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Canon XF Series HD Camcorders
Canon XF305, XF205 and XF105 (with SDI), Canon XF300, XF200 and XF100 (without SDI).


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Old January 29th, 2010, 02:29 PM   #196
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Daniel, I think you'll find it's a fact that the diffraction limit gets lower the smaller the film/chip size. So with an 8x10 camera you're happy well down to f45, a Hasselblad is OK to f11, but 35mm starts to lose resolution at f5.6-8. For 1/3" chips it's down around f4! You obviously have access to science that I don't.
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Old January 29th, 2010, 03:17 PM   #197
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Originally Posted by Steve Phillipps View Post
Daniel, I think you'll find it's a fact that the diffraction limit gets lower the smaller the film/chip size. So with an 8x10 camera you're happy well down to f45, a Hasselblad is OK to f11, but 35mm starts to lose resolution at f5.6-8. For 1/3" chips it's down around f4!
You have the correct principle (the f-number scales with chip size), but your math is still way off. For any given display size, the following have the exact same diffraction, depth of field, (and angle of view and focus distance of course):

f/4 on 1/3" (5.1mm width)
f/7.5 on 2/3" (9.6mm)
f/17.5 on APS-C (22.5mm)
f/28 on FF (36mm)
f/44 on Hasselblad 645 (56mm)
f/198 on 8x10 (254mm)

As I said, diffraction scales with DOF. When you said that diffraction prevents the possibility of stopping down FF35 to match the DOF of 1/3", you were wrong.

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You obviously have access to science that I don't.
You obviously resort to insults when proven wrong.
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Old January 29th, 2010, 03:22 PM   #198
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Didn't mean it to be an insult, sorry you took it that way.
I still don't think I am wrong, in your example you say stopping down to f28 on 35mm, are you really telling me this won't cause the image to be affected by diffraction? I simply don't believe it.
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Old January 29th, 2010, 03:25 PM   #199
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Well I don't want this thread to get too out of hand here...

My experience with shooting with the XL H1S, 5D Mark 2, and 7D is that the XL/XH still seemingly have greater overall dynamic range. The SLRs seem to have less, despite the sensor size. I assume this has to do with the heavy pixel count on the sensors.

Wasn't it also Barry Green or Adam Wilt that measured the range as around 8 stops? I can't remember...
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Old January 29th, 2010, 03:32 PM   #200
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Didn't mean it to be an insult, sorry you took it that way.
I was wrong to have taken it the wrong way. I apologize. Thank you for the clarification.

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I still don't think I am wrong, in your example you say stopping down to f28 on 35mm, are you really telling me this won't cause the image to be affected by diffraction? I simply don't believe it.
No, I am not saying it will not be affected by diffraction. I am saying that f/28 on 35mm will be affected by diffraction to the exact same degree as f/4 on 1/3". Look it up in a diffraction calculator, there are several of them around the web. Just be sure that you set the calculator to use the same CoC (i.e. same display size and resolution). For example, set both to a 1080p monitor or a 4x6 print.

If you prefer to look at test images instead of calculators, you can download the raw files for the images I posted earlier:

Comparison images
  • Picture b1: 70mm, f/11.3, ISO 200, 12.5x8.5mm sensor
  • Picture b2: 200mm, f/32, ISO 200, 36x24mm sensor

One of the images is f/32, which is even narrower than f/28. It shows the same level of diffraction as a smaller sensor at f/11.3.
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Old January 29th, 2010, 03:36 PM   #201
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I have to admit the science is a bit beyond me. I've always been told that on 35mm you don't want to go beyond about f8, f5.6 on 2/3" etc. I was just responding to the idea that getting big DoF on DSLRs is no problem as you can just shut the aperture well down - didn't seem to be as good an idea as the poster suggested.
Cheers,
Steve
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Old January 29th, 2010, 03:47 PM   #202
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I've always been told that on 35mm you don't want to go beyond about f8, f5.6 on 2/3" etc.
That's probably because the advice is geared towards a resolution far higher than 1080p (which is just 2 MP).

