Topcon TTL Contrast Modulator

[AgX]

What is the idea behind it?


The metering cell is behind the mirror, with its slitted coating:

Thus just this cross structure is least measured.

 

[cowanw]

Did you see this?
http://www.shutterbug.com/content/topcon-re-super-first-35mm-slr-ttl-metering#ot93SKbRQzRU8rTV.97

 

[AgX]

Thank you: I did not know that article.
But still it does not explain that cross.

 

[cowanw]

The dark lines represent the areas where light is allowed through to impact on the meter. the pattern reflects the chosen optimum between viewfinder brightness and averaging metering. The area of the cross would be brighter in the viewfinder as it lost less light in transmission to the meter. Presumably the engineers at Topcon thought that those areas were most important for composing the image. The Auto version of Topcon had leaf lenses and a different pattern of slits.

 

[AgX]

Typically TTL meters do meter a center spot, or a center-ballasted zone.
That Topcon does the opposite, with that cross. That is puzzling me.

 

[cowanw]

Well it was the first try at TTL! Perhaps they had not made the leap of concept from simple averaging metering. Or, as the concept made the viewfinder 7% dimmer, this was the best compromise.

 

[Paul Howell]

I think Miranda used a similar concept on the Senormate and Sensormate EE, slits on the mirror with the sensor in , rather than a cross hatch Miranda metering used a bottom weight pattern. The down side is that over the years the constant slapping of the mirror takes it toll on the connections.

 

[AgX]

The down side is that over the years the constant slapping of the mirror takes it toll on the connections.

Pentacon avoided that by locating the cds-cell at the side of the mirror-box and mounting a light-reflector system at the rear of the mirror, reflecting the light laterally.

 

[Paul Howell]

The other thing is that being bottom weighted, worked well for landscapes not so good with a vertical, the EE has a spot meter as well as average, when using the Sensoret I use a hand held meter.

 

[wiltw]

The Topcon RE Super (a.k.a. 'Super D' in USA) was the world's first TTL metering SLR to be offered commercially, launched about 1963. The mirror pattern was on the Super D, the D-1, and the Auto 100. Only the Auto 100 was leaf shuttered, the Super D was horizontal focal plane, and the D-1 used the Copal vertical focal plane shutter.

The Topcon 0.05mm wide pattern allowed 7% of the light to go to a CdS cell on the backside of the mirror, without visible darkening of the focusing screen. The pattern was designed to give a full area averaged metering, and was designed to permit metering no matter which focusing screen, and even with the pentaprism removed from the camera. No literature existed for why the apparent 'pattern'.

Today's dSLRs pass significant amount of light thru the semisilvered reflex mirror to the metering sensor, which is why the AF cameras use focusing screens which are lower in focus precision, being brighter and finer textured than film camera manually focused SLRs. The Topcons could focus with usual (coarser) focusing screens.