ITF rusty on a Coronado BF15

Use this section to discuss "standard" Baader/Coronado/ Lunt SolarView/ Daystar, etc… filters, cameras and scopes. No mods, just questions/ answers and reviews.
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jacquesfrr
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ITF rusty on a Coronado BF15

Post by jacquesfrr » Tue Apr 14, 2015 1:50 pm

Hello,

My ITF filter is oxidizing at the periphery :
http://www.webastro.net/upload/images/7 ... 016792.jpg

I have read that the Maier ITF is a good replacement.

How Is the view through a Maier ITF ? Some say the view is less good, some say better than the Coronado ITF, so I don't know ?

Thank you
Jacques

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marktownley
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Re: ITF rusty on a Coronado BF15

Post by marktownley » Tue Apr 14, 2015 7:03 pm

Hi Jacques,

Yes, that is definitely oxidizing. I have the Maier on a BF15 and it works just fine :)

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Re: ITF rusty on a Coronado BF15

Post by jacquesfrr » Tue Apr 14, 2015 8:45 pm

Thank you Mark,

Do you use your BF15 on a Solarmax filter ? In visual mode, would you say the Maier is better than the Coronado ITF ?

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04Stefan07
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Re: ITF rusty on a Coronado BF15

Post by 04Stefan07 » Tue Apr 14, 2015 9:37 pm

How come the filters start to oxidize over time?

Is it a design flaw or that's just the way it is?
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Re: ITF rusty on a Coronado BF15

Post by swisswalter » Wed Apr 15, 2015 4:55 am

Hi Jacques

for imaging a mod can not do much harm. I wouldn't use it for viewing though
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Re: ITF rusty on a Coronado BF15

Post by marktownley » Wed Apr 15, 2015 5:23 am

jacquesfrr wrote:Thank you Mark,

Do you use your BF15 on a Solarmax filter ? In visual mode, would you say the Maier is better than the Coronado ITF ?
Visually I can tell no difference, for imaging it lets a little more light through.
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Bob Yoesle
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Re: ITF rusty on a Coronado BF15

Post by Bob Yoesle » Wed Apr 15, 2015 6:30 am

How come the filters start to oxidize over time?

Is it a design flaw or that's just the way it is?
The ITF is susceptible to deterioration from thermal loading and cycling from ERFs that have no IR blocking. To help prevent this you should use an ERF, such as the Lunt or the Baader, that incorporates IR blocking as well a s UV (usually provided by the RG630 glass substrate itself.)

The ITF is a "sandwich" filter that incorporates metallic silver layers, and is sealed around the edge with epoxy. However, thermal loading and cycling can cause small cracks in the epoxy, which will admit atmospheric moisture, and the deterioration begins at the periphery and moves inward over time, as can be seen in the picture.

Additionally, using an IR blocked ERF ahead of the etalon will help with thermal stability of the etalon itself, which will give more uniform contrast when the filter is initially set up.
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