or f/11, but, odds are whatever you are shooting has moved on in the 5+ seconds it took to lock focus. And in some cases, it wont lock focus at all.

So, gaining f/8 auto-focus is more about the ability to use teleconverters on lenses that are already a little slow. A 2x on a lens that ends at f/4 or a 1.4x on a lens that ends at f/5.6. Generally its important for wildlife shooters, which is why it makes sense that a 7DII might have it (and say, a T5i wouldn't)


----------



## Orangutan (Aug 26, 2014)

liongate said:


> I'm still confused. Are you saying that my lens would autofocus at f5.6 or f6.3 but not at f8 or f11 and that I should be using manual focus at any aperture smaller than f5.6?



When a DSLR auto-focuses it does so with the aperture wide open, regardless of the aperture to be used for the photo capture. Once focus is achieved, it stops down the aperture to the desired size and takes the picture.

Because of the physical construction of autofocus modules, it becomes hard to make them work well when "aperture wide open" is f8, so typically only high-end cameras have this extra engineering. When you add a teleconverter to a lens you increase the focal length, and therefore increase the "wide open" aperture. E.g. a 400 f5.6 might become an 800 f8 lens with a teleconverter. I.e., "wide open" is now f8. That won't work for a 20D.

We can help you better if you'll tell us what lens you're using with the 20D, and if you're using a teleconverter.


----------



## NancyP (Aug 27, 2014)

Correction: the 400mm f/5.6L plus 1.4x teleconverter is now f/8, 560mm.


----------



## liongate (Aug 27, 2014)

Orangutan said:


> We can help you better if you'll tell us what lens you're using with the 20D, and if you're using a teleconverter.



Thanks, folks, for all the info. It's really not about the 20D. I'm waiting for the 7DII to come out with some anticipation. I just didn't understand some of the conversations about the specs.


----------



## Famateur (Aug 27, 2014)

Orangutan said:


> When a DSLR auto-focuses it does so with the aperture wide open, regardless of the aperture to be used for the photo capture. Once focus is achieved, it stops down the aperture to the desired size and takes the picture.



This is probably the answer you were looking for.

For example, if you had an F2.8 lens and set the aperture for the photo to F16, the camera would auto-focus with the aperture at its maximum of F2.8, then close down to F16 for the shutter release. If the max aperture of the lens (or effective max aperture, if used in combination with teleconverters) is F8 or smaller, it will not auto-focus (except on some pro bodies and, hopefully, the 7DII). 

This is my understanding, anyway. Take anonymous internet info for what it's worth!


----------



## Mt Spokane Photography (Aug 27, 2014)

And, to further confuse the issue, the 70D will autofocus f/11 lenses. This is only possible while using live view, autofocusing of that 400mm f/5.6 lens with a 2X TC attached is allowed.

I'd expect to see this feature on the 7D MK II, but no live AF beyond f/11.


----------



## neuroanatomist (Aug 27, 2014)

Mt Spokane Photography said:


> And, to further confuse the issue, the 70D will autofocus f/11 lenses. This is only possible while using live view, autofocusing of that 400mm f/5.6 lens with a 2X TC attached is allowed.
> 
> I'd expect to see this feature on the 7D MK II, but no live AF beyond f/11.



Even the current 7D will AF an f/11 lens (e.g. 100-400L + 2x) with live view, using contrast detect AF.


----------



## mackguyver (Aug 27, 2014)

Check out this thread I started a while back:

Autofocus at f/8 and Beyond


----------



## Mt Spokane Photography (Aug 27, 2014)

neuroanatomist said:


> Mt Spokane Photography said:
> 
> 
> > And, to further confuse the issue, the 70D will autofocus f/11 lenses. This is only possible while using live view, autofocusing of that 400mm f/5.6 lens with a 2X TC attached is allowed.
> ...



Is it spec'd that way? I could not use AF at f/11 with my 1D MK III and live AF. Sometimes when pre=focused to be close, it would snap into focus. I never tried it with either of my 7D's. My 5D MK III acts much like the 1D MK III, is occasional snaps in to focus at f/11 when using live AF.


----------



## neuroanatomist (Aug 27, 2014)

Mt Spokane Photography said:


> neuroanatomist said:
> 
> 
> > Mt Spokane Photography said:
> ...



I don't think it's spec'd at all. But the 7D + 100-400 + 2xII combo focused reliably, albeit slowly (even if IQ was nothing to write home about).


