What the heck is an f-stop?

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Paul Anderegg
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What the heck is an f-stop?
5 months ago

I am may be in the market for a broadcast video camera soon, and am having some issues understanding the relationship between sensor size and f-stops.

For those not familiar with broadcast video cameras, the sensitivity is rated as f-stop at 2000 lux necessary to produce a certain video signal level (brightness).. The first generation of CCD video cameras, 1990, were rated at f5.6 @ 2000. The next generation, around 1993, was rated at f8, then f11 hit around 1996. The best ever standard definition cameras were the Panasonics, which reached f13 @ 2000 around 2004.  These ratings are for the 0db (no gain up) settings of a video camera.

So fast forward to today, and you've got mostly f10 @ 2000 HD gear, with a few more expensive f11 and maybe 2 or 3 at f12. Which brings me to my inquiry. I am trying to figure out which of the following two cameras would be best suited for night and low light use. A JVC GY-HM890 (f11@2000 1/3" chips) with a constant f1.4 lens, or a Panasonic HPX600 (f12@2000 2/3" chip) with an f1.8/wide-f2.3/tele lens.

With the same 18x series lens, the JVC would be f1.4 at full telephoto, where the Panasonic would be at f2.3. My confusion with this results from not understanding how f-stops relate to sensor size. Is an f11@2000 rating for a 1/3" the same as an f11@2000 rating for a 2/3", or is that aperture just some random number once you start playing around with sensor size? Short of putting two cameras side by side in the same light, there seems to be no technical info about this on the internet that I can locate with google.

Although this is a video inquiry, it would seem that the PHOTOGRAPHY world would be better equipped to technically answer this question. Also, in the video world, Canon and Fujinon sell the same series lenses in 2/3", 1/2", and 1/3" versions, so I am assuming they are the same glass. Not sure why the 1/3" versions all have constant apertures, perhaps the small sensor just takes advantage of the larger glass elements designed for the larger sensors? Thanks in advance.

Paul Anderegg

bobn2
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Re: What the heck is an f-stop?
In reply to Paul Anderegg, 5 months ago

Paul Anderegg wrote:

I am may be in the market for a broadcast video camera soon, and am having some issues understanding the relationship between sensor size and f-stops.

For those not familiar with broadcast video cameras, the sensitivity is rated as f-stop at 2000 lux necessary to produce a certain video signal level (brightness).. The first generation of CCD video cameras, 1990, were rated at f5.6 @ 2000. The next generation, around 1993, was rated at f8, then f11 hit around 1996. The best ever standard definition cameras were the Panasonics, which reached f13 @ 2000 around 2004. These ratings are for the 0db (no gain up) settings of a video camera.

So fast forward to today, and you've got mostly f10 @ 2000 HD gear, with a few more expensive f11 and maybe 2 or 3 at f12. Which brings me to my inquiry. I am trying to figure out which of the following two cameras would be best suited for night and low light use. A JVC GY-HM890 (f11@2000 1/3" chips) with a constant f1.4 lens, or a Panasonic HPX600 (f12@2000 2/3" chip) with an f1.8/wide-f2.3/tele lens.

With the same 18x series lens, the JVC would be f1.4 at full telephoto, where the Panasonic would be at f2.3. My confusion with this results from not understanding how f-stops relate to sensor size. Is an f11@2000 rating for a 1/3" the same as an f11@2000 rating for a 2/3", or is that aperture just some random number once you start playing around with sensor size? Short of putting two cameras side by side in the same light, there seems to be no technical info about this on the internet that I can locate with google.

Although this is a video inquiry, it would seem that the PHOTOGRAPHY world would be better equipped to technically answer this question. Also, in the video world, Canon and Fujinon sell the same series lenses in 2/3", 1/2", and 1/3" versions, so I am assuming they are the same glass. Not sure why the 1/3" versions all have constant apertures, perhaps the small sensor just takes advantage of the larger glass elements designed for the larger sensors? Thanks in advance.

Paul Anderegg

OK, let's go through this a bit at a time.

