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I purchased a GH4 after realizing that the FF advantage is a myth


jcs
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The Northrup video (thanks KarimNassar for posting) got me thinking about the following math to match a crop sensor to an FF sensor camera (this was also helpful: http://www.josephjamesphotography.com/equivalence/#introduction ):

  • Multiply the focal length by the crop factor
  • Multiply the f-stop by the crop factor
  • Divide the ISO by the square of the crop factor

The first two equations deal with the difference in scale. The physical aperture (light opening, "entrance pupil") will be exactly the same:

 

Given:

 

f-stop = focal-length/aperture-diameter

aperture-diameter = focal-length/f-stop

 

GH4 Lens: 25mm f2.8

5D3 Lens: 50mm f5.6

 

GH4 aperture-diameter = 25mm/2.8 = 8.93mm

5D3 aperture-diameter = 50/5.6 = 8.93mm

 

Thus, the aperture diameter or entrance pupil will let in exactly the same amount of light. The 5D3 sensor has a focal length that is 2x farther from the entrance pupil, and since the sensor is 2x bigger, it captures the larger projection of exactly the same amount of photons. Since we've spread the projection of photons out with a 2x larger area, the sensels will get 2*2 (area) = 4 times less light than a 2x crop sensor. So, we have to boost sensor gain 4x to match the crop sensor. Now, if due to manufacturing or technology advantages the full frame sensor is more sensitive per sensel vs. the crop sensor, then a 4x gain boost to match cameras won't be accurate. FOV and DOF will be exactly the same regardless of sensor technologies. The only differences will be sensitivity, noise, and color characteristics.

 

After starting with a 5D Mark II, then going to a 5D Mark III, then adding a FS700+SpeedBooster, I began to suspect that there was nothing inherently special about FF. After reading about and understanding this math and physics, it's clear that there is no mathematical or physics-based advantage (in terms of light and photons) to FF over smaller sensors. Only when a larger sensor can be made more sensitive, less noisy, and/or provide improved color processing can a FF sensor perform better than a crop sensor.

 

The main reason the 5D2/5D3 became so popular was due to Canon's superior color processing. The 5D3's softness combined with low aliasing and excellent color processing for skin tones helped make it very popular as that is similar behavior to film. The ARRI Alexa has the best color processing and until the Dragon was released, the most dynamic range (not clear yet if the Dragon has matched or passed the Alexa, however it does an excellent job with skintones).

 

If we consider the SpeedBooster, using the same lens on both cameras, so the entrance pupil is the same size and the focal length is the same, then we'll have exactly the same FOV and DOF when the focal reducer shrinks the image circle down to the crop sensor. This means the f-stop is not changed, just the t-stop (the SpeedBooster for Canon EF to NEX is really a 1.1 crop, however the bokeh was nearly the same in testing between the 5D3 and FS700 with the 24-105mm F4L lens). This is one case where the smaller sensor has an advantage: since we're shrinking the photon projection area, we are increasing the amount of light to the sensor (thus gaining the ~1 stop of light increase in the EF to NEX case).

 

A current market advantage for FF over 2x crop is that there are more fast lenses for FF. We had to get a Voigtlander 25mm F.95 to come close to a 50mm F1.4 on FF. We'd need a 25mm F.7 to match the 50mm F1.4's entrance pupil size and thus bokeh. To match the 50mm 1.2, we'd need a 25mm F.6! Other than available/affordable lens choices, sensor technologies and color science, there's no mathematical or physical advantage to FF over crop sensor cameras. The noise characteristics of the GH4 are finer and nicer than the 5D3 and FS700 in low-light testing so far. The detail captured by the GH4 exceeds the FS700 (and slightly passes the C100/C300 (for 4K downsampled to 1080p)). 5D3 RAW still has the nicest skintones, however we're still learning to use the GH4. Understanding that there's nothing magical about FF got me more interested in giving a 2x crop sensor camera a try- so far the quality is impressive.

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Guest Ebrahim Saadawi

Interesting. I am nearly sold on this theory. You make sense.


Can't wait to watch the upcoming war on this thread though. :D

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I buy the argument that there is no mathematical argument for FF over say m43. There is no mathematical reason why the ecosystems couldn't offer exactly the same stuff.

 

But as you yourself say. they don't offer the same stuff. The lenses you might want, and can get on FF, don't exist for m43. They could exist. But don't. Maybe they will one day, but for now the native lenses are overpriced and comparatively limited. Speedboosters do a lot for that, but really, should we need these?

 

What I am hoping happens is that as the cameras get better and the consumers get more educated, the lens makers will offer more compelling choices for the smaller formats.

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Understanding that there's nothing magical about FF got me more interested in giving a 2x crop sensor camera a try- so far the quality is impressive.

 

If you're making an argument, comparing FF to MFT in PHOTOGRAPHY, then you have to factor in the diffraction of light and the width of each sensel on the sensor.  

