Timotheus

Let me get this straight - are you denying that the combination of an 80mm lens with a 0.7x focal reducer is a 56mm lens?

@tupp, while we agree the two images are not exact, it was acknowledged that it was not possible to make the settings exact for equivalence. I don't see anything significantly special or magical about the full frame image, and most people cannot even see a difference without a blink test:

The simulations showed a perfect match, hopefully this simple diagram will show why:

If we take a movie projector and increase the distance from the projector to the screen, the image grows larger and vice versa. Does the image significantly change other than size? This should make it clear that sensor size by itself does not do anything special for the projected or recorded image. Are we in agreement?
Now does the size, shape, curvature, and number of lens elements make a difference with respect to DOF, bokeh, and overall image character? Of course, no one has argued that point as these changes occur between lenses designed for the same format, for example the Canon 50mm 1.4 vs the Canon 50mm 1.2. The 1.2 has a much larger lens and of course a larger aperture. What happens when we set both lenses to F1.4, or F2.0? Is there still something 'magical' about the 1.2 lens with the much larger glass?

Are they different? Sure they are. Is it significant? Does it matter- we're using the same sensor size?
Much more comparisons here between the 1.8, 1.4, and 1.2: https://www.slrlounge.com/canon-50mm-prime/
We haven't changed sensor size, only lenses, and the bokeh and character is quite different, right?
Want crazy/weird/artistic bokeh on full frame? Here you go ( http://allphotolenses.com/gallery/item/c_7319.html ):

Everyone agrees that lenses make a huge difference and some full frame lenses have bigger optics than some medium format lenses, right? If you still feel that sensor size affects the final projected/captured image, can you provide supporting math, physics, diagrams, and real-world examples supporting your hypothesis?

So if we focus on the art, the emotion of the combined 'lens filter', we can categorize looks so others can replicate themselves* and quit arguing about sensor size. I think Mattias' pics look cool, and if a MF->FF focal reducer plus cheap MF lenses can be used to recreate those looks, that's pretty neat- gives new love to neglected unused MF lenses
 
* this was not meant as a cloning comment  

Of course results are what count. My 2 cents: just don't get caught up in a possibly expensive quest for medium format glass assuming there is a super different, unique, mythical look to be achieved. (Not to say that hunting down and using vintage glass is a blast!).
Understanding equivalence can help one understand what results can be expected from any combination of sensor size and lens. Yes, there are unique combo's at the extremes of the range (no m43 equivalent lens for a 50mm f1.0 on full frame). But in general: for the most frequently used focal lengths, you can find equivalent lenses for the current different sensor sizes, thus yielding (close to) identical optical results.

This discussion reminds me of similar ones for analog vs. digital audio, vinyl/tape vs. digital, tubes vs. MOSFETs, one preamp vs. another preamp, one mic vs. another, crisp and clinical vs. warm and creamy, etc. Head on over to GearSlutz for a taste of audio drama for those inclined: https://www.gearslutz.com/board/ (around 10 million posts!). It's a great resource for audio related questions for filmmaking too.
In agreement with what @Brian Caldwell just said- these lens combos are creating interesting character, analog optical filters (transfer functions), which is art, and that is cool. It has nothing to do with sensor size per se, only the combination of optics to get the desired (or discovered!) look.
Here's an example of Shane Hurlbut comparing Leica Summicron-C to Cooke S4, same sensor size (Super35), and getting vastly different results (his perception, some of you may even disagree with his results):
http://www.thehurlblog.com/lens-tests-leica-summicron-c-vs-cooke-s4-film-education/
To wrap it all up:
Leica Summicron-C Lenses:
Flatter image Makes Monette look more sophisticated and older Makes her look wider than the Cooke S4 More of a white out with lens flares; doesn’t do as well as the Cooke S4 with lens flares. Bokeh less stop signing, more round Neutral lens Less detail in her face Doesn’t hold highlights as well as Cooke S4 Less contrast
  Cooke S4 Lenses:
More three dimensional quality Makes Monette look younger Makes her look skinnier Better with lens flares than the Summicron-C lenses Slightly more yellow than the Summicron-C Bokeh has more of a stop signing effect More detail in her face Holds highlights more than the Summicron lenses More contrast Thanks @bunk for creating these excellent computer renderings, which physically simulate perfect lenses and sensors via ray tracing photon paths for different sensor sizes and using perfect mathematical equivalence with pixel perfect results:
http://www.eoshd.com/comments/topic/20975-full-frame-aesthetic/?do=findComment&comment=167154