'f-stop' in its absolute sense means the ratio of the focal length to the aperture. So, if the focal length of the lens if 16 times the aperture, then the f-stop is 16. The f-stop, along withe the amount of light coming from the subject, controls the density (amount of light per unit area) at the focal plane. Conventionally aperture controls are marked in f-stops, rather than absolute aperture sizes (although in film and video often 'T-stop' is preferred, which is f-stop adjusted for the light loss within the lens). Thereon, thing get a bit more complex.

By and large, equipment users like to work with quite simple rules, rather than going back to the basics of how things work. The simple rules evolve quite differently according to the use case, so they are different in stills, to video, to cinema camera to broadcast camera.

Looking at the broadcast camera rule what you have is a simple rule defining 'sensitivity' 'brightness' and 'f-stop', but what's behind the rule is not so simple. Canon has a nice paper on their C300 camera here:

http://cpn.canon-europe.com/files/product/cinema_eos/menu/EOS-C300-Sensitometric-Characteristics-White-paper.pdf

That defines the f-stop rating as follows:

The traditional broadcast video specification for lens-camera sensitivity is measured by the lens aperture setting in F-stop required to achieve 100 IRE units of Luma when the system is imaging a reference white chart having 89.9% reflectance under 2000 Lux of 3200 degree Kelvin illumination (with Camera Master Gain set to 0 dB, Gamma switched off, and all image enhancement switch off). The amount of electronic noise in the image is another important issue closely allied with this sensitivity specification because of its bearing on dynamic range. Under these conditions, the EOS C300 camera has a reference sensitivity rating of F-10 and a Luma signal to noise ratio of 54 dB.

As Canon points out, it's important to specify the SNR, because in principle any sensor illumination can produce any output luma signal you like, so long as you'll tolerate the noise.

So, to bring that back to your question. The problem with a smaller sensor is that it has less area to intercept the light, so at the same f-stop, the image will be more noisy. Or to put it another way, for equal efficiency sensors, a smaller sensor will require a smaller f-stop (bigger aperture) to achieve the same SNR. So, all else being equal, reducing the sensor size will increase the noise. You don't know whether different manufacturers F stop ratings take this into account without looking at the small print and seeing if they specify the SNR which the F stop rating applies to - quite likely they haven't, often the consumer is expected to know that a smaller sensor will give more noise at the same F stop.

If they are not, then a fair assumption is that the F stop rating (to output the same noise) is in proportion to the linear ratio between the two sensors. So, taking your example of F-10 rated cameras with 1/3 and 2/3 inch chips. In this case, they'll both produce the same brightness, but the noise won't be the same. The linear ratio between 1/3 and 2/3 is 11:6 or 1.8, so to find the F stop on the 1/3 sensor that will produce the same noise as f/10 on the 2/3 sensor, we multiply by 1.8, or f/18.

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Paul Anderegg
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Re: What the heck is an f-stop?
In reply to bobn2, 5 months ago

Thanks for the reply Bob, the math formulas were informative.  All broadcast video cameras rate their s/n ratio at 0db.  My f13@2000 2/3" standard definition Panasonic is rated at 65db, and my f10@2000 2/3" high definition Panasonic is rated at 54db.  Obviously those big SD pixels play a role in that!

My problem with the current selection of new and used 1/3", 1/2", and 2/3" cameras, is there ability to obtain luminance in very low light.  I am a news shooter, so I rely on each 6db (1 stop) I can get my hands on to boost the picture.  The Panasonic HPX600 referenced above, will only gain up to 18db, or roughly 3 stops above 0db gain.  The JVC will gain up to 24db, which would be roughly 4 stops above absolute 0.  Obviously, in a news environment, being able to click that one extra 6bd doubles your picture brightness, an can mean the difference between seeing the SWAT officer hiding behind a bush, and not.  The JVC can go down to 1/4th sec shutter, the Panasonic only down to 1/15th.

I guess my main question would be the following.  At 0db, with identical shutter speed, which camera would provide the most luminance at wide open (f1.4/f1.8) aperture?  Second question, at full telephoto, with the 1/3" at f1.4 and the 2/3" at f2.3, what would be the luminance difference between the two cameras?  90% of what I shoot at night is shot wide open, and exposure is adjusted by gaining up.  Night is night, you work with what you have in news.  Thanks!

