Myth busted: larger sensors have thinner DOF.

[Daniel Browning]

Larger sensors are capable of the same DOF and noise as smaller sensors, so they are only worth the extra money if you are going to have more light or thinner DOF.

To make the point easier to illustrate, I've simplified the conditions. Below there is a discussion of the effect of the simplifications, but generally they match reality to within 1/3 to 2/3 stop.

Given any number of cameras all matching the following conditions:

• The same scene and perspective.
• Lenses with the same field of view and maximum f/stop.
• Lenses with the same DOF at narrowest f/stop.
• Sensors with the same sensitivity per area.
• Sensors with the same read noise per area.
• Sensors with the same full well capacity per area.
• Sensors with the same total resolution and relative OLPF.
• The same raw recording and processing.
• Displayed at the same size and resolution.
• Distance is large enough to avoid bellows factor.

In ample light, the large sensor is capable of:

• Less noise for any given DOF.
• The same amount of diffraction for any given DOF.
• Even the very deepest DOF are the same with less noise.

In low light, the large sensor is capable of:

• The same DOF and same noise.
• Thinner DOF and less noise.

General conclusions:

• The large sensor is capable of everything the small sensor is.
• The small sensor is not capable of deeper DOF.
• The large sensor will not be better unless you have more light or thinner DOF.

So it all comes down to money. If you shoot in low light and can not handle thinner DOF, then the large sensor will be more expensive with no benefit. But at least it will be able to do everything the small one did, including the same DOF. On the other hand, if you shoot in ample light or you can handle thinner DOF, then the large sensor will provide a benefit.

The reason why this is true essentially comes down to aperture. Not the f/number (which is "relative" aperture), but the the physical aperture, absolute opening, or "hole in space". When the per-area performance of the sensor is the same (as in assumptions above and most real life situations), then the DOF, light gathering ability, and noise all depends on only one thing: the aperture of the lens.

The physical aperture of 32mm f/1.2 is 26.6mm. The physical aperture of 50mm f/2.0 is 25mm. They both provide the same FOV on S35 and FF35, respectively, and the DOF is the same because the physical aperture is also the same (~25mm). Light gathering ability and noise, too, are the same: one focuses the light in a smaller space with more intensity, the other spreads it out over a larger space with less intensity. In either case, the total amount of light is the same.

This is true of all formats when given the above assumptions. From 1/3", 2/3", S35, FF35, 645, all the way up to 617. Larger sensors get the same DOF/light/noise by through longer focal lengths, narrower f/numbers, and smaller reproduction ratios. Smaller formats have the same DOF/light/noise through shorter focal lengths, wider f/numbers, and larger reproduction ratios. For example, with a 16.4-foot subject distance, all of the following camera/lens combinations will have the same 40 degree horizontal AOV and 6.7 feet DOF (using h/CoC=1200):

2/3":             14mm f/0.9
4/3":             24mm f/1.6
Super35:          34mm f/2.2
Still FF35:       49mm f/3.2
645:              76mm f/5.0
617:              220mm f/14

They all have approximately 15mm physical aperture despite the 7-stop difference in f/numbers.

Another way to see it is like this:

2/3":             15mm aperture, 14mm focal length
4/3":             15mm aperture, 24mm focal length
Super35:          15mm aperture, 34mm focal length
Still FF35:       15mm aperture, 49mm focal length
645:              15mm aperture, 76mm focal length
617:              15mm aperture, 220mm focal length

For a given capture and display resolution, they all have the same level of diffraction as well, since that, too, depends on physical aperture. Smaller sensors are magnified very much for display, so diffraction is visible at wider f/stops. Larger sensors are not magnified as much, so it takes a much narrower f/stop to get the same effect of diffraction. When the focal length is equalized for field of view, the amount of diffraction is perfectly described by the physical aperture.

The f/number is inversely proportional to the reproduction ratio for any amount of DOF or diffraction for any sensor size.

So as you can see, the physical aperture is a big factor in a lot of things. Many photographers tend to focus on f/number ("relative" aperture), whereas other fields (e.g. astronomy) use the word "aperture" in the correct sense, which is physical aperture.

How what happens when the conditions/assumptions vary?

• The same scene and perspective.

