An Unusual Metering Phenomena

[stevewillard]

I am not sure if I can put this into words so please be patient with my fumbling.

Currently. I am using a Zone VI modified Pentax Spot meter. There are times at dusk or

dawn when I meter areas in the scene that seem to contradict my observations. In

particular, there have been far off areas that appear to be very dark with minimal detail.

My expectation is that they would meter at a Zone II placement relative to other values.

However, when I actual meter these dark areas they have the same EV value as some of the

brighter areas in the scene that are closer to a Zone VI or VII placement.

 

For example, when I metered the dark mountain in the center background of the attached

photograph, I got the same EV value as the brightly light green grass throughout the

photograph.

 

Can anyone explain this phenomena?

[silent1]

I think your meter isn't looking the same place as the aiming device attached to it.

 

Try metering a very small light source in darkness -- the Moon, distant streetlight, etc. -- you're likely to find you have to move the meter around a lot, and may find it quite difficult to get the light to meter at all if your meter has a narrower "spot" than one degree.

 

Since I'm not familiar with that meter, I'm not sure how to recommend correcting the problem -- but if Zone VI modified the meter (presumably adding Zone System markings, possibly narrowing the field of view) they'd be the first place to turn for problems with aiming.

[capocheny]

Stephen,

 

I believe the meter you have is a 1 degree spotmeter and, if this is the case, then you

should be measuring the area you're pointing it at.

 

Your confusion is that you're forgetting that you're "placing" the Zone II reading. In

other words, when you "read" the area with your meter you're actually still in Zone V.

As a result, when you read another area (a highlight area) and compare it with the

Zone V reading... of course, you're going to be closer to the Zone VI or VII reading.

 

However, if you "place" the initial reading onto Zone II and, THEN, compare this to the

Zone VI or VII reading...the spread will now be greater. If the spread is greater than

that which you desire then you would have a contraction situation. If the spread is

less than that which you desire then you would have an expansion situation. But,

whatever the case, PLACE the initial reading and then see where the highlight

readings fall in the scene.

 

The concept is a bit confusing and it might be useful to draw the situation out onto

paper. For a good book on this... look for "The Zone System Simplified." I'm sorry I

can't recall the name of the author (Zakia???). Perhaps someone else on this site will

remember. It's about 81/2x11 in size with about 275 or 300 pages... it's quite a good

read and will get you on the right track.

 

Hope this makes good sense.

 

Cheers

[capocheny]

Addendum to my previous reply...

 

Stephen, sorry I didn't notice the example... if you're getting identical readings in

both the dark mountain area and the brightly lit green of the field then I think the

problem lies with your meter's calibration/cell.

 

I would think that the reading would be somewhere in the neighbourhood of 125@f16

(if you're using ASA 100 film). The darker area of the mountain appears to be about 2

stops darker from what I see (and based on my computer's screen.)

 

I'd consider sending the meter into Pentax or back to Zone VI for adjustments...

 

Cheers

[User_503771]

Have you tried a test to see if the meter is measuring the the spot that is represented by the circle in the view when you're looking?

 

One of the posters above suggested that you try metering something like a streetlight at night or the moon. I'd say, the smaller the target the better. Try getting a reading when the streetlight is right in the circle in the middle of the view. Then swing the meter around a bit and see if the EV value reading goes up. Could be that the alignment is off, that the 1 degree reading is coming from somewhere outside the little circle.

 

Another thing might be flare. Perhaps if you put a lens shade on the meter? But, that being said, that dark mountain area in the print looks far too big to be giving you that identical reading, even if flare is the culprit.

 

I don't know that meter, but if I recall correctly, the Zone VI modified ones are the 1 degree-only spot meters, not the 1/21 degree spots that Pentax made. But I'm not sure. SO, is it the meter that gives a reading for both 1 degree and 21 degrees? If that were the case, maybe you need to change the setting.

 

I did a test when I first got my old Soligor 1 degree spot (not modified) to make sure that the meter measures what's actually within the little circle. I have noticed that sometimes, I think the reading is influenced a little bit by flare, but it's not that big a difference.

