Target Framing, Imaging FOV

Astrophotography: share your photos & discuss techniques
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rjbokleman
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Joined: Fri Dec 19, 2014 11:09 pm

Target Framing, Imaging FOV

Unread post by rjbokleman »

Given the recent discussion about framing your target and plate solving, I'm attaching the FOV image below w/Andy's NGC 2336 / IC 467.

This was done in SkySafari Pro 5.0 on macOS, but similar features exist in many other planetarium applications like Stellarium and StarryNight. You can also use tools on the web like http://astronomy.tools for such calculations. This is a good place to start when choosing what camera/scope combination is going to yield the optimal framing for your target. (Assuming you have more than one choice, of course!)

The inner most square (Green Arrow) is Andy's scope w/the QSI640 [ http://www.qsimaging.com/640-overview.html ]. The scope is set at 317mm x 2130mm w/the camera chip on the QSI640 at 15mm x 15mm (4.2MP). Hopefully that's correct.

The next square (Yellow Arrow) is a C8 EdgeHD 203mm x 2032mm w/ASI1600MM-C 17.7mm x 13.4mm.

Finally, the outer most rectangle is my AT130EDT 130mm x 910mm w//ASI1600MM-C 17.7mm x 13.4mm.

Other things come into play here like camera pixel size and focal length (sampling), but that's another discussion for another time.
Attachments
FOV
FOV
NGC2336_IC467.jpg (70.63 KiB) Viewed 5435 times
Ron B.
T5i/700D, ASI1600MM-C, ASI120MM, ASI174MM, XAGYL 7x36mm FW
Astronomik Deep-Sky(RGB), CLS, Ha, OIII, SII
SV60EDS 60mm f/5.5 APO
AT65EDQ 65mm f/6.5 ED Quadruplet
SW ProED 100mm f/9.0 Doublet APO
C8 EdgeHD, AT130EDT
AVX, iEQ45 Pro

http://www.astrobin.com/users/rjbokleman/
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rjbokleman
Posts: 517
Joined: Fri Dec 19, 2014 11:09 pm

Re: Target Framing, Imaging FOV

Unread post by rjbokleman »

Additionally here's my IC 405 framing w/the same scopes and cameras with the addition of the Orange Arrow that shows my AT130EDT w/0.8x Focal Reducer/Field Flattener which brings the scope down to 728mm.

You can see how much wider a field can be captured with the same camera...which is why I used the 0.8x FR/FF on this target with this scope/camera combination.

Hope this helps some folks who are getting started...
Attachments
FOV IC 405
FOV IC 405
IC405_FOV.jpg (148.89 KiB) Viewed 5434 times
Ron B.
T5i/700D, ASI1600MM-C, ASI120MM, ASI174MM, XAGYL 7x36mm FW
Astronomik Deep-Sky(RGB), CLS, Ha, OIII, SII
SV60EDS 60mm f/5.5 APO
AT65EDQ 65mm f/6.5 ED Quadruplet
SW ProED 100mm f/9.0 Doublet APO
C8 EdgeHD, AT130EDT
AVX, iEQ45 Pro

http://www.astrobin.com/users/rjbokleman/
Chuck
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Joined: Tue Mar 31, 2015 1:14 pm

Re: Target Framing, Imaging FOV

Unread post by Chuck »

Good info Ron. I'm currently using Stellarium to do essentially the same thing. It's also got settings for an Off-Axis guider that I've been playing around with while I'm in the planning stages for an OAG and camera.

---- Chuck
Chuck M.

Meade 8" LX200 Classic OTA
iOptron CEM40EC and MiniPier on Meade classic field tripod
Canon EF 200mm f/2.8L II
Canon 7D Mark II
ZWO 60mm f/4.6 GS with ASI120MM-S camera
Starizona SCT Corrector II and Virtual View 2" Rotating Visual Back
Pegasus Astro Pocket Powerbox
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Pete
Astro Day Coordinator
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Re: Target Framing, Imaging FOV

Unread post by Pete »

Lot of work changing setups like that. Need new flats for every time you change a setup, and since I do tee shirt twilight flats it's a bit of work.

Pete
Pete P.
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AndyG
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Re: Target Framing, Imaging FOV

Unread post by AndyG »

Good info Ron, always nice to have good visual examples.

An excellent free tool I find myself using all the time for computing & displaying image scale and field of view is CCDCalc.
Andy
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menardre
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Re: Target Framing, Imaging FOV

Unread post by menardre »

Ron

Thanks for your discussion about framing and plate solving. I am not yet at the point of using either, but from my cursory investigation it looks complex.

Good explanation. I will use your discussion when I advance to that stage of astrophotography.

