Flat Frames

[smithn00]

When making light box flat frames, how do I tell if the photosites are 1/2 to 2/3 full?

[astronomynut]

Thanks for both this Forum and this Topic.

 

I just received my Spike-A-Flat, which I needed for my New 8" RC OTA.  This uses edge mounted LED's all the way around the perimeter.  Instructions require you to set the Histogram to between 1/3 and 2/3.  I believe that BYEOS has a sort of Histogram.  Exactly what am I looking for in BYEOS when I start adjusting the Spike-A-Flat panel intensity setting?  Does the BYEOS move around?

 

I know all of what I wrote probably sounds dumb, but I really never paid attention to the Histogram in this software before getting this panel.  Seems I need to pay more attention from now on.  Caley

[s3igell]

The BYE Histogram, which is displayed for every completed Capture Plan Image, has a little button on the right to display guide lines in either 1/2s or 1/3rds or 1/4ths.  It also has buttons to toggle between "L" (Luminence only) and "RGB" Histograms.

 

It will be the Humps of the Histogram for your Images that moves within the frame of the Histogram Graph, not the BYE Histogram Frame itself, depending on the results of your Flats Exposures.

If you have BYE v3.1.2 Premium, you also have the "Spot Histogram Tool" - a Popup Histogram that is activated at the Mouse Cursor when you Right-Click on a Displayed Image (either Captured or Preview).

[astronomynut]

Thanks for the information.  I've printed your explanation out for use the next time I am out at the observatory.  I would imagine that I should be able to figure it out by playing with things, based on what you wrote, and what my instruction sheet said. 

[astroman133]

Look at the histogram.  The shoulders should be well away from both the left and right edges and the peak should be around the center.

[s3igell]

Many of us use Tv mode and allow the Camera to perform the Metering...

 

In general, since the DSLR Metering is designed for Daytime Photography, it'll Under-Expose when faced with a Uniformly Lit Surface.  So, we set Exposure Compensation to +2.

(If you use your DSLR for Daytime Imaging too - Remember to RESET the EC value...)

 

Depending on the Light Source in your Light Box, you'll need to lower your ISO on Flats to 100ISO so that you get Shutter Speeds that are Multiple Times whatever Flicker Rate your Light Source produces - EL Panels, Incandescents, Fluorescents, etc.

 

With my EL Panel, I use 100ISO and 1/20sec; with my Lamp-lit Wall, I use 100ISO and 1/40-1/20sec.

[smithn00]

Flicker Rate is a new term to me. What does it mean?  My device is edge-lit  with LEDs by Spika-a.

[s3igell]

Any Light Source that is powered by AC will produce Light that reaches a Brightness Peak and then Falls Off with the Current.  Incandescents.  This can even be true of some LEDs, depending on the design of the Power Supply/Converter.

 

Any Light Source that works by Fluorescence - EL Panels, most LCD Screens, CFLs - will also have a Flicker Rate for similar reasons.