Star Diagonal Service Life

Hi all,

I've had an enhanced star diagonal for almost six years that I've used for about 600-900 hours. Having recalled reading a post here that enhanced star diagonals will degrade over time, I'm wondering if it's time to replace it. If its reflectivity out of the box was 98% (it's a 2004 William Optics 2" diagonal), how long would it take for it to deteriorate to a reflectivity of less than 87%?

If I have to replace it, I'll do it with a dielectric star diagonal which I understand won't deteriorate significantly over time. Is this correct?

Thanks in advance for your responses and advice.

Mark Costello
Matthews, NC

You won't notice 87%. That is not the reason to get a dielectric.

Dielectrics are cleanable without developing micro scratches, which degrade planetary contrast. If you never look at the planets, you won't see much or any difference on deep sky objects.

Rolando