The same scene should always be given. There are many times when perspective cannot be changed, such as when a cliff prevents forward movement or a wall prevents backward movement. Other times, it is possible to change the perspective, but it is undesirable for artistic reasons (e.g. distortion/compression). In any case, changing perspective is like changing angle of view, scene, or lighting: it's a fundamental element of composition that must be kept constant for any comparison to make sense.

• Lenses with the same field of view and maximum f/stop.

The field of view is just as important in composition as perspective, and can't be compensated other ways for the same reasons. The same maximum f/stop condition is only necessary for larger formats to be capable of thinner DOF. If instead the condition was "same maximum physical aperture (not f/number)", then all formats would be capable of the same DOF. In some comparisons, the smaller format is capable of much thinner DOF (e.g. FF35 vs. MFDB) due to wider physical apertures.

• Lenses with the same DOF at narrowest f/stop.

This condition basically states that lenses for larger formats can stop down smaller than lenses of smaller formats, but that's not necessarily the case. For example, if a FF35 lens can activate f/32, and a S35 lens can activate f/20, then they are both capable of the same DOF at their narrowest f/stop. But if the S35 can also activate f/32, then the FF35 will never be able to achieve that very deep DOF. In practice, this is usually not an issue because few people shoot at the very narrowest stop.

• Sensors with the same sensitivity per area.
• Sensors with the same read noise per area.
• Sensors with the same full well capacity per area.

Modern sensors have been within 1/3 stop of the same sensitivity for the last few years. Read noise, on the other hand, has more variety among manufacturers and models. Generally, the smaller the sensor, the less read noise per area. The same is true for FWC. So the amount that a given sensor is better in this area will change the results, even as much as 1/3 stop just for a lower read noise.

• Sensors with the same total resolution and relative OLPF.

The resolution requirement is just to simplify DOF calculations. A higher resolution sensor is capable of thinner DOF if the lens is. You can compensate for that in post processing by softening the image or displaying it at a size that has low enough resolution that the capture resolution is the same as the compared camera. For the purpose of discussion, it's easier to assume they're both the same.

• The same raw recording and processing.

Raw recording is important, because underexposure only works if response is linear (or curve is well tuned). A nonlinear response (like film) will lose more than 4 stops of information if it is 4 stops underexposed, because it is nonlinear.

The same processing is pretty obvious, as sharpening, demosiac, etc. can have a big effect on DOF.

• Displayed at the same size and resolution.

If a sensor has larger capture resolution, and displayed at a larger size and resolution, then it will be capable of thinner DOF. For that reason, a smaller sensor with the same aperture and higher resolution actually has thinner DOF than a larger sensor.

So it basically comes down to money. Larger sensors are capable of the same DOF and noise as smaller sensors, so they are only worth the extra money if you are going to have more light or thinner DOF.

 

[David Mullen ASC]

Daniel, I can't really agree with your conclusion unless you change the title of your post because it's not a myth.

You can certainly compensate by manipulating the f-stop of a lens within the limits of the range of the lens... but to say that larger sensors don't really give you less depth of field once you match distance and field of view by comparing a 14mm on a 2/3" camera at f/0.9 to a 49mm on a FF35 camera at f/3.2 -- well, it just proves the opposite, that you can't maintain the same depth of field without compensating with the f-stop.

So given that, how can you say that it's a myth that larger sensors have lower depth of field characteristics when what you are actually saying is that larger sensors DO have lower depth of field characteristics... but that higher sensitivity and less noise give you greater freedom to compensate by stopping down?

People are going to read your post and assume that they can move up to giant sensor formats and just keep on shooting the way they always been on smaller-sensor camera and focusing won't be an issue because this depth of field difference is a "myth".

Personally, I'd be inclined to say the opposite, that they are going to have to factor in the lower depth of field when planning their photography, either by stopping down or hiring a really, really good focus puller.

Look at what's been happening in the jump from 2/3" sensor cameras to S35 cameras -- focus-pullers are finding things a lot harder because often a cinematographer will light an interior to near the maximum aperture of the lens. If you can put a f/1.4 lens on a FF35 camera, you can bet some DP is going to what to shoot a scene at f/1.4 and telling him he should now be trying to always work near a f/4 at the widest is going to fall on deaf ears.

