Luna Pro Oddity

[cooltouch]

I'm posting my message here because I figure a fair number of y'all are more familiar with light meters than the folks in the other format forums.

I have both a Luna Pro F and a Luna Pro SBC. I've already determined that they are accurate to about 1/3 stop of each other.

I bid on and won over at eBay the variable angle attachment that Gossen made for these meters. It has 15 and 7.5 degree fields of view. I used to have one of these a long time ago that I used often with a standard LP I owned back then, and it worked well. I guess.

Here's the curious thing: Let's say I'm metering an evenly lit scene, like blue sky with my back to the sun. When I mount the attachment to either of my LP meters, I lose 1 stop of light at the 15 degree setting and 3 stops at the 7.5 degree setting. If I use my trusty old Pentax Spotmeter V (a 1 degree field of view), it agrees exactly with with my LP F, which is the way I think it should. Namely, 1 degree of an evenly lit scene should read the same as, say 30 degrees or more of this same evenly lit scene, since the light values are the same.

I examined the angle attachment carefully to see if the lenses that the meter looks through were dirty or fungused up or whatever, and they're quite clear. So, the light falloff is not occurring due to clouded up optics.

As I say, curious. Any ideas what's going on here?

EDIT: Sorry, I probably should have posted this over in the building/repairs area. Think I'll do that now

Best,

Michael

 

[AgX]

That attachment (original designation `tele´) needs correcting of the reading. This should be done by readjusting the scale when it is attached:

With ambient light metering:

15° = +1
7.5° = +3

With flash metering (in case of the Lunasix F)

15° = +1
7.5° = +2

 

[Curt]

My instructions state: Adjust the dial on the meter accordingly.

15 degrees = +1 1/3
7.5 degrees = +3

 

[AgX]

Curt,

I had my attachment not at hand, so I looked it up in the printed instructions.

 

[cooltouch]

Guys, all I can say is "wow." Thanks for your prompt responses! Of course, this eBay find came without instructions. I think I'll tape a note to that effect as a reminder onto the attachment.

Best,

Michael

 

[Curt]

http://www.butkus.org/chinon/flashes_meters/luna-pro_f/luna-pro_f.pdf

I got the information from this pdf for Luna Pro F, I have the attachment too and use this info for the settings. Look at Section IV.

 

[AgX]

Michael,

That `Tele´-atachment has got a silver label on its down-side, with the same figures as I gave above.
That thing is seemingly lost on yours.
(To open that thing one has to take off that label, or, much better, cut the label with a razor blade.)

 

[Ian Grant]

There's no label on my spot (tele) attachment either but the meter scale is marked at 1 1/3 & 3 stops with colour symbols that correspond to the 7.5° & 15° of slider on the attachment.

They must have changed them.

Ian

 

[AgX]

Ian,

Those marks of yours are on the Lunasix 3 (the meter that attachment was originally designed for). Michael has used the Lunasix F and Profisix though. Those have no marks.

That 1/3 stop difference is probably something related to that Lunasix 3.


What is important is that for the tele-attachment (and to my understanding all non- electrically connected attachments) an adjustment or corrected reading at the meter has to take place.
Anyway, one then can calibrate ones meter-scale easily to ones tele-attachment.

 

[Ian Grant]

Not sure about that, I don't own a Lunasix 3, but I do have a Luna-Pro, and another that I've yet to see (as it's in the UK) I think an SBC.

Ian

 

[AgX]

Lunasix 3 = Luna Pro

Lunasix F = Luna Pro F

Profisix = Luna Pro SBC

This double designation is very annoying; especially as even at the official Gossen site those 2nd designations do not show up...

 

[Ian Grant]

Thanks that's helpful.

Ian

 

[cooltouch]

Aqx is correct. Neither my F nor my SBC have the markings at the 1-1/3 and 3 locations. Nor did the attachment still have the silver label. I took care of that, though. I taped a note to the attachment as a reminder to myself.

Best,

Michael

 

[Q.G.]

My Tele attachment already had a note taped to it when i got it: Gossen put directions underneath.
It It says +1 EV for both flash and continuous light at the 15 degree setting.
And +2 for flash, or +3 for continuous light at the 7.5 degree setting.

The mention of flash indicates it was made for the Lunasix F. But also works on the Profisix (and Mastersix).

 

[Curt]

Did Gossen get the information wrong for the attachment on a Luna Pro F then?

 

[Q.G.]

Not that i have noticed.
Could be me, of course.

The manual agrees with what it says on the thing itself.

 

[Curt]

The manual for the Lunasix is different than the manual for the Luna Pro F .PDF I have. The Lunasix is 1,3 with the tele attachment and for the Luna Pro F it gives 1 1/3, 3. Apparently the two meters are different and the Luna Pro F needs an additional 1/3 stop with the tele attachment. I'm not going to lose any sleep over the 1/3 stop because I only have the Luna Pro F. I bought it as a backup to my 1 degree meter. Gossen meters are really nice and mine takes a common 9 volt battery.