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11-17-2016, 08:45 AM   #1
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Questions re manual (no A) lens exposure; specular highlights; 67 lens on K-1

Hi all,


Have skimmed through the manual lens thread but did not find a solution or explanation for the problem I am having -- I am using my first k lens without an A setting -- the k28 3.5 on the the k-1 and my exposures using the green button are continually 2 to 2 1/2 stops overexposed. The green button metering does stop down the lens and change as I change apertures. I thought at first the lens simply wasn't stopping down to the proper fstop when shot is taken but I took the lens indoors to a dark scene with a 5 second and longer exposures and the fstop does stop down. In even indoor light I do seem to get a much better exposure but outdoors is a disaster. I also just received a fotodiox adapter so I tried my 67 lens 135 mm and I generally got proper exposures with this lens. Exposures with my dfa lenses is usually spot on. Could there be a problem with the k28 lens and are there any suggestions as to what else I could try or test with this lens.


I also found that multi-segment metering mode is not available with either of the two manual lenses above -- is this mode not available for manual lenses?


Side question: For designating 67 lenses focal length for shake reduction do I just use the focal length of the lens (135 for the 135mm) or do I need to apply a conversion factor?


With all lenses (manual without a, manual with A setting, dfa) -- in bright light I am getting a large red spike on the right side of the histogram that takes up to 2 stops of underexposure to bring into line -- this happens even with sidelit scenes -- I know I had seen a thread about this a while back but could not find it again -- is this normal for the k-1?


Thanks for any help or insight you could provide.


Rich

11-17-2016, 09:02 AM   #2
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Well, here's a thought...

Is the aperture stopping down fast enough for short shutter speeds in bright light? It's not unusual to find a vintage lens with a sluggish aperture - either due to some oil creeping onto the aperture blades, or the linkage getting gummed and sluggish since it was last serviced (or since it left the factory).

So, if you're shooting at 1/125 in sunshine at F11, maybe the aperture only gets to f5.6 by the time the shutter closes - so you're at least 2 stops over.

Indoors, with a much slower speed, the lens gets to its setting after a fraction of a second, and most the exposure time is perfect. You may not notice the slight extra exposure from the early part of the shutter opening time.

So, first things first, I'd check the aperture was quick and snappy (by flicking the lever on the back of the mount). If not, it needs servicing. If it's fine, then the problem's elsewhere.
11-17-2016, 09:07 AM   #3
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Great suggestion from Ontarian50.

Your other questions:
As you've found multi-segment is not available with K/M lenses.
You dial in the true focal length for SR to work, also for 6x7 lenses (135mm for a 135mm lens).
11-17-2016, 09:12 AM   #4
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Thanks for the quick replies Ontarion50 and Ole --
Just checked the aperture lever and it works quickly and smoothly at all apertures so this does not seem to be the problem.






QuoteOriginally posted by Ole Quote
Great suggestion from Ontarian50.

Your other questions:
As you've found multi-segment is not available with K/M lenses.
You dial in the true focal length for SR to work, also for 6x7 lenses (135mm for a 135mm lens).


