diff --git a/README.md b/README.md
index 24c89c1..34bff34 100644
--- a/README.md
+++ b/README.md
@@ -34,10 +34,10 @@ Contributions are welcome. Please read the [contributing guideline](CONTRIBUTING
 - [DeepSkyStacker vs PixInsight](https://web.archive.org/web/20230408140244/https://www.lightvortexastronomy.com/image-pre-processing-deepskystacker-vs-pixinsight.html) - A detailed comparison of the pre-processing features.
 - [Drift Alignment by Robert Vice (D.A.R.V)](https://www.cloudynights.com/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760) - Accurate alignment in just a matter of minutes.
 - [Flat Fields and Stray Light in Amateur Telescopes](https://diffractionlimited.com/flat-fields-stray-light-amateur-telescopes/) - A great resource to help one identify and resolve flat-fielding issues.
-- [Guide Scope vs. Off-Axis Guider: Which is Better for Astrophotography?](https://optcorp.com/blogs/deep-sky-imaging/guide-scope-vs-off-axis-guider) - Compares the two guiding options in details.
+- [Guide Scope vs. Off-Axis Guider: Which is Better for Astrophotography?](https://web.archive.org/web/20240928205001/https://optcorp.com/blogs/deep-sky-imaging/guide-scope-vs-off-axis-guider) - Compares the two guiding options in details.
 - [Guide to Focal Reducers for Astronomy](https://agenaastro.com/articles/focal-reducers-guide.html) - How focal reducers work, what types are there, and how to use them.
 - [Guide to Preprocessing of Raw Data With PixInsight](https://pixinsight.com/forum/index.php?threads/guide-to-preprocessing-of-raw-data-with-pixinsight.11547/) - Mistakes that happen during the pre-processing stages cannot be corrected anymore in post-processing. This guide from Bernd Landmann acquaints fellow astrophotographers with PixInsight's tools needed for recognising and avoiding such mistakes.
-- [How to Set the Correct Back Focus](https://optcorp.com/blogs/deep-sky-imaging/how-to-set-the-correct-back-focus) - An easy to follow guide on what back focus is and how to set it.
+- [How to Set the Correct Back Focus](https://web.archive.org/web/20240928205054/https://optcorp.com/blogs/deep-sky-imaging/how-to-set-the-correct-back-focus) - An easy to follow guide on what back focus is and how to set it.
 - [Lights and Shadows](https://ciechanow.ski/lights-and-shadows/) - This interactive guide to light by Bartosz Ciechanowski, teaches about travel vectors, irradiance, radiance, angles, luminance, and more.
 - [Master PixInsight's Astrophotography Statistics: Analyze, Adjust, Enhance](https://www.kozmosi.io/articles/a-to-z-of-pixinsight-statistics-panel) - Successfully processing astronomical images entails a series of informed decisions. Understanding the data is crucial. This article provides a comprehensive guide to the Statistics process in PixInsight.
 - [Mastering Flat Frames: Gain matching](https://www.astroworldcreations.com/blog/understanding-flats-part-1-gain-matching) - This blog series by Willem Jan Drijfhout will take you on a deep dive into the topic of flat frames ([Part 2: Flat Panels compared](https://www.astroworldcreations.com/blog/understanding-flats-part-2-flat-panels-compared), and [Part 3: Bias, Flat-Darks and Conclusions](https://www.astroworldcreations.com/blog/understanding-flats-part3-conclusions)).