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07-18-2013, 07:45 AM   #1
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Old Pentax lenses on the newer Pentax DSLRs

Hi all,

I'm just posting in light of my Pentax P30N breaking a few days ago. I thought that now might be the time to move from film to digital. I have a couple of Pentax KA type lenses, and I was hoping to use those on a Pentax DSLR (currently tossing up between the K-30 and the K-5 IIs). However, I've been reading that apparently the older lenses, while still being compatible, don't take pictures quite like they do on film? I'm not really sure how to explain it, but it has something to do with the sensor in a DSLR being a crop sensor rather than a full frame.

Simply put I'm asking if I used these older lenses on a DSLR what would be different about the images produced? Should this discourage me from moving to digital?

Thanks,

Michael

07-18-2013, 07:55 AM   #2
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QuoteOriginally posted by mn_raf123 Quote
Hi all,

I'm just posting in light of my Pentax P30N breaking a few days ago. I thought that now might be the time to move from film to digital. I have a couple of Pentax KA type lenses, and I was hoping to use those on a Pentax DSLR (currently tossing up between the K-30 and the K-5 IIs). However, I've been reading that apparently the older lenses, while still being compatible, don't take pictures quite like they do on film? I'm not really sure how to explain it, but it has something to do with the sensor in a DSLR being a crop sensor rather than a full frame.

Simply put I'm asking if I used these older lenses on a DSLR what would be different about the images produced? Should this discourage me from moving to digital?

Thanks,

Michael
The only difference (apart from more discernible aberrations, perhaps) is the field of view. Your lenses won't be as wide on digital as they are on film; a 50mm on digital will feel like a 75mm on film (1.5x crop factor).

Adam
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07-18-2013, 07:56 AM   #3
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Some older lenses are stunning, giving better color and contrast than modern lenses. Some are poor, and have resolution lower than modern lenses, leading to soft images or lots of artifacts.

It all depends on what you have in your kit, and how much time you want to take composing images.

Don't let it discourage you from making the move to digital, far from it. Even older kit lenses - if you have hoods and understand exposure - can be very nice on a digital body.
07-18-2013, 08:01 AM   #4
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Don't think about all the crop discussion, you will always get what the viewfinder shows regardless.
The "A" lenses will work the same way as on the film cam.

07-18-2013, 08:18 AM   #5
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One issue that shows up on digital, but not film, is purple fringing. In areas of extreme contrast (like a black shirt against a bright sky), you might get a purple fringe on the border between the light and dark area. Some lenses do this more than others, but most lenses made for digital have coatings to prevent this.

It's not a huge problem, though. It occurs less if you stop down, and there are tools to effortlessly remove it from the picture on the computer.
07-18-2013, 08:21 AM   #6
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QuoteOriginally posted by Adam Quote
The only difference (apart from more discernible aberrations, perhaps) is the field of view. Your lenses won't be as wide on digital as they are on film; a 50mm on digital will feel like a 75mm on film (1.5x crop factor).
So would I also get the associated effect of a 75mm lens? Stuff like the slight background compression in comparison to a 50mm?
07-18-2013, 08:27 AM   #7
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Many seek out the older film lenses for use on their dSLRs because of a variety of advantages.
07-18-2013, 08:33 AM   #8
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QuoteOriginally posted by mn_raf123 Quote
So would I also get the associated effect of a 75mm lens? Stuff like the slight background compression in comparison to a 50mm?
Yes, pretty much just like using a 75 mm lens. All your lenses will be "promoted" in the telephoto direction.

So, you might find yourself needing to acquire a new wide angle lens, or a wider-angle zoom.

07-18-2013, 08:47 AM   #9
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What are your older lenses?
07-18-2013, 08:50 AM   #10
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QuoteOriginally posted by Billy Joe Quote
What are your older lenses?
I have a Pentax-A 50mm f2.8 Macro lens and a Seimar-Donnex 28-135mm f3.8 lens.
07-18-2013, 09:47 AM   #11
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That A-50 macro will be a winner on a modern body. It's one I've considered buying myself.
If you don't have a hood for it, you might want one in the bright sunlight though.

The crop effect is this - if you put the 50 on a crop-sensor body it will be like using a 75mm on a full-frame. That's all. The optics are still great and there's one potential benefit. If your lens vignetted significantly on full frame, it may not on the crop sensor.

Oh, and the crop sensor viewfinders are smaller and a little darker, compared with full-frame. There are workarounds, and you can even install a split-focus screen if you want. There are long threads discussing this modification on the forum.
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