Using a full frame lens on a cropped sensor body

A Quick FAQ for one of the most sensitive and hottest topics in forums. It stirs controversy not only because people don't fully understand, it causes anguish because people end up supplying answers to different questions.

Q1. Do I dial in a different ISO/shutter speed / f/no with the same lens on bodies with different sized sensors?
Ans: No, You use the same parameters

Q2. Do I get a different image "quality" if I use the same lens on different sensors?
Ans:

• It varies depending on some factors but overall, yes, the final image when enlarged from the sensor size to the final size of screen or print will show that the full frame image with less image noise, all things being equal. 
• It may not be exactly proportional to the sensor size ratios because all things are not always equal. 
• The increase in noise is due to the fact that the smaller sensor only sees a small part of the full frame image and you have to magnify the image more to fit the final size screen or print. 
• Some people want to explain it a different way and say that the smaller sensor has "lost" light - in one way, it has, because the smaller sensor cannot see part of the image. In another way, it has not - whatever light that does fall onto the sensor, is the same brightness per area.
• Also an issue is that people often want X megapixels (let us say 20 Mp) whether they use a cropped sensor camera or a full frame camera. That means that cropped sensor makers have to fit a higher pixel density (more pixels per area) onto a smaller sensor. This makes the pixel smaller on a cropped sensor camera. These are all theoretical design issues. At the end of the day, people compare real, practical cameras with real sensors - due to different technological edge, the superiority may not be proportional as prescribed by theory.

Q3. Will the amount of blur background be different when you use the same lens on different sized sensors for the same subject size in the frame.
Ans.

• Yes, there will be different background blur, all things being equal. This is where the notorious phrase - "f/2 on a MFT sensor is equivalent to f/... on a full frame sensor"
• A simplified visual simulator that you can interact with on the web is here:
  https://dofsimulator.net/en/
• An Android App that allows you to understand subject dimensions in the parameters of depth of field is the DOF and Hyperfocal Calculator by Cunning Dog.

Q4: If you fit a 50mm full frame lens on a cropped sensor body, what happens to the f/no?

Ans:

• The f/no stays the same - it is a property of the lens, not the camera body.

Q5: Isn't background blur the same as depth of field?

Ans: No, they are not the same. 

• Depth of field depends on camera to subject distance
• Background blur depends on camera to background distance

Q6. Will the inherent creaminess of a bokeh ball in the centre of the frame be different between the two bodies?
Ans. Likely the bokeh ball will be the same character of wiryness, onion skin, or bokeh ball shape.

Q7: Isn't bokeh the same as background blur?
Ans: Not, they are not the same. The original definition for bokeh is about the creaminess of the blur for the same amount of blur, not how blurred the background is.

Q8. Will the whole frame blur and bokeh effect be different between the two bodies with different sensor size with the same lens?
Ans. Yes, the full frame style of picture will be different because the smaller sensor does not show you the blurry bits and vignetting of the lens that is around the edge of the frame

Q9: If you fit a 50mm full frame lens onto say an MFT sensor body, will it become 100mm?
Ans: No.

• 50mm focal length is a property of the lens. 
• When you fit this lens on a cropped sensor body (whether it be MFT or APS-C), part of the image will not be seen by the sensor because the sensor is smaller (hence the name Cropped) than the Circle of Coverage of the full frame lens. 
• To ensure that you see the full height of the subject using a cropped sensor body, you will have to walk backwards - i.e. increase your camera to subject distance.
• People will then say that if you stand at the same spot but do not move back, you are using the equivalent of a 100mm lens on a full frame body, when you use a 50mm lens on a MFT body.

Having said all the above, let's look at an entertaining and illustrative video that combines some of these points together and..... potentially (if you didn't read above) fills your head with conflicting information (unless you sit down and calmly deconstruct the impact James is saying point by point)

Oh, Ok, so it wasn't that quick. Did you learn something?

For ease of access, here is a DOF calculator by PhotoPills

The Four Thirds and Micro Four Thirds Standards

Olympus and Panasonic have just announced the Micro Four Thirds Standard. It's obvious that this is a significant milestone in the evolution of the digital camera. To the extent that Phil Askey penned a short commentary when reporting the announcement.

What's so significant?

1. Commercially, the Four Thirds Standard and the Micro Four Thirds Standard had to come from companies that did not have a strong vested interest in keeping pre-digital legacy lens mounts, lens catalogues.
2. Although it is not clear to me whether the Four Thirds and Micro Four Thirds Standard is truly Open Standard (as in Intellectual Property, free availability of engineering specs), these "Standards" are purposely declared to be available so that other companies do not have to reverse engineer the electronic and mechanical interfaces. I don't know what it costs financially to gain a ticket to these Open Standards for a would be manufacturer, but it is, shall we say, not specifically a closed door.

The significance is that there is a possibility that Kodak + Panasonic supply a sensor, Olympus and Panasonic (maybe others will join) that supply more than one body, Olympus, Panasonic, Leica, Sigma, maybe Schneider Kreuznach can supply Four Thirds and Micro Four Thirds lenses.

If any other brand can supply just one thing - either a sensor or a body or a lens, the empire and diversity of parts to mix and match will grow. If nobody wants to join the club, then this is just another proprietary, locked in, dead end idea.

