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09-16-2014, 11:45 AM   #1
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Use of Pentax-F 50mm f/1.7 lens on Kx camera

I recently went to a tag sale on Long Island to look at a Rolleiflex TLR. They wanted $400 so I lost interest. They also had for sale several Pentax bodies and assorted lenses. I picked up a mint Pentax-F 50mm, f/1.7 lens with a Pentax skylite filter for $13. I was delighted to find from reviews in this website that this lens is top-rated. I put it on my Kx and set the aperture ring to f/8, the dial to AV aperture control, and the ISO to 400. I took some flower photos and found that the photos weren't very sharp and the DOF was very narrow. When I uploaded the photos to iPhoto I found that the apertures were all f/1.7 and the speeds were adjusted to give the correct exposure. Clearly I had the settings wrong. I think I could figure out what to do to get aperture control by trial and error, but I welcome advice from anyone to avoid wasting time. How is it done?

09-16-2014, 11:51 AM   #2
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Put the aperture ring on A, everything will be fine. Al the Pentax DSLRs want to control the aperture via the camera body (aperture ring on A). You can use the aperture ring but the aperture does not stop down unless you change a custom setting, only use M mode, and take extra steps metering. This is extra trouble for no benefit.
09-16-2014, 12:17 PM   #3
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QuoteOriginally posted by P. Soo Quote
I picked up a mint Pentax-F 50mm, f/1.7 lens with a Pentax skylite filter for $13.
Indeed, a great score!

Let us know how you get along with this super lens.
09-16-2014, 12:39 PM   #4
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QuoteOriginally posted by Just1MoreDave Quote
Put the aperture ring on A, everything will be fine. Al the Pentax DSLRs want to control the aperture via the camera body (aperture ring on A). You can use the aperture ring but the aperture does not stop down unless you change a custom setting, only use M mode, and take extra steps metering. This is extra trouble for no benefit.
Hi Dave. Thanks for your prompt advice. I did as you said and set the aperture ring to A and shot a few pictures. Everything turned out well with nice sharp results. I had originally wanted to stop down to around f/8 to get good DOF but the camera set at 400 ISO was stopping down to f/5.6 and f/6.7. This gave enough DOF to keep my objects in focus. Thanks again.

09-16-2014, 01:13 PM   #5
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QuoteOriginally posted by P. Soo Quote
Hi Dave. Thanks for your prompt advice. I did as you said and set the aperture ring to A and shot a few pictures. Everything turned out well with nice sharp results. I had originally wanted to stop down to around f/8 to get good DOF but the camera set at 400 ISO was stopping down to f/5.6 and f/6.7. This gave enough DOF to keep my objects in focus. Thanks again.
Put the camera in Av mode and set the aperture to whatever you want.
09-17-2014, 08:00 AM   #6
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Hi Boris. Initially, I did set the camera to AV and the aperture to f/8 as I said in my post. However, the photos were all taken at f/1.7, the maximum lens aperture. I reset the aperture to A and the apertures were set automatically as were the speeds. Results were OK. Clearly, my lens/camera combination does not allow me to select an aperture while setting the dial to AV.
09-17-2014, 08:05 AM   #7
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QuoteOriginally posted by P. Soo Quote
Hi Boris. Initially, I did set the camera to AV and the aperture to f/8 as I said in my post. However, the photos were all taken at f/1.7, the maximum lens aperture. I reset the aperture to A and the apertures were set automatically as were the speeds. Results were OK. Clearly, my lens/camera combination does not allow me to select an aperture while setting the dial to AV.
You have a little misunderstanding of the lens and camera combination. The aperture ring is to allow older cameras that do not have automatic aperture control to function. With the k-x and all Pentax digital SLR cameras, the "A" position allows the camera to control the aperture directly. When you move the aperture ring on a Pentax digital SLR camera off "A", the camera assumes the lens is a manual lens only and will not stop the aperture down in Av/Sv/Tv mode.

I hope the above helps you understand what exactly is happening. In summary, for your camera and the F50 1.7, you should just leave the ring on "A" to allow your rear dial to change the aperture automatically.
09-17-2014, 08:54 AM   #8
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Thanks Jin.

09-17-2014, 09:14 AM   #9
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Just so you don't feel too smug about it, I picked my Pentax-F 50mm f1.7 at a thrift store for $5 (used my 30% student discount for that day, I know I'm despicable..) for a total of $3.5 out of the door. That said I've loved this little gem to bits, it was the lens that made me look at the -F series in a whole new light. To this day is one of the sharpest 50mm primes I own (and I have some nice Zeiss and Sigma glass) Enjoy this little gem, it's truly brilliant.

Last edited by Stavri; 09-17-2014 at 12:23 PM.
09-17-2014, 12:05 PM   #10
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OMG I was overcharged! I'm sorry I bought it.
09-17-2014, 12:25 PM   #11
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QuoteOriginally posted by P. Soo Quote
I'm sorry I bought it.
No problem, sell it to me for $20
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