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A7s, Depth-of-Field, and the Micro-4/3 Advantage


KrisAK

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Does the A7s' high-ISO capability effectively negate the dof advantage I’d otherwise get by choosing a Micro 4/3 camera? (Assuming I’m trying to achieve maximum dof.)
 
In other words, shouldn't I be able to match even the deepest dof I could get with an m4/3, just by stopping-down and boosting the ISO…and of course changing the lens to match perspective, etc?
 
Here's the thing: I'm bumping up from teeny-chip camcorders with 10x (yes, that’s double-digits) crop factors, and from this point-of-view, and in light of the A7s, the dof advantage of a 2x crop vs. FF seems almost non-existent. I’m wondering if I shouldn't skip over the m4/3 sensors and go with the A7s. (I’m usually in low-light, high-contrast environments, so the appeal of the A7s on other fronts is obvious.)
 
There are a boatload of questions about the still-unreleased A7s, but in terms of dof, does my thinking make sense? Thanks.
 
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If I can find the time I will shoot some tests with my medium format dof adaptor vs full frame vs aps-c later today.  There is a difference.  Neither one nor the other is better or worse.  They're jus

I'm using the BMCC edition SB on mine for everything but Defy G2 shots (which functions much better with minimal weight).  It definitely produces a nicer image and the extra stop+ is an additional per

Are you are referring to the differences between how a larger sensor/longer/slower lens renders in and out of focus areas differently to a smaller sensor/wider/faster lens?  If so, I too wish there we

Yes it does, in theory. MFT is 2x crop over fullframe. That means you get 2x the dof, but since the sensor is smaller, you can also say the low light performance is 2 stops worse. So ISO 6400 on fullframe gives the same results as ISO 1600 on a MFT sensor.

 

With raw photo files this theory is pretty much reality. You can compare this at dpreview.com. For example:

 

fullframe_vs_mft.jpg

 

When shooting compressed movie files results might be different because of all the image processing going on vs raw files, but fullframe will always have an advantage when it comes to noise. I think the A7S will hold up at ISO 6400 vs ISO 1600 on the GH4.

 

So in a way neither camera/system has a dof advantage or disadvantage.

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Also the smaller the sensor, the shittier the DOF behaviour. Someday I will write a text on the reasons because I couldn't find any online. This means that 24 f0.95 will not look as good as 50mm f2. neither will 24mm f2.8 look as good as 50 f5.6.

But for now, trust me ;)

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Im finding the GH4 is quite good in Low Light but talking with a buddy who has the BMCC Speedbooster, he says that small device has really opened up his camera to many things saying it makes it a whole new image.  

 

I'm using the BMCC edition SB on mine for everything but Defy G2 shots (which functions much better with minimal weight).  It definitely produces a nicer image and the extra stop+ is an additional perk.

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Also the smaller the sensor, the shittier the DOF behaviour. Someday I will write a text on the reasons because I couldn't find any online. This means that 24 f0.95 will not look as good as 50mm f2. neither will 24mm f2.8 look as good as 50 f5.6.

But for now, trust me ;)

 

 

Are you are referring to the differences between how a larger sensor/longer/slower lens renders in and out of focus areas differently to a smaller sensor/wider/faster lens?  If so, I too wish there were published tests and explanations on this interesting subject.  I notice the difference - and I know a lot of people don't realise the difference.  To me an 80mm f2.8 on medium format looks nicer than a 50mm f1.2 on full frame even though the fov and dof are matched on paper, the look is completely different 

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To me an 80mm f2.8 on medium format looks nicer than a 50mm f1.2 on full frame even though the fov and dof are matched on paper, the look is completely different 

 

Though when people take photos and compare different (but matched) focal lengths, they actually match up almost 100%.

 

Is this the camera equivalent of hifi-placebo?

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Though when people take photos and compare different (but matched) focal lengths, they actually match up almost 100%.

 

Is this the camera equivalent of hifi-placebo?

 

I think the main issue is that it has to be a specific type of shot to really highlight the differences.  For instance there will be a certain distance where that 'POP' from a longer focal length in combination with the field of view and size of in-focus subject benefits from the subtle differences in in-focus fall off.  I also think that it is to do with the actual lens performance too.  for example most 80mm f2.8 medium format lenses will deliver better overall performance/sharpness/contrast than the 50mm f1.2 you'll need to use wide open to match the fov and shallowness of the dof.  Sure a Canon 50mm f1.2L is great wide open, but its not as sharp as a 80mm planar f2.8 wide open.  

 

 

I definitely dont think it is a placebo effect.  I think the differences between the way a longer focal length and slower aperture separates the in and out of focus areas in a different way to a wider lens and bigger aperture is a lot more quantifiable than the differences between certain 'copper cable technology' and other such hi-fi placebos. ( I have some history designing within the esoteric hi-fi market as it happens, and am very aware of some of the crap the marketing teams come up with)  I think it's more accurate to compare the format/lens combination to the intricate differences between vinyl and cd.  Neither one is better than the other, but to a certain group of people, vinyl sounds better than a cd and vice versa.

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Telephoto compression plays a major part, longer FL means less perspective.

 

'Equivalent focal length' seems to forget this.

 

A zoom and dolly shot popular in movies of the 80s, keeping the same framing, illustrates this perfectly

Perspective is the same on all focal length at the same distance, the crop doesn't matter either. The only thing that changes is distortion and the part of the perspective you get to see.

You could take a picture with a 50mm and crop it to get the same compression as if it were taken with a 200mm. But the rendering is obviously a lot different.

The explanation about why larger formats rock is rather easy, but I want to explain it also with mathematical formulas so the "I have no live and talent at all" trolls don't eat me alive.

 

Btw, have you ever shot with a pentax 67? It's amazing, I got used to the weight in one day and ever since I don't want to touch my little nikons...

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I feel you need to revisit this assertion.

 

Why? It's the truth. You can try it out yourself if you have a 50mm and 200mm. Or whatever focal lengths....

 

The bokeh quality is an interesting topic. I think bokeh 'roll off / smoothness' is better with bigger sensors vs same bokeh equivalents on smaller sensors. Would be nice to see a test of this. Might try something myself.

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I feel you need to revisit this assertion.

I don't see why perspective should change from the same viewpoint.

Anyway, you have some reason in what you say. I am an architect, and while being an ignorant student I always wondered why professional architecture photography and specially old photography always looked so much better compared to what I could achive with my aps-c camera and wide angle optics (and I'm not talking about straight lines with a shift objective). In the end I've come to the conclusion (I haven't really dedicated too much time investigating it deeper so don't take this too seriously) that the problem comes from the distortion or corrected fields from retrofocus designes that first SLRs and then digital sensors (telecentricity,lightangle) introduce into the image. This makes the images look bad, I can't really explain it. But when you get into longer focal length this problem disappears (55-135mm) and thats why with FF sensors these are the most pleasing focal length (at least they are too me).

So yes, perspective kinda changes, but as I said, it's not exacly the perspective what changes. Something similar must happen with anamorphics, the perspective doesn't seem to be the same when cropping to the same equivalent, I guess that is related to the uneven stretch and/or the way the light changes direction.

I wish someone with accurate knowledge would explain me the exact reasons.

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Also the smaller the sensor, the shittier the DOF behaviour. Someday I will write a text on the reasons because I couldn't find any online. This means that 24 f0.95 will not look as good as 50mm f2. neither will 24mm f2.8 look as good as 50 f5.6.

But for now, trust me ;)

 

Not looking far away, please explain not the theory, but in practice - the difference (FF advantage) on following examples (from EOSHD):

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