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mikezip007
09-21-2009, 09:35 PM
Due to the smaller sensor size, the 7D will have a more depth of field than the full frame 5D2. How much more? As a cinematographer, I LOVE shallow DOF of the 5D2, but in a practical, "keep a moving thing in focus" or "make this an accurate rack focus" the super shallow DOF of the 5D2 can be a hindrance.

What can we expect from the 7D compared to the 5D2?

I have a 30D. Can i set up a test between the 2 cameras to see the DOF difference? Would that be accurate? Say, set both cameras to F2.8 on the same lens, 100 ISO, and the same shutter speed, Can i compare the two photos and get the difference in full frame and APS-C sensor DOF?

morgan_moore
09-21-2009, 09:39 PM
yes yes yes

ydgmdlu
09-21-2009, 09:48 PM
Due to the smaller sensor size, the 7D will have a more depth of field than the full frame 5D2.
Technically, this is untrue. You'll have more DOF because you'll need shorter lenses in order to achieve the same FOV.


How much more?
I've read that the difference is about two F-stops. There was a thread about this a few months ago in the GH1 forum.


As a cinematographer, I LOVE shallow DOF of the 5D2, but in a practical, "keep a moving thing in focus" or "make this an accurate rack focus" the super shallow DOF of the 5D2 can be a hindrance.
What's your background? In actual movies, the DOF is nowhere near as shallow as what it tends to be with the 5D. Most features are shot at T4.0 to T5.6. There normally isn't this obsession with getting the least DOF possible.


I have a 30D. Can i set up a test between the 2 cameras to see the DOF difference? Would that be accurate?
Yes, perfectly accurate.


Say, set both cameras to F2.8 on the same lens, 100 ISO, and the same shutter speed, Can i compare the two photos and get the difference in full frame and APS-C sensor DOF?
And here we have the problem. Like I said above, the sensor is not responsible for the difference in DOF. DOF is a property of the lens. If you use the same lens at the same F-stop on the two different cameras, the DOF will be exactly the same. The only difference that you'll see is that the 30D will have a narrower FOV, which is due to the sensor being smaller. That's it.

Loic
09-21-2009, 10:03 PM
I've heard that in shooting conditions, the mark ii is not that portable compared to 4/3 sensors for the same reasons you are talking about. Focus assist is critical, hence the fact that you need more light then the 7D to get deeper depth of field. Does it make 5D mrkii heavier on lighting gear to have a reasonable amount of dof without always having only one meter of clear focus? Also it's harder for the talent because he is told to stay exacly in the position where the focus is. There is a chance of having more takes because of this issue.


BTW it only means you can achieve at f4 on a 5D mark ii the same DOF as the 7D on f1.8. I mean that it's a question of needing to open more on a smaller sensor then on a FF sensor. You need less light on 5D mkii then the 7D for the same effect.

I am not saying they are the same, 5D mkii have a ridiculously small dof achivable. It dosen't mean it's better.

It's like when video guys discovered 35mm lens adapters for video. They would crank the lens at f1.8 only to make a statement : I can have shallow dof! Great! But it looks stupid when there are 5 rack focus in the shot because we can't see both actors at the same time talking!!!!!&?%&%

On regular 35mm film dof is not always shallow. It's the choice of the DOP. It serves an aesthetic purpose to hold the narrative. With the 5D mrkii you have alot more chances to have to deal with it, you want it or not.

Loic
09-21-2009, 10:13 PM
And here we have the problem. Like I said above, the sensor is not responsible for the difference in DOF. DOF is a property of the lens. If you use the same lens at the same F-stop on the two different cameras, the DOF will be exactly the same. The only difference that you'll see is that the 30D will have a narrower FOV, which is due to the sensor being smaller. That's it.

About that last comment I have a question: sensor size means different sensitivity right? So to have the same exposure, a 5D mrkii at 100 iso 48thsec F4 has the same exposure then a 7D 100 iso 48thsec f2.8 right? Hense the fact it's not the same thing from one camera to the other. The lense does need to compensate. Am I mistaken here?


