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Old Feb 4, 2005, 2:18 AM   #1
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Sorry for this editing because an unknown problem caused an incomplete upload.

This is the third installment of my "SLR Lens on DC" series. The first discusses a possible way of converting a Nikon SLR lens for the use of a Coolpix 4500 with the help of a BR-3 reversing ring, a LE-Adapter and a William Optics 25mm eyepiece. This post is available here: http://forums.dpreview.com/forums/re...ssage=12038191 The second installment extends what I learned from the first to macro photography using the Kenko 3-tube set extension tubes and a Nikon AFD 60mm Micro Nikkor. Magnification (or reproduction ratio) values obtained were 0.4X (4500) to 2.7X (with Kenko tubes of 12mm, 20mm and 36mm). This installment is available here:http://forums.dpreview.com/forums/read.asp?forum=1007&message=12073488 This third installment is the telephoto part.

Equipment used included a Nikon AFD 80-200mm F2.8 and the eyepiece setup used in the previous two installments:

With the eyepiece mounted, it is a "long" lens:

Since the longest focal length of the 80-200mm is 200mm and since the eyepiece has a focal length of 25mm, the combo becomes an afocal monoscope of power 200/25 = 8X. If you don't like this setup, you might want to use the 180mm F2.8 because the 180mm is smaller and lighter than the 80-200 and because in most cases we use the 200mm end:

The following is the test scene taken with a Coolpix 4500. The 135mm equivalent focal length is about 150mm. The distance from the shooting location to the subject is perhaps slightly more than a mile.

To test this 8X combo, which has a 135mm equivalent focal length of 1200mm, a series of photos were taken with the 80-200mm set to use f/2.8 and f/8.0. The reason is simple. I wanted to see how good the image quality is if the aperture is stopped down to the nearly optimal aperture of the 80-200. In the following, the first image was taken with f/2.8 and the second with f/8.0:

It is obvious that the f/8.0 version has significant light fall-off; however, it is sharper than the f/2.8 version. This is demonstrated by the following two images are 100% the crops from the f/2.8 (top) and the f/8.0 (bottom) version.

The following are 100% crops of the right portion of each image:

As you can see chromatic aberrations in terms of purple and green fringes are there; but, the f/8.0 looks better. In general, the f/8.0 version is sharper with higher contrast and less chromatic aberration. So, in a sunny day, whenever it is possible, stopped down a little does help make the resulting image better. The drawbacks are (1) light fall-off is significant, and (2) shutter speed on the Coolpix 4500 is slower.

The CrystalVue 8X monoscope is popular among 4500/995/990/950 users. It would be interesting if we can see the differences between a $150+ cheap 8X monoscope and a $1,000+ 8X combo. The following is the result taken by a CrystalVue SharpShooter 8X and the same aperture on a 4500:

Apparently, the CrystalVue's image is of lower sharpness and lower contrast than the 80-200 at f/2.8. The following are the 100% crops of the center and right areas of the CrystalVue 8X image:

It is obvious that the 80-200mm has a much better image definition and higher contrast than the CrystalVue 8x. The CrystalVue 8X has low contrast and higher chromatic aberration. However, it does resolve a the bars and window frames on the building slightly better than those of the 80-200mm.

In summary, if you have a good 200mm lens (e.g., the MF Nikkor 200mm F4 (AI or AIS) and MF Micro Nikkor 200mm F4, 80-200 F2.8, etc) and have a Coolpix 4500 in hand, you can easily convert your SLR lens to a 8X monoscope and give you a 1200mm focal length. The quality is better than the commonly used CrystalVue 8X and hence better than the Kenko 8X. Unfortunately, since the G lenses (e.g., 70-200mm F2.8 VR G) have no aperture ring, you can only shoot wide open. Of course, if you have a 300mm lens, you will have a 12X monoscope, providing a combo 1800mm; however, the image quality may not be satisfactory.

Discussions and comparisons of the CrystalVue 8x can be found here:http://www.cs.mtu.edu/~shene/DigiCam...-8x/6x-8x.html and here: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/Odd-Stuff/14x-8x-8x-6x/14x-8x-8x-6x.html



Nikon Coolpix 950/990/995/2500/4500/5700 and Panasonic FZ-10 User Guides

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