Greetings Everyone.
My contribution to the inspiring collection of proms on display here!
Cheers, Peter.
July 2 Proms
- ffellah
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Re: July 2 Proms
Peter,
Lots of detail in the image. Having seen your rig on another thread, can I ask if the telecentric magnification is optimal
for the Daystar or could it be reduced for a less magnified view ( without resorting to a reducer ) ?
Best wishes,
David
Lots of detail in the image. Having seen your rig on another thread, can I ask if the telecentric magnification is optimal
for the Daystar or could it be reduced for a less magnified view ( without resorting to a reducer ) ?
Best wishes,
David
Making the possible difficult and the difficult impossible.
Photos : https://www.flickr.com/photos/daviddench/albums/
Photos : https://www.flickr.com/photos/daviddench/albums/
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Re: July 2 Proms
Thanks Franco and David.
David: My motivation for using a high magnification telecentric comes from the calculations of Christian Vladrich (http://www.astrosurf.com/viladrich/astr ... lar/FP.htm), in partricular this figure: http://www.astrosurf.com/viladrich/astr ... FWHM-N.JPG. Here, Christian has plotted the bandpass fwhm as a function of focal ratio (f#) for a mica-spaced F-P etalon like the Daystar. Daystar recommends f#>30 for their etalons but you can see from the graph that there is room for improvement by pushing to ~f#=50. I wanted to be sure to maximize the performance of my filter and also had in mind to try stacking the Daystar with a Lunt LS50 etalon. The Lunt is even more sensitive to focal ratio, again according to Christian's calculations. I was even contemplating telecentric designs as high as f#=80 but found it too difficult to reduce to reasonable focal ratios (~ 25 to 35) without severe vignetting. As it is, there is pretty significant vignetting (at the Daystar filter) when I use my 4.6x telecentric design and reduce to ~f#=25 but it can be successfully flat-fielded out.
Cheers, Peter.
David: My motivation for using a high magnification telecentric comes from the calculations of Christian Vladrich (http://www.astrosurf.com/viladrich/astr ... lar/FP.htm), in partricular this figure: http://www.astrosurf.com/viladrich/astr ... FWHM-N.JPG. Here, Christian has plotted the bandpass fwhm as a function of focal ratio (f#) for a mica-spaced F-P etalon like the Daystar. Daystar recommends f#>30 for their etalons but you can see from the graph that there is room for improvement by pushing to ~f#=50. I wanted to be sure to maximize the performance of my filter and also had in mind to try stacking the Daystar with a Lunt LS50 etalon. The Lunt is even more sensitive to focal ratio, again according to Christian's calculations. I was even contemplating telecentric designs as high as f#=80 but found it too difficult to reduce to reasonable focal ratios (~ 25 to 35) without severe vignetting. As it is, there is pretty significant vignetting (at the Daystar filter) when I use my 4.6x telecentric design and reduce to ~f#=25 but it can be successfully flat-fielded out.
Cheers, Peter.
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Re: July 2 Proms
Here's an example of vignetting with f46 at the Daystar filter and focal reduction to about f25.
Stacked, deconvoluted, sharpened image on the left, contrast enhancement on the right.
(No flat fielding!)
Cheers, Peter.
Stacked, deconvoluted, sharpened image on the left, contrast enhancement on the right.
(No flat fielding!)
Cheers, Peter.
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Re: July 2 Proms
Hi Peter,
I believe this vignetting is due the Celestron telescope and the reducer, not the filter. Filter is just a several plates.
Flat fielding, of course, will make your images excellet in evenness.
Prominences do not require FF at all.
And you prominences image is quite good for the start with a new setup.
Valery
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.
Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.