Paul

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Martin.au
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Re: What the heck is an f-stop?
In reply to Paul Anderegg, 5 months ago

It goes at the end of sentences. Sometimes you may use other punctuation marks.

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bobn2
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Re: What the heck is an f-stop?
In reply to Paul Anderegg, 5 months ago

Paul Anderegg wrote:

Thanks for the reply Bob, the math formulas were informative. All broadcast video cameras rate their s/n ratio at 0db.

Where 0dB means not 'gained up'. The problem is that these terms are really based on old analog tech where the output from the vidicon was suitably amplified and formed the signal. It doesn't really describe what's happening nowadays. '0dB' is purely arbitrary, so far as the sensor is concerned - much the same as 'base ISO' in still terms.

My f13@2000 2/3" standard definition Panasonic is rated at 65db, and my f10@2000 2/3" high definition Panasonic is rated at 54db. Obviously those big SD pixels play a role in that!

Indeed, strictly speaking, SNR is bandwidth related, as sound engineers know. SD is about 1/4 MP per frame, while HD is about 2MP, that's 8 times the bandwidth at the same frame rate. 8 times the bandwidth, which just about gives the spec difference.

My problem with the current selection of new and used 1/3", 1/2", and 2/3" cameras, is there ability to obtain luminance in very low light.

In the end, this ability is down to (assuming exposure time limited by frame rate):

The SNR you can tolerate,

The f-number of the lens,

The scene luminance,

The efficiency of the sensor,

The size of the sensor.

Generally sensors of a generation have similar efficiency - so that can often be discounted.

I am a news shooter, so I rely on each 6db (1 stop) I can get my hands on to boost the picture. The Panasonic HPX600 referenced above, will only gain up to 18db, or roughly 3 stops above 0db gain. The JVC will gain up to 24db, which would be roughly 4 stops above absolute 0.

And of course, there is what the control that the manufacturer gives you.

Obviously, in a news environment, being able to click that one extra 6bd doubles your picture brightness, an can mean the difference between seeing the SWAT officer hiding behind a bush, and not. The JVC can go down to 1/4th sec shutter, the Panasonic only down to 1/15th.

I guess my main question would be the following. At 0db, with identical shutter speed, which camera would provide the most luminance at wide open (f1.4/f1.8) aperture?

If luminance is your only concern, then assuming that you have the same max aperture available, you will full luminance available is proportional to 12*(log2 F-stop) + gain-up above 0dB, and the sensor size doesn't come into it. The first term gives you luminance available above a reference of f/1 (arbitrary but easy to calculate). So the Panasonic gives you 12*(log2 10) + 18 = 40 + 18 = 58. I don't know the f-stop rating of the JVC. But if you're willing to blur it with the slow shutter the JVC is obviously giving you 2 extra stops on top.

Second question, at full telephoto, with the 1/3" at f1.4 and the 2/3" at f2.3, what would be the luminance difference between the two cameras?

Again, for luminance, regardless of noise, the sensor size is irrelevant, so your luminance difference will be down to the F-stop rating of the cameras and available gain as above and then the difference in f-stop of the lens, which is 1.3 stops (7.8 dB) between f/1.4 and f/2.3.

90% of what I shoot at night is shot wide open, and exposure is adjusted by gaining up.

Strictly, you can't adjust exposure by 'gaining up', gain isn't a part of the exposure, what you're changing is the luminance for the exposure you're using.

Night is night, you work with what you have in news. Thanks!

Paul

If it's quality as well as luminance, then you need to take the total light captured into account, which is the combination of sensor size and minimum f-stop lens available.

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GeraldW
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Re: What the heck is an f-stop?
In reply to Paul Anderegg, 5 months ago

Paul,

Bob has done a great job explaining things.  The one item left hanging is the relationship of lens speeds.  Since the f number is a linear ratio of aperture to focal length, and the light transmitted by the lens is proportional to the area of the aperture; you need to square the f/# to aseess relative light gathering.  So, 1.8^2 = 3.24, and 1.4^2 = 1.96; then the relative light gathering is 3.24/1.96 = 1.65.  The significance of 1.65 is that it is the ratio of shutter speeds needed to gather the same amount of light a those apertures.  So, if the f/1.8 lens is shooting at 1/100, then the f/1.4 lens can use 1/165.  In digital, it might also be the ratio of ISO settings needed to maintain the same shutter speed.

