Checking Accuracy (Boggled)

[kb244]

I got a Minolta Auto Meter IVf and I'm having a woe of a time trying to figure out if its really accurate or not as it is not exactly matching up to my Gossen Lunasix mechanical light meter. Would seem the minolta would give a reading almost 1 to 2 stops slower than the gossen. However I did drop the gossen once a couple weeks ago, and had to adjust it ( so then its like which one is wrong, or is both wrong ). And I've heard about how mechanicals can easily die from droping.

Anyways it doesnt help that when I first got the meter the reading would seem odd where I'll take an ambient reading in direct sunlight and It'll say something like 1/125 @ f/32 at ISO 100 and I'm thinking "Is it really that bright out here?" and I'm hoping that was a one time fluke.

So decided to take another approach Took my Sunpak 5000AF set the back to Manual, at 1/64th power, set the ISO and Aperture to 100 @ f/8 so I can get a distance estimate, shows 1/64th power @ 100/8 will be for 1.6 feet, so I set the minolta in non-corded flash reading mode, set it approximatly 1.6 to 2ft from me point the flash at it, and hit the test button. The meter would show exactly f/8.0 as the reading.

Now I'm not sure if corded/non-corded mode is gona be any different than an ambient reading, but I would assume that if the light sensor recorded a flash burst correctly then the same light sensor would meter sunlight and other ambient light correctly. But least a flash is a controlled form of lighting as opposed to trying to take a reading off say a 60 watt light bulb.

-Tips
-Pointers
-Questions
-Etc?

Oh and if anyone has the Manuals for it (PDF, etc) let me know, apparently konica-minolta no longer hosts them on their site.

 

[Dan Fromm]

Testing a flash meter is easy. Ask it what to do at a given flash power setting for a "medium" target, shoot a color slide/transparency taking taking the meter's advice. And then if the slide/transparency is ok, the meter is doing what it should.

If I were you, I'd send both meters for service. It sounds like you broke your LunaSix good. Also that your IVf arrived out-of-calibration. Rule of thumb: used meters are wrong when received even if they seem to function. Responding to light and measuring accurately aren't the same.

 

[kb244]

Testing a flash meter is easy. Ask it what to do at a given flash power setting for a "medium" target, shoot a color slide/transparency taking taking the meter's advice. And then if the slide/transparency is ok, the meter is doing what it should.

If I were you, I'd send both meters for service. It sounds like you broke your LunaSix good. Also that your IVf arrived out-of-calibration. Rule of thumb: used meters are wrong when received even if they seem to function. Responding to light and measuring accurately aren't the same.

My concern is, sending the minolta in will be like what I heard floating on the net that it cost 150$ and up just to 'fix' the calibration. But when I said responding to the flash, I was refering that if I set the flash up where f/8 would be proper exposure on the camera, the meter would pop up f/8 when I flashed at it, same with other settings. I just didnt have a means to test ambient light and know for sure what EV that light was.

 

[Nick Zentena]

The problem using the flash and just metering is it doesn't prove if anything is right. Or if it's wrong what is wrong. What happens if the flash is putting out F/9 when you set it to F/8? Actually taking a photo gets you closer since you can check if the photo is under/over exposed.

The manuals might be on one of the Sony websites. I think it's Sony. I saw some a few weeks ago while looking for something else.

I don't know those meters. I guess the IVf is a spot meter? The other one an incident? In reflected mode did you take into account how the metered subject reflects light?

 

[Chan Tran]

Using the flash as a standard light source to check the meter is not a very good idea. I found that published guide number especially at fractional setting is not very reliable. I have the Sunpak 5000AF also. I bought 2 used Minolta meter, the flashmeter III and spotmeter M. Both give me reading within 1/10 stop as compared to my brand new flashmeter VI. So I would say they are all accurate.
When you said you got 1/125@f/32 with ISO100 reading, which meter gave you that reading? I would say that it read about 2 stops too high. I don't have the IVf but all Minolta meter has an adjustment for +/- 1 stop.