I can predict this: most DP's work around an f/2.8 when lighting a typical night interior scene and when the FF35 EPIC's come out, they will continue lighting to an f/2.8 -- they will use the greater sensitivity to cut their light levels, not to stop down the lens. And thus focus-pullers will be struggling with a lower depth of field compared to what they had on a S35 camera. Same thing happens in 35mm anamorphic photography -- most ignore the advice to stick to an f/4 and instead just go for the lower depth of field of an f/2.8.

I mean, isn't one of the big selling points of the RED ONE is that you can get 35mm depth of field characteristics compared to a smaller sensor HD camera? By your own logic, that's a "myth".

 

[J. Eric Camp]

100% behind everything David said.

Daniel's point seems to be based on physical Aperture size, versus the relative aperture or f-stop we all use.

Daniel's point has mathematical relevance. However I am of the belief that the relative aperture is the working tool and if compensation is required then all things are not equal.

However Daniel's points on sensor size for the sake of it versus actual gains are interesting.

However I feel that this is a debate of semantics. The relative aperture is the tool used. That is how we know to work. The different formats have different characteristics. A Small format lens will achieve a small final physical aperture than a large format. In kind the large format will achieve a larger open physical aperture. Those f-stop will have characteristics that are incapable of being achieved (mostly) from the other sized formats.

The reality for me is, the formats work the way they work and I will continue to use them as such. This seems a debate for the sake of it's self.

 

[Joe Walker]

Amen!

 

[Julio Quintana]

Although David is 100% right (of course), I do think it is a valid point that as people clamor to get bigger sensors, they should keep in mind that it can potentially make their jobs harder in terms of lighting and focus pulling...Or maybe that's David's point. Either way the thread title is a little misleading/inaccurate.

 

[Joel Kaye]

I can predict this: most DP's work around an f/2.8 when lighting a typical night interior scene and when the FF35 EPIC's come out, they will continue lighting to an f/2.8 -- they will use the greater sensitivity to cut their light levels, not to stop down the lens.

Yep.

Really, if you're shooting tungsten it probably looks better at F2 on RED (ie ISO is more like 200). It costs a lot of light (for us low budget guys) to get up to F4 at ISO 200 and it alters the way the practicals in the scene expose their surroundings.

Then there's the additional data of FF to handle in post. FF might be nice for outdoor day where you really want some super wide angles.

I think I'm sticking with S35. It's tough enough to handle. I can admit at this point I don't need more resolution or a more difficult shoot. I could use another stop of ISO and more dynamic range though so long as I get it at S35.

 

[Daniel Browning]

Thank you very much for your reply, David.

You can certainly compensate by manipulating the f-stop of a lens within the limits of the range of the lens... but to say that larger sensors don't really give you less depth of field once you match distance and field of view by comparing a 14mm on a 2/3" camera at f/0.9 to a 49mm on a FF35 camera at f/3.2 -- well, it just proves the opposite, that you can't maintain the same depth of field without compensating with the f-stop.

14mm f/0.9 and 49mm f/3.2 both have the same aperture: 15mm.

"Compensate" implies that something is being changed, but it's not: you're keeping things the same. If you don't use the same aperture, then you've just changed something. For example, 49mm f/0.9 would be a 54.4mm aperture. That is much wider than the aperture of 14mm f/0.9: 15.5mm aperture. Shooting both at f/0.9 would give drastically different results because of the huge difference in aperture. Keeping things the same would be using 49mm f/3.2.

When you keep the aperture (not f/number) the same, DOF, light gathering ability, and diffraction stay the same across all sensor sizes.

It's not always the larger sensor that has lenses with wider apertures. Medium format lenses, for example, have maximum apertures around 20-50mm (e.g. 135mm f/4.0). FF35 lenses with the same field of view have much wider apertures, such as 40-70mm (85mm f/1.2). This leads to the situation where a smaller sensor (FF35) is capable of thinner DOF than a larger sensor (MFDB, Medium Format Digital Back).

I'm trying to show things from a totally different point of view; a paradigm shift. The normal, natural, and commonly-accepted way of looking at things is to assume the larger format is used much larger apertures (longer focal length with the same f/stop). However, I think that it is misleading, and a better way of looking at it is to know that a larger format can be used at the same aperture to get the same results.

