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Thread: MC Gemini Wide Auto for Pentax K mount - What's 'auto'

  1. #1

    MC Gemini Wide Auto for Pentax K mount - What's 'auto'?

    I have an old Pentax K1000 and a few lenses from (many) years back. I'm in the process of rediscovering these lenses. One of them is an MC Gemini Wide-Auto 1:2.8 f=28mm. I've always been treating it as a fully manual lens since there is nothing auto about the K1000*. I'm wondering though what is meant by the auto part in 'Wide-Auto'.

    Is anyone familiar with this lens?

    Here are some pictures:
    MC Gemini Wide Auto for Pentax K mount - What's 'auto'
    MC Gemini Wide Auto for Pentax K mount - What's 'auto'
    MC Gemini Wide Auto for Pentax K mount - What's 'auto'

    * Except the K1000 has an exceptionally useful light meter.
    Last edited by kib; 2nd June 2013 at 05:25 AM.

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    Re: MC Gemini Wide Auto for Pentax K mount - What's 'auto'?

    From the photo of its rear I think I see the lever* which the camera presses to close the aperture to the pre-detirmined f/stop and was 'auto' in its day so you can focus wide open but when you press the trigger it closes down .. somewhat similar to the modern digital camera which focuses wide open etc. You do not show us all the sides and I would be looking for an 'Auto/Manual' [ A-M ] sliding switch which Takumars had which in todays camera one focus wide open and then slide the switch to work at a desired aperture and the digital camera will re-adjust its shuuter speed if working in A Mode. After using auto digital for quite a few years it took a little while to get the hang of working this way when I use my 50mm Takumar on a digital camera, E-PL1 Olympus, but it isn't a problem now. My 35mm Takumar has a lever to do this function.

    I had a K1000 but I don't remember it having any other connections such as what looks like a row of round contacts at 11o'clock on the back photo so perhaps the lens was designed for a more modern model than the K-1000 which I never had.

    *if with an apertureyou press it and if I'm right the iris will close from its default wide open position to what you selected. If those buttons are contacts, andthere is no A/M slide, it is possible the camera has to tell it what aperture to use?

    LOL I am quite wrong I went to Wikipedia and discovered that lever is a focusing connection
    http://en.wikipedia.org/wiki/Pentax_K_mount
    Gemini is listed there
    I guess I didn't have a K1000 but an earlier model and used an adaptor ring to adapt it for my M42 lenses
    Last edited by jcuknz; 2nd June 2013 at 06:49 AM.

  3. #3
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    Re: MC Gemini Wide Auto for Pentax K mount - What's 'auto'?

    I have a Pentax K20D, and while that doesn't make me an expert it appears that if the red dot is moved to below the green AP it will work in auto mode. The contacts above connect to the camera and all settings can be done through the camera. The "wide" refers to the "angle of view" the lens has.
    I sometime use an early K-mount 135mm lens which is auto except that it is manual focus but with focus confirmation.
    Hope this helps.

  4. #4

    Re: MC Gemini Wide Auto for Pentax K mount - What's 'auto'?

    Thanks jcuknz and Mito for the responses. It seems Mito is right, turning the aperture to match up the green circle with the red diamond enables auto mode and the aperture can be set by the camera. There are no other switches on the camera.

    Thanks again.

  5. #5

    Re: MC Gemini Wide Auto for Pentax K mount - What's 'auto'?

    I had some time to take some controlled photos with this lens. Not particularly photogenic but they demonstrate the lens' capability:

    MC Gemini Wide Auto for Pentax K mount - What's 'auto'
    ISO 100; 28mm; f/2.8; 1/500

    MC Gemini Wide Auto for Pentax K mount - What's 'auto'
    ISO 1600; 28mm; f/2.8; 1/800

    MC Gemini Wide Auto for Pentax K mount - What's 'auto'
    ISO 800; 28mm; f/2.8; 1/125

  6. #6

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    Re: MC Gemini Wide Auto for Pentax K mount - What's 'auto'?

    Auto, before the event of automatic exposure and automatic focus cameras, on SLR lenses, was the designation on Pentax lenses that automatically closed the diaphragm to the chosen value, by pushing in the pin at the rear of the lens. The first SLR cameras did not have this capability, but there were instead often two rings for the diaphragm, one to set the value, the other to actually close it down.

    Focusing is best accomplished with the lens wide open, and therefore lenses were by design wide open for focusing and were stopped down only when the image was actually taken, or when a preview button or lever was actuated, or with the twin rings, it was stopped down by turning the second ring till it stopped against the other. Auto thus was that the lens was stopped down to chosen value when the release button was pressed for taking the picture.

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