A depth of focus look at HD DSLR video and the image size

I feel a little confident to post this blog.  I am a filmmaker who loves the science behind filmmaking and I wanted to get to the bottom of the DSLR revolution in translation to video and film with regards to image resolution, size, depth of field and normal lens focal length.  For instance it is common knowledge that a 35 mm film requires a 50 mm lens to be considered normal focal length and for you film buffs a 16 mm film requires a 25 mm lens to be considered a normal focal length lens.  A normal lens on a 70 mm film requiers an 80 mm lens.  Don't ask me what the conversion factor is but the fact is the larger the image size the longer the focal length of the lens has to be to be considered normal.  Generally the larger the image size a stronger depth of field is present on the image.  It is widely agreed that film and digital are different animals and rightly so.  However, the basic physics of image size and and normal focal length of a lens can not be ignored.



Depth of field stays the same, but angle of view changes when you put that same lens on a camera with a smaller negative. Essentially the lens becomes the equivalent of twice the focal length when going from 35mm to 16mm, so you'd need to switch to a lens with half the focal length to maintain the same view. Hence why lens sets for 16mm tend to start at much shorter focal lengths. 

Read more: http://www.cinematography.com/index.php?showtopic=12505#ixzz1BY4cxb3a

Depth of Field Explained

It is a common misconception that all DSLR camera is the equivalent of a 35 mm film camera.  That could not be more false.

A full-frame digital SLR is a digital single-lens reflex camera (DSLR) fitted with an image sensor that is the same size as a 35 mm (36×24 mm) film frame.[1][2] This is in contrast to cameras with smaller sensors, typically of a size equivalent to APS-C-size film, much smaller than a full 35 mm frame.

The image senser on a Full-frame DSLR is the equivalent of 35 mm film is 36 × 24 mm.  35 mm film's image dimensions is 18.0 × 24.0 mm.  as you can see the ccd image is larger then 35 mm film.

I found that the 1" ccd with a normal lens of 16 mm is really the equivalent of 8mm film.  Hence is why people for many years have been complaining about the depth of field and the normal focal length of the lens size.  Its sad even the highest priced HD cam on BH photo video can't even come close to the same normal 50mm focal length that is so accustom to 35mm.

Digital still

In digital photography, the sensor "type" is not the sensor diameter:(*) refers to TV tube diameters that were standards in the 50s. The normal lens focal length is roughly 2/3 of the TV tube diameter.(**) this is a mathematical calculation because most of the cameras are equipped with zoom lenses.

Sensor type	TV-tube diameter *	Image dimensions	Image diagonal	Normal lens focal length **
1/3.6"	7.1 mm	4.0 × 3.0 mm	5.0 mm	5 mm
1/3.2"	7.9 mm	4.5 × 3.4 mm	5.7 mm	5.7 mm
1/3"	8.5 mm	4.8 × 3.6 mm	6.0 mm	6 mm
1/2.7"	9.4 mm	5.4 × 4.0 mm	6.7 mm	6.7 mm
1/2.5"	10.2 mm	5.8 × 4.3 mm	7.2 mm	7 mm
1/2"	12.7 mm	6.4 × 4.8 mm	8.0 mm	8 mm
1/1.8"	14.1 mm	7.2 × 5.3 mm	8.9 mm	9 mm
1/1.7"	14.9 mm	7.6 × 5.7 mm	9.5 mm	9.5 mm
2/3"	16.9 mm	8.8 × 6.6 mm	11.0 mm	11 mm
1"	25.4 mm	12.8 × 9.6 mm	16.0 mm	16 mm
Four Thirds[3]	33.9 mm	17.3 × 13 mm[4]	21.63 mm	22 mm
4/3"	33.9 mm	18.0 × 13.5 mm	22.5 mm	23 mm
APS-C	45.7 mm	22.7 × 15.1 mm	27.3 mm	27 mm
DX	n/a	23.7 × 15.8	28.4 mm	28 mm
FF (35 mm film)	n/a	36 × 24 mm	43.3 mm	50 mm
(6 × 5 cm)	n/a	49.0 × 36.7 mm	61.2 mm

Cinema

In cinematography, a focal length roughly equivalent to twice the diagonal of the image projected within the camera is considered normal, since movies are typically viewed from a distance of about twice the screen diagonal.