So given that, how can you say that it's a myth that larger sensors have lower depth of field characteristics when what you are actually saying is that larger sensors DO have lower depth of field characteristics... but that higher sensitivity and less noise give you greater freedom to compensate by stopping down?

What I dislike about my title is that it gives the impression that larger sensors aren't even *capable* of thinner DOF, which is untrue in most circumstances (Medium Format vs. 35mm is one exception, wildlife is another exception). However, it was the best abbreviation I could think of for this: "Myth busted: Larger sensors cannot achieve the same DOF and noise level as smaller sensors in low light; larger sensors are capable of the same DOF and noise as smaller sensors, so they are only worth the extra money if you are going to have more light or thinner DOF."

People are going to read your post and assume that they can move up to giant sensor formats and just keep on shooting the way they always been on smaller-sensor camera and focusing won't be an issue because this depth of field difference is a "myth".

I want people to be aware that they can, if they want, do exactly that, though it would probably be a waste of money.

[We are, of course, setting aside the oft-discussed topic of lens mechanics; FF35, e.g., does not have lenses with mechanics that are as smooth as S35 when it comes to pulling focus.]

Look at what's been happening in the jump from 2/3" sensor cameras to S35 cameras -- focus-pullers are finding things a lot harder because often a cinematographer will light an interior to near the maximum aperture of the lens. If you can put a f/1.4 lens on a FF35 camera, you can bet some DP is going to what to shoot a scene at f/1.4 and telling him he should now be trying to always work near a f/4 at the widest is going to fall on deaf ears.

That's a social problem; it shouldn't be blamed on the sensor size. If the cinematographer kept the lighting the same, and the aperture the same, it would be just as easy on the focus puller as a 2/3" sensor was.

It can be a problem of expectations. If the DP has higher expectations from larger sensors, those expectations will not be met unless DOF is thinner or there is more light. However, if the DP expects the same from the larger sensor, that expectation will be met for the same DOF and same light.

I'm trying to correct the impression that larger sensors can't even manage the same level of performance (for a given DOF) as a smaller one. They can, it's just not usually worth the extra money.

I can predict this: most DP's work around an f/2.8 when lighting a typical night interior scene and when the FF35 EPIC's come out, they will continue lighting to an f/2.8 -- they will use the greater sensitivity to cut their light levels, not to stop down the lens. And thus focus-pullers will be struggling with a lower depth of field compared to what they had on a S35 camera. Same thing happens in 35mm anamorphic photography -- most ignore the advice to stick to an f/4 and instead just go for the lower depth of field of an f/2.8.

I totally agree. If those DP's read this thread, they would know that it doesn't have to be that way; they could, if desired, keep aperture the same and DOF/noise, too, will remain the same.

I mean, isn't one of the big selling points of the RED ONE is that you can get 35mm depth of field characteristics compared to a smaller sensor HD camera? By your own logic, that's a "myth".

RED ONE only has thinner DOF if you also use a lens with wider aperture (setting aside 4K-vs-HD and raw-vs-video). If you need and desire the deep DOF of a 2/3" camera in low light, upgrading to S35 will not help. S35 can match 2/3" in low light by using the same aperture, but it will only be equal. And why spend more if it's only equal? One reason would be if you wanted the advantage for the times when light is ample, or when you're willing to deal with thinner DOF in low light.

Rather than say "Larger sensors have thinner DOF than smaller ones", I'd say "Lenses with wider apertures, no matter the sensor size, have thinner DOF". Granted, it's typical to use wider apertures on larger formats. But it's not necessary or always advantagous, such as when you need to keep DOF the same.

Another exception similar to Medium Format is when shooting with super telephoto lenses (e.g. wildlife). If you're already carrying the heaviest lens in existence (or your back can manage without breaking), S35 will be incapable of thinner DOF than 2/3". Because to get thinner DOF would require even wider aperture, which is heavier weight (and probably not even made by anyone). So you'd have to settle for the same aperture, and so the same DOF. For example, 100mm aperture on a 2/3" camera (e.g. 400mm f/4) gives the same DOF as the equivalent lens on S35 (1400mm f/14, if such a lens existed).

