Macro Lenses

From : Alan Wood

Macro lenses provide the best and most convenient method of taking close-ups, but they are expensive. They differ from ordinary lenses in having an extended focusing mount that can focus from infinity to a magnification of ×0.5 or ×1.0 simply by turning the focusing ring. Their optical performance is optimised for short working distances instead of infinity, and they are often more highly corrected than ordinary lenses. For 35 mm cameras, they come in focal lengths of about 50-60 mm, and in longer lengths between 90 and 105 mm and between 180 and 200 mm; they are also available for roll-film cameras. The longer focal length lenses provide greater working distances, which allows more room for lighting and helps to avoid alarming live subjects. The 50 mm lenses can be used as a standard lens in place of one with a restricted focusing range. If you do not use a TTL meter, exposures must be adjusted as the magnification is increased beyond ×0.1.

Additional Extension

If your macro lens incorporates floating elements for better performance at short distances, then you should make sure that the lens is set for close focus (not for infinity focus) if you use it on extension tubes or .

Reverse Mounting

You should also set the lens for close focus if you use it with a reversing ring. Reversing the lens exposes the rear element and various coupling mechanisms that are protected when the lens is mounted normally. You can provide them with some protection by adding a short extension tube to act as a makeshift lens hood; an old manual tube will do. You can also buy special adapters that allow a filter or a lens hood to be attached to the rear of a lens.

Focusing

Depth of field is very small at ×0.5 or ×1.0, so to you may find it easier to focus exactly where you want if the auto focus is turned off. You will probably find it easier to focus by moving the camera backwards and forwards after setting the magnification that you want.

Using a Precise Magnification

Focusing by turning the focusing ring or using autofocus changes the magnification. If you want to use a particular magnification that is engraved on the lens, turn off the autofocus, set the focus ring for the magnification you want, and then focus by moving the camera backwards and forwards until the image in the viewfinder is sharp. If you are using a tripod or a macro stand, then a focusing rail makes it easy to focus this way. Focusing by moving the whole camera also makes it easier to focus at around life-size, where manual focusing can be imprecise because turning the focusing ring causes simultaneous changes in the extension and the working distance that interact in such a way as to have little effect on the focus.

Good points

• Excellent results.
• Automatic diaphragm and automatic exposure are normal.
• Automatic focusing is available if the camera system supports it.
• Can be used instead of a standard or portrait lens.

Bad points

• Expensive.
• Bigger and heavier than an ordinary lens of the same focal length.
• May not have as fast a maximum aperture as an ordinary lens of the same focal length.
• Automatic focusing may not focus on exactly the right point.

Close-up Lenses

From : Alan Wood

Close-up lenses (also called supplementary lenses) screw into the filter mount on the front of the lens that is fitted to your camera, and bring the focusing range of the camera's lens closer to the camera. The power of close-up lenses is normally specified in dioptres; higher numbers are more powerful. With the camera's lens focused on infinity and a +1 dioptre close-up lens fitted, the maximum focusing distance becomes 1 metre, with a +2 it becomes 0.5 metres, and with a +4 it becomes 0.25 metres.

Close-up lenses for 35 mm cameras are commonly available with strengths of +1, +2, +3 and +4, but intermediate and higher strengths are also available. The lenses of digital cameras have shorter focal lengths than those for 35 mm cameras, and so they need stronger close-up lenses such as +7 and +10; these are often of too small a diameter and insufficient quality to be used on 35 mm cameras.

Close-up lenses are not usually corrected for optical aberrations, so you need to stop down the camera lens to at least f/8. The effects on image quality are greater with camera lenses of longer focal length, so better quality (and much more expensive) close-up lenses are needed for telephoto lenses and for roll-film cameras. Two-element achromatic close-up lenses are available: Nikon produce +1.5 and +2.9, Canon produce +2 and +4, and Hoya produce +10. Specially-matched close-up lenses are available for some macro lenses and medical lenses.

You can use two close-up lenses at a time, with the stronger one closer to the camera lens. The effect is additive, so a combination of a +1 and a +2 has the same power as a +3 close-up lens. Combining close-up lenses makes the drop in quality worse.

Close-up lenses are cheap, easy to use, cause no exposure problems, and do not darken the viewfinder, but they cannot match the quality of a macro lens. They are readily available, and are made by camera manufacturers and by independent companies.

The following tables show the subject area, working distance and magnification with the camera lens focused at infinity and at its closest distance. Focusing at closer distances gives greater magnification, shorter working distance and smaller subject area.

