Using legacy eclipse photography software poses a significant challenge: it requires constant updates to accurately predict event times. For instance, tools like Solar Eclipse Maestro and Fred Espenak's websites haven't been updated since the 2010s. Since then, "delta T"—a critical prediction input—has shifted dramatically. While it increased steadily throughout the 2010s, it flattened out around 2019 and is now trending negative. A prediction for the August 20, 2026 eclipse made using the older trend line would have assumed a delta T of 72.4 seconds. The actual value was 69.0909 seconds. This discrepancy shifts contact times by 3.5 seconds, which could cause you to miss imaging the contacts entirely or mistime other exposures. Although CE 2.3 includes updated figures for 2027 that are closer to reality, they may still be off by up to 0.5 seconds. Additionally, version 2.3 did not update any eclipses beyond 2027.
The final Intel-compatible release of CE (version 2.3.1) includes a feature that allows you to use a custom Bessel model for predictions. This guide explains how to use this capability to extend the life of your software.
Get the correct Bessel for your eclipse
Download the file that corresponds to the eclipse you are interested in. G CE version 2.3.1 allows you to use a custom Bessel file (i.e. what give the prediction engine its values). Let's first start by downloading the correct one
Rename the file
change its name to CustomBessel.xml
Move the file to the CaptureEclipse directory
Move (or copy) the file to the CaptureEclipse->Bessel directory
Select it
Now create a new site and select CustomBessel (scroll to bottom of list) instead of the default
My plan is to continue providing up to date Custom Bessel files to replace the ones built into your program. Should I not be able to (or you do not trust me) this section will define a procedure to update the files above yourself (or to check my work)
Update the ΔT
If I have not updated the file within 180 days of the eclipse then you will have to use the procedure below to obtain the correct value of ΔT and edit the file.
Using an xml editor such as xml notepad edit the file. You will want to change two fields
To achieve sub-second camera sync and precise path alignment, CaptureEclipse requires an accurate Delta-T value. Because the international community has frozen leap seconds at 37, you can calculate the exact value for any current eclipse using a single live number from the official text bulletins.
UT1-UTC column (this is your DUT1 value). It will be a small decimal like -0.152 or 0.084.Instead of calculating the formula manually, enter the value you found into the utility tool below: