Welcome to lensspecs.com

Without knowing where it lead me, it all started in August 2008. Someone started a thread at the bulletin board diskusjon.no asking for which extension tubes he should use on his lens. Which extension tube(s) to use depends on several factors and the Excel-nerd in me liked the talk about magnification ratio, internal focus length, focal length and minimum focus distance. It didn't take long before I had made a spreadsheet that did whatever calculations was needed. In my spreadsheet I gathered the size of the most popular extension tubes and the users had to do some digging by themselves to figure out some of the technical values for the lens. The spreadsheet calculated the internal focus distance and the magnification ratio for all extension tubes were also available in the spreadsheet. It displayed how long extension tube you had to use to get the magical 1:1 magnification ratio as well.

Extension tubes are something which is frequently asked about and when the topic rose again in March 2015 on Pentaxianere i Norge (a group on Facebook with Norwegian users of Pentax) I decided to improve my spreadsheet. I made a list with every crop-factor, full format and medium-format format available for Pentax, 140 and something in total. I added information for magnification ratio, focal length and minimum focus distance. Using a drop-down list for selecting lenses, the spreadsheet already had all the values it needed and it did the calculations which are necessary to figure out what kind of extension tube you need to get 1:1 magnification for any lens for Pentax. Suddenly it all became a lot easier for the user.

After I had gathered all this information I started to think bigger. What if I gathered even more information about the lenses? Information such as aperture, if the camera is still in production, if the lens has an internal focus engine, what kind of focus engine it (potentially) uses, weight, physical dimensions, which image sensor(s) it fits, filter size, maximum diameter of the lens, angle of view, if it is weather proof or not, the optical construction and circular aperture - all of these are things stated for lenses and I found myself wanting them all in my spreadsheet.

For some reason I like to use Big data in Excel. Even though Big data is a broad therm for large data sets which are analysed, extracted and visualized - this would be Big data in a miniature shell. In my search for the above information I had to search on numerous sites so that if I added similar data for lenses for Canon, Sony and Nikon I would have thousands of data entries for hundreds of lenses stored in one sheet and it would simplify the search for technical data for lenses. The imagination is the limit on how all this data can be presented.

I still need to gather more technical data before (fun) "Big data" can be presented. The information presented per se is somewhat limited to the first edition of my spreadsheet. In time I will concentrate on gathering technical information about lenses for Pentax and crop size and Full Frame lenses for other brands. I have no plans of gathering information about Micro Four Thirds system (MFT) or medium format lenses for other brands than Pentax but that _may_ change in time when I have gathered all the other information.

I started this project because of a discussion about which equipment for macro photography to use and how to use it. Dealing with macro photography you normally shoot from a very close distance. You have lenses between 100mm and 200mm that you may use to take pictures of bugs from a certain distance but normally you are just centimetres or millimetres from your subject. Many photographers look upon the 1:1 as the golden rule macro photography but sometimes you need more magnification than this.

Macro lenses of different focal lengths find different uses:

The magnification ratio is the relationship between the size of the subject's projection on the imaging sensor and the subject's size in reality. Suppose that you are photographing a child, 1 meter in height. Imagine that the height of the child's projection onto the sensor is 1 cm. The magnification ratio is 1cm/100cm, or 1/100. Magnification is typically notated using a colon, so we write this as 1:100. This is pronounce "one to one hundred", which means the child is 100 times larger in real life than its image as projected on the sensor. If the subject is a 10cm long lizard, and its projection on the sensor is 2cm long, the magnification ratio is 2cm/10cm or 1:5. The lizard is five times larger in real life than its projection on the sensor. If we shoot a 1cm fly and it's projection on the sensor measures 1cm as well, the magnification is 1:1. The 1:1 ratio has an important meaning for macro enthusiasts. Technically speaking, macro photography means shooting at a magnification ratio of at least 1:1. Therefore, a true macro lens has the ability to produce a magnification ratio of 1:1, or higher. Normal lenses will not be able to focus at close distances but macro lenses can do this. A macro lens also allows photography of a focused subject in 1:1 at minimum focus distance and they often have a closer minimum focus distance than non-macro lenses.

If you have a zoom lens that also is a macro lens you may not get 1:1 in magnification ratio while using a longer focus range but it will be close to this "golden rule". Using a longer focus distance means the magnification will be somewhat lower. Macro lenses specifically designed for close-up work, with a long barrel for close focusing and optimized for high reproduction ratios, are one of the most common tools for macro photography. Most modern macro lenses can focus continuously to infinity as well and can provide excellent optical quality for normal photography.

Using macro lens is not the only tool you may use for close-up pictures. Extending the distance between the lens and the sensor (or film), by inserting either extension tubes or a continuously adjustable bellows, are other equipment options for macro photography. Bellows or tubes eliminate infinity focus and using such "extreme measures" gives a really close focus distance and higher magnification. If you want to take pictures of a bug or flower with extension tubes or bellows you have to take lots of pictures and stack them because of the narrow depth of field. The further the lens is from the film or sensor, the closer the focusing distance and the greater the magnification becomes. Tubes of various lengths can be stacked, decreasing lens-to-subject distance and increasing magnification. When used with extension tubes or bellows, a highly versatile, true macro system can be assembled.

A third option for extreme macro is placing an auxiliary lens in front of the camera's lens. These lenses add diopters to the optical power of the lens, decreasing the minimum focusing distance, and allowing the camera to get closer to the subject. Using this option the lenses are stacked to achieve the desired magnification. The lenses are attached to each other using a "reversing ring." This ring is attached to the filter thread on the front of a lens and makes it possible to attach the lens in reverse. It is possible to connect lenses with different diameter but it is preferable that the lenses have the same diameter. Excellent quality results up to 4x life-size magnification are possible. For cameras with all-electronic communications between the lens and the camera body speciality reversing rings are available which preserve these communications. The magnification ratio on this setup is calculated by dividing the focal length of the normally mounted lens by the focal length of the reversed lens (e.g., when an 18 mm lens is reverse mounted on a 300 mm lens the reproduction ratio is 300/18 = 16:1). The use of automatic focus is not advisable if the first lens is not of the internal-focusing type, as the extra weight of the reverse-mounted lens could damage the autofocus mechanism. As with extension tubes and bellows the focus length is extremely short.