----------



## Mt Spokane Photography (Aug 27, 2014)

neuroanatomist said:


> Is it spec'd that way? I could not use AF at f/11 with my 1D MK III and live AF. Sometimes when pre=focused to be close, it would snap into focus. I never tried it with either of my 7D's. My 5D MK III acts much like the 1D MK III, is occasional snaps in to focus at f/11 when using live AF.



I don't think it's spec'd at all. But the 7D + 100-400 + 2xII combo focused reliably, albeit slowly (even if IQ was nothing to write home about).
[/quote]

I'm not expecting to get a 7D MK II, but I am interested in being able to reliably autofocus at f/11.


----------



## Keith_Reeder (Aug 27, 2014)

Just some Real World experience to add to the mix: the 7D will AF _usefully_ quickly for bird photography at f/8 (eg Canon 100-400mm and taped or non-reporting 1.4x TC) _ off the central AF points_. Use it on the peripheral points, and it's actually not bad at all.

For example - 600mm, handheld, (Kenko non-reporting 1._5_ TC), peripheral AF point on the bird's eye.

And another.

The 70D (mine, and that of at least two other users that I asked to test this) _will_ AF at f/8 on _all_ AF points. Again, it's not lightning fast, but it works.


----------



## rs (Aug 27, 2014)

Keith_Reeder said:


> Just some Real World experience to add to the mix: the 7D will AF _usefully_ quickly for bird photography at f/8 (eg Canon 100-400mm and taped or non-reporting 1.4x TC) _ off the central AF points_. Use it on the peripheral points, and it's actually not bad at all.
> 
> For example - 600mm, handheld, (Kenko non-reporting 1._5_ TC), peripheral AF point on the bird's eye.
> 
> ...


The hardware may be capable in certain situations of working, but if the central AF point doesn't function, or the reliability doesn't meet the manufacturers stringent testing standards, it's much simpler for them to simply mask out this borderline operation via the firmware.


----------



## Keith_Reeder (Aug 27, 2014)

Yep, fully aware of that, but it's beside the point: I'm letting people know that despite suggestions to the contrary, both the 7D and the 70D _will_ work in circumstances which some on here have stated they _won't _ work in.


----------



## FEBS (Aug 27, 2014)

Keith_Reeder said:


> Yep, fully aware of that, but it's beside the point: I'm letting people know that despite suggestions to the contrary, both the 7D and the 70D _will_ work in circumstances which some on here have stated they _won't _ work in.



But you need to use then a third party extender for fooling around the body concerning available max aperture. My opinion, the Canon extenders still deliver the best quality on Canon lenses. So, I would like to see a photo of the 100-400 + 1.4 extender on the tele end and taken on a 7D or 70D, as I have my question about IQ at that moment.


----------



## rs (Aug 27, 2014)

FEBS said:


> Keith_Reeder said:
> 
> 
> > Yep, fully aware of that, but it's beside the point: I'm letting people know that despite suggestions to the contrary, both the 7D and the 70D _will_ work in circumstances which some on here have stated they _won't _ work in.
> ...


Will a 60D do?

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=113&Camera=736&Sample=0&FLI=8&API=0&LensComp=0&CameraComp=0&SampleComp=0&FLIComp=0&APIComp=0


----------



## FEBS (Aug 27, 2014)

rs said:


> Will a 60D do?
> 
> http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=113&Camera=736&Sample=0&FLI=8&API=0&LensComp=0&CameraComp=0&SampleComp=0&FLIComp=0&APIComp=0



If there is sufficient of light then then 60D might do that, just as the 7D or the 70D could do it over there. there is however no guarantee that you can do it from Canon, as it is not build in in the design of the camera. I am not aware which firmware this even might block, but I think Canon could have done this. Did you look at the quality of your link to digital picture? even in the center the sharpness is gone when you compare the 560mm with the 400mm.


----------



## rs (Aug 27, 2014)

FEBS said:


> rs said:
> 
> 
> > Will a 60D do?
> ...


This combo is f8 wide open at the long end. Due to the pixel density of the 60D, diffraction starts to limit resolution at f6.9, so smaller apertures don't have much scope to tidy up the already quite bad resolving power of that lens/TC combo in the centre.

There are no rumours of the hardware in any of the existing Canon crop bodies being capable of autofocusing at f8, so as far as I know there is no possibility of a firmware update for a 60D, 70D or 7D to allow for this feature. There's nothing stopping you from manually focusing it, trying out AF through live view, or even taping over the extra pins on the TC to trick the camera into attempting autofocus.

