Sekonic L188 Meter readings off

[gone]

I just got a Sekonic l188 meter in the mail, but it's readings are about 3-4 stops off. I can reset the ASA and get good readings outdoors, but then they're off indoors. These are CDS meters, got a fresh battery in it, and I see no way to center the needle or adjust anything. This is the first one I've seen that is like this. Any ideas on what might be wrong? It's clean as a whistle inside.

 

[Dali]

Cannot help you as I am in the same situation with a couple of CDS meters.... Batteries were changed (and of the right type), contacts are clean but meters are off and not linear.

 

[ic-racer]

Find another.

 

[MattKing]

Are you using a silver oxide battery?
It could be 42 years old. I know that I'm different than I was 42 years ago ....

 

[bernard_L]

Question: is there a way to accurately meter light to calibrate your light meters? There must be some kind of physics hack, like adjusting rangefinders without infinity. I am thinking about a reliable light source with a known output within predetermined distance from a 18% grey card in complete darkness, but finding a light source like that is probably difficult.

Palm of hand, summer noon, should be Zone VI. Meaning EI 125, 1/250 f/16. Not scientific, but more than good enough for all negative films. Also a critical test for Selenium meters, that usually fail most at high EV, due to increased internal resistance of the photocell.

 

[Chan Tran]

Question: is there a way to accurately meter light to calibrate your light meters? There must be some kind of physics hack, like adjusting rangefinders without infinity. I am thinking about a reliable light source with a known output within predetermined distance from a 18% grey card in complete darkness, but finding a light source like that is probably difficult.

First you must determine if you can calibrate the meter. Can the meter be adjusted for offset and gain? If you determine that you can then you can buy calibrated light source. They are expensive or you can borrow a known good meter to compare. The fact that the OP knew the meter is incorrect he must have some mean to compare.

 

[Nicholas Lindan]

The most likely cause is a CdS cell that has degraded and needs to be replaced.

The problem with finding a replacement is knowing the cell's resistance and sensitivity.

If you can find these specifications then you can buy a replacement cell. If possible get a hermetically sealed cell that won't go bad. Camera and meter makers tended to put very cheesy cells in their products; moisture would get to the cell and, well, cause it to rot.

https://www.digikey.com/en/products...?s=N4IgTCBcDaIMYBMDOACADgCwPYBctwFMAbIkAXQF8g

 

[bernard_L]

The problem with finding a replacement is knowing the cell's resistance and sensitivity.

Finding the proper replacement is virtually impossible. While CdS cells have a linear current-voltage relation (at a fixed illumination), the other relation, current versus illumination at constant voltage, is non-linear; generally, doubling the illumination causes less than doubling the current. That is beneficial for lightmeter design, because the dynamic range of light values is compressed and made more manageable. But that extra parameter --the degree of non-linearity-- makes it virtually impossible to find a cell matched to the lightmeter design and scales. As an example, see the datasheet from one of the cells shown in the ink provided by N.Lindan:

You can see that, going from 2ftc to 100ftc illumination, 50 times more, the resistance drops from 1500ohms to 150ohms, just a factor of 10.

it's readings are about 3-4 stops off

Which way is it off? Telling you to expose more than the correct value? or less?

got a fresh battery in it

Did you clean the battery contacts? Use very fine abrasive paper, or a "fiberglass pen", or an eraser for ink (becoming a rare item). Absent these, try the abrasive powder for kitchen pans, followed with careful wiping.

 

[Chan Tran]

I would just buy another meter. One that uses silicon cell.

 

[Nicholas Lindan]

"Finding the proper replacement is virtually impossible."

Can't argue that. But can you get close enough?

The properties of Cadmium Sulfide are intrinsic to the compound. CdS resistance will usually fall by a factor of 0.7 for each unit change in light falling on the cell and this doesn't change all that much from one cell type to another.

The parameters that do change are the length, width and depth of the squiggly channel of CdS applied to the cell; this geometry determines the dark resistance (not of much interest in this application) and the resistance at the standard 10 Lux illumination. Note that the 10 Lux resistance varies over a nominal 2:1 range and the meter will have a potentiometer to compensate for this parameter.

If you can find a cell with about the right 10 Lux resistance it should work in the application. The problem is knowing the resistance.

The other parameter in CdS cells, their power handling capacity, is irrelevant in light meter applications.

Mr. Racer's advice to "Buy another meter" is probably the best you are going to get.

 

[Sirius Glass]

Send it to Quality Light Metric for recalibration.

 

[hap]

Send it to Quality Light Metric for recalibration.

Sorry to bring bad news. George Melton has retired and Quality Light Metric out of business. I talked to him several times about fixing my Luna Pro S and he said
"no mas".

 

[hap]

George gave me the name Spectra Cine in LA as an alternative. they are not interested in dealing with old meters. They suggested I contact Gossen. They responded that it
is not a service they offer, ie old meters are not of interest to them.

 

[Chan Tran]

George gave me the name Spectra Cine in LA as an alternative. they are not interested in dealing with old meters. They suggested I contact Gossen. They responded that it
is not a service they offer, ie old meters are not of interest to them.

