Pentacon Six TTL Prism Prisma Circuit Schaltung

Deutsch weiter unten...

Attention: On hold; some additional research needed...

The original text is in the next contribution. This version I try to keep updated that readers can find the relevant information in an easy way.

Calibration

The following picture shows the meter from the top. The leatherette covering the adjustable resistors is removed.

Anhang 80779

R1 and R2 are used to calibrate the sensitivity of the ISO / Time Dial respectively potentiometer.
R3 is used to "calibrate the needle". The screwdriver has an attached self-adhesive paper which indicates the angle. The following recipe assumes that you are familiar how to operate the Pentacon Six and its meter prism.

The preliminary recipe may allow you to calibrate your camera to normal light condition. The reason and usage of R4 is still not completely understood and hence not used. My feeling however is that R4 allows to calibrate for two different sets of light conditions: Bright light conditions with R4 used and low light condition with R4 not used. This would explain why R4 is shortened for stop down metering (see at circuit).

Preliminary Recipe:

1. Determine the angles of R1 and R2 and mark them by lines. Take care to not change them!
2. Determine the angles of R3 and R4 and mark them by lines.
3. Turn potentiometer R4 completely to the right.
4. Turn potentiometer R3 half the angle towards right as you turned R4.
5. Use a gray card or an appropriate replacement (e.g. grass) and measure it with a trustable camera at ISO 100 on a sunny day. Take care that there are no light consuming filters on the lense! Read the time for e.g. iris 16.
6. Set the Pentacon Six meter to open iris of the lense (e.g. 2.8), to the respective ISO (100) and the respective time (e.g. 125) to the respective iris e.g. 16.
7. If the needle is not in middle: turn R3 left/right until needle is in middle
8. Set the aperture of lense and meter to 16. Set also time ring of the meter (e.g. 125 at iris 16).
9. Stop down the lense (Never forget to stop down the lense at that point!!) and prove whether needle is in middle. If yes: Done. If not: prove the deviance by changing time ring. If error is small (less than 1/2 time value, e.g. between 60 and 125 or 125 and 250) following improvement may be possible without changing R1 and R2: set time back (e.g. 125 at 16) and carefully re-adjust R3 so that needle goes half way to middle. Go back to 5. If error is bigger: R1 and R2 need calibration.

R1 and R2 need calibration: Be careful! Both, R1 and R2, must be calibrated to the same value. While R1 has 0 Ohms when turned to left (counter clock wise) R2 has 0 Ohms when turned to the right (clock wise).

10. (To be done only once) Make sure that you marked the original settings and that they are visible!
Turn R2 completely to right and R1 completely to the left. Is the angle you turned to right respectively left identical? If yes: turn them back to original setting. If no: is one of them approximately 60-90 degree and the other far away? If yes: set both to that angle between 60-90 degree (since this seems to be the original calibration...). If no: set them both to an angle of approximately 80 degrees. If you changed a setting continue with step five otherwise 11.

11. Mark last positions. Change both resistors R1 and R2 by approximately 15 degrees (e.g. R1 to left, R2 to right). Repeat steps 5-9. If now worse: turn 15 degrees from last position in other direction (e.g. R1 to right R2 to left). Repeat step 11, maybe with smaller getting angle, until success in step 9.



The source and a variant

This recipe is mainly based on some contributions by Subbarayan Prasanna. He explains how to calibrate a Praktica MTL ( https://www.photo.net/discuss/thread...ok-for.337096/).

In step 11 you may also follow his suggestion to start with 0 Ohms respectively 0 degrees and change from there (my recommendation: initially by 30 degrees each). Here his explanation:

"Try and keep VR2 (Here R1!) and VR3 (Here R2!) as low as possible. Then check if the needle moves faster and gets more sensitive. You should be able arrive at a reasonable level of indication...Since your needle is moving freely now keep VR2 and VR3 equal [or near equal] and try adjust VR1 (Here R3!) to get the needle to zero. In the absence any instrumentation and specifications from the factory this seems to be the way to do it."

