Tag Archives: lenses

HD lenses for 1/2″ Cameras like the EX3, PMW-320 and new PMW-300.

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.

How big a compromise is using a DSLR zoom on a 4K camera?

This came up as a question in response to the post about my prototype lens adapter. The adapter is based around an electronic Canon EF mount and the question was, what do I think about DSLR zooms?

There is a lot of variation between lenses when it comes to sharpness, contrast and distortions. A zoom will always be a compromise compared to a prime lens. DSLR lenses are designed to work with 24MP sensors. A 4K camera only has around 9MP, so your working well within the design limits of the lens even at 4K. While a dedicated PL mount zoom like an Angenieux Optimo will most likely out perform a similar DSLR zoom. The difference at like for like apertures will not be huge when using smaller zoom ratios (say 4x). But 10x and 14x zooms make more compromises in image quality, perhaps a bit of corner softness or more CA and these imperfections will be better or worse at different focal lengths and apertures. At the end of the day zooms are compromises but for many shoots it may simply be that it is only by accepting some small compromises that you will get the shots you want. Take my storm chasing shoots. I could use primes and get better image quality, but when you only have 90 seconds to get a shot there simply isn’t time to swap lenses, so if you end up with a wide on the camera when a long lens is what is really needed, your just not going to get the shot. Using a zoom means I will get the shot. It might not be the very best quality possible but it will look good. It is going to be better than I could get with an HD camera and a very slightly compromised shot is better than no shot at all.
If the budget would allow I would have a couple of cameras with different prime lenses ready to go. Or I would use a big, heavy and expensive PL zoom and have an assistant or team tasked solely with getting the tripod set up and ready asap. But my budget isn’t that big. I could spend weeks out storm chasing before I get a decent shot, so anything I can do to minimise costs is important.
It’s all about checks and balances. It is a compromise, but a necessary one. It’s not a huge compromise as I suspect the end viewer is not going to look at the shot and say “why is that so soft” unless they have a side by side, like for like shot to compare. DSLR zooms are not that bad! So yes, using a DSLR zoom is not going to deliver quality to match that of a similar dedicated PL zoom in most cases, but the difference is likely to be so small that the end viewer will never notice and thats a compromise I’m prepared to accept in order to get a portable camera that shoots 4K with a 14x zoom lens.

What about DSLR primes and why have I chosen the Canon Mount?

This is where the image performance gap gets even narrower. A high quality DSLR prime can perform just as well as many much more expensive PL mount lenses. The difference here is more about the usability of the lens. Some DSLR lenses can be tiny and this makes them fiddly to use. They are all All sorts of sizes, so swapping lenses may mean swapping Matte boxes or follow focus positions etc. Talking of focus, very often the focus travel on a DSLR lens is very, very short so focussing is fiddly. If the lens has an aperture ring it will probably have click stops making smooth aperture changes mid shot difficult. My prime lenses are de-clicked or never had clicks in the first place (like the Samyang Cine Primes). It’s not so much the issue of requiring a finer step than the one stop click, but more the ability to pull aperture during the shot. It’s not something I need to do often, but if I suddenly find I need to do it, I want a smooth aperture change. That being said, one of the issues with using Canon EF lenses with their electronic iris is that they operate in 1/8th stop steps and this is visible in any footage. Ultimately I am still committed to using the Canon mount lenses simply because there are so many to choose from and they focus in the right direction unlike Nikon lenses which focus back to front. For primes I’m using the excellent and fully manual Samyang T1.5 Cine Primes. I really like these lenses and they produce beautiful images at a fraction of the price of a PL mount lens. My zoom selection is a bit of a mish-mash. One thing about having a Canon mount on the camera is that I can still use Nikon lenses if I fit the lens with a low cost Nikon to Canon adapter ring. If you do this you can only use lenses with an actual iris ring, so generally these are slightly older lenses, but for example I have a nice Sigma 24-70mm f2.8 with a manual iris ring (and it focusses the RIGHT way, like most Sigmas but unlike most Nikon mount lenses). In addition I have a 70-300mm f4 Nikon mount Sigma as well as an Old Tokina 28-70mm f2.6 (lovely lens, a little soft but very nice warm colour). One thing I have found is that most of the Nikon to Canon adapter rings are little bit on the thin side. This prevents any zooms from being Parfocal as it puts the back focus out. Most of the adpaters are made in two parts and it’s quite easy to take the front and back parts apart and add shims made out of of thin plastic sheet or even card between the two halves to correct the back focus distance.

