What factors are important for DSLR lenses for shooting video?

Question

I'm about to upgrade my DSLR camera from a Canon XSi (450D) to either a Canon 7D or T3i (600D). I'm largely interested in the video features of the camera. I have several mid/high-end lenses that I already use for still photography, but I don't have any "general purpose" zoom lenses (since I prefer to use a prime lens for most of my stills).

So, I'd like to get a general-purpose zoom lens (something that covers at least the 20-70mm range, or so) to use for shooting video.

My primary question is, how important is lens quality for videography? I know that "quality" can mean many different things, so let me break this question down a little bit more.

1. How important is sharpness? 1080p video is barely 2 megapixels, so it would stand to reason that an ultra-sharp lens is not really necessary to get sharp-looking video. Is this an accurate assumption?

   My approach for buying lenses for still photography has usually been to buy the best lens I can afford for the application I'm interested in. I'm wondering/hoping that it might be reasonable to buy a cheaper lens for video, and not feel like I'm sacrificing image quality, since the output resolution is so much lower than with stills. Is this just wishful thinking?

2. Obviously a large aperture is a bonus for video, since long exposures can't be used. But when shooting in low-light, again, it would stand to reason that I might be able to use a higher ISO to compensate for a slower lens, with less noticeable impact, since I'm recording at a much lower resolution than I would be for still photography. Is this also true? How fast of a lens do I need to be able to record in an average indoor lighting setting (no studio lighting), without a high ISO becoming noticeable?

3. Is image stabilization a pro or a con for hand-held video recording? I can imagine the sound of the motor might be a nuisance if picked up by the microphone. What impact does it have on the video itself?

4. I'm guessing a USM for auto focus probably won't matter a whole lot, since what I've read suggests that live auto-focus doesn't work very well in video mode. But even so, I suppose a USM AF would be a bonus, if/when it does work.

5. The ability for a lens to retain focus when zooming seems like it might be of particular importance when shooting video on a zoom lens.

Are there other factors I ought to consider when selecting a lens specifically for video?

I'm not really interested in pointers on which focal lengths I ought to use for what type of shooting, or specific lens recommendations... I'm interested in more general pointers, that will apply to all video shooting.

Answer 1

How important is sharpness? 1080p video is barely 2 megapixels, so it would stand to reason that an ultra-sharp lens is not really necessary to get sharp-looking video. Is this an accurate assumption?

It depends on the way the DSLR is capturing it's video from the sensor. The first method is the most obvious one, take the image and scale it, but there's also another; use only the pixels across the sensor's area that approximately "line up" with the pixels in the final resolution. I.e. in a 1080p image only every third or fourth scan line would be used resulting in one sensor pixel being used to produce one pixel in the video image.

I would hazard a guess that an "acceptably sharp" lens would be okay for video, though not ideal and probably for more reasons than image sharpness.

My approach for buying lenses for still photography has usually been to buy the best lens I can afford for the application I'm interested in. I'm wondering/hoping that it might be reasonable to buy a cheaper lens for video, and not feel like I'm sacrificing image quality, since the output resolution is so much lower than with stills. Is this just wishful thinking?

As my above answer suggested, there are other aspects of the lens you need to keep in mind when choosing a video lens and these may be:

• Maximum aperture for low-light.
• Fixed aperture for consistent exposure when zooming.
• Image stabilisation is especially useful when not using a steadicam or other stabilising rig or device.
• Ease of use, especially when it comes to the focus ring. Canon USM lenses in particular have a very smooth, usually well placed and grippy focus ring. Kit lenses aren't so good in comparison.

Obviously a large aperture is a bonus for video, since long exposures can't be used. But when shooting in low-light, again, it would stand to reason that I might be able to use a higher ISO to compensate for a slower lens, with less noticeable impact, since I'm recording at a much lower resolution than I would be for still photography. Is this also true? How fast of a lens do I need to be able to record in an average indoor lighting setting (no studio lighting), without a high ISO becoming noticeable?

I think you'll find with most typical video DSLR's is that the ISO performance for video isn't quite as great as you might assume, but it in no way bad. I'd say ISO 1600-3200 lives up to most expectations on the 18mp APS-C sensors, but beyond that it's quite noticeable.

