The Charlie Bates Solar Astronomy Project is proudly sponsored by the following fine companies:
ImageImageImageImage
Image
Image
Lou took this great image of a prom with his Lunt152 double stacked with a Quark

Welcome to Solar Chat! The best forum for Solar Astronomy
Moving forward from solar cycle 24 to 25

PST mod on a C14

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
Post Reply
oli14
The Sun?
The Sun?
Posts: 1
Joined: Mon Aug 19, 2019 11:32 am

PST mod on a C14

Post by oli14 » Sun Nov 03, 2019 7:33 pm

Hello,

I'm trying to make the PST mod on my C14 with an off-axis 160 ERF-D filter and a BF1800 Lunt. I have already made this modification on a tecnosky telescope of 152.
3.jpg
3.jpg (95.3 KiB) Viewed 225 times
During my first attempt I did not succes to do the focus. I did several tests with long rings.
4.jpg
4.jpg (119.61 KiB) Viewed 225 times

Valery in this old post :
viewtopic.php?t=17989

You wrote :
Large ERF (say, for a C14) has another option. If the seeing does not cooperate, one can just stop the aperture with 6" off axis mask.
Do you think this setup can work ?
The initial F/D goes from 3910/355 = 11 to about 3910/140 = 27.9.The diameter is reduced with the ERF filter. I take as 140 diameter because the erf 160 is a little eclipsed by the support of the secondary mirror.

PST Fabry-Perrot is optimal at F/D = 10. Maybe it's the problem if my F/D is at about 28 in this configuration ?

Thank you.

Olivier

AndiesHandyHandies
Ohhhhhh My!
Ohhhhhh My!
Posts: 114
Joined: Fri Mar 30, 2018 6:46 am

Re: PST mod on a C14

Post by AndiesHandyHandies » Wed Nov 06, 2019 3:47 pm

Hi

At F28 you can remove the collimating lens from the front of the PST as its near enough to F-Infinity, or F40 for a air spaced etalon.

The re-focusing lens will just about preserve the back focus from the PST.

On a 127mm F7.5 with 2x ED Barlow element before PST with Collimating lens at the front removed, working at 4X as Barlow 200mm effectively before the focal point (Rather than 100mm), so F30, I got a good result, with the Re-focusing lens in place.

Andrew

george9
Ohhhhhh My!
Ohhhhhh My!
Posts: 118
Joined: Tue Jan 26, 2016 1:28 am

Re: PST mod on a C14

Post by george9 » Wed Nov 06, 2019 4:14 pm

If you use an off-axis mask, you will likely need to tilt the etalon towards the incoming light if the normal tuning range is not wide enough to get to H-alpha with a tilt. E.g., the Quark Combo comes with a tilt adapter for off-axis SCTs.

George

User avatar
marktownley
Librarian
Librarian
Posts: 26336
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: PST mod on a C14

Post by marktownley » Wed Nov 06, 2019 8:30 pm

You haven't got -200mm of back focus needed. Without using a larger ERF I would just use the setup on the 152 frac assuming it is f10.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

User avatar
marktownley
Librarian
Librarian
Posts: 26336
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: PST mod on a C14

Post by marktownley » Wed Nov 06, 2019 8:43 pm

AndiesHandyHandies wrote:
Wed Nov 06, 2019 3:47 pm
Hi

At F28 you can remove the collimating lens from the front of the PST as its near enough to F-Infinity, or F40 for a air spaced etalon.

The re-focusing lens will just about preserve the back focus from the PST.

On a 127mm F7.5 with 2x ED Barlow element before PST with Collimating lens at the front removed, working at 4X as Barlow 200mm effectively before the focal point (Rather than 100mm), so F30, I got a good result, with the Re-focusing lens in place.

Andrew
Hmmm. Not sure I agree with the theory. I tried my rather nice PST etalon without collimating lens in my 8" HaT in an f28 telecentric configuration, and the increase in bandwidth of the etalon in this setup is huge compared to the same etalon in a collimated configuration. Using barlowed as opposed to telecentric configurations is just going to result in a sweet spot.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

christian viladrich
Almost There...
Almost There...
Posts: 560
Joined: Sun Jun 14, 2015 4:46 pm
Location: France
Contact:

Re: PST mod on a C14

Post by christian viladrich » Fri Nov 08, 2019 1:13 pm

Indeed,in a telecentric system:
- F/30 and above is "good" with mica-spaced etalons:
Image

- F/50 and above is needed for air-spaced etalons :
Image

In a collimated beam, you need to have the same f-ratio on both the collimating lens and the telescope.

The differences between the telescentric and the collimated mounts is:
- the field is uniform with telecentric, but there is a broadening of the FWHM,
- the is no broadening of the FWHM with the collimating beam, but there is a shift of central wavelenght, i.e. a sweet spot.

There is no free lunch ...
Christian Viladrich
Co-author of "Astronomie Planétaire"
http://www.astroplanetes.com/
Co-author of "Astronomie Solaire"
http://www.astronomiesolaire.com/

christian viladrich
Almost There...
Almost There...
Posts: 560
Joined: Sun Jun 14, 2015 4:46 pm
Location: France
Contact:

Re: PST mod on a C14

Post by christian viladrich » Fri Nov 08, 2019 1:39 pm

Here is the sweet spot radius depending on the max CWL allowed and on the focal length of the telescope:
Image
Christian Viladrich
Co-author of "Astronomie Planétaire"
http://www.astroplanetes.com/
Co-author of "Astronomie Solaire"
http://www.astronomiesolaire.com/

User avatar
marktownley
Librarian
Librarian
Posts: 26336
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: PST mod on a C14

Post by marktownley » Fri Nov 08, 2019 9:50 pm

f50 with air spaced etalons needs rather perfect seeing to say the least.
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

christian viladrich
Almost There...
Almost There...
Posts: 560
Joined: Sun Jun 14, 2015 4:46 pm
Location: France
Contact:

Re: PST mod on a C14

Post by christian viladrich » Sat Nov 09, 2019 7:16 pm

It would also need large pixel size and / or a focal reducer after the etalon. Otherwise, the image scale would be way too large.
Christian Viladrich
Co-author of "Astronomie Planétaire"
http://www.astroplanetes.com/
Co-author of "Astronomie Solaire"
http://www.astronomiesolaire.com/

AndiesHandyHandies
Ohhhhhh My!
Ohhhhhh My!
Posts: 114
Joined: Fri Mar 30, 2018 6:46 am

Re: PST mod on a C14

Post by AndiesHandyHandies » Mon Nov 11, 2019 11:23 am

Hi

I appreciate my use of an ED Barlow and at F30 with a PST Etalon was not optimum but I could see as much detail as in Pedros image with a tad more contrast.

I am retired and cannot justify a 180mm+ DERF and a Baader Telecentric Barlow to just observe optimally a few days a year.

People image at F16 with Daystars because of seeing restrictions so observing at F30 with a PST is similar.

Its a hobby for me. And If I can do visually the same as imagers see I would be happy.

I am about to try imaging on the Vixen with my GX80 camera. The Sun just fits in. I could not take a snap because the battery had run down and the date lost I found out.

Andrew.

User avatar
marktownley
Librarian
Librarian
Posts: 26336
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Contact:

Re: PST mod on a C14

Post by marktownley » Mon Nov 11, 2019 8:36 pm

If you're happy with the results you're getting then all is good Andrew :)
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

Post Reply