#anyone know the thickness of ZWO filters?

2 messages · Page 1 of 1 (latest)

sick remnant
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I'm trying to tune the backfocus of my optical train to my camera according to https://www.svbony.com/blog/what-is-the-back-focus/

This video goes into a little more detail about how filters impact the travel https://www.youtube.com/watch?v=iyDECOauzew

(TL;DR take the thickness of your filter and divide by 3)

But I'm struggling to find any specs on the thickness of filters, or their refractive indexes, or just general rules of thumb on a per filter basis.

Here's an example: https://www.zwoastro.com/product/ircut-filters/

This says the thickness is 5mm but it's unclear if that means the product itself (not the glass) adds 5mm of physical travel, or if it is 5mm of glass (in which case it's unclear what the physical travel is). I don't have the precision tools to be able to measure this myself.

So does anybody happen to know the thickness for these filters, or just some general rules?

Svbony Blog
What is the back focus?

Determining the correct back focus for your telescope can be a daunting task for both beginners and experienced astrophotographers. In this article, we’ll discuss why back focus distance is so important, all the factors you need to consider for back focus distance, and how to use adapters and spacers to get the perfect back focus distance.

YouTube
AstroBlender
Back-Focus 101: How Filters Affect Back-Focus

In this episode of Back-Focus 101, I describe how filters change the back-focus requirement of your optical system, both visually and mathematically. Filters don't change the back-focus distance by much (in most cases), but it is critical to compensate for the change as your focal ratio decreases (or, as the "speed" of the optical system increas...

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Discovery Astrophotography with ZWO ASTRO
samanthaMa
UV IR CUT Filters - Discovery Astrophotography with ZWO ASTRO

UV IR CUT filter – 1.25″ ZWO 1.25″ IR UV CUT filter is suitable for color camera with AR protect window. The ZWO IR-Cut Filter blocks infrared light from reaching…

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if I make the assumption that the ZWO docs are trying to clunkily say that it adds 7mm of physical travel for a 5mm piece of glass, I should add 8.67mm of backfocus.