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05-10-2009, 02:19 PM   #1
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Old film lens compatible with new dslr bodies?

So I have a Pentax MX Asahi and it's my baby, i love it. but i want a digital slr for professional purposes. My lens is a SMC Pentax-M 1:1.4 50mm 7131020 Asahi Lens! Would i be able to just click it in with let's say, i don't know, a pentax k20d or one of the nicer models? Also, since this lens is pretty old, I can't get a lot of the dust off myself, any tips? Thanks

05-10-2009, 02:29 PM   #2
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QuoteOriginally posted by nessamento Quote
So I have a Pentax MX Asahi and it's my baby, i love it. but i want a digital slr for professional purposes. My lens is a SMC Pentax-M 1:1.4 50mm 7131020 Asahi Lens! Would i be able to just click it in with let's say, i don't know, a pentax k20d or one of the nicer models? Also, since this lens is pretty old, I can't get a lot of the dust off myself, any tips? Thanks
You can certainly use the lens. It will just click into place. As you are already using an MX, you will find it easy to manually meter with the K20 or K10. You will need to enable the aperture ring to use an M lens, and set the DOF preview lever to Optical to use the scale metering to set the exposure.

Also, using the green button to set the shutter speed works, sort of. Unless you change the focusing screen to an LL-60 (that's sixty, not eighty) M lenses won't meter evenly across the aperture scale. You can do a search on this in the forums. It took the others a while to convince me, but both my M's now work perfectly.
05-10-2009, 02:35 PM   #3
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i don't know much about lens, what exactly does it mean if it's an M lens?
05-10-2009, 02:37 PM   #4
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also what is this DOF preview lever?

05-10-2009, 03:02 PM   #5
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QuoteOriginally posted by nessamento Quote
i don't know much about lens, what exactly does it mean if it's an M lens?
A K-mount lens that is totaly manual.

What is K-mount?

Pentaxes' introduction to a new way to mount lenses.

Instead of screwing the lens to the camera body, you line up the red dots, turn and click.

What is a DOP preview lever?

A switch on the camera that allows you to stop down the lens at a certain aperture to check the depth of field. (DOP)
DOP; How much of the image is in focus from in front and behind the focal point.

Decide on a camera then ask more questions.

There are plenty out there to choose from.
05-10-2009, 03:24 PM   #6
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QuoteOriginally posted by nessamento Quote
also what is this DOF preview lever?
If you look at the power switch on a Pentax DSLR, you will see OFF ON and a circle. You can hold it over to the circle position (with the custom menu set to optical preview only) and the lens will stop down to the taking aperture. The original use (and I still use it for this) was to preview how much depth of field you had at the aperture. With the DSLR in M (manual) mode, it also lights up the metering scale (K10, K20) or a set of numbers (Kx00) at the bottom right of the screen that indicate how far off your selected exposure is from the one the camera would select in an automatic mode.
05-10-2009, 03:33 PM   #7
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QuoteOriginally posted by nessamento Quote
i don't know much about lens, what exactly does it mean if it's an M lens?
It is a lens series. The lens will be labeled as an M lens. My two are labelled

SMC Pentax-M DENTAL MACRO 1:4 100mm
SMC Pentax-M 1:5.6 400mm

People also refer to K lenses, but there is no K on them. The mount was called PK, and my 400mm lens' predecessor would be labelled

SMC Pentax 1:5.6 400mm

They thing that causes the metering problem is that there is no A position on the aperture ring, which enables the DSLR to operate the aperture, and there are no electrical contacts to tell the camera body what the lens is, so we have to work around it. Pentax "crippled" the lens mount. One lever and all its mechanism was removed from the camera bodies. This lever told the camera body where the aperture ring was set in the absence of the electrical connections.
05-15-2009, 11:04 AM   #8
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K Lenses and M lenses

QuoteOriginally posted by nessamento Quote
i don't know much about lens, what exactly does it mean if it's an M lens?
When the K2 and K1000 were introduced in 1976, Pentax also introduced the k-mount bayonet lens mounting system. Many of the lenses introduced at that time, and for several years after, were reworked Super-Takumar and SMC-Takumar, screw-mount lenses. They were the same optically and the same size, as well.

Then, sometime around 1980, Pentax, in response to the success of the Olympus OM series cameras, introduced the M-series cameras, which were much smaller and lighter than the first-generation k-mount cameras. A new series of lenses was introduced at the same time, the M-series. The M-series lenses had no major new features, there were just in smaller packages, to match the smaller cameras.

What many people call K lenses (Canada Rockies is correct about the true nomenclature) and the M-series lenses are pretty much interchangeable, with no loss of features. That is, an original PK lens can be used on an M-series camera, or an M-series lens can be used on a K-1000, with equal funtionality. In fact, the K-1000 lasted so long that it was delivered, over the years, with whatever Pentax lens was then current, whether it was PK, M-series or the later A-series.

After the M-series lenses, came the A-series, which first appeared on cameras like the Program Plus and AutoProgram. These lenses have electrical contacts for the lens and camera to better communicate, especially aperture information.

Pentax likes to brag that ANY lens ever made for a Pentax 35mm camera can be used on their new digital cameras. This appears to be true. I use the 50mm, f/1.4 Super-Tak that came on my Spotmatic, on my K10D and it works perfectly. Of course, I don't get autofocus or autoexposure, but I do get nice, sharp pictures. I just set the camera in Av mode.

05-17-2009, 04:16 AM   #9
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And thats why i love PENTAX for its Backwards compatibility!!
05-21-2009, 08:16 AM   #10
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The new K7 will be the dream of all manual focusing lenses. Liveview is so good to focus manual lenses. I tried on Panasonic G1 and turned out fantastic. 100% coverage is another plus. Don't ignor that new focusing screen which is said to improves manual focus readiness too.
05-21-2009, 10:57 PM   #11
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QuoteOriginally posted by Canada_Rockies Quote
If you look at the power switch on a Pentax DSLR, you will see OFF ON and a circle. You can hold it over to the circle position (with the custom menu set to optical preview only) and the lens will stop down to the taking aperture. The original use (and I still use it for this) was to preview how much depth of field you had at the aperture. With the DSLR in M (manual) mode, it also lights up the metering scale (K10, K20) or a set of numbers (Kx00) at the bottom right of the screen that indicate how far off your selected exposure is from the one the camera would select in an automatic mode.
Wow, that option does a lot more than I realized. I only thought of it as a way to, "take a shot without saving to memory." With a 2 GB memory card I didn't need to conserve memory. Thank you for the additional information.

Occasionally I used it when I had a IR filter on the lens and the optical viewfinder was dark.

Last edited by LeoTaylor; 05-21-2009 at 10:58 PM. Reason: added sentence
05-22-2009, 08:58 AM   #12
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QuoteOriginally posted by LeoTaylor Quote
Wow, that option does a lot more than I realized. I only thought of it as a way to, "take a shot without saving to memory."
It only does that if you set the DOF preview to the "digital" rather than "optical" option in the custom menu. Why that was made the default is beyond me, but when using manual lenses, the optical preview is definitely the one you want, since it's the only way to get the meter to display. Although the K-m doesn't provide this option.
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