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|Dec 8, 2003, 11:59 AM||#1|
Join Date: Oct 2002
Minolta A1 vs. Nikon 5700 III: Macro
This post is about the general macro capability of Minolta A1 compared against the Nikon Coolpix 5700. This is actually the third installments of a series of posts comparing the A1 and the 5700. The first installment deals with general operational issues and can be found here:
The second installment is about lens converters, and can be found here
Note that no image quality issue is covered. Image quality will be discussed in future posts.
(1) Macro with the on-camera lenses.
The Minolta A1 lens has two positions for macro shooting, one at the long end (i.e., 200mm) and the other at the short end (i.e., 28mm). The lens barrel has a macro setting switch. When the lens is zoomed all the way out to 28mm and the macro switch is set, the lens cannot be zoomed until the switch is reset to the normal shooting position. I personally do not think shooting macro at 28mm would provide much benefit due to perspective exaggeration, barrel distortion and less magnification. So, this post only discusses macro shooting at the longer end. When the lens is zoomed to 200mm and the switch is set to macro, the lens can then be zoomed back a little. Note that the macro switch can only be set when the lens is zoomed to either 28mm or 200mm.
On the other hand, the 5700 has a wider range of focal length for shooting macro. More precisely, the 5700 macro range (i.e., when the macro icon, a flower symbol, turns yellow/green) is between 12.7mm and 27.3mm. Translating to 35mm format yields 50mm and 107mm. Thus, Nikon's approach, which restricts the macro focal length between normal (50mm) and 100mm, IMO, is very reasonable, because the most commonly used SLR macro/micro lenses are the 50/60mm and 90/105mm. On the other hand, most zoom lenses have their "macro" setting at the longer end. While this provides a higher magnification, optical quality may be lower because most zoom lens have better optical quality in the lower 2/3 or 3/4 focal length range. Making the macro focal length 200mm, however, does have its advantage, because the working distance (i.e., the distance between the subject and the front end of the lens) is larger, making lighting and composition easier.
(2) Close-Up Lenses and Magnification.
The question is how the macro capability of the A1 be compared with the 5700. The following six images provide you with all needed information. The first two shows the best I can get with the 5700 and A1 at their minimum working distances. Note that some discrepancies are possible; however, these variations will not affect the calculated magnification too much. As you can see, the 5700 covers a much smaller area of a one dollar bill.
I want to know how the A1 macro capability can be brought to a level similar to that of the 5700. This is the following two images. They were shot with a +1 and a +2 close-up lenses. Obviously, the image with a +1 close-up lens covers a smaller area than the A1's macro at 200mm; however, the one taken with +2 is only slightly better than that of the +1.
The next two were shot with a +4 close-up lens, and +4 and +2 close-up lenses. The +4 one is better than the +2 one, and the +2 plus +4 one is even better. However, even with +6 (+4 and +2), A1 still covers an area that is larger than that of the 5700 macro mode.
We should understand that macro capability is not about working distance (e.g, 1cm, 2cm, 4cm, etc). It is about magnification. Magnification of a lens is defined as Y/X, where X is the length of a subject and Y is the length of the subject recorded on film/sensor. Macro lenses with different focal lengths can produce the same magnification. To determine the magnification of a lens we need to measure X and Y. From the above images, we see that the 5700 recorded 29mm for the longer edge of the image frame, while the A1, A1 plus +1, A1 plus +2, A1 plus +4, and A1 plus +2 and +4 recorded 52mm, 47mm, 44mm, 35mm and 33mm, respectively. These are the X values. The 5700 and A1 use the same 2/3" sensor that has a dimension of 8.8mm x 6.6mm. Thus, its longer side is 8.8mm. The magnification of the 5700 is 8.8/29=0.30, which means the recorded image is 0.3X of the actual subject. By the same reason, the calculated magnifications of the above lenses are:
Consequently, the 5700 has a magnification 1.76 times higher than that of the A1, and, of course, the 5700 has better macro capability although the working distance of the 5700 is about 3cm that does not provide much space for lighting and the use of other accessories.
