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12-16-2015, 02:02 AM   #16
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Yes KCOPET and that was the reason why I bought the Pentax 20D. I was also informed by a guy also taking cricket photos at our local match that old Nikon lenses are the same they can be used on any Nikon body. Unfortunately I have never met a Nikon user with old lenses, they usually have equipment that are as expensive as my car. Has anybody used an old Nikon lens on a Nikon Camera?

12-16-2015, 08:18 AM   #17
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QuoteOriginally posted by galelegg Quote
Has anybody used an old Nikon lens on a Nikon Camera?
FYI see
Nikon Lens Compatibility
12-17-2015, 11:23 AM   #18
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QuoteOriginally posted by galelegg Quote
The green button press technique on the Pentax 20D I have found to be rather misleading, often exaggerating the amount of light required.
The stop-down metering on bodies prior to the K-7 is unreliable. Depending on chosen aperture and lens, the shutter speed may be as much as three stops out. Current models do a much better job with M-mode being somewhat more accurate, in my experience, than Av-mode (YMMV).

I might add that unreliable stop-down metering has not just been a Pentax problem. I am not up on the current status of things, but six or seven years ago there were loud complaints from Nikon and Canon users with similar problems. The causes are complex, but have been assumed to be related to meter optimization routines built into the firmware that work great when the maximum aperture is known to the camera and not so great when it is not.

QuoteOriginally posted by KC0PET Quote
Unfortunately the green button stop down metering is typically not on the correct exposure and takes some "bracketing"
Bracketing is a good option as is simply chimping the histogram. It would been nice if one could also include exposure compensation as an option, but the utility there is sort of limited. When I still had my K10D, a lens that was 1 stop underexpose at f/2 might be spot on at f/5.6 and 1.5 overexpose at f/8.


Steve

Last edited by stevebrot; 12-17-2015 at 11:37 AM.
12-17-2015, 01:09 PM   #19
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QuoteOriginally posted by stevebrot Quote
The stop-down metering on bodies prior to the K-7 is unreliable.
One footnote to the list of stop-down metering considerations is meter range. The K20D has meter low end sensitivity of EV(100) 0. This works well for open-aperture readings and is equivalent to the light available for a 4s exposure at f/2 at ISO 100. Yes, that is not very much light. What's more, it is a hard limit. There is no way to make the meter provide an accurate reading below that level and the camera display will blink as an indicator when the limit is exceeded. This is true regardless of the ISO setting.

Where things get interesting is when you meter stopped down. The light to the meter (measured off the focus screen) may be a fraction of that coming from the subject, but the camera body has no way of "knowing" what that fraction is and cannot flag the user. Fortunately, the limits are easy enough to calculate and stop-down metered cameras such as the Pentax Spotmatic typically included a chart in the user manual showing the upper and lower limits for shutter speed at a given ASA(ISO) with the meter needle centered. Above or below those limits the meter would not be accurate.

What is not obvious is how quickly those limits might be approached in moderately dim conditions. Consider the following case:
  • Dimly lit home interior...e.g. EV(100) 5
  • Pentax-M 50/2 mounted to a K20D
  • Shooting at ISO 800
At f/2 the amount of light to the meter is well above its minimum sensitivity and a green button exposure will be somewhere close to the appropriate 1/60s exposure at ISO 800. However, aperture ring to f/11 and the light to the meter will be at its low limit when stopped down. The green button may well set a time shorter than the indicated 1/2s shutter speed.

Translation?
If the light is dim and you are shooting with a lens lacking the A contacts, a sensitive hand-held meter or educated guess may be preferable to the camera's meter. For guidelines on "educated guess" see:

Ultimate Exposure Computer

The above link gives common exposure values (EV) for various subjects along with a chart for calculating exposure by EV and ISO.


Steve


Last edited by stevebrot; 12-17-2015 at 01:14 PM.
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