September 15, 2014, 12:24:30 AM

Author Topic: Focus indication with manual lenses  (Read 1835 times)

racebit

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Focus indication with manual lenses
« on: April 22, 2014, 06:21:21 AM »
Could anyone please explain why cameras (like my 7D) do not give focus indication with full manual lenses (that is no aperture data).
I would think the camera would be able to know if the focus is one direction or the other, so it could use two arrows to report the info it gets from the AF sensor.
It seems that only works with lenses that provide aperture data, but I am not figuring what the aperture is needed for.
If there is really no way that it works, I am at least expecting the new Dual-Pixel cameras will solve that.
Thanks in advance for any help

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Focus indication with manual lenses
« on: April 22, 2014, 06:21:21 AM »

e17paul

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Re: Focus indication with manual lenses
« Reply #1 on: April 22, 2014, 08:03:28 AM »
I use my ancient Zuiko OM lenses on my 6D via a Fotodiox Pro Om to Eos adaptor with Dandelion chip. Focus confirm works fine.

I'm no expert, but you may be that you need an adapter with the necessary electronics built in for focus confirm to work. I'm assuming that you are using classic manual focus lenses on some kind of adaptor.

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MatC

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Re: Focus indication with manual lenses
« Reply #2 on: April 22, 2014, 08:09:58 AM »
The focal length divided by the aperture (ie f/ number) isn't just total light availability:  it also defines the angle of the incoming cone of light that focusses onto the film/chip.

This has caused a lot of confusion, with people wondering why we can't use an f/8 lens in bright sunlight even though focussing at f/5.6 works in near-dark conditions.

Phase detect AF (the good and fast one that we all love) samples from two points in the incoming light cone, and the phase difference between them shows the amount and direction of focus needed.  (Obviously this is per focus point, we're just looking at the centre point).  Out of focus images show an image shift depending on which part of the incoming light cone is being looked at.

The further apart you sample in this light cone, the better the parallax and the easier it is to focus.

- Most cameras sample the cone at the equivalent of f/5.6 (39.3 degree light cone)

- Some also do f/2.8 (wider cone, so accurate and fast when available).

- f/8 (28.1 degree light cone) is rare and expensive because the cone is narrow and the difference between images at each focus sensor is relatively small.

Different sensors are chosen depending on the lens attached and its current zoom (which usually affects the f/ number).  This is why your camera cares about getting aperture info.

There is no reason it couldn't TRY to use its narrowest AF and report to you what it thinks is going on.
There is however a business reason:  Why would Canon want to make it easier/nicer for you to use non-EF lenses?


Keem

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Re: Focus indication with manual lenses
« Reply #3 on: April 22, 2014, 09:19:37 AM »
If your full manual lens is fast enough (f5.6 or faster for 7D) and has a chipped adapter (you can find many chepo-chinese adapters at fleeBay) you should get focus confirmation. You can even find a chip to be sticked to the lens adapter. With this situation you are using PHASE Detect AF (you will get confirmation as you look through the viewfinder) as MatC has explained in detail. For the dual-pixel system is designed for live-view/video recording situation. You will still need a chipped adapter.

If you can mention the type/mount of manual focus lens you have, the community can give you better advice...

polarhannes

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Re: Focus indication with manual lenses
« Reply #4 on: April 22, 2014, 10:14:39 AM »
The focal length divided by the aperture (ie f/ number) isn't just total light availability:  it also defines the angle of the incoming cone of light that focusses onto the film/chip.

This has caused a lot of confusion, with people wondering why we can't use an f/8 lens in bright sunlight even though focussing at f/5.6 works in near-dark conditions.

Phase detect AF (the good and fast one that we all love) samples from two points in the incoming light cone, and the phase difference between them shows the amount and direction of focus needed.  (Obviously this is per focus point, we're just looking at the centre point).  Out of focus images show an image shift depending on which part of the incoming light cone is being looked at.

The further apart you sample in this light cone, the better the parallax and the easier it is to focus.

- Most cameras sample the cone at the equivalent of f/5.6 (39.3 degree light cone)

- Some also do f/2.8 (wider cone, so accurate and fast when available).

- f/8 (28.1 degree light cone) is rare and expensive because the cone is narrow and the difference between images at each focus sensor is relatively small.

Different sensors are chosen depending on the lens attached and its current zoom (which usually affects the f/ number).  This is why your camera cares about getting aperture info.

There is no reason it couldn't TRY to use its narrowest AF and report to you what it thinks is going on.
There is however a business reason:  Why would Canon want to make it easier/nicer for you to use non-EF lenses?

Excellent explanation, thank you - always good to learn something new.
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racebit

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Re: Focus indication with manual lenses
« Reply #5 on: April 22, 2014, 12:34:09 PM »
Thank you all for your replies, but I do not use any adapter, nor intend to. I use EOS manual lenses (e.g Samyang 85mm 1.4).
My question was exactly why are electronics needed. The camera has the sensors that react to the light coming from the lenses. Why does the camera need to know the aperture settings of the lens?

If electronics on lens are really needed for manual focus, then I will get the 7D2 with dual-pixel as soon as possible.

Edit: Can it be that the 70D/7D2 dual-pixel also needs electronics on the lenses? :-\

« Last Edit: April 22, 2014, 12:38:02 PM by racebit »

neuroanatomist

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Re: Focus indication with manual lenses
« Reply #6 on: April 22, 2014, 12:37:00 PM »
Why does the camera need to know the aperture settings of the lens?