Thinking in terms of aperture instead of f/number makes everything much clearer: larger formats can do everything the smaller ones can; but they can do more if you add more light or use thinner DOF.

 

[Daniel Browning]

The relative aperture is the tool used. That is how we know to work. The different formats have different characteristics.

Yes, relative aperture (f/number) is is the tool everyone uses, and yes, that is how everyone knows to work. Within the confines of one format size in isolation (just 2/3" or just S35 or just FF35), relative aperture works perfectly to describe everything about DOF/noise/diffraction: wider relative aperture = thinner DOF, less noise, less diffraction. Narrower relative aperture = deeper DOF, more noise, more diffraction.

The problem is when you leave the confines of one single format to start comparing formats of different sizes. Then relative aperture does *not* work to describe everything about DOF/noise/diffraction. Using relative aperture to discuss different format sizes leads to incorrect conclusions, such as:

• Medium Format is capable of thinner DOF than FF35.
• S35 is not capable of the same DOF/noise/diffraction as 2/3" in low light.

Looking at those from the point of physical aperture reveals those to be false.

This seems a debate for the sake of it's self.

That was not my intention. I'm trying to correct what I believe are commonly held misconceptions.

 

[J. Eric Camp]

Rather than say "Larger sensors have thinner DOF than smaller ones", I'd say "Lenses with wider apertures, no matter the sensor size, have thinner DOF".
.

Well said.

I retract my comment about of "Debate for the sake of debate." Chalk it up to resistance to change.

What you are talking about require DP's or lens manufacturers to think "against" the tools we have been reared on. Not to say that is something to shy away from. I see your point with regards to physical aperture and it's use as a gold standard.

 

[David Mullen ASC]

I get what you're saying -- I often find myself at the opposite end when people complain that they can't get 35mm depth of field with a 2/3" camera. Sure you can... if you can use really fast lenses on the 2/3" camera and you don't mind the look of 35mm shot at f/4 and higher. At that point, you could argue that the 2/3" format is more of a plus than a minus since it allows you to work in less light at wider apertures and still maintain a practical depth of field for focusing.

It really just comes down to lens aperture and what you can achieve with the lenses and light level you have.

The FF35 format is only a practical 1.5-stop compensation that you have to find compared to S35 in order to maintain depth of field characteristics, which is generally not the end of the world (the 2.5-stop jump from 2/3" to 35mm is a bigger hurdle in comparison). If the FF35 camera allows you to double the ASA rating with no relative difference in noise level, then you're almost there, practically-speaking.

On the other hand, the RED seems practically to be a 320 ASA camera and most people shooting on S35 film are used to 500 ASA levels, so the question is whether the FF35 EPIC will look good at ratings higher than 500 ASA in order for it to be relatively easy to stop down a little. If the FF35 EPIC ends up having to be shot at 320 or 400 ASA just to look good, then more people are going to complain about having to light to a little higher levels just to maintain a workable depth of field. So there are still some unknowns here about this FF35 system.

 

[XiaoSu Han]

Just use the focal length and aperture to calculate the depth of field, just because to get the same lens angle you would use a 25mm lens on S16 and a 50mm lens on S35, does not make the 25mm lens a 50mm lens and vice versa?

I've read "a 50mm is a 50mm is a 50mm" once and stick to that.

Calculate the depth of field from a 50mm lens at 2.8 for example and then you can calculate for the angle of view regarding what format you're shooting. As simple as that or am I wrong?

 

[Johan Lindgren]

I Think it will be long before we see any 2/3" that have a lesser f-stop number than 1.7f since the beamsplitting in 3ccd cameras wont allow it. Iknow the digiprimes are 1.4f but they are projecting the colors in a manner that suits beamsplitters.

Johlan

 

[David Mullen ASC]

Yes and no -- there is also the issue of the Circle of Confusion figure chosen, but generally the real problem is that lenses are chosen primarily for their field of view. So if you lose half your field of view by switching to a smaller sensor format, it's silly to ignore the fact that you are going to switch to a shorter focal length to compensate.