So there you have it. Overall DSLR lenses are not a huge compromise. Of course I would love to own a flight case full of good quality PL mount, 4K ready, glass. Perhaps one day I will, but it’s a serious investment. Currently I use DSLR lenses for my own projects and then hire in better glass where the budget will allow. For any commercials or features this normally means renting in a set of Ultra Primes or similar.  I am keeping a close eye on the developments from Zunow. I like their 16-28mm f2.8 and the prototype PL primes I saw at NAB look very good. I also like the look of the Zeiss 15.5 to 45 light weight zoom. Then of course there is the excellent Fujinon 19-90mm Cabrio servo zoom, but these are all big bucks. Hopefully I’ll get some nice big projects to work on this year that will allow me to invest in some top end lenses.

Using DSLR lenses on 3D rigs.

Just a quick note on a rather obscure subject. I do a lot of 3D work. Buying pairs of PL mount lenses for my F3’s is beyond my budget right now, so I hire in lenses when I need them. However for my own projects I use DSLR lenses, mainly Nikkors and Tokina’s. One thing that i have discovered is that many of the older manual Nikkors have a tendency to shift the image left and right when you focus. This then miss-aligns the rig. The more modern internal focussing lenses are much, much better in this respect with little or no shift at all. The only problem with the more modern IF lenses is that they often don’t have iris rings (so iris is adjusted with a MTF adapter) and the focus control often has a slipping clutch making repeatable focussing a little harder. So neither is perfect. For 3D applications I think the more modern IF lenses are preferable.

Adaptimax Lens Mount Adapters for PMW-F3, Canon and Nikon.

IMG_0648-300x224 Adaptimax Lens Mount Adapters for PMW-F3, Canon and Nikon.
Adaptimax F3 to Canon and Nikon lens mounts

I was sent a couple of Adaptimax lens mount adapters to test on my PMW-F3. I have used some of their EX3 adapters in the past and these worked very well. The new PMW-F3 adapters are finished with a very nice hard black anodised finish and look very smart indeed. I had 3 adapters to try, one F3 to Canon and two F3 to Nikon adapters. The Canon adapter is a “dumb” adapter, so there is no way to control the lenses iris. If your using Canon lenses this means using a DSLR body to set the iris before using the lens on the F3. Obviously this is not ideal, but you do have to consider that there is a massive range of lenses that can be used with this Canon adapter via a secondary adapter ring.

Canon’s flange back distance (the sensor to lens distance) is the shortest in the DSLR world. So this means that there is space to adapt to other lens mounts with longer flange back distances such as M42, Nikon, Pentax, Pentacon etc. This opens up a whole world of possibilities as now you can use those nice M42 Zeiss lenses that can be picked up cheap on ebay by adding a cheap M42 to Canon adapter.

IMG_0651-300x224 Adaptimax Lens Mount Adapters for PMW-F3, Canon and Nikon.
Nikon 50mm f1.8 with Adaptimax F3 Mount.

If you have already invested in Nikon fit glass then you can use a Nikon to Canon adapter or you can use one of Adaptimax’s purpose built F3 to Nikon adapters.

There are two varieties, the original Adaptimax and the Adaptimax Plus. The Plus version includes a long screw that pushes the iris pin on the rear of the lens to give you iris control even when the lens does not have an iris ring. While this is not as elegant as MTF Services rotating adapter barrel, it works fine and the simplicity of the design means the adapter is a little cheaper. The standard version has no iris control, so you need to ensure your lens has a proper iris ring. Priced at £255 for the standard adapters and £265 for the plus versions these are good value for money.

Focal length conversion factor should apply to the camera not the lens.

I was asked in some post comments whether the a 50mm PL mount lens would give a wider picture than a 50mm DSLR lens. This confusion comes about I believe because of all the talk about focal length conversion factors. I don’t think this concept is well understood by some people as the implication is that somehow the lens is changing when its used on different cameras, when in fact it’s the camera that is different, not the lens.

