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Canon EOS Crop Sensor for HD
APS-C sensor cameras including the 80D, 70D, 7D Mk. II, 7D, EOS M and Rebel models for HD video recording.


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Old February 25th, 2011, 03:28 PM   #1
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Maintaining Focus

Guys,

Im a newbie to shooting video with my 7D, my big problem is focus most of the time.

Im fine with a relatively fixed subject, I zoom in to x10 on my screen, pull focus and then zoom out and shoot. Under these circumstances I understand how to adjust my aperture to get the desired DOF I need.

The problem arises when Im shooting on the wing so to speak. In these instances I am more interested in a much wider DOF with as much as possible in focus. Can I ask where abouts in the f-range should I be for this? I often crank it down to f16 or less.

Is there a point where increasing the f-value gives me nothing extra in terms of DOF?
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Old February 25th, 2011, 05:45 PM   #2
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Re: Maintaining Focus

this ought to help
Online Depth of Field Calculator
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Old February 26th, 2011, 01:22 AM   #3
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Re: Maintaining Focus

Thank you Chris, that is a really useful tool.
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Old February 26th, 2011, 04:29 AM   #4
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Re: Maintaining Focus

In documentary work you can sometimes get away with rocking back and forth to check focus. The screen on the 7D is quite clear and the subject will look crisp when rocked into focus. Obviously I am not talking huge changes in focus, but a twist of just a few degrees to ensure you're in focus.

Also, learn which way is near and far, and how far it is from one to the other on your favorite lenses.

I try not to get down farther than f/8, but I do from time to time.
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Old February 26th, 2011, 07:58 AM   #5
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Re: Maintaining Focus

Practice!!!!!
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Old February 27th, 2011, 02:26 AM   #6
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Re: Maintaining Focus

Yeah, the online DOF calculator should help. But if you're always closing down your camera's iris in an attempt to increase the DOF, why are you shooting video with a DSLR? The only reason to shoot video with a DSLR is so you have access to fast lenses and a larger sensor which allow for increased low light sensitivity and shallow DOF.

Sure, focusing is a pain at fast apertures, but that's the whole point of a DSLR, isn't it? Pick up a Z-FInder or LCDVF or an external monitor with focus peaking. Or if you don't want to deal with the hassle, just ditch the DSLR and buy a video camera.
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Old February 28th, 2011, 07:49 PM   #7
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Re: Maintaining Focus

"The only reason to shoot video with a DSLR is so you have access to fast lenses and a larger sensor which allow for increased low light sensitivity and shallow DOF."

Disagree.

Hypothetical shooting situation. Outside, daytime, and light sensitivity is not part of the equation. DSLR and Video Camera are stopped down with everything in focus. Both camera's shots are framed similarly. Even with a cheap lens, the DSLR image is better than the video camera image. Even in these conditions favorable in every way to my EX1, the 7D dominates. In fact, I have found no shooting environment in which the EX1 can claim superior image.

Even if you disagree with my first point, objectively, here's something else you overlooked. This question... "Are you shooting video?" I regularly get this question from bridesmaids over an hour into pre-ceremony coverage. It fills me with joy. The DSLR is so less threatening than the video camera. Your opportunities to capture real candor are much greater.
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Old March 1st, 2011, 03:16 AM   #8
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Re: Maintaining Focus

Quote:
Originally Posted by Craig Terott View Post
Hypothetical shooting situation. Outside, daytime, and light sensitivity is not part of the equation. DSLR and Video Camera are stopped down with everything in focus. Both camera's shots are framed similarly. Even with a cheap lens, the DSLR image is better than the video camera image. Even in these conditions favorable in every way to my EX1, the 7D dominates. In fact, I have found no shooting environment in which the EX1 can claim superior image.
Define "superior" as the 7D image has less detail & suffers from moire & aliasing. Shallow DOF & smooth bokeh can make the image preferable & there are all sorts of reasons for using a DSLR but there is no way that the image is "superior" to a camera like an EX1.

Quote:
Originally Posted by Craig Terott View Post
Even if you disagree with my first point, objectively, here's something else you overlooked. This question... "Are you shooting video?" I regularly get this question from bridesmaids over an hour into pre-ceremony coverage. It fills me with joy. The DSLR is so less threatening than the video camera. Your opportunities to capture real candor are much greater.
This is one of the greatest advantages of using a DSLR & a very good reason not to trick them out with rails, matte box, loupe etc

Last edited by Nigel Barker; March 1st, 2011 at 12:38 PM.
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Old March 1st, 2011, 08:30 AM   #9
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Re: Maintaining Focus

The answer to your question is indeed - PRACTICE.

Pulling focus is a skill. It is not a trivial skill to master. Lord knows I'm still working on it.
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Old March 1st, 2011, 02:55 PM   #10
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Re: Maintaining Focus

Quote:
Originally Posted by Craig Terott View Post
Hypothetical shooting situation. Outside, daytime, and light sensitivity is not part of the equation. DSLR and Video Camera are stopped down with everything in focus. Both camera's shots are framed similarly. Even with a cheap lens, the DSLR image is better than the video camera image. Even in these conditions favorable in every way to my EX1, the 7D dominates. In fact, I have found no shooting environment in which the EX1 can claim superior image.
Light sensitivity is ALWAYS part of the equation and when I am outside in daylight I almost always shoot with a neutral density filter so I don't have to stop down as much.

