Big C11 options....

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Big C11 options....

Post by PEterW » Fri Mar 27, 2015 7:40 pm

Right, I know a guy with an 11” SCT who is bored of imaging the planets…. Didn't think he could observe the sun with it. I mentioned Baader foil and then we got thinking. So for white light some ND3 imaging baader foil over the front and a narrow filter… continuum of maybe a NIR filter to help improve the seeing… Should do quite well on the granulation.
The scope is native f10… Which is the same as the PST, so would it be possible to put a PST mod into the back of the scope (again with baader nd3 foil on the front) and do hydrogen alpha? Wonder if there Is enough focus in travel and not sure where you would put the ERF to reject the out of band wavelengths, maybe with the baader film you could just use a few stacked 2” filters.

Calcium ought to be possible the same way with baader foil taking the light levels down a safe level for a lunt cak filter on its own that then would give the narrow line width necessary.

Comments, experience please. Wondering if you could find some lower ND foil to keep the exposure times down for high magnification viewing.

Cheers

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Re: Big C11 options....

Post by Valery » Fri Mar 27, 2015 7:48 pm

PEterW wrote:Right, I know a guy with an 11” SCT who is bored of imaging the planets…. Didn't think he could observe the sun with it. I mentioned Baader foil and then we got thinking. So for white light some ND3 imaging baader foil over the front and a narrow filter… continuum of maybe a NIR filter to help improve the seeing… Should do quite well on the granulation.
The scope is native f10… Which is the same as the PST, so would it be possible to put a PST mod into the back of the scope (again with baader nd3 foil on the front) and do hydrogen alpha? Wonder if there Is enough focus in travel and not sure where you would put the ERF to reject the out of band wavelengths, maybe with the baader film you could just use a few stacked 2” filters.

Calcium ought to be possible the same way with baader foil taking the light levels down a safe level for a lunt cak filter on its own that then would give the narrow line width necessary.

Comments, experience please. Wondering if you could find some lower ND foil to keep the exposure times down for high magnification viewing.

Cheers

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Re: Big C11 options....

Post by marktownley » Sat Mar 28, 2015 6:23 am

You wont get enough light through like Valery says. Also, the SCT is a compound optical system, and while the overall EFR is f10, the focal ratio of the secondary is somewhere between f3 and f4 - not the same light cone for the optics in the PST etalon...
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Re: Big C11 options....

Post by Valery » Sat Mar 28, 2015 9:23 am

marktownley wrote:You wont get enough light through like Valery says. Also, the SCT is a compound optical system, and while the overall EFR is f10, the focal ratio of the secondary is somewhere between f3 and f4 - not the same light cone for the optics in the PST etalon...
Mark,

The PST etalon will work with the final F/D of the SCT F/10. Perfect match. The only two problems:

1. Full aperture, good optical quality ERF filter.

2. very small field of view with PST etalon - about 1/10 solar diameter, not more.


BTW. If that guy with C11 is so much interested in H-a imaging through C11 (will be a leader in the size of the instrument in the amateur H-a imaging community) he can contact me and we can make such a full aperture filter for him. Four samples are in the progress now.


Valery.
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Re: Big C11 options....

Post by DSobserver » Sat Mar 28, 2015 3:28 pm

And what about placing 4 to 6 smaller erf in front like this : Image ?

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Re: Big C11 options....

Post by fjabet » Sun Mar 29, 2015 2:53 pm

Your PSF will be quite weird with those aperture.
Note also that SCT are very poor in UV.
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Re: Big C11 options....

Post by Valery » Mon Mar 30, 2015 5:33 am

fjabet wrote: Note also that SCT are very poor in UV.
Not so catastrophically, as one may think. Can be corrected easily with SAFIX.
Last edited by Valery on Mon Mar 30, 2015 11:54 am, edited 1 time in total.
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Re: Big C11 options....

Post by DSobserver » Mon Mar 30, 2015 11:07 am

fjabet wrote:Your PSF will be quite weird with those aperture.
Note also that SCT are very poor in UV.
Indeed aperture would be strange, but could it works?

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Re: Big C11 options....

Post by zorgdotnl » Mon Mar 30, 2015 2:24 pm

DSobserver wrote:
fjabet wrote:Your PSF will be quite weird with those aperture.
Note also that SCT are very poor in UV.
Indeed aperture would be strange, but could it works?
It's easy to test that solution on the polar or Jupiter with holes on paperboard ;) If it's OK then we can test on the sun with 4 or 5 (100-150mm) erf on a 400mm ;)

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Re: Big C11 options....

