Question about back filters (Daystar, Solar spectrum)

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Geremia Forino
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Question about back filters (Daystar, Solar spectrum)

Post by Geremia Forino » Fri Aug 14, 2015 8:10 pm

maybe it will be a stupid question, but, since the filter concept are similar, why Daystar employs so short focal points while Solar Spectrum has a long focal train ?
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Bob Yoesle
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Re: Question about back filters (Daystar, Solar spectrum)

Post by Bob Yoesle » Sat Aug 15, 2015 2:27 am

The Baader telecentric lenses are true telecentric designs which will have optimum performance with an objective with a 800 ml FL. They will perform well with other FL objectives if they are not too short a FL.

The DayStar filters do not have custom telecentric units designed for them, and are usually meant to be used with "telecentric barlows." These are not as well optimized and will suffer more from band-pass broadening and sweet spots, but do have the "shorter focal points." See Christian Valadrich's excellent analysis here: http://www.astrosurf.com/viladrich/astr ... lar/FP.htm

You could of course use a DayStar filter with a Baader telecentric lens.
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Geremia Forino
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Re: Question about back filters (Daystar, Solar spectrum)

Post by Geremia Forino » Sat Aug 15, 2015 10:08 am

Bob thanks for your clarification.

my question born from wanting to achieve f / 30 on my Tec140 f/7 scope, I tried to push my powermate 4X (f/28), as in the diagram of Televue It shows that, at a distance of 100mm, you get a 4.4X (f/30.8).

Now I have another question, according to the diagram of Televue, 100mm should be measured to the etalon or the camera chip ?
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Re: Question about back filters (Daystar, Solar spectrum)

Post by Valery » Sat Aug 15, 2015 6:22 pm

Geremia Forino wrote:Bob thanks for your clarification.

my question born from wanting to achieve f / 30 on my Tec140 f/7 scope, I tried to push my powermate 4X (f/28), as in the diagram of Televue It shows that, at a distance of 100mm, you get a 4.4X (f/30.8).

Now I have another question, according to the diagram of Televue, 100mm should be measured to the etalon or the camera chip ?
To the camera chip. The distance will include the height of the filter (with it's body). So, the filter will work in a F/31 cone.


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Geremia Forino
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Re: Question about back filters (Daystar, Solar spectrum)

Post by Geremia Forino » Sat Aug 15, 2015 10:06 pm

Valery,
just to clarify, if the chip is at 100mm distance from barlow (4.4X (f/30.8), the etalon, being first, will be at f/29 considering graph Televue

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Re: Question about back filters (Daystar, Solar spectrum)

Post by Valery » Sun Aug 16, 2015 4:21 pm

Geremia Forino wrote:Valery,
just to clarify, if the chip is at 100mm distance from barlow (4.4X (f/30.8), the etalon, being first, will be at f/29 considering graph Televue
No no no! It will work at F/31 !


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Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.

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Re: Question about back filters (Daystar, Solar spectrum)

Post by Geremia Forino » Sun Aug 16, 2015 6:11 pm

I'm glad to hear this, but we are talking about a f/7 scope.
I'm confused :roll: , if from 0 to 100mm the f/. increases exponentially, how can an optical, placed before the other having a major factor ?

we are talking about, Barlow > DaystarQuantum > Chip see image below, if I'm wrong, sorry, maybe I omit some details which I am not aware.
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Re: Question about back filters (Daystar, Solar spectrum)

Post by Valery » Mon Aug 17, 2015 11:00 am

Geremia Forino wrote:
we are talking about, Barlow > DaystarQuantum > Chip
You nail it. Exactly.


Valery
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Re: Question about back filters (Daystar, Solar spectrum)

Post by Geremia Forino » Mon Aug 17, 2015 2:06 pm

:bow2

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