@Mattias Burling offered $100 if the images matched perfectly (if I read the thread correctly, see link above). Mattias did you pay bunk? The time and effort to set up and render those examples was worth way more than $100, and should end any further arguments regarding sensor size for anyone interested in a scientific and rational discussion (bunk also included the Cinema 4D project files for anyone to replicate as per the Scientific Method). @gatopardo replicated the results with VRay (another photon ray tracer) and 3DSMax.
Mattias' comments on medium format lenses being very cheap and 'free' in some cases is very useful information for those admiring the kinds of looks possible with a focal reducer and old medium format lenses, which create interesting analog filters which a lot of people love. As noted by Hurlbut and others, the Cooke S4 causes distortion and has other artifacts which make people look thinner, more 3D, better highlights, etc. Imperfection is the spice of art- makes the flavor interesting which will be loved by many where different forms of spice will be loved by others (or for some uses, no spice at all- clinically accurate (Sony/Zeiss for example)). Like comparing Neve/Avalon preamps (warm/colored) to Grace (clinically clean). Neither better than the other, chocolate vs. vanilla...

Character/rendering are entirely separate issues from photographic basics like DOF and perspective.  Certainly, if you like the character then there's nothing wrong with that.  Heck, if you find that using an 80mm lens with both a 1.4x teleconverter and 0.7x focal reducer (in series!)  to get back to 80mm but with some funky aberrations gives you the results you want then you should certainly do it.  My only real objection is with pseudo-explanations - basically "fake physics" - that cross the line into mysticism.
Mini correction:  techically, aberrations can and do influence DOF.

Of course results are what count. My 2 cents: just don't get caught up in a possibly expensive quest for medium format glass assuming there is a super different, unique, mythical look to be achieved. (Not to say that hunting down and using vintage glass is a blast!).
Understanding equivalence can help one understand what results can be expected from any combination of sensor size and lens. Yes, there are unique combo's at the extremes of the range (no m43 equivalent lens for a 50mm f1.0 on full frame). But in general: for the most frequently used focal lengths, you can find equivalent lenses for the current different sensor sizes, thus yielding (close to) identical optical results.

Of course results are what count. My 2 cents: just don't get caught up in a possibly expensive quest for medium format glass assuming there is a super different, unique, mythical look to be achieved. (Not to say that hunting down and using vintage glass is a blast!).
Understanding equivalence can help one understand what results can be expected from any combination of sensor size and lens. Yes, there are unique combo's at the extremes of the range (no m43 equivalent lens for a 50mm f1.0 on full frame). But in general: for the most frequently used focal lengths, you can find equivalent lenses for the current different sensor sizes, thus yielding (close to) identical optical results.

Of course results are what count. My 2 cents: just don't get caught up in a possibly expensive quest for medium format glass assuming there is a super different, unique, mythical look to be achieved. (Not to say that hunting down and using vintage glass is a blast!).
Understanding equivalence can help one understand what results can be expected from any combination of sensor size and lens. Yes, there are unique combo's at the extremes of the range (no m43 equivalent lens for a 50mm f1.0 on full frame). But in general: for the most frequently used focal lengths, you can find equivalent lenses for the current different sensor sizes, thus yielding (close to) identical optical results.