(4) Raynox MSN-500
The +1, +2 and +4 close-up lenses are the most commonly used ones. There are close-up lenses with higher magnification (e.g., Hoya has a +10 close-up lens). Moreover, Raynox also have a number of close-up lenses most of which may cause vignetting on A1. To see how well the Raynox lenses performs with a A1, I chose the one I have, a Raynox MSN-500. This is a close-up lens built for Nikon Coolpix 9xx and 4500 series cameras. Since it has a 37mm thread, it can also be used with other digital cameras with thread size 37mm. My Raynox MSN-500 comes with a 28-37mm step-up ring which will not be used in this testing. Instead, for the Nikon Coolpix 5700, I used Nextphoto's Coolfix 5700 adapter available here http://www.nextphoto.net Since the front thread of this adapter is 62mm, a 62-49 step-down ring and a 49-37 step-down ring were used (see the image below). Since the A1 has a 49mm thread, only a 49-37mm step-down ring was used.
The following shows the configuration of mounting this Raynox MSN-500 on the 5700 and A1
Note that to achieve the maximum magnification, the zoom lens should be zoomed all the way in!
The following comparison shots were not done at the same environment and had some white balance shift. Since our concern is about magnification, this white balance difference is not a major problem. The following was taken with a 5700 plus a Raynox MSN-500 at 280mm and minimum focus distance. Since the sensor size is 6.6mm x 8.8mm, the magnification of this setup is 6.6/3.5 = 1.9, which is larger than (i.e., nearly twice) life size.
The following image was taken with the A1 plus Raynox MSN-500 at 200mm and minimum focus distance. The magnification is 8.8/5.5=1.6, which is slightly smaller than that of the 5700.
From both images, it is not difficult to see that edge sharpness is not good, although the center portion is very good. The one taken by the A1 has serious vignetting due to the shorter focal length of the A1 (i.e., 200mm), and the one by the 5700 has some corner light fall-off because the 5700 focal length is longer. Therefore, combined with the above discussion, the longer focal length 5700 does have an edge. The following summarizes what we have so far:
(5) The Reverse Mounting Technique
There is another technique for high magnification close-up photography. This is done by mounting reversely a high quality SLR lens on a digicam. If the camera lens has focal length Y and the reversely mounted lens has focal length X, the magnification of the combo is Y/X. The focal lengths of the 5700 and A1 are 8.9-71.2mm and 7.2-50.8mm, respectively. If a 50mm SLR lens is mounted reversely on a 5700 (resp., A1), the maximum magnification of the combo is 71.2/50=1.4X (resp., 50.8/50=1X). Therefore, due to the longer maximum available focal length of the 5700, it has a higher magnification with the reverse-mounting technique.
To use this reverse mounting technique, the 5700 requires an adapter (preferably Nextphoto's Coolfix 5700), a high quality SLR lens (preferably a 50mm), a macro coupler, and step-rings. The image below shows a Minolta 50mm F1.4 with a 49mm thread, a 49-52mm macro coupler, a 62-52mm step-down ring and a Nextphoto Coolfix 5700 adapter.
A macro coupler is an adapter ring with two MALE threads. The 49mm end of the 49-52 macro coupler screws on to the 50mm lens, while its 52mm end screws on to the 62-52mm step-down ring. The 62mm end of the step-down ring screws on to the Coolfix 5700 adapter. Then, this setup is mounted on to the 5700. Note that before turning on the 5700, the Coolfix 5700 adapter should be extended to its fullest length. Then, turn on the camera, zoom the lens all the way in to get the maximum focal length and pull the adapter back so that the reverse mounted SLR lens and the camera lens will have a minimal gap. This is shown in the image below:
The A1 is easier to use. It only needs a 49-49mm macro coupler
as shown below:
Screw the 49-49mm macro coupler on to the SLR lens and then mount the setup to A1's lens. Make sure the lens is zoomed all the way in to 200mm. You don't need to use the macro setting on the A1. The following shows the setup:
How good is this setup? We know that the theoretical results for the 5700 and A1 are 1.4X and 1X, respectively, as mentioned earlier. We can also measure the magnification directly. The image below was taken with the 5700 with the above setup at the maximum magnification. The recorded height is 5.5mm. Since the sensor has a height of 6.6mm, the recorded magnification is 6.6/5.5 = 1.2X.
The following is an image taken with the Minolta A1 setup at the maximum magnification. It recorded a height of 7mm. Therefore, the calculated magnification is 6.6/7=0.94X.