On the first question I would say:

I've heard that in shooting conditions, the mark ii is not that portable compared to 4/3 sensors for the same reasons you are talking about. Focus assist is critical, hence the fact that you need more light then the 7D to get deeper depth of field. Does it make 5D mrkii heavier on lighting gear to have a reasonable amount of dof without always having only one meter of clear focus? Also it's harder for the talent because he is told to stay exacly in the position where the focus is. There is a chance of having more takes because of this issue.


BTW it only means you can achieve at f4 on a 5D mark ii the same DOF as the 7D on f1.8. I mean that it's a question of needing to open more on a smaller sensor then on a FF sensor. You need less light on 5D mkii then the 7D for the same effect.

I am not saying they are the same, 5D mkii have a ridiculously small dof achivable. It dosen't mean it's better.

It's like when video guys discovered 35mm lens adapters for video. They would crank the lens at f1.8 only to make a statement : I can have shallow dof! Great! But it looks stupid when there are 5 rack focus in the shot because we can't see both actors at the same time talking!

On regular 35mm film dof is not always shallow. It's the choice from the DOP. It serves an aesthetic purpose to hold the narrative. With the 5D mrkii you have alot more chances to have to deal with it, you want it or not.

Huy Vu
09-21-2009, 10:21 PM
So to have the same exposure, a 5D mrkii at 100 iso 48thsec F4 has the same exposure then a 7D 100 iso 48thsec f2.8 right? Hense the fact it's not the same thing from one camera to the other. The lense does need to compensate. Am I mistaken here?



Not necessarily. Having a larger sensor means that you can have bigger pixel that can enhance sensitivity, but sometimes the manufacturer makes the decision to pack more pixel into the larger sensor which can decrease sensitivity. So while in general you can expect better light performance with larger sensor camera, it's not possible to look at the sensor spec and immediately say that this camera is X stop faster. It depends on a multitude of factor and you'd have to conduct tests to find out how sensitive the camera is.

ydgmdlu
09-21-2009, 10:32 PM
About that last comment I have a question: sensor size means different sensitivity right?
Sensitivity is determined primarily by the size of the pixels, not the size of the sensor. Larger sensors just happen to have larger pixels as well.


So to have the same exposure, a 5D mrkii at 100 iso 48thsec F4 has the same exposure then a 7D 100 iso 48thsec f2.8 right? Hense the fact it's not the same thing from one camera to the other. The lense does need to compensate. Am I mistaken here?
That's completely wrong. Sensitivity is mostly relevant in regards to how much gain is needed in order to achieve the desired exposure in lower light levels. The less sensitive a chip is, the more gain is needed, and hence there will be a higher noise level.

A 7D with an F4.0 lens at ISO 100 will give approximately the same exposure as a 5D with an F4.0 lens at ISO 100. You can think of ISO as basically standardized brightness levels. One camera at ISO 100 isn't going to be noticeably dimmer than another. At ISO 1600, the cameras will still give you the same exposure, but the 7D will be noisier at that level of gain

And by the way, when you want to "compensate" for the exposure, you don't need to change the aperture. Just change the ISO.

ydgmdlu
09-21-2009, 10:40 PM
Here, I found the calculations for the DOF difference between the 5D and the GH1: http://www.dvxuser.com/V6/showpost.php?p=1651158&postcount=37

Just as I remembered, the difference is almost exactly two stops. The GH1's 2.0X crop sensor, in widescreen mode, is very close in size to the 7D's 1.6X crop sensor. So the difference in DOF between a lens on the 5D and a different lens on the 7D, that provide the same FOV, should be between a stop and a half and two stops.

TimurCivan
09-22-2009, 02:16 AM
Does it make 5D mrkii heavier on lighting gear to have a reasonable amount of dof without always having only one meter of clear focus?



one meter? try one inch. @F4 the dof is about three inches @ 50mm. on a 50mm F1.4 its about a half an inch. its especially visible at 1080P what is and isnt in focus...

this is what youre working with wide open. http://vimeo.com/6697662

commanderspike
09-22-2009, 04:05 AM
DOF on a fast portrait lens like an F1.4 85MM is always going to be difficult to manage wide open. It's difficult enough on a GH1 with it's 2x crop.

