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11-01-2011, 08:30 AM   #1
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How compatible are Pentax DSLRs with old lenses?

I've heard again and again that with Pentax cameras you have access to all of the old Pentax lenses. But is that just referring to the fact that the lens mount is compatible? Do any of the old lenses have autofocus that's compatible with current Pentax DSLR cameras? (I'm asking especially about compatibility with my K-x.)

11-01-2011, 08:34 AM   #2
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QuoteOriginally posted by stainsor Quote
I've heard again and again that with Pentax cameras you have access to all of the old Pentax lenses. But is that just referring to the fact that the lens mount is compatible? Do any of the old lenses have autofocus that's compatible with current Pentax DSLR cameras? (I'm asking especially about compatibility with my K-x.)
If they are AF lenses, yes the AF will still work. And if it is "A" lens but no AF, then you get to use auto-aperture. So yeah, no features are crippled. Only difference is the crop factor for the digital sensor...
11-01-2011, 08:38 AM   #3
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I think the only AF lens that would not autofocus on a Pentax DSLR is this one:

Pentax-AF 35-70mm F2.8 Reviews - Non-& Other Zoom Lenses - Pentax Lens Reviews & Lens Database

It was an oddball that was made especially for the Pentax ME-F 35mm SLR. The AF motor mechanism is in the lens itself, so that's why the AF is incompatible with anything other than an ME-F body.

Otherwise, every lens past or present, as far as I know, is compatible with a Pentax DSLR. Any Pentax K-mount AF lens will work correctly on a Pentax DSLR with full autofocus capabilities.
11-01-2011, 08:41 AM   #4
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QuoteOriginally posted by vonBaloney Quote
So yeah, no features are crippled.
That's a bit of a stretch. The K and M lenses certainly support open aperture metering on older bodies. But stop down metering isn't that bad, I suppose. I use them quite a lot.

11-01-2011, 08:46 AM   #5
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Every Pentax-compatable lens ever made will work on your Kr. Screwmount lenses need adapters, PK bayonet-mount lenses don't. Every Pentax-compatable screw-drive AF lens ever made will AF on your Kr. Every A-type lens will work with aperture automation and exposure control. Every M-type lens will work either in Av or M mode, with some aperture diddling.

EXCEPTIONS: A very few Vivitar PK-mount lenses have an aperture-link shield that's too big; it's easily shaved-down or removed. And some few Ricoh-compatable lenses have the infamous Ricoh Pin that can get stuck in the AF drive slot; it's easily glued-down or removed. And that pioneering AF lens mentioned above won't AF on your Kr. All else are good to go.
11-01-2011, 08:54 AM   #6
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Don't forget the M42 thread mount lenses from Pentax and other manufactures that are quite reasonable and some are very good quality as well. You should use the genuine Pentax M42 to K mount adapter which is quite reasonable.

You can also add the Pentax 6X7 as well as 645 full series of lenses that work as manual lenses with the proper Pentax adapter. These lenses are fine quality but larger and heavier. A few are quite reasonable especially the 6X7 Takumars.
11-01-2011, 10:04 AM   #7
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QuoteOriginally posted by drougge Quote
That's a bit of a stretch. The K and M lenses certainly support open aperture metering on older bodies. But stop down metering isn't that bad, I suppose. I use them quite a lot.
I meant no features of the *lens* are crippled. Metering procedure with some lenses will be different (namely you have to hit the green button to take a reading at your selected aperture), but that is a difference in the camera. (And If the lens is new enough to have an "A" aperture setting, there are no differences in usage.)

You are not losing any abilities of the lens.

Actually, with m42 lenses you do as they will become fully manual with the adapter...
11-01-2011, 10:47 AM   #8
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QuoteOriginally posted by stainsor Quote
Do any of the old lenses have autofocus that's compatible with current Pentax DSLR cameras? (I'm asking especially about compatibility with my K-x.)
Unlike Nikon and Canon (lower end Nikons can't focus older glass, and Canon changed from FD to EF mount in the 80's) there has been no insurmountable change in the lensmount or the way autofocus is used in Pentax cameras going waaay back.

Not only that, all lenses (whether AF or not, Pentax or not) have the modern benefits of in-body stabilization (shake reduction where you manually enter the focal length) and "focus confirmation" in the viewfinder when you nail the manual focus on a focus point. All on your K-x!

So, I'd say "really, really compatible," given how many quality lenses predate AF, much less stabilization!

11-01-2011, 11:15 AM   #9
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Now the new lenses are another story...no aperture ring. If pentax wanted to remain different from CaNikon, they should've kept aperture rings on the newer lenses. I guess not
11-01-2011, 02:12 PM   #10
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QuoteOriginally posted by vonBaloney Quote
I meant no features of the *lens* are crippled. Metering procedure with some lenses will be different (namely you have to hit the green button to take a reading at your selected aperture), but that is a difference in the camera. (And If the lens is new enough to have an "A" aperture setting, there are no differences in usage.)