 

With both MFT and FF video sample sensels on a chip which leads to a trade-off. FF, less diffraction and more DOF, but less sharpness, because pixels are farther apart.  MFT, more sharpness because pixels are closer together, but more diffraction and noise in low light.  

 

If one is to buy this argument, why not go back to camcorders, which use smaller sensors than MFT?  

 

Both the 5D3 and GH4 are camera platforms originally built for photography.  Because the chips are made for large resolution images. Both cameras bastardize the original image for video.  The GH4 is now bastardizing it less by save more of the pixels the sensor was designed to capture. 

 

You don't see the trade-offs in focal reducers when shooting video because video does not maximize the quality of the MFT or FF sensor.  If you were to shoot serious photography, you would see that focal reducers are no free lunch.

 

I agree.  there is nothing "magical" about FF video.  Quite the opposite.  I would take MFT video of FF video because the spread of the FF sensor creates too much aliasing/moire problems.  The calculations you're going through explain why most cameras can take the same image in good light with modest color-depth needs.  When you need really shallow DOF, or less diffraction in low light, then the calculations don't tell the whole story.

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And I do see some FF advantages:

  • wider dynamic range (and color depth?): GH4 has new, very good sensor (released in 2014) so it looks nice, but only compared to old FF sensors (5D3 is 2 years old now). FF A7s (and more today's / upcoming FF sensors) will be probably noticeable better.
  • f/2 lenses renders image much better than f/1 lenses (resolution, coma, abberations...): m43 25mm/0.95 @0.95 will look much worse than FF 50mm @ 1.8. In theory SpeedBooster would help, but there is no SB currently changing GH4 2.2x crop to 1.0x.
  • SB is not a perfect solution: additional cost, not native lenses = no AF (so much less usable for stills), sometimes bigger lens than necessary, some small technical problems (focus to infinity, weak aperture ring on adapter, soft edges..), one SB cost per lens mount (with A7s you can use many lens mounts with cheap simple adapters).
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I'm still trying to decide if I'll use a GH4 or not by playing with lots of native footage

 

I wouldn't use it without speed booster though, since it turns it into an APS-C sensor, which is great.

 

The extra light allows you to use less gain too and cleans it up, so yes, for all intents and purposes it becomes Super 35.

 

Some cameras are Super without a speed booster though....

 

The only thing that doesn't impress me that much so far on the GH4 is colour.

 

I also currently playing with a C100 and colour is wonderful on it.

 

Like it or not, when footage is compressed, the colour response at the sensor and in the digital processing matters an awful lot.

 

Even if it weren't compressed, even if it were raw, it would still matter. It's where a lot of the character comes from.

 

Without colour matrix control, or some kind of picture style editor, I can't reprogram GH4 to my tastes. Do these exist for Panasonic?

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I'm still trying to decide if I'll use a GH4 or not by playing with lots of native footage

 

I wouldn't use it without speed booster though, since it turns it into an APS-C sensor, which is great.

 

The extra light allows you to use less gain too and cleans it up, so yes, for all intents and purposes it becomes Super 35.

 

...

 

Why

 

so many

 

blank

 

lines?

 

:)

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  • wider dynamic range (and color depth?): GH4 has new, very good sensor (released in 2014) so it looks nice, but only compared to old FF sensors (5D3 is 2 years old now). FF A7s (and more today's / upcoming FF sensors) will be probably noticeable better.


Does the the fact that one sensor is overall bigger really create more DR? I'm under the impression that isn't the case. Its a combination of sensor tech and photosite size IMO, not overall size of the grid. Remember, the sensor overall is just a grid of photosites. You could have a smaller sensor with the same sized photosites (just not as many of them) and same tech generation producing the same results as the full frame one. Or heck, even BETTER results. While the examples you give are somewhat accurate, it is not necessarily on account of one sensor being larger. You are just comparing two specific models with circumstantial data!

  • f/2 lenses renders image much better than f/1 lenses (resolution, coma, abberations...): m43 25mm/0.95 @0.95 will look much worse than FF 50mm @ 1.8. In theory SpeedBooster would help, but there is no SB currently changing GH4 2.2x crop to 1.0x.


That has to do with the quality control of glass at that size. Here's the thing- smaller lenses are actually easier to built with higher precision. So you may actually find that a full frame 1.4 wide open is softer in the middle than a native micro 4/3 of the same aperture is. That's why they are able to make those tiny lenses for small chip camcorders and cell phones so sharp, whereas if you blew up a SLR photo from the same area of glass, it would likely be noticeably softer. But anyway, this is mostly relevant for photography, as the resolution for video is much more forgiving.

  • SB is not a perfect solution: additional cost, not native lenses = no AF (so much less usable for stills), sometimes bigger lens than necessary, some small technical problems (focus to infinity, weak aperture ring on adapter, soft edges..), one SB cost per lens mount (with A7s you can use many lens mounts with cheap simple adapters).


