1.4x and 500m F4
The majority of my images using this combination with the EOS MkIII, are soft see my Martial Eagle postings. I have tried calibrating but it does not seem to improve much if anything, the problems are most noticable when the subject is a very long way awy. Does anybody have any ideas?
Have you tried using a target and checking? Would try with the lens only first then go to the converter Do the test under ideal conditions using a test target. Could substitute for a newspaper, book etc
btw on your soft images are they consistently soft or are you having some soft/sharp? Are your images consistently sharp with other lenses?
With the convertor they are almost all soft, without and with other lenses they are prtty sharp.
I will have another go at calibration, would it be best to set up the target at a long distance?
Warning: long post. Perhaps more than you wanted to know! ;)Originally Posted by Ken Watkins
There are several things that could produce what you are reporting, and it is difficult to say which are involved without further exploration. As Alfred mentions, careful testing is an absolute must. And it would be helpful to know if your lens has IS or VR and what kind of tripod and support you use. Some of the possibilities are discussed below. Good luck in tracking down the underlying source of what you are seeing.
1. 1.4X teleconverter is defective
2. Calibration is OK with lens but off with 1.4X teleconverter
3. Support and/or technique is adequate for bare lens but not for lens + 1.4X
4. Lens + 1.4X is used at longer distances, thus magnifying residual vibration
5. Expectations for lens + 1.4X are too high
1. 1.4X teleconverter is defective. No way to know for sure without trying another one, in which case the current one must be repaired or replaced. But first, make sure your test procedures are sound enough to actually differentiate a bad converter from other possible explanations, see below.
2. Calibration is off with 1.4X. Checking calibration again is a good idea. If the problem is calibration, then something in the field of view should be in focus even if the intended subject is not. Here are a couple of links to autofocus test targets and write-ups on how to use them. Theoretically, calibration is best done at the intended distance from the subject. This is completely impractical so pick something representative between MFD and infinity.
http://www.focustestchart.com/chart.html
http://www.hkdotnet.com/FrancisPhoto...Test/index.htm
3. Support and/or technique. The longer the lens focal length, the more vibration is magnified -- even with IS/VR. IS/VR does not eliminate vibration, it simply reduces it. It is possible (though admittedly unlikely) that your support and technique are adequate for the bare lens but marginal when the 1.4X is added. The only way to know for sure is to use a test target and to carefully control the test. I use the the USAF 1951 test target sold by Edmund Optics (see link below) but a newspaper or dollar bill are time-honored substitutes. The target should be as exactly parallel to the plane of the sensor as possible and you should use mirror lockup and lock down the controls on your tripod head. Release the shutter either via timer delay or remote release to eliminate the element of technique. If you are really obsessive about testing, plopping a bean bag over the top of the 500 will further stabilize the lens.
http://www.edmundoptics.com/onlineca...=1665&search=1
4. Effect of distance on sharpness. It seems obvious, but many people forget that the farther away the subject, the more any vibration blurs the image. This is true because vibration of a long lens barrel has a strong angular component. For close subjects that matters little. But, any residual camera/lens angular motion is magnified by long distance into a large linear displacement at the subject, especially at slow shutter speeds -- which must result in a loss of sharpness. This makes it surprisingly difficult to make sharp images at great distances, telephoto lenses and teleconverters notwithstanding. There was a long running thread on another site about loss of sharpness for distant subjects that might be of interest. (Are we allowed to mention other sites here!!? :D)
http://naturescapes.net/phpBB3/viewt...p?f=1&t=128729
The bottom line conclusion by the original poster after extensive testing: "For my mind at least, this puts to rest anything to do with technique, tripod, mounts, etc. etc. It is just more of a distance physics thing."
5. High expectations. One often hears that primes used with 1.4X teleconverters produce images that are just as sharp as those with the bare lens. This is, of course, not true, as the briefest of glances at the MTF curves in Canon's Lens Work book or any other source of MTF data will immediately verify. Or controlled and careful testing against a test target with lots of fine detail. The myth persists because the difference isn't that great and only shows up on large prints. The difference is much more pronounced with a 2X teleconverter -- but even so plenty of people get very usable images with the 2X. Some even do well with stacked teleconverters (though I'm not one of them; inadequate technique. :().
Good luck! :)
I use the 500 plus 1.4x Canon TC very often and don't have any problems. If the bare lens is fine, you might consider experimenting with the microadjustment feature in the 1D3. Long distances itself could be the problem if there is heat distortion or do you have the problems on cold days with low humidity, too? Do you photograph out of your car? The engine block produces a lot of heat flare.
Hi Ken,
Without more info on your technique its hard to give advice. I agree with the previous advice given though. I would use a tripod and use enough ISO to give you 1/1600 or 1/2000 and shoot a 45 degree test target to check for focus accuracy. The MKIII focus cal works well.
With proper technique results with a 500mm bare and with a 1.4 should be almost indistinguishable. If not try another 1.4X.
Robert
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