It is important to understand that a 50mm lens will always be a 50mm lens. That is it’s focal length. It is determined by the shape of the glass elements and no matter what camera you put it on it will still be a 50mm lens. A 50mm DSLR lens has the same focal length as a 50mm PL mount and as a 50mm 2/3″ broadcast lens. In addition the lens focuses a set distance behind the rear element, agin the distance between the rear element and where it focuses does not change when it’s put on different cameras, so an adapter or spacer must be used to keep the designed distance between the lens and sensor, this distance is called the “flange back”.

The key thing is that it’s not the lens or it’s focal length that changes when you swap between different cameras. It is the size of the sensor that changes.

Imagine a projector shining an image on a screen so that the picture fills the screen. The projector is our “lens”. Without changing anything on the projector what happens if you move the screen closer or further away from the projector? The image projected on the screen will go in and out of focus, so that’s not good, we must keep the projector to screen distance constant, just like the lens to sensor distance (flange back) for any given lens remains constant.

What happens if we make the screen smaller? Well the image remains the same size but we see less of it as some of the image falls of the edge of the screen. If our projected picture was that of a wide landscape then on the reduced screen size what would now be seen would not appear less wide as we are now only seeing the middle part of the picture. The width of the view would be decreased, in other words the FIELD OF VIEW HAS NARROWED. The focal length has not changed.

This is what is happening inside cameras with different size sensors, the lens isn’t changing, just how much of the lenses projected image is falling on or off the sensor.

So the multiplication factor should be considered more accurately as being applied to the camera, not the lens and the multiplication factor changes the field of view, not the focal length.

So whether it is a PL mount lens, a Nikon or Canon DSLR lens or a Fujinon video lens, if it’s a 50mm lens then it’s a 50mm lens and the focal length is the same for all. However the field of view (width and height of the viewed image) will depend on the size of the sensor. So a 50mm PL lens will give the same field of view as a 50mm DSLR lens (no matter what camera the lens was designed for) on the same video camera.

The only other thing to consider is that lenses are designed to work with certain sizes of sensor. A lens designed for a full frame 35mm sensor will completely cover that size of sensor as well as any sensor smaller than that. On the other hand a 2/3? broadcast lens will only cover a 2/3? sensor, so if you try to use it on a larger sensor the image will not fill the frame.
The sensors in the Sony F3 and FS100 are “Super 35mm”. That is about the same size as APS-C. So lenses designed for Full frame 35mm can be used as well as lenses designed for 35mm cine film (35mm PL) and lenses designed for APS-C DSLR’s such as the Nikon DX series and Canon EF-S.

See also http://www.abelcine.com/fov/

 

Lens Tests at F3 Dubai Workshop.

Off to the airport to fly home in a minute, but I thought I would jot down some notes about the various lenses we were able to look at during the F3 workshop I ran here in Dubai. We had a set of the Sony PL primes, a Zeiss CP2, some Zeiss ZF.2 stills lenses, a Nikon 50mm and a Tokina 28-70mm ATX pro zoom. The stills lenses were all attached to the F3 using an MTF to Nikon adapter.

It was hard to see any difference between the Sony primes and the CP2, this was kind of expected. When comapring the PL’s to the Tokina zoom, the zoom was a little soft wide open at f2.6. Stopped down half a stop and it looked much better, but it needed to go down to f4 before it came close to matching the PL’s. Even then the PL’s had the edge, but then this is comparing a zoom to a prime. I would certainly have no hesitation over using the Tokina at f4 or more closed. The Nikon 50mm pancake, f1.8 was surprisingly good. Even wide open it produced a respectable image, stopped down to f2.8 it was a very close match to the PL’s. The Zeiss ZF.2’s were the budget stars of the show as even wide open these produced sharp, clean images with very similar bokeh and flare performance to the primes, very impressive performance.