You know, the EOS to NEX speedbooster DOES support electronics to make it act native? I think you even get IS. They haven't brought that to MFT yet, but plan to as well. So yes, right now you can buy a crop Sony, throw an EOS SB on it and use native EOS lenses for photography, with AF. As I understand it, the AF performance isn't as quick, but again- we're really discussing for video here anyway.
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That is quite a strange argument you have put forth, jcs. It is the same as saying there is no portability disadvantage in carrying camera A which is four times as big as camera B since you can put it in the hands of someone four times as big. The previous statement is mathematically correct but what are the odds of there being someone that huge?

The keyword here is availability.

The situation is the same with focal reducers. Mathematically, FF sensors can benefit from focal reducers too. But nobody consider this possibility an advantage of FF, why? Because the Medium Format or whatever type of lens big enough for FF focal reducers aren't easy to come by.

So both the FF sensors' size advantage and the mirrorless crop sensors' focal reduction advantage all come down to availability.

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Mathematically, FF sensors can benefit from focal reducers too. But nobody consider this possibility an advantage of FF, why? Because the

Medium Format or whatever type of lens big enough for FF focal reducers aren't easy to come by

.

 

Try ebay.  I have more medium format lenses than 35mm lenses or APS-C lenses.  Actually the price of medium format lenses really make m4/3 lens prices look ludicrious.  And they do have adapters for mounting them on 35mm cameras just nothing like speedboosters.

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Does the the fact that one sensor is overall bigger really create more DR? I'm under the impression that isn't the case. Its a combination of sensor tech and photosite size IMO, not overall size of the grid. Remember, the sensor overall is just a grid of photosites. You could have a smaller sensor with the same sized photosites (just not as many of them) and same tech generation producing the same results as the full frame one. Or heck, even BETTER results. While the examples you give are somewhat accurate, it is not necessarily on account of one sensor being larger. You are just comparing two specific models with circumstantial data!

 

I'm talking about avarage. Most of m43 sensors have worse DR than FF sensors released in the same time. Just read random reviews or look at http://www.dxomark.com/Cameras/Ratings/List-view/%28type%29/usecase_landscape . I don't care why. Maybe it will change in future, but for now the best m43 sensors have worse DR than most modern FF sensors.

 

That has to do with the quality control of glass at that size. Here's the thing- smaller lenses are actually easier to built with higher precision. So you may actually find that a full frame 1.4 wide open is softer in the middle than a native micro 4/3 of the same aperture is. That's why they are able to make those tiny lenses for small chip camcorders and cell phones so sharp, whereas if you blew up a SLR photo from the same area of glass, it would likely be noticeably softer. But anyway, this is mostly relevant for photography, as the resolution for video is much more forgiving.

 

But you said in the beginning that you should compare GH4 Lens: 25mm f2.8 to 5D3 Lens: 50mm f5.6. And now you are comparing FF 1.4 to m43 1.4? :huh:

 

You know, the EOS to NEX speedbooster DOES support electronics to make it act native? I think you even get IS. They haven't brought that to MFT yet, but plan to as well. So yes, right now you can buy a crop Sony, throw an EOS SB on it and use native EOS lenses for photography, with AF. As I understand it, the AF performance isn't as quick, but again- we're really discussing for video here anyway.

 

That AF is very poor. No m43 version yet. Does not solve other SB issues.

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I'm talking about avarage. Most of m43 sensors have worse DR than FF sensors released in the same time.


The OM-D actually has 12.7 stops vs the 5D's 11.7. There are quite a few pro photographers that have blogged about adopting the OM-D, biggest downside compared to the 5D being the crop sensor meaning they have to rethink their DOF calculation.

Can't generalize all MFT sensors based on your experience with a particular one, is all I'm saying. You can like the 5D more than the GH4, but don't say its because the bigger sensor automatically gives it more DR. :P
 

But you said in the beginning that you should compare GH4 Lens: 25mm f2.8 to 5D3 Lens: 50mm f5.6. And now you are comparing FF 1.4 to m43 1.4? :huh:


Now I'm confused. If you are referring to that other discussion, I was the one who was rallying for 1.4 is a 1.4 is a 1.4. Aperture is rated in f-stops and is consistent across formats. A wider aperture lens is more complicated to build than a smaller one. Its harder to make large glass equally sharp to cover a wider FOV than a smaller one. All of the above statements are true to the best of my knowledge.
 

That AF is very poor. No m43 version yet. Does not solve other SB issues.


The AF isn't bad for the occasional snapshot, but I did admit that it isn't a strength of the platform. There isn't an m43 version yet just because metabones is supposedly working out the electronics to communicate (they had already figured out how to do it with Sony a while back, guess m43 is more complicated). This isn't a fault of the concept, its just that only one company has decided to do it and they're taking their time before bringing it to market. This isn't a fault of focal reducers as a concept. Again, you are generalizing about a concept based on specific examples that may-or-may-not really be applicable as a whole.

Also, what do you mean "other SB issues"? Gaining a stop of light? Does that sound awful to you? :P
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