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Top glass not needed for DSLR Video?

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Jack Rusak
Top glass not needed for DSLR Video?
on Jan 14, 2012 at 7:00:32 pm

I saw an interesting statement the other day that top flight glass was not necessary for good Dslr video because even at HD, video doesn't use that much resolution and opposed to still pictures.
The author mentioned video "only" made use of about 2000k, though I don't know what that means exactly.

I've tried to research this on the web but having no luck, probably not asking the right question.

Would appreciate any insights or links to in depth technical resources that can help me understand this as I am looking at this 24-120mm f/4G ED VR lens for Dslr video, even though it doesn't get high marks from the reviewers for still work.


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Joseph W. Bourke
Re: Top glass not needed for DSLR Video?
on Jan 14, 2012 at 8:45:34 pm

My opinion is that you need top end lenses for the speed of the lens, not necessarily for the "quality of the glass". While a cheaper lens may get you the same level of sharpness at certain settings, you lose out in the fact that your low light capabilities are reduced, as well, which means noise. It doesn't much matter how sharp your shot is if it's noisy.

Here are some really good opinions on lensing for DSLRs:

http://nofilmschool.com/dslr/lenses-primes-brands/

Here's some more good information:

http://www.hurlbutvisuals.com/blog/2010/02/06/still-lenses/

Joe Bourke
Owner/Creative Director
Bourke Media
http://www.bourkemedia.com


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Colin McQuillan
Re: Top glass not needed for DSLR Video?
on Jan 14, 2012 at 9:07:32 pm

[Jack Rusak] "The author mentioned video "only" made use of about 2000k"

I would imagine he is referring to the width of HD video (1980 pixels wide) as compared to the resolution of still photos.

Like all things it really comes down to application as to whether or not you should be trying to get away with cheap lens'.

You will get sharper, better video from better lens'. In personal tests I have done comparisons between the 50 1.8 and 50 1.4, and also a cheaper 70-300 and a higher end 70-200. There were noticeable differences with the higher end glass producing better pictures and well as smother operation.

You also pay for build quality.
With a higher end lens you will get smoother focusing. Cheaper lens will have some play on the focus ring.
Constant aperture is something to look for as well. For my work, I often am lighting scenes - with this in mind having a variable aperture lower-end lens would be difficult to work with as the iris would change if I zoom the lens to re-frame.

Bokeh (smoothness of the out-of-focus areas) will not be as pleasing, as cheaper lenses tend to have fewer aperture blades and a slower max aperture.

Does this mean you need to pay top dollar for top end glass - not necessarily. It comes down to your needs. For broadcast level, high-end event/corporate, or cinematic purposes I would go for the best, fastest glass you can afford. For other purposes maybe you can get away with saving money on cheaper lens'.

Colin McQuillan
Vancouver, B.C.



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Steve Crow
Re: Top glass not needed for DSLR Video?
on Jan 14, 2012 at 9:44:47 pm

Yeah that was me and I was dancing on the very edge of my knowledge when I posted that so it's no surprise to me that it came back to bite me in the ass ha ha!

From what I understand ONE advantage of the more expensive glass is that it can be sharper/offer higher resolution photographs. When you have cameras creating still images that are 3456 X 5184 (around 3.5K resolution then) or even much higher then, yes, keeping all those pixels sharp and in-focus is something that STILL photographers like to see.

But when even HD video is "only" 1920 x 1080 pixels AND when you consider how many of us adjust our cameras to turn the video sharpness waaaaay down then I have to question the value of these lenses to the video dslr guy or gal. On the other hand, I've read the other posts in this thread and there are some good comments that I didn't take into account. For instance, IF an L series lens gives you a more wide open lens (faster/lower f-stop number) then that's a factor and if the bokah really IS better well that's obviously good too.

I guess my point is that you shouldn't feel bad if you can only afford the more consumer level glass - that most people probably won't notice the difference in image quality or give a darn if you point it out to them.


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Andrew Somers
Re: Top glass not needed for DSLR Video?
on Jan 15, 2012 at 7:45:47 pm

I saw an interesting statement the other day that top flight glass was not necessary for good Dslr video because even at HD, video doesn't use that much resolution and opposed to still pictures.
The author mentioned video "only" made use of about 2000k, though I don't know what that means exactly.


The author of that statement is wrong, and IMO he lacks an understanding of the benefits of "good" vs "cheap" glass. Hint: It's not about resolution.

His statement regarding "2000k" is that in HD (and even at 2K) we are only using about 2 to 2.3 million pixels for the image. This *may* have an effect on the effective minimum circle of confusion relative to a still image - depending on the size of the still image - or it may not. The minimum circle of confusion is "more" related to enlargement size and viewing distance than sensor pixel density.

But more to the point: Feature films shot on 35mm film are typically scanned into a 2K DPX file - 2.3 megapixels. And that is projected onto a screen 40 feet wide. And do you see cheap lenses on a Panavision? No you see *really expensive* exotic high end glass !!! Glass made by Nikon, Zeiss or Leica.


But perhaps more to the point: image *sharpness* is not the most defining characteristic of *image fidelity*.


Think about how much time we often spend making an image LESS sharp - ProMist filters, hazers on set, etc. etc.

And THEN take a look at images that you love, that are full of depth and "intimate feeling" - and THEN notice that in fact, the *majority* of the image is out of focus. (In particular, the background.)

Look at the out of focus areas - are they smooth, with a creamy blur? Or is the blur have nasty "defined" edges and contrast? The quality of these out of focus areas is referred to as "bokeh". The quality of the bokeh is one of the prime aspects of a quality lens. Personally, I never choose a lens for its "sharpness" (except when doing product shots) - for most subjects, I choose a lens based on its bokeh - in other words, I choose a lens first based on how the OUT OF FOCUS areas appear.


