# Mirrorless question Med. format. Compression of image quality and distortion.



## Soocom1 (Jun 1, 2021)

I am strongly leaning to getting a medium format mirrorless. Brand yet unknown.

But yesterday I was doing some thinking on this and want some input from those who understand the physics of this.

The primary advantage of the mirrorless system is just that. It’s mirrorless. No shutter and no mirror. OK So weight reduction aspects aside, it dawned on me that the DISTANCE of the lens to the image plane is highly reduced and thus lenses dedicated to the mirrorless must have a magnification effect of a fairly strong level with the rear element in order to create an image circle large enough to cover the sensor.

This translates to a reciprocating level of distortion involved and would it not also create a serious change in the DoF aspect overall? Thus somewhat mitigating one of the primary aspects of Med. Format to begin with? PLUS, given the compression of the distance, would this not also translate to a compression of image quality? Ergo lines of resolution?

Yes?

No?


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## Ysarex (Jun 1, 2021)

Soocom1 said:


> I am strongly leaning to getting a medium format mirrorless. Brand yet unknown.
> 
> But yesterday I was doing some thinking on this and want some input from those who understand the physics of this.
> 
> ...


No.

The flange distance for mirrorless cameras is being returned to where it's ideal as opposed to forced forward to provide clearance for the mirror flapping up and down.

My first mirrorless camera wasn't purchased because it was mirrorless. When I decided to upgrade to a smaller sensor from FF I started by shopping for lenses and for me that means first shopping for the most important lens with an angle of view of 80 degrees (I see wide). For the APS-C camera that I purchased that would be a 14mm lens. I found the Fuji 14mm f/2.8 and that determined my camera body purchase which wound up being mirrorless.

That lens remains one of the best lenses I've ever owned and with that angle of view it is entirely free of distortion. You can't buy a lens with a similar angle of view for any SLR that is likewise distortion free because the compromises in lens design to deal with the increased flange distance to clear the mirror make it too difficult to design out the distortion.

You've had some experience with Hasselblads -- look at the flange distance for this camera which is where it should be: The Hasselblad Superwide


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## Soocom1 (Jun 1, 2021)

No.. 
let me re-phrase this. 

The flange distance is the flange distance. 
That's not what I am talking about. 

On a mirrorless camera the flange distance is shorter than a SLR body. 
The Nikon Z5 has a flange distance (registration distance) of 16mm The flange distance on a D3 is 46.5mm.  That is a difference of 30.5mm. 
So the rear element and overall lens design is for that distance to allow infinity focus. 
Stop there. 

thus, The lens that is designed for a mirrorless is designed for that 16mm. Or an adapter for a F mount. fine. 

But that means that the mirrorless lens must have a rear or set of rear elements that allows the projection of an image circle that is more extreme in angle due to the close distance vs. a SLR. 

Thus, to have a clean image there is a proportional amount of distortion (albeit corrected to whatever degree) to accommodate the extreme angle. 

I don't have actual numbers, but consider this. (I am making up the numbers but the purpose is there.) 

At 46.5mm (F mount) with say a 50mm lens; lets say the angle of the light after the focal point is 45 degrees. Leave it at that. 
With a mirrorless, the angle of the light rays from the focal point must now be more extreme, let's say 78 degrees from the focal point to make the same sized image circle. (given that a FF D3 vs the FF Z5. )

Is there not a distortion effect taking place at such an extreme angle?


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## nokk (Jun 1, 2021)

i use the fuji 50r.  i haven't noticed any distortion.  but fuji corrects their distortion in camera too, so who knows.


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## ac12 (Jun 26, 2021)

I think it is the opposite of what you are saying.
As I remember, a wide angle SLR/dSLR lens has a reverse tele, as the rear optics of the lens, to allow the lens to be located far enough from the film plane, to clear the mirror.  

The shorter the focal length, the closer the unmodified optics are to the film plane. *
But there is an issue with SLRs and dSLRs.
The location of the lens flange itself is not the limiting factor.  The problem was and still is the mirror.

Way back in my early days, I remember lenses that projected into the camera, past the lens flange.
The problem was, they had to be used with the mirror locked UP, because the back of the lens stuck so far into the mirror chamber that the lens would hit the mirror, or the mirror hit the lens.

In order to avoid having to lock up the mirror, optics were added to the rear of the lens to move the lens forward, enough to clear the mirror.

* On the other end of the focal length spectrum are the long lenses, which illustrate this in reverse.
My brother has a 600mm tele.  The entire back half is an empty tube, no optics.
Telephoto lenses, then did the reverse of the wide angle lenses.  They used optics on the rear of the lens to move the lens closer to the film plane.  This was to shorten the physical length of the lens.


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## vintagesnaps (Jun 26, 2021)

I don't get any distortion with my digital mirrorless. I use the same lenses with it and with my film rangefinders. The difference is I can use a 135mm and on the digital camera it's more like having a 200mm lens on the camera.


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