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I was just responding to the idea that getting big DoF on DSLRs is no problem as you can just shut the aperture well down - didn't seem to be as good an idea as the poster suggested.
I think it's a great idea!
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Old January 29th, 2010, 03:53 PM   #203
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Unfortunately, I haven't seen anything with an impressive dynamic range from the video on a DSLR. The colour depth (space?) from the video on a DSLR, you're the first person I've heard make that claim, usually it's described using terms like fragile. I can understand people saying positive things about a RED in this regard.

I was referring to a constant aperture zoom for the Canon would be physically larger than the current 20x lens, which does have a pretty large aperture ramp. Not always an issue, but as it can cause an issue if this noticeablely kicks in earlier than say half way through the zoom range.
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Old January 29th, 2010, 04:11 PM   #204
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Unfortunately, I haven't seen anything with an impressive dynamic range from the video on a DSLR.
I'll have to shoot a comparison between the XH-A1 and 5D2 sometime.

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The colour depth (space?) from the video on a DSLR, you're the first person I've heard make that claim, usually it's described using terms like fragile. I can understand people saying positive things about a RED in this regard.
I did not mean color space. I wrote "improved color depth (i.e. SNR over the used dynamic range)". What it means is that SNR (Signal to Noise ratio) over the part of the dynamic range that is used in the image is higher. For example, if you take a tone that is five stops below saturation on the XH-A1, the SNR is very poor. The low SNR negatively effects in the image in a variety of ways, including the reduction of the possible number of tonal levels (even in 8-bit recording). By comparison, the 5D2 color depth is much higher (at the same exposure, not the same DOF).

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I was referring to a constant aperture zoom for the Canon would be physically larger than the current 20x lens, which does have a pretty large aperture ramp. Not always an issue, but as it can cause an issue if this noticeablely kicks in earlier than say half way through the zoom range.
I see. Thanks for the clarification.
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Old January 29th, 2010, 04:14 PM   #205
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They already invented that -- just use the f-number. On FF35, you get the exact same effect by switching between f/2.8 and f/24. f/24 (and high ISO) gives you the same (poor) low light performance and deep DOF as 1/3", while f/2.8 (and low ISO) gives you the super thin DOF and amazingly good low light performance of super large sensors.
While that is true, one would have to add a fair amount of ISO (gain) to make f24 = f2.8 Which would lead to noisy and trending to flat images.

I just tested this on my 5DMkII and to get f4 @100 iso to equal f22 I had to go to iso 3200. Not exactly the cleanest setting.

Ideally one would want clean images for whatever they shot...
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Old January 29th, 2010, 04:21 PM   #206
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Daniel, one way of looking at what you're saying is that f28 on 35mm is the same as f4 on 1/3" so it's OK. The other way of looking at it is that f28 on 35mm is majorly diffraction affected and therefore so is f4 on the 1/3" chip - that's the way I see it. I thought that was one of the issues broadcasters had with 1/3" chips - the lenses were diffraction limited at every aperture!
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Old January 29th, 2010, 05:00 PM   #207
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While that is true, one would have to add a fair amount of ISO (gain) to make f24 = f2.8 Which would lead to noisy and trending to flat images.
Yes, it does lead to noisy images, but only in the exact same proportion as going to smaller sensors leads to noisy images.

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I just tested this on my 5DMkII and to get f4 @100 iso to equal f22 I had to go to iso 3200. Not exactly the cleanest setting.

Ideally one would want clean images for whatever they shot...
Yes, you're right. Compared to itself, the 5D2 at ISO 3200 is not that clean. But have you compared it to a 1/3" single-chip camcorder in the same low light and DOF?

In my experience, the 5D2 is noisier, but not as much as you might expect from a 5-stop difference in f-number. Ideally, the 5D2 at f/22 ISO 3200 would match even the 3-chip camcorders in the same low light situation (e.g. XH-A1 at f/3.1). The reason it doesn't right now is what I explained in the big post above, and it's the reason why 3-chip will always be around for low light work: they have three times the amount of light for any given DOF. If you compared the 5D2 with a single-chip camera, it comes out more favorable, because then they both get the same total amount of light.