This is where it comes down to practical reality versus what a textbook would tell you. Practical reality is that the size of the sensor determines what focal length you tend to select for the shot, and that determines what depth of field characteristics you are likely to deal with. Practical reality also is that we almost always run into low-light situations where we use the widest aperture available to us in order to get enough exposure. So given those two real-world situations -- (1) we choose lenses for their field of view, and (2) we run into situations where we work near the widest aperture available to us -- then there are some depth of field challenges to deal with no matter what, so it is helpful to the cinematographer to understand what he needs to do in order to handle these situations. Maybe he can compensate by stopping down, either by raising the light levels or rating the camera faster (underexposing), or maybe he just needs to be very careful about focusing...

 

[Daniel Browning]

I get what you're saying -- I often find myself at the opposite end when people complain that they can't get 35mm depth of field with a 2/3" camera. Sure you can... if you can use really fast lenses on the 2/3" camera and you don't mind the look of 35mm shot at f/4 and higher. At that point, you could argue that the 2/3" format is more of a plus than a minus since it allows you to work in less light at wider apertures and still maintain a practical depth of field for focusing.

Agreed. That's a good example.

If the FF35 camera allows you to double the ASA rating with no relative difference in noise level, then you're almost there, practically-speaking.

One of my central points is that this is not an "if": it has always been this way for raw digital photography. The only thing that changes it is when one of the sensors has much lower read noise per area; even then it's usually only 1/3 stop difference. If one is compressed (e.g. REDCODE), that might also cause a difference (1/6 stop?).

However, the same is not true of film, because unlike linear raw digitial, it has nonlinear response. Underexposing digital by 5 stops gives you 5 stops less information. Doing the same in film loses *more* than 5 stops of information, because more of the information falls in the nonlinear portion of the curve.

Imagine Super8 film with dimensions of 5.46mm X 3.07mm (1.78 aspect). A 7mm lens would have a 42 degree AOV. Shooting in relatively low light, say the best exposure is at T/2.8 (for a nice, meaty neg). On top of that, the very deep DOF provided by a 7mm T/2.8 on Super8 is critical for the shot.

Then imagine a VistaVision camera with 1.78 aspect and the same film stock as in the Super8, a 46mm lens is needed (for the same 42-degree AOV and perspective). Shooting at f/2.8 would also yeild a nice, meaty negative of much higher quality than the Super8, but it would also cause much, much thinner DOF, ruining the shot (or at least making it much more challenging on the puller!). One must stop down to f/18 to get the same, deep DOF and focus pulling difficulty (or lack thereof). That's over five stops of underexposure. Even though the VistaVision has over 50 times more area, the underexposure will cause *more* than 50 times less light to be recorded on the film, because more of it falls on the non-linear part of the negative.

(That's my understanding, at least. I don't know if flashing the film with 5 stops of light would get enough of the response up into the linear range to get results as good as the Super8, but it would be neat if it did.)

With RAW uncompressed digital, 50 times more area perfectly compensates for 50 times less intensity per-area.

On the other hand, the RED seems practically to be a 320 ASA camera and most people shooting on S35 film are used to 500 ASA levels, so the question is whether the FF35 EPIC will look good at ratings higher than 500 ASA in order for it to be relatively easy to stop down a little. If the FF35 EPIC ends up having to be shot at 320 or 400 ASA just to look good, then more people are going to complain about having to light to a little higher levels just to maintain a workable depth of field. So there are still some unknowns here about this FF35 system.

Agreed.

 

[J. Eric Camp]

A big part of it comes back around to the optics available. While it might be possible for me to achieve the same mathematical ends, the quality of glass, as we all know, varies through out it's range. Each format and it's corresponding optics, which are restrained by physics and geometry, will have sweet spots unattainable by another combination.

 

[Michael Brennan]

For those who may be a bit crosseyed at all the figures I offer the basic facts;

1/ smaller image planes (ie 2/3 inch) need wider lenses to get same angle of view (shot size) compared to larger image planes (ie 35mm)
2/ Wider lenses have more depth of field than longer lenses.
3/ So it follows that there is more DoF at a given aperture on 2/3 inch sensor than 35mm
4/ And so there is less DoF at a given aperture on 35mm than 2/3 inch sensor
5/ Minimum lens aperture on 2/3 inch is limited to f1.4 prism in the lens.