Close-up lenses with 50 mm lens on 35 mm camera (infinity focus)

Dioptres	Focal length	Working distance	Subject size	Magnification
+1	1000 mm	1000 mm	720 × 480 mm	0.05
+2	500 mm	500 mm	360 × 240 mm	0.1
+2.5	400 mm	400 mm	288 × 192 mm	0.125
+3	333 mm	333 mm	240 × 160 mm	0.15
+4	250 mm	250 mm	180 × 120 mm	0.2
+10	100 mm	100 mm	72 × 48 mm	0.5

Close-up lenses with 50 mm lens on 35 mm camera (closest focus)

Dioptres	Focal length	Working distance	Subject size	Magnification
none		360 mm	237 × 158 mm	0.15
+1	1000 mm	264 mm	176 × 117 mm	0.21
+2	500 mm	210 mm	140 × 93 mm	0.26
+2.5	400 mm	184 mm	125 × 83 mm	0.29
+3	333 mm	172 mm	117 × 78 mm	0.31
+4	250 mm	146 mm	99 × 66 mm	0.36
+10	100 mm	74 mm	53 × 35 mm	0.69

Range of magnifications with 50 mm lens on 35 mm camera

Dioptres	Magnification
	0.05	0.10	0.15	0.20	0.25	0.30	0.35
none
+1
+2
+3
+4

Calculations for digital cameras must be based on the actual focal length of the camera lens, not the commonly-quoted 35 mm equivalent. Digital cameras do not all have the same chip size, so the subject area can only be approximate; the ones given were measured with a Kodak DC-4800.

Close-up lenses with 18 mm lens on digital camera

Dioptres	Focal length	Working distance	Subject size	Magnification
+4	250 mm	250 mm	108 × 72 mm	0.07
+7	143 mm	143 mm	62 × 41 mm	0.126
+10	100 mm	100 mm	45 × 30 mm	0.18
+10 plus +7	59 mm	59 mm	27 × 18 mm	0.305

Good points

• Small, light weight, easily portable.
• Not expensive.
• Don't affect exposure.
• Don't darken SLR's viewfinder or digital camera's LCD screen.
• Autofocus still works.

Bad points

• Can't be used at wide apertures.
• Awkward to add, remove and combine in order to change magnification.
• Definition not as good as a macro lens.
• May need more than one for camera lenses with different filter sizes.

Raw image format

From Wikipedia, the free encyclopedia

RAW image file
File extension: .raf (Fuji)
.crw .cr2 (Canon)
.tif .kdc .dcr (Kodak)
.mrw (Minolta)
.nef (Nikon)
.orf (Olympus)
.dng (Adobe)
.ptx .pef (Pentax)
.arw .srf (Sony)
.x3f (Sigma)
.erf (Epson)
.mef .mos (Mamiya)
.raw (Panasonic)
.r3d (Red)


A raw image file (sometimes written RAW image file[1]) contains minimally processed data from the image sensor of a digital camera or image scanner. Raw files are so named because they are not yet processed and ready to be used with a bitmap graphics editor or printed. Normally, the image will be processed by a raw converter in a wide-gamut internal colorspace where precise adjustments can be made before conversion to an RGB file format such as TIFF or JPEG for storage, printing, or further manipulation.

Raw image files are sometimes called digital negatives, as they fulfill the same role as film negatives in traditional chemical photography: that is, the negative is not directly usable as an image, but has all of the information needed to create an image. In addition to raw files from cameras, raw data from film scanners can also be referred to as digital negatives. Likewise, the process of converting a raw image file into a viewable format is sometimes called developing a raw image, by analogy with the film development.

Like a photographic negative, a digital negative may have a wider dynamic range or color gamut than the eventual final image format. The selection of the final choice of image rendering is part of the process of white balancing and color grading.

File contents

Providing a detailed and concise description of the content of raw files is highly problematic. There is no single raw format; formats can be similar or radically different. Different manufacturers use their own proprietary and typically undocumented formats, which are collectively known as raw format. Often they also change the format from one camera model to the next. At least one manufacturer, Nikon, encrypts portions of the file in an attempt to prevent third-party tools from accessing them.[2] This industry-wide situation has concerned many photographers, who worry that their very valuable raw photos may someday become inaccessible, as operating systems and applications become obsolete and abandoned raw formats are dropped from new software. The availability of high-quality open source software which decodes raw image formats, particularly dcraw, has helped to alleviate these concerns. Adobe has developed and promoted a standardized raw image format called DNG ("digital negative"); this has been received enthusiastically by open-source developers[2] but has received little support from major camera makers other than Pentax.

Ultimately, any raw format's purpose is to faithfully record both 100% of exactly what the sensor "saw" (the data) and the conditions surrounding the recording of the image (the metadata).

