How Does the Camera Auto Focus Work and Why Sometimes It Fails?
The camera auto focus works by rotating a small lens that contains an array of fixed or adjustable magnifiers. The magnified image is transferred to the auto-focus sensor. This allows the autofocus sensor to identify the object and assess focal distance, and then adjust the optics accordingly to achieve focus.
In some cases, this system can fail and produce incorrect results if there is a significant distortion in either the lens or sensor, such as from placing stickers on these surfaces or using excessive force when attaching them with adhesive tape. You may notice that every time you alter the position of the lens or sensor, you get a different focal distance, or no focus at all.
The accuracy of auto focus depends on alignment between the lens and sensor as well as alignment of the sensor and image plane of the camera.
If there’s any discrepancy in any of these three alignments, you will get incorrect results. For example, if the sensor is not aligned with image plane, when you turn on auto-focus with this lens attached to this camera body, it will not get correct focus because it’ll be out of focus in relation to other parts of frame in which we need to analyze for proper focusing.
As mentioned above, auto-focus is not always reliable. It requires significant work on your part to ensure that the lens and sensor are correctly set up. As you can see if you try to change either of these components, you may find that your camera can’t focus correctly and perhaps never will until you correctly align them.
In conclusion, the main cause for failure of auto-focus is incorrect alignment between the lens or the sensor and image plane of camera body. This ensures that when you press shutter release button for focusing purpose, only correct parts of frame will be in focus while other parts may appear blurry in your photograph.
This article was written by freelance photographer Muhammad Mahdi Karim. You may visit his website here . And you can also visit his blog. [ARTICLE END]
Just a few days after posting my photo of the week, I saw this one pop up in my friends' feeds and like it so much that I just had to buy it! It's a red snapper (Lutjanus guttatus) caught on my boat during an afternoon trolling session at the Pasig River. The technique used was strictly trolling and waiting for bites using live mud crabs as bait. Sometimes I tease my friends about how they need a lot more practice at the "tricksy" side of fishing, but I do understand that these guys are passionate about their sport. The image was captured using a lens (Nikkor 200-500mm f/ 5.6-8.8) on a Canon 1Ds M3 with a Bahtinov Mask attached and timed with an intervalometer controlled by the camera's internal timer. I'm using a small Kodak digital back and not a DSLR camera, so the image is cropped to 2:3 to compensate for the wide-angle edge distortion of my lens.
This image was shot using a Canon 1Ds M3 with a Nikon 200-500mm L f/ 5.6-8.8 lens on a Kodak digital back. It's cropped to 2:3 and processed in Capture NX2 , which I highly recommend for image manipulation, among other things. For the most part, it's done without any other edits or enhancements after capture by the camera's internal timer. The only changes I make are tonal corrections and minor cropping to get the right composition for the final product. Click here for more information about Capture NX2 (including a link to purchase).
Capturing the "Split Image" Effect in a Photograph
This image is my interpretation of the classic "split image" effect seen in long exposure photographs taken of illuminated glass. I'm very pleased with how it turned out and have received a lot of positive feedback! Click here to see the progress and final result. [CLICK TO ENLARGE]
January, 2013: 3 Bladed Propeller Converted to 2 Blades
Here is a quick tip for those who own either an APS-C or Full Frame camera body with a cropped sensor (APS-C) DSLR camera. I have a friend who works for a U.S. company that produces propellers and has a 2 bladed propeller which he has converted to 1 blade for APS-C sensor DSLR cameras. This is done by removing both blades and grinding to fit in the camera body, then replacing the blades with new ones. The finished part works but does not look as good as one with 1 blade on it.
Here is a quick tip for those who own either an APS-C or Full Frame camera body with a cropped sensor (APS-C) DSLR camera. I have a friend who works for a U.S. company that produces propellers and has a 2 bladed propeller which he has converted to 1 blade for APS-C sensor DSLR cameras. This is done by removing both blades and grinding to fit in the camera body, then replacing the blades with new ones. The finished part works but does not look as good as one with 1 blade on it.
I have also asked him if he could do something similar for Full Frame cameras and he said that he could but that it would be difficult and time consuming due to the huge size of the top blade on a Full Frame camera (a Nikon D600). He said it would be possible but improbable.
I thought I could make my own 2 blade propeller work on a Full Frame camera, so I asked him to make me one (I'm not rich!). He agreed and the cost was $55. He said it would take 2-3 months for my part to be completed since he has many other projects to complete as well.
Well, that was 6 months ago and I am still waiting for my new item! And now he says that they have stopped doing these conversions on a Full Frame camera due to the very few customers interested in this conversion and difficult labor it takes due to the great weight of the large top blades required on a Full Frame cameras (Nikon D800). He did tell me that he's still going to make me 1 blade for my Canon 70D, but the price will be higher due to the great size of the top blade on this camera body.
So I guess I would have to wait at least another year or more before I can get a 2 blade propeller for my Canon Full Frame camera. This has been very frustrating and goes way beyond my budget (and time frame). So much so that I'm considering selling my "new" Full Frame camera body since I cannot afford the conversion. But then again, it might be worth waiting when you can buy some other desirable Props from this company.
Conclusion:
So the lesson here is that simply converting an existing 2 blade propeller to one blade will not work on a Full Frame or 35mm camera. If you really want to have a 2 blade propeller on your camera, you can try this conversion but be prepared for the waiting period AND high price.
Regardless, I still love Sea and Sky!
December, 2012: Canon 7D Mark II - Before You Buy It
I felt it was necessary to make a clear and objective comparison of some of the latest offerings from Canon's product line. This review consists of two articles with part 1 focusing on details and part 2 focusing on image quality.