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20 Aug 2017
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TOPIC: HFR DSLR & FWHM

HFR DSLR & FWHM 6 days 21 hours ago #19390

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Hi

While playing with my focuser and my Canon 700D I wonder what the "HFR" value actually means?
Is it related somehow with the "FWHM" that I can analyse on stars in my postprocessing
software?

What HFR values would you expect with your DSLR similar to my Canon700D?
My best HFR on my 150/600 Newton with the Canon was ~3.6.

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--= human, without Windows™ =--
pls excuse my bad english! :)
Last Edit: by pauledd.

HFR DSLR & FWHM 6 days 21 hours ago #19391

Half-Flux-Radius. It is generally between than FWHM and does not fluctuate as much due to seeing..etc. It is pixel based as well. Google would help as well :D

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Jasem Mutlaq
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HFR DSLR & FWHM 6 days 20 hours ago #19392

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Thanks, I found a good short explanation:
www.diffractionlimited.com/help/maximdl/Half-Flux.htm

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HFR DSLR & FWHM 6 days 16 hours ago #19395

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pauledd wrote:
What HFR values would you expect with your DSLR similar to my Canon700D?


It depends on the star you are trying to focus and focus accuracy (motor / manual). In autofocus my 550D usually has values around 1.2 - 1.5. Sometimes more than that. Usually I make a motorized (accufocus) manual focus and can achieve 0.8 to 1.0. But only on very steady nights.

Try to manually select a not too bright star, medim to small sized, and then use autofocus or manual focus. Also do not push the ISO as it tends to "burn" out the star. ISO800/ISO1600 should do it but it also depends on model/make of the camera.

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(PT) SC@ROS Observatory
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Last Edit: by nmac.

HFR DSLR & FWHM 6 days 14 hours ago #19400

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1.2 - 1.5 ... wow okay. I usually use ISO400 and 0.5seconds to focus and as you wrote medium to small stars. But I live in a slight valley in a mid-big city with a river in front of my telescope, so I would not expect a much lower HFR here dye to atmospheric conditions but I am still practizing all the stuff :)

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Last Edit: by pauledd.

HFR DSLR & FWHM 6 days 8 hours ago #19420

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I am just making a session right now and I got 1.4 on focus. That's the best for tonight, the sky is not very steady. Also I live in a suburban area so I have some light pollution adding to that.

Well having a river near can be kind of problematic because of ascending water heat currents. They tend to mess up images.


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(PT) SC@ROS Observatory
RPi3 / Explore Scientific ES80480 / Canon 550D / ESFF 2" / ASI120MM / Arduino Moonlite DC Clone- HEQ5 Pro
RPi2 / Orion 120ST / Atik 420m / WOIII / SSAG - Arduino Moonlite DC Clone - LXD75
www.flickr.com/photos/139335144@N03/
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HFR DSLR & FWHM 3 days 20 hours ago #19509

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My HFR did also improve the last session to 2.3, but I had to focus manually. I think I need to tweak the step size in ekos and/or if possible, smaller step size in the astroberry focuser code, my stepper currently run at 1/2 step size...

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HFR DSLR & FWHM 3 days 17 hours ago #19535

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Yes I had to do that on mine as I had too much steps and I could not find the center spot.
Try to do it cutting the current steps in half and so on.

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(PT) SC@ROS Observatory
RPi3 / Explore Scientific ES80480 / Canon 550D / ESFF 2" / ASI120MM / Arduino Moonlite DC Clone- HEQ5 Pro
RPi2 / Orion 120ST / Atik 420m / WOIII / SSAG - Arduino Moonlite DC Clone - LXD75
www.flickr.com/photos/139335144@N03/
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