Digital camera raw files contain the pixel data from a rectangular image sensor, the modern equivalent of traditional film, usually at 12 or 14 bits per sensor bucket. The sensor is almost invariably overlaid with a so-called Bayer filter, consisting of a mosaic of red, blue and green filters in alternating rows of RG and GB. Given that three colors fit uncomfortably in a rectangular grid, green was chosen to be doubly present, since the human eye is more sensitive to it. Green also often serves as the luminance channel, and as the dominant channel for in-camera black-and-white conversions. To retrieve an image from a raw file, this mosaic of data must be converted into a full RGB image. This is formally known as demosaicing, but is often referred to as digital development, by analogy with the development process used to convert photographic film into viewable prints.

One variation on the Bayer scheme is the RGBE sensor of the Sony DSC-F828, which experimented with exchanging the green in the RG rows with Emerald (cyan). Other sensors, such as the Foveon X3 sensor capture information directly in RGB form, having three pixel sensors in each location, one for each color component; these camera RGB raw data still need to be processed to make an image file.

Flatbed and film scanner sensors are typically straight narrow RGB or RGBI (where "I" is infrared) strips that are swept across an image; other than that, the remainder of the discussion about raw files applies to them as well. (Some scanners do not allow the user access to the raw data at all, as a speed compromise. The raw data is processed very rapidly inside the scanner to select out the best part of the available dynamic range so only the result is passed to the computer for permanent storage.)

The contents of raw files include more information, and potentially higher quality, than the converted results, in which the rendering parameters are fixed, the color gamut is clipped, and there may be quantization and compression artifacts. Each pixel in a raw file has a greater bit-depth (compared to typical 8-bit renderings), and can thus store more subtle variations and range in color and detail. Hence, large transformations of the data, such as increasing the exposure of a dramatically under-exposed photo, result in less visible artifacts when done from raw data than when done from already rendered image files. Raw data leaves more scope for both corrections and artistic manipulations, without resulting in images with visible flaws such as posterization.

The generally-accepted standard for digital negatives in the digital cinema industry is the SMPTE DPX format.

Benefits

Nearly all digital cameras can process the image from the sensor into a JPEG file using settings for white balance, color saturation, contrast, and sharpness that are either selected automatically or entered by the photographer before taking the picture. Cameras that support raw files save these settings in the file, but defer the processing. This results in an extra step for the photographer, so raw is normally only used when additional computer processing is intended. However, raw permits much greater control than JPEG for several reasons:

* Finer control is easier for the settings when a mouse and keyboard are available to set them. For example, the white point can be set to any value, not just discrete values like "daylight" or "incandescent".
* The settings can be previewed and tweaked to obtain the best quality image or desired effect. (With in-camera processing, the values must be set before the exposure). This is especially pertinent to the white balance setting since color casts can be difficult to correct after the conversion to RGB is done.
* Camera raw files have 12 or 14 bits of intensity information, not the gamma-compressed 8 bits typically stored in processed TIFF and JPEG files; since the data are not yet rendered and clipped to a color space gamut, more precision may be available in highlights, shadows, and saturated colors.
* The working color space can be set to whatever is desired.
* Different demosaicing algorithms can be used, not just the one coded into the camera.

Drawbacks

Camera raw files are typically 2–6 times larger than JPEG files.[citation needed] Some raw formats do not use compression, some implement lossless data compression to reduce the size of the files without affecting image quality and others use lossy data compression where quantization and filtering is performed on the image data. While use of raw formats avoids the compression artifacts inherent in JPEG, fewer images can fit on a given memory card. It also takes longer for the camera to write raw images to the card, so fewer pictures can be taken in quick succession (affecting the ability to take, for example, a sports sequence).

There is still no widely accepted standard raw format. Adobe's Digital Negative (DNG) format has been put forward as a standard, but has not been adopted by many major camera companies; Pentax's K10D is one recent DSLR camera that can shoot directly into DNG format. Numerous different raw formats are currently in use and new raw formats keep appearing, while others are abandoned.[3]

Because of the lack of a standard raw format, more specialized software may be required to open raw files than for standardized formats like JPEG or TIFF. Software developers are also having to frequently update their products to support the raw formats of the latest cameras.

The time taken in the image workflow is an important factor when choosing between raw and ready-to-use image formats.

Software support

Cameras that support raw files typically come with proprietary software for conversion of their raw format to TIFF or JPEG. Other conversion programs and plugins are available from vendors that have either licensed the technology from the camera manufacturer or reverse-engineered the particular raw format. A portable open source program, dcraw, supports most raw formats and can be made to run on operating systems not supported by most commercial software (such as Unix).