If you don't want to sacrifice low light performance and need a more manageable DOF on a camera like the 5D then you have to go wide.

I don't think there is a night & day difference between DOF on the 5D and 7D. But here is where my knowledge runs aground - is DOF on a larger sensor due to more of the image circle from the lens being shown and this is cropped out on a 1.6x cropped sensor more, or is there something else at play? If not then can't you just crop 1080p to 720p to simulate the smaller sensor or use the 5D in EFS mode? I am guessing not?

Ian-T
09-22-2009, 05:46 AM
If not then can't you just crop 1080p to 720p to simulate the smaller sensor or use the 5D in EFS mode? I am guessing not?
You could do that but then youd take an obvious hit in resolution compared to the 7Ds 1080p.

ydgmdlu
09-22-2009, 06:22 AM
But here is where my knowledge runs aground - is DOF on a larger sensor due to more of the image circle from the lens being shown and this is cropped out on a 1.6x cropped sensor more, or is there something else at play?
DOF is a property of a lens. It is determined by only three factors: focal length, aperture, and subject to camera distance. Once again, the reason why people say that smaller formats "have more DOF" is only because shorter/wider lenses are necessary to match FOV with larger formats, thereby resulting in more DOF for the equivalent FOV. The same lens, at the same aperture, on two different-sized sensors, pointing at the same object, at the same distance will have exactly the same DOF.


If not then can't you just crop 1080p to 720p to simulate the smaller sensor or use the 5D in EFS mode? I am guessing not?
That would work, if your objective were to visualize the FOV difference with the smaller sensor. I don't know why you'd do this, though.

studio1972
09-22-2009, 07:22 AM
If not then can't you just crop 1080p to 720p to simulate the smaller sensor or use the 5D in EFS mode? I am guessing not?

A far better solution would be to stop down the lens in the 5D and increase the ISO to compensate. The 5D has less grain than the 7D at high ISO values so this shouldn't be a problem.

xbourque
09-22-2009, 07:46 AM
The same lens, at the same aperture, on two different-sized sensors, pointing at the same object, at the same distance will have exactly the same DOF.

But different shots because of the different FOV recorded by the 2 different sensors.

Barry_Green
09-22-2009, 08:53 AM
Sensitivity is determined primarily by the size of the pixels, not the size of the sensor. Larger sensors just happen to have larger pixels as well.
Well, no, let's correct that statement too -- Larger sensors USUALLY happen to have larger pixels. But not always. The DVX100 has 1/3" chips but has way better low light performance than the XDCAM-HD cameras with their 1/2" chips.

The more pixels you pack on a chip, the smaller they must be, to all fit. And the smaller they are, the worse the sensitivity (all other things being equal). More megapixels = worse sensitivity.

xbourque
09-22-2009, 09:19 AM
More megapixels = worse sensitivity.

Or more precisely:

More pixel density = worse sensitivity

Barry_Green
09-22-2009, 09:30 AM
Yep, good refinement there.

For HDTV, bigger pixels are your friend. Anything more than about 3 megapixels on a one-chip camera and you're hurting your image.

J Davis
09-22-2009, 12:06 PM
More megapixels = worse sensitivity.



Barry ... have you read this?


Myth busted: small pixels have worse performance than large pixels
http://www.reduser.net/forum/showthread.php?t=30076

edit: I'm not saying you are wrong, just pointing out that someone such as yourself might find it an interesting read

dadoboy
09-22-2009, 12:14 PM
This is written all over the place by people here and everywhere else, but its basically not true. Sensor size does make a difference in DOF using same focal length/stop/distance, due to circles of confusion. Theoretically and practically I've seen it in play. I don't want to get into a huge discussion about it because it's exasperating for me having to explain it again - I've done that in a previous thread somewhere at dvxuser.


