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Old December 16th, 2007, 04:52 AM   #1
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2x convertor

What happens when you put one of these in front of a prime or zoom lens on an adaptor like the LEX

I seem to recall that the aperture is doubled - I've got a 70-200 zoom 2.8 so that means it would become 5.6?

What's the advantage or disadvantage of adding one of these to a set of 35mm lenses?
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Old December 16th, 2007, 09:24 AM   #2
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The only 2x or doublers I have encountered go on the back of the lens between the mount and the camera. A 2x on a lens will reduce the amount of light it will pass through as you suggest. Another bad which may happen is bits of dust on the rear element of the lens you attach the doubler to may show as soft shadows, so cleanliness wil be next to godliness in some instances.

The Sigma 50mm-500mm zoom will also clash its rear travelling element against the front of the 2x. There is a lockout which will prevent this but you must remember to select it on. Some other lenses may do likewise and may not have this safety feature.

But back to your Letus35 Extreme. I understand it to be superior to the original but the benchmark P+S Technik is not recommended by the manufacturer to have apertures tighter than f5.6. IN the realworld, you can sometimes get away with it so there may be soime exceptions with the new Letus as well.

The doubler will also increase any softness inherent to the lens which goes on it.

Last edited by Bob Hart; December 16th, 2007 at 09:27 AM. Reason: added text
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Old December 16th, 2007, 08:34 PM   #3
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Thanks Bob,

is there anything you don't know about lenses & adaptors?

While I'm asking, what focal length (is that the right term?) would it give the lens I mentioned - would a 2x converter make a 70-200mm into a 140-400mm?

I'm going to be getting footage of surfers and I figure a long zoom lens on the end of the LEX would be the best bet - it should be pretty bright out there and I'm not overly concerned with DOF but rather than be out on the rocks in the spray worrying about the camera - I want to get further back with a longer lens.
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Old December 17th, 2007, 05:32 AM   #4
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Paul.

Don't put to much stock in what I seem to know. Jacks of all trades tend to know just enough to burn themselves like in trying to light a candle to go looking for a gas leak inside the caravan at night. - I didn't do that by the way.

The 2x makes my Sigma 50mm - 500mm in effect 100mm - 1000mm. With the Sigma, there is a wrinkle. The back of the lens is a travelling element which goes forwards when the zoom is racked to long and comes right back on wide.

The front of the doubler clouts that rear element when it comes back.

Zoom lenses built like that may not be able to go fully wide. The Sigma therefore only goes 200mm - 1000mm. I think Carl Zeiss Jenazooms are built similarly but also may have their own solution for doubling.

With your zooms I think you will be okay for exposure. You may get fixed pattern on the sky and the bright foam once the waves go over but except for the burned out moments before the foam starts to patch out there is probably going to be enough texture in the shot to hide most of any fixed pattern if it shows up.

While you are doing all this, try a polariser. You may be happy you did. If you only have a crappy tripod without good fluid dampening, fasten a broomstick along the tripod handle poking well back and also sticking out in front. Use one hand on the long handle behind and one on the long handle in front when not chasing focus.

Work the broomstick like a see-saw or an old set of balance weighing scales. With the handles long providing leverage, learning over a low set tripod and using the LCD, you can get quite good control with this rather crude method. You don't do so much of a see-saw action as also partly using a bit of your back movement to rock the tripod head and camera over a centre, forward and reverse.

Like with aquiring aircraft in flight, finding the surfer may be initially difficult, which is why you want a zoom as I am sure you already know. Starting at 140mm might be a bit difficult so you may need to make a simple ring-sight and harmonise this to your camera eyepiece viewfinder.

Search with left eye, get distant subject in centre of ring, use right eye for eyepiece, surfer pops into image - got him.

If you set the tripod low and work over the top of it, you may need to use a spare human to aquire for you using the eyepiece, then switch to the LCD for you to follow. Unlike chasing aeroplanes, your surfer once up and running is a bit more predictable so you may well be able to stand the tripod at normal height, cross the broomsitck from right to left to come out for your left hand under the lens and use your left hand well forward and your right hand well back to control the shot and keep your fingers close to work the focus.

The alternative is to mount two cams on the same tripod on a bar, one with long lens, one standard, so the image centres coincide at wide on the long lens and long on the standard camera, then use the standard camera as a spotter or even shoot with it. You will find the moves you shoot on that when tracking with the long camera will be incredibly smooth.

Depending on your lenses apertures and exit pupil size, you may get a distinct hotspot with the new Letus but I really only guessing here.

Cut up a weeties box to make a hood for your LCD screen.

Last edited by Bob Hart; December 17th, 2007 at 06:04 AM. Reason: added text
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