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

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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/

 

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Storm Chasing and Video Production Workshop.

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alister-and-supercell-300x225 Storm Chasing and Video Production Workshop.
Shooting a Supercell Storm

Just a reminder that I am running a documentary production workshop between the 7th and 15th of June. Based out of Denver, USA this will be an amazing adventure, road-trip and intensive workshop all rolled into one week. Only 3 places remain at just $1,500 USD per person, plus accommodation. Please see this page for full details. This year is a La Nina year, so we can expect more storms and tornadoes than on average years. May and June are the peak months for severe storms in the USA. We have seen in the past week the power of these storms. One important note is that the storms that killed so many people last week were travelling at 50 to 60 mph across the ground. One of the reasons for chasing in June is that the storms tend to move much more slowly, often only 20 mph so there are far more opportunities to stop and shoot. In addition the weather systems move onto the wide open plains of Colorado, Nebraska and the Dakotas giving incredible vistas.

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3D Workshop at Samy’s Camera (Fairfax store) LA. Also Cinegear appearance.

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I shall be in LA with the Genus Hurricane Rig for Cinegear at the beginning of June. Then on June the 5th and 6th I am running a two day 3D workshop where you can gain full certified Hurricane Rig accreditation. The normal fee for the full two days is $500 USD however if you purchase a hurricane rig between now and then the course is free and you get the option to do the second day hurricane rig accreditation workshop again for free. If you just want to attend the first day and the intro to 3D workshop then you can attend for just $50. Make any purchases at Samy’s totalling $500 or more and the day is free. Lunch will be provided and it should be a lot of fun as well as an interesting insight into the world of S3D. See http://www.samys.com for more details.

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35mm World Workshops at Haydock Park (UK) on May 12th.

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I’m presenting a couple of 35mm world sessions at the BPV Northern Expo at Haydock Park on May 12th. These are free sessions, around 90mins each. They will focus on the Sony F3 and FS100, but will also touch on the f65 and f35. The aim is to take a look at the pro’s and con’s of shooting with a camera with a Super35mm sensor as well as to give an understanding of which cameras are appropriate for which jobs. Hopefully we will have an interesting discussion session at the end of each workshop and the chance to get hands on the FS100 and F3. More details here: http://www.bpv.org.uk/

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Updated notes for FS100 – F3 Video Review.

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To see the video scroll down to the next blog entry.

