Archived posting to the Leica Users Group, 1999/05/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. - ------ =_NextPart_000_01BE9C64.3091B270 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable > -----Urspr=FCngliche Nachricht----- > Von: Michael Dienert=20 > Gesendet am: Dienstag, 11. Mai 1999 19:54 > An: leica-users@mejac.palo-alto.ca.us > Betreff: How to trim a CL's lightmeter >=20 > dear luggers, >=20 > below is my first attempt to send the procedure to the mail-server. > but to my surprise it didn't show up on the list. so i think the > server rejected it because of a 70k attachment. this attachment was a > ms-word document which i omit this time. if you look at the size of > the html-file you will see how many resrouces on your harddisk and on > the net are wasted by using billy's rubbish. >=20 > hello my leica-(CL)-friends, >=20 > as promised i want to post a procedure how one can calibrate the > lightmeter circuitry of a CL. it's attached in different text = formats. > i hope everyone can open them. i know about the problems with > differing versions of ms-word. >=20 > =20 > any comments and questions to the procedure are appreciated.=20 > i calibrated my own CL exactly this way and am very happy with the > results. i used a gossen-metrawatt lightmeter as a reference. >=20 > so good luck to all CL-users, >=20 > yours >=20 > michael - ------ =_NextPart_000_01BE9C64.3091B270 Content-Type: text/html; name="CL_PROC.html" Content-Transfer-Encoding: quoted-printable Content-Disposition: attachment; filename="CL_PROC.html" <HTML> <HEAD> <META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; = charset=3Dwindows-1252"> <META NAME=3D"Generator" CONTENT=3D"Microsoft Word 97"> <TITLE>Trimming of the LEICA-CL Lightmeter</TITLE> </HEAD> <BODY> <B><P ALIGN=3D"CENTER">Trimming of the LEICA-CL Lightmeter</P> </B><P> </P> <P> </P><DIR> <DIR> <B><P>Some basics on CdS-lightmetering</P> </B><P> </P> <P>The CL=91s lightmeter uses a CdS-photoresistor (LDR =3D light = dependent resistor). The LDR=91s resistance is strongly dependent on = the intensity of light which hits it=91s surface. The relationship is: = the more intensive the light is, the lower the resistance becomes. In a = double logarithmic scale the LDR=91s characteristic is rather a = straight line. <BR> <BR> With the help of a battery and some additional resistors with constant = values the LDR=91s changing resistance is converted into a changing = voltage which is measured with a voltmeter. The voltmeter=91s needle is = what you see in your finder. </P> <P> </P> <P>The energy to operate the voltmeter is delivered by the battery. = Therefore the deflection of the voltmeter is dependent on the voltage = of the battery. Mercury and silver-oxide batteries have slightly = different voltages. </P> <P> </P> <P>LDR=91s have some unwanted features: <BR> <BR> They are not only light dependent but also temperature dependent. This = effect is compensated in the electronic circuit described above.<BR> <BR> Their response to a change of the intensity of light is very slow. = Especially for very low light it may take seconds until the LDR settles = to it=91s final value. So be patient measuring in dim light.<BR> <BR> And last: LDRs change their characteristic over time. And that=91s the = reason why older lightmeters must be calibrated from time to time.</P> <P> </P> <B><P> Finding the circuit inside the CL</B><BR> <BR> The circuitry which converts the LDR=91s signal to the proper setting = of the lightmeter=91s needle is right to the film cartridge. Take the = backcover of the CL away and hold the camera in a way that you would = look on the eyelets of the straps. Then you should see a black = aluminium foil at the side of the groove where the film cartridge = normally fits in. This foil is self adhesive and sticks to the case. = Remove it. <BR> <BR> Beneath this foil you will see 4 little holes. With a little = (electronic) screwdiver one can turn trimming resistors through this = holes.<BR> <BR> The holes and the corresponding trimmers are numbered by Leica as = follows:<BR> <BR> The one nearest to the top of the camera is R3. If you still hold the = camera as described above it is the most left one.<BR> <BR> The next ones are R4, R5 and R6. So from top to bottom (or left to = right) you have the order R3, R4, R5, R6. By the way: R comes from = Resistor.</P> <P> </P> <B><P>Trimming procedure</P> <P> </P></DIR> </DIR> <OL> </B><LI>Put in a <B>new</B> battery. After calibration you must always = use this type of battery (I don=92t mean the maker but wether it=92s = mercury or silver-oxide)</LI> <LI>Set the film sensitivity dial to 17 DIN (approx. 50 ASA)</LI> <LI>Set the shutter dial to =961000-.</LI> <LI>Point the camera to you slide screen and light it with a very = bright light source. Use a good, calibrated lightmeter or another = camera you trust, point it to the screen, read the aperture at 17DIN, = 1/1000s and set the CL=91s aperture to the same value. You can use = whatever lens you want. Now the needle in the finder must correspond = with the notch of the lightmeter. If not, turn R3 clock- or = counterclockwise until it does. Of course you must turn on the CL=92s = lightmeter by pulling the transport lever.</LI> <LI>Set the shutter dial to =9630-. Measure again with your second = lightmeter and transfer the aperture. Turn R4 until the needle is = OK.</LI> <LI>The setting of R4 has an influence on the setting of R3. So you = must repeat the last to steps until the needle corresponds with the = notch at 1/1000 and 1/30.</LI> <LI>Set the shutter dial to -2-. Again, estimate the aperture at 17DIN, = 1/2s, transfer it to the CL=92s lens and now turn R5 until the needle = is in coincidence with the notch. Turning R5 has an influence on the = setting of R3 and R4. So you must repeat the preceding procedures until = you have coincidence in all of the 3 cases.</LI> <LI>Leica announces that this calibration will give you a tolerance of = 2 DIN (film sensitivity)</LI> <LI>A hint: in the original Leica procedure a special calibrated light = source with variable intensity recommended. In my procedure this is = substituted by a screen, any lightsource and a second lightmeter. So = your calibration will not be better than the lightmeter which you use = as a reference. It may happen that from 1/1000s to 1/2s you may not = obtain apertures which you can set on the CL=92s lens. In that case you = can change the intensity of your lightsource. E.g. at 1/1000 use your = slide projector, at 1/2s use a 25W lamp at an appropriate distance to = light the screen. Just take care that the screen is lit well-balanced. = Or at least use the same spot on the screen to measure with the = reference lightmeter and the CL.</LI> <LI>Last step: Set the shutter dial as to measure battery power, press = the battery measuring button and set R6 until the needle is in the = middle of the notch. This trimming has no effect on the lightmeter, it = just calibrates the battery measurement.</LI></OL> </BODY> </HTML> - ------ =_NextPart_000_01BE9C64.3091B270--