Various calculations associated with the hardware.
My Hardware - Details specifications on hardware used for imaging and calculations below.
Catching The Light: - Image Scale equation and explanation on utilization.
Astronetry.net - Website allows you to upload your image and it calculates various information associated with it including Pixel Scale, Image Size, and Celestial Coordinates of image.
How to set the correct back focus for your telescope (Guide)
Provided below is a review of calculating the Back Focus.
References
C-11 Imaging Train (QHY 128c)
Type |
Recommended Nominal Back Focus (NBF) |
Visual Back Adapter |
Tilt Plate |
Off Axes Guider |
Filter Wheel |
Camera |
Total | |
Primary Focus |
146.05mm |
67mm |
16.5mm |
5mm |
17.5mm |
22mm |
12.5mm |
140.5mm |
Focal Reducer |
146.05mm? |
67mm |
16.5mm |
5mm |
17.5mm |
22mm |
12.5mm |
140.5mm |
HyperStar
|
|
Spacer |
Filter Tray |
Adjustment Ring |
|
|
Camera |
|
HyperStar
|
55mm |
18mm |
17mm |
6mm |
N/A |
N/A |
18mm
|
59mm |
C-11 Imaging Train (ZWO ASI 6200)
Type |
Recommended Nominal Back Focus (NBF) |
ARCO 2" Rotator |
Visual Back Adapter |
Filter Tray |
Off Axes Guider |
Filter Wheel |
Camera |
Total | |
Primary Focus |
146.05mm |
67mm |
22mm |
16.5mm |
17.5mm |
N/A |
N/A |
12.5mm |
135.5mm |
Focal Reducer |
146.05mm? |
67mm |
22mm |
16.5mm |
17.5mm |
N/A |
N/A |
12.5mm |
135.5mm |
HyperStar
|
|
Spacer |
|
|
|
|
|
|
|
HyperStar
|
55mm |
|
|
|
42.0 mm |
N/A |
N/A |
12.5mm |
54.5mm |
Note the ESATTO Focuser has a 15mm travel range, assuming we start at dead center of travel range, we have a +/- adjustment range of about 7mm.
Image scale calculations require you know the Focal Length of your optical train. This can be rather difficult with the various possible hardware configurations. It may be easier and more accurate to obtain the Image scale by taking a photo with the configuration and obtain the Image Scale from Astronetry.net, and back-calculate the Focal Length. This is how the values below were calculated.
Image Scale: How to determine Image Scale for your setup
P" = (8×S)/FL
Focal Length: How to determine Image Scale for your setup
FL = (8×S)/P"
Where :
P” = Image scale/pixel in Arc seconds
S = Size of pixel in microns
FL = Focal Length in inches
Under/Over sampled?
Typical Seeing Conditions = 2 arc Seconds this means Ideal image scale should be 1.0 to 1.5 arc seconds/pixel.
In the table below purple values represent calculated values while green values represent measured or provided by vendor.
Telescope Configuration |
Focal Length (FL) (Inches) |
FL (mm) |
Sensor Pixel Size (S) (Microns um) |
Measured Image Scale (P") (arcsec/pixel) |
Under/Over Sampled |
Measured Image Size (arcmin or Deg) |
Comments |
C-11 HD | ZWO ASI-6200 | |
110.24" |
2800 mm |
3.76 um |
0.280 |
OverSampled |
44' 39.1" x 29' 47.2" |
Ideal 0.67" - 2" |
C-11 HD | Reducer | ZWO ASI-6200 | |
77" |
1960 mm |
3.76 um |
0.393 |
Slight OverSample |
62' 39.5" x 41' 47.9" |
|
C-11 HD | HyperStar | ZWO ASI-6200 | |
21.26" |
540 mm |
3.76 um |
*1.4 |
OverSampled |
|
|
C-11 HD | ZWO ASI-6200 | Bin 2x2 | |
110.24" |
2800 mm |
7.52 um |
|
|
|
Ideal 0.67" - 2" |
C-11 HD | Reducer | ZWO ASI-6200 | Bin 2x2 |
|
77" |
1960 mm |
7.52 um |
0.783 |
Good |
62.5 x 41.7 |
|
C-11 HD | HyperStar | ZWO ASI-6200 | Bin 2x2 | |
21.26" |
540 mm |
7.52 um |
*0.55"
|
Slight Oversample |
|
|
C-11 HD | ZWO ASI-6200 | |
110.24" |
2800mm |
3.76 um |
0.273" |
Oversample |
|
Typical Primary Configuration indicates you should process as 2x2 bin for 0.546" image scale |
C-11 HD | QHY128 | |
110.24" |
2800mm |
5.97 um |
0.444 |
Oversampled |
44.9' x 30.2' |
Typical Primary Configuration |
C-11 HD | Reducer | QHY128 |
77" |
1960 mm |
5.97 um |
*0.62 |
Oversampled |
*60' x 45' |
Typical Reducer Configuration |
C-11 HD| Reducer | ZWO ASI-6200 | |
77" |
1960 mm |
3.76 um |
0.391" |
Oversampled |
|
Typical Reducer Configuration indicaste you should process as 2x2 bin for 0.781" image scale |
C-11 HD | HyperStar | QHY128 |
21.26" |
540mm |
5.97 um |
*2.25 |
Undersampled |
*3.8° x 2.5° |
Typical HyperStar Configuration |
C-11 HD | TeleVue Barlow 2X | QHY128 |
95.329" |
2,422mm |
5.97 um |
0.501 |
Oversampled |
25.3' x 17' |
|
C-11 HD | TeleVue Barlow 4X | QHY128 |
|
|
5.97 um |
|
|
|
|
Takhashi FS-60C | ZWO 17mm Mini |
13.7478" |
349mm |
5.86 um |
3.41 |
Undersampled |
110' x 69' |
Standard Finderscope Configuration |
TPO UtraWide 180 F/4.5 | ZWO 17mm Mini |
7.087 |
180mm |
5.86 um |
6.73 |
Undersampled |
3.62deg x 2.27deg |
Standard Finderscope Configuration |
Resources:
What is Dithering - Astro Backyard
Use Hubble's Drizzle to improve your Astrophotos! Drizzle history and tutorial in Pixinsight - Dylan O'Donnell
Drizzle: Reconstructing Undersampled Images - A.S. Fruchter & R.N. Hook
Dither is a technique used when capturing images in astrophotography to help create a better signal-to-noise ratio and is the process of slightly shifting the pointing direction of your telescope between exposures.
Drizzle is a technique applied after images have been captured and was developed by NASA to reconstruct undersampled images. In the Image below, the Top Left image represents the original object, the Bottom Left is the captured image, and the Bottom Right is the captured image with Drizzle applied to it. This technique is applied to images when processing (IE in Pixinsight)
Ref: Drizzle: Reconstructing Undersampled Images - A.S. Fruchter & R.N. Hook
Image scale calculations require you
Stark Labs: Gain Offset and Bit Depth - Great details on how this stuff comes together
ZWO: Pixel Binning - Calculations on binning.
Sky Background Electron Rate - Details specifications on hardware used for imaging and calculations below.
Camera |
Bin |
|
Comments |
ZWO ASI6200 Pro |
1x1 |
|
|
ZWO ASI6200 Pro |
2x2 |
|
|