 

The other poster above, who suggests getting the calibration electronics checked, makes good sense. Perhaps you should call Zone VI first and inquire; maybe they're familiar with the problem already.

 

Oh, one more thing! How old are the batteries? I remember once I started getting weird readings from a Luna Pro, and these cleaned right up when I got and installed new batteries for it.

 

Let us know what happens.

[alec1]

Yes, Stephen, it does sound like your meter needs recalibration if your descriptions are correct.

 

However, the solutions presented so far don't help much. First, Pentax won't work on the meter because Zone VI replaced the metering cell with a better one. Second, Zone VI does NOT Exist anymore. It went out of business years ago. Calumet bought it, and owns the name. Either send it to them, or [my choice] send it to Richard Ritter at: http://www.lg4mat.net/ He performed the meter modifications for Fred Picker at Zone VI and knows more about them than anyone. Fine fellow too!

[jakub_ulanowski]

Maybe <a href=http://kazzuya.com/duddie/pics/misc/illusion.jpg>this picture</a> can explaing the phenomena. Btw, how is this effect called?

[d_poinsett]

If your meter appears to be working in other settings, I would be very suspicious of flare. Given the orientation of the sun in your example, a little crud on the meter lens is all it would take.

 

You don't say whether you are using the digital or analog Pentax Spotmeter. I'm under the impression that the lens coating on the digital model is somewhat better than that of the analog model and more immune to flare.

 

The Zone VI modifications include improvements to minimize internal flare but I don't think they alter the lens. Any dirt/dust/grime on the lens would cause serious flare even with good coatings and internal baffling.

[l_a_k_h_i_n_d_e_r]

I think it is Flare. The closer you are to a brighter region, more skewed are the meter readings for dark areas. Even if the lens flare is well controlled, a minor 0.1% leakage from the brighter area will jack up the exposure reading easily by a stop or more! After all, this is a logrithmic scale, and a contasty shot with 10 EV range can easily bring zone 0 to zone 1, with 0.1% flare!

[stevewillard]

I have been out of town for the past several days, so I am sorry about being tardy

with more information. I just love the intelligence that comes to bear at this site. We all

benefit from it, the beginner and the expert.

 

I have notice this behavior over many years. I have also metered hundreds of scenes

throughout that time, and I have always ended up with a correct exposure. I did meter a

bright light

source in the dark, and the results I expected did occur. So, I do not believe the meter

guts are the problem.

 

To get a correct exposure for the picture I included, I ended up metering the shadows in

the riverbed. The reading I got there was what I expect. If had relied on the dark

mountain shadow reading in the background, the exposure would have been wrong.

 

My suspicion is flare. The problem always occurs with backlight subjects as seen in the

picture and noted above. I believe this phenomena is closely related to pre-exposures

outlined in Adams book the "Negative". This technique is used to bright shadows by

adding an even layer of light to the entire negative (flare in my case). The concept

demonstrates a little extra light can elevate the shadows by one or two stops while having

almost zero impact on the highlights. In my case. the flare probably was extreme and

elevated the mountain shadow reading to almost the same level as the highlights. When I

metered the shadows in the riverbed, my meter was pointed downward, and there was

probably little flare. Hence the correct reading.

 

I did not make this connection until I read all your responses. Thanks you. As a result, I

intend to build myself a long tubular lens hood for my meter and use it when metering

into the sun. I will soon find out if this helps. Thanks for all your comments.

 

-Stephen

[d_poinsett]

A couple of related points...

 

One, in addition to flare, atmospheric haze can also raise the tonal value of shadow areas and reduce contrast in outdoor scenes of long distance vistas. These effects can be substantial (1 or 2 stops) even in relatively clean air and at shorter distances also.

 

Two, whatever the meter sees, the film might see. In other words, if your meter measurements are being affected by flare and atmospheric haze, it is possible for the camera to be affected. Lens coating, compendium shade, internal baffling and reflections can be different between camera and lens but they can be similar too. Meter measurements that seems 'off' under conditions discussed in this thread may actually be a relatively accurate indication of what the film will see.