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Newb - 2 questions Focus and No image



Hello,  Astrophotography newbie here. Purchased EOS and have used twice now with my Canon 70D and kit lenses. 

Question 1 : Focus,  I used my 24-55mm to get a wide field Milky Way and focus was great!  Next outing I used the 55-250mm lens on M81 / M82 (still pretty widefeild) and the focus was pretty off. I used the same procedure for focus both times. (Also watched a YouTube of a 2 hourish live stream where you talked about it. It I think I'm still not understanding something. ). 


Question 2:  I have not been able to reproduce this reliablely. Now and then I get into a state where BYE will control the camera and the shutter fires , but in one case the file was not written to the hard drive and in the other the preview did not display but the image was recorded to the HD. So I'm not sure what happened to cause that. Stopping BYE turning off the camera and then turning it all back on did the trick. 


Thanks in advance !!!

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6 answers to this question

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Question 1: You didn't really ask a question or say how you focused! At shorter focal lengths the camera is more forgiving for being out of focus. At the longer focal length you need to use BYE's FWHM or HFD focus metric to get good focus. If you have a bright star available then you may be able to use LiveView for faster focusing. If not you will have to take short "snap" exposures for focusing.

Question 2: Again not really a question there. Issues such as what you are experiencing are likely due to either a cabling issue or saturation of the PC's USB hub. Try to re-create with a short cable and/or plug just the camera into a USB port on the other side of the PC. This will often use a different internal hub.

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I used the same procedure in both instances, find a bright star and turn the focus ring back and forth until I get the lowest number possible on the frame and focus module.   Is there a different procedure to focus on deep sky objects like specific galaxy's?  Vs this process where my "foreground stars" were in focus but the galaxy behind was not?

Is there more detailed documentation on the different focus functions?  Maybe if I read about them I'll understand it better.  


I do use a 10' USB extention cable for USB 3.0 and I purchased the one with gold contacts fearing this might end up a factor. However I am plugging that into the "normal" 4-6' USB cable that came with the camera (total about 16') I will try replacing it with a higher quality cable for that last run into the camera body. 

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All night sky objects from the moon to distant galaxies are in focus at the same time since from the camera's perspective they are all at an infinite distance. So you focus on bright stars and you will be in focus for galaxies, as well. Basically, it is not possible for the foreground stars to be in focus, but a galaxy to be out of focus. Have you ever seen such a picture? Also, the BYE focus metrics will not work on a galaxy or nebula.

When manually focusing my stock lenses, the lens is in manual focus mode. With the camera pointed upward the lens focus tends to shift due to gravity. I use blue painter's tape or gaffer's tape to keep focus from shifting. I would recommend taping the focus ring in place after you have achieved critical focus on a bright star..

According to the USB specification, the max distance for USB 2.0 cabling is 5 meters or 16.5 ft. USB 3.0 cable specs are even shorter. If you are able to test successfully using only the cable that came with the camera then I would recommend that you replace your long USB 3.0 cable with good quality USB 2.0 Active Extension cable.

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Unless you are shooting with a Very Fast Lens (eg: Canon 200mm f/2.8 L), you are not going to capture enough signal in less than 15-30sec Exposure in order to make ANY Galaxy or Nebula (OK, the brightest bits of M42 or core of M31) visible.

So, Focus on a Moderately Bright Star using one of the BYE Focus Aids, then Slew to your Target Galaxy and start taking Longer Exposures.

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