Also, in terms of sheer resolution, the 7D is inferior to the EX1 and any other truly HD video camera. Not to mention the camera's less than ideal compression codec, 12 minute recording limit, and horrible AGC. As DSLR shooters we forgive the inadequacies of our cameras because of the shallow DOF, low light sensitivity and pretty bokeh,

And if you haven't encountered an environment wherein the 7D's flaws are clearly evident, then you're not shooting enough. Try a wide angle lens in a downtown environment or any environment where there are horizontal and vertical lines and you're going to see some very ugly moire patterns. Also, try some medium to fast panning for some equally ugly rolling shutter issues.

Also, I have found the DSLR to be a problem at events because people assumes I'm shooting stills and suddenly goes into "pose mode".

I love my DSLR's but by no means are they ideal video capture devices.
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Old March 1st, 2011, 11:29 PM   #11
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Re: Maintaining Focus

You really just need to get lots of camera hours up. It's been said, practice. Set yourself weekend challenges.

Go out and film people walking towards you on a long lens, then try something faster like a car. Walk behind someone and keep them in focus. Just build up those camera hours and you will eventually do it without even thinking, it will just be apart of your normal operation.
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Old March 2nd, 2011, 09:26 AM   #12
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Re: Maintaining Focus

Quote:
Originally Posted by Alan Maughan View Post
Can I ask where abouts in the f-range should I be for this? I often crank it down to f16 or less.
The smaller the aperture, the deeper the focus; in this respect, there's no limit to how much you should stop down the lens. However, with certain lenses, stopping down too far can actually cause diffraction. So research the particular lenses you're using to see if this is the case.

An argument against stopping down is that the bokeh can become ugly, so that out of focus parts of the image do not look smooth or "pleasant." Of course you may desire this look for a particular shot.

As Lance mentions, using an external monitor is a huge help. You've got an advantage having the 7D, which outputs a 1080i signal while recording unlike Canon's other DSLRs.
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Old March 2nd, 2011, 09:43 AM   #13
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Re: Maintaining Focus

Quote:
Originally Posted by Lance Watts View Post
Light sensitivity is ALWAYS part of the equation and when I am outside in daylight I almost always shoot with a neutral density filter so I don't have to stop down as much.
I was providing one hypothetical shooting situation wherein the EX1 would not be at a disadvantage. I didn't say "this is how to shoot with a 7D"

Quote:
Originally Posted by Lance Watts View Post
Also, in terms of sheer resolution, the 7D is inferior to the EX1 and any other truly HD video camera.
Are you sure about that statement Lance? I guess you'll need to define that technical term "sheer resolution" :) because the image sensors are larger on 7D and both capture in full HD.

Quote:
Originally Posted by Lance Watts View Post
Not to mention the camera's less than ideal compression codec
You can say this about any compression codec. Your video camera's compression codec is less than ideal. Put the 7D image/video on a 30" monitor and lets compare.

Quote:
Originally Posted by Lance Watts View Post
As DSLR shooters we forgive the inadequacies of our cameras because of the shallow DOF, low light sensitivity and pretty bokeh,
Of course I do. Respectfully, there's no new incite.

Quote:
Originally Posted by Lance Watts View Post
And if you haven't encountered an environment wherein the 7D's flaws are clearly evident, then you're not shooting enough. Try a wide angle lens in a downtown environment or any environment where there are horizontal and vertical lines and you're going to see some very ugly moire patterns. Also, try some medium to fast panning for some equally ugly rolling shutter issues.
I did an engagement shoot "downtown" at night. It's absolutely gorgeous looking video. Among the 3 lenses I used was a wide angle, beautiful results.

Moire patterns will be more prominent with higher shutter speeds. Dial back your shutter and it's no big issue.

My EX1 has a rolling shutter which looks equallly disgusting, therefore the EX1 has no advantage on this point.


Quote:
Originally Posted by Lance Watts View Post
I love my DSLR's but by no means are they ideal video capture devices.
You've made an non-specific statement that can't be disagreed with. Yes, they are not IDEAL video capture devices. What camera can live up to every criteria to a point that it can be deemed "ideal"? Answer - none.
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Old March 2nd, 2011, 11:54 AM   #14
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Re: Maintaining Focus

Quote:
need to define that technical term "sheer resolution" :) because the image sensors are larger on 7D and both capture in full HD.
DSLRs have roughly nine times as many dots as 1080p has pixels. The problem is that DSLRs use a shortcut to get all that data recorded as 1080p video. As far as I can tell, only one of every two or three lines is used, giving high resolution, but with terrible aliasing. Horizontally, three samples are mushed together, reducing aliasing, but killing the resolution.

The bottom line is that DSLRs are fairly pathetic in the resolution department. It's a mix of mush (horizontal) and crud (vertical). That said, shoot an organic object like a face or flower over an out of focus background and it looks great.

And here's a tip: when shooting deep focus on a tripod, snap a photo of the background. The photo will have clean resolution well beyond 1080p. If the video shows background aliasing, paint in the photo in post. :)

With the target cost of DSLRs combined with the available processing and the speed of the sensors, the line skipping and pixel binning was necessary to make the whole video-DSLR market a reality. Hopefully, camera engineers are coming up with new architectures, faster sensors, and improved designs that will allow the next generation of DSLRs deliver true 1080p resolution without aliasing. If they can do that and reduce the rolling shutter effect, I'll gladly upgrade.
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Old March 6th, 2011, 10:12 AM   #15
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Re: Maintaining Focus

I personally have noticed a "muddy" image at times that I had always (perhaps incorrectly) attributed to the glass. The lack of resolution makes sense.

What doesn't make sense to me is ...typically soon after any new cam comes out (especially a "game-changer" like this one), the elite in our industry dissect it relentlessly right down to every nuance. Wouldn't this have been totally apparent on the day-one review with a resolution chart? Strange .
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