Tag Archives: MTF

MTF Services to provide 4/3rds and FZ mount options for Fujinon MK lenses.

MTF-FZ-MK-895x1024 MTF Services to provide 4/3rds and FZ mount options for Fujinon MK lenses.In addition to the recent announcement from Duclos, MTF services in the UK have just announced that they will be introducing a conversion service for the popular new Fujinon MK zoom lenses. Currently these lenses are E-Mount only, but MTF will be producing kits to convert the lens mounts so that they can be used with cameras that use the micro 4/3rds mount as well as the Sony FZ mount. This is great news for owners of Sony’s F5 and F55 cameras.

Here’s the text of their press release:

Since the launch of Fujinon’s MK lenses in February this year, users have continued to request a greater range of mounts beyond the native E-Mount that can be found on the 18-55mm and 50-135mm lenses. MTF have now addressed these requests and have designed brand new solutions to convert the lenses to Micro four thirds and FZ mount systems

Mike Tapa, Managing Director at MTF Services said: “Since these excellent lenses from Fujinon were launched earlier this year, we’ve had more and more of our customers asking for us to produce a solution to open up the use of the MK lenses for use across a broader range of camera bodies. We’re now pleased to announce that we have designed brand-new adapter mounts for both micro four thirds and FZ systems to work seamlessly with both the 18-55mm and 50-135mm lenses.

Fitting service

 

Fitting the new mount options for the Fujinon MK lenses will be offered as a service from the team at MTF Services. Simply ship your lens over to MTF’s London-based workshop, and the team will fit your preferred mount before shipping back to you, fully tested, professionally adapted, cleaned and ready for use before being safely couriered back to your door.

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Image quality with B4 ENG lenses on large sensor cameras.

DSC02056 Image quality with B4 ENG lenses on large sensor cameras.
2/3″ B4 lens on the FS700via the MTF adapter.

This is something that comes up a lot and I get many questions about. In part because I designed the MTF B4 to Canon, FZ and E-Mount adapters. Budget adapters that allow you to use a 2/3″ B4 ENG lens on a Super 35mm sensor by using the lenses 2x extender or on a center crop sensor without the 2x.

The question is… what will the pictures look like?

The answer is… it depends on the lens.

Not a very helpful answer perhaps, but that’s the truth of it. Different lenses perform very differently. For a start I would say forget 4K. At best these lenses are suitable for HD and you want to have a great HD lens if you want good HD pictures.

But what about the “look” of the images? My experience is that if you put a wide range ENG zoom on a S35mm camera the look that you get can be best described as “2/3″ ENG look with maybe shallow depth of field”. Lets face it, ENG lenses are full of compromises. To get those great big zoom ranges with par-focal focus there are a lot of glass elements in those lenses. Lot’s of elements means lots of places where CA and flare can occur. The end result is often a lowering of contrast and color fringing on hard edges, the very same look that we are used to seeing on 2/3″ cameras.  Typical cine or DSLR lenses tend to have simpler optical designs. Prime lenses are normally sharper and show better contrast with less flare than zooms due to there simpler internal design.

So don’t expect to put a typical B4 ENG lens on your S35mm camcorder and still have that crisp, high contrast digital cinema look. Of course B4 zooms are handy for the ability to zoom in and out through huge ranges while holding focus. So an adapter and lens may well make your S35mm camera more versatile. But if you want the best possible images stick to cine style lenses, DSLR lenses or zooms designed for S35.

 

Contrast and Resolution, intricately linked.

This is one of those topics that keeps coming back around time and time again. The link between contrast and resolution. So I thought I would take a few minutes to create some simple illustrations to demonstrate the point.

contrast1 Contrast and Resolution, intricately linked.
Best Contrast.

This first image represents a nice high contrast picture. The white background and dark lines have high contrast and as a result you can “see” resolution a long way to the right of the image as indicated by the arrow.

contrast2 Contrast and Resolution, intricately linked.
Lower contrast.

