Teleconverter questions... (Canon FD specific)

Discussion in '35mm Cameras and Accessories' started by Markster, Feb 24, 2011.

  1. Markster

    Markster Member

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    So I've just read some things about these 1.4x and 2x teleconverters. Basically magnifying glasses for your lenses.

    I'm interested in learning a bit more about them. I have read some comments about getting what you pay for, just like lenses. Some are worse than others, etc.

    With the Canon FD mount, how does this work with the aperature? Do you have to fix the aperature ring in the lens proper, or does the camera body still control the lens aperature through the teleconverter somehow?

    With a teleconverter I have read about the loss of light. Is this automatically accounted for in the camera's light meter? Say I have a 200mm zoom with a minimum f/5.6 stop mounted on a 2x teleconverter that takes up 2 stops of light. Okay, so minimally speaking you would have to operate that lense at f/11, right? Does the light meter in a camera take this into account, or are they too dumb/simple to do that? They might say "needs f/5.6" still, and you have to mentally adjust the shutter to reach f/11, right?

    Granted this will vary with the quality of the teleconverter, but are you sacrificing something specific, like sharpness or contrast?

    Also I'm not finding much luck to confirm you retain full infinity focus on teleconverters (not to be confused with extender tubes which lose that focus). One or two blurbs state you should, but other comments say they don't. Can anybody confirm this? Is it only for macro work, or close in work? That is, you can't use it to zoom in on a mountain peak or on a picture of your downtown area from afar?
     
  2. MattKing

    MattKing Subscriber

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    Lots of questions here :smile:.

    A teleconverter designed for the FD mount should operate with the aperture in the lens in the same way as the lens itself works. One exception might be an older teleconverter, designed for an FL lens, which I would assume would work with an FD lens, but would necessitate stop-down metering.

    Meters in FD mount cameras don't actually know what aperture you've set. They just know that the aperture you've set lets in 1, 2, 3-3/4 or whatever number of stops of light then the maximum aperture of your lens. (The EF lens Canon cameras are different - they stubbornly want to be able to tell you the exact number of the f/stop set).

    So the meter reacts to a 2x teleconverter exactly the same way it responds to a 2x neutral density filter - it sees one stop less light, and instructs you accordingly.

    Teleconverters add all sorts of distortions/aberrations, in varying amounts. Chromatic aberration, spherical aberration, pincushion distortion, barrel distortion - they are all possible. The distortions/aberrations will also depend on the teleconverter/lens combination - for example, a lens with a moderate amount of pincushion distortion might be a perfect complement to a teleconverter that adds barrel distortion.

    Some teleconverters are designed for close focus work - and some of them are limited to close focus work, while others (most I would say) do permit infinity focus. As in most lenses, teleconverters often give optimum results with particular lenses, at particular subject distances. That is why you see teleconverters from the lens manufacturers that are described as being for use only with certain lenses.

    I have and use a Vivitar macro-focus teleconverter with my Olympus OM equipment. It gives acceptable results at infinity, but really shines at close distances.

    One final point- I see from your signature line that your longer lenses are zooms. In my totally unscientific opinion, teleconverters tend to work better with fixed-focus lenses.

    Hope this helps.
     
  3. Rol_Lei Nut

    Rol_Lei Nut Member

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    You lose 2 apertures with a 2x converter and 1 aperture with a 1.4x converter.

    If your camera's meter reads through the lens, then the light difference is automatically compensated
    (some more modern cameras might show the nominal aperture rather than the effective in the viewfinder, but that has no practical consequence).

    If you're using a hand held or a not therough the lens meter, then you need to compensate by hand (on a 2x, if your meter says, say, 1/250 f/8.0, then you need to set the lens' ring to f/4.0).

    Full infinity focus is kept (unless you have a real dog!)

    Quality can vary drastically: some are specifically designed to work with particular lenses (or a particular range of lenses), some are apo-corrected, in combination with apo teles, they are still better than non-apo teles without a converter. At the other end, some are just murky or barely decent.

    IMHO it's worth investing in a really good one, possibly designed for a particular high quality tele, otherwise the results don't justify its drawbacks. I had several "o.k." ones in the past (supposedly fairly good old-school 7 element Kenkos) and never used them, while the "good" one I now have sees lots of use.

    As the previous poster stated, I'd seriously doubt if you'd get very good quality using a converter on zooms (also due to light loss requiring longer exposeres and so on...).
     
  4. Markster

    Markster Member

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    Some of the folks on the Internet are saying they did tests with zooms and compared 300mm without the converter with 150 with 2x converter and you cannot tell a difference when blown up into 8" prints. Granted I take that with a grain of salt because maybe they just had the right combination.