Film format	Image dimensions	Image diagonal	Normal lens focal length
Standard 8	3.7 × 4.9 mm	6.11 mm	12–15 mm
Single-8 (FUJI)	4.2 × 6.2 mm	7.5 mm	15–17 mm
Super-8	4.2 × 6.2 mm	7.5 mm	15–17 mm
9.5 mm	6.5 × 8.5 mm	10.7 mm	20 mm
16 mm	7.5 × 10.3 mm	12.7 mm	25 mm
35 mm	18.0 × 24.0 mm	30.0 mm	60 mm
35 mm, sound	16.0 × 22.0 mm	27.2 mm	50 mm
65 mm
70 mm	52.6 × 23.0 mm	57.4 mm

The Sony HDW-F900 only has a 2/3 image sensor the normal lens on this camera is 11 mm.

Even my Canon xha1 does not even come close with only a 1/3 image sensor and the normal lens for this camera is 6 mm.

Table of sensor sizes

Inch-based sensor formats are not standardized. Originally, they were the outer diameters of image tubes used in the 1950's. Exact dimensions may vary, but those listed are typical.

Type	1/8"	1/6"	1/4"	1/3.6"	1/3.2"	1/3"	1/2.7"	1/2.5"	1/2.3"	1/2"	1/1.8"	1/1.7"	1/1.6"	2/3"	Super 16mm	1"	4/3"	Canon APS-C	Pentax SonyNikon DX	Canon APS-H	35mm	Leica S2	Pentax 645D	Kodak KAF 39000[8]	Leaf AFi 10	Phase One P 65+
Diagonal (mm)	2.00	3.00	4.00	5.00	5.68	6.00	6.72	7.18	7.7	8.00	8.93	9.50	10.07	11.0	14.54	16.0	21.6	26.7-27.3	28.4	34.5	43.3	54	55	61.3	66.57	67.4
Width (mm)	1.60	2.40	3.20	4.00	4.54	4.80	5.37	5.76	6.16	6.40	7.18	7.60	8.08	8.80	12.52	12.8	17.3	22.2-22.7	23.6-23.7	28.7	36	45	44	49	56	53.9
Height (mm)	1.20	1.80	2.40	3.00	3.42	3.60	4.04	4.29	4.62	4.80	5.32	5.70	6.01	6.60	7.41	9.6	13.0	14.8-15.1	15.5-15.8	19.1	24	30	33	36.8	36	40.4
Area (mm2)	1.92	4.32	7.68	12.0	15.5	17.3	21.7	24.7	28.5	30.7	38.2	43.3	48.56	58.1	92.8	123	225	329-343	366-374	548	864	1350	1452	1803	2016	2178
Crop factor[9]	21.65	14.14	10.83	8.65	7.61	7.21	6.44	6.02	5.62	5.41	4.84	4.55	4.3	3.93	2.97	2.70	2.00	1.62-1.58	1.52	1.26	1.0	0.8	0.79	0.71	0.65	0.64

So all this time Filmmakers are so frustrated trying to find the solution with what camcorder will do the trick to solve there filmmic look problem is so far off its not even funny.  In fact you can not find a camcorder with an image size that will match the normal lens equivalent of 50 mm let alone a 8mm film or 16mm film.  I kinda found this out today as I wanted to understand more about this whole DSLR revolution.  The shocker is that the Canon T2i is the rough equivalent of 16 mm film as far as the 25 mm normal lens goes.  The normal lens on a Canon T2i is 27 mm because it has the APS-C Image sensor (22.7 × 15.1 mm).  Hence is why it has an incredible depth of field.  The only major draw back is that it is an DSLR body rather then a Camcorder body.


Why its so hard for camcorder manufactures to adjust to this simple standard is beyond me especially when I can buy the Canon T2i for under $900.  This is chump change for some of the prosumer HDV cameras ranging from $2,000 and $20,000.  Even the best DSLR that shoots true HD video only cost $3,299.00 according to bh photo and video.

Canon EOS 5D Mark II Digital Camera

The only camcorder that is on the market and is not even a camcorder at all is the Red digital cinema camera.  The Red like a DSLR on steroids.