Now look at what happens as you slowly reduce the contrast in the image. As the contrast reduces the amount of resolution that you can see reduces. Keep reducing the contrast and the resolution continues to decrease.

contrast4 Contrast and Resolution, intricately linked.
Low Contrast.

Eventually if you keep reducing the contrast enough you end up with no resolution as you can no longer differentiate between light and dark.

Now look at what happens when you reduce the resolution by blurring the image, the equivalent of using a less “sharp” lower resolution lens for example. What happens to the black lines? Well the become less dark and start to look grey, the contrast is reducing.

contrast5 Contrast and Resolution, intricately linked.
Reduced resolution.

Hopefully these simple images show that contrast and resolution are intrinsically linked. You can’t have one without the other. So when choosing lenses in particular you need to look at not just resolution but also contrast. Contrast in a lens is affected by many things including flare where brighter parts of the scene bleed into darker parts. Flare also comes from light sources that may not be in your shot but the light is still entering the lens, bouncing around inside and reducing contrast as a result. These things often don’t show up if you use just a simple resolution chart. A good lens hood or matte box with flags can be a big help reduce stray light and flare, so in fact a matte box could actually make your pictures sharper. They are not just for pimping up your rig, they really can improve the quality of your images.

The measurement for resolution and contrast is called the MTF or modulation transfer function. This is normally used  to measure lens performance and the ability of a lens to pass the light from a scene or test chart to the film or sensor. It takes into account both resolution and contrast so tells you a lot about the lens or imaging systems performance and is normally presented as a graph of contrast levels over a scale of ever increasing resolution.

Frame Grabs from MTF B4 2/3″ to Canon C300, 7D, 550D, Sony F3, FS100 etc adapter.

MTF-B4-Canon-adapter-wide-300x168 Frame Grabs from MTF B4 2/3" to Canon C300, 7D, 550D, Sony F3, FS100 etc adapter.
Canon J16 SD 2/3" lens on a Canon C300, Wide.

I’ve been asked a couple of times for some frame grabs shot with one of the MTF B4 to super 35MM adapters that I designed. Well, here they are. Shot on a Canon C300 fitted with the adapter and an old standard definition Canon J16 zoom lens. It was late in the day when I shot this so it’s not showing the adapter in its best light and of course an HD lens would be even better.

 

MTF-B4-Canon-adapter-tele-300x168 Frame Grabs from MTF B4 2/3" to Canon C300, 7D, 550D, Sony F3, FS100 etc adapter.
Canon J16 2/3" SD zoom on a Canon C300, Tele.

Click on the thumbnails to view a larger image or the full resolution image. I love the fact that even when using a super35mm sensor you can still have this great par-focal zoom range. Put a 20x ENG zoom and you can get both wider and closer!

http://www.mtfservices.com/home.html?page=shop.product_details&flypage=flypage.tpl&product_id=110&category_id=2

Measuring Resolution, Nyquist and Aliasing.