 

[kb244]

The problem using the flash and just metering is it doesn't prove if anything is right. Or if it's wrong what is wrong. What happens if the flash is putting out F/9 when you set it to F/8? Actually taking a photo gets you closer since you can check if the photo is under/over exposed.

The manuals might be on one of the Sony websites. I think it's Sony. I saw some a few weeks ago while looking for something else.

I don't know those meters. I guess the IVf is a spot meter? The other one an incident? In reflected mode did you take into account how the metered subject reflects light?

I thought I specified the brand above....

Its a Minolta Auto Meter IVf , which is a Ambient/Flash meter.
The Gossen LunaSix is both, you just remove the dome for reflective.

 

[kb244]

Using the flash as a standard light source to check the meter is not a very good idea. I found that published guide number especially at fractional setting is not very reliable. I have the Sunpak 5000AF also. I bought 2 used Minolta meter, the flashmeter III and spotmeter M. Both give me reading within 1/10 stop as compared to my brand new flashmeter VI. So I would say they are all accurate.
When you said you got 1/125@f/32 with ISO100 reading, which meter gave you that reading? I would say that it read about 2 stops too high. I don't have the IVf but all Minolta meter has an adjustment for +/- 1 stop.

Was the minolta that gave that reading, but what I'm gona do today is retest it, I havent had much time since I work 9 hour days, and 7 days a week. Also the Minolta does have an adjustment, but not nearly a stop, more like -/+ .2 to .6

 

[Chan Tran]

I do have a pdf copy of the manual, PM me if you're interested. I assume that you did the test in incident mode. There is a switch on the meter that senses whether the reflected light adaptor is mounted instead of the dome. When this switch is pushed down the meter increases its reading by about 2.7 stops. You may want to check and see if this switch is stuck down or electrically shorted. Sometimes pushing and releasing the switch several times would fix the problem. The way to check if the switch works as intended is to remove the dome and take a reading. Then take another reading with the switch pushed down. You should have 2.7 stops higher reading when the switch is pushed down. If not the switch is defective.

 

[kb244]

As per your note, I'm here at work, bunch of florescent lights near me. I took a reading with the dome on, and got the following (if theres a number after _ is cuz that number was subscripted after the aperture)

With Dome On
1/125, f/1.4_6 @ ISO 100 (I guess if you round up its f/2.0)

With Dome Off ( in the same position, pointing up as well)
1/125, f/4.0_1 @ ISO 100

 

[Chan Tran]

Actually what I meant was to leave the dome off then take 2 readings. One with the switch depressed and another with the switch undepressed. The switch looks like a small pin aprox 1/10 inch diameter and you should see it on the left side of the sensor when you take the dome off. The purpose is to check if the switch still works. If the switch is stuck in the depressed position it would give too high a reading which I think your meter does.

 

[kb244]

Don't see a switch, the dome goes on and you turn it to put it in place, the grooves which the tabs fit into seem to have two metal bars I guess to create tension when you turn the dome on so that it doesnt just fall off.

Here a pic of it, as you'll notice the dome does not depress the botton on the bottom right ( as if it never was intended ) and the needle on the top isnt depressed either cuz the lip of the dom has that section hollowed out when attached.

 

[Chan Tran]

The needle on the top is not supposed to be depressed when the dome is mounted. It is depressed when the reflected light adapter is mounted. I would try to depress the needle and see if it give different reading. It should. If it does not then it may be in the depressed position already (either mechanically or electrically like a short)

 

[kb244]

I think yer right, I actually ended up opening the head and checking the connections. The need on the top when depressed actually supposed to disconnect a circuit, where as the button on the lower right makes a connection, now if one is connected (needle) and the other is not then thats assumes the dome is on, the other way would be when the needle is depressed (top connection disconnected) and button on lower right is pressed (connection made) then thats when the special attachment is on. ( having the needle depressed, and the button not, doesnt do anything so I assume they work together )

After unscreing the head assembly and taking appart the top, and making sure the wires were good, and the solders were there, and that nothing was bent out of shape and re-screwing firmly and such. Everything works fine in two tests.

