So, which one correspond to this ? I have a RJ Nikon to mf3 adapter (an old version). But what else is out there and are they worthwhile ? What other change the RJ adapters offers now and is it worth the change ?

Thanks to answer

RARE: 16-160MM CONSTANT F/2 M4/3 CINEMA SPEED LENS IMMACULATE CONDITION

1. INFINITY FOCUS. The lens is made "parfocal", providing proper infinity focus. Minimum focusing distance with this lens is about 3 to 4 feet.

2. PRECISION GLASS. Manufactured in Japan, this zoom precision lens is nearly perfect in optical quality. As the photos demonstrate, the glass on this lens is stunning, though it only resolves 1080p.

3. PARFOCAL. With most zooms you lose focus as you zoom the lens. However, this lens maintains perfect focus throughout the entire zoom range of 16mm to 160mm. (See photos straight off GH2)

4. ZOOM. The zoom throw on this lens is about 55 degrees, the zoom barrel is tight with no play. It is smooth and a pleasure to shoot with.

5. VERY FAST. This is a constant F/2 lens which is an exceptional low light performer. An 8 blade aperture produces a nice round bokeh. The declicked aperture for silent, butter smooth operation. Aperture throw is 45 degrees.

6. NO VIGNETTING. As set up and tested on the BMPCC and the GH4 in 4K in UHD, there is no vignetting anywhere on this lens. This lens covers the 4K image circle on the GH4, but it only really resolves 1080p resolution, you need Canon Cinema lenses to resolve 4K… As you consider, remember that this lens has a CONSTANT aperture of f/2 all the way out to 160mm! Please be aware, the lens has better sharpness at F/5.6... F/2.0 wide open, like any lens, is relatively soft.

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Contact: Brennan Kirkpatrick brennan@infinichair.ca 613-466-0222

The biggest benefit I can think of is that the exposure will stay constant as you zoom. You can fix the shutter speed, focal ratio, and ISO values and then zoom without needing to change them. That sounds great but do we really need that?

With cameras that have Auto ISO available in manual mode can’t you just let the auto ISO control the exposure while you zoom?

Also aren’t all lenses constant aperture, just not always at their wide open apertures? If you stop down to the minimum aperture of the lens then the aperture will remain fixed in aperture priority or manual mode while you zoom even if the lens isn’t a true “Constant Aperture” lens.

What happens as you zoom? Aren’t these lenses still changing the aperture in order to keep it constant? Doesn’t that mean that your depth of field will change as you zoom? If the focal ratio of a not constant aperture zoom lens increases as you zoom in could it then keep depth of field constant as you zoom if so desired? Would that ever be desirable?

Couldn’t a constant aperture zoom lens have a slightly wider aperture or slightly longer focal length if it wasn’t a constant aperture lens wide open? Aren’t they crippling the lens slightly in order to make it constant aperture wide open?

Also what about being parfocal. Isn’t maintaining focus as you zoom more important than maintaining focal ratio especially in cases where you can let Auto ISO solve the changing exposure issue?

I am just curious as to why we insist on having constant aperture lenses. To me the benefits of a constant aperture lens do not outweigh the benefits of a non-constant aperture lens as long as your camera allows auto ISO in the modes you are shooting with.

With that being said the 35-100mm F2.8 is pretty much the only lens I use on my GH4 now. However, I really don’t zoom that often while filming so I am not sure I use it to its full abilities.

reviews: http://www.thephoblographer.com/2013/04/30/review-tamron-70-200mm-f2-8-sp-di-vc-usd-canon-ef/ http://photo.net/equipment/tamron/70-200vc