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#21 | |
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Join Date: Oct 2002
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jcr wrote:
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A few words about a problem. Some misinformation about teleconverter power initially generated on DPreview.com now has started showing up here on this board. (1) Brand A 1.7X (or 1.5X) converter is not 1.7X (or 1.5X). Don't be misled by this wrong concept. Tele and wide angle converter power is not measured as those misinformation state. The power of a teleconverter is defined, independent of the camera being used, as the ratio of the focal length of the "front" glass and the focal length of the "rear" glass. Moreover, camera lenses are calibrated at infinity rather than at close range. If brand X lens is claimed to be 1.7X, it is possible, due to rounding and manufacturing tolerance, that the actual power measured without a camera would be 1.72X or 1.67X. The same 1.7X converter used on a different camera with a different focal length CAN yield different power "measured" by images taken with that camera. In other words, a 1.7X converter on camera A could be measured as 1.5X at close distance, 1.65X at long distance and 1.7X at infinity (because this is the standard). If the same 1.7X lens is mounted on another camera with different focal length, the "measured" magnification can be 1.8X! Here are the discussions of this misinformation: http://forums.dpreview.com/forums/re...ssage=14156233and http://forums.dpreview.com/forums/re...ssage=14214535 Just skip all the calculation, which is for those who can follow, and jump to the conclusion part. Then, you will see what I said. (2) The gap between the rear glass elements and the camera lens front glass element has to be x.yz mm, or to be as close as possible. This is also a misinformation. This gap depends on so many factors, which include the optical formulas of the converter and the camera being used, and, as a result, there is no fixed value. For example, some Nikon converters used on some Canon cameras (e.g., A95 and A80) requires a larger gap (i.e., moving the lens away from the camera lens). Another good example is the Olympus WCON-07 0.7X wide angle. If it is too close to FZ-30'scamera lens, you will see a blurred spot at the center, perhaps (just perhaps) due to field curvature. In this case, the WCON-07 has to be moved away from the camera. This problem surfaced initially on Asia's BBS/forum discussion right after the FZ-30 was released, and many proposals were suggested to solve the problem. Please see this thread for more information: http://forums.dpreview.com/forums/re...ssage=15143199 Now I see more solutions available. On the other hand, some wide angle converter lenses have to be very close to the camera lens in order to avoid vignetting at the corners, the Raynox DCR-6600 being a good example. The problem comes from the image circle formed by the lens being a little smaller than the entrance pupil (i.e., the hole for the sensor to see through at maximum aperture, in this case). Some DIY solutions to this type of problem may include the removal of the 1 or 2 mm from the lens tube (or the mounting thread) or do whatever you can to bring the lens closer to the camera lens. (3) The gap would affect the image quality. This holds in the most general way; but, it is not always true in the micro way. When you hold a converter in front of you and see through from the center, you will find the center portion being sharper than the edge portion. This is completely normal due tothe rules of physics. If a lens is moved too far away, the cameras lens will pickup the peripheral area which is not sharp. However, this will take a rather large distance movement. In general, the movement of 1mm is perhaps still within the tolerance of manufacturing. So, just don't worry that 1mm gap difference. Most claims in this regard do not have clear evidence that can show image quality difference. In fact, some are purely speculation or just "claims." If you wish to try it, you may mount a converter specially made for a particular camera. Then, take an image after each 1/4 turn to see how much difference you can find. An updated version of my teleconverter comparisons is now part of my to-be-announced FZ-30 user guide here: http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/FZ-30/ There will be four to five testing scenes that cover most commonly shooting occasions. Currently, only the second scene is online and I am working on the 1st scene. Other tests will be posted in the near future. Hope this helps clear up some doubts. CK http://www.cs.mtu.edu/~shene/DigiCam Nikon Coolpix 950/990/995/2500/4500/5700, Panasonic FZ-10 and Canon A95 User Guides |
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#22 |
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Join Date: Jun 2005
Posts: 60
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shene:
