Understanding Lens Turbo (or any other booster) and the one stop advantage..got a question.

Discussion in 'Adapted Lenses' started by shaolin95, Jul 19, 2014.

  1. shaolin95

    shaolin95 TalkEmount Top Veteran

    942
    Jul 3, 2013
    Hello!
    So I keep reading that the booster gives you a one stop advantage and its true, I have tested it that way but my question is....on APC-C when using a legacy lens say, a F2.8 lens with a normal adapter...is it really just giving me an F4 stop just the same way as instead of a 24mm I am getting a 35mm range equivalent? Or is the F stop not affected so that 24mm F2.8 lens is still giving me 2.8 but at ~35mm ?
    I am trying to clarify now to understand if I am then suddenly "turning" my 24mm 2.8 lens into a 1.4 for real.
    Hope that is clear :D
     
  2. Poki

    Poki TalkEmount Hall of Famer

    Aug 30, 2011
    Austria
    A f/2.8 lens will ALWAYS give you a 2.8 aperture (i.e. f-stop). The reason simply is that the f-stop is simply the calculated aperture diameter in relation to the focal length - very simple math. What won't be similar is the T-stop. The T-stop tells you how much light is passing through the lens and reaching the sensor. A f/2.8 lens can, at most, transmit t/2.8, usually it's closer to t/2.9 - t/3.2 because of internal reflections and the not 100% transmission rate of optical glass.

    All speed boosters (i.e. focal length reducers) do is "reduce" the focal length of a lens, i.e. focusing the light which comes through the lens on a smaller surface. Due to this, you get a brighter beam of light - I'm sure you burnt ants with a loupe at some point - it's the same effect. The result is that you can take advantage of all the light transmitted through the lens, compared to only the cropped frame when using 35mm lenses on APS-C sensors. The APS-C sensor camera will show this as a stop faster, so you can make your 24mm f/2.8 lens, which formerly was comparable to a 36mm f/2.8 lens on a full frame camera, to a lens which is comparable to a 24mm f/2 lens on a full frame body.

    So in fact, you can sidestep the "full frame advantage" of higher ISO capacity because you can get more light on each pixel of your APS-C sensor. The downside, of course, is that more glass elements are added, so you will loose at least some light (although a tiny amount) compared to using the same lens on an 35mm body. Also, the speed booster might degrade the quality of the images, but that's up to the quality of the optical assembly in the respective speed booster.
     
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  3. shaolin95

    shaolin95 TalkEmount Top Veteran

    942
    Jul 3, 2013
    That clarifies everything for me and its great to have a full stop of gain indeed. I tested it and the drop in ISO or gains in Shutter speed were always one full stop so I am a happy camper plus IQ is excellent as well. :)
     
  4. Mattithjah

    Mattithjah TalkEmount Veteran

    244
    Jan 17, 2013
    Czech Republic
    Matěj
    Nice to hear… I would like to try SB as well, so what type of SB works for you so good? Thanx!

    Matej (sent from phone)
     
  5. shaolin95

    shaolin95 TalkEmount Top Veteran

    942
    Jul 3, 2013
    I bought the Canon FD Lens Turbo 2 but is my one and only experience with boosters :)
     
  6. Mattithjah

    Mattithjah TalkEmount Veteran

    244
    Jan 17, 2013
    Czech Republic
    Matěj
    Ok, thanx. Do you have any experience with Canon FL lenses on this SB? Does they fit and work?

    Matej (sent from phone)
     
  7. shaolin95

    shaolin95 TalkEmount Top Veteran

    942
    Jul 3, 2013
    Honestly, I havent tried any yet. I only have been buying the FDn ones and that one Vivitar. If I get my hands on one I will surely post about it though :)
     
  8. jai

    jai TalkEmount Top Veteran

    589
    Feb 4, 2013
    The main downside seems to be extra size and weight.

    A full frame legacy lens with a speedbooster is bigger and heavier than an APSC E-mount lens would have to be even if it was 1 stop faster. So you aren't getting something for nothing.

    My 35mm F2.8 MD Rokkor with Metabones is a lot bigger and heavier than the Sony Zeiss 24mm F1.8.

    A lot of people mention the degradation in image quality from extra glass, but actually I have found the opposite. Other than some significant vignetting (which a lot of the time I actually like) the image quality actually improves with the extra glass. When you focus the full 35mm image circle down to APSC size you end up with higher contrast.
     
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  9. roundball

    roundball TalkEmount Hall of Famer

    Oct 8, 2013
    USA