newton PST mod

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DSobserver
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newton PST mod

Post by DSobserver » Tue May 26, 2015 9:23 pm

Hello,

A new idea : I saw that according to f/d telescope, secondary newton mirror can resist against solar heat without any filter.

According to this, we can imagine to place a smaller erf on the foscuser just before a PST mod.

What do you think?
will a 6" f/2,8 could be ok?

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Re: newton PST mod

Post by swisswalter » Wed May 27, 2015 3:58 am

Hi Vincent

will you be stripping the main mirror ?
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Re: newton PST mod

Post by DSobserver » Wed May 27, 2015 5:39 am

no

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Re: newton PST mod

Post by Marcello » Wed May 27, 2015 2:04 pm

Interesting idea!

Is there any formula to calculate heat according to focal?

Why not placing the ERF just before the secondary with a proper cell/support?


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Re: newton PST mod

Post by swisswalter » Thu May 28, 2015 4:16 am

DSobserver wrote:no
Hi Vincent


Oh, that will be an extremely hot instrument
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Re: newton PST mod

Post by marktownley » Thu May 28, 2015 8:03 am

DSobserver wrote:
According to this, we can imagine to place a smaller erf on the foscuser just before a PST mod.

What do you think?
I think it will focus the reflected energy back on the primary mirror...
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Re: newton PST mod

Post by Marcello » Thu May 28, 2015 8:23 am

What about tilting then the ERF say at 45° ?
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Re: newton PST mod

Post by GreatAttractor » Thu May 28, 2015 10:26 am

Uncoated mirrors are great for white light, but remember that for Hα we shouldn't waste photons. A D-ERF has 90% transmission in Hα, and this becomes much darker after passing through the etalon+blocking filter. Using one uncoated mirror would reduce this final light by a factor of ~20. I guess it can be acceptable, e.g. I use around 0.3-0.4 ms exposure with my current setup (D-ERF + Lunt35 ERF & etalon + Lunt B600, final ratio of f/12.6). 20x that is 6 ms, which still isn't bad.

As for strongly tilting the ERF, it's not a good idea - would introduce lots of astigmatism (optics experts, please correct me if I'm wrong).

From what I've seen here on Solarchat, when the refractor guys use a sub-aperture ERF, it's not much smaller than the objective – maybe 1.2-1.5 times (by diameter), which implies it's safe for the ERF irradiance to be around ~2x larger than compared to front-mounted option.
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Re: newton PST mod

Post by mdwmark » Fri May 29, 2015 12:54 am

If you put the bandpass type ERF in front of the secondary. Then just tilt it so that it reflects the beam down in the corner some place.
OR
If you use a 45% cold mirror the IR goes on through . Then block the rest of the reflected light with a piece of RG630. Then the filter.
Just an idea
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