5Dmk2/7D lens comparison test



Field of View Comparator
http://www.abelcine.com/fov/

A Lens Is a Lens is a Lens


A lens is a lens is a lens, and it doesn’t know what size sensor or film gate is placed behind it. A lens projects light and the magnification size of that projection is determined by its focal length.

Nevertheless, there has always been a great deal of confusion associated with the focal length of lenses and their relationship to the size of the image area.

I’ve read many explanations in various books and on the internet over the years and authored some of them myself. But often written explanations confuse as much as they explain. If a picture is worth a 1000 words, I figure this video is equal to a small novella on the subject. Many people seem to use the various optical terms incorrectly or interchangeably, so I figured showing what happens would help demystify the concepts involved.

Its really a DSLR camera with all the bells and whistles that cinematographers need and probably don't need but its there anyways for glits and glamour.  This camera fully decked out should cost around $50,000.  It's a lot less then the $80,000 Sony HDW-F900R CineAlta 24P HDCAM that isn't even decked out at all.  The CCD image size of the red is the Equivalent to S35mm (Motion) / APS-H (Still) lenses, hence it takes a normal 50 mm lens and rightly so.  

Keep in mind I am not even talking about image resolution, Just the image size and normal focal length.  The APS-H Image Format 29.2 x 20.2mm.

So where do you filmmakers go from here.  Personally I am not entirely sure of that my self.  But what I can say is we are one step closer to the age of independence from the Hollywood film studio and we have come to the age of the backpack filmmaker.  I think there are allot of kinks to work out but the fact that I can make my feature work with only 5 - 10 k of basic equipment such as a mac laptop the Finalcut studio and the Canon T2i and a mic with the basic accessories then I am set.   Funny thing is I know I can put all this in one back pack and probably have room for a light or 2.  

++= Hollywood Studio

Right now the sony HD cam can capture at around 200 Mb/s + or -.  HDV can capture around 25 Mb/s + or - depending on how its captured.  DSLR's as far as I know capture at 15 Mb/s / 45 Mb/s depending.  

However according to Magic Lantern

http://magiclantern.wikia.com/wiki/550D

The creator has been able to hack the firmware and capture HD 24 fps video at a steady 66 Mbps.  The setting can be higher but the buffer can only handle so many minuts of film too high then it can only capture seconds of film.

Just to show you How different the expensive red one Digital cinema camera is to popular prosumer DSLR's here is a fantastic video.

Red One, Canon 5D Mk II, and Panasonic Lumix GH1 Footage Comparison


Red One, Canon 5D Mk II, and Panasonic Lumix GH1 Footage Comparison from Birns and Sawyer on Vimeo.


http://vimeo.com/5981422



h.264 qscales

The Canon function mvrSetDefQScale(int16_t *) (2.0.8 0xff990188) sets the quality parameter to the camera's h.264 encoder. If the CF card is not able to keep up, the camera will display a buffer-level bar on the right side of the LCD and stop recording when it hits full. The parameter does not have any effect unless fixed bit rate encoding is selected via mvrFixQScale(int16_t *) (2.0.8 0xff9905d4).

The default q-scale is -8 in VBR mode and has a nominal 42 Mbps with the 2.0.8 firmware. The 24p tests were done with the camera on a tripod writing to a Lexar 400x UDMA 16 GB card with all Magic Lantern tasks disabled (no zebras, cropmarks, etc). qscales less than -12 occasionally stopped recording.
Q-scaleFPSMbpsNotes
+8 30p 7 Mbps Very low quality
-9 24p 32 Mbps
-10 24p 41 Mbps
-11 24p 51 Mbps
-12 24p 59 Mbps
-13 24p 62 Mbps
-14 24p 66 Mbps Best, sustainable in 24p mode?
-15 24p 68 Mbps 2 buffer bars
-16 24p 76 Mbps Only a few seconds



Keep in mind this is not megabytes per second its megabits per second. This data rate however is far better then the standard HDV 25 Mbps.