Part of the reason why the current DSLRS can't match the low noise level of camcorders (at the same DOF) is because they have additional handicaps on top of only a single senor: row skipping, which reduces the total amount of light by 1+2/3 stops, and suboptimal resampling algorithms which alias the noise power from higher spatial frequencies into the 1080p Nyquist. But they also have advantages, such as better read noise performance per area. After the other problems are addressed in the future, this performance advantage may be enough to offet the fact that it only has one sensor instead of three.

In any case, even if we compare just the cameras that are on the market now (like the 5D2), there are some situations where the extremely deep DOF of the 1/3" camcorders isn't needed. So instead of stopping down all the way to f/22 ISO 3200 to get an exact match, it may be acceptable (sometimes) to use only f/11 ISO 800 (or whatever the exact setting is that matches the noise level). The DOF will be thinner, but still deep enough for some applications. And at f/11 ISO 800, the noise level will be a much closer match to f/3.1 on the XH-A1. (Of course, these DSLRs are unsuitable for most applications for other reasons -- I'm just addressing the DOF/noise issue.)

Quote:
Originally Posted by Steve Phillipps View Post
The other way of looking at it is that f28 on 35mm is majorly diffraction affected and therefore so is f4 on the 1/3" chip - that's the way I see it.
Yes, either way works for me.
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Old January 29th, 2010, 05:48 PM   #208
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Wait till you see what CANON will be offering. After NAB, they will introduce a solid state camera that is niether HDV or AVCHD. Later this year or early next year look for a camera that will give SONY a 'run for the money.'


Probably the Canon 5d mark 11 chips?

High ISO/gain with minimal grain......shoot in ambient light w/o a light

Only time will tell.

BTW: The JVC XH A1S will still be in the lineup due to good sales.
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Old January 29th, 2010, 06:08 PM   #209
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BTW: The JVC XH A1S will still be in the lineup due to good sales.
Do you mean Canon?

JVC already makes a solid state cam that is neither HDV or AVCHD (actually a couple).

JVC also doesn't make the XH-A1s, but it has occurred to me that JVC isn't all that shy about coloring outside the lines, and if any of the majors took the guts of a DSLR and made a video came with it, it wouldn't surprise me if JVC was the one to do it.
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Old January 29th, 2010, 06:14 PM   #210
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Daniel, one way of looking at what you're saying is that f28 on 35mm is the same as f4 on 1/3" so it's OK.
What is of significance regarding diffraction is the actual physical dimension of the aperture, not the f stop. That's because nothing can be done about the wavelength of light. ("Ye canna change the laws of physics!") What f no that corresponds to will depend on focal length.

Hence a given diameter of aperture may correspond to f4 for a short focal length lens, but f28 or whatever for a lens of longer focal length - which is Daniels fundamental point.
Quote:
I thought that was one of the issues broadcasters had with 1/3" chips - the lenses were diffraction limited at every aperture!
Steve
Not quite. Diffraction will limit the smallest acceptable aperture, and engineering considerations will limit the largest aperture. (Together with cost.) The problem with 1/3" chips is that the limits effectively close together to leave a usable adjustment window of only a stop or two - not much use if you're following a subject from a sunny area to a shaded one, for example.

That doesn't apply with bigger sensors as it's normally possible to make lenses with max apertures much greater than the diffraction limited minimum - provided the cost, size and weight issues are tolerable. Cost and weight aside, you SHOULD be able to get around f2 for any chip size, so the bigger the chip, the bigger the usable f stop range possible. It will just cost more - a lot more.

The other (separate but related) issue is depth of field. Even wide open, the lens on a 1/3" chipped camera normally gives too much depth of field for any real control.

Hence the desire to use 2/3" cameras as a sensible compromise, and if they are just too big, then 1/2" is far better than 1/3".

Broadly, I agree with Daniels reasoning, but the only factor that seems to be left out is the relative efficiencies of single chip v 3 chip. For the same resolution and overall imaging size, 3 chip must always be more efficient than single chip as no light gets lost in the filtration.
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