Author Topic: af motor control and focus peak  (Read 3223 times)

calypsob

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af motor control and focus peak
« on: November 14, 2013, 07:52:24 AM »
AF microadjustment
Not possible to control AF outside LiveView.
I was kind of confused by this and I hope I am not asking a question that overlaps this statement.

I am not sure if anyone on here has ever tried out backyard eos before but it is kind of like eos utility only revamped for astrophotography with canon dslr's.  It has a really awesome frame and focus mode which uses a graph with a value beneath it that gets closer to one as the image becomes sharper, also the graph shows the picture of a giant peek which gets sharper as the image does.  In addition to this back yard eos allows control of the AF motor similar to how Eos utility works, there are 3 speeds, full, medium, and low.  Instead of auto focusing the image the arrows are pushed and the AF motor inside of an AF lens responds to the speed control commands.  This would be very useful for DSLR users who use an Astrotrac, polarie, or skytracker for focusing out in remote locations where a laptop is not convenient to bring along. The main purpose of this would be to assist with star focusing, it would not work with a wide lens as well as it would a telephoto.  Also one last idea which I believe to be far fetched but what the hell might as well ask, has anyone ever investigated dark frame removal from the noisy live  view screen generated during lowlight or high iso conditions?  I can do it on my computer with PHD and an orion star shoot CCD camera by covering the camera, allowing it to take 10 dark exposures, and uncovering.  The software subtracts the darkframes and the signal to noise ratio increases dramatically and the stars are much more clear, the black background is much more clear due to the removal of noise in the image.  Like I said its out there but if the camera can do it that would be great for everyone.

While I am thinking about it, another good use for full control of the af motor in a variable speed selection would be while using a teleconverter on a telephoto.  This usually prevents autofocus from working because the light is so low, however manual control of the autofocus would allow the user to decide when the image was in focus via live view to take a picture.  Left and Right arrows to control in-out focus and map Up Down to adjust between 3 speeds.
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dmilligan

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Re: af motor control and focus peak
« Reply #1 on: November 14, 2013, 02:24:33 PM »
Here's what I do to focus for astrophotography:

FPS Override to 1 or 2 fps (use 'low light' mode)
LV Display Gain +4 or so
Enter LV
Zoom in 10x on a bright star
Adjust focus manually until star size is minimized

On my AF lenses, I found that manual focus is much more acurate and easy than stepping the focus with the AF motors (which you can do BTW, http://wiki.magiclantern.fm/userguide#follow_focus). On my manual lenses and telescope, obviously I have to manual focus anyway.

I don't really see why you'd need to do dark frame subtraction on the LV, you can see well enough to focus, and I don't think dark frame subtraction would help you much in that regard, yeah the picture would look a tiny bit cleaner, but so what? It's not really going to help you focus.

calypsob

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Re: af motor control and focus peak
« Reply #2 on: November 16, 2013, 02:09:06 AM »
without a cls ccd filter in the camera it is pretty easy to see stars but with the filter it is really hard which is why I suggest the darks, cleaner star and bahtinov results that way.  I was unaware of the stepper feature though thanks for the link.
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