The same lens, at the same aperture, on two different-sized sensors, pointing at the same object, at the same distance will have exactly the same DOF..

ydgmdlu
09-22-2009, 12:15 PM
Well, no, let's correct that statement too -- Larger sensors USUALLY happen to have larger pixels. But not always. The DVX100 has 1/3" chips but has way better low light performance than the XDCAM-HD cameras with their 1/2" chips.

The more pixels you pack on a chip, the smaller they must be, to all fit. And the smaller they are, the worse the sensitivity (all other things being equal). More megapixels = worse sensitivity.
Yes, I knew that; my point was about why people associate larger sensors with better low-light performance.

commanderspike
09-22-2009, 12:25 PM
Yes, I knew that; my point was about why people associate larger sensors with better low-light performance.

People do that for sake of brevity. They may know the details and how it works, but for the sake of terminology talk about 'large sensors' when it comes to influencing low light performance.

The DPReview.com camera comparison chart has the pixel density for almost every DSLR on the market, inc. the up and coming 7D.

But even pixel size & density is not the whole story. It depends on numerous other factors including the read out, photosite design, micro lenses and technology (i.e. backlit, etc.)

The 7D has an improved microlens design over previous CMOS sensors, but more than double the pixel density compared to the 5D. So since it has a slightly higher density to the GH1 but an improved design and a higher number of megapixels on a larger chip, it will sit somewhere between the 5D and GH1 for low light performance.

The higher the total resoloution, the more noise is removed in downsampling the image to 1080p. So 18 megapixels crammed onto a APS-C sized sensor is not without it's advantages. I don't agree with the talk of huge 3 megapixel CMOS sensors. Meh.

ydgmdlu
09-22-2009, 12:29 PM
Have you read this?


Myth busted: small pixels have worse performance than large pixels
http://www.reduser.net/forum/showthread.php?t=30076
It's not a myth in the most basic sense. After glancing over the posts in that thread, what becomes clear is that it's a very complicated issue. Notice, for example, that in the section where the OP talks about sensor size, he never really supports the claim that sensor size, in itself, is responsible for differences in performance; he mentions, as I've said in the past, that smaller sensors are typically used with lenses with far smaller absolute apertures, which means that far less light is being collected, which results in poorer performance.


Even the size of the lens points to this fact: the large sensor will require a lens that is perhaps 50 times larger and heavier for the same f-number and angle of view, and that lens will focus a far greater quantity of light than the very tiny lens on a digicam. When they are both displayed or used in the same way, the large sensor will have far less noise, despite the smaller pixels.

ydgmdlu
09-22-2009, 12:32 PM
People do that for sake of brevity. They may know the details and how it works, but for the sake of terminology talk about 'large sensors' when it comes to influencing low light performance.
Actually, from what I've read, most people think that sensor size is a direct factor in low-light performance. I've even debated with people here at DVXuser who took that position.

ydgmdlu
09-22-2009, 12:59 PM
This is written all over the place by people here and everywhere else, but its basically not true. Sensor size does make a difference in DOF using same focal length/stop/distance, due to circles of confusion. Theoretically and practically I've seen it in play. I don't want to get into a huge discussion about it because it's exasperating for me having to explain it again - I've done that in a previous thread somewhere at dvxuser.
Admittedly, it's actually a more complicated issue than either of us has made it seem.

What is meant by "depth of field"? Does it refer to a property of how an image looks, or is it something more abstract?

Depth of field is, basically, a property of the lens. It is wholly determined by the principles of optics. It refers to a distance around the subject within which things will appear sharp. This cannot change due to the size of the sensor.

However, when we talk about DOF, informally other things are at play. For example, when you use a longer lens, you will get a flatter image. When the background is out of focus, it will look very different from the OOF background of a deeper image. Because the image is flatter, background objects will appear larger in proportion to foreground objects, resulting in less overall scene detail. So the image would appear to have less DOF, in an informal sense, than a deeper image, even if the DOF is technically equal in both.