The main aim of the shoot was to see how the FS100 held up against the F3. We shot on a bright sunny day by the River Thames and again in the evening in a typically lit living room. There were no big surprises. The FS100 is remarkably close to the F3. You would have no problems cutting between the two of them in a project.
I did find that the FS100 LCD appeared less sharp and not quite as good as the F3’s even though they both use the same underlying panel. This is probably down to the additional layers required for touch screen operation on the FS100. I also did not like the 18-200mm f5.6 kit lens. There was too much lag in the focus and iris controls, but the beauty of this camera is that you can use a multitude of lenses. For the evening shoot I used a Nikon 50mm f1.8 which was so much nicer to use. On reviewing the footage I did find that we were tending to over expose the FS100 by half a stop to a stop, this does make making accurate comparisons difficult and I apologise for this. I believe this was down to the slightly different images we were seeing on the LCD’s. I did use the histograms on both cameras to try to ensure even exposure, but even so there is a difference. A small part of this is also likely down to the very slightly different contrast ranges of the two cameras.
Oe thing we discovered, not mentioned in the video is that when you use a full frame lens, like the Nikon 50mm. You must ensure that the E-Mount adapter you use has an internal baffle or choke. If it doesn’t you will suffer from excessive flare. The adapter I had did not have a baffle and some shots (not used) were spoilt by flare. The adapter I have from MTF for the F3 has a baffle as do MTF’s E-Mount adapters, so these should not suffer from this issue.
The FS100 performance is so very close to that of the F3’s (at 8 bit 4:2:0, 35Mb/s) that it is hard to tell the two apart. I believe the F3’s images are just a tiny bit richer, with about half a stop more dynamic range, in most cases it takes a direct side by side comparison to show up the differences.
The range of camera settings and adjustments on the FS100 is not quite as extensive as on the F3, nor do the adjustments have such a broad range. However there is plenty of flexibility for most productions.
If you don’t need 10 bit 4:2:2 then it is hard to justify the additional cost of the F3, both cameras really are very good. Despite some other reports else where I felt the build quality to be very good and the buttons, while small, are big enough and well placed. If you do want autofocus then you will be pleased to know that it actually works pretty well on the FS100 with only minimal hunting (of course you must use an AF compatible lens).
I did also record the HDMI output to one of my NanoFlashes at 100Mb/s. Comparing these side by side it is extremely hard to see any difference. It is only when you start to heavily grade the material that the advantage of the higher bit rate Nanoflash material becomes apparent. There is less mosquito noise in the NanoFlash material. I was really impressed by the AVCHD material. The lack of noise in the images really helps.
The FS100 really is the F3’s little brother. The pictures are remarkably close, which they should be as they share the same sensor. The FS100 packs down into a remarkably small size for transport. The loan camera from Sony was actually packed in a case designed for the MC1P mini-cam, about 15″x10″x5″ so very compact indeed. The F3 is considerably larger and bulkier, in part due to the extra space taken up by the built in ND filters.
The lack of ND filters does need to be considered. There are some clever solutions in the pipelines from various manufacturers as well as existing solutions such as vari ND’s, screw on ND’s and a Matte Box with ND’s, so it’s not a deal breaker
I think there is every chance that the FS100 will be the first NXCAM camera that I will purchase. It will be a good companion to my F3. It’s modular design will allow me to get shots that are not possible with the F3. I felt that the FS100 (with the 18-200mm lens that I don’t like) was better suited to “run and gun” than my F3 with either manual DSLR lenses or PL glass. You can, with the FS100 simply point the camera at your subject and hit the one push auto focus and auto iris and have an in-focus, correctly exposed shot. This is much more like a traditional small sensor camcorder in this respect. The long zoom range also makes this more like a conventional camcorder, although there is no servo for the zoom.

In conclusion, in my opinion, for “run and gun” or quick and dirty setups the FS100 with the 18-200mm lens has an edge over the F3 due to the fast auto focus and auto iris one-push controls. For more precise work and shallow DoF your going to want a different lens, something with manual control and calibrated focus and iris scales. For more demanding shoots then the F3 is probably the better choice with it’s slightly improved dynamic range and the ability to use S-Log and 4:4:4. In either case these cameras can produce highly cinematic pictures and I see no reason why you could not shoot a great looking feature with either.

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Is this the future of 3D?

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I am a big fan of 3D. I designed a a 3D rig, so I must be an enthusiast! However even I don’t believe that 3D is the future for all video production, but I do believe it is here to stay. I think it is for special event television, special features, movies and specialist presentations. I have long said that many of these non-movie productions will end up in the cinema. This has been born out by the release of a 3D film about the Isle of man TT races. TT3D, Closer to the edge, released just 4 days ago has shot straight into the top 10 of the UK box office charts making it one of the most successful documentary releases in UK cinema history.

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The Difference Between Detail Correction and Aperture.

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Just to clarify the differences between Detail settings and the Aperture setting.

Detail has a sub set of settings including: frequency, level, crispening, knee aperture, black and white limit. These sub settings all affect the amount and level of detail correction applied.

Aperture is a completely separate type of adjustment.

Detail works on contrast. The higher the contrast in an image, the sharper it appears. A bright sunny day will look sharper that a dull cloudy day because there is more contrast. detail works by increasing contrast by adding black or white edges to any parts of the image where the contrast changes rapidly, for example the edge of an object silhouetted against the sky. This increases contrast still further, making the image appear sharper. The crispening setting sets the contrast threshold at which detail gets added, level adjusts the amount.

Aperture is a simple high frequency boost. As fine details and textures are normally represented by high frequencies within the image, boosting high frequencies can help compensate for the natural fall off in lens and sensor performance at higher frequencies. This helps enhance textures and other subtle, fine details within the image look clearer.

Neither setting will increase the cameras resolution. Both make the image “appear” sharper. Detail correction IMHO is very un-natural looking and electronic, while careful use of aperture can help sharpen the image without necessarily looking un-natural.