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bobn2
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Re: What the heck is an f-stop?
In reply to GeraldW, 5 months ago

GeraldW wrote:

Paul,

Bob has done a great job explaining things. The one item left hanging is the relationship of lens speeds. Since the f number is a linear ratio of aperture to focal length, and the light transmitted by the lens is proportional to the area of the aperture; you need to square the f/# to aseess relative light gathering. So, 1.8^2 = 3.24, and 1.4^2 = 1.96; then the relative light gathering is 3.24/1.96 = 1.65. The significance of 1.65 is that it is the ratio of shutter speeds needed to gather the same amount of light a those apertures. So, if the f/1.8 lens is shooting at 1/100, then the f/1.4 lens can use 1/165. In digital, it might also be the ratio of ISO settings needed to maintain the same shutter speed.

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Jerry

Thanks for that, yes I had left that hanging, and just to add, the 'stops' value is the log2 of that ratio, in the case of  this example, log2 1.65 = 0.7 stops (usually thought of a 'two thirds of a stop' or sometimes 'three quarters of a stop' depending on the f-number sequence being used).

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D Cox
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Re: What the heck is an f-stop?
In reply to GeraldW, 5 months ago

GeraldW wrote:

Paul,

Bob has done a great job explaining things. The one item left hanging is the relationship of lens speeds. Since the f number is a linear ratio of aperture to focal length, and the light transmitted by the lens is proportional to the area of the aperture; you need to square the f/# to aseess relative light gathering.

The light transmitted by the lens is proportional to the area of the aperture, but it is then spread over an area of image that is proportional to the square of the focal length (because a longer length lens is further from the image plane).

So the illuminance is directly proportional to the f number. That is the reason f numbers were introduced -- so that you can match up exposures with different focal lengths.

So, 1.8^2 = 3.24, and 1.4^2 = 1.96; then the relative light gathering is 3.24/1.96 = 1.65. The significance of 1.65 is that it is the ratio of shutter speeds needed to gather the same amount of light a those apertures. So, if the f/1.8 lens is shooting at 1/100, then the f/1.4 lens can use 1/165. In digital, it might also be the ratio of ISO settings needed to maintain the same shutter speed.

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Paul Anderegg
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Re: What the heck is an f-stop?
In reply to D Cox, 5 months ago

It would be important to point out at this point that for shooting in low light, practically ANY broadcast video camera will be set to 1/30 second shutter speed.  Broadcast cameras also only have THREE gain switch settings, normally 0db, 9db, and 18db, although these can be adjusted for shoot conditions.  Typically you want your 0db, then your aggressive darkness high gain, and a medium to split the difference.

My main confusion here is with similar f10@2000sensitivity ratings, but with the dissimilar maximum f-stop ratings.  Is it as simple as if both the 1/3" and 2/3" are 100IRE at 2000 lux at f11, then the 1/3" sensor will produce a brighter picture at f1.4 than the 2/3" at f1.8 if both are set to their lowest and default 0db gain setting, because it can "open wider"?  My limited understanding of the math involved would seem to indicate that I am confused here.

Noise in the video world is simply accepted at the price level you are able to compete in.   For cameras with a fixed 0-18db gain/ISO range, you've got the lowest setting, the highest value, and a choice in between available in a three position flip switch.  When everyone is shooting a scene at 18db, noise becomes irrelevant, and the main priority is to actually be able to discern detail in the darker areas, with the limited amount of on camera lighting you have available.

Paul

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bobn2
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Re: What the heck is an f-stop?
In reply to Paul Anderegg, 5 months ago

Paul Anderegg wrote:

My main confusion here is with similar f10@2000 sensitivity ratings, but with the dissimilar maximum f-stop ratings.

I'm presuming that you mean minimum f-stop rating of the lens, that is the maximum aperture available from the lens. Remember f-stop goes down as aperture goes up.

Is it as simple as if both the 1/3" and 2/3" are 100IRE at 2000 lux at f11, then the 1/3" sensor will produce a brighter picture at f1.4 than the 2/3" at f1.8 if both are set to their lowest and default 0db gain setting, because it can "open wider"? My limited understanding of the math involved would seem to indicate that I am confused here.