Make a lot of sense.

 

[ic-racer]

I have the schematic for this Rollie 35 LED camera, and have traced the voltages in the circuit. The CDS cell is faulty. You can see my solution that I recommend highly.

 

[gone]

Like you Matt, I've changed a bit over 42 years too, but we're better! I was able to calibrate it by using my N70. The negs look fine. That's the best way to ck meter accuracy Gregg. AF Nikon cameras have meters that are spot on, and you can ck it w/ spot, center, or matrix. However, with this Sekonic, if I calibrate it w/ the Nikon for outdoors, it has to be recalibrated again for low light indoors, which makes it essentially useless.

The best suggestion here is to just buy another meter. The seller offered a full refund, but by the time I add what I paid for shipping to me, then again to them, it doesn't make any sense. Now to figure out which meter to buy. It should be: small, cheap and accurate. CDS is fine for my needs. There's a lot of those on fleabay, the hard part is looking at the descriptions and trying to figure out if it will be accurate. I'm going to look for one that has a screw to center the thing.

 

[Nicholas Lindan]

CDS is fine for my needs. ... the hard part is looking at the descriptions and trying to figure out if it will be accurate.

That's why CdS doesn't make sense any more. Even if it is accurate today it may be a different story next year.

A meter with a silicon cell will not go out of whack. The current crop of small ~$50 digital clip-on meters will stay accurate for a very, very long time.

 

[gone]

You're surely right Nicholas, but I like a dial. Tried some digital meters some years ago and they just didn't work. On a conventional dial meter, I can tell at a glance where all the speeds and f stops are. That's a nice feature to have. Silicon is better, but those meters tend to be big and/or pricey.

 

[hap]

Make a lot of sense.

Well, I wasn't particularly over joyed at their "rationalism". And as far as Gossen is concerned, I figured out how to fix my Luna Pro S and then bought a new SEkonic. I guess they don't really understand how to support their brand long term. One customer at a time.

 

[RalphLambrecht]

Question: is there a way to accurately meter light to calibrate your light meters? There must be some kind of physics hack, like adjusting rangefinders without infinity. I am thinking about a reliable light source with a known output within predetermined distance from a 18% grey card in complete darkness, but finding a light source like that is probably difficult.

not at all;we all have a very constant and reliable light source.Most of us call it the 'sun'. full sunlight between 10am and4pm, regardless of season or location on earth reads almost exactly at EV15.

 

[Chan Tran]

Well, I wasn't particularly over joyed at their "rationalism". And as far as Gossen is concerned, I figured out how to fix my Luna Pro S and then bought a new SEkonic. I guess they don't really understand how to support their brand long term. One customer at a time.

But it makes sense because they are in business to make money and it's tough to make money fixing old meter.

 

[MattKing]

You're surely right Nicholas, but I like a dial. Tried some digital meters some years ago and they just didn't work. On a conventional dial meter, I can tell at a glance where all the speeds and f stops are. That's a nice feature to have. Silicon is better, but those meters tend to be big and/or pricey.

Small and accurate with a dial (of sorts) - a Digisix or Digiflash.
Reasonable, but not cheap.
The meter displays a number (EV), you turn the dial to that number, and all the combinations available are right there.

 

[Nicholas Lindan]

... I like a dial. Tried some digital meters some years ago and they just didn't work. On a conventional dial meter, I can tell at a glance where all the speeds and f stops are.

I agree. I don't know why every meter doesn't have a dial. The lack of a dial is the most anoying thing about hand-held digital lightmeters. The Pentax digital spot meter has a dial you transfer the digital reading to. I like it.

With cheap 16 and 24 bit A/D converters and even cheaper powerful microprocessors making a superbly accurate meter is a breeze compared to the old moving needle analog meters.

Maybe a meter with digital innards could have a 'dial under glass' that the meter rotates with a servomotor when you take a reading. I think that would be ideal. With 3-d printing the costs for tooling a housing are minimal. And the meter dial can be a label from, say, Cincinnati Metalphoto.

I'm afraid, though, there is not a large enough market to support the development costs. I'm tempted, though.

 

[Kodachromeguy]

That's why CdS doesn't make sense any more. Even if it is accurate today it may be a different story next year.

A meter with a silicon cell will not go out of whack. The current crop of small ~$50 digital clip-on meters will stay accurate for a very, very long time.

This is good advice. Most of the CDS cell meters are getting on to 20 or 30 years old. Also, many or possibly most of them required the Mercury battery to serve as a calibration constant because of the 1.35 volt output.

Gossen made some SBC cell meters with dials. They include the Luna Pro SBC and the Super Pilot SBC (these are the US market names).

 

[RalphLambrecht]

Small and accurate with a dial (of sorts) - a Digisix or Digiflash.
Reasonable, but not cheap.
The meter displays a number (EV), you turn the dial to that number, and all the combinations available are right there.

Make a lot of sense.

strange; Gossen fixed two of mine for just €50 each.