Using a crop sensor gets you essentially the same result as if you were to simply make a crop of the center part of a full-frame image in post. For that reason, in the most basic technical sense, the DOF between the image from the two sensors is exactly the same. The images themselves are essentially exactly the same, except that one has a narrower FOV than another. HOWEVER, most often the image from the smaller sensor is blown-up to more or less match the image from the larger sensor. For our purposes, we're trying to obtain a 1920x1080 image from both. When you enlarge the image from the smaller sensor, of course the circles of confusion in the resultant image will become larger as well. But the DOF of the original image, the image projected from the lens onto either sensor, has same-sized circles of confusion, no matter what the size of the sensor is. So that explains what you've seen in your experience.

So, basically, we're both right.

studio1972
09-22-2009, 04:26 PM
When people say they want shallow DoF, in many cases, they actually want to blur the background. This is actually a different thing and can be achieved with a narrower field of view or by physically moving the subject further from the background, even if the DoF is actually not very shallow.

Ian-T
09-22-2009, 04:56 PM
In regards to the almost identical image detail and sharpness of the 7D compared to the 5Dll, does the fact that it has a higher percentage of pixels in its smaller APC-S sized sensor contribute to that? Before I watched the test footage (from Bloom and Co.) that we've all seen I expected the 5Dll to be more detailed...but honestly.... their images look identical.

ydgmdlu
09-22-2009, 05:04 PM
When people say they want shallow DoF, in many cases, they actually want to blur the background. This is actually a different thing and can be achieved with a narrower field of view or by physically moving the subject further from the background, even if the DoF is actually not very shallow.
But subject-to-camera distance is a factor in DOF...

tnle2
09-22-2009, 05:17 PM
dadoboy is right, DOF depends on sensor size. Just look at the mathematical equations. DOF has the "c" term in the near and far equations and this "c" stands for circle of confusion. The circle of confusion is different for each sensor size because you're magnifying the image different amounts. It's simple--it's right in the equations. I have no idea why people argue that it isn't. They just end up confusing people. The math doesn't lie.

http://en.wikipedia.org/wiki/Depth_of_field
http://en.wikipedia.org/wiki/Circle_of_confusion

commanderspike
09-22-2009, 05:27 PM
Actually, from what I've read, most people think that sensor size is a direct factor in low-light performance. I've even debated with people here at DVXuser who took that position.

Sorry do disagree with you yet again :) But if you think about it, that is actually the dominant factor - sensor size.

If you have a large sensor and fill it with too many megapixels, the photosites may be small and densely packed but the image will scale down from a higher resolution to 1080p, and so the noise will be reduced in the process. Witness viewing a noisy 12 megapixel ISO 3200 photo at 640x480 as an extreme example.

Now if you had a large sensor with fewer megapixels, you also win, because the pixel density is so low.

Whatever way you slice it a small sensor is always a disadvantage when it comes to noise & low light performance.

The only way a small sensor can match a larger one is for the sensor technology itself to be less noisy and more sensitive to light on a photosite by photosite basis.

It is not 100% true that a small sensor with a low pixel density can out perform a large sensor with a high pixel density, either.

The Fuji F31 with it's 6 megapixel 1/1.7" has a pixel density of 14MP/cm2. The Fuji F100 had a slightly larger 1/1.6" chip with a silly high pixel density of 25MP/cm2 - nearly dounle the pixel density. Yet when the image is resized from 12 megapixels to 6, it can almost match the F31 for low light noise pixel by pixel.

This is part of the reason 1080p from a RED ONE looks better recorded at 4k rather than at 2k.

ydgmdlu
09-22-2009, 05:44 PM
Sorry do disagree with you yet again :) But if you think about it, that is actually the dominant factor - sensor size.
See, now what we're doing is arguing over semantics. You make good points, and I don't disagree at all, nor have I ever contradicted them. But the problem is that sensor size is an indirect factor, however "important" it may be. The size of the chip is not going to make the photosites any more sensitive than they are. That's the point that I'm making.


Whatever way you slice it a small sensor is always a disadvantage when it comes to noise & low light performance.How so? If you take the same photosites (same size, same technology, etc.) and spread them across a larger area, would you suddenly get a better image because the sensor is bigger?