If they both have the same brightness at f/11, then they will have the same brightness at any f-stop, and if one has a smaller f-stop it will be brighter (or, the other way, give the same brightness in lower light). So if they are both 100IRE @ 2000, f/11and one has an f/1.4 lens while the other has an f/1.8 lens, then the f/1.4 lens will give more brightness in the same light, or will give 100 IRE in lower light. That might be the way to think of it. If 2000 lux gives 100 IRE at f/11, and f/1.8 gives 5.25 stops (37.5 times) more light than f/11, then f/1.8 will give 100 IRE at 2000/37.5 = 53.3 lux. By the same token f/1.4 gives 6 stops (64 x) more light than f/11, so f/1.4 will give 100 IRE at 2000/64 = 31.3 lux. So the smaller sensor with lower f-stop lens will give you 100 IRE in lower light, but the quality will be lower, since the sensor isn't receiving as much light.

Noise in the video world is simply accepted at the price level you are able to compete in. For cameras with a fixed 0-18db gain/ISO range, you've got the lowest setting, the highest value, and a choice in between available in a three position flip switch. When everyone is shooting a scene at 18db, noise becomes irrelevant, and the main priority is to actually be able to discern detail in the darker areas, with the limited amount of on camera lighting you have available.

Remember that the SNR is ultimately determined by the amount of light that the sensor collects. Remebering that the linear ration between 1/3" and 2/3" is 1.8, which gives an area ratio of 3.24 or 1.7 stops. So in the example above, you gain 0.7 stop going from f/1.4 to f/1.8 and lose 1.7 stops due to the smaller sensor. So in the end the smaller sensor is losing you a stop in terms of total light. If the question is, what is the lowest light for a given quality (discerning detail in the darker areas) the you are better off with the 2/3" f/1.8 combination gained up 0.7 stop above the 1/3" f/1.4 combination.

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Paul Anderegg
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Re: What the heck is an f-stop?
In reply to bobn2, 5 months ago

Remember that the SNR is ultimately determined by the amount of light that the sensor collects. Remebering that the linear ration between 1/3" and 2/3" is 1.8, which gives an area ratio of 3.24 or 1.7 stops. So in the example above, you gain 0.7 stop going from f/1.4 to f/1.8 and lose 1.7 stops due to the smaller sensor. So in the end the smaller sensor is losing you a stop in terms of total light. If the question is, what is the lowest light for a given quality (discerning detail in the darker areas) the you are better off with the 2/3" f/1.8 combination gained up 0.7 stop above the 1/3" f/1.4 combination.

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Bob

Just to make sure there is no misunderstanding here.........the lenses in question, be they the f1.4, or f1.8, are specific to the sensor size mount, and not interchangeable.  I will give you three links of the "same" lens (would appear) in different mounts, so you can give your take on if they are the same "glass".  This identical lens series thing has been around as long as CCD video cameras have been.

Fujinon 18x7.6BERM 2/3"

Fujinon 18x5.5BERM 1/2"

Fujinon 18x4.2BERM 1/3"

The constant aperture of the 1/3" model still baffles me.

Paul

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Great Bustard
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Re: What the heck is an f-stop?
In reply to Martin.au, 5 months ago

Martin.au wrote:

It goes at the end of sentences. Sometimes you may use other punctuation marks.

What other kinds of punctuation marks? 

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bobn2
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Re: What the heck is an f-stop?
In reply to Paul Anderegg, 5 months ago

Paul Anderegg wrote:

Remember that the SNR is ultimately determined by the amount of light that the sensor collects. Remebering that the linear ration between 1/3" and 2/3" is 1.8, which gives an area ratio of 3.24 or 1.7 stops. So in the example above, you gain 0.7 stop going from f/1.4 to f/1.8 and lose 1.7 stops due to the smaller sensor. So in the end the smaller sensor is losing you a stop in terms of total light. If the question is, what is the lowest light for a given quality (discerning detail in the darker areas) the you are better off with the 2/3" f/1.8 combination gained up 0.7 stop above the 1/3" f/1.4 combination.

