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05-09-2020, 12:00 AM   #1
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Pentax 645 shutter speed questions.

Hello, I recently got a Pentax 645 original version. I want to ask some minor questions to the users of the camera.

I read some posts that on pentax 645 you could use iso button as an exposure compensation.
But when I make changes on the iso by 1/3 stops, the shutter speed stays the same on the viewfinder.
Also, mine has exposure compensation dial instead of c/s switch. When I switch it to +0.5/-0.5, the apparent shutter speed stays the same as well.
Only when I make change in full stop then the shutter speed will change in full stop accordingly.

Is it normal for the shutter speed to stay the same even when you tweak the iso, the exposure compensation dial by 1/3, 1/2 stops?
Or does the actual shutter speed indeed change by 1/3,1/2 stops but is not shown on the viewfinder?
Thanks

05-09-2020, 01:32 AM   #2
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QuoteOriginally posted by nate0395 Quote
I read some posts that on pentax 645 you could use iso button as an exposure compensation.
But when I make changes on the iso by 1/3 stops, the shutter speed stays the same on the viewfinder.
Also, mine has exposure compensation dial instead of c/s switch. When I switch it to +0.5/-0.5, the apparent shutter speed stays the same as well.
Only when I make change in full stop then the shutter speed will change in full stop accordingly.

Is it normal for the shutter speed to stay the same even when you tweak the iso, the exposure compensation dial by 1/3, 1/2 stops?
Or does the actual shutter speed indeed change by 1/3,1/2 stops but is not shown on the viewfinder?
On a standard Pentax 645 the ISO changes in 1/3 EV steps. The Exposure Compensation button changes whole EVs between +3EV to -3EV. And then most lens apertures had 1/2 EV and shutter speeds change 1 whole EV steps.
It should also be noted that in LS, 60, or B mode, exposure compensation does NOT work, although the info on the display will appear otherwise.

The 645N does have 1/3 EV steps on the exposure compensation dial.

Are you sure you have a 645 and not the 645N? The 645N has a switch that allows you to change auto bracketing from 0, 1/3, 2/3, or 1 EV +/-. Are you talking about this switch?

If you have the original 645, then to answer your question: yes, it is normal that if you only tweak the ISO or exposure compensation by 1/2 EV or less, because the shutter speeds are whole steps, it did not change. If it says 1/250", it's more or less 1/250". In the 645N, while in AV mode, the shutter speeds are stepless.
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