Raw file formats are proprietary, and differ greatly from one manufacturer to another, and sometimes between cameras made by one manufacturer. In 2004 Adobe Systems published the Digital Negative Specification (DNG), which is intended to be a unified raw format. Adobe Photoshop CS2 and CS3 contain extensive support of RAW as does Adobe Photoshop Lightroom. As of 2006, several camera manufacturers have started to announce support for DNG in newer camera models, including Leica, Samsung, Ricoh, Pentax (native camera support) and Hasselblad (export). The Leica Digital-Modul-R (DMR) was first to use DNG as its native format.

Microsoft's Digital Image 2006 was able to recognize and organize raw image formats such as .crw, .cr2, and .nef, which are file formats produced by Canon and Nikon,[citation needed] but that product was discontinued in 2007.[4] For Windows XP, there is a free download available that integrates viewing and printing into other included photo tools, but it is not supported by Microsoft.[5] Also, Windows Photo Gallery and Windows Live Photo Gallery can view any raw image format if the necessary WIC codecs are installed. Camera manufacturers Canon, Nikon, Sony, Olympus and Pentax have released WIC codecs. [6] A commercial DNG codec is also available from Ardfry Imaging. [7] These applications however only open raw images when double-clicked. They do not automatically associate with the raw file extensions.

In 2005, Apple Computer introduced several products which offered raw file support. In January, Apple released iPhoto 5, which offered basic support for viewing and editing raw files. In April, Apple introduced a new version of its operating system, Mac OS X v10.4, which added raw support directly to the operating system, as part of the ImageIO framework, which adds raw support automatically to the majority of Mac OS X applications both from Apple (such as Preview, Mac OS X's PDF and image viewing application and Aperture, a photo post-production software package for professionals) as well as all third party applications which make use of the ImageIO frameworks. Semi-regular updates to OS X generally include updated support for new RAW file formats introduced in the intervening months by camera makers.

There are many other "raw workflow applications" designed to provide efficient processing and post-processing of raw images, including Helicon Filter, Phase One's Capture One and Bibble Labs' Bibble Pro. Like Apple Aperture, Adobe Photoshop, Adobe Photoshop Lightroom and PhotoLine, these programs provide sophisticated controls for processing the information stored in the Raw file and converting raw files to JPEG or TIFF. Picasa, a free image editing and cataloguing program from Google, can read and display many raw formats, but like iPhoto, Picasa provides only limited tools for processing the data in a raw file.

UFRaw is free software based on dcraw. It can be used as a GIMP plugin and is available for most operating systems.

RawShooter Essentials 2005/6 was free software developed by Pixmantec. In 2006 Adobe Systems Inc acquired the assets of Pixmantec ApS. RawShooter Essentials is no longer being updated (The last update added support for the Canon 5D and the Nikon D200). It could still be downloaded as a free product until Adobe's Photoshop Lightroom 1.0 was released in March 2007. The software was fully featured, including wide support for various raw formats, file priority sorting and batch processing. Light Crafts' LightZone photo editing software provides the ability to edit RAW natively. Most tools are "raw converters," but LightZone allows a user to edit RAW just as if it were TIFF or JPEG.

Processing

There is no single standard algorithm for converting data from a Bayer filter or Foveon sensor into RGB format; a number of different algorithms have been proposed, and some have been patented in the USA. Different programs may give slightly different results, better or worse subjectively, for any particular image.

Although the term "raw" describes files in the classical sense of "raw data" vs. "cooked data", raw files typically are slightly processed in the camera. In general, this processing is limited to algorithms that require direct access to the camera's hardware. This includes "long exposure noise reduction" (aka “dark frame subtraction”) and the mapping out of "hot" (too bright) or "dead" (too dim) pixels. Also information about standard processing parameters are stored in the file (so a Raw converter can generate the same JPEG file as the camera would create).

Some newer Raw formats also allow nonlinear quantization. This better allows to compress the raw data without visible degradation of the image by removing invisible and irrelevant information from the image. Although noise is discarded this has nothing to do with (visible) noise reduction.

Technical Stuff - Shutters Speeds and Apertures

What do the numbers mean?

If you look at the exposure display in your viewfinder you will see two numbers. On a normal sunny day you might see something like '125 16' or '500 5.6'. The first number is the 'shutter speed' and is simply the time that the shutter will be open for, expressed as a fraction of a second. So 125 means that the shutter will be open for 1/125th of a second, and 500 means that it will be open for 1/500th of a second.

