⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by TheSkyBurner » Thu Oct 04, 2018 8:33 am

I am sadded to have another complaint report for chroma filters.

The 1.25” filter mounts they are using are too tight, and the retaining ring has pinched my very expensive filter causing a thermal induced stress crack.

This was a low energy event, brought upon by bringing my scope from outside from the field into an air conditioned house. I heard an audible “clink” and inspected every part on my scope. Unfortunatley it was the most important part.

Due to the very tight tolerance of the metal cell, The swelling and shrinking of the retaining ring pinched the glass.

As a result of this event i can no longer recommend chroma 1.25” filters until they figure out how to resolve the issue.

I have reported this event to chroma, but it would appear that i am SOL.
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What a coincidence that i literally was just talking about cold shock thermal stress caused by filter cells on another thread.
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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by MalVeauX » Thu Oct 04, 2018 9:52 am

Sorry to hear about that, that sucks...

Was this with an ERF in front of it?

Very best,

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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by krakatoa1883 » Thu Oct 04, 2018 12:57 pm

Sorry to know this, Apollo. Yes, most probably it's the same that occurred to my red filter.
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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by marktownley » Thu Oct 04, 2018 5:13 pm

Ouch!
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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by christian viladrich » Thu Oct 04, 2018 6:19 pm

What were the indoor and outdoor temperatures ?
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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by TheSkyBurner » Thu Oct 04, 2018 8:02 pm

christian viladrich wrote:
Thu Oct 04, 2018 6:19 pm
What were the indoor and outdoor temperatures ?
MalVeauX wrote:
Thu Oct 04, 2018 9:52 am
Sorry to hear about that, that sucks...

Was this with an ERF in front of it?

Very best,
I actually had four ERF filters in front of it. beloptik kg3, baader b-ccd, , my kg3 achromat, and the chroma 393.4bp1 , . The filter was inside an f30 negative image beam and so was not exposed to any heating. The ambient temperature was 33c, the objective was 90mm.

The problem was caused by thermal shrink of the retaining ring. Chroma informed me that they cemented the filter into the 1.25" cell. The metal retaining ring was solid tight against the glass and over tightened right out of the factory.

using the telescope outside in a 95 degree atmosphere for over an hour, and then bringing it in the house to a 68 degree atmosphere.

I informed chroma that they need to replace the metal rings with Delrin.

They have offered to replace the filter, which I am very thankful for.

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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by MalVeauX » Thu Oct 04, 2018 8:25 pm

Ahh, I understand now, still, you'd think any filter made for solar use would be fit in a loose fashion for filter cell holding.

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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by TheSkyBurner » Thu Oct 04, 2018 10:52 pm

MalVeauX wrote:
Thu Oct 04, 2018 8:25 pm
Ahh, I understand now, still, you'd think any filter made for solar use would be fit in a loose fashion for filter cell holding.

Very best,
well chroma does not make solar filters, and by all means the 393.37nm filter is not a solar filter :) (it was an experiment exclusively made for skybender)


The lesson to learn from this, never cement a filter inside of a filter holder. Never use metal retaining rings, never over tighten the retaining ring. Never use a tight tolerance. Always leave wiggle room.

It probably would of never happened with delrin, but i cant be certain.

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Re: ⚠️ ⚠️ Chroma 1.25” filter cell thermal fracture

Post by Bob Yoesle » Fri Oct 05, 2018 6:30 pm

Thanks for the heads up Apollo.

I checked my filter and it uses a plastic retaining ring. I loosened it up when I got it and there is a slight rattle to it when gently shaken, so hopefully I'll have no issues. It is a hard coated filter on a fused silica substrate so it should be quite stable thermally, so any expansion/contraction issues would have to be the cell's.
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