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Bob

Just to make sure there is no misunderstanding here.........the lenses in question, be they the f1.4, or f1.8, are specific to the sensor size mount, and not interchangeable. I will give you three links of the "same" lens (would appear) in different mounts, so you can give your take on if they are the same "glass". This identical lens series thing has been around as long as CCD video cameras have been.

Fujinon 18x7.6BERM 2/3"

Fujinon 18x5.5BERM 1/2"

Fujinon 18x4.2BERM 1/3"

The constant aperture of the 1/3" model still baffles me.

Paul

That's some serious outlay on lenses. The 1/3" one isn't constant aperture, it's constant f-number, the aperture will change as it zooms to keep the f-number constant. This occurs because the zoom lens is a prime lens with an 'afocal converter' on the front, and the 'aperture' is the size of the aperture stop viewed through the front, so the zoom converter changes the apparent size as it zooms. In the larger format lenses they didn't make it quite big enough, so it forms the restriction on aperture size at lower f-numbers and longer focal lengths.

I would hazard a guess that front of the lens (afocal converter) is the same, linked to a different back half to give the appropriate FL range for the format.

However, given the cost of the lenses, I'd be going with the 2/3" and the extra 1 stop of light on the sensor when the difference in the f-number has worked itself out.

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bobn2
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Re: What the heck is an f-stop?
In reply to Great Bustard, 5 months ago

Great Bustard wrote:

Martin.au wrote:

It goes at the end of sentences. Sometimes you may use other punctuation marks.

What other kinds of punctuation marks?

Most of the other f's are expletives rather than punctuation marks, though for some they are interchangeable.

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Great Bustard
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Sensor size, f-stop, exposure, total light, and noise.
In reply to Paul Anderegg, 5 months ago

Paul Anderegg wrote:

So fast forward to today, and you've got mostly f10 @ 2000 HD gear, with a few more expensive f11 and maybe 2 or 3 at f12. Which brings me to my inquiry. I am trying to figure out which of the following two cameras would be best suited for night and low light use. A JVC GY-HM890 (f11@2000 1/3" chips) with a constant f1.4 lens, or a Panasonic HPX600 (f12@2000 2/3" chip) with an f1.8/wide-f2.3/tele lens.

First, some important background to answering your question.

There are two primary forms of noise in a photo: luminance noise, which is a function of the total amount of light falling on the sensor (photon noise) and the sensor efficiency, and the chroma noise, which is a function of the CFA (Color Filter Array).

The total amount of light falling on the sensor is the product of the exposure and area of the sensor. For example, if you quadruple the sensor area then, for a given exposure, 4x as much light will fall on the sensor, and the photon noise will be half as much.

The sensor efficiency is a function of the QE and the read noise. The QE is the Quantum Efficiency, which is the proportion of light falling on the sensor that gets recorded. For example, if a sensor has a QE of 0.5, then half of the light falling on it gets recorded. The read noise is the additional noise added by the sensor and supporting hardware, and is usually small compared to the photon noise except for shadows at low ISO and progressively more and more of the photo as the light lessens and we raise the ISO to compensate for the lower brightness.

OK, let's say we have two sensors, one 1/3" and the other 2/3".  Let's also assume the 2/3" sensor is twice the size (4x the area).

For a given lens and exposure (say, f/1.4 1/30), 4x as much light will fall on the 2/3" sensor as the 1/3" sensor, which will result in half the noise if the sensors were equally efficient.  If we instead used f/2 (half the aperture diameter and thus 1/4 the aperture area) 1/30 for the 2/3" sensor (doubling the ISO to compensate for the lower brightness), then the same total amount of light would fall on each sensor, resulting in the same noise if both sensors were equally efficient.

So, an f/1.4 lens on a 1/3 sensor is equivalent to an f/2 lens on a 2/3" sensor, as it will project the same total amount of light on the sensor for a given shutter speed (given equal transmission), thus resulting in the same noise for equally efficiency sensors.

However, the transmission is not necessarily the same for both lenses wide open.  The f/1.4 lens might have a transmission of 70% (1/2 of a stop light lost) and the f/2 lens might have a transmission of 90% (1/6 of a stop light lost).  Thus, 1/3 of a stop more light would fall on the 2/3" sensor than the 1/3" sensor.