    However as a man of budget constraints I am very curious. It might make my 200mm zoom into a 400mm zoom. THAT would be impressive. The problems become the speed of the lenses and available light, then.
     
  5. OldBikerPete

    OldBikerPete Member

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    If you are using lenses which are just adequate in resolving power (and if you're using zooms, you are) then the resolving power of the combination will be reduced at least by the power of the teleconverter assuming the teleconverter itself is perfect. ie if your lens is capable of 80 line-pairs-per-millimetre (lp) alone, then the combination will be capable of a maximmum of only 40 lp with a perfect 2x telconverter and in practice, less than that.
    If the lens alone is capable of 300 lp (and some are on an optical bench) and the 2x teleconverter is just as good then you won't notice any difference in sharpness because the finest-grained B&W films are only capable of about 140lp in daylight.

    Peter.
     
  6. Markster

    Markster Member

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    Doing some reading today about the speeds, loss of light, etc... Looking at my f/5 200mm zoom, that would be a real pain to try and shoot even in bright daylight.

    I guess I need (aka want?) some faster zooms. I don't suppose there are many good 80-200 range zooms with f/2.8 or less?

    Or am I just dreaming now?
     
  7. Andrew K

    Andrew K Subscriber

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    Teleconvertors are a cheap way to get a longer focal length lens - and using genuine Canon lenses with a teleconvertor the results are usually sharper than using non-Canon branded tele lenses..

    Canon made 3 - teleconvertors - a 1.4 and 2 different 2X/

    the 2xA was for lenses 300mm and over..

    the 2XB was for lenses up to 300mm

    they were designed for optimal results with the dedicated lenses.

    Also if you are buying Canon teleconvertors make sure they will fit on the lens you intend to use - some like the 1.4 will only work with certain lenses...

    And when using ANY Teleconvertors or Extension tubes on Canon FD - ALWAYS mount the convertor/tude to the body first - then mount the lens onto the convertor/tube.

    You will get into all sorts of coupling issues if you do it differently...it was one of the more common complaints from people when I worked as a camera technician at Canon....

    Personally I would pick up a 200/2.8NFD and a Canon 2XB - you get 400/5.6 and pretty sharp results..

    Or pick up a second hand Canon 300/4....or if you need a real tele the Russian MTO 500 mirror lenses are very sharp in the middle..they vignette a bit, but the ones I've had have all been sharp...
     
  8. Markster

    Markster Member

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    I can see that it was really intended for use with primes because of their faster speeds, but with the prices involved I would hesitate. I'm thinking of moving away from primes simply because the framing isn't there.

    I'm not cropping/blowingup in the printing process (I don't make my own) so I have to put in the effort to frame it right and keep it as the way it prints the first time.

    This has been quite enlightening, but perhaps I won't go this route. Zooms aren't fast enough and that 2X-b costs a lot these days. 2X-a is plentiful and cheap, but doesn't help as much since my biggest lens tops out 200mm.
     
  9. Djangaroo

    Djangaroo Member

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    Picking up this thread four years later... I always read that 2x converters lose two stops of light. I was today trying a Tamron 2x FD fit with my Canon 135mm f2.8 (on a Canon A1) and the viewfinder lightmeter showed f4; if I then went for a quicker shutter speed or focused on darker light the f4 flashed. So I am confused since I was apparently only losing one stop.
     
  10. gzhuang

    gzhuang Inactive

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    Well, if you really need extra reach just buy a FD mount mirror lens. They're amazing. :tongue:
     
  11. MattKing

    MattKing Subscriber

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    Most likely the change in field of view caused the meter to read from a different portion of the scene, resulting in a different reading.
     
  12. Andrew K

    Andrew K Subscriber

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    Sorry but it's a simple mathematical/optical fact - fit a 2X teleconvertor to a lens with a f2.8 maximum aperture and your max aperture becomes f5.6. Fit a 1.4 teleconvertor to a f2.8 lens and the maximum aperture becomes f4. This cannot change..

    With your camera I think the answer is that the full aperture signal pin data is not being transferred to the body correctly by a non - Canon teleconvertor (yes I was a camera tech at Canon back in the days when FD cameras were sold new..).

    Yes - the lens tells a A or T series camera what it's full aperture is - the bump on the rear of the lens pushes the cylindrical hollow silver pin (that's on the lower left looking from the front of the camera) - how far it's pushed in tells the camera the maximum aperture of the lens.

    I learn't this the hard way as I can recall a customer who had a similar problem with a non - Canon lens. In the end I glued a washer to the back of the lens so it set the aperture correctly - not a standard repair, but as it was the only lens they owned it worked, and I did it as a favor because I was only supposed to be repairning the camera body....

    This is most likely why the A1 is showing f4 instead of f5.6.

    I