A "full stop", or Exposure Value (EV) is an aperture unit that halves the amount of light that comes into the camera. There is a full stop between f/1 and f/1.4. There is another full stop between f/1.4 and f/2. The series then goes on f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 and so on.
If you stop down once from f/4, you will set the aperture to f/5.6, and let half as much light into the camera.
The values can be calculated by multiplying the previous value by the square root of 2. The square root of two is approximately 1.414213562373095048... but luckily camera manufacturers only use one decimal.
Saturday, December 5, 2009
F-stop illustrated
One of the more confusing things in photography is the f-stop values (also called focal ratio, f-ratio, relative aperture or f-numbers). They usually have values like f/1.4, f/2, f/2.8, f/4, f/5.6 and so on. The confusing thing is that a higher number means a smaller aperture. Understanding why this is the case may make your life easier and even your pictures better.
The number is calculated by this formula: (focal length)/(Diameter of the entrance hole). Usually a long lens has a long focal length - it is very roughly the distance between the end of the lens and the sensor. The "entrance hole" is the hole in the aperture mechanism.
In the diagram above, the f-stop number is f/2, as the focal length is twice the Diameter of the entrance pupil.
In the diagram above, the f-stop number is f/4, as the focal length is four times the diameter of the entrance pupil. The value is higher, as the aperture is smaller.
In this last aperture diagram, the f-stop number is also f/4. This time, it is not the entrance hole that is smaller, but the focal length that is bigger than in the first diagram. (Click on the diagrams to display them in real size, if you do not believe me.)
If you change from f/2 to f/4 on your camera, you will cut the diameter by half, and consequently you cut the amount of light by four.
In other words, if you have a situation where you have set the camera aperture to f/2 and the shutter speed to 1/400 of a second, and you then change the aperture to f/4, you can keep the same amount of light by slowing the shutter speed down to 1/100 of a second.
So why is it called stop? It seems to be mostly old habit. The aperture hole, the entrance hole or "entrance pupil" as it is also called, "stops" light from getting in to the camera.
The number is calculated by this formula: (focal length)/(Diameter of the entrance hole). Usually a long lens has a long focal length - it is very roughly the distance between the end of the lens and the sensor. The "entrance hole" is the hole in the aperture mechanism.
In the diagram above, the f-stop number is f/2, as the focal length is twice the Diameter of the entrance pupil.
In the diagram above, the f-stop number is f/4, as the focal length is four times the diameter of the entrance pupil. The value is higher, as the aperture is smaller.
In this last aperture diagram, the f-stop number is also f/4. This time, it is not the entrance hole that is smaller, but the focal length that is bigger than in the first diagram. (Click on the diagrams to display them in real size, if you do not believe me.)
If you change from f/2 to f/4 on your camera, you will cut the diameter by half, and consequently you cut the amount of light by four.
In other words, if you have a situation where you have set the camera aperture to f/2 and the shutter speed to 1/400 of a second, and you then change the aperture to f/4, you can keep the same amount of light by slowing the shutter speed down to 1/100 of a second.
So why is it called stop? It seems to be mostly old habit. The aperture hole, the entrance hole or "entrance pupil" as it is also called, "stops" light from getting in to the camera.
Sunday, October 4, 2009
D5000 slow Live View focus
The Nikon D5000 has an excellent swivel monitor which you can use with Live View to take pictures in positions you could not possibly reach if you were using the standard Viewfinder. The problem, the huge problem, is that it focuses very slowly. You can count on several seconds after you press the shutter-release button before the picture is taken.
The solution to this is: manual focus. It is far from an ideal solution. In some situations you cannot manually focus fast enough. However, in some situations, if you set the lens to manually focus, you can take the picture instantly, before Live view has decided that the focus is accurate.
The solution to this is: manual focus. It is far from an ideal solution. In some situations you cannot manually focus fast enough. However, in some situations, if you set the lens to manually focus, you can take the picture instantly, before Live view has decided that the focus is accurate.
Saturday, September 19, 2009
View NX is working with Snow Leopard - finally
The below text is now luckily obsolete. After almost half a year, Nikon finally fixed their applications so they can run with Snow Leopard.