1) Pointing a digital rebel ( which I know's auto meter works ok ) at a grey card under indoor lighting, and comparing to the light meter @ ISO 400 equiv.

Rebel Gave - 1/60 @ f/2.0
Meter Prior to Disassembly - 1/60 @ f/8
Meter After Disassembly - 1/60 @ f/2.0 (or in between f/2.0 and f/2.8, it swings around a lil between)

2) Daylight reading. Knowing that the meter should give approximatly f/16 when set to 1/250 at ISO 250.

Meter Prior to Disassembly - f/32 - f/45
Meter After Disassembly - f/16

I think I may have fixed it by disassembly and resecuring screws and preasure plates and what not.

IF the preasure plates losen again, i'll just stick a peice of eletrical tape between the contacts for the button on the bottom right so that it'll never be in a depressed state. Since its not like I plan on buying that semi-spot meter attachment any time soon ( heard its supposed to be real expensive. )

Thanks for the help thus far.

 

[DBP]

IF the preasure plates losen again, i'll just stick a peice of eletrical tape between the contacts for the button on the bottom right so that it'll never be in a depressed state.

Would that it were that easy to keep other things cheerful.

 

[kb244]

Would that it were that easy to keep other things cheerful.

I'm having trouble decyphering the grammer of what you just said.

 

[Chan Tran]

By the way if you still need the manual, I have a copy of the pdf file. I tried to PM it to you but I don't know how to do an attachment in PM. So if you want it please give an email address. I think you have a good meter now. I have 3 Minolta meters and their readings are no more than 1/10 stop different from each others.

 

[Dan Henderson]

kb: I suggest you take the Gossen to Peter's Camera Repair at Plainfield and Leonard. He can check the accuracy for you, and then calibrate if needed. I don't know about the digital meter though. He's an old school analog guy. However, I did take my Pentax digital spotmeter in there after it went for a swim and he cleaned, dried, and calibrated it for me.

 

[kb244]

kb: I suggest you take the Gossen to Peter's Camera Repair at Plainfield and Leonard. He can check the accuracy for you, and then calibrate if needed. I don't know about the digital meter though. He's an old school analog guy. However, I did take my Pentax digital spotmeter in there after it went for a swim and he cleaned, dried, and calibrated it for me.

I work at the Camera Center, in Grand Rapids, Mi , so I know who Peter is. I just don't like spending money if I dont have to (not being cheap, just money isnt something I come by in the past).

 

[Claire Senft]

I have a Minolta Auto-meter IVF. It works nicely for me. Set your film speed to 120, set the shutter speed to 125. Go out at 11am to 3 pm. Stand in the sunlight and point the dome directly at the sun and take an ambient reading of the unobscured sun. When I do this my meter reads F16.3. This has been the nicest meter I have ever owned. If you open the battery compartment there is a screw driver adjustment that allows up to a 6/10th stop adjustment. Put the dome in place with the Gossen. Take a reading under the same conditions outlined above. Note the difference. Reset your film speed on the Gossen so that it reads very close to the Minolta. Repeat the readings in the shade. How well do the meters match?

 

[kb244]

Went outside, its about 12 noon right now, sun is out got a slight haze and some clouds but quite distinguishible shadows. The Minolta Read 11.8 , The gossen read between 11 and 16 (near 16 like past 11.5) .

Indoors where I sit. Gossen gives 1/15 @ f/1.4 (ISO 120) , Minolta gives 1/15 @ 1/1.4_3 (ie: .3).

 

[Claire Senft]

That is about as close to each other as you are likely to get. Choose one of these as your primary meter..when you use the other set the film spped bt one third stop difference. I would not spend any money to get the meters recalibrated.