Thank you for your user guides. Have you done any test on Raynox DCR-6600? I would be interested to know how does it compared to WCON-08B (sharpness, light fall-off, vignetting, etc.) on both FZ20 and FZ30. I currently have WCON-08B and like its quality but sometimes find it not wide enough. So I am debating whether I should sell it and get HD-6600 or not and would like to hear your professional opinion. I will be using it with both FZ20 and FZ30. Thanks. |
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#23 | ||
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Join Date: Feb 2005
Posts: 1,288
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jcr wrote:
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Here are the test results between the FZ10 and the FZ30 closeness counts $20.00 bill The reason the pictures are not sharp enough is because the magnification exceeds the definition of the image. These are two test shots of the DCR250 with the FZ10 w/ CRing adapter and FZ30 Both are done with the standard Raynox spring mount. From what I see my special TRing will produce a better image. I do not have the tools to mock up the results. I tried to make the shots asclose as possible. Can you see a difference? I sure can. FZ10 w/ DCR250 Aperture: f/4.0 ISO: 100 Focal Length: 72mm (432mm 35mm) Exposure Time: 0.2s (10/50) JPEG Quality: fine FZ30 w/ DCR250 Aperture: f/5.0 ISO: 100 Focal Length: 88.8mm (444mm 35mm) Exposure Time: 0.5s (10/20) JPEG Quality: fine ONE ![]() TWO ![]() ONE CROP ![]() TWO CROP ![]() |
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#24 | |
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Join Date: Feb 2005
Posts: 1,288
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skyrocketfw wrote:
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On the FZ30 the DCR6600 with a special ring or the new HD6600 -55produce the best widest images with the least amount of distortion and no vignetting.You just can not do any better on this camera. ![]() Notice the stop sign? Leica at 35mm ![]() |
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#25 | |||||||||
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Join Date: Feb 2005
Posts: 1,288
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#26 |
Senior Member
Join Date: Jun 2002
Posts: 242
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shene wrote:
(3) The gap would affect the image quality. This holds in the most general way; but, it is not always true in the micro way. When you hold a converter in front of you and see through from the center, you will find the center portion being sharper than the edge portion. This is completely normal due tothe rules of physics. If a lens is moved too far away, the cameras lens will pickup the peripheral area which is not sharp. However, this will take a rather large distance movement. In general, the movement of 1mm is perhaps still within the tolerance of manufacturing. So, just don't worry that 1mm gap difference. Most claims in this regard do not have clear evidence that can show image quality difference. In fact, some are purely speculation or just "claims." If you wish to try it, you may mount a converter specially made for a particular camera. Then, take an image after each 1/4 turn to see how much difference you can find. I see posts of how close a converter lens should be mounted from the camera's front lens. i.e. Iscloseralways better oris there an optimum gap [distance] to mount a specific lens from the FZ30: for say the TCON 17 and other popular lenses? What are the reference surfaces to measure the gap? Another question: What is the pitch of the mounting threads of the lenses so I can figure out what is the change in the gap is for each 1/4 turn? Thank you Stan |
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#27 | |
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Join Date: Jun 2005
Posts: 60
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LoveLife wrote:
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Do you have photo taken by WCON-08B as well? I would like to see how much wider DCR-6600 produced. I am deciding whether to sell WCON-08B or not. I will be using it with both FZ20 and FZ30, so which one do you think is the better choice? Thanks. |
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#28 | |
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Join Date: Jan 2005
Posts: 152
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LoveLife wrote:
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Witch one is fz10 and Fz30 ? for me the "One" is shaper |
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#29 | |
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Join Date: Jan 2005
Posts: 152
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shene wrote:
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Thanks Shene, for the good explanation and those transcriptions |
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#30 | |
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Join Date: Feb 2005
Posts: 1,288
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stnkline wrote:
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