Another source

Another instruction can be found here: https://esclo.wordpress.com/2009/07/26/ttl-metered-prism-p6-part2/. After using this instruction my stop down metering did not work anymore at all. In my opinion this instruction has some errors. Therefore I had a look to the circuit of the Pentacon Six meter prism and found out, that it is more or less the same as in the Praktica TL series as described by Subbarayan Prasanna. Nevertheless from this source I borrowed the idea to stop down the lense rather than to look for other light conditions for calibration check for R1 and R2.

The circuit

The following picture shows the top view of the circuit.

Anhang 80746

The pins of R1, R2, R3, R4 are numbered 1 (middle), 2 and 3. The ISO /Time Resistor including some mechanics is visible in the middle. The light dependent resistor LDR is not visible in the picture as well as the switches S1 (on/off) and S2 (hidden under the ISO/Time resistor).

The next figure shows the circuit:

Anhang 80747

By measuring the maximum Ohms R1, R2, R3 seem to have 20K while R4 has 7,5K or 10K.

R1 and R3 are set to higher Ohms when turning right, while R2 and R4 are set to higher Ohms when turning left.

Interestingly R4 is shortened when the prism is set to stop down metering (S2 closed). Hence for me right now it makes no real sense to use R4 for calibration.

Needle calibration

Another finding is, that the needle of the meter is not in middle/zero when the prism is switched off which may cause problems with different voltages. For me it was not possible to calibrate the needle to zero: I could not turn the screw with my available screwdrivers.

Open issues

Open questions so far: why the shortened R4? Improved calibration? Which type of photo resistor is used?

Suggestions for improvement welcome!

Deutsch:

Der orginale Text ist im nächsten Beitrag unten. Diesen Text halte ich aktuell, um Notwendige Informationen leicht zu finden.

Demnächst hier: Kochrezept zum Abgleichen. Bitte derweil wenn möglich auf Englisch lesen!

Ich wollte mein Prsma neu kalibrieren und habe dazu eine Anleitung gefunden (https://esclo.wordpress.com/2009/07/...rism-p6-part2/). Danach hat allerdings die Arbeitsblendenmessung nicht mehr funktioniert. Auch sonst kam mir die Ausführung etwas eigenartig vor und ich habe mein Prisma aufgemacht, um die Schaltung zu analysieren.

Die Anschlüsse der Widerstände R1, R2, R3 und R4 habe ich Ausgehend vom Mittenanschluss mit 1 , 2 und 3 im Uhrzeigersinn nummeriert. Der Iso Zeit Potentiometer mit Teilen seiner Mechanik befindet sich in der Mitte. Der Photowiderstand (LDR) ist nicht im Bild, genauso wie die Schalter S1 (an/aus) und S2 (versteckt unter dem ISO/Zeit Poti).

Durch Messung im eingebauten Zustand scheinen die Potis R1, R2, R3 jeweils 20KOhm und R4 7,5KOhm oder 10KOhm zu haben.

R1 and R3 werden im Uhrzeigersinn gedreht größer, R2 and R4 gegen den Uhrzeigersinn.

R4 ist kurzgeschlossen (S2 zu), wenn das Prisma auf Arbeitsblendenmessung gestellt wird. Von daher erscheint es mir unsinnig R4 zur Kalibrierung zu verwenden.

Die Nadel der Anzeige ist nicht in 0, wenn das Prisma ausgeschaltet ist. Das kann Probleme bei nicht stabiler Batteriespannung verursachen. Ich konnte die Nadel aber nicht auf null kalibrieren, weil ich mit meinen Schraubendrehern die entsprechende Kalibrierschraube nicht drehen konnte.

Derzeit offene Fragen: Warum wird R4 kurzgeschlossen? Mit welchem systematischen Vorgehen kalibriert man das Prisma? Welcher Typ von Photowiderstand ist verbaut?

Verbesserungsvorschläge willkommen!

Deutsch weiter unten...

Original text.

