true aperture values of CV 15 mm

[joop]

Since some time I started shooting slide film (sensia-100) in my non-metered M

(M4) the 15 mm shot are consistantly underexposed, while other lenses deliver

good results. It seems the true values of the f-stop differ from whats noted on

the lens. With this lens I shoot mainly at f/8 and f/11 to avoid/reduce vignetting.

Did anyone else notice the same?

Before I used my hexarRF for slides, since that one meters TTL, i did not have

this problem. Due to larger exsposure lattitude, I never noticed it before with

Black-White films in my M4. I'll do a test making some over-exposures +0.5 EV.

Any comments? Thanks,

<br>

<br>

<center><img

src="http://www.nat.vu.nl/~mes/SCAN/15mm/paulstefan0002.jpg"></center> </p>

<center><i>What should we do? (CV 15 mm) </i></center>

[al_kaplan1]

I've been shooting a lot of film with my 15, but mostly B&W and no slides. I tend to be "generous" with exposure on negative film, both color and B&W. I doubt that the 15 is giving us a full equivalent of the marked f-stops because of the number of elements and air/glass surfaces. You're the lucky bugger with both an M4 and another camera that meters through the lens. How about you doing some readings and/or test exposures with the 15 and another less radical lens at various f-stops. The pro motion picture folks get their lenses calibrated in T-stops for actual transmission. The 15/4.5 is probably less than T/5.6 in the center and about T/8, maybe less, at the corners. Let us know your results.

[joop]

The HexarRF is in still repair since oktober 2005. (*%$#!!!)

So it's not possible to do meterings with several lenses and compare the values....

[al_kaplan1]

Sorry about your Hexar. SOMEBODY here must have done the comparison. Speak up if you have. Even just a bracketed series of exposures with the 15 and another lens on slide film would let you compare density.

[ben conover]

Interesting focal length, if you know it underexposes I guess you could just compensate. Nice photo.

 

Cheers.

[vivek iyer]

Joop, Depends on how you do your metering. Does the meter use the appropriate wide angle attachment? This is no ordinary wide angle lens, as you know!

 

With the Bessa-L' meter, I have no problem with slides, color negative, B&W films etc.

 

I keep the lens' front and rear immaculately clean ALL the time. This is very important if you do not want ghots/flares while shooting against point light sources. If the lens' surface (front/rear) is covered with an invisible layer of dirt (or whatever), light transmission goes down.

 

Recently, after a lot of struggle, I fashioned a rear filter for the 15mm lens. Even with the filter in place, metering is just fine on Bessa-L and R. On the CL, it is even more straight forward.

[blakley]

Don't know about the internal meter on your camera, but when I use an external incident meter with my CV 15mm on either my iiif or my M3, my exposures are accurate. Are you sure you're not confusing underexposure with vignetting? The CV 15mm, like all 15mm lenses, has significant light fall-off toward the edges of the frame.

[james_elwing]

my exposures have always been accurate. I suppose your meter is accurate?

[roger_hicks1]

Dear Joop,

 

I'm with Bob. I've used my 15 on a wide variety of cameras -- Bessas L, R, T, R2, Leicas M2, M4-P, MP -- and while there is some vignetting, I don't need to make exposure compensations. My wife's 35/5.5 Apo-Grandagon on 6x9 Alpa, roughly 15mm equivalent, is another matter but I think this is down to shutter efficiency.

 

Cheers,

 

Roger (www.rogerandfrances.com)

[SCL]

I'm still getting used to mine...I did have slight underexposure in the first roll I used it on (basis was against a 35mm summicron, same settings, same shots, same roll of film)...but I'm not yet at the point I can say definitely I need to factor in a correction.

[astral]

I used my 15mm on a Bessa R2 for many hundreds of photos while in Arizona in June 2004. The film was normally Fuji Astia or Provia 100F, depending on circumstances. There are no signs of underexposure and very little vignetting in those high lux conditions. I used the camera's meter for many shots (compensating for a bright sky if necessary) plus a Sekonic incident/spot meter. The apertures marked on my Heliar appear to be well within 1/3 stop of the actual value, and results compare favourably with several other CV lenses. My R2 meter gives consistent readings compared to the Sekonic (allowing for field of views, etc).

 

Unless the diaphragm/iris on your Heliar is out of specification I would guess that your meter and/or metering approach is something to check (and compare against the Hexar's TTL). 1/2 EV difference between different meters is pretty common, however.

[andrew1]

I tend to agree with those who said you seem to be confusing the vignetting of this

lens with exposure errors. The center of the image you posted looks a little hot,

maybe half a stop...<p>I have owned two of these lenses (had one, sold it, regretted

it,

bought another), and neither of them showed any significant difference in f-stop

rating from any other lens I have used. TTL metering with it can be tricky due to the

extreme coverage, but when handled correctly mine have always been right on.

Check

your metering methods, allow for some vingetting, and maybe get your lens checked

out. Good luck.

[joop]

I use a digisix, which so far seems to be accurate.

Other lenses give good exposures.

I usually take a reflected light measurements

(don't have a wide angle attachment).

I will work a bit more on my metering-skills.

I'll try more incident light measurements for the 15mm.

For projection the slides look just a bit dark,

not too bad. But when I try to scan them with my ScanDual-4

it turns out they're too dark to get a decent scan.<div></div>

[SCL]

Joop - A little touch of Photoshopping can improve the shadow areas a little.<div></div>

[ronald_moravec1]

I use the same stops on the 12/15 CV lenses as the rest of my Leica wides without a problem.

 

Some corner darkening is normal specially with the 12.

 

Cut a 6 or 8 in hole in some cardboard and dodge all four corners of the print for 15% of the exposure time. Just raise it up to the lens after 15% is over. Line it up with the red filter before you start. You will need to make a holding fixture if you print color.

 

You can brighten the corners with photoshop too.

[eliot_rosen1]

I believe that the digisix gives a reading that is roughly the equivalent of a 90 mm lens (about 27 or 30 degrees in maximum dimension). The 15 mm lens has a diagonal angle of acceptance of 105 degrees. Thus, you are metering only a fraction of the scene that will be recorded by the lens. This difference could result in the wrong exposure if you are not careful that the metered area is representative of the entire scene as a whole.

[astral]

Joop - a quick thought .... a touch of fill-in flash (a 'no-no' for some Leica users) could help in such images as the colour one above. But all the fun went out of flash photography when magnesium flash powder became unavailable over the counter! Personally, I never got the hang of fill-in flash, and without the bang and lots of smoke it's an anticlimax anyway. Hope you get it sorted - it's nice to hear some folks (you, me and a few die-hards) still project slides. AC