Nasty color bleed on pushed A7III RAW (compressed, silent shutter)

Started 7 months ago | Discussions thread
JimKasson Forum Pro • Posts: 21,078
Signing off

PhozoKozmos wrote:

JimKasson wrote:

PhozoKozmos wrote:

JimKasson wrote:

PhozoKozmos wrote:

as long as "exit pupil" is not "body-flange-to-sensor dimension"

i'm thinking you are simply referering to the opening where light exits the rear optic of an attachable lens (which is all i am referring to)

i am uncertain if you mean "exit pupil" may be "aperture iris within the lens body"

  • (if so, then i'm not referring to that, because the RAY PATH distance from aperture iris, is way beyond both LSFD, and unrelated to body-flange-sensor dimension.)

Neither. Did you read the Wikipedia article I linked to above?


it did not change my position.

because it lacked key labeled dimensions


I was hoping that I didn't have to make it this complicated, but the plane I'm referring to is also know as the "rear principle plane". That plane crosses the lens axis at the "rear nodal point".

this is more useful: it has a diagram with more useful labeled dimensions ...

■ here:

Supposing LENS BARREL is on LEFTSIDE, and SENSOR PLANE in BODY is off to the RIGHTSIDE.

■ Top Illustration:

LSFD = Starts @ V' and extends rightwards to Sensor @ S (not shown)

  • this type of lens, has a short-parallel LSFD (typically) = better (good) optics
  • not unusual for LSFD to be shorter than body-flange to sensor dimension (not shown)

■ Bottom Illustration:

LSFD = Spans V' to F', where Sensor is @ S is at F' (as shown)

  • so, LSFD = BFL (is this your "exit pupil" dimension?)

No! EFL!


  • a short BFL means short EFL by association = short LSFD
  • a long BFL means long EFL by association = long LSFD
  • EFL only helps address theta ray angle geometries (mathematical nodal values)
  • BFL determines PHYSICAL BOUNDARIES (one cannot have optical parts collide) = LSFD
  • i'm saying:
  • longer LSFD, is longer BFL (on lower diagram) = better optical lenses; where LSFD exceeds body-flange to sensor dimensions (BFSD, not shown) especially on "mirrorless" bodies with very short BFSD:
  • 18mm for Sony (FF), and
  • 26.7mm for Fujifilm G (MF)
  • but:
  • i'm SPECIFICALLY saying: too short LSFD, is too short BFL = poor/worse problematic optical lenses, especially image must be projected on a larger wider sensor width in relation to a very short LSFD (on FF Sony FE Bodies especially)
  • in this latter case, angle of convergence "theta" is higher from lens axis, like a "fisheye" short-throw projection

Longer LSFD = shallower angled theta vs Shorter LSFD = steeper wider angled theta (wrt lens axis)

e.g. Fujinon 250mm f4 (Med.Fmt) G lens for GFX50S:

  • LSFD (BFL on lower diagram) is 57.1mm (V' to F')
  • even though GFX50S has a short 26.7mm BF-S dimension (BFSD)
  • it's optics should be excellent, because of super-long LSFD of 57.1mm (approx)
  • lens has a HUGE lens hollow-space of about 30.4mm deep in the REAR of the lens
  • this is not shown in diagrams, but the LONG front protrusion on the new 1.4x TELECONVERTER, is ~30.4mm long (not explicitly detailed in owner's manual). this protrusion readily FILLS the huge hollow-space in back of the new prime 250mm lens

i use LSFD (V' to F') = BFL, instead of BFSD, because "flange-focal-distance" (ffd) no longer work for "mirrorless" cameras with very short BFSD.

in the old SLR or new dSLR era, ffd is more common, for mirrored TTL-OVF designed cameras, where longer LSFD included space for mirror. Others may even have longer LSFD to fit more than just a moving mirror, so obviously optimal lens projection geometry dimensions being even longer was never a bad thing (it was more a good thing)

Sony basically carried over ultra-short-paralle LSFD (top diagram) from its Cybershots, over to mirrorless, but included compromised short LSFD (bottom diagram) designs, too.

in order to work around short LSFD (bottom diagram) poor optical (cheaper compact) lenses, Sony instead resorted to longer LSFD (bottom diagram) to get better optical lenses (pricier, heavier, longer)

■ why i use LSFD (V' F') instead of old ffd:

  • too many newcomers to "mirrorless" think Sony mirrorless has short ffd, and think it's great ... not really
  • reality is: i point out Sony's worse lenses have shorter LSFD (may coincide with ffd); but Sony's better lenses will have longer LSFD (unrelated to ffd). where Sony mirrorless ffd does not really exist (focal distance varies beyond the flange position, or deeper into body, closer to sensor stack)

hope that clarifies my position

Your position is even clearer. That doesn't make it correct. It is still wrong. Ray angles are not determined by the measure you're using.


I make no claim about theta being determined by BFL; while obviously, its pivots on NODAL point N & N' for EFL = irrelevant for PHYSICAL dimensions

Physical dimension MATTER more, because one cannot PHYSICALLY design optics elements that crash into each other ... like fujifilm G 1.4x teleconverter CANNOT have PROTRUSION DIMENSIONS that damages REAR OPTIC of its prime 250mm f4!!!

thus, measuring from N' nodal point (aka P') does NOT play part in LSFD (BFL) !

my point being:

  • short LSFD has: short BFL (includes short EFL, obviously) = shallow low theta
  • long LSFD has: long BFL (includes long EFL, obviously) = (too) steep (too) high theta
  • Consider a true telephoto design. Greater off-perpendicular angles of incidence than you'd think by looking at the rear element location.

EXACTLY: this is long-shallow theta LSFD, or ultra-short-parallel LSFD (both low theta)

  • Consider a retrofocus design. Lower off-perpendicular angles of incidence than you'd think by looking at the rear element location.

AGAIN: low theta a must for great optics

high theta = poor design with extreme convergent theta

Until we get this straight, we can't intelligently discuss the effect of off-perpendicular angles of incidence, about which I also disagree with you.


my point remains:

  • low shallow theta rules best optics: (long LSFD shallow convergence, and ultra-short LSFD = parallel = where sensor is "next optical element" nearly sandwiched to last lens element)
  • high steep theta commonplace on worse optics (short LSFD, steep convergence) ... Sony's high theta surpasses all other mfrs (no exceptions)


dSLRs using LONG LSFD:

  • NEVER need to resort to EXTREME high steep theta ray angle CONVERGENCE
  • because they TYPICALLY use low shallow theta ray angle CONVERGENCE

mirrorless dcams using too short LSFD:

  • EITHER need to resort to EXTREME high steep theta ray angle CONVERGENCE (cheap compact lenses with POOR optics)
  • OR resort ATYPICALLY to using low shallow theta ray angle CONVERGENCE (USING LONGER LSFD like dSLRs) by ADDING extra hollow space in rear of lenses) for more expensive bigger heavier lenses with better optics) ... Sony short LSFD conundrum
  • OR resort to old ultra-short (Cybershot) parallel (zero rear-theta of front-focal designs) with no extreme convergence to worry about

I give up. I have tried to reason with you. You are ignoring years and years of optics in favor of promulgating what is essentially voodoo. I thought that maybe I could get you to try to look at whatever it is that you are trying to say in terms of actual optical theory, but you have resisted that.

I see no hope of establishing meaning ful communications with you now, and thus I am giving up.

Your whole thesis is flawed and serves more to confuse that elucidate, and the features that you are attributing to E mount lenses are just wrong.


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