Is image stabilization a pro or a con for hand-held video recording? I can imagine the sound of the motor might be a nuisance if picked up by the microphone. What impact does it have on the video itself?

For music videos and other videos where sound is not used, IS is fantastic and goes a long way to ensuring the video is jitter free, but if you need the sound and it's potentially a quiet environment, it might be prudent to use an external, higher quality mic attached to say, the hot shoe via a mount.

I'm guessing a USM for auto focus probably won't matter a whole lot, since what I've read suggests that live auto-focus doesn't work very well in video mode. But even so, I suppose a USM AF would be a bonus, if/when it does work.

The ability for a lens to retain focus when zooming seems like it might be of particular importance when shooting video on a zoom lens.

As above, Canon USM lenses (whether L or standard) have very usable focus rings. Provide good grip and are very smooth to focus with.

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I personally use a Canon EOS 60D with an EF-S 17-55mm F/2.8 IS USM lens and find it a great combination at those focal lengths. The IS in that lens is quite remarkable and the USM focus ring makes it very smooth and accurate to focus. When I turn the IS off, I can instantly see the jittery movement from my hands trying to hold a 2kg camera setup.

Answer 2

I do video with my Canon 5d Mkii. I am a beginner at video, but I have done photography for years.

1) How important is sharpness?

My lenses are all about the same sharpness, and I've never A/B'ed two different lenses at the same focal length. In my experience, lens sharpness is at the bottom of the list of problems with a shot. Getting enough light, getting the focus right, the composition, tracking any movements accurately, these are all much more pronounced issues than lens sharpness.

2) How fast of a lens do I need?

I have found that shooting indoors in normal households in northern california even wider than f/2 I have to crank the ISO up to about 1000. On my 5d, ISO starts to get very noticeable at about 600 or 800. I suspect that there is a separate noise reduction implementation for video, because I can shoot stills up to ISO 2000 without any noticeable noise.

3) Is image stabilization a pro or a con for hand-held video recording?

If you are using the built-in microphone on the camera, pretty much every minor touch of the camera and movement will come across as very loud. For this reason, I don't use the built-in mic at all. I suspect that stabilization would very audible. You can get a decent mic that fits into the hotshoe for about $100.

Stabilization after the fact works OK, but it does look manipulated to me. Virgin eyes might not pick it up though.

4) I'm guessing a USM for auto focus probably won't matter a whole lot

Autofocus has never worked for me at all. I can see the camera trying, but it is just far too slow and inaccurate to be useful. I usually start with AF in "photo" mode and then focus by hand while shooting video.

5) The ability for a lens to retain focus when zooming

I believe all zooms keep the same focal point while zooming? I don't have any zooms, but I think that is the case.

Answer 3

#2 - You definitely want the largest aperture you can afford for video. The higher ISOs very quickly add a lot of noise, and you won't want to drop below a 1/60 exposure (180° shutter "rule"), which only leaves aperture.

#3 - I haven't done alot of comparison, but I've never noticed any noise from it. The general consensus on this thread seems to be that it's useful for video at times.

Answer 4

I answer your question with a video that helped me.

http://vimeo.com/videoschool/lesson/13/dslr-lenses

Basically, you need to take into consideration fStop as well. This allows you to change the amount of blur the background.

1. Very important. You can't fix crappy/not sharp video. If the lens looses quality at the very limit of the zoom, then that will not effect the video. But, if the lens produces blurry shots on any focal length, it will show up in your video
2. Shutter speed has no effect on the video, as the shutter stays open for filming.
3. It all depends. I have had no experience with VR, but I always keep it on. If you are using a shotgun mic, then any lens sounds will not be picked up. I don't have much experience here, so not my place to comment.
4. Continuous Auto Focus is a camera function (AF-S AF-A for Nikon users)
5. Telephoto lens do not retain focus when zooming. When the focal length chances a small amount, then its not noticeable (18mm to 25mm wont be that visible a change), but from 70mm to 240mm will loose all focus.

Even thou you did not ask for it...

Get the 7D (The use it to film House).

For staring I would get the Kit Lens or a 18-55mm or 24-105mm, but really, any lens will do.

More Reading:

• http://www.reelseo.com/hd-video-dslr-camera/