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INDI Library v1.8.6 Released (21 Aug 2020)

August 2020 release of INDI Library v1.8.6 introduces new drivers while providing fixes and improvements to existing devices and core framework.

coma corrector increases focal lenght?

5 years 4 months ago
pauledd
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coma corrector increases focal lenght? #4056
Hi there
I recently bought an coma corrector for my f5 (200/1000) Newton. It is said it has an reduction factor 0,95. Doesnt this mean it reduces my telesope focal lenght by .95 from 1000mm to 950mm? But when I attach the corrector to the scope and take an image ekos complains after solving the alignment about a wrong focal lenght and I should correct it to 1141.79mm :huh: .

--= human, without Windows™ =--
pls excuse my bad english! :)

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5 years 4 months ago
fliker09
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coma corrector increases focal lenght? #4057
Don't trust Astrometry - for my 3950 it told me to correct to 4167 :) But may be it is right - my C14 is EdgeHD one... :unsure:

Linux Mint 17.1 + Kubuntu 14.10 hybrid OS, using PPA for latest KStars-bleeding and INDI

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5 years 4 months ago
pauledd
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coma corrector increases focal lenght? #4058
hm ok. I will try once more with and without reducer and compare again. I thought astrometry was quite accurate. I recently took an picture with my DSLR and an tele lens manually set to 200mm. Then I let astrometry solve it. That gave me an value of the image width in arcminutes. Then I calculated
(img_width_pixels*pixelsize*206.3)/img_width_arcs
and viola I got exactly 200mm.

PS.
I just solved one of that raw image taken by ekos again with solve-field. It reported Field size: 84.6535 x 56.6225 arcminutes. Raw dimesnions are 5208 x 3476. Canon700D pixelsize is 4.3.
(5208*4.3*206.3)/(84.6535*60)=909,6mm :blink: So my guess is this is not an astrometry issue?

--= human, without Windows™ =--
pls excuse my bad english! :)

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5 years 4 months ago
knro
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coma corrector increases focal lenght? #4060
What's the pixel scale reported by Astrometry.net?

Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
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5 years 4 months ago
pauledd
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coma corrector increases focal lenght? #4061
pixel scale 0.973685 arcsec/pix
Warning: Spoiler! [ Click to expand ]

--= human, without Windows™ =--
pls excuse my bad english! :)

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5 years 4 months ago
knro
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coma corrector increases focal lenght? #4063
Well, the equation used is:
solver_focal_length = (206.264 * ccd_hor_pixel) / pixscale * binx;

So using 0.973685, we should end up with 910.10 mm. I added one more statement to display the final solver RA, DEC, Orientation and Pixel Scale, so try after tomorrow's update and see if these values mismatch any value from the astromentry.net solver, which I highly doubt it, but there must be a source for this calculation error.

Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
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5 years 4 months ago
pauledd
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coma corrector increases focal lenght? #4066
Strange things here. I just tried again to solve in ekos. Old code, no update. But I used "Load&Slew" to solve the same image as from the comandline. It wont solve until I delete all the prefilled stuff in the plate solve options (-L 48.8141 -H 80.8356 -u aw -3 52.575 -4 59.9908 -5 30 -W) but then It solved and it says
" Current focal length is 1000 mm while computed focal length from the solver is 909.53 mm."
investigating further...

--= human, without Windows™ =--
pls excuse my bad english! :)

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5 years 4 months ago 5 years 4 months ago by pauledd.
pauledd
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coma corrector increases focal lenght? #4067
Solved. I just tried all the calculations with the same values except of ekos pixelsize value set to its default to 5.4 and that gives the mystical 1142mm focal length. I think I AGAIN somehow missed to set my pixelsize prior all other tasks in ekos, that caused the wrong focal lenght. For me that rises again the question of the ability to keep the pixelsize settings from one kstars session to another. Its quite annoying to set these values again and again on restart and I think my equipment will not change for the next year. Just one more question, what is this about the elevation value? Does this affect any calculations or can this ignored completely?
And please apologize for the inconvenience :whistle:

--= human, without Windows™ =--
pls excuse my bad english! :)

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5 years 4 months ago
knro
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coma corrector increases focal lenght? #4068
Pixel size for GPhoto driver is saved, just go to options and click "Save" next to Configuration property, it should load up the next time. Elevation is currently not used.

Jasem Mutlaq
Support INDI & Ekos; Get StellarMate Astrophotography Gadget.
How to Submit Logs when you have problems?
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5 years 4 months ago 5 years 4 months ago by klaus.
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coma corrector increases focal lenght? #4070
I would appreciate having the elevation stored in the resulting fits file as this value is used by my photometry app to calculate the scintillation noise value.


Forget it for now. I need to think about that a bit longer.

CS Klaus

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