When measuring the resolution of a well designed video camera, you never want to see resolution that is significantly higher than HALF of the sensors resolution. Why is this? Why don’t I get 1920 x1080 resolution from an EX1, which we know has 1920 x1080 pixels, why is the measured resolution often around half to three quarters what you would expect?
There should be an optical low pass filter in front of the sensor in a well designed video camera that prevents frequencies above approx half of the sensors native resolution getting to the sensor. This filter will not have an instantaneous cut off, instead attenuating fine detail at ever increasing amounts centered somewhere around the Nyquist limit for the sensor. The Nyquist limit is normally half of the pixel count with a 3 chip camera or somewhat less than this for a bayer sensor. As a result measured resolution gradually tails off somewhere a little above Nyquist or half of the expected pixel resolution, but why is this?
It is theoretically possible for a sensor to resolve an image at it’s full pixel resolution. If you could line up the black and white lines on a test chart perfectly with the pixels on a 1920 x 1080 sensor then you could resolve 1920 x 1080 lines. But what happens when those lines no longer line up absolutely perfectly with the pixels? lets imagine that each line is offset by exactly half a pixel, what would you see? Well each pixel would see half of the black line and half white line. So each pixel would see 50% white, 50% black and the output from that pixel would be mid grey. With the adjacent pixels all seeing the same thing they would all output mid grey. So by panning the image by half a pixel, instead of now seeing 1920×1080 black and white lines all we see is a totally grey frame. As you continued to shift the chart relative to the pixels, say by panning across it, it would flicker between pin sharp lines and grey. If the camera was not perfectly aligned with the chart some of the image would appear grey or different shades of grey depending on the exact pixel to chart alignment while other parts may show distinct black and white lines. This is aliasing and it’s not nice to look at and can in effect reduce the resolution of the final image to zero. So to counter this you deliberately reduce the system resolution (lens + sensor) to around half the pixel count so that it is impossible for any one pixel to only see one object. By blurring the image across two pixels you ensure that aliasing wont occur. It should also be noted that the same thing can happen with a display or monitor, so trying to show a 1920×1080 image on a 1920×1080 monitor can have the same effect.
When I did my recent F3 resolution tests I used a term called the MTF or modulation transfer function, which is a measure of the contrast between adjacent pixels, so MTF 50 is where there is a 50% of maximum contrast difference between the black and white lines on the test chart.
When visually observing a resolution chart you can see where the lines on the chart can no longer be distinguished from one another, this is the resolution vanishing point and is typically somewhere around MTF15 to MTF5, ie. the contrast between the black and white lines becomes so low that you can no longer distinguish one from the other. But the problem with this is that as you are looking for the point where you can no longer see any difference, you are attempting to measure the invisible so it is prone to gross inaccuracies. In addition the contrast at MTF10 or the vanishing point between black and white will be very, very low, so in a real world image you would often struggle to ever see fine detail at MTF10 unless it was strong black and white edges.
So for resolution tests a more consistent result can be obtained by measuring the point at which the contrast between the black and white lines on the chart reduces to 50% of maximum, or MTF50 (as resolution decreases so too does contrast). So while MTF50 does not determine the ultimate resolution of the system, it gives a very reliable performance indicator that is repeatable and consistent from test to test. What it will tell you is how sharp one camera will appear to be compared to the next.
As the Nyquist frequency  is half the sampling frequency of the system, for a 1920 x 1080 sensor anything over 540 LP/ph will potentially aliase, so we don’t want lots of detail above this.  As Optical Low Pass filters cannot instantly cut off unwanted frequencies there will be a gradual resolution tail off that spans the Nyquist frequency and there is a fine balance between getting a sharp image and excessive aliasing. In addition as real world images are rarely black and white lines (square waves) and fixed high contrast patterns you can afford to push things a little above Nyquist to gain some extra sharpness. A well designed 1920 x 1080 HD video camera should resolve around 1000TVL. This where seeing the MTF curve helps, as it’s important to see how quickly the resolution is attenuated past MTF50.
With Bayer pattern sensors it’s even more problematic due to the reduced pixel count for the R and B samples compared to G.
The resolution of the EX1 and F3 is excellent for a 1080 camera, cameras that boast resolutions significantly higher than 1000TVL will have aliasing issues, indeed the EX1/EX3 can aliase in some situations as does the F3. These cameras are right at the limits of what will allow for a good, sharp image at 1920×1080.

MTF services to produce Nikon adapter for F3


Well no surprises here to be honest but Mike Tapa of MTF has already finalised the design of an adapter that will allow users of Sony’s still to be released PMW-F3 to use low cost (compared to PL) Nikon DSLR lenses. This open up a huge range of lens options and I’m quite sure that with good high end lenses the results will be very good. It’s certainly the way  I will be going.

http://www.lensadaptor.com/