Of course ergonomically the PL’s were better. Bigger focus rings, bigger iris rings and better focus scales. The CP2 impressed with it’s near 360 degrees rotation of the focus ring with very clear and accurate witness marks and wide distance spacing even approaching infinity. If I could afford a set of CP2’s that’s what I would buy, but I can’t. The Sony PL’s are good lenses, they don’t quite have the build quality of the CP2’s but they do represent excellent value for the money. If your budget won’t stretch to PL glass then the Zeiss ZF.2’s are about as close as you’ll get to a PL lens, but do watch out for the amount of telescoping when you focus the longer focal length ones. That can make using a matte box very tricky. I know my Nikon 50mm and Tokina 28mm primes work well. The Tokina 28-70 while not as sharp as the primes will still make a good all-round lens. All I need now is to get a nice 85mm and 135mm and I’ll be happy. Maybe a couple of ZF’s.

PMW-F3 and Stills Glass, some observations.

I have been using my F3 with a range of stills lenses via the MTF F3 to Nikon adapter. Overall everything works very well and I am pleased with the quality of the images I have been getting. However the use of stills glass is not as easy as using dedicated PL lenses. The main issue for me is iris control. With a PL mount lens you have a nice big iris ring so you know exactly where your exposure is. With some of my stills lenses I do have a traditional iris ring and with these lenses all is good. But as so many DSLR’s these days have electronic iris control many of the lenses I have don’t have an iris control ring. Mike Tapa’s adapter can control the iris of a Nikon DSLR lens by moving the blade that controls the shutter on the rear of the lens, but there are no markings or any way way of knowing what the iris is set to. This makes judging when to use more ND or where you are regarding DoF impossible to judge other than via a monitor. You can’t tell whether you are operating the lens at it’s optimum settings. In addition many of the Nikon DX lenses don’t have calibrated focus scales, so again it all comes down to guess work and the monitor.

With well designed stills glass things work well. My older Tokina 28-70 AT-X pro works very well with an accurate focus scale and proper iris control. My Nikon 50mm f1.8 manual lens and Tokina 28mm f2.8 lens also work nicely, but the Nikon DX lenses I have are far from ideal. I’m considering getting a set of Zeiss ZF.2 stills lenses as these appear to be very good lenses. I really need a prime in the 85mm range for interviews and portrait type shots.

The focal lengths I use the most are: 28mm, 50mm and  70mm. I would use a bit longer if I had the right lens. I don’t use the 18mm very often except for panoramas and landscapes.

So…. PL would be nice, but at the moment my budget won’t stretch to that. The Sony kit lenses are certainly great value for the money, but really 35mm isn’t wide enough so I would have to add a wider lens anyway. Stills glass can produce great results, but is not quite so user friendly.

Low Cost 2/3? HD Lenses.

OK, here’s my take on the situation.

If money is no problem then the safest bet is to purchase a good quality HD lens, expect to spend at least £8k.

If you budget is restricted then the situation is much less clear. There are now several low cost 2/3? HD lenses designed for cameras such as the Panasonic HPX500. In my opinion these lenses are just not worth the money. They might be cheap (£4k ish) but the one’s I’ve played with have been pretty grim, suffering from lots of CA and soft corners.

If your on a tight budget the best thing you can do is take your camera to a good dealer and go through their second hand lenses, trying them on the camera. Check for resolution (use a chart), corner softness, CA and contrast. I did this and ended up with a Canon 16x8x2 IF lens. I found that lenses with lower zoom ratios tended to be better than those with higher ratios. I’m really pleased with my lens and when compared to the latest HD equivalents I can not tell the difference in real world use. It certainly outperforms all the budget HD lenses I’ve tried.

One interesting thing that I have discovered in my research into this subject is that Contrast is what makes the biggest difference in lens performance, not simply resolution as one might expect. Visually the next thing you notice is CA. This is a tough one as when you increase the resolution or sharpness of a lens you also tend to increase the CA.

Until lens manufacturers start to release MTF curves for their lenses the only thing we have as buyers to go on is the advertising blurb. It’s easy for a manufacturer to claim improved performance or new glass or other technology, but without accurate MTF curves it’s all pretty meaningless. You would only need the tiniest resolution improvement to be able to claim that you new HD lens range is sharper than your SD range, it could just be a fraction of a percent difference.