Frame and Focus

[Farzad_K]

Hello,

 

I have now tried the Frame and Focus a few times in the field and I am not able to see anything once the Live View gets started. What do I need to do in order to be able to work with this feature?

 

Thanks

[admin]

Define not able to see anything.

1) Are you seeing just noise?  If yes you are grossly out of focus.  You need to be close to focus for any starts to resolve.  

2) Is the live view simply not working? Not even on the camera LCD?  

Try in the day time first, it will be easier to confirm the 2 above.

[Farzad_K]

Sorry, I should have been more clear: when I start frame and focus, and after the shutter opens and remains open, no stars appear on the BYN user interface screen which is black except for the center marking. I do adjust the zoom and check for scope cap to have been removed too!

The Live View on camera is functional. And when BYN is not connected, and when I activate Live View on my camera, and after hearing the shutter sound, the camera rear display is also solid black with no stars.

[astroman133]

My reply assumes that you have the camera attached to a telescope at prime focus.

So, there could be a number of reasons why you are not seeing stars in the LiveView display.

1) If you are way out of focus the stars are so large that one star could fill the entire screen, making it seem uniformly dark. You need to achieve a rough focus by first looking through the camera's viewfinder. If you have no idea of how far out the drawtube must be then aim the scope at something that is far away at the horizon, before sunset, and adjust focus while looking through the viewfinder. That should get you close enough.

2) You need to be sure that Exposure preview is turned on in the camera's menu (if your camera allows you to turn it off). I would suggest that you can verify that Exposure preview is working by testing the camera in a daytime setting with a lens attached. Turn on LiveView and adjust the ISO and exposure to see how the screen brightness changes. You should see that the display brightens as you increase the ISO. It will also brighten as you increase the exposure setting, up to a point. Beyond a certain point (like 2 seconds) increasing the exposure does not cause the image to brighten further. Setting the exposure to BULB may cause it to dim. So to make it easiest to see bright stars you will likely need to set the ISO to maximum and the exposure to 2 seconds. You could also select the Maximum Sensitivity setting in BYN.

3) You need to point your telescope so that a bright star is anywhere near the middle of the field-of-view. During spring and summer Arcturus is a good choice.

LiveView is not very sensitive because the actual exposure duration is only a few milliseconds long. This is so the camera can update the LiveView screen several times per second and is perfectly OK for daytime use, which is what it is really designed for. When you change ISO and exposure duration you are changing how much each live view image is brightened. You are not changing the actual duration. Only the brightest stars will show up in the live frame and focus display, even when BYN is set for maximum sensitivity. Even then they will appear as small dim dots on the black background that are easy to overlook.

I am a Canon owner so I am not sure whether this next comment works the same for a Nikon camera or not. Once you can see the star on the BYE LiveView display you can move the focus rectangle (double-click to lock and unlock the rectangle) so it surrounds the star. Then you can adjust focus to minimize the FWHM or HFD focus metric.

If you are not able to see any stars in the LiveView screen, then you will have to take short snap images, say 2-5 seconds at ISO 1600, while adjusting the focuser. If you put the focus rectangle around one of the stars in the image you will still be able to use the numeric focus metrics to achieve critical focus.