C 50mm f/4.5

  • Angle of View: 82 deg
  • Construction: 11 elements/8 groups
  • Filter Size: 77mm
  • Minimum Focus: .13 ft
  • Weight: 780g
  • Floating Element:  This lens has a floating element which is moved by a seperate ring marked with green numbers, located in the front of the shutter speed ring. Most lenses, like this one, are designed to have the best sharpness when focused at infinity. Other lenses, like many macro lenses, are designed to have the best sharpness when focused closely. The floating element allows you to get the best sharpness at a range of focusing distances.
  • Notes: Acceptable results can be had by setting the floating element ring at infinity. This will give acceptable focus from about 7 feet to infinity. Setting the ring at 3.3 feet gives acceptable result from 3.3  to about 7 feet. If focusing closer, set at 3.3 feet at stop down as much as possible.
  • Using: To use the lens, first focus with the bellows focusing. Second, use the focusing scale on the side of the body or a tape measure to find the focusing distance. Third, align the floating element ring so that the green number matching the distance lines up with the red dot on the depth of field scale


6 responses to “C 50mm f/4.5”

  1. Panoramic PEI Avatar
    Panoramic PEI

    I recently purchased some Mamiya RB SD gear separately from all over the place.
    I just received the 50mm RB Sekor C Lens, although I haven’t received the Mamiya RB SD Body as yet.
    There is a noticeable clunking sound as some slight glass movement, just wondering if this is normal as it might something to do with the floating element or is it a defect? All appears normal visually.
    Also this lens has a silver collar on the rear of the lens, would it signify I will absolutely need the Mamiya Spacer Adapter for use with the Mamiya RB SD? Your replies are greatly appreciated.

    1. jodys Avatar

      The clunking sound does not sound right. I have the 50mm C and I do not have any clunking noise. The outer elements should not move at all when focusing.

      As to the spacer, Mamiya indicates that they are required. However, I do not always use a spacer on my SD and I have not had any noticeable issues, either mechanical or with light leaks. Perhaps it is more important on heavier or longer lens (like 360mm or 500mm lenses).

      1. Panoramic PEI Avatar
        Panoramic PEI

        Actually some describe the clunking sound as a rattle when inverting the lens in your hand.
        Apparently some RB lens owners also noticed the rattle & go on to mention that Mamiya explains it is the bearings & that some lenses will rattle. Not to be alarmed, it will not affect the function or quality of the lens.
        The elements do not move in this Lens.
        I have no choice but to wait until I can test further when I receive the SD Camera & Back since the optics are perfect visually & the shutter functions as it should & sounds accurate. The diaphragm operates normally. It also appears cosmetically as well taken care of.
        Worse to worse if found defective according to the image test results, I will have the Dealer repair it than return it & look for another Lens.
        I will not bother with the Spacer for starters, other things to think about first.
        Your reply is greatly appreciated!

  2. […] Mamiya Sekor C 50mm f/4.5 […]

  3. art Avatar

    Hi, ı have just got my Mamiya Rb Sd and this camera came with the 127 mm lens which has floating elements .When ı Inverted the lens ı have heard the same sounds . Even tough my lack of experience , I didn’t think it was a fault . after ı read your answer , relaxed . Did you find anything .


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