The aperture setting is irrelevant, but the max aperture of the lens must be communicated to the camera.
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Re: Focus indication with manual lenses
« Reply #6 on: April 22, 2014, 12:37:00 PM »

racebit

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Re: Focus indication with manual lenses
« Reply #7 on: April 22, 2014, 12:52:43 PM »
Why does the camera need to know the aperture settings of the lens?

The aperture setting is irrelevant, but the max aperture of the lens must be communicated to the camera.

Why does it need the max aperture? Couldn't it just work with whatever light reaches the AF sensor? The little I think know is that the AF sensor checks if the light reaching two pixels is equal (focus) or different (not focus), and that difference tells the distance to focus, and the sign of that difference tells the direction.

Even needing to know the max aperture, why not the camera:
1. Allow max aperture to be set, one more parameter in some menu page, rather than forcing electronics on every lenses for such small (and constant) piece of info?
2. Assume some value (e.g 5.6), at least it would work in most cases, whereas like this it never works...
 
Does the 70D dual-pixel also needs electronics on the lenses?

Thanks.
« Last Edit: April 22, 2014, 01:09:08 PM by racebit »

neuroanatomist

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Re: Focus indication with manual lenses
« Reply #8 on: April 22, 2014, 01:14:32 PM »
Then why not the camera:
1. Check the several sensors for the light coming in? If the wider sensors are not receiving light but the narrower ones are, then it could use the narrower ones. It would always use the wider ones receiving enough light. I must be missing something...
2. Allow max aperture to be set, one more parameter in some menu page, rather than forcing electronics on every lenses for such small (and constant) piece of info?
3. Assume some value (e.g 5.6), at least it would work in most cases, whereas like this it never works...

Why not?  Because Canon does not currently sell any lenses which do not report the max aperture to the camera electronically.
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racebit

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Re: Focus indication with manual lenses
« Reply #9 on: April 22, 2014, 02:36:00 PM »
Why not?  Because Canon does not currently sell any lenses which do not report the max aperture to the camera electronically.

ah...  well then... this is a dog world...
To make it worse Dual-pixel will not solve it, as even many Canon lenses do not work with Dual-pixel due to the lens CPU...  dog world...

http://www.the-digital-picture.com/News/News-Post.aspx?News=7260

Jeffrey

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Re: Focus indication with manual lenses
« Reply #10 on: April 22, 2014, 06:23:03 PM »
I have to say that when shooting the Canon 100mm macro lens or the Zeiss Otus lens on my Canon 1D-X, I never pay attention to anything that would indicate perfect focus on the camera for a manual focus lens. Sometimes I will go into live view and zoom in but then leave live view and go back to the viewfinder to make sure the focus is where I want it.

Manual focusing after a while becomes almost second nature and you know when it it right. My success rate increases the more I shoot in manual focus.

sagittariansrock

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Re: Focus indication with manual lenses
« Reply #11 on: April 22, 2014, 06:40:57 PM »
Why does the camera need to know the aperture settings of the lens?

The aperture setting is irrelevant, but the max aperture of the lens must be communicated to the camera.

So it is an arbitrary requirement set into the camera, like a number it needs to plug in before testing for focusing, rather than information actually used for the AF confirmation process?
Here's why I ask- if you set the chip on a Samyang to f/2.8 and then manually select the aperture to f/4 [which in this case is the aperture at focusing and metering, unlike auto-aperture (for lack of a better word) lenses which stop down only to take the shot]- it will still work. Meaning the f-stop information is necessary for focus confirmation, but not actually used.
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neuroanatomist

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Re: Focus indication with manual lenses
« Reply #12 on: April 22, 2014, 06:55:44 PM »
Why does the camera need to know the aperture settings of the lens?

The aperture setting is irrelevant, but the max aperture of the lens must be communicated to the camera.

So it is an arbitrary requirement set into the camera, like a number it needs to plug in before testing for focusing, rather than information actually used for the AF confirmation process?
Here's why I ask- if you set the chip on a Samyang to f/2.8 and then manually select the aperture to f/4 [which in this case is the aperture at focusing and metering, unlike auto-aperture (for lack of a better word) lenses which stop down only to take the shot]- it will still work. Meaning the f-stop information is necessary for focus confirmation, but not actually used.

That makes sense, and Canon would have no reason (of benefit to them) to code the firmware otherwise.
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Re: Focus indication with manual lenses
« Reply #12 on: April 22, 2014, 06:55:44 PM »

racebit

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Re: Focus indication with manual lenses
« Reply #13 on: April 23, 2014, 02:39:27 PM »
I have to say that when shooting the Canon 100mm macro lens or the Zeiss Otus lens on my Canon 1D-X, I never pay attention to anything that would indicate perfect focus on the camera for a manual focus lens. Sometimes I will go into live view and zoom in but then leave live view and go back to the viewfinder to make sure the focus is where I want it.

Manual focusing after a while becomes almost second nature and you know when it it right. My success rate increases the more I shoot in manual focus.

I find the 7D screen is not aggressive enough for good focus. Do you use 1DX standard screen?
Yes I think focus of Otus lenses have a major need for ultra-precise focusing. No one will pay Otus price to sacrifice sharpness with slightly off focus.

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Re: Focus indication with manual lenses
« Reply #13 on: April 23, 2014, 02:39:27 PM »