If you launch ViewNX 1.4 under Mac OS X 10.6 (Snow Leopard), all text labels may be replaced by strange strings like IDS_MENU_FILE and a lot of other strings beginning with IDS. There are apparently problems with Capture NX 2 as well.
Your system is fine. The problem is with the software itself, and we have to wait for an update from Nikon.
There is a web page from Nikon that clarifies the situation. It is not very flattering for Nikon.
The page explains what Nikon planned to start with. Capture NX 1 is not part of the software that was supposed to work, and they will not do anything to make it work in the future. Nikon has pretty much abandoned Capture NX 1, so those of us who buy new cameras, like the D5000, have to upgrade to Capture NX 2, which does not work with Snow Leopard, which... Well, the situation is not ideal.
If you launch ViewNX 1.4 under Mac OS X 10.6 (Snow Leopard), all text labels may be replaced by strange strings like IDS_MENU_FILE and a lot of other strings beginning with IDS. There are apparently problems with Capture NX 2 as well.
Your system is fine. The problem is with the software itself, and we have to wait for an update from Nikon.
There is a web page from Nikon that clarifies the situation. It is not very flattering for Nikon.
The page explains what Nikon planned to start with. Capture NX 1 is not part of the software that was supposed to work, and they will not do anything to make it work in the future. Nikon has pretty much abandoned Capture NX 1, so those of us who buy new cameras, like the D5000, have to upgrade to Capture NX 2, which does not work with Snow Leopard, which... Well, the situation is not ideal.
Wednesday, April 29, 2009
Which lenses autofocus on a D40, D40X, D60 or D5000?
The low range Nikon cameras D40, D40X, D60 or D5000 can only autofocus with lenses with built in motor, for example Nikon's own Silent Wave Motor (SWM). These cameras lack autofocus motor themselves - something which makes them smaller, lighter and cheaper.
Nikkor lenses with "AF-S" in their name should auto-focus on these cameras.
Sigma lenses with "HSM" (Hyper Sonic Motor) in their name should auto-focus on these cameras.
There are also a number of Tamron lenses that should auto-focus on these cameras, but I have not found any reliable way to tell which ones. The secret letters to look for may be "di" (digitally integrated), but there seems to be no confirmation that it is a fool proof sign.
Nikkor lenses with "AF-S" in their name should auto-focus on these cameras.
Sigma lenses with "HSM" (Hyper Sonic Motor) in their name should auto-focus on these cameras.
There are also a number of Tamron lenses that should auto-focus on these cameras, but I have not found any reliable way to tell which ones. The secret letters to look for may be "di" (digitally integrated), but there seems to be no confirmation that it is a fool proof sign.
Sunday, April 26, 2009
Using "hidden" NEF data in Photoshop or Aperture
If you shoot raw nef files with your Nikon camera, you may have camera settings that are not readable by non-Nikon applications. One of the most striking ones is if you choose to set the picture controls to create a black-and-white picture. When you open that nef file in Photoshop or Aperture, for example, the colour will come back.
To see this kind of information in non-Nikon applications, you will have to convert the files in a Nikon application. You can for example batch process all your nef files to jpeg or tiff format using View NX (menu File > Convert Files...) or Capture NX (menu item Batch). Then import the tiff files to the other application.
But don't forget that conversion from nef to both jpeg and tiff will lose some data. Tiff is a lossless format, but the only thing that is lossless is what is visible. In the nef file you can always go back and change the picture controls to some other setting. However, there is no way you can get the colour back in a black-and-white tiff file. In other words, it is always good to keep the nef as backup, in case you need to make some other modifications.
To see this kind of information in non-Nikon applications, you will have to convert the files in a Nikon application. You can for example batch process all your nef files to jpeg or tiff format using View NX (menu File > Convert Files...) or Capture NX (menu item Batch). Then import the tiff files to the other application.
But don't forget that conversion from nef to both jpeg and tiff will lose some data. Tiff is a lossless format, but the only thing that is lossless is what is visible. In the nef file you can always go back and change the picture controls to some other setting. However, there is no way you can get the colour back in a black-and-white tiff file. In other words, it is always good to keep the nef as backup, in case you need to make some other modifications.