I wanted to calibrate my Pentacon Six TTL prism and found an instruction (https://esclo.wordpress.com/2009/07/26/ttl-metered-prism-p6-part2/). After using this instruction stop down metering did not work anymore. Further I had some general doubts about the instruction which made me opening the prism to analyse the circuit.

The following picture shows the top view of the circuit.

Anhang 80746

The pins of R1, R2, R3, R4 are numbered 1 (middle), 2 and 3. The ISO /Time Resistor including some mechanics is visible in the middle. The light dependent resistor LDR is not visible in the picture as well as the switches S1 (on/off) and S2 (hidden under the ISO/Time resistor).

The next figure shows the circuit:

Anhang 80747

By measuring the maximum Ohms R1, R2, R3 seem to have 20K while R4 has 7,5K or 10K.

R1 and R3 are set to higher Ohms when turning right, while R2 and R4 are set to higher Ohms when turning left.

Interestingly R4 is shortened when the prism is set to stop down metering (S2 closed). Hence for me right now it makes no real sense to use R4 for calibration.

Another finding is, that the needle of the meter is not in zero when the prism is switched off which may cause problems with different voltages. For me it was not possible to calibrate the needle to zero: I could not turn the screw with my available screwdrivers.

Open questions so far: why the shortened R4? How to calibrate in a straight forward way? Which type of photo resistor is used? Most likely the circuit is with except of R4 more or less standard, so that somebody may know it.

Would be good to find answers. In the future I could do some further investigations, e.g. soldering off the meter to determine its resistor and how much Amps the meter needs for which angle in order to do some simulations.


Deutsch:

Orginaler Text

Ich wollte mein Prsma neu kalibrieren und habe dazu eine Anleitung gefunden (https://esclo.wordpress.com/2009/07/...rism-p6-part2/). Danach hat allerdings die Arbeitsblendenmessung nicht mehr funktioniert. Auch sonst kam mir die Ausführung etwas eigenartig vor und ich habe mein Prisma aufgemacht, um die Schaltung zu analysieren.

Die Anschlüsse der Widerstände R1, R2, R3 und R4 habe ich Ausgehend vom Mittenanschluss mit 1 , 2 und 3 im Uhrzeigersinn nummeriert. Der Iso Zeit Potentiometer mit Teilen seiner Mechanik befindet sich in der Mitte. Der Photowiderstand (LDR) ist nicht im Bild, genauso wie die Schalter S1 (an/aus) und S2 (versteckt unter dem ISO/Zeit Poti).

Durch Messung im eingebauten Zustand scheinen die Potis R1, R2, R3 jeweils 20KOhm und R4 7,5KOhm oder 10KOhm zu haben.

R1 and R3 werden im Uhrzeigersinn gedreht größer, R2 and R4 gegen den Uhrzeigersinn.

R4 ist kurzgeschlossen (S2 zu), wenn das Prisma auf Arbeitsblendenmessung gestellt wird. Von daher erscheint es mir unsinnig R4 zur Kalibrierung zu verwenden.

Die Nadel der Anzeige ist nicht in 0, wenn das Prisma ausgeschaltet ist. Das kann Probleme bei nicht stabiler Batteriespannung verursachen. Ich konnte die Nadel aber nicht auf null kalibrieren, weil ich mit meinen Schraubendrehern die entsprechende Kalibrierschraube nicht drehen konnte.

Derzeit offene Fragen: Warum wird R4 kurzgeschlossen? Mit welchem systematischen Vorgehen kalibriert man das Prisma? Welcher Typ von Photowiderstand ist verbaut? Wahrscheinlich ist die Schaltung mit Ausnahme des R4 ziemlich Standard, so dass vielleicht jemand die Fragen beantworten kann.

Es wäre schön wenn wir Antworten dazu finden. In Zukunft kann ich vielleicht nochmal Zeit investieren, um das Anzeigeinstroment abzulöten damit der Widerstand und die für welchen Ausschlagwinkel notwendige Stromstärke bestimmt werden kann.

Der R4 wird wohl verwendet um hohe Lichtstärken zu berücksichtigen. Mir ist noch nicht ganz klar nach welcher Systematik abgeglichen werden muss.