However f8 autofocus on the 7D mk II is a distinct possibility, even if the rumoured pixel density will mean apertures smaller than f6.6 will run into resolution limiting diffraction.


----------



## hendrik-sg (Aug 27, 2014)

FEBS said:


> rs said:
> 
> 
> > Will a 60D do?
> ...




It may be interesting from a technical Point of view if it works or not. But:

(My expierience is based on a 50d, with 300 2.8 IS (original one) and Ext 2x iii)

with extender one needs 3 stops more light, 2 stops get lost by the extender and with 2x maginifcation one needs 2x faster shutter Speed.

in a situation where ISO 400 works ISO 3200 would be necessary. this ISO value is already quite bad for a crop camera. Next the quality reduction by the extender and poor AF performance comes to the equation. 

With all of this, in my expierience, the lighting situation must be really great that the extender gives a really better result than cropping, but the risk to completely loose the shot (by to finding the subject in the viewfinder until ist gone, by motion blur, by trying to low ISO, by poor AF, by bad framing, etc) is much higher.

means, for my use, i would ot nmeed a long reach tele combination with F8 opening on a crop camera, F5.6 is bad enough. Maybe with lots of practise, there may be a benefit in a 840mm F8 combination, but this needs lots of skill, ond if one has These skills, one knows how to handle the difficulties, and taping the extender may be the smallest difficulty


----------



## dgatwood (Aug 27, 2014)

neuroanatomist said:


> Mt Spokane Photography said:
> 
> 
> > And, to further confuse the issue, the 70D will autofocus f/11 lenses. This is only possible while using live view, autofocusing of that 400mm f/5.6 lens with a 2X TC attached is allowed.
> ...



I've used my 6D's live view autofocus at almost f/24 (an f/5.6 lens with stacked 1.4x and 3x TCs). It has a bad miss rate (mostly because I can't hold the camera still enough at 1260mm even with the 70–300L's IS system), but it does function....


----------



## Mt Spokane Photography (Aug 27, 2014)

Keith_Reeder said:


> Yep, fully aware of that, but it's beside the point: I'm letting people know that despite suggestions to the contrary, both the 7D and the 70D _will_ work in circumstances which some on here have stated they _won't _ work in.



If you use a non reporting TC, even a old 10D will autofocus at f/8 with some lenses. Others do not work. I've tried in numerous bodies and lens combinations over the years. The TC you use also makes a huge difference, some work better than others.

They do not track a subject fast enough for bif, but for a still object in bright light, they work fine. My 5D MK III worked much the same way before the firmware update. It is now more stable with F/8 AF then it was with taped contacts or non reporting TC. With some lenses, it just rapidly vibrated the focus at F/8.


----------



## mnclayshooter (Aug 27, 2014)

> When a DSLR auto-focuses it does so with the aperture wide open, regardless of the aperture to be used for the photo capture. Once focus is achieved, it stops down the aperture to the desired size and takes the picture.



Thanks for beating me to this. This is often the main point of confusion for most people about this topic. The camera will AF with F40, only because it checks focus with wide-open aperture and then before exposing the image, sets the aperture. (Hence the change in viewfinder brightness when you hit the "DOF preview" button - on my 6D it's the button under the lens mount on the body.)

So when you stack your TC onto a lens and make its _widest possible_  aperture less than F8 (or whatever minimum your particular camera AF's at in normal lighting conditions), you'll have problems with consistent, if any AF.


----------



## Keith_Reeder (Aug 28, 2014)

mnclayshooter said:


> So when you stack your TC onto a lens and make its _widest possible_  aperture less than F8 (or whatever minimum your particular camera AF's at in normal lighting conditions), you'll have problems with consistent, if any AF.



And yet again, the theory isn't borne out by practical experience.

We've been "taping the pins" on TCs _for years_ to get lenses and cameras to play nice together at f/8: and - as a trip round Google will amply confirm - thousands and thousands of users have found this to be an _entirely_ workable solution for getting out to 560mm, or 600mm or whatever, with XXD bodies and nominally f/5.6 lenses.

My old Kenko 1.4x was never off my 30D/100-400mm combo back in the day, and it worked brilliantly as long as expectations were realistic: AF more than fast enough for anything other than fast BIFs, and sharpness a-plenty.

I've also posted up examples from my 7D/Kenko non-reporting 1.5x TC/100-400mm, and - frankly - they're as good as a lot of stuff I see from supposedly far superior combos.

