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10-24-2013, 04:12 PM   #1
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Focal length for manual zoom on K-5

Hi guys!

I am new here and hope you can help. I have a 25 years old 28-70 zoom lens I was using on my old film Pentax SLR. After having my K-5 for more than 2 years and trying several lenses on it, I remembered this very old lens and decided to give it a try. I don't mind having to zoom manually. Now, the thing is that I am not sure which focal length I should set when turning the camera on. I tried to search the Internet and this forum, but the few info I managed to find are contradictory.

Am I right to assume that the value I am entering is only going to influence the amount of SR the camera is going to apply, and that the bigger the number, the more SR will be used? Since the lens is 28-70 in 35mm, that would be 42-105 on APS-C. Some recommendations are to use the setting closest to the mid focal length, some others say to use the shortest, but there are even some telling you to use the longest.

I shoot handheld with SR on most of the time and don't want to have to change the input every time I zoom in or out. So, what would you recommend, to use 50, 75, or 100mm?

Thanks!

10-24-2013, 04:29 PM   #2
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Hi
I use an old 50mm manual lens regularly as well as an old 35-70mm. With the 50mm, I set it to 50mm, and I get very sharp focus. With the 35-70mm, I've gone mid-way, i.e. 50mm too, (near enough!) and have had reasonable success with that too. I'm not convinced that it's neccesary or better to make a calculation from FF to APS-C. Regardless of what camera it's used on, it's still a 35-70mm lens, i.e. you're not getting any more zoom with an FF lens. Whatyou're dealing with is a crop factor, not a change in focal length.
Happy to be proved wrong, of course!
Regards,
Mark
10-24-2013, 04:34 PM   #3
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How long, Oh, How Long?

Hello Prepelica, Welcome to the Forum!
I don't know the answer from any formula or equation, but I do know what works for me: Set it at the longest FL that's actually printed on the lens, disregarding the 'crop' factor. In your case, 70mm or 75mm.
JMO,
Ron
10-24-2013, 04:59 PM   #4
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Use the actual millimeters of the lens. However, the SR will always be wrong to a degree unless your zoom happens to be at the same setting. It is a problematic thing about manual zooms. I would set it in the middle and not worry about it. I'm guessing it will probably be better than turned off.

10-24-2013, 04:59 PM   #5
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Thanks Mark, now that you have explained it, it makes sense, of course! It's still the same lens, no recalculation is needed. What's cropped is cropped, but that's another story.

Thanks Ron, this seems to be a sound advice, especially when shooting closer to the longest focal length.
10-24-2013, 06:47 PM   #6
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You're welcome. Now you'll have to post some photos!
10-25-2013, 03:40 AM   #7
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Mark, I just might. As soon as I figure out how to upload them. I am still absolutely new here, so please give me some time to get oriented and fit in!

SpecialK, thanks for the input, it's appreciated.
10-26-2013, 07:34 AM   #8
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I use my A35-105mm a lot and I will change the focal length for SR occasionally but usually leave it set at either 50 or 75.

10-26-2013, 12:20 PM - 1 Like   #9
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QuoteOriginally posted by bass3587 Quote
I use my A35-105mm a lot and I will change the focal length for SR occasionally but usually leave it set at either 50 or 75.
I've realized that the best thing for me to do is to set it to 50mm for most of the time, and only set it to 70mm or more when I am shooting at the longer focal lengths. Thanks bass!


And here is a photo I took with that lens when the setting was 100mm.
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10-29-2013, 06:03 PM   #10
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QuoteOriginally posted by prepelica Quote
I've realized that the best thing for me to do is to set it to 50mm for most of the time, and only set it to 70mm or more when I am shooting at the longer focal lengths. Thanks bass!


And here is a photo I took with that lens when the setting was 100mm.
Very shallow depth of field. Was that intentional? Nice bokeh off that lens.
10-30-2013, 06:57 AM   #11
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QuoteOriginally posted by MarkJerling Quote
Very shallow depth of field. Was that intentional? Nice bokeh off that lens.
Mark, yes, that was planned. I was just testing the lens, I did not use it in years and never on this body, so I was trying different settings, to see how it performs. The lens has a 5x optical close up, so the magnification, being close to the subject and the fastest aperture of this lens of 3.5 gave so shallow DOF.

I like the way this lens works on my K-5, but will have to take it to some real shooting before I decide how frequently it will be on the camera. Manual focus is not a problem, but it focuses to the opposite direction from Pentax lenses, and that can be confusing if I am changing the lenses while shooting.
10-30-2013, 01:57 PM   #12
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QuoteOriginally posted by prepelica Quote
Mark, yes, that was planned. I was just testing the lens, I did not use it in years and never on this body, so I was trying different settings, to see how it performs. The lens has a 5x optical close up, so the magnification, being close to the subject and the fastest aperture of this lens of 3.5 gave so shallow DOF.

I like the way this lens works on my K-5, but will have to take it to some real shooting before I decide how frequently it will be on the camera. Manual focus is not a problem, but it focuses to the opposite direction from Pentax lenses, and that can be confusing if I am changing the lenses while shooting.
That makes sense for the DOF. I carry 4 lenses with me at all times: 18-55mm WR kit lens (for when it's raining), the 70-300mm zoom (wish I had a longer zoom!), the 50mm 1.7 manual lens (it's just such a nice lens!) and the 35-70mm lens which is nice on macro. I must give the 28mm Cosina a try again - I tend to forget I have that lens and that it's good on macro too. Your post has given me a reminder!
10-31-2013, 06:16 AM   #13
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QuoteOriginally posted by MarkJerling Quote
That makes sense for the DOF. I carry 4 lenses with me at all times: 18-55mm WR kit lens (for when it's raining), the 70-300mm zoom (wish I had a longer zoom!), the 50mm 1.7 manual lens (it's just such a nice lens!) and the 35-70mm lens which is nice on macro. I must give the 28mm Cosina a try again - I tend to forget I have that lens and that it's good on macro too. Your post has given me a reminder!
Glad I was of some help!
I recently had 40mm limited on the camera most of the times. I just bought a 70mm limited, I want to work more on the portrait shooting, because I know it is my weakest point in photography and hope this lens will be good for that. It's not big and will be with me all the times. I have a Tamron 70-300mm, but never got any good shots with it (the tripod is usually at home or in the car, but not with me when I need it). Even when the photos are in focus, the IQ is not good enough. The lens is relatively big, so recently I am mainly leaving it at home. This old manual zoom can be an alternative to the 18-55mm WR kit zoom that I also have always with me. When I think I'll have some time to fool around, I also take my Lensbaby with me.
10-31-2013, 03:40 PM   #14
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QuoteOriginally posted by prepelica Quote
Glad I was of some help!
I want to work more on the portrait shooting, because I know it is my weakest point in photography .
Me too!
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