It is not 100% true that a small sensor with a low pixel density can out perform a large sensor with a high pixel density, either.

The Fuji F31 with it's 6 megapixel 1/1.7" has a pixel density of 14MP/cm2. The Fuji F100 had a slightly larger 1/1.6" chip with a silly high pixel density of 25MP/cm2 - nearly dounle the pixel density. Yet when the image is resized from 12 megapixels to 6, it can almost match the F31 for low light noise.Nobody here has disagreed with that, not even Barry.

Once again, the whole matter is very complicated. There are too many confounding factors such that no general statement can be made without a lot of qualification. I suggest that we stop talking about sensor size, photosite size, and pixel density altogether. It doesn't get us anywhere and can only cause confusion. We should just accept that some chips don't perform as well as others and leave it at that.

The 7D doesn't perform as well as the 5D in low light, and we don't have to say (nor should we say) that it's because of a smaller sensor, smaller photosites, or higher pixel density. It just is. After all, the 7D is considered a "lesser" model. Perhaps that's what we should say from now on: The 5D performs better because it's higher-end.

ydgmdlu
09-22-2009, 07:45 PM
After doing some more thinking, I've decided to slightly reverse my position. But I still stand by most of what I've said. And even in admitting that sensor size is some sort of factor in low-light performance, I still say that it comes with a lot of caveats, such that it doesn't really make a difference.

If you think about it, there are no real tests that we can do to support any of the general statements that we're making. Every comparison that we might try to make is deeply flawed; the comparisons wouldn't be fair. For instance, you can try to compare the DVX with the EX1, but one's SD and the other is HD, so how do you determine which one has better low-light performance in any meaningful sense? The EX1 might have more noise, but it also has way more resolution to make that noise, as well the intended details, much more perceptible. You can try to compare the 7D with the 50D, but the 7D has better sensor technology to make up for its greater pixel density and (maybe) smaller pixels. The 5D may outperform the 7D, but it has bigger pixels and higher resolution, so what does that say about sensor size as a factor? And if you try to compare the big pixels from one sensor to the smaller pixels from another sensor, you have another problem: Where are you going to find two differently-sized pixels that share the same design but for the size? After all, camera makers are constantly improving sensor technology with every new camera, and different manufacturers and brands use different designs.

Ultimately, what's more important than numbers (be it sensor size, pixel density, etc.) is results. So as I suggested previously, that's what we should be talking about, rather than these silly numbers.

Barry_Green
09-22-2009, 08:06 PM
ALL these discussions HAVE to be suffixed with "all other things being equal". And as vdgmdlu has pointed out, all other things are basically *never* equal. Comparing a DVX with an EX1, the DVX is more sensitive even though it has a smaller chip. But it's noisier, and then we have to factor in that one's HD and the other's SD, one's CCD and the other's CMOS, and one is from 2002 and the other's 2008. There's simply no way to do a direct comparison.

Shortly, hopefully, there will finally be a bit of a way; with the Epic and Scarlet we'll have different-sized chips using the exact-same technology. If we can compare a Mysterium-X of one size against a Mysterium-X of another size, then we'll finally have a chance at "all other things being equal."

Until then, it's all lips flapping to no definitive conclusion.

mikezip007
09-25-2009, 08:45 PM
Here's a very small test I tried. I know it's not scientific, but it alludes to the answer I think I was out to get in the first place. Comparing the DoF of a full sized sensor to a crop with the same field of view. Both cameras set to:

ISO 200
f4.5
1/100

the 30D (crop sensor) at 70mm
5D2 (full frame) at 105mm

I eye-balled the framing to make it similar (this isn't rocket surgery so I know they are not identical) but you can see the DoF differences.

30D (crop sensor)
http://i14.photobucket.com/albums/a331/MikeZip007/IMG_0697_1.jpg

5D2 (full frame)
http://i14.photobucket.com/albums/a331/MikeZip007/IMG_8890_1.jpg

mikezip007
09-28-2009, 08:32 PM
no?