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July 15 2017: LS50 + CT152

solar imaging accessories
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#1 RickV

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Posted 17 July 2017 - 02:04 PM

For July 15 2017, the Ottawa weather forecast was for "Mainly sunny". lol.gif

Ottawa Forecast.jpg

The Ottawa Clear Sky Chart was for average Transparency and average Seeing.

Ottawa Clear Sky-2.jpg

Not great but Hey... at least it was not clouds and rain as it had been... for a long time!

 

The camera that I used for imaging was a Celestron NexImage 10 color camera (1.67 micron pixels).  During subsequent processing, for each image, the Red, Green and Blue histograms were equalized and then the RGB image converted to grey scale.

 

Here's an grey scale image of the full solar disk obtained with my Lunt LS50THa/B600, focal length = 350mm.

LS50 Grey-800.jpg
 

Here's the RGB false color image of the same.
LS50 RGB-800.jpg

 

Continued in the next post...


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#2 RickV

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Posted 17 July 2017 - 02:11 PM

I added a Vivitar C-mount 1.5X Barlow to the camera... spacing it out from the camera with 8 C-rings... that gave a measured magnification of 2X.

Here's a grey scale image of the sun obtained with my Lunt LS50THa/B600 with 2X Barlow, focal length = 700mm.

LS50+2X Grey-800.jpg

 

Here's a RGB false color image of the same.

LS50+2X RGB-800.jpg

 

I had purposely purchased a Lunt LS50 because I could breach load it into my Canadian Telescope 152mm, F/5.9 with a focal length of 900mm.  I unscrewed the LS50 objective and replaced it with a Lunt energy rejection filter, then inserted the LS50 into the 3 inch focuser of the CT152... three rubber O-rings hold the LS50 in place.  To keep the system an F/7 as was the Lunt LS50, I cut an aperture mask from black plastic and placed that over the 152mm objective lens of the CT152, reducing the aperture to 128.6mm.

CT152 Setup.jpg

 

Continued in the next post...


Edited by RickV, 17 July 2017 - 06:12 PM.

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#3 RickV

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Posted 17 July 2017 - 02:18 PM

Here's an grey scale image of a solar prominence obtained with my CT152/LS50 combo with a measured focal length of 956mm.

CT152+LS50 Prom Grey-800.jpg

 

Here's the RGB false color image of the same.

CT152+LS50 Prom RGB-800.jpg

 

I added a 1.5X Vivitar C-mount Barlow to the camera, spaced with 8 C-rings as before.  The setup looked like this.

CT152 Setup2.jpg

 

Here's a grey scale image of that solar prominence obtained with my CT152/LS50 combo + 2X Barlow with a measured focal length of 1820mm.

CT152+1.5X+LS50 Prom Grey-800.jpg

 

 

Here's a RGB false color image of the same.

CT152+1.5X+LS50 Prom RGB-800.jpg

 

Continued in the next post...



#4 RickV

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Posted 17 July 2017 - 02:20 PM

Here's a grey scale image of sunspot 2665 obtained with my CT152/LS50 combo + 2X Barlow with a measured focal length of 1820mm.

CT152+1.5x+LS50 Sunspot Grey-800.jpg

 

Here's a RGB false color image of the same.
CT152+1.5x+LS50 Sunspot RGB-800.jpg

 

That's all I wrote...
Comments & suggestions are welcome.


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#5 mach2512

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Posted 17 July 2017 - 03:10 PM

I love your ingenuity! 

 

Cheers



#6 ValeryD

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Posted 21 July 2017 - 03:48 PM

>>Comments & suggestions are welcome.

 

Rick,

 

If the whole telescope system  Lunt 50THa has a final F/7,  this does not necessary mean that it's objective is F/7 !!!

 

Youu can measure it's  F/D  very easily.

 

Also, you do not really need an aperture mask at your CT152 objective.  If the Lunt50Tha  objective is really slower than your CT152,  the the etalon optics automatically cuts down the F/6 light cone from your CT152 objective.

If,  however, the Lunt50THa objective is faster than F/6 then you will need to move the etalon closer to the objective so, that it's front lens will intercepts the ligh cone in full 22mm wide.

 

 

Valery



#7 RickV

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Posted 21 July 2017 - 04:43 PM

Hi Valery,

 

final F/7:
a) The LS50 is F/7, 350mm focal length and 50mm objective.  i.e. F# = 350/50 = F/7
b) The CT152 is F/5.9, 900mm focal length and 152mm objective.  i.e. F# = 900/152 = F/5.9

 

c) Combo CT152+LS50

NOTE: In the combo, the 50mm, 350mm focal length objective lens of the LS50 is removed - replaced by an energy rejection filter.  So the Lunt LS50 objective lens plays no role in the combo.

 

I wanted to keep the same F/7 angles for the cone of light in the combo.  To do that I "thought" that I needed to adjust the CT152 from F/5.9 to F/7.  With an objective lens aperture mask of 128.5mm, the F# of the CT152 becomes F# = 900/128.5 = F/7

"Thought": It may be that leaving the CT152 at full aperture of 152mm (F/5.9) would have little effect but since I didn't measure and compare results to a 128.5 masked aperture - who knew for certain.  I will measure that effect in future.

 

Thanks



#8 ValeryD

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Posted 23 July 2017 - 07:32 PM

Rick,

 

You obviously missed the point.  The telescope is F/7 as a whole system.  More detailed:  the refocusing lens in this telescopes has F/7.   This is because of blocking filters native limitations. 

The aperture objective itself can be F/4 or F/5 or F/6 or F/7 or F/8 and so on.  To be sure what the objective F/D really is, you need just to measure it's focal length. Point the objective at the sun and measure where it creates the sun image.

Then calculate the real F/D.  It may be F/7,  but it may be another value.  If it is F/6 than you will win and your scope can

work at a full aperture.

 

 

Valery



#9 RickV

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Posted 24 July 2017 - 07:09 PM

It was cloudy and rainy today... so I measured the focal length inside.

Focal Length = 1 / [ (1/a) + (1/a') ], where
a  = distance from point light source to lens and
a' = distance from lens to place where light focuses to smallest diameter.

 

In my case:
I measured:

The diameter of active objective lens of Lunt LS50 as 50.0mm
a = 346.5  inches (8.8011 meters or 8801.1 mm)
a' = 14.75 inches (374.65 mm)
Focal Length = 1 / [ (1/a) + (1/a') ] = 1 / [(1/8801.1 mm) + (1/374.65 mm) ]
                      = 359.4 mm

F Number: F/ = Focal Length / Lens Diameter = 359.4 mm / 50.0 mm
F/ = 7.2


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