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Small differences in flange distance are less important than is often thought in the photo-tech-gawking sphere because it doesn't per se limit the back-focal di

Small differences in flange distance are less important than is often thought in the photo-tech-gawking sphere because it doesn't per se limit the back-focal distance of a lens design; note how in most non-tele lenses the back element is inside the mount or protudes out of the lens mount. Flange distance is merely a property of the mechanical interface, not an optical property. E.g. some people argue that Canon RF has to be worse than Nikon Z because the flange distance is 2 mm longer, but if you look at the available designs both have lenses with a BFD of 10 or 11 mm. The article mentions image-side telecentrism for reduced aberrations. This is another talking point often brought forth; "the big mount allows a rear element so big that it can cover the image sensor with a near-telecentric swath of rays". Again, if you do a reality check here you'll notice that the chief ray angle (the angle between the chief ray of a ray bundle on the image circle to the image plane; chief rays are those crossing the center of the aperture) in actual lens designs is nowhere near 0° and is instead somewhere between 35-50°. Part of that equation is certainly that microlenses are offset as you leave the center of the sensor, so essentially sensors are designed for a particular range of CRAs and will not do well if you go way out of that range. Like the wide-angle rangefinder primes usually did: putting these on a digital camera results in strange color shifts towards the edges of the frame.

azalemeth 5y ago
I'm moderately convinced that this is all about manufacturing costs. SLRs are complex beasts with mechanical parts that need to be made to very tight tolerances and eventually wear out. The physicist in my knows that numerical aperture, the various inevitable trade-offs made in lens design and ultimately sensor size are really what limits optical performance. Going mirrorless means that you can spend the budget on these components rather than the mirrorbox and pentaprism / pentamirror on the top and the associated electronics with the viewfinder. It's not necessarily a bad thing, but it is above all a business decision and not really a scientific one. I personally like my [pentax] dSLR a lot -- the batteries last for ever as a consequence of the fact that most of the time all the power-hungry electrical components are off. The optical compensation with the viewfinder and my eye works perfectly, and I like the fact that, unlike an EVF, it will give me a human representation of how bright or dark a scene is. Put a long telephoto lens on, and watch everything get darker. I very much "feel" that the process of pressing the shutter button connects me with the physics of what I am doing in a very visceral way.
- xdennis 5y ago
  How so? Aren't DSLRs cheaper than mirrorless cameras?
  - pas 5y ago
    Are they cheaper on a cost basis or cheaper due to current supply-demand? (Ie mirrorless is in demand, DSLRs are not.)
- to11mtm 5y ago
  Manufacturing costs are a big part of it. Its safe to assume the AF Sensors for a given segment (often as much a differentiator as megapixels in DSLRs) are fairly custom/proprietary widgets and thus more expensive, compared to Sensors where often costs are more amortized (i.e. Nikon using Sony sensors.)
- Tagbert 5y ago
  Cost and customer preference for a more compact camera.
  - jacquesm 5y ago
    And quite importantly: lighter, and longer battery life. Displays, CPU, RAM, flashlights and storage use a ton of power, anything that can save on that is useful.
    - azalemeth 5y ago
      Ironically, those are all arguments against a mirrorless camera and towards a DSLR, swapping an EVF's circuitry and screen for five lightweight mirrors. My Pentax is built like a brick and quite sturdy, but a modern low-end Canon DSLR is amazingly light and really quite surprisingly so: the 250D is 419 g.
      - jacquesm 5y ago
        Interesting, yes, that is a good point if the camera is 'on' more than off between shots. The DSLrs that I'm familiar with all have whopping large batteries vs the mirrorless ones that come with puny little cells.
dheera 5y ago
Shorter flange distances do mean that retrofocusing design can be avoided, and an equivalent optical setup can be made much smaller. For example, a Voigtlander 35/1.2 lens for mirrorless full frame is about 60mm (diameter) x 60mm (length) while I don't know of any equivalent lens for an SLR that is less than 90x120mm. Also, you can't have the rear element go too far behind the flange distance of an SLR without getting smacked by the mirror. With mirrorless this isn't an issue. But you don't want your ray angles to be too extreme or the microlenses won't focus well onto the photosite.

azalemeth 5y ago

I'm moderately convinced that this is all about manufacturing costs. SLRs are complex beasts with mechanical parts that need to be made to very tight tolerances and eventually wear out. The physicist in my knows that numerical aperture, the various inevitable trade-offs made in lens design and ultimately sensor size are really what limits optical performance. Going mirrorless means that you can spend the budget on these components rather than the mirrorbox and pentaprism / pentamirror on the top and the associated electronics with the viewfinder. It's not necessarily a bad thing, but it is above all a business decision and not really a scientific one. I personally like my [pentax] dSLR a lot -- the batteries last for ever as a consequence of the fact that most of the time all the power-hungry electrical components are off. The optical compensation with the viewfinder and my eye works perfectly, and I like the fact that, unlike an EVF, it will give me a human representation of how bright or dark a scene is. Put a long telephoto lens on, and watch everything get darker. I very much "feel" that the process of pressing the shutter button connects me with the physics of what I am doing in a very visceral way.

xdennis 5y ago
How so? Aren't DSLRs cheaper than mirrorless cameras?
- pas 5y ago
  Are they cheaper on a cost basis or cheaper due to current supply-demand? (Ie mirrorless is in demand, DSLRs are not.)
to11mtm 5y ago
Manufacturing costs are a big part of it. Its safe to assume the AF Sensors for a given segment (often as much a differentiator as megapixels in DSLRs) are fairly custom/proprietary widgets and thus more expensive, compared to Sensors where often costs are more amortized (i.e. Nikon using Sony sensors.)
Tagbert 5y ago
Cost and customer preference for a more compact camera.
- jacquesm 5y ago
  And quite importantly: lighter, and longer battery life. Displays, CPU, RAM, flashlights and storage use a ton of power, anything that can save on that is useful.
  - azalemeth 5y ago
    Ironically, those are all arguments against a mirrorless camera and towards a DSLR, swapping an EVF's circuitry and screen for five lightweight mirrors. My Pentax is built like a brick and quite sturdy, but a modern low-end Canon DSLR is amazingly light and really quite surprisingly so: the 250D is 419 g.
    - jacquesm 5y ago
      Interesting, yes, that is a good point if the camera is 'on' more than off between shots. The DSLrs that I'm familiar with all have whopping large batteries vs the mirrorless ones that come with puny little cells.

dheera 5y ago

Shorter flange distances do mean that retrofocusing design can be avoided, and an equivalent optical setup can be made much smaller. For example, a Voigtlander 35/1.2 lens for mirrorless full frame is about 60mm (diameter) x 60mm (length) while I don't know of any equivalent lens for an SLR that is less than 90x120mm. Also, you can't have the rear element go too far behind the flange distance of an SLR without getting smacked by the mirror. With mirrorless this isn't an issue. But you don't want your ray angles to be too extreme or the microlenses won't focus well onto the photosite.