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lens question

Discussion in 'Lens Lust' started by commtrd, Aug 21, 2008.

  1. Why is it not possible to make a lens that does not attenuate light at all? As far as I know, there are no lenses available with max aperture < f1.4? What limits the creation of say a f0.5 lens for instance?

    BTW I just got the Sigma 150 macro and the Nikon 14-24 for use on D300. I hate to say it but the Sigma may actually be superior to my 105 VR micro lens. However I will never sell the 105 because that is such a great focal length. Can't wait to someday get a D3 for the 14-24, 24-70, and 105 VR for weddings and events etc. I am torn between getting a 200 f2 someday or acquiring a 70-200 if Nikon updates the lens.
     
  2. There are enough compromises involved that they are typically fixed focus, with an extremely close focus distance as well.

    I've owned a number of the f/0.75, f/0.8, and f/1.1 Rodenstock and Kowa lenses, and used Bjørn's Repro-Nikkor. They're all very interesting lenses, but somewhat limited in what you can do with them.

    Everything from coatings to having enough elements to adequately correct the optical design can influence the light transmission to the point where the maximum f/stop would exceed the maximum t-stop (transmission of light) to the point where they would no longer match up. I don't know of any still camera lenses that are designed in such a way.
     
  3. pforsell

    pforsell

    Jan 15, 2008
    Hi,
    currently in Nikon lineup there is a Nikkor AIS 50 mm f/1.2 lens but as far as I know Nikon has not made faster than f/1.2 lenses for the F-mount. Canon has had a 50 mm f/0.95 lens but that was prior to the EOS line, if I remember correctly. And the last speculation is that I have a faint memory of reading at some point that the theoretical maximum F-stop for a lens is f/0.5. Beyond that the lens would project the image inside the lens and not be able to produce a real image at all.

    Current high-ISO cameras have reduced the need for ultrafast apertures. Lenses with max aperture near or less than f/1 tend to be big, heavy and expensive and thus there is not much market for those. The bread and butter lenses for manufacturers are those 16-85 f/3.5~5.6 lenses anyway.

    Someone wanting only the ultrathin DOF of an ultrafast lens can use digital effects or tilt/shift lenses for many of those needs.
     
  4. The reason is their very short register distance. I have 3 of these lenses (incl. the TV-Heligon 42mm/0.75), one of them, a Rayxar 50mm/0.75, has a register distance of 0.8 (!) mm. In their original application, these lenses are able to focus to a wider distance (don't know if this includes infinity), but on a DSLR these lenses can be used only at macro distance.
    As a consequence, the effective aperture also changes. I have read somewhere that the effective aperture of the TV-Heligon 42/0.75 on a Nikon DSLR is somewhere around f/1.0.

    Anyway, it is fun to use those lenses for creative work - for anything else they are less useful :smile:.

    You can see a few examples here

    Cheers
     
  5. pforsell

    pforsell

    Jan 15, 2008
    As far as I remember correctly, at f/0.5 the register distance becomes negative. CBA to google any documents to prove that faint recollection right or wrong.

    Beautiful images in the gallery!!
     
  6. Seems logical. So, why not place the sensor inside the lens :biggrin:?

    Well, thanks!

    Cheers
     
  7. There is a non-attenuating lens ... it is called a pinhole camera; however, the F/# is rather high. :smile: In an actual practical lens using glass elements, the internal absorption of the glass, scatter, surface reflection losses (coatings mitigate this to a large degree), etc. result in light loss. Important number is the T/# for exposure (F/# divided by transmittance) while F/# is for DOF.

    The minimum F/# is 0.5 when a lens is aplanatic, i.e., free of spherical aberration and linear coma. If this restriction is removed, then a parabolic mirror can have a F/# as small as 0.25. While free of spherical aberration, it suffers from horrid coma. In general, a lens faster than F/0.9 is going to be not so good overall and I have seen few faster than F/1.2 that are good.

    FWIW, I have designed (and made a few) special-purpose all-mirror lenses that had unobscurred pupils and F/# <2. The FOV was about 5-8 degs. In this case, the T/# and F/# were close. These lenses are heavy and cost a lot as they were custom made. Also, they were not for 35mm cameras. :wink:

    Regards,
     
  8. max aperture

    Very good information. The thread was just hypothetically wondering what the max aperture could be for a lens and still be useable. Probably suffice to say that a max aperture of f 1.4 will be effectively all that would be needed especially now that there are digital cameras that have very good high-ISO capability.
     
  9. Hi.

    Canon produced a 1.0/50 mm lens not long ago. EOS-era ... no idea, whether it's still in production.

    Actually, the "aperture number" does not mean the light transmission is reduced by this factor - it only describes the relation between the focal length and the maximum lens diameter within the lens.

    So, a lens of 50 mm focal length needs a 25 mm lens diameter to become a f1:2/50 mm ... or 50 mm diameter to become a f1:1/50 mm.

    Not really interesting regarding the applicability, I admit. But maybe not bad to know ...

    Regards,

    Mattes
     
  10. marioni

    marioni

    808
    Jan 22, 2006
    Of course there are.

    Nikon themselves have made a 55/1.2, 50/1.2 and 58/1.2. In the good old days, I think just about every half-decent camera company made a f/1.2 lens. Canon have made 50/1 (slr) and 50/0.95 (rangefinder) lenses. Leica has a 50/1 which is the mother of all 50mm lenses. :wink:

    Why there are no f/0.5? Why make something that wouldnt be practical at all, and no one would be able to afford it anyway? I have no idea if it's even possible to make something that fast. I would settle for f/1 and f/1.2 lenses. :wink:

    No, sorry. Show me a f/1.4 lens that gives images like Leica Noctilux.. High ISO capability of D3/D700 has nothing to do with fast lenses.
     
  11. paulskimcb

    paulskimcb

    577
    Feb 12, 2007
    Midwest
    Great shots there. Do you have any pictures of the lenses themselves?
     
  12. Agreed - partly. But the applicability of faster than 1.4 on FF is extremely limited. Even 1.4 is difficulr to use. While I like the ability of isolating subjects with my 28/1.4, I hardly ever use 1.4 with the 85/1.4 when shooting portraits. IMO it looks very strange when the eyes are tack sharp but the nose is already fairly blurred.

    Cheers
     
  13. Thanks Paul!

    Actually, not. However, that reminds me to take some images.

    Cheers
     
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