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Old January 2nd, 2010, 07:57 PM   #1
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n00b question: what lenses can i use on a letus extreme?

i have a canon xh-a1 camera and plan to get a letus extreme. i see that there are different mounts for different lens types like nikon, canon, m42, etc.

how do i know what lenses i can buy for the letus? if i get a nikon lens mount does that mean i can buy any type of nikon lens and it will work? i just want to know how to distinguish between lenses that will work and ones that wont when i buy them online. thanks for any help!
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Old January 2nd, 2010, 10:26 PM   #2
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People seem to be more commonly using Nikons. Canons are fine but some which have automatic exposure controls do not have manual iris control which you need when using the Letus. The flange to focal plane distance for the Canons is about 44mm, the Nikons is 46.5mm.

This means you can buy a simple adaptor to fit Nikons to a Canon mount but not the other way around.

Your lenses of whatever brand, preferably should be prime lenses and preferably of f1.8 or wider apertures. Popular and older lenses seem to be the Nikon 50mm f1.4, 50mm f1.2, 55mm f1.2, ( Noct Nikkor 58mm f1.2 and 28mm f1.4 if you can afford them.) Nikon 35mm f1.4, Nikon 14mm f2.8.

These have metal barrels and a friction lube which dampens the focus movement.

Some older Nikons have a deeper shoulder ring which comes back over and around the mount. This interferes with the mount on newer Nikons, on the Letus and P+S Technik Mini35 Nikon style mounts and prevents the lens from seating correctly on the flange face.

Sigma-for-Nikon lenses in f1.8 which are adequate are 20mm and 28mm. The 28mm autofocus lens can be a bit sloppy.

Try to stay with manual focus lenses. The manual-autofocus lenses tend to have shorter throws on the focus ring which is harder to manage and the moving lens groups tend to be a slack frictionless fit, a necessity with tiny servo motors but which leads to undesirable movement of the frame in focus pulls.

The f1.4 lenses you would not typically use at f1.4 unles you are chasing very thin depths-of-field. That is a novelty which will wear off fairly quickly and is the signature of the new adopter of groundglass imaging. With many stills lenses, the last 1.5 to 2 f-stops can yield a less crisp image and confer some flare. So f2.8 selected in a f1.4 lens is already in or closer to the optical sweet spot than a f2.8 lens wide-open might be.

That said, the newer Nikon f2 lenses are regard by some as just as good wide-open as older Nikon f1.4 lenses at f2. Still, you lose that extra lightgathering when you might need it and can live with slightly softer image.

Avoid digital SLR lenses including digital-only Nikon lenses altogether. These cover a smaller image frame and you will get a vignette with the 35mm groundglass adaptors. They also may not have a manual aperture control or a reversed mechanical iris control link to the camera body which has to be wedged wide-open before the manual iris ring will work.

Some users will extoll the virtues of zooms. Some are more equal than others. Select a zoom which has a shorter throw and a constant aperture through the zoom range. Nikon do some good ones in f2.8.

Be aware that the backfocus or collimation for zoom lenses relative to the focal plane (groundglass) has to be spot on otherwise there is a focus shift through the zoom range.

Due to wear and tear and operator interference with focus barrels on older lenses sometimes prime lenses are also not equal. Whilst they will focus, the witness marks will not be correct.

Most stills lenses, even the older Nikons have a shorter focus barrel throw than cine lenses which can be a full turn and often meet a common standard.

There is a ruile-of-thumb fior groundglass imaging that f5.6 is the limit you can close the aperture to before a groundglass artifact becomes apparent. 1/100th second shutter is about as fast as you can go and a sort of law of reciprocity applies in that the faster the shutter, the wide the iris setting needed to minimise a groudnglass artifact.

Try to value-add with supplemental lighting or reflectors rather than select video gain up in the camera. The groundglass confers some "texture or grain noise" which becomes additive with camera sensor "gain noise" in challenging the video compression codec.

The outcome is the camera throws away resolution to preserve frame rate and you get a softer image.


Enjoy.

Last edited by Bob Hart; January 2nd, 2010 at 10:37 PM. Reason: error
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Old January 3rd, 2010, 08:20 AM   #3
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Michael,
Right after getting my Letus extreme, I started looking for lenses. I was luicky and found my lenses on craigslist and ebay, and bhphoto used. I stuck with older Nikon manual lenses ( except for one Tokina) and they work great.
Here's what I got:
Nikon 24mm f2.8
Nikon 35mm f 2.0
Nikon 50mm f 1.4
Nikon 105mm f 1.8 ( beutifull lens)
Nikon 135mm f 2,8
Nikon teleconverter for the 135- turns it into about 180 mm but you lose a couple of stops. Good for outdoors where f 4 is fine.

then I picked up the lens that I use most ofeten, especially when there's no time to be changing lenses and moving the tripod back and forth. It's the tokina ATX 28-70mm f2.8. I really like this lens, especially outdoors where 2.8 is plenty fast. The only other similar zoom that I ould reccomend is the Nikon 80-200, which unlike the 70-200 vr, has a manual aperture ring. Between the 28-70 and the 80-200, you could do most of our work.

You should be able to get all of the Nikon primes for $100 (or less ) each, except for the 105 f 1.8, which is very desirable and a bit more money. I bought the Tokina used at BH for around $225. You'd probably have to pay at least $500 for a used 80-200.
I would deinatley go with the Nikon mount on the Letus.
Good luck.
Bruce Yarock
Yarock Video and Photo
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