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09-03-2010, 07:58 PM   #1
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Controlling Aperture with DoF Preview Button?

Quick question: on a film SLR (Pentax KM in my case), can I safely (i.e. without damaging my camera) use the depth of field preview button to stop-down digital lenses that lack an external aperture control?

Here's where I'm going with this. I'd like to try a little experiment (without damaging my camera):

1) Meter the scene wide-open and adjust shutter speed (since aperture is set at wide-open and ISO is fixed on a film camera)
2) Lower the shutter speed the desired number of stops from wide open aperture. For example, let's say you have an F2.8 lens and would like to shoot at F8, and your shutter speed wide-open is 1/1000. Set the shutter speed to 1/125s. The exposure needle will sky-rocket from the overexposure you've just dialed-in. Relax.
3) With your middle finger on the DoF preview button and your index finger on the shutter release, push the DoF preview button in until the metering needle reads the same desired exposure obtained in 1) above.
4) Without removing your middle finger from the DoF preview button, release shutter using your index finger.
5) Obtain ibuprofen to relieve joint pain in right hand.

This method wouldn't be particularly useful for, well, just about anything that moves where you want to stop-down. However, it might open-up some interesting still-life shooting options for those who are very determined to do so. For example, I'd like to try my Sigma 10-20 at 13-15mm on my KM and this might allow me to shoot at F8-F11 with this lens.

Thanks in advance for any insights!

09-03-2010, 09:41 PM   #2
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You can certainly use the DOF preview button with DA lenses- it won't cause the camera any harm. However, I'm pretty sure that the camera will stop the lens all the way down to F22 even if you hold the DOF preview lever at F8, since it only prevents the lever from going the other way (i.e. toward the wide-open side).

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09-04-2010, 01:16 PM   #3
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Thanks for your quick response, Adam!

<Sigh> So, some of those shots I took of the kids in the family room last night with my DA35 at F2.8 will be rather dark, then, won't they? Lesson learned.

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