Bringing sensor attributes, namely sensitivity and noise vs sensor size, into the equation is best left to a test using specific models of camera. Acceptable signal to noise ratio is is both subject dependent and subjective.


May I add that larger pixels are;
1/ inherently less noisy than small pixels.
2/ collect more electrons so for practical purposes said to be "more sensitive"
3/ Manufacturers may choose to use larger pixels in larger sensors to keep noise down and improve sensitivity.
For instance a 645 size sensor with just 4k pixels would be many stops faster than REDone with same signal to noise (but not necessarily in practice equal depth of field because the 645 needs longer lenses for the same shot size)

Im hoping that RED will make a super fast, large sensor using large pixels and although it may well have less depth of field it would be a an innovative new tool.



Mike Brennan

 

[Douglas Underdahl]

Posted the following over on a Tokina 11-16 thread.

Oh, here's why you get effectively a shallower depth of field with larger sensors/formats:

Let's say you are shooting with a 35mm movie sized sensor camera, like an Arri 235 or a RED. You have a nice head and shoulders shot of your lead actor, who is Mickey Rourke (seems to be the actor of the day). You're using a 30mm lens, or thereabouts, which is about a "normal" lens for that format.

Now, you pull out your "full frame" Scarlet, or Epic, which has a sensor about the same size as your old Nikon still film camera. To get that same head and shoulders shot of Mickey - that is, keeping the same head and shoulders composition of him - you have to use something like a 50mm lens. Your depth of field is shallower because you have to use a longer lens. The longer 50mm lens is "normal" - not telephoto or wide angle - for the full frame sensor.

And that's a bitch, because boy howdy it's already hard to keep actors in focus with 30mm lenses in 35mm 4 perf at 2-2.8. Even F4. Just watch Keifer Sutherland's ears have all the focus in 24, but not his eyes, on some shots!! Gadzooks. So going to a larger sensor is going to be that much more difficult - unless you can stop down, which means that for me, I'm really going to need a faster full frame sensor. Like, shoot all the interiors at 5.6-8 split. So, ASA 1600 would be nice. Fingers crossed.

PS - David Mullen is always right.

 

[Justin Anderson]

"David: On the other hand, the RED seems practically to be a 320 ASA camera and most people shooting on S35 film are used to 500 ASA levels, so the question is whether the FF35 EPIC will look good at ratings higher than 500 ASA in order for it to be relatively easy to stop down a little."

My hope is that the Epic will remain a 320 or 400 ASA camera but with significantly cleaner noise so that I can shoot at 500 like a typical production or I can shoot at 320 if I want it a bit cleaner.

Thoughts?

 

[David Mullen ASC]

Yes, one hopes an extended dynamic range will allow one to use slower ASA ratings for filming outdoors in sunlight so you aren't stuck using ND1.2's and heavier.

 

[David Rasberry]

The reason why this is true essentially comes down to aperture. Not the f/number (which is "relative" aperture), but the the physical aperture, absolute opening, or "hole in space". When the per-area performance of the sensor is the same (as in assumptions above and most real life situations), then the DOF, light gathering ability, and noise all depends on only one thing: the aperture of the lens.

The physical aperture of 32mm f/1.2 is 26.6mm. The physical aperture of 50mm f/2.0 is 25mm. They both provide the same FOV on S35 and FF35, respectively, and the DOF is the same because the physical aperture is also the same (~25mm). Light gathering ability and noise, too, are the same: one focuses the light in a smaller space with more intensity, the other spreads it out over a larger space with less intensity. In either case, the total amount of light is the same.

• Sensors with the same sensitivity per area.
• Sensors with the same read noise per area.
• Sensors with the same full well capacity per area.

You are missing the significance of a basic law of physics, the inverse square law. For a fixed physical aperture and amount of light, a larger sensor with twice the area of a smaller sensor will be receiving only 1/4 of the light intensity per area. Assuming equal performance for the two sensors, to get the same dynamic range and signal to noise ratio requires exposing at the same relative aperture. The larger sensor at the same physical aperture and shutter speed will be two stops under exposed.

Astronomers work with physical apertures because the telescopes have fixed physical apertures. They adjust exposure by time.