In addition, the efficiency of the microlens covering of the sensor might result in additional light losses reaching the photosensitive portion of the sensor, which will be more pronounced at f/1.4 than it will at f/2 (despite the sensors being otherwise equally efficient), so there could be, say, an additional 1/3 stop more light falling on the 2/3" sensor, resulting in a total gain of 2/3 of a stop more light being recorded on the 2/3 sensor.

So, as we can see, the specifics of the transmissivity of the lens, the efficiency of the microlens covering also play important roles at low f-ratios (the microlens issue quickly dissipates after f/2, however).

Hope this helps!

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gianstam
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It was the usual way...
In reply to Paul Anderegg, 5 months ago

... for a thread to be filled (150 posts) during one day. But something wrong happened. 12 hours after the OP and just 14 posts. Amazing!

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bobn2
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In reply to gianstam, 5 months ago

gianstam wrote:

... for a thread to be filled (150 posts) during one day. But something wrong happened. 12 hours after the OP and just 14 posts. Amazing!

But he's asking a different question. The 'f-stop' he's asking about is the broadcast camera equivalent of ISO

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Martin.au
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Re: What the heck is an f-stop?
In reply to Great Bustard, 5 months ago

Great Bustard wrote:

Martin.au wrote:

It goes at the end of sentences. Sometimes you may use other punctuation marks.

What other kinds of punctuation marks?

Don't start!

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Paul Anderegg
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Re: Sensor size, f-stop, exposure, total light, and noise.
In reply to Great Bustard, 5 months ago

That does help, which brings me to another question.  Assuming the two f10@2000 1/3" and 2/3" models considered above..........that f10 isn't really the same is it?  I will give a hypothetical example based on two small camcorders I own.  Sony CX900 and Panasonic x920.  Both provide the same picture brightness (luminance, zebras set to 80IRE would zig and zag in the same spots) at wide open aperture and no gain (0db).  Both also provide the same amount of sensitivity boost, and provide comparable ability to discern (brightness-wise) a line of trees at night against a lit skyline.

The Sony has a 1" sensor, the Panasonic a 1/2.3".....it's actually probably 1/4", but that isn't completely relevant.  The Panasonic has a maximum aperture of f1.5, the Sony an f2.8.  Due to the larger chip in the Sony, that f2.8 "rating" is enough to provide enough light on the sensor to provide a brighter picture than the f1.5 lightfall on the tinier Panasonic sensor.  At all gain settings, the Sony is also MUCH cleaner.

Noise aside, please take the following hypothetical into consideration when answering the follow-up question.  Given as I said they produce the same luminance wide open at no gain/ISO boost, if the Sony was rated at f2.8@2000, and the Panasonic was rated at f1.5@2000, then those f10@2000 ratings for the professional camcorders would be similarly skewed?  If both cameras, 1/3" and 2/3" provide that critical measured 100IRE at f10@2000, then would not the 1/3" camera be able to provide a brighter image at wide open iris, because it could open past f1.8?

I just need to know if the 1/3" camera/lens combo first proposed would have a brighter image (more IRE's!) at 0db, no gain, lowest settings, boost set to off etc, at full wide, and then again at full telephoto, given the lenses listed in the B&H links.  I actually use the 18x4.2BERm lens every night for my job, and it doesn't get darker when you zoom in through to full telephoto.  All cheap 1/3" mount "pro" lenses do ramp the aperture down, as do all 2/3" mount lenses.  this little secret nugget of high end 1/3" lenses got me thinking they could actually beat out the larger sensor better low light sensitive 2/3" models simply do to the wins they see in the math game.

Paul

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Martin.au
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Re: What the heck is an f-stop?
In reply to bobn2, 5 months ago

bobn2 wrote:

Great Bustard wrote:

Martin.au wrote:

It goes at the end of sentences. Sometimes you may use other punctuation marks.

What other kinds of punctuation marks?

Most of the other f's are expletives rather than punctuation marks, though for some they are interchangeable.

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Bob

If it's an expletive, then that would refer to the f-stop that occurs when the car in front of you stops suddenly, not punctuation marks.

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