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Shift lens

Discussion in 'Pentax Chat' started by Gromit, Apr 30, 2013.

  1. Gromit

    Gromit RIP

    Now I haven't tried this yet, but shift lenses can usually be used to correct converging verticals. This video shows how to use the sensor shift on some Pentax camera to create the same effect.

    Shift lens

    It might be worth experimenting with.
     
  2. Done_rundleCams

    Done_rundleCams AP Forum Ambassador to Canada

    Very cool, indeed, Grom and the K30 has it as well :)

    Cheers,

    Jack
     
  3. LargeFormat

    LargeFormat Well-Known Member

    It is interesting but it is so easy to correct converging verticals and so forth in software that my 4 x 5 and 35mm shift lenses have been retired.
     
  4. Gromit

    Gromit RIP

    Yes you're right, it's very easy to correct verticals in software. It's the way I've always done it. However software conversion does effect the image quality to some degree. I'm not sure if shifting the sensor would affect the focal distance throughout the frame, any ideas?

    Discussing it with a few friends I found that Hasselblad use a sensor shift to increase the pixel count. This should achieve the same thing for Pentax users. Admittedly you could only use it on static images.

    Panoramas should also be possible by moving the sensor rather than the camera. This way each image should stay in perfect registration.

    I must get time with the camera to experiment.
     
  5. steveandthedogs

    steveandthedogs Well-Known Member

    Have always used software, but this is impressive, anyone want to buy me a K5IIs? Would rather do it in camera, suspect the result will be better.
     
  6. Done_rundleCams

    Done_rundleCams AP Forum Ambassador to Canada

    I think I'd like to do just to get people/other photogs come up and
    ask me what I'm doing :D

    Jack
     
  7. daft_biker

    daft_biker Action Man!

    Applying shift on a shift lens means using a weaker part of the image circle than if you used the centre of the image circle so it also effects image quality.

    Unless you're shooting close up to things I doubt you'll notice the focus distance change though.....it's not going to change any more than it does normally.
     
  8. Benchista

    Benchista Which Tyler

    That's true, but as a result, such lenses have larger imaging circles than normal for the format so that the impact of this is reduced. The weakness of this sensor-based approach is that that won't be the case, so you are likely to be using pretty much the extreme edge of the imaging circle, which will quite probably have an impact on image quality. It wouldn't surprise me at all if the software solution wasn't thus better - it'll depend on individual lenses, of course. Still, an interesting use of the technology.
     
  9. Gromit

    Gromit RIP

    So ideally you need to use FF lenses for this to work best, pity I don't have any now :(. Vignetting could also be a problem without the extra coverage of a FF lens.

    It's an interesting concept but it looks like there will have to be a batch of tests and comparisons to see how useful it could be.
     
  10. Benchista

    Benchista Which Tyler

    Yes, on all counts.
     
  11. daft_biker

    daft_biker Action Man!

    Aye, there's no obvious loss of IQ even if I apply the maximum 11mm of shift to my shift lens, at least not when stopped down enough. Using a lens that could cover 6x6 on APS-C is possibly a bit OTT though :D

    Using sensor shift to correct converging verticals implies the use of rectilinear wide angle lenses to me.....and ones that have a large enough image circle for at least 35mm and are still wide when used on APS-C at that. I suspect that kind of limits lens choice to being no wider than about 20mm? Then there's drawing distortion to consider and how difficult it might be to correct when the sensor isn't in the centre of the centre of the image circle. All that coupled with the restricted space to move and impact on image quality already mentioned doesn't make sensor shift sound particularly useful for correcting converging verticals.

    I could however see it being useful with something like a 100mm macro so you can adjust the composition whilst leaving the plane of focus where it is. Hopefully a high quality macro lens for FF will be good enough over a large enough area to allow for some movement without a significant drop in IQ. I wouldn't mind trying it anyway! :)
     
  12. PeteE

    PeteE Well-Known Member

    I got the 75mm f4.5 'shift' lens for my Pentax 6x7 many years ago in 1979 I think it was - I did a lot of Architectural work on 120 slide film for a company which went broke and all the work dried up , same as the requirement for 'slide film' all want 'Digital files' now and I have loads of E6 slide films not being used up in my fridge!
    [​IMG]
    Pentax 6x7 03 by pentaxpete, on Flickr

    This is the lens on my later Mk II 6x7 Pentax
     
  13. Benchista

    Benchista Which Tyler

    Very nice.

    Made me think about using a shift lens with further sensor shift - that could be excellent for panoramics. ;)
     
  14. Gromit

    Gromit RIP

    Now that's just being greedy ;)
     
  15. daft_biker

    daft_biker Action Man!

    Could be useful for just extending the range of shift available too.

    It could also be interesting when combined with tilt.....rather than use the weakest part of the useable image circle at max tilt it might be helpful to shift the sensor back towards the centre so you get the same amount of tilt from a better bit of the image circle. Maybe!....I think it should work even if it means I need more extension tubes:confused:
     

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