Leica M5 metering with the Zeiss Biogon 25 mm f/2.8

[john_falloon1]

<p>Can someone provide me some guidance on how to meter my Zeiss 25 mm Biogon on my Leica M5?<br>

What framelines should I be using. I have seen some people say that it is the "90 mm" frame selector - push the frame selector to the extreme right.<br>

Would it be better to use a hand held incident / spot meter (a Sekonic 758DR) instead of using the internal M5 meter<br>

with this wide 25 mm. Biogon.<br>

Any thoughts on this combination would be most appreciated.</p>

<p>John Falloon</p>

[SCL]

<p>The M5 instructions state that metering with the Elmarit 28/f2.8 (SN >2314920) the metering field is the 90mm frame, no mention is made of metering with wider focal length lenses. I would suggest just noting the reading you get with your Biogon mounted and and compare the results to a handheld meter (which you should know the angle of acceptance of as well) against a gray card . If they are similar or match, you're good to go. If not, then you would want to take meter readings of the light and dark areas and average them (assuming you want to expose for average readings of a scene).</p>

[christopher_junker1]

<p>My understanding is the M5 meter captures only an 8mm diameter circle through the mounted lens. The actual lineal width and height captured by the meter will vary greatly by the mounted lens's focal length and your distance from the metered object. As the meter is very close to being what is known as a "spot" meter and not a "weighted average" meter biased to the middle of the entire viewing frame like an SLR, an M5 user needs to remember that what is being metered is just what is in the spot, not the entire frame. The meter will capture a great deal of what you see through the accessory shoe mounted 25mm finder, considerably more than what you see M5's meter reading in the camera viewfinder. The M5 meter is accurate only for the metered area, but a 25mm lens is actually metering a much wider area that you can't see in the 50mm frame lines of the M5 viewfinder. Metering works, but you need to recognize and adjust for the wider metered area you aren't seeing in the M5 viewfinder.</p>

[rgerraty]

First, I mounted mine without thinking. It's ok on the M5. I use sunny 16 or a hand held. If I want a meter reading with the

camera I point it to the ground to cut the sky out of the metering frame.

[aplumpton]

<p>My subjects usually have widely varying reflectances and with a 21 mm on my M9 and a sunny day I just point it at a clear blue portion of the sky and compare that with the reading I get when pointed at the subject. The blue sky reading (not always equivalent to "sunny f16") is often better than the partial field metered result. On a cloudy day, a spread of foreground rich green grass comes close to an average reading, if I am looking for an average reading.</p>

[Bill Blackwell Images]

<p>The M5 has no 28mm framelines (that's what the 25mm Biogon brings up on an M6/7/P). The 28mm framelines are paired with the 90mm framelines on those cameras, so your M5 thinks it's looking into a 90mm lens. </p>

<p>The M5 meter is a spot meter, so the meter reading will be coming from what would approximate your M5's RF patch.</p>

<p>Hope this helps.</p>

[rgerraty]

<p>No Bill, the area metered is not constant and expands with increasing field of view of the lens. The manual details this for the frame lines supplied, the metered area being the next smallest bound area, specifically defined for the 50, the RF patch for the 90, the 135 frame lines for the 35, and the 90mm frame lines for the 28, even though there aren't 28 frame lines. With a wide angle like a 25 the metered area will be much bigger than the RF patch and bigger than the 90mm frame lines.</p>

<p>Arthur, I am not sure what you do with the sky reading. Even pointing a 21 straight ahead will produce underexposure if letting the in-camera meter determine the exposure. From 28 and wider, inclusion of the sky will cause consistent underexposure by an automatic meter like the M9's and with manual settings determined only by a behind the lens meter. Maybe a sky reading would work if you then add two stops of exposure.</p>

[aplumpton]

<p>Richard, I cannot explain the physics to you, but here in Quebec when you point the in camera meter (M8 or M9 in my case) and lens at the blue sky (N.B: away from direct sun), taking care not to include anything else (a bit difficult with a 21 mm lens), the reading is very close to being right on for normal shots (anything from a grey card to subjects before the lens of widely varying reflectivity).</p>

<p>With any selective or "near" spot in-camera meter and various optics of differing fields of view, and the attendant difficulty of measuring what you want to, this method works well. Otherwise, I like to use a true spot meter and place the various point readings (including statistiacal averaging) as I may wish.</p>

[christopher_junker1]

<p>The M5 meter reads exactly what is in the meter spot with a 50 mm lens. The 50 mm lens on a 35 camera has a horizontal field of view of 39.6 degrees. The horizontal field of view for the 25 mm lens is about 76 degrees so 36 degrees total or 18 degrees on either side of the field of view are outside the M5 meter reading area. Close up ithe meter reading may be accurate, however the further the object is away from the camera, the greater horizontal (and vertical) footage that is outside the meter reading area and the greater potential for M5 meter reading error. If the M5 and 25 mm lens are going to be used for distance as well as close in work, a spot meter is probably a good idea. </p>

[rgerraty]

Thanks Arthur. Australia latitude 35 S is very bright but I will test it out here.

[knut_schwinzer]

<p>Use the upcoming 90mm generousely as the meter patch and you should be fine.<br>

As the meter is 8mm in diameter, you can just think of it as the center 1/3 of the height of the neg - 24mm. Apply this rule of thumbs to the external finder and you're done.<br>

Hope that helps.</p>