

LinkBack  Thread Tools  Search this Thread 
Mar 14, 2005, 2:14 AM  #1 
Senior Member
Join Date: Oct 2002
Posts: 579

This is my third post about the use of Nikon lenses on A95. Here is a list of previous posts:
(1) Adapter Tubes: http://www.stevesforums.com/forums/view_topic.php?id=50412&forum_id=15 (2) Fisheye lenses:http://www.stevesforums.com/forums/view_topic.php?id=50422&forum_id=15 This one is about closeup lenses, one of the most popular equipment among shooters. Since there are so many closeup lenses available, I will not restrict to Nikon products in this installment. CLOSEUP LENSES Most closeup lenses are marked with a +d number in diopter unit, the power of the lens. The diopter (or power) of a lens is defined as 1000/f, where f is the focal length of the lens measured in mm. Thus, a lens of 50mm has a diopter of +20 = 1000/50, and a +4 diopter closeup lens has a focal length of 250mm = 1000/4. A closeup lens with larger diopter value means higher magnification. Not all lens makers mark their closeup lenses with diopter values. For example, Canon has 250D and 500D, where 250 and 500 are focal lengths of the 250D and 500D, respectively. Thus, the 250D and 500D closeup lenses have diopters +4 = 1000/250 and +2 = 1000/500, respectively. Nikon do not even print any hit on their closeup lenses. For example, the better Nikon closeup lenses are #3T, #4T, #5T and #6T, where #3T and #5T have diopter +1.5 and #4T and #6T have diopter +2.9. Stacking two closeup lenses is possible; however, to yield a better result, the stronger one (i.e., the one with higher diopter) should be the one on the camera lens. Moreover, stacking three or more closeup lenses are in general not advised because of lower image quality and lower contrast. The combined diopter of the two stacked lenses is "approximately" the sum of the individual diopter values. Thus, stacking +1 and +2 closeup lenses yields a closeup lens of diopter +3. Note that this is true only if the closeup lenses are very close to each other. Normally, cheap closeup lenses are of single element design (i.e., one glass element per lens), and are cheaper. One can usually buy single element closeup lenses in a set (e.g., +1, +2 and +4). Single element closeup lenses may not correct all optical aberrations (e.g., spherical and chromatic aberrations), and usually have lower image quality. This is especially true when we stack two closeup lenses together. Doublets (i.e., twoelement design) are usually better in terms of resolution, aberration correction and contrast. Thus, if possible, use doublets. LENSES USED IN THIS POST The following image shows some commonly mentioned closeup lenses. The front row, right to left, shows a Tiffen 3lens set of +4, +2 and +1 (37mm). The back row, right to left, has a Raynox MSN500 Super Micro (37mm and 28mm) (http://www.raynox.co.jp/comparison/digital/comp_e995.htm#msn500), Nikon #3T +1.5, Nikon #4T +2.9, and a Hoya +10 macro closeup lenses (http://www.thkphoto.com/products/hoya/oef13.html) The Nikon #3T and #4T are only available in 52mm thread, and #5T and #6T in 62mm thread. MAGNIFICATION, COVERAGE AND WORKING DISTANCE The magnification of a lens is defined as the ratio of the image length and subject length. Details can be found here: http://www.cs.mtu.edu/~shene/DigiCam/UserGuide/CloseUp/BASICS/Magnification.html To obtain maximum magnification, the camera lens is normally zoomed all the way in to its longest focal length. In addition to magnification, many vendors also use "coverage" as a measure of closeup capability. For example, the A95 can take images of an area of 56mm x 42mm and 87mm x 65mm at the widest and longest focal length, respectively. In fact, this "coverage" data and magnification is interchangeable. See the above mentioned magnification page. Some vendors and writers prefer to use "working distance" as a key factor of macro photography. Working distance is the distance between the lens front element and the subject. The use of working distance is somewhat misleading because, while shorter working distance can cover a smaller area, a lens with longer working distance can still provide the same coverage. Moreover, very short working distance could make composition and lighting very difficult, and in many cases one simply cannot get close to the subject. Therefore, in what follows, magnification will be used to gauge the capability of various closeup lenses. If you have a closeup lens with a similar diopter value, you can either do the same to determine its magnification or use the table at the end as an approximation. FINDING THE FACTS Since magnification tells us how powerful a lens is, it would be very useful if we know the magnification before shooting. In this way, we can determine the closeup lenses to be used. An easy way of determining the magnification of a closeup lens is taking an image of a ruler. Then, we can count the number of ticks recorded, which gives us the recorded subject length. For example, if a lens records 10mm of the ruler along the vertical edge, then the subject length is 10mm. If we also know the sensor size in the vertical direction, say V mm, then the 10mm subject has an image length of V mm. Recall that magnification is (image length)/(subject length). In this example, the magnification is V/10. The A95 uses a 1/1.8" sensor with a dimension of 7.176mm x 5.319mm (http://www.dpreview.com/news/0210/02100402sensorsizes.asp) If the ruler is placed vertically and each tick is 1mm, the magnification is 5.319/(# of ticks). The following has the test images in two groups. The first group has the Tiffen +1, +2 and +4 closeup lenses in various combinations so that we can obtain +1, +2, +3, +4, +5, +6 and +7 diopters. The other group shows the results of nonTiffen set. The following is the images of the first group. Note that all results are approximations. A95 at wide angle : recorded length = 41.5mm, magnification = 0.13 Tiffen +1: recorded length = 72mm, magnification = 0.07 Tiffen +2: recorded length = 60mm, magnification = 0.09 Tiffen +3 (1+2): recorded length = 47mm, magnification = 0.11 Tiffen +4: recorded length = 42.5mm, magnification = 0.13 Tiffen +5 (1+4): recorded length = 35.5mm, magnification = 0.15 Tiffen +6 (2+4): recorded length = 31.5mm, magnification = 0.17 Tiffen +7 (1+2+4): recorded length = 28.5mm, magnification = 0.19 From these results, we can easily see that the A95 at the wide angle end is approximately equal to adding a +4 closeup to the telephoto end. The best result here is the +7 case, which has a magnification of 0.19X of the real subject (i.e., a 1cm subject appears on the image as 0.19cm). Moreover, the magnification increases as the diopter value increases. Compared with other cameras that are better known for their macro capability (e.g., Nikon Coolpix 4500 at 0.43X), the A95 is kind of weak in the closeup department. The following has the results from the second group. Nikon #3T (+1.5): recorded length = 68.5mm, magnification = 0.08 Nikon #4T (+2.9): recorded length = 50mm, magnification = 0.11 Nikon #3T and #4T (+4.4 = 1.5+2.9): recorded length = 40mm, magnification = 0.13 Hoya +10: recorded length = 22mm, magnification = 0.24 Raynox MSN500: recorded length = 7mm, magnification = 0.76 Obviously, the Raynox MSN500 has a very high diopter that can produce a 0.76X of life size magnification. The Hoya +10 is way behind the Raynox MSN500. Therefore, if you wish to do very high magnification (e.g., near life size) closeup, this Raynox MSN500 may be a very good option. All the other +1 to +4 closeup lenses are for lower magnification shooting. However, do keep in mind that high magnification closeup lenses are usually sharp in the center and soft near the corner. This will be very visible when shooting flat and high contrast subjects. Moreover, chromatic aberration in the form of purple and greenish fringes can appear easily in high diopter closeup lenses. The following table summarizes our results, including the working distances. CK http://www.cs.mtu.edu/~shene/DigiCam Nikon Coolpix 950/990/995/2500/4500/5700 and Panasonic FZ10 User Guides 
Sponsored Links 

Thread Tools  Search this Thread 

