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View Full Version : ZD 14-35 is actually f1.8 to f2!


oly_om
19th January 2014, 09:50 AM
Interesting observation...

Some of us realise that the ZD 7-14 is actually f2.8 (7mm) to f4 (14mm).

You can test this on the camera by pressing the lens release button on the camera (or on the mFT->FT adapter for a mFT camera). You will see at 7mm @ f4 half the shutter speed for the lens at 7mm and the release button pressed. Basically it's the lens firmware that closes down the aperture to give the constant f4 over the range.

Now, I noticed the burst rate slow on the camera when using the 14-35 on the wide end. This is a common problem on the FT lenses - they weren't designed for the E-M1's 10fps burst rate. If you shoot anything other than wide open, there is a lag as the aperture closes down.

So shooting at f2@14mm should be wide open and therefore no lag? Wrong - there is, so I tried the same trick. 1/80s became 1/100s. This corresponds to f1.8 ( f2 / SQRT(100/80) ) at the wide end.

I need to do some tests to see how the base aperture varies over the range.

Andy

David Morison
19th January 2014, 10:27 AM
That's interesting Andy. I unfortunately dropped my 7-14 in it's soft pouch on to a carpeted floor in Lacock Abbey. Although it still works OK I think the diaphragm has been damaged as it clicks when I zoom in, so your post would explain this. Not bothering to get it repaired as it still works Ok.

David

David M
19th January 2014, 02:52 PM
I wouldn't be surprised if all the constant aperture SHG zooms were the same. They could all be faster at the short end if the lens designers had wanted variable aperture designs. One thing to consider is the lenses were probably designed as constant aperture so no consideration would have been given for performance at wider than specified apertures.

photo_owl
19th January 2014, 03:59 PM
I wouldn't be surprised if all the constant aperture SHG zooms were the same. They could all be faster at the short end if the lens designers had wanted variable aperture designs. One thing to consider is the lenses were probably designed as constant aperture so no consideration would have been given for performance at wider than specified apertures.

they are all the same.

as I understand it, it was a design principle around ultimate performance 'wide open' over possible paper specs at the wider end.

whilst I used to trick the 7-14 occasionally I no longer bother given the huge steps forward in both IS and ISO - ie at the wider end the max aperture isn't anything like as relevant at with the long glass. I've never used the 35/1.4 in anger (but then again I have a 30/1.4 Sigma anyway!