Post by DSobserver » Mon Mar 30, 2015 8:30 pm

zorgdotnl wrote:
DSobserver wrote:
fjabet wrote:Your PSF will be quite weird with those aperture.
Note also that SCT are very poor in UV.
Indeed aperture would be strange, but could it works?
It's easy to test that solution on the polar or Jupiter with holes on paperboard ;) If it's OK then we can test on the sun with 4 or 5 (100-150mm) erf on a 400mm ;)
If you don't mind I'll try first on my C11 ;)

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Re: Big C11 options....

Post by fjabet » Tue Mar 31, 2015 6:23 am

You will gain resolution only on the ERF axis, and it'd better be symmetrical.
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Re: Big C11 options....

Post by DSobserver » Tue Mar 31, 2015 2:04 pm

fjabet wrote:You will gain resolution only on the ERF axis
Not sure to understand it correctly....

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Re: Big C11 options....

Post by DSobserver » Tue Mar 31, 2015 6:49 pm

Well I think that C.viladrich already more or less answered to my question....

http://www.cloudynights.com/topic/49178 ... ?p=6460933

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Re: Big C11 options....

Post by Merlin66 » Wed Apr 01, 2015 5:32 am

Re the UV with SCT's....
I regularly use the C11 with the Spectra-L200 (with ATiK 314L) for spectroscopy and can image spectra well below 4000A
The attached is a spectrum of Sirius down to 3700A
sirius_blue.jpg
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Re: Big C11 options....

Post by swisswalter » Thu Apr 02, 2015 4:22 am

Hi Ken

a very fine plot
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Re: Big C11 options....

Post by Marcello » Thu Apr 02, 2015 1:44 pm

Very interesting post.. no way to put the ERF between the primary and the secondary? Too much heat trapped in the tube?

The ERF reflects the heat, this couldn't be directed outside by tilting the ERF ?

just my imagination..
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Re: Big C11 options....

Post by marktownley » Fri Apr 03, 2015 3:40 pm

Marcello wrote:Very interesting post.. no way to put the ERF between the primary and the secondary? Too much heat trapped in the tube?

The ERF reflects the heat, this couldn't be directed outside by tilting the ERF ?

just my imagination..
Yes, but bear in mind all that heat makes the air warm in the tube and that is what causes the problem...
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Re: Big C11 options....

Post by zorgdotnl » Sat Apr 04, 2015 3:31 pm

DSobserver wrote:Well I think that C.viladrich already more or less answered to my question....

http://www.cloudynights.com/topic/49178 ... ?p=6460933
As it's cloudy, I made some simulations, with a closer spacing than C. viladrich. It's promising resolution wise, even the first ring is interesting.
Ready to try with 4 erf or 4 FP? ;)

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Re: Big C11 options....

Post by dellecavet » Sat Apr 04, 2015 3:48 pm

But excuse me, probably i' have not understand.

How you would make it closer if you have a central obstruction coming from the secondary ?

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Re: Big C11 options....

Post by DSobserver » Sat Apr 04, 2015 4:29 pm

dellecavet wrote:But excuse my, probably i' have not understand.

How you would make it closer if you have a central obstruction coming from the secondary ?
+1 ;)

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Re: Big C11 options....

Post by zorgdotnl » Sat Apr 04, 2015 4:46 pm

With the pattern simulated, central obstruction is (2-sqrt(2))/(2+sqrt(2))=17% (if my maths are correct), it would fit tight a newton ;) Sorry for Cats ;)
5 or 6 holes version for cats?

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Re: Big C11 options....

Post by DSobserver » Sat Apr 04, 2015 5:49 pm

zorgdotnl wrote:With the pattern simulated, central obstruction is (2-sqrt(2))/(2+sqrt(2))=17% (if my maths are correct), it would fit tight a newton ;) Sorry for Cats ;)
5 or 6 holes version for cats?
5 please! ;)

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Re: Big C11 options....

Post by dellecavet » Sat Apr 04, 2015 5:52 pm

:) ;)

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Re: Big C11 options....

Post by zorgdotnl » Sat Apr 04, 2015 7:03 pm

It looks quite good with 5 holes (obstruction is 26%, small diameter is 37% full one), here it is:

Image


The 6 holes version (obstruction is 33%, small diameter hole is 33% the full one):

Image

It seems that with odd number of holes, less energy is poiled on the rings, so contrast should be better.

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Re: Big C11 options....

Post by DSobserver » Sat Apr 04, 2015 9:43 pm

Would it make sense to use 2" Baader CCD Filter red as a front erf

Image

followed by a 2" KG3 UV/IR from beloptik before a Ha system like PST or quark?

Image

Like this, changing the red front filter to blue one, we can move change from Ha with a PST to Cak with Lunt Cak filter.

Would this cheap idea intelligent and safe for a C11 SCT????

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