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03-28-2009, 08:52 PM   #1
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Pentax 'Pre-set' aperture question

I'm wondering if anyone can explain the 'dual aperture rings' of a Pentax Tele-Takumar 300mm lens that I own.

I understand aperture, just not how the two rings work together. I recently had a chance to buy another similar lens, but haven't yet.

Any help would be appreciated.

thanks,
John

03-28-2009, 09:34 PM   #2
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Pretty straight forward on the couple of preset lenses I've used. One ring has click stops and aperture settings (2.8, 4, 5.6, etc.) marked on it. The other ring rotates freely and is what you use to actually change the aperture. You set the aperture you want to shoot at using the ring with click stops, and you can then rotate the ring that controls the aperture back and forth between wide open and the aperture value you pre-selected.

The benefit of a preset lens is that you can pre-select an aperture, compose and focus wide open, and then rotate the aperture control ring from wide open to the preset aperture to meter and shoot, all by touch and without having to take your eye away from the view finder.
03-28-2009, 09:37 PM   #3
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QuoteOriginally posted by Steinback Quote
Pretty straight forward on the couple of preset lenses I've used. One ring has click stops and aperture settings (2.8, 4, 5.6, etc.) marked on it. The other ring rotates freely and is what you use to actually change the aperture. You set the aperture you want to shoot at using the ring with click stops, and you can then rotate the ring that controls the aperture back and forth between wide open and the aperture value you pre-selected.

The benefit of a preset lens is that you can pre-select an aperture, compose and focus wide open, and then rotate the aperture control ring from wide open to the preset aperture to meter and shoot, all by touch and without having to take your eye away from the view finder.
Very accurate and succinct explanation. I'll just add that using the preset becomes second nature very quickly. After a few weeks, back in 1961 when I bought my first Pentax, the open/focus/stop down became automatic.
03-29-2009, 07:29 PM   #4
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Wow....thanks very much.

Makes sense now that you explain it.............thanks again!

John

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