Gossen Lunastar F2 spot accessory question

[Ulophot]

Probably few around now have had experience with this, but it's worth a try.
The accessory is the 5-degree spot attachment for the Lunastar F2. Note that this is not the same as the 7/15-degree LunaPro attachment. I would like to know if, when attached, the reading remains the same, if reading, say, a large gray card, or if the attachment requires some compensation.
I ask because I think I recall mine needing none (again, unlike the LunaPro attachment, previously owned); that is, the reading of a suitably large even-toned, even-value surface remained the same with it on or off. But it has been a good while since I used it. Attaching it now, it needs compensation. I no longer need it, but I don't want to sell it claiming i is working properly if it is not. I cannot find documentation on it.

 

[AgX]

The manual of the meter does not say so. However it states that the sensitivity of the combo is reduced by several stops. With the much older attachment "Tele" for the Profisix etc. one has to manually re-set the dial by some stops.

But nevermind: just aim your meter at a plane of even luminosity that extends beyond the nornal angle of view of 30°. Meter, and then mount the attachment and meter again. If the reading remains the same, you do not have to set anything.

 

[Ulophot]

The manual of the meter does not say so. However it states that the sensitivity of the combo is reduced by several stops. With the much older attachment "Tele" for the Profisix etc. one has to manually re-set the dial by some stops.

But nevermind: just aim your meter at a plane of even luminosity that extends beyond the nornal angle of view of 30°. Meter, and then mount the attachment and meter again. If the reading remains the same, you do not have to set anything.

Thank you for checking. As I said, it was trying to indicate, it does give a different reading now, roughly 2.5 stops; I thought it had previously not done this, which was a nice change form the LunoPro, as I seem to recall.
If others have different experience/results, please chime in. Thanks.

 

[AgX]

Sorry, I did not realize that you got 2.5 stops difference in reading.

The matter is complicated, as 2 things matter.
-) the metering angle
-) the aperture of the attachment lens
-) the sensor size within the meter
(This makes it in the case of the "Tele" atttachment on Lunasix F even more comopex regarding re-setting, than in your case.)

 

[AgX]

I was puzzled by that 2.5 stops as the stated loss in sensitivity for the combo compared to the pure meter is larger.
But I realized that there is a manual for your attachment itself, and it says that the sensitivity compensation is taken care of automatically.

Now we have to find out where your 2.5 stops deviation comes from. Weird....

 

[Ulophot]

The manual makes perfect sense then: if the meter normally compensates automatically, it would then render the same reading. When mine stopped doing so -- I was obviously right that the readings used to be identical -- it was due to a malfunction. This could be due to the servicing the meter received -- a lost connection to the electronic contact that the spot attachment uses. It's not something I need to deal with any longer, but I am grateful for having the mystery evidently resolved.

 

[AgX]

What I meant as puzzling was, that with a broken contact the difference in reading should be bigger.
I advise to check the difference in reading you get before any inportant metering so to be sure on the compensation to set.