Big C11 options....

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Big C11 options....

Post by PEterW »

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

PEterW


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Re: Big C11 options....

Post by Valery »

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

PEterW
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Re: Big C11 options....

Post by marktownley »

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 »

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.


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Re: Big C11 options....

Post by DSobserver »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

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 »

Hi Ken

a very fine plot


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Re: Big C11 options....

Post by Marcello »

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 »

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 »

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? ;)

Image


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Re: Big C11 options....

Post by dellecavet »

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 »

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 »

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 »

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 »

:) ;)


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Re: Big C11 options....

Post by zorgdotnl »

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 »

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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Re: Big C11 options....

Post by Valery »

zorgdotnl wrote:It looks quite good with 5 holes (obstruction is 26%, small diameter is 37% full one), here it is:
It will work such as simulated in the case you place all small filters perfectly parallel. Otherwise there will be no single image
and no correct interference to create such a single image. Or there must be no glass in the holes.


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Re: Big C11 options....

Post by zorgdotnl »

+1 with Valery.
Stuff from the same batch.
I did some biblio. Here are some interesting simulations optimizing the sub apertures diameters, and relative positions (the 4 subs is interesting) I will run the psf on them when clouds come back ;)

I think DSobserver will have some stuff to test on his C11 ;)

http://laurent.mugnier.free.fr/publis/M ... SAA-96.pdf


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Re: Big C11 options....

Post by DSobserver »

Zorg

can you make a last simulation for a 200mm SCT using 5 and 7 2" IR cut filters like baader or astronomik one's?

Anyone against this idea if before eyepiece I place an last KG3 filter from beloptic for security reason?


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Re: Big C11 options....

Post by zorgdotnl »

Some very interesting references if you want some clues about optimizing positions/sub apertures:
http://www.rop.cnrs.fr/IMG/pdf/F_Cassaing.pdf
https://tel.archives-ouvertes.fr/tel-00140049/document


I did the simulations: The five is still better ;)

Image

Image


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Re: Big C11 options....

Post by swisswalter »

Hi loic

that looks good


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Re: Big C11 options....

Post by DSobserver »

hello during our last french solar meeting we had the opportunity to try this new mod on a C8 SCT using x3 2" UV/IR cut baader filter on a home made mask :

Image

We placed a pst body on its back protected by an other UV/IR cut filter (just in case):

Image

Previous night, star test show exactly the results mentioned by zorgdotnl (that you can see on previous picture ;) )

Before placing our eyes we check that the 3 UV/IR cut filter were good enough to block IR filters : placing our hands on focus point we couldn't suffer any burning feeling.

The results on the sun were really interesting and we could get the focus.

I'll post some pictures as soon as possible....


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Re: Big C11 options....

Post by swisswalter »

Hi Vincent

that looks great


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