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Question: Is there a difference between DG PRO Kenko 1.4 converter and the DGX PRO? I am seeing different prices between them, with the DG costing more.
Document: This is new DGX model of the popular Kenko 1.4x Pro series teleconverter. The main difference between DG and DGX is DG doesn't correct aperture of the lens and DGX does. For example, Tamron 70-200mm has wide open f2.8 aperture that reduces to f4.0 when used with 1.4x teleconverter. DG version would still show you f2.8 and new DGX will display correct number f4.0.
Most cameras have problems focusing with lens that have less then f5.6 aperture. Any 1.4x teleconverter loose 1 stop of light. If you want to extend reach of slow lens (f5.6 and less) be prepared to loose or reduce auto-focus functionality. It doesn't depend on teleconverters - so don't blame them!I used Kenko 1.4 PRO 300 DGX on Nikon D300 with Tamron 70-200mm f2.8 lens.
I bought the new DGX version (not the older DG), because other reviews indicated it now gives correct exif data to the camera (such as correct f-stop, focal length,etc). I found this to indeed be the case: it has worked correctly on all my lenses. (even the two zoom lenses, which combination most do not recommend) Pictures come out stellar...superb...with the Nikon 300mm f/4 AFS.
And you can find a way to afford them.If you are an amateur who is looking for a way to get CLOSER to something that it is impossible to get physically closer to- and you are not independently wealthy!- the Kenko 1.4 Pro 300 DGX is a very good option. It requires strong light to really get good results but for relatively few dollars it can help out a great deal much of the time.
I can't tell the difference in the result I received judging from the sharpness, colors, contrast, and ease of use with this Kenko on and off - and that's looking at the pictures blown up to actual size on my 25" desktop monitor. I don't see any ill effects as some of the posts here mentioned. This is impressive. With only one stop loss, I find the tele-converter to be very practical to get that slight longer reach. Its light weight but seems quite sturdy.
I've used the Nikon 1.4X, and the Kenko is its equal, at roughly half of the cost. I use it primarily on my Nikkor 300mm F/4 and 80-200mm F/2.8. This is an outstanding bargain!
I am delighted with the Kenko 1.4x Pro Teleconverter DGX. I used it a lot on a recent shoot in Hawaii and found it increased the range and alternatives with my Nikon 70-300, 18-200, 18-55 and 60 mm lenses. I could not be happier and know the Nikon TC would not have worked as well.
First of all, I'm a photo enthusiast not a pro. I use a D90 with this Kenko 1.4x Pro 300 DGX, then I mount the Nikon 80-200 f2.8 lens which I bought used. Yes immediately I checked and see that at wide-open, camera shows aperture now at f4 as expected. Went to the backyard late afternoon while it's still sunny and snapped away at flowers, trees, neighbor's cabana roof top and so on.
Keep in mind however, that even the TC1.4 from Nikon loses some sharpness on the zoom lenses that it fits on. I have not tried the Kenko on a prime lens. Note that the tests I did was from a tripod using the same settings and zoom, with and without the Kenko, and then viewing the images on an iMac.If you only need 1.4x telephoto to bring stuff closer and you are not concerned about the slight blurriness when viewing at 100%, this unit is fine.
update 2014-1-21: This teleconverter is made by Kenko International at kenkoglobal.com. You can download a PDF list ,"Kenko Teleplus DGX series Compatibility List", for compatible camera/lens combinations at  "SUPPORT" - "download" - "instruction" tab.
Answer: yes - exactly the same except, for example, the X shows XIF data as an aperture of 4.0 instead of 2.8 which is the actual lens f stop loss of a 1.4 teleconverter.   The X wasn't out when I bought mine  but I'm not sure I would have cared anyway. Take care.