[Steve Belcoski]

I am working through some techniques for long exposure photography as discussed in a popular book by a well-known author. When I meter the sky through the viewfinder of a k-1 with a 31mm limited, correct exposure is achieved for 1/8000th of a second @ F2.0 and by live view the settings for correct exposure are identical. I have my C1 menu for 1EV Steps set for 1/2 EV. Once I have installed the the B+W filter, I must increase shutter speed by 20 1/2 EV steps or 10 full EV in order to achieve a correct exposure ( what you expect for a 1000x ) an this is confirmed by the metering displayed in the viewfinder
However the image is underexposed by 2 EV. When I switch to live view, it is clear that the exposure is not accurate until I add two more EV to the shutter speed to get an accurate exposure. I use live view often, especially for very sharp focusing with manual lenses but even with a hoodman to view the LCD is cumbersome. Is there any reason why there is a difference for correct exposure via viewfinder vs live view. Thank you in advance for any ideas about this.

[stevebrot]

Is there any reason why there is a difference for correct exposure via viewfinder vs live view.

I am not sure how you are defining "correct exposure", but I can provide an explanation why there might be a difference between a metered live view exposure and that done through the optical viewfinder. The most common cause is metering using the optical viewfinder with one's eye away from the eyepiece. In that situation, light may freely enter the camera from the rear and may significantly bias the meter reading. The common solution is to use the slide-on shade included with the camera or to place one's thumb over the eyepiece when taking the reading.

Of course, there may be other explanations, but this is a start.


Steve

[Megapixelmk]

Agreeing with Steve.
Having the slide on cover over the viewfinder while using Live view is absolutely essential to getting accurate exposure with long exposure

[stevebrot]

Agreeing with Steve.
Having the slide on cover over the viewfinder while using Live view is absolutely essential to getting accurate exposure with long exposure

Thanks for elaborating a little more on the light-through-the-eyepiece risks. To summarize the full concerns:

• Unwanted light to the meter when using regular open-aperture metering will bias the reading. The bias is magnified when doing stop-down metering.
• Some risk of extra light when metering in live view due light penetrating around the raised mirror. This risk is much lower than in the point above.
• Extraneous light during long exposures resulting in lowered contrast and the equivalent of veiling flare. The risk increases with the intensity of light striking the eyepiece and the length of the exposure.

To impact of not having the viewfinder shaded is greatest when light striking the eyepiece is direct and bright relative to that admitted through the lens. Example: low angle sunlight from behind the camera. During exposure, bright light from the eyepiece may find its way past the edges of the raised mirror and onto the sensor. An extreme example may be demonstrated by a darkened room exposure with lens cap on and hand-held flash directed at the eyepiece.

Whether there will be a problem for a particular subject and setup is hard to predict. It is best to shade the eyepiece.


Steve

[Steve Belcoski]

I am not sure how you are defining "correct exposure", but I can provide an explanation why there might be a difference between a metered live view exposure and that done through the optical viewfinder. The most common cause is metering using the optical viewfinder with one's eye away from the eyepiece. In that situation, light may freely enter the camera from the rear and may significantly bias the meter reading. The common solution is to use the slide-on shade included with the camera or to place one's thumb over the eyepiece when taking the reading.

Of course, there may be other explanations, but this is a start.


Steve

Thank you for your suggestion. That sounds very plausible. I have the piece supplied by Pentax to cover the eyecup and now having read your response I remember reading this somewhere but have never had a need for this before and actually at the time questioned myself like " really, how much light can be getting in there". I know that 2 stops of light seems like a lot but over a long exposure it is accumulative and just a little light slipping in through can have a substantial effect. As far as my interpretation of correct exposure, it is done by lining up the exposure to be in the middle of the scale and confirmed by the histogram. From my research, sometimes under exposure can preferential for contrast but I'll remain technically correct until I'm better prepared to be creatively correct. Thanks again . Have a good day.

---------- Post added 03-30-19 at 08:35 AM ----------

Thanks for elaborating a little more on the light-through-the-eyepiece risks. To summarize the full concerns:

• Unwanted light to the meter when using regular open-aperture metering will bias the reading. The bias is magnified when doing stop-down metering.
• Some risk of extra light when metering in live view due light penetrating around the raised mirror. This risk is much lower than in the point above.
• Extraneous light during long exposures resulting in lowered contrast and the equivalent of veiling flare. The risk increases with the intensity of light striking the eyepiece and the length of the exposure.

To impact of not having the viewfinder shaded is greatest when light striking the eyepiece is direct and bright relative to that admitted through the lens. Example: low angle sunlight from behind the camera. During exposure, bright light from the eyepiece may find its way past the edges of the raised mirror and onto the sensor. An extreme example may be demonstrated by a darkened room exposure with lens cap on and hand-held flash directed at the eyepiece.

Whether there will be a problem for a particular subject and setup is hard to predict. It is best to shade the eyepiece.


Steve

Thank you. I am glad to hear back from you so soon. I was thinking about what I had written, and realized that my interpretation of the problem would have caused an over-exposure.
So, the mechanics of what is happening is that the meter says the light is good but in reality the light coming in through the eyecup does not reach the sensor during the exposure and hence causes a deficit. Got it!