And - again - my 70D AFs on every AF point with my Kenko 1.5 and 100-400mm, as do the 70Ds of three other friends who own the camera and 100-400mms, to whom I've loaned the Kenko.

(I'll concede that this combo likes good light and plenty of contrast, _but it works_).

Can we _please_ stop regurgitating internet "wisdom" and replace it with actual experience? Just once in a while?


----------



## Keith_Reeder (Aug 28, 2014)

Mt Spokane Photography said:


> If you use a non reporting TC, even a old 10D will autofocus at f/8 with some lenses. Others do not work. I've tried in numerous bodies and lens combinations over the years. The TC you use also makes a huge difference, some work better than others.



Again beside the point, though. 

The claims by some here are that AF _simply won't work_ in the circumstances we're discussing: I'm saying that I've got a shed-load of actual personal experience - over a number of years, bodies and TCs - that flies directly counter to the "facts" being stated by these individuals.

_Of course_ there's an element of compromise to this, and _of course_ some combos work better than others; but the fact is that _they work_, despite these authoritative claims that they simply can't.

The only body I couldn't get to AF at all with a TC and my 100-400mm was the 40D; in fact, I believe I was the first person to break this news, on DP Review.

But others could get AF with that body and a TC using the 400mm f/5.6 prime, so - even there - the blanket "can't work" claim was utterly bogus.

*All I'm really saying is this: don't take it as gospel that your camera won't AF at f/8 simply because some "expert" on the internet says it won't. Try it yourself*


----------



## rs (Aug 28, 2014)

Keith_Reeder said:


> Mt Spokane Photography said:
> 
> 
> > If you use a non reporting TC, even a old 10D will autofocus at f/8 with some lenses. Others do not work. I've tried in numerous bodies and lens combinations over the years. The TC you use also makes a huge difference, some work better than others.
> ...


Before you get too critical of other peoples opinions here on this thread, just take a moment to read what they're saying. It's all identical to your findings, just some are saying the glass is half empty while others are saying the glass is half full. It all amounts to the same thing. AF can and does work with some/many f8 lens/TC combos and f5.6 capable bodies, but it can't be guaranteed to work reliably with every f8 lens/TC combo and every f5.6 body in every typical shooting scenario.


----------



## wjm (Aug 28, 2014)

Famateur said:


> Orangutan said:
> 
> 
> > When a DSLR auto-focuses it does so with the aperture wide open, regardless of the aperture to be used for the photo capture. Once focus is achieved, it stops down the aperture to the desired size and takes the picture.
> ...



You can also see it: Select F16 of F22. If you look into the lens you cannot see the aperture. If you press the shutter release and you can see de aperture close (and open). If you change the aperture while looking into the lens you won't see any difference. Only when pressing the shutter release.


----------



## 2n10 (Aug 28, 2014)

Keith_Reeder said:


> Just some Real World experience to add to the mix: the 7D will AF _usefully_ quickly for bird photography at f/8 (eg Canon 100-400mm and taped or non-reporting 1.4x TC) _ off the central AF points_. Use it on the peripheral points, and it's actually not bad at all.
> 
> For example - 600mm, handheld, (Kenko non-reporting 1._5_ TC), peripheral AF point on the bird's eye.
> 
> ...



Thanks for the info. I had read not to use the center focus point but your statement of using the peripheral points is a big help. Now to test it out as you have stated.


----------



## mnclayshooter (Aug 28, 2014)

Keith_Reeder said:


> And yet again, the theory isn't borne out by practical experience.
> 
> 
> 
> ...


----------



## 2n10 (Aug 29, 2014)

Keith_Reeder said:


> Just some Real World experience to add to the mix: the 7D will AF _usefully_ quickly for bird photography at f/8 (eg Canon 100-400mm and taped or non-reporting 1.4x TC) _ off the central AF points_. Use it on the peripheral points, and it's actually not bad at all.
> 
> For example - 600mm, handheld, (Kenko non-reporting 1._5_ TC), peripheral AF point on the bird's eye.
> 
> ...



I put Keith's suggestion to work and the AF is pretty fast with my 7D with the 100-400 and a 1.4X non-reporting TC. You need decent light with nice contrast in your subjects. I got some nice shots with the sun behind some clouds this afternoon. Heavy shade was a bust as was shade with the sun behind clouds with a low contrast subject. Moving subjects are an issue when coming more or less directly at you or heading away. I did not get an opportunity to try with subjects moving in a more parallel vector.


----------