You are not losing any abilities of the lens.
Open aperture metering needs camera support to work, certainly, but it also needs lens support. Either the camera controls the aperture (A lenses and newer), or the lens has to tell the camera what you set the aperture ring to. M and K lenses do this, but the modern cameras don't listen. Thus, a feature of the lens is lost.
11-01-2011, 06:46 PM   #11
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That sounds great! Just the kind of answers I was hoping for.
...
Okay, I'm still a newbie. Could you explain a few terms for me? (Or point me to an explanation?)
Open aperture metering
stop down metering
aperture ring
screwdrive mount vs bayonet mount

Thanks!!
11-01-2011, 08:33 PM   #12
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QuoteOriginally posted by stainsor Quote
That sounds great! Just the kind of answers I was hoping for.
...
Okay, I'm still a newbie. Could you explain a few terms for me? (Or point me to an explanation?)
Open aperture metering
stop down metering
aperture ring
screwdrive mount vs bayonet mount

Thanks!!
You might try using a search engine, as these are all common photographic terms naming some of the most basic camera functions.. You may want to get more specific for the last items on your list. Try M42 screw mount and Pentax K mount.

You might also be wise to invest in a good photography book as that is a more systematic and efficient way of learning the basics than is asking questions on the Web.
11-01-2011, 11:21 PM   #13
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QuoteOriginally posted by drougge Quote
Open aperture metering needs camera support to work, certainly, but it also needs lens support. Either the camera controls the aperture (A lenses and newer), or the lens has to tell the camera what you set the aperture ring to. M and K lenses do this, but the modern cameras don't listen. Thus, a feature of the lens is lost.
I think you're splitting hairs. With a M lens on a (say) K1000, you move the aperture ring (and the aperture stays open while you do) and the meter needle moves up and down. With the same lens on a modern DSLR, you move the aperture ring (and the aperture stays open while you do), but now you need to hit the green button to take a reading, which closes the aperture to the current setting for a split second and gives you the reading (usually by setting the shutter speed if you have the option set). The procedure is different, but you aren't really hampered by anything because it is so easy to do and the result is the same. But I actually do prefer to use the fully manual lenses (no auto-aperture at all) on the DSLRs since then you can just put in Av mode instead of M, and you'll see the readings change as you move the ring (probably after you focused with aperture open). But the green button method in M mode is painless enough...
11-01-2011, 11:38 PM - 1 Like   #14
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QuoteOriginally posted by stainsor Quote
Open aperture metering
stop down metering
aperture ring
screwdrive mount vs bayonet mount
Open-aperture metering: The aperture remains open when you press the shutter button to meter and expose. Common with some manual lenses.

Stop-down metering: The iris DOES stop down. Thus you can frame a shot with the aperture open, yet meter and expose at the desired aperture.

Aperture ring: Something not found on DA/digital lenses, where aperture is controlled from the camera. This ring allows you to select an aperture.

Screwdrive: The Pentax autofocus mechanism, only found on bayonet-mount lenses, those in the F, FA, and DA series. Not related to screwmount.

Screwmount: A threaded rather than quick-change lens mount. The vast majority of Pentax screwmount lenses use the M42 standard; a couple used M37. Leica Thread Mount (LTM) lenses use the L39 standard and can't be adapted to Pentax cameras. Many Russian lenses use the M39 standard, which CAN be adapted to Pentax. Other screwmounts exist but don't worry about them.

Bayonet mount: The quick-change mount type used by most modern SLRs. The Pentax design is called PK; it has evolved through several versions.

For more info, see Wikipedia and Google.

Last edited by RioRico; 11-01-2011 at 11:43 PM.
11-02-2011, 01:36 AM   #15
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QuoteOriginally posted by vonBaloney Quote
I think you're splitting hairs.
That's because you choose to compare with a camera without an Av mode. As you yourself say:
QuoteOriginally posted by vonBaloney Quote
But I actually do prefer to use the fully manual lenses (no auto-aperture at all) on the DSLRs since then you can just put in Av mode instead of M, and you'll see the readings change as you move the ring (probably after you focused with aperture open). But the green button method in M mode is painless enough...
On every reasonably old Pentax camera with Av mode support, this mode works just fine on M lenses. The modern ones do not give us this luxury. With an aperture feeler both Av and TAv could work. Since they require a more modern lens, despite these older lenses actually supporting everything needed for the feature to work, they are in my opinion removing a feature from the lens. (If you want the permanent stop down behaviour you can unmount the lens a little, but I like to see what I'm doing, so I'm stuck with M mode. Not that I don't like M mode, but not always.)

It's actually (by quite a margin) my number one complaint about my K5, so to me it's not hair splitting.
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