Baader Telecentric - Lower flux in blue/CaK?

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allhoest
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Baader Telecentric - Lower flux in blue/CaK?

Post by allhoest » Sun Jul 01, 2018 7:42 pm

Hi,

While using a Baader TZ4 for CaK imaging, I noticed that the sensor exposure time was ~5x longer than it should normally be.
Is the coating characteristics of these baader TZ2/TZ4 known?

I guess that the TZ3 is designed for the new Triband-SCT, thus leaving the blue spectrum passing through.
Maybe a new generation of TZ2/TZ4 have a blue friendly coating (Mine is quite old).

CS
Alex

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Re: Baader Telecentric - Lower flux in blue/CaK?

Post by Merlin66 » Sun Jul 01, 2018 11:38 pm

What exposure times are you comparing it to??
Which camera?
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allhoest
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Re: Baader Telecentric - Lower flux in blue/CaK?

Post by allhoest » Mon Jul 02, 2018 12:17 pm

Hi!

The camera is a ZWO ASI174MM
The CaK partially moded -> first 2 filters removed, replaced by a KLine. There is a prefilter.

The scope is a Newton D250mm
I have made several tests with the same setup, just changing the amplification with different “barlows”: powermate x2, x2.4, x4, TZ4 and custom made TZ5.

The exposure time with the TZ4 was about 8ms, while it should be around 1.5ms. These 1.5ms can be easily estimated while considering the “TZ4” final focal ratio by relative comparison it with other setup.
With the custom made TZ5, the exposure time is about 2ms, which is as expected.

It looks there is something unusual with the TZ4.

CS
Alex

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Re: Baader Telecentric - Lower flux in blue/CaK?

Post by mdwmark » Mon Jul 02, 2018 11:43 pm

It may be something with the AR's. Must broadband AR's are designed from 400 to 700nm. If they where using TIO2 as the high index then you will be getting absorption from it(this is the most common design). It also maybe where the AR designed was centered. If they are a MGF2 AR centered at Ha then you going to be loosing light below 400nm also.
Mark

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Re: Baader Telecentric - Lower flux in blue/CaK?

Post by allhoest » Tue Jul 03, 2018 7:14 pm

From an other forum, I get that the coating was not the same on the different version of the TZ4
CS
Alex

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