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12-14-2019, 01:46 PM   #1
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Vivitar 28-70 Problems

As I'm rather new to ILC cameras and Pentax, perhaps I'm doing something wrong or misunderstand how things work, but I'm having an issue with this lens that I just picked up. The lens is a Vivitar 28-70 1:3.5-4.8 Macro Zoom.


Since this is a lens with an A mode, shouldn't the lens communicate to the camera the focal length as well as aperture settings and whatnot? When I turn my K-7 on, it asks me for the focal length like it does for my M50. Is this normal or is this something else that isn't working correctly? If it's normal, how do I go about changing the setting as I zoom in/out? Do I have to turn the camera off and back on and select what I'm changing the focal length to every time? What is the easiest way to verify that the aperture is actually working correctly in auto mode? It does seem to detect that 3.5 is the fastest setting, but if I zoom out to where it should change to 4.8, the camera still stays set to 3.5. Is this just how this lens works on these cameras or is there something wrong with my copy?

Also, when rotating the lens, I can hear what sounds like something broken inside the lens falling around inside the lens. There's also a scratch across the glass that was not advertised nor shown in the pictures. (It was shipped in a bubble-wrap padded envelope, so it might have been working fine when they sent it but got busted in transit?)


I bought it as used but fully operational and functioning. The rattling inside is worrisome as I've no idea what that could be and I don't know if that's just how these lenses work in regards to focal length and aperture. Should I request a refund for it not being as advertised?


Any help you can give is appreciated.

12-14-2019, 04:30 PM   #2
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The camera will ask for the focal length to be entered for any non-autofocus lens, so this is normal, the procedure being that one "should" reset the focal length whenever there's any significant change in the zoom setting, it'll be up to the operator as to how much "leeway" to allow the camera before intervening. No need to turn off, (though it may be as quick) but if there's a configurable "control panel" or Info screen on the K-7 you may be able to change the focal length there (or in the menus) ... however the "rattling" is definitely a cause for concern, as is the scratch, definitely a case for return for a refund!
12-14-2019, 04:45 PM   #3
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QuoteOriginally posted by kypfer Quote
The camera will ask for the focal length to be entered for any non-autofocus lens, so this is normal, the procedure being that one "should" reset the focal length whenever there's any significant change in the zoom setting, it'll be up to the operator as to how much "leeway" to allow the camera before intervening. No need to turn off, (though it may be as quick) but if there's a configurable "control panel" or Info screen on the K-7 you may be able to change the focal length there (or in the menus) ... however the "rattling" is definitely a cause for concern, as is the scratch, definitely a case for return for a refund!
Thank you! I didn't realize it was only AF lenses that sent the focal length information, I thought it was sent with the aperture settings.

As for setting the focal length, it looks like I can't do that from the info screen on the K-7.

Due to the rattling, I guess I'll contact the seller and see what we can work out.
12-14-2019, 07:16 PM   #4
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QuoteOriginally posted by Gorgarath Quote
I didn't realize it was only AF lenses that sent the focal length information, I thought it was sent with the aperture settings.
On the A-series mount, only the aperture range is communicated, as a code via the row of contacts/insulators on the mount. The code indicates the largest and smallest apertures the lens is capable of. The camera sets the aperture by the number of steps it moves from the largest aperture (or smallest, I forget). It's all very 1980s technology. It wasn't until the F-series lenses that the "data" pin was added, which passes actual lens info in a digital stream. There are a handful of modern manual-focus lenses that have the data pin, but most A-series lenses, (especially vintage ones), aren't going to communicate focal length.

12-14-2019, 08:16 PM   #5
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QuoteOriginally posted by THoog Quote
On the A-series mount, only the aperture range is communicated, as a code via the row of contacts/insulators on the mount. The code indicates the largest and smallest apertures the lens is capable of. The camera sets the aperture by the number of steps it moves from the largest aperture (or smallest, I forget). It's all very 1980s technology. It wasn't until the F-series lenses that the "data" pin was added, which passes actual lens info in a digital stream. There are a handful of modern manual-focus lenses that have the data pin, but most A-series lenses, (especially vintage ones), aren't going to communicate focal length.
Thank you for the additional information. I'm thinking that with zooms, it might be easier to go with F-series and newer then (I think this corresponds with the first version of the KAF (and newer) mount as opposed to just the K mount?) just to have all the data available and not have to take notes as I'm terrible at notes. I'm kind of curious as to how it would work if I left the camera set at 3.5 as I zoomed out to where it has a 4.8 maximum aperture. Assuming the lens would only go to 4.8 but the camera would record it at 3.5? I've already packed it back up so I probably won't test this. Not to mention, I'm not sure how to determine what the lens actually did.

For primes, A series I think would be nice just so the data gets recorded in the EXIF, though I've had a little bit of fun trying to figure out how to work my M-50 and am looking forward to playing with it a bit more. I really need to get faster at focusing, but it'll hopefully come over time. I was skeptical on how much I'd use the all manual prime, but I rather enjoy it.
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