Some people are struggling with lens options for the Sony half inch interchangeable lens cameras. Many try to use 2/3″ lenses via the ACM-21 with disappointing results. Lenses are designed to meet certain criterion. The lenses for the PMW-EX3 and PMW-320 actually perform very well, yet these are inexpensive lenses, so why when you use a much more expensive 2/3″ ENG zoom lens can the results be disappointing?
There is a very big difference between the way most typical ENG lens focus and the way an EX1/3, PMW-320 or PMW-200 lens focusses. An ENG lens will be a Par Focal lens, a lens that maintains constant focus throughout the zoom range. This is incredibly difficult to design especially with large zoom ranges and is one of the reasons ENG zooms are normally expensive pieces of glass.
The lenses used on the EX1/EX3, PMW-320 are not Par Focal, this makes them much cheaper, the focus shifts and changes as you zoom….. But clever electronics inside the camera and lens compensates for this by adjusting the lenses focus as you zoom so that in practice the lens appears to stay in perfect focus. An electronically compensated lens like this is lower cost to produce than a sophisticated typical ENG type zoom and makes the lens compact and lightweight as well as much cheaper.
Another factor is that as you increase the resolution of a lens, trying to bring everything in to focus on an ever smaller point, you run in to more and more problems with chromatic aberrations. Different wavelengths (and thus colours) of light get bent by different amounts when they pass through a glass lens. As you make the focussed light for one single colour smaller and sharper, the other colours of the spectrum become more dispersed. As a result, generally a softer lens, for example an SD lens (lower MTF) will exhibit fewer colour aberrations than a sharper HD lens. To compensate for these aberrations lens manufactures use very exotic types of glass with different refraction indexes to try to cancel out or at least minimise CA (chromatic aberration), but this glass is extremely expensive. The higher the resolution of the lens, the more expensive the glass gets.
With a camera like the EX1/EX3, PMW-320, PMW-200 when you know the exact characteristics of the lens (as they all use essentially the same lens) instead of employing exotic glass, you can program the camera to electronically remove or reduce the appearance of the CA and this happens inside the EX1/EX3, 320 and PMW-200 etc.
Next you must take in to account pixel size. In simple terms to work with the resolution of the cameras sensor, the lens has to be able to focus a point of light small enough to hit only one pixel. A typical 2/3″ HD camera has much bigger pixels that the pixels on the 1/2″ sensor of the PMW-320. As a result a lens that is only just able to achieve HD resolution on a 2/3″ camera, will not achieve HD resolution on the PMW-320 with it’s smaller pixels, it’s simply not designed to work with such small pixels. This means that you really need an HD lens designed for the 1/2″ sensor size and the corresponding pixel size.
These factors combined mean that the standard kit lens on the EX3, PMW-320 etc appears to perform very well and it takes a much more expensive, designed for 1/2″ lens to even match this apparent performance in most cases. Perhaps the new 16x lens coming for the PMW-300 will be available to purchase on it’s own. This would offer EX3 and PMW-320 owners the option of a high performing lens with a greater zoom range, probably for less than a similar performance conventional lens.
This article is really useful Alister. Thank you.
Thank you Alister.
Our PMW320K came with a 16x lens. The slightly longer reach is useful – just wish it had OIS like the EX1R. We leave steadyshot engaged even on a tripod – very useful at the long end. Not spotted any adverse effects. Does the PMW300 include OIS?
I think the 14x has OIS. Don’t know about the 16x.
Thanks Alister. What about using DSLR telephoto lenses instead of broadcast lenses with PMW-EX3/PMW-300? Do they produce also bad and unsharp image, because they are designed for larger sensor cameras?
Depends on the quality of the lens. DSLR lenses are designed for much higher resolutions than HD, so a good, sharp, DSLR lens can perform quite well.
Thanks Alister. I have been debating upgrading from a PMW-200 to a PMW-300 and using my 2/3″ lenses. It would appear that I should consider the PMW-400 instead….a real 2/3″ chip camera.
If lens focus an image on 2/3 area, why the image will be bad on part of it of 1/2 inch area ? or size of chip affects somehow focusing ability of lens? meantime – 2/3 should give less abberation; for me the idea then 2/3 inch lens will work bad concerning the resolution on 1/2 cam looks ubsolutely unprofessional.
It’s down to the pixel size. A 1/2″ sensor will have much smaller pixels than a 2/3″ sensor. A 2/3″ lens only needs to be good enough to focus on the bigger 2/3″ pixels, so when you use it with smaller pixels the image may be soft as the lens isn’t sharp enough to focus on the very small pixels of the smaller sensor.
A good Canon HJ18ex28 on an EX3 works well in my experience. But I would not assume therefore that any broadcast HD 2/3″ lenses will be good enough too.
Can I use a Nikon DSLR lens on a PMW-400?