General modding questions.

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Merlin66
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Re: General modding questions.

Post by Merlin66 » Sun Mar 31, 2013 8:25 am

Because the PST is designed for an f10 system..that's the prefered donor.
If you use, say, the f7.5 80mm (600mm fl)it will end up an effective 60mm aperture!
I have a write-up available on PST mods...just drop me an email for a copy.
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Re: General modding questions.

Post by swisswalter » Sun Mar 31, 2013 8:37 am

Hi John

start with the SW70 f/10, that can work perfect without altering the scope. happy easter
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Re: General modding questions.

Post by marktownley » Sun Mar 31, 2013 9:07 am

Definitely start with the 70mm f10, that will be the most cost effective method to start with. Main things you will need is someway to connect the PST black box to the ota, and some kind of ERF - do you have a 2" nightime Ha filter?
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Re: General modding questions.

Post by colinsk » Sun Mar 31, 2013 8:50 pm

A point to remember is as you increase aperture you will decrease the on band field of view unless you have a larger etalon. If you are looking for a full disk you are on the wrong path. If you are looking for good close ups then crash ahead.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: General modding questions.

Post by colinsk » Mon Apr 01, 2013 12:17 am

In order for the entire field of view to be on band you can not have the etalon be smaller than half of the objective size for an air spaced etalon. The reason for this is the angles that each ray takes through the etalon has to be as straight as possible for it to be on band. If the sun was a point source this would be easy. Since the sun is .5 deg wide it is more complicated.

If you want to take small fields of view this is not a problem.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: General modding questions.

Post by colinsk » Mon Apr 01, 2013 12:21 am

The other way of doing full disks by mosaics is still an option.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: General modding questions.

Post by Merlin66 » Mon Apr 01, 2013 12:50 am

To fit the whole solar disk in a small CCD chip requires an effective focal length of close to 400mm....
With most (read: all) of the PST mods the focal lengths are closer to 900mm and above.
You could use a reducer (after the etalon) to bring it back down to 400mm or continue to use mosaics....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: General modding questions.

Post by colinsk » Mon Apr 01, 2013 2:16 am

To fit the whole solar disk in a small CCD chip requires an effective focal length of close to 400mm....
With most (read: all) of the PST mods the focal lengths are closer to 900mm and above.
You could use a reducer (after the etalon) to bring it back down to 400mm or continue to use mosaics....

But we also have the issue of field angles in the etalon. A reducer does not help that.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: General modding questions.

Post by Merlin66 » Mon Apr 01, 2013 2:16 am

A Stage 1 mod does nothing to improve the available back focus. You are still restricted by the "black box"
When you move to the Stage 2 Mod you have many more options.....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: General modding questions.

Post by colinsk » Mon Apr 01, 2013 3:23 am

A Stage 1 mod does nothing to improve the available back focus. You are still restricted by the "black box"
When you move to the Stage 2 Mod you have many more options.....

Ken, I think we are misunderstanding each other.

1. The definition of collimation is f1+f2=total length the focal ratios are not important.

2. The available field of view is a function of the angles of the light going through the etalon tempered by the index of refraction of the etalon gap. Air is 1. So air is the most unforgiving.

The result is a full solar disk can not be on band if an airspaced etalon is less than 1/2 the diameter of the objective in a collimated system. A telecentric system is a little better.

Is that your experience?
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: General modding questions.

Post by Merlin66 » Mon Apr 01, 2013 4:39 am

Colin,
No debate!
I was answering the question on adding a reducer well after the PST etalon assembly and the associated lenses....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: General modding questions.

Post by MapleRidge » Mon Apr 01, 2013 2:01 pm

Hi Mark and all...

I am still tinkering with a PST mod, but may move it to a smaller OTA. I see you have referenced using a deep sky Ha filetr an ERF...is this adequate to moutn in front of a 50mm objective or slightly behind a 60-70mm one?

I have a Baader 2" Ha filter that is not beign used...hadn't really considered utilizing it but cold be incorporated in the project.

Any thoughts or comments?

Thanks,
Brian
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Re: General modding questions.

Post by marktownley » Mon Apr 01, 2013 2:21 pm

Been away for Easter, so slow to respond to this one.

Colin is spot on with what he says regards aperture size and etalon size, I made a (ota native focal length) 70mm f6 PST mod - it actually runs at closer to 500mm (420-120+200) - with this and my DMK31 I could do a 6 pane full disk mosaic but I can see where the image is starting to go offband across the frame (sweetspot) - I could do it in 4 but wouldn't have the overlap of panes that I like and sweetspotting effects would be worse. I prefer to run at 800mm plus in which case the number of panes goes up but so does the detail...

However, do not despair! You are an engineer as you say and so this is quite simply a case of taking the parts you have and making them work ;)

You would be running at 70mm f10 (700mm fl) with the mod that you propose, now, i'm confident with the small chip of a DMK21 you would get away with imaging in the 'good part' at the centre of the sweetspot quite easily, so much so, I reckon if you use the 0.8x reducer you have aswell - which would put you at 560mm fl - which would reduce still further the number of panes you will need. If you had a larger chipped camera you would not get away with using the reducer as would accentuate the sweetspot.

What do you have to use as a ERF for this project?
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Re: General modding questions.

Post by marktownley » Mon Apr 01, 2013 2:26 pm

Hi Mark and all...

I am still tinkering with a PST mod, but may move it to a smaller OTA. I see you have referenced using a deep sky Ha filetr an ERF...is this adequate to moutn in front of a 50mm objective or slightly behind a 60-70mm one?

I have a Baader 2" Ha filter that is not beign used...hadn't really considered utilizing it but cold be incorporated in the project.

Any thoughts or comments?

Thanks,
Brian

Hi Brian.

I use a Baader 2" Ha filter upfront on my DS40. It would work just aswell on a 70mm scope mounted internally in the tube

Mark :)
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Re: General modding questions.

Post by brianb11213 » Mon Apr 01, 2013 4:46 pm

I am still tinkering with a PST mod, but may move it to a smaller OTA. I see you have referenced using a deep sky Ha filetr an ERF...is this adequate to moutn in front of a 50mm objective or slightly behind a 60-70mm one?

I have a Baader 2" Ha filter that is not beign used...hadn't really considered utilizing it but cold be incorporated in the project.

Any thoughts or comments?
Just to point out that the clear aperture of a 2" screw-in fit filter is around 45mm (the thread is 48mm dia x 0.75mm pitch)

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