16 Unique Features That Your Camera Probably Doesn't Have

Started 3 months ago | Discussions thread
ahaslett
ahaslett Veteran Member • Posts: 8,871
Re: Telecentric .... or not.

Raist3d wrote:

ahaslett wrote:

Muster Mark wrote:

Guy Parsons wrote:

Guy Parsons wrote:

I am sure that my bunch of old 4/3 lenses stored somewhere are a mix of possibly "telecentric" and impossible to be "telecentric" lenses, due to that rear element measurement.

So it was mainly to do with marketing - the reliable source of most baloney in any industry.

When the sun comes up here in Oz I will look through a few of the old 4/3 lenses to see how they obey the test stated in Wiki as "Image-space telecentric lenses have an exit pupil infinitely far in front of the lens; that is, if one looks in the back of the lens, the image of the aperture is very far away." I'll try to remember to report back on that.

Back again after looking at my old 4/3 lenses.

Lens.................Rear element approx........telecentric (as per view test above)

50/2 macro................23mm.....No, but a very mild effect of aperture seems further away.

35/3.5 macro..............15mm................................No

14-54/2.8-3.5...............19mm.........................No, but very very mild effect like the 50mm

11-22/2.8-3.5................19mm..............................No

14-45/3.5-5.6.................18mm.............................No

40-150/3.5-4.5................21mm.......................No, but very very mild effect like the 50mm

40-150/4-5.6......................13mm...........................No

The last lens came with a very early E-PL1 kit and with the MMF-2 to adapt it to the E-PL1. The rear element needs to be about 22mm or bigger to allow any chance of true image side telecentricity.

So nothing there that leads me to believe that "telecentricity" was a global design feature in the 4/3 lens range. The very mild effect noted on some of the lenses made the aperture look as though it was slightly further inside the lens than where I expected it to be, but certainly not distant as the Wiki page test indicated.

Summary: As usual, the telecentric issue was 99.99% baloney from the marketing people, and people believed it without testing if it was true.

To get the aperture visible, I set the A mode to f/5.6, set a button to DOF preview, then held down the button while removing the lens keeping the camera turned on. That way the aperture stays at f/5.6 on the removed lens and makes it easier to do the view test. No damage happens as pressing the lens release always disconnects power from the lens.

I think before judging it to be 99.99% baloney one should compare to lenses on other systems (I am not saying you personally should have, sounds like a lot of work), but I don't think we have the information to judge yet. Their stated goal was to have more perpendicular light across the frame. Obviously a telocentric design means a mathematically 90 degree angle of incidence. It doesn't need to be mathematically perfect to get the optical benefits though.

You showed it can't actually be perfectly telocentric on a lot of the lenses, or perfectly 90 degrees. Ok. Sure, that doesn't means the angle of incidence is not a lot closer to 90 degrees than traditional dslr lenses which was the point. Anyway, I am sure if you looked at a 2x crop of the central part of a FF sensor, it would look pretty telocentric too, so ultimately I am not sure what to think I guess.

But the article is nonsense because it is plain wrong about MFT lenses. They are neither telecentric nor need to be.

Yes but in this sub-thread we are talking about whether 4/3rds was or not.

Andrew

The SHG lenses are pretty special.  Sadly the used price of the 14-35/2 never touched my target price.  Close but not quite there.

LCE on The Strand had an 80-250 for several years and I used to remind myself just how big it was on every visit.

Andrew

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