Roger
Roger M.
Celestron CPC1100 EDGE, Stellarvue 130T refractor dual mounted on iOptron CEM120 on permanent pier mounted in Observatory. Imaging camera ZWO ASI2600 OSC, guide camera Lodestar or ZWO ASI290MM.
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AndyG
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Re: Target Framing, Imaging FOV

Unread post by AndyG »

menardre wrote:from my cursory investigation it looks complex.
I think you will be pleasantly surprised at how easy it is to setup and use. A lot of work has gone in to making it easy to use.
Andy
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rjbokleman
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Re: Target Framing, Imaging FOV

Unread post by rjbokleman »

Roger,

I would agree with Andy on that. It looks complex at first, but it's not all that difficult. We (speaking for myself at least) can certainly help you out when you're ready.
Ron B.
T5i/700D, ASI1600MM-C, ASI120MM, ASI174MM, XAGYL 7x36mm FW
Astronomik Deep-Sky(RGB), CLS, Ha, OIII, SII
SV60EDS 60mm f/5.5 APO
AT65EDQ 65mm f/6.5 ED Quadruplet
SW ProED 100mm f/9.0 Doublet APO
C8 EdgeHD, AT130EDT
AVX, iEQ45 Pro

http://www.astrobin.com/users/rjbokleman/
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rjbokleman
Posts: 517
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Re: Target Framing, Imaging FOV

Unread post by rjbokleman »

Just to continue this a little further, especially for those interested in Astrophotography, how do these applications calculate these values? What is the mathematical formula and does it carry any other significant value, use or meaning?

The purpose of a sensor in any camera is, of course, to capture photons. Sensors vary in size and shape as well as the number of pixels. In essence the size of the sensor and size of the pixels (in microns) determine what is often called Sampling Rate in Arc Seconds per pixel and is calculated as follows:

Code: Select all

Sampling rate (theoretical resolution) in arc seconds = (Sensor Pixel Size / Telescope Focal Length) * 206.265
Or

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Sampling rate (theoretical resolution) in arc seconds = Sensor Pixel Size * (206.265 / Telescope Focal Length)
Another way to think about this is how many arc sec of the night sky does each pixel on the camera sensor actually cover or gather photons from?
  • My Canon 700D/T5i has a sensor size of 5184px * 3456px (17,915,904px) or ~18 Megapixels with physical dimensions of 22.3mm x 14.9mm. Each pixel on the sensor is 4.3um or microns in size.
  • My ZWO ASI1600MM-Cool has a sensor size of 4656px * 3520px (16,389,120px) or ~16 Megapixels with physical dimensions of 17.3mm x 13mm. Each pixel on the sensor is 3.8um or microns in size.
  • My QHYCCD QHY5L-II and ZWO ASI120MM/S guide cameras both use the same sensor (MT9M001) with a 1280px * 960px (1,228,800) or ~1.3 megapixels with physical dimensions of ~4.86mm * ~3.66mm.
Now, let’s take a telescope with an f/9.0 focal ratio: 100mm x 900mm and apply this formula:

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(3.8um (ASI 1600) / 900mm) * 206.265 = 0.870896666666667 arc sec / px
(4.3um (T5i) / 900mm) * 206.265 = 0.985488333333333 arc sec / px
or if you prefer

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(206.265 / 900mm) * 3.8um (ASI 1600) = 0.870896666666667 arc sec / px
(206.265 / 900mm) * 4.3um (T5i) = 0.985488333333333 arc sec / px
Big deal, you say? How does this play into actual Field of View (FOV) in degrees?

If we now take our known Sampling Rate value and multiply it by the number of pixels along each of the sensors X and Y axis we can determine our actual FOV in degrees.

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FOV (degrees) = (Sampling Rate * Sensor Width) / 3600
FOV (degrees) = (Sampling Rate * Sensor Height) / 3600
For the T5i with a sensor size of 5184px * 3456px things now look like this:

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(0.985488333333333 * 5184w) / 3600 = 1.4191032 degrees (W)
(0.985488333333333 * 3456h) / 3600 = 0.9460688 degrees (H)
For the ASI1600 with sensor size of 4656px * 3520px things now look like this:

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(0.870896666666667 * 4656w) / 3600 = 1.126359688888889 (W)
(0.870896666666667 * 3520h) / 3600  = 0.851543407407408 (H)
Wasn’t that fun?

These numbers have value far beyond calculating FOV in degrees. They can influence the overall quality of your images (star roundness), impact guiding, guiding accuracy, and play a very important role in getting Plate Solving working with your particular Camera/Sensor/Telescope combination.

Now, a bit of a challenge. Run your equipment through this process and see what you come up with and reply back to this thread with the results!
Last edited by rjbokleman on Thu Apr 20, 2017 6:30 am, edited 1 time in total.
Ron B.
T5i/700D, ASI1600MM-C, ASI120MM, ASI174MM, XAGYL 7x36mm FW
Astronomik Deep-Sky(RGB), CLS, Ha, OIII, SII
SV60EDS 60mm f/5.5 APO
AT65EDQ 65mm f/6.5 ED Quadruplet
SW ProED 100mm f/9.0 Doublet APO
C8 EdgeHD, AT130EDT
AVX, iEQ45 Pro

http://www.astrobin.com/users/rjbokleman/
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Pete
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Re: Target Framing, Imaging FOV

Unread post by Pete »

I'm running about 1.7 arc-seconds/pixel - slightly oversampled. Given typical local seeing conditions of 3 to 5 arc seconds the Nyquest theory's optimum 2 arc-seconds/pixel seems a reasonable goal for my astrometry application, and probably for general imaging as well.

Pete
Pete P.
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