Chromatic Aberration
Chromatic aberration is a consequence of the fact that light of different colours do not focus on the same plane when they go through glass. Think of a simple prism, where white light goes in and a rainbow of colours come out.
Camera lenses are not always good at compensating for this, and the result may be a blue thin line around objects.
To get rid of the line semi-automatically, you can use tools like:
If you do not succeed in getting rid of the chromatic aberration, do not feel bad about it. It is a tricky thing to handle. Good software takes into account the camera and the lens. As an example, Canon's RAW editing software Digital Photo Professional does not make the Chromatic Aberration correction tool available for pictures taken with the Canon EOS D20. Neither does it attempt to correct TIFF or JPEG pictures. This is undoubtedly because Canon knows they cannot make good enough corrections for those pictures.
Wikipedia has a more information on the subject.
The Lens Correction tab in Adobe Camera Raw.
Example of a picture with both green and red chromatic aberration.
Detail showing red aberration on one of the birds.
Detail showing green aberration on another of the birds.
Camera lenses are not always good at compensating for this, and the result may be a blue thin line around objects.
To get rid of the line semi-automatically, you can use tools like:
- Adobe Photoshop - Filter > Distort > Lens Correction. Adjust the slides in the box "Chromatic Aberration".
- Adobe Camera Raw - Open the file. (If it is not a raw file, you right-click on it in Bridge and select "Open in Camera Raw..."). Click on Lens Correction. Adjust the slides in the box "Chromatic Aberration".
- Capture NX - In the Edit List, click on "New Step". Select Adjustment > Correct > Color Aberration Control.
If you do not succeed in getting rid of the chromatic aberration, do not feel bad about it. It is a tricky thing to handle. Good software takes into account the camera and the lens. As an example, Canon's RAW editing software Digital Photo Professional does not make the Chromatic Aberration correction tool available for pictures taken with the Canon EOS D20. Neither does it attempt to correct TIFF or JPEG pictures. This is undoubtedly because Canon knows they cannot make good enough corrections for those pictures.
Wikipedia has a more information on the subject.
The Lens Correction tab in Adobe Camera Raw.
Example of a picture with both green and red chromatic aberration.
Detail showing red aberration on one of the birds.
Detail showing green aberration on another of the birds.
Sunday, March 8, 2009
Incompatible "DNG" files
On the home page for Scott Kelby's book Lightroom 2 Book for Digital Photographers, one can download several hundred megabytes of sample files. Strangely enough, many of the sample "DNG" images cannot be opened in Adobe CS4 Bridge or Photoshop - at least not unless you have Lightroom installed. It turns out that many of them, like SaveYourPresets1.dng or SaveYourPresets2.dng are not dng files at all, but psd files with the wrong extension. Funnily enough, many of the correct dng files contain features that make them incompatible with Mac OS X 10.5.6, which in theory opens dng files.
I take this as yet another proof that dng is not a more compatible or safer format than many other raw formats, even though it probably is due to some bug in Lightroom.
It may seem strange that Scott managed to miss this, but Lightroom reads the files without problems, and if you double click on them within Lightroom a copy of them opens in Photoshop, so it looks like they are dng files, even though they are not.
How to fix it? Simply change the extension from dng to psd, and you will be able to open the files in programs that support the extension.
How I figured out that they were PhotoShop files? I opened the files in the Terminal text editor less, and noticed that they contain the code 8BIM, which is a Macintosh Photoshop extension.
I take this as yet another proof that dng is not a more compatible or safer format than many other raw formats, even though it probably is due to some bug in Lightroom.
It may seem strange that Scott managed to miss this, but Lightroom reads the files without problems, and if you double click on them within Lightroom a copy of them opens in Photoshop, so it looks like they are dng files, even though they are not.
How to fix it? Simply change the extension from dng to psd, and you will be able to open the files in programs that support the extension.
How I figured out that they were PhotoShop files? I opened the files in the Terminal text editor less, and noticed that they contain the code 8BIM, which is a Macintosh Photoshop extension.
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