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Working out Field of View for ASTAP?

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#1 bluesilver

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Posted 24 July 2021 - 03:45 AM

Hi,  I am going to give ASTAP a go with point craft in the program Astrophotography tool ( APT )

I was just going through reading the download information  / instructions for ASTAP

It was talking about installing either the H17 star database or the H18 Star Database

It then goes on to say:

Select the H18 if your FOV is less then one degree

 

So i am just a tad stuck on trying to figure out what by actual field of view is.

I have been playing around with astronomy.tools calculator to try and work things out,  but i think i might be miss reading the information.

 

My scope is a Skywatcher Evostar150ED

Camera is ASI2600MC

 

Using the imaging tab with all the details entered i get a figure in the field of view of 1.12° x 0.75°

 

So sorry for going over what i guess must be the basics,  but from this would that suggest that i would be best of going with the H18 Star database?

Just as i am a tad over 1 degree in one way but under in the other.

 

Any advise would be appreciated.

Thanks.

 



#2 han.k

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Posted 24 July 2021 - 06:05 AM

There is no penalty for installing the H18 except for some more disk space usage (1 gbyte instead of 580 mbytes).

 

The FOV is for ASTAP defined as the image height. So the field of view is then 0.75° assuming you image is in landscape You can check your FOV by blind solving  an image in ASTAP or nova.astrometry.net. For blind solving in ASTAP, load an raw image in the ASTAP program, go to the stack menu (ctrl+A), select tab alignment and select in "Field of view (height)" AUTO and in "Radius search area" 180 degrees. Then hit the button "Solve current image". After a few minutes the image is most likely solved and the image height will be displayed. After solving the Image dimensions in degrees are also visible in the status bar of the viewer.

 

There is also a FOV calculator in ASTAP in the tab "Pixel math 2"

 

Han



#3 alphatripleplus

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Posted 24 July 2021 - 08:09 AM

Moving from EAA to Astronomy Software & Computers for a better fit.



#4 bluesilver

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Posted 24 July 2021 - 05:46 PM

Thanks for the reply,  a pretty good detailed reply there.

There is a lot to learn with a program that i haven't used yet unfortunately.

 

I have found out now how astronomy.tools calculator got those numbers and i think they could be a tad out,   as using the chip size of the ASI2600MC 23.5 x 17.5mm and the focal length of the scope 1200mm 

you get the figures of 1.12° X 0.83°  vs astronomy.tools figures of 1.12° x 0.75°

 

So 1.12° X 0.83° gives you a figure of 0.93° for the fov

 

Dose all this sound about right?

Therefore i should be looking at the H18 star map as it is for a fov less than 1°


Edited by bluesilver, 24 July 2021 - 06:18 PM.


#5 han.k

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Posted 24 July 2021 - 11:09 PM

Yes install the H18.

 

I checked here and a 1200 mm telescope combined with a sensor pixel size of 3.76um and 6248x 4176 pixels gives 1.12 x 0.75°.  I assume a small part of the 23.5 x 17.5 mm sensor is not used for imaging. The FOV setting of ASTAP is not so critical but I would recommend to be within ±5% correct.

 

If you solve an image, you will most likely notice that the actual FOV is a little different depending on the distance of the camera from the telescope. but it all doesn't matter so much for solving. For a good quality image, an FOV error of 30% will still result in correct solving but less reliable. ASTAP will give a warning if the specified FOV is more than 5% different then found by solving.

 

Han



#6 bluesilver

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Posted 25 July 2021 - 02:03 AM

Thanks heaps,

I will go with the H18

Very much appreciated




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