You are expecting a level of precision in this comparison that is entirely unreasonable.  Little things like changes in distortion and entrance pupil position during zooming make it impractical to make a blink comparator test completely perfect.  What the comparison does show - with more than sufficient precision - is that you can optically reproduce all aspects of an image shot on a large format with one shot on a smaller format - or vice versa.  
The notion that, say, an 80mm medium format lens has some inherent "80mm-ness" or "medium formatishness" that somehow stays with that lens after you attach a focal reducer is just silliness.  The combination of a 0.7x focal reducer and an 80mm lens is a 56mm lens.  Period.  Put that 56mm lens on a 24x36mm format camera and it will behave just like any other 56mm lens attached to that camera, the only caveats being related to aberrations and other flaws in the lens and focal reducer.

Thanks for creating the animated gif which clearly shows equivalence, even when the settings aren't exact (which mostly effects shadows- bokeh matches pretty nicely). If you want to see perfection, dig up the computer graphics renderings from one of the "FF/MF look" threads on this forum: the results are pixel perfect (probably (photon) ray-traced optics).
I think what people are liking about the MF lenses is their character, and even what some might call artifacts (including artifacts from the focal reducer).

You should be aware that this is a religious discussion.  Comparisons, and discussions about comparisons, should be avoided and only discussed in private!

It is an AgaScope lens. It was built by a Swedish industrial firm during the widescreen craze of the late 50s/early 60s. It was mainly used in Sweden, although some sets made it to Eastern Europe. The set was fairly sparse and included a 46mm and a 75mm. There weren't any zooms or wide focal lengths available, so the modern day appeal of these lenses is limited. Quality should be on par with other early anamorphic systems of continental Europe like Dyaliscope or Totalvision.

SLR Magic rangefinder lived on my camera for couple days, and went back home:)
it softens picture, not a lot, but still, and it makes setup bulky, for the same reason i am not after Core DNA, not giving up my small form factor for anything, well relatively small,
so most likely Isco 36 or 42, but i still can't decide between single focus and 2x squeeze, 2x is so freakin good, i just love it!
 

Use Tito's calculator :-)
http://www.tferradans.com/blog/?p=13386

Use Tito's calculator :-)
http://www.tferradans.com/blog/?p=13386

Use Tito's calculator :-)
http://www.tferradans.com/blog/?p=13386

Use Tito's calculator :-)
http://www.tferradans.com/blog/?p=13386

Maybe on a 4:3 crop you feel less guilty of the crop, when reviewing your footage the 3.56:1 composition sometimes looks so great that you don't want to adhere to the cinema "standard", if the camera is doing it for you is as we say in México "eyes that don't see, heart that doesn't feel " (ojos que no ven, corazón que no siente) :D

Some quick and initial tests with my new system:
5D III (ML RAW) - Bolex 16/32/1.5x - Rectilux Hardcore DNA
 
 
 

Mind power cropping! Should be able to manage...now on to mind power desqueezing! :-p
Found another test vid btw, not too bad either.
 

Mind power cropping! Should be able to manage...now on to mind power desqueezing! :-p
Found another test vid btw, not too bad either.
 

Thanks Timotheus! I'm happy to hear!

Yeah, I thought about that, but if I didn't test it on full frame, people would be asking about that. And to figure out APS-C, you can disregard most of the edges anyway and visualize with... *the power of your mind!*. hahahahaha. Just kidding on that last bit, but I think it's easier to estimate APS-C performance from full frame footage than the other way around. What do you think?

Very nice to see a new review Tito, always happy to get a notification of a new video of yours! On topic: as SLR Magic specifically markets this as a MFT/S35 solution, I wondered why you didn't use it as such (S35 mode on your A7S2)? I realize time is a scarce commodity, but this not-quite stellar FF performance perhaps leads us to criticizing the lens on a performance it was not intended for...

They mention it being used with full frame in their B & H listing.
"Please note that SLR Magic cautions that for full frame work a 75mm taking lens is required, a 50mm taking lens may only cover when your camera is in APS-C or S35/APS-C sensor mode. When using this adapter on a 25mm , the image will cover a Four Thirds sensor."