HDV Specs The basic idea behind HDV is to store high-def MPEG-2 video on standard DV media (DV or Mini DV cassette tape), and stream it across standard FireWire / IEEE 1394 interfaces. The HDV video format supports MPEG-2 compressed video (MP@H-14), at two 16:9 resolutions: - 720p (1280 x 720, progressive), at approximately 19 Mbps data rate - 1080i (1440 x 1080, interlaced), at approximately 25 Mbps data rate


So if HDV peeks out at 25 Mbps then 25 megabits = 3.12500 megabytes. The DSLR with Magic Lantern firmware can get 66 Mbps on a steady capture with out running out of cache. 66 megabits = 8.25 megabytes. With out the magic lantern the canon T2i can get full HD bitrate = 43 Mbps. make sure if you do record with these types of settings you use a class 10 SDXC card (read/write up to 25MB/S, speed of 10MB/S is guaranteed)  or SDXC UHS-1 (Minimum data transfer speed of 10MB/sec) or a class 10 SDHD.  The SDHD cards seem to be better priced but the others such as the UHS-1 should reduce in camera cache speed problems capturing at higher Mbps.  Right now the fastes SD card on the market is the SanDisk 16GB Extreme Pro - SDHC - UHS Speed Class 1 - High Performance memory card at 45Mb/s.  With the advent of the Magic lantern firmware reaching 60 Mb/s a second plus faster cards are needed in order to keep up with any demanding data usage.  All cannons HDSLR cameras have a catch, but that only goes so far.
   

 

Note that the Canon 60D manual says "SDHC and SDXC cards featuring UHS (Ultra High Speed) enable a maximum writing speed of SD Speed Class 10". We asked Canon for clarification on this, and they said the Canon 60D is not UHS-I compliant but should work with UHS cards at up to SD Class 10 speeds.

Not sure if this means the magic lantern firmware fixes this limitation, but this is just how canon made there cameras.  Not sure if it means anything, but in any case why risk having less performing, lower quality cards? 

 XDCAM HD gets 50 mbps on its tiny 2/3" CCD. So this little $900 Canon T2i with Magic Lantern firmware installed will out do the $40,000 camera in data comparison. Native HDCAM is 140 Mbps. 140 megabits = 17.5 megabytes.  Even the best Sony HDcam only has 2.2 megapixels.  The canon T2i has Approximately 18 Megapixels.  I don't even think this is even a competition.  Its more like a slam, bam, rub your face in do do humiliation kinda thing.

REDCODE RAW is a variable bit rate wavelet codec which allows raw sensor data at resolutions of up to 4,096×2,304 to be compressed sufficiently for practical on-camera recording. Two variants were offered previously, one with a maximum data rate of 28 MB/s (224 megabit/s), and one with a maximum data rate of 36 MB/s (288 megabit/s), but the camera was recently updated to record with an additional data rate option of 42 MB/s (336 megabit/s). Compared with the uncompressed data captured by the sensor, these bit rates represent compression ratios of about 12:1, 9:1, and 8:1 respectively.


Red can capture up two 6k raw.  The reality is that 2 k is the standard of theater distribution and 4 k is really used for those high end epic movies.  8 k is only used for Imax cinema. 1920 x 1080 is so close to 2k its not even funny.

I am sure the future of these cameras can get better, but for now its good enough to do even the biggest feature project.   I know because Star Wars - Episode I was shot on the fancy Sony HDcam and crank 2: high voltage was shot using the Canon xha1.

So what are you waiting for.  Do you need some fancy million $ budget to make a good movie?  Or can you do it for 10 k or less.  In fact, crank was done for 10 mill but all the money went mostly into the cast and other things rather then the film medium and equipment.

The movie industry is changing rapidly and people who start looking for a new business model rather then focusing on the old hollywood methed will succeed.  People don't care what you shot on or what fancy this or that you had.  As long as you are able to get the shot and tell the story then who cares.  I can name 2 major success movies that where shot on DV and the audence just keept coming back for more.  First is Open Water and the second is Paranormal Activity.  Open water was produced for 50 k and paranormal activity was produced for 11k.  Both films did not have known actors or directors or fancy what ever you call its.  People still love a good story.  Yes its nice to have a nice image, but at what cost.  If its going to stop you from making the story or even worse make the story turn out bad because the there is not enough in the budget then what is the point.

I have seen so many amateur videos using the Canon T2i and so many of them look like they came out of a movie.  It just looks that good and I feel good knowing that I don't have to riesle with an inadequate image just because it fits the budget.

By
Robert Sawin