3. The aim of the Four Thirds Standard is to make a smaller DSLR body and lens for the same telephoto magnification. The aim of the Micro Four Thirds Standard is to make a camera smaller than a DSLR and grow up the bridge prosumer camera to a larger sensor. This means you have one sensor size and in the long term, two lens systems, the longer one being useable on the shorter one.
4. It is difficult to do this in the shoes of the Big Two - Canon and Nikon - they are committed to
   1. the 24x36mm sensor size (requiring true full frame lenses)
   2. the APS-C sensor size (another lens system)
   3. if they want to independently create a Micro Four Thirds competitor, they have to come out with a short flange lens mount. (yet another lens system)

That's three lens systems they have to support and grow. If they decide to mount their full frame lenses on the APS-C sensor body, they don't enjoy any reduction in package bulk or size.

1. The Micro Four Thirds Standard can use :
   1. "legacy" Four Thirds Lenses that already exist, in autofocus and body image stabiliser mode. Thus scarcity of lenses is not as much an issue. True, the compactness of the Micro Four Thirds camera body with a Four Thirds lens would not be pretty, but you have a lens that may auto-focus, image stabilise and with no crop factor or magnification change.
   2. legacy manual focus lenses for various brands - Minolta, Nikon, Olympus, Pentax K, M42 - already exist for the Four Thirds bodies, then the Micro Four Thirds Standard will also fit those with the relevant adaptors.
   3. with enough reverse engineering, will and skill, current competitor autofocus lens systems in autofocus mode - since the flange distance will be shorter than any DSLR lens mount.
2. The purchasing public has long asked for an EVIL (Electronic Viewfinder, Interchangeable Lens) alternative to the DSLR (Digital Single Lens Reflex) with an OVF (Optical View Finder). There have been some prototypes and navel gazes but at the end of the day, the following cause some concern:
   1. How do you establish a commercially viable line of new lenses for the system?
   2. Who will expend resources and costs on initiating the proprietary lens system?
   3. At the end of the day, what is the ROI (Return of Investment) on such a venture, given that traditionally camera companies "own" the mount and thus other companies will be reluctant to support it.
   4. How will the pricing and price categorisation be viable given that that EVIL has to compete against the so called Bridge Prosumer Cameras and the entry level DSLRs - a very "hot" price level with lower volume sales than the USD 100 compact.
3. The camera body makers can choose to:
   1. make expensive Micro Four Thirds bodies
   2. make cheaper Micro Four Thirds bodies
   3. make bulky Micro Four Thirds bodies
   4. make more compact Micro Four Thirds bodies
   5. incorporate optical rangefinder mechanisms
   6. incorporate Electronic Viewfinder in addition to an LCD screen
   7. simply just have only an LCD or OLED screen.

Not every Micro Four Thirds Body and not every Micro Four Thirds Lens has to be tiny. This is a Standard / System. You can Mix and Match! Build them good, let them come.

del.icio.us Tags: Four Thirds,Olympus,Panasonic,DSLR,EVIL,LCD,Photography,Sensor Size

Photographic Terminology Part 1

It's an interesting time for participating in web forums on photography, equipment and taking photos. Newbies and seasoned photographers often scratch their head when they read abbreviations or terms in forum posts. I'll try to keep a record of the various abbreviations.

Abbreviation	Elucidation
AOV	In photography, angle of view describes the angular extent of a given scene that is imaged by a camera. It parallels, and may be used interchangeably with, the more general visual term field of view. (Wikipedia) See: Bernd Harlos's interactive demonstration (specific to the Four Thirds sensor size), Tamron's interactive Focal Length Comparison and the Contra-zoom aka dolly zoom animation from Wikipedia
FOV	The field of view (also field of vision) is the angular extent of the observable world that is seen at any given moment. (Wikipedia)
Digital Sensor Crop Factor vs FF (35mm Full Frame)	In 1913, Oskar Barnack developed the prototype Leica camera around the 24x36mm film size. This became the standard film size 35mm film SLRs. When the Digital DSLR was invented, it was a different medium and it was expensive to make such a large sensor. So different brands used as a basis, a smaller sensors. When you take any lens and fit it on a camera successfully, that camera's true optical focal length(s). Let us take for example, 50mm on a 35mm film camera. Now, for the Four Thirds consortium, their reference sensor is not 24x36mm, it is 13.5x18mm. Even if the lens displays a large area, the sensor only sees a smaller rectangle of it, the rest of the image is "wasted". Put it simply, it's like taking masking paper and cropping away the "unseen" area. This crop factor for Four Thirds is 2x. Take 2 people. Stand away from them with a film camera and the 50mm lens. You take a photo of 2 people. Take that same lens, same scene, but mount the lens on a Four Thirds camera. You will see 1 person in the photo. It feels to you that you are magnifying the scene by 2x. If you walk backwards a bit, you can fit both people into the photo, but you will have now changed your distance and your perspective. Since longer lenses magnify things, it appears that this real 50mm lens when mounted on a Four Thirds camera works like a 100mm lens in terms of AOV.

del.icio.us Tags: Four Thirds,Crop Factor,FOV,AOV,Sensor Size