Focussing numbers and image quality

[melvin]

Hi I managed to download onto my Toughbook laptop and have been watching and reading the various tutorials but I am really struggling with three things at the moment. Before I use bye in the field I need to better understand how it works.

1) how can I adjust the numbers ( right hand side of screen just above the x's slider) . I have tried moving the camera lens adjusting the magnification altered the ISO and shutter speed, but nothing. The reading furthest right says the best number is !!! but I cannot get them to read the same. To get the best focus I look at the picture

2) in the camera at the top of the screen when I go into 'image' the quality is Raw/JPEG but in 'frame' it is S. I have ensured the setting on the actual camera is raw/jpeg and also within bye, what do I need to do to change one or the other.

3) I take a pic and it looks nothing like live view. How can I ensure the two are the same

I hope that makes sense

[astroman133]

Melvin,

 

I am assuming that you have your camera connected to your telescope at prime focus and you are pointed in the sky.

 

Answer to question #1

 

Did you read the User Manual regarding how to focus?  Read the section entitled "Zoom Box Center" under "Frame & Focus". You need to get a bright star (like Vega, Capella, or Arcturus, etc.) in the field of view and it needs to be fairly well focused to start. How you do that depends on your equipment.  You may have to look through the camera's viewfinder to position the star and get a rough focus.  Then if you activate BYE and LiveView in Frame & Focus you should be able to see the star on the PC screen.  It will help to set the exposure to 2 seconds and the ISO to the largest value in the list. This will brighten the LiveView frame as much as it can be.

 

With the star visible in the Frame & Focus image area in BYE, you need to move the Zoom Box so that it surrounds the star.  Double-click on the image to unlock the zoom box. Now it follows the mouse pointer. Move the Zoom Box so that it surrounds the star. Double-click again to lock it at the new position. Now if you look at the Zoom Box Center on the right side of BYE's window you should see the star and the focus value (FWHM or HFD) should change as new LiveView frames are received.  With all that working you should now be able to adjust the telescope's focus. Your goal is to minimize the FWHM or HFD value for the star in the Zoom Box by adjusting your focuser. It helps if you can adjust your focuser from the computer, but you can also adjust the focuser manually while watching the PC screen.

 

If you have a short focal length lens on the camera rather than a telescope, you may not be able to use LiveView focusing, except when aiming at the moon. And then you will not be able to use the FWHM or HFD values for focusing since the moon is not a point source, as a star is. Instead, you will need to fine tune the focus by taking 5-10 second Snap exposures with LiveView paused.  You can still use the Zoom Box to surround a star in your snap image and the focus metric values or a Bahtinov mask to check how well you are focused. I would suggest putting the lens in MF (manual focus) mode turning the focus ring all the way to Infinity and then make very small changes to the focus ring while taking Snap exposures and monitoring the resulting change in the FWHM or HFD.

 

The sky is all at "infinite distance" so if you are well focused on the moon you should be well focused on any other objects in the sky.

 

 

Answer to question #2

 

LiveView frames are Small JPG images, regardless of the settings in the camera or the setting for Image Quality on the Settings dialog.  That is because they are intended to be displayed on the camera's LCD screen. You cannot change this. 

 

You control the what types of images are captured via the Imaging screen through the choices that you make on the Settings dialog. Here the quality choices are:

 

In-camera - BYE uses the settings for quality that are set via the in-camera menu.

RAW  - BYE will capture and store a RAW (.CR2) image

JPG - BYE will capture and store a Large JPG image

RAW+JPG - BYE will capture and store both a RAW and a JPG image.

 

 

Answer to question #3

 

LiveView frames (images) are very short exposures. On the order of 1/20th of a second.  The ISO and Shutter settings act only to brighten or darken the image. They do not change the actual exposure with remains at around 1/20th of a second.  Typically your still images will be much longer in duration.  So while LiveView only shows the brightest features in a frame, your still exposures will show all kinds of detail.