Here is an extended summary that includes the reverse mounting technique.
Note that both images show softness near the edge and corners. The A1 has significant vignetting at the corners, while the 5700 shows visible vignetting in the corners. It is obvious that the close-up capability of the 5700 is better than that of the A1. This is mainly because the 5700 has a long focal length (and hence smaller angle of view that is blocked only slightly by the reversed SLR lens) and because the front lens element is smaller (32mm) than that of the A1 (40mm). Note that the reverse mount technique with both 5700 and A1 produced better results than those obtained with the Raynox MSN-500 because the latter has a smaller usable (i.e., sharp) area.
In summary, the 5700 has a much better macro capability than that of the A1 due to its longer focal length and a wider range of macro capable focal lengths. It is hard to bring the A1 with accessories to the level of the 5700.
(6) Some Technical Information.
Some believe that the diopter value such as +6 and +10 is the magnification of a lens. This is incorrect. Here are some notes.
(a) If a lens has focal length X, measured in mm, its power or diopter is 1000/X. Thus, a lens of 50mm has a power or diopter of 1000/50=20, written as +20. On the other hand, a lens of diopter +5 has a focal length of 1000/5=200mm.
(b) Given two lenses of diopters +a and +b, if they are very close to each other, the combo has a diopter +(a+b). Thus, stacking close-up lenses of +2 and +3 together yields a close-up lens of +5.
(c) The use of close-up lens brings the camera closer to the subject by reducing its focal length. Let the camera lens have focal length F and the added close-up lens have diopter +D. Then, the camera lens has diopter 1000/F. The combo has diopter D+1000/F, and focal length f=1000/(D+1000/F)=F/(1+DF/1000). Since DF/1000 is always greater than zero, 1+DF/1000 is always greater than 1. Therefore, the new focal length f is always less than the original focal length F. In fact, a larger diopter +D yields a smaller combined focal length f. Since a shorter focal length lens focuses nearer than a longer focal length lens, "close-up" lenses bring the camera closer to the subject.
(d) A SLR lens of 50mm (resp., 24mm) has a diopter value of 1000/50=20 (resp., 1000/24=41.7). Thus, reverse mounting a SLR lens on to a camera is equivalent to mount a high diopter close-up lens. Conversely, when a close-up lens of diopter +d is mounted, it is equivalent to say that we are mounting a lens of focal length 1000/d to a lens. The magnification is F/(1000/d), where F is the focal length of the camera lens. This magnification is M=(Fd)/1000. Take the A1 as an example. The A1 has maximum focal length of 50.8mm. If a +4 diopter is mounted, the magnification is M=(50.8*4)/1000=0.2X, which is very close to what we measured above. In this way, magnification, reverse-mounting, and diopter values are all tied together.
(e) Keep in mind that the camera lens must be zoomed all the way in to yield the maximum magnification. However, since a high ratio zoom has its poorest performance at the long end. This makes the image quality of reverse-mounting and/or high diopter close-up not as high as expected. On the other hand, if the lens is not zoomed all the way in, its angle of view may be too large to be covered by the front end of the reversed lens, and, as a result, vignetting and.or light fall-off will occur. In SLR close-up photography, one usually uses the same brand lenses that can match with each other very well. In general, it is not the case for consumer level digital cameras. The digital camera lenses are usually not designed to have reverse mounting in mind. Thus, the reverse mounting technique may not yield the desired results if the camera lens and the reversed lens do not match well. Extensive testing may be needed to find the best match.
(f) When using close-up lenses, especially those larger diopter ones, use those doublet type (i.e., lenses use two glass elements cemented together to reduce chromatic aberration). Companies like Canon and Nikon have two types of close-up lenses, one for focal lengths less than 50mm or 70mm, while the other for focal lengths larger than 70mm. The reason for such a distinction is to make better correction for telephoto type lenses that can easily produce chromatic aberration. Most digital cameras have a focal length less than 70mm, and, as a result, one does not have to buy the more expensive close-up lenses.
(g) For more details, including an example of using D100 and a 200mm plus reversed 50mm (and 24mm), can be found at Steves' Digicam forum:
Nikon Coolpix 950/990/995/2500/4500 User Guide
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