11-17-2016, 10:23 AM   #5
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QuoteOriginally posted by travelswsage Quote
I am using my first k lens without an A setting -- the k28 3.5 on the the k-1 and my exposures using the green button are continually 2 to 2 1/2 stops overexposed.
This behavior has a long history and is frequently touched on in discussions on this site. Here are the pertinent bullet points. Read them and weep (or not):
  • Stop down metering (both green button and manual aperture in Av mode) is inherently unreliable on your K-1. Metered exposure is often close enough, but not predictably so.
  • This is a pervasive problem with AF SLR cameras across brands
  • The cause is related to loss of light at the main mirror for the PDAF sensor coupled with focus screen optimization to compensate for the light loss. The metered reading is skewed to accommodate the screen quirks. This approach only works properly with open aperture metering when the camera "knows" the maximum aperture and when the body controls the aperture stop-down.
  • The effect is that meter response is not consistent or fully linear at all apertures and varies by lens. Because of this, dialing in exposure compensation may or may not be a reasonable solution.
  • The problem was much worse on bodies earlier than the K-7
  • My experience has been that metering with most lenses is essentially accurate and linear between at apertures narrower than about f/4
  • The above point fails as light levels fall and apertures become narrow. The hidden gotcha with stop-down metering is that light to the meter may easily fall below the lower limits of meter sensitivity as one stops down. Gross underexposure is the result.*
  • My experience on the K-3 has been that M mode with green button or DOF preview is more reliable than Av mode, even with manual aperture on M42 lenses. Whether this is true on the K-1, I don't know.
So, what to do? Here is my flow:
  • Use M mode
  • Set aperture
  • Do an initial green button or DOF preview reading. For tricky lighting a gray card may be useful.
  • Make test exposure and adjust shutter speed to center the histogram
  • Shoot using these settings until either the subject or light changes
Don't sweat the fact that there is no real time metering of the subject. If you must, use Av mode and EC, but my experience has been that ability is highly overrated. I have found that a hand-held light meter using traditional technique is incredibly useful when working with vintage lenses and for many subjects will outperform the camera's evaluative metering when used skillfully.


Steve

* This is a long-standing issue with stop-down meter bodies at some EVs. Spotmatic models actually have a feature where there is a red flag visible through a small window for certain combinations of ASA (ISO) and shutter speed. The was also a table of valid exposure settings included in the user manual.

Last edited by stevebrot; 11-17-2016 at 10:34 AM.
11-17-2016, 06:11 PM   #6
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Thanks Steve -- I used your workflow for the 67 lens with fotodiox adapter -- for this lens the exposures for the most part were pretty good to begin with and using the shutter speed dial allowed a light correction when needed. The k28 is still way overexposed on most shots -- it just seems like the lens is not stopping down properly when the shot is taken. When I have the k28 on in manual mode and I rotate the aperture ring nothing happens -- it stays wide open -- when rotating the aperture dial is the lens supposed to stop down? -- or is the camera at that point stopping it down only when the picture is taken. The 67 lens stops down as the aperture dial is rotated and I figured that was because of the intervening "dead" adapter, but I'm not really sure how the non-A lenses K lenses are supposed to operate. If I pick up m42 lenses in the future will they operate the same way as the 67 lenses?


Thanks again for taking the time to respond.


Rich
11-17-2016, 09:20 PM   #7
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QuoteOriginally posted by travelswsage Quote
When I have the k28 on in manual mode and I rotate the aperture ring nothing happens -- it stays wide open -- when rotating the aperture dial is the lens supposed to stop down?
Your K 28/3.8 is a K-series (no "A" contacts), K-mount lens and features automatic aperture actuation. As such it will stop down:
  • Immediately before the shutter is triggered for an exposure, but only in M, X, and B modes
  • When the green button is pressed in M mode
  • When optical DOF preview is used in M mode
  • When the lens is removed from the camera
At other times and other modes, the lens aperture is held full open regardless of the aperture ring position. You can confirm the aperture operation with the lens off camera and the actuator mechanism by manually flicking the lever on the back of the lens. On camera, you can confirm by choosing a long exposure time in M mode and simply looking through the front to the lens. To confirm the aperture accuracy do a manual exposure series:
  • M mode
  • Constant light
  • Blank wall
  • Do a series of exposures at different apertures, but the same Exposure Value (EV). Example:
    • f/4 @ 1/30s
    • f/5.6 @ 1/15s
    • f/8 @ 1/8s
    • f/11 @ 1/4s
    • f/16 @ 1/2s
    • f/22 @ 1s
  • Each of the resulting images should have essentially identical exposure
If the last point is not true, there is a problem with the aperture mechanism. (Assumption is that the shutter is accurate and that ISO is kept constant.)


Steve
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