Related to boken is depth of field - and a *high end* lens is also often going to be "faster" meaning that you can open the aperture wider, resulting is narrower depth of field. This allows for more selective focusing to draw the viewer's attention to a specific subject.


Another factor in lenses is the "diffraction limited resolution" which like circle of confusion is related to viewing size, and also to sensor (imaging area) size.

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

You might be interested to know that as you increase the imaging area size, the circle of confusion increases in size, and so does the diffraction limited resolution, such that in fact, as you increase imaging area size, you can actually use a *LOWER* quality lens. Note that on large 4x5 view camera's, the lens is quite simple, and not particularly fast - yet the image *quality* is astounding because of the very large imaging area.

As you reduce the imaging area size, then lens quality become increasingly important, as you are resolving light onto a much smaller area, and diffraction limited resolution plays a much more important role. And this is certainly the case with cheap HDV cameras with tiny 1/3" sensors.



The nice thing about dSLRs (DX format) is that they have an imaging area very similar to 35mm motion picture film, and as such focal length and aperture choices will be virtually the same as when shooing with a 35mm motion picture camera.

The implication here too, then is that you would also want to be using *LENSES* that are of a similar quality. The *LENS* is the most important part of any camera system - Canon L series, Nikon pro lenses, etc. etc. are all still quite important when shooting HD on a dSLR.


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Rafael Amador
Re: Top glass not needed for DSLR Video?
on Jan 16, 2012 at 1:51:04 am

DSLRs do not use only the 1920x1080 central pixels.
Any camera with just one captor using just these 1920x1080 pixel could never compete in quality with a camera using three 1920x1080 captors (as the EX-1/3).
The camera needs more pixels to get electronically the three channels than a 3 captors camera gets mechanically (prisms or mirrors).
The picture is then cropped and downscaled.
using good lenses, is not just about sharpness, but also about f.stops.
rafael

http://www.nagavideo.com


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Andrew Somers
Re: Top glass not needed for DSLR Video?
on Jan 16, 2012 at 5:10:37 am

DSLRs do not use only the 1920x1080 central pixels.
Any camera with just one captor using just these 1920x1080 pixel could never compete in quality with a camera using three 1920x1080 captors


Most dSLRs use the entire imaging area of the sensor, and downconvert to 1920x1080. However, the D4 can use the full FX sensor area, or reduce down to the DX area, or reduce further to use only the 1920x1080 area in the center of the sensor. This is an important feature that allows for increasing or decreasing the depth of field and field of view with a given lens

I am assuming that by "captor" you means "sensor" - I'll guess that some automatic translator mangled that word.

As far as if a 3 chip camera is "better" than a single chip camera - there is more to image fidelity than simply the methodology of capture and the number of pixels in a sensor. There are advantages and disadvantages to *both* methodologies - and it is a misconception that somehow a single-chip sensor with a bayer filter is inferior as this is certainly not the case.

The fact is that *every* high-end larger-format camera uses a single chip design. Hasselblad, PhaseOne, Canon and Nikon professional still cameras are all single chip designs, as are the Red, Sony F35, Arri, and the other major digital "film sized" cinema cameras. They all also have large imaging areas which is a key consideration.


The cameras that are using 3 chip designs are cameras with VERY SMALL SENSORS. 1/3rd" and 1/2" sensors are so small that there is an advantage to using a "3 chip" design. But even so, don't assume that all 3 chip cameras are in fact 3 chips at a native 1920x1080 res - many, including those from Panasonic are actually using lower res sensors, and using pixel shifting to increase the apparent resolution - well, LOL, this is essentially what a single chip bayer filter sensor does. But when you use three *small* chips, you can do it cheaper.

Now the Sony EX-3 you mention uses 3 chips at an "effective" native 1920x1080 res - but still, these are a tiny 1/2" in size - no where near the imaging area of even a DX (APS-C) format dSLR which has nearly four times the imaging area.

Using 3 chips, you can have a larger pixel pitch for lower noise and better dynamic range - but with 3 chips you lose one or more stops of light due to the beamsplitter. With 3 chips you have more total pixels capturing light at a lower cost and with better noise dynamic range than if you were to increase the pixel density on a single chip of the same size. Plus the advantage that in a 3 chip design you don't need the extra digital processing of the debayering stage.

HOWEVER

When you increase the total imaging area, to say the size of film, such as in a dSLR or a "Super 35" sized sensor, then you can have large pixel pitch *and* all three colors on a single chip. You no longer gain a "substantial" benefit from a 3 chip with beamsplitter design. Certainly not in terms of cost.

For instance take the new Nikon D4. It is a single chip sensor, but is full sized (FX) - and with 16 Megapixels, it still has larger pixels than the Sony EX-3, which only has 2 mega-pixels. The D4 has nearly 8 times the imaging area of the EX-3.

And at 16 megapixels, it is nearly exceeding the resolving power of most of the best lenses. This is partly why there is no "real" benefit to using a 3 chip design in *large* sized image sensors, while with tiny sensors, there is a significant benefit.

Also to be mentioned is the advancement of debayering algorithms which have had a significant impact on the image quality available from a single chip solution. Modern demosaicing algorithms avoid the problems that gave single chip cameras their "bad reputation" decades ago.


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Rafael Amador
Re: Top glass not needed for DSLR Video?
on Jan 16, 2012 at 3:07:50 pm

Hi Andrew,
What I tried to say to explain to Steve is that with one "sensor" we need a bigger size, because we need to allot pixels to the tree colors, while on a 3 chips camera each one is already dedicated to a single color.
Using just 1920x1080 from a single sensor I guess would be good enough to get a decent SD picture but no for 1080 or even 720.
Your explanation has been clear and precise.
rafael

http://www.nagavideo.com


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