The second number, sometimes referred to as the f-stop, tells you the size of the hole (aperture) in the lens. This number is also a fraction. The number represents the focal length of the lens divided by the diameter of the aperture. So an aperture that is 10mm in diameter in an 80mm lens will have an f number of f/8 and the setting f/16 on the same lens will be 5mm across.

From this you can see that if you change the lens to one of, say, 160mm focal length then the size of the f8 aperture will be 20mm. However, because the diaphragm is now twice the distance from the film the same amount of light will reach the film. This is a bit complex but if you have a mathematical bent and you draw it all on paper you will see why . If not, just take my word for it. Now you can see that a larger 'f' number, say f/16, is actually a smaller hole and lets in less light than f/8.

	Large aperture = small f number
	Small aperture = larger f number

To make matters even more complicated, modern lenses, sophisticated beasts that they are, are not always physically the same as their focal length. So the good old f-stop acts as a nominal indicator of how much light will reach the film, rather than an accurate measurement of aperture size. This amount of light is independent of the focal length of the lens.

What to look for when buying a tripod.

Don't buy a tiddly little thing just because it will fit into your gadget bag. Most of them are worse than useless. The trick is to get the right balance between weight and strength. It's no good if it's so heavy that you never want to take it anywhere and it's no good if it won't support the camera properly. The manufacturers seem to delight in over estimating what their tripods will support. Buy one that's man enough for the job. Then go to the gym and build up your muscles.

Which brand?

This, of course, is the big question that you really want an answer to and you know that nobody is going to give you one. If you ask anyone who already has a camera most will support the brand of the camera they have unless they have had some trouble with it, even then people are very forgiving. I think the reason for this is that people think that, if they have made the wrong choice it is because they have somehow failed, and they are not going to admit their failure. Back in the 1980s I had a camera shop in England and at the time a lot of people, who already owned an SLR, were buying compact cameras 'for the wife'. They would ask me which brand was the best and, if I didn't already know, I would discreetly try to find out which brand of SLR they owned, then I would recommend the same brand of compact camera. Trying to sell them another brand was like telling them they had made a wrong choice when buying their old camera and was likely to lose me a sale. So I'd better have a really good reason for not recommending the Canon, Olympus, Nikon, Pentax or whatever and I didn't have one. All of the well known brands produce similar cameras at similar prices and, by and large, you get what you pay for.

I will stick my neck out a little bit here and say that in my humble opinion the manufacturers who make the best film cameras the Japanese Nikon, Canon, Olympus, Pentax, Minolta and the German Contax and Leica seem to make the best digital cameras. I would not be too happy to put my trust in brands whose traditional expertise is in other fields when there are such good cameras available from the traditional

How Many Pixels?

Until recently the quality of digital cameras was measured by how many pixels they boasted. Now we have cameras that can produce tens of millions and it has ceased to be the only test of quality. In the real world the number of pixels you need depends on how big you want to print your pictures. If you mainly want postcard size or A5 then I would consider 4 million pixels to be perfectly adequate. Even at A4 size I would be hard pushed to tell the difference between my 4 million pixel camera and my 6.5 million pixel camera. Don't forget though that your cropping in the camera may not always be perfect so you may be enlarging only a portion of the image and so only using a portion of the available pixels.

Although an adequate number of pixels is important, the quality of your picture will be greatly affected by the quality of the lens. When Canon recently updated the EOS 300D (digital rebel) with 6.5 million pixels to the EOS 350D with 8 million pixels, the general consensus amongst reviewers seemed to be that the money you needed to spend on an upgrade would be better spent on a better quality lens. So the answer to the pixel question is that we seem to have now reached a point where enough is enough.

There is also a school of thought that we have reached the limit of the number of photo sensors that we can fit on a chip and that a greater number will cause the indivdual cells to be too small compared to the space in between them. Usually though, when someone says something like that, the following week the boffins announce a breakthrough which makes it all nonsense. You may have seen adverts for cameras, costing many thousands, that have 16 or 20 million pixels. These have sensors that are twice the size of those in the consumer cameras, hence the price. To me, the resolution of a 6 or 8 million pixel camera with a decent lens seems good enough for most purposes and on a par with the quality I used to get from a 35mm film camera.

In the past I have spent a lot of time and money in the pursuit of ultimate quality, I have owned a 5x4inch plate camera, a Hassleblad and two Mamiya medium format cameras, every major brand of 35mm camera and in the end, I would be hard pushed to tell you which photo on the wall was taken with which camera. A fellow photographer once observed that photographers tend to smell pictures rather than look at them, by which he meant that they were more interested in the graininess and sharpness of the image than the actual image itself.