Introduction

Here we will cover the basics on optimal hardware setup for imaging Solar System Objects.

References

Imaging times

Reference: A Guide to DSLR Planetary Imaging: Planetary Rotation and Detail Smearing

When using lucky Imaging, time is limited due to the fact the object may be rotating.  Here is a summary of rule-of-thumb imaging time limits for video capture assuming 0.5 arcseconds of detail smearing allowance:

Object

Max Time

Sunspots

3 minutes

Jupiter

2 minutes

Saturn

5 minutes

Mars

4 minutes

Moon

5 minutes

Barlow Lens

Reference: A Guide to DSLR Planetary Imaging: Sampling

 

First we need to determine the Optimal Magnification for our hardware.  We want to get the most detail possible given the seeing conditions, scope and camera capabilities  This is determined by the following variables:

We start with the assumption that the Optimal Focal Ratio (Ofr) of the imaging system should be 5-7 times the camera pixel size based on seeing conditions (5 for average, 7 for exceptional), so we will go with 6 time the pixel size in these calculations.

Ofr = 6Cps

Assuming our camera and our scope are not easily changed, we cant change those variables, what we can do is change the Imaging System Focal Ratio by adding a Barlow lens if necessary to try to get to the Optimal Focal Ratio (Ofr), or use Eyepiece Projection.  Here we determine the appropriate Barlow Lens Magnification (Bx)

Bx = (5-7)Cps/Sfr

Here is what I have calculated for some hardware, where Barlow Magnification magnification is from good to excellent conditions (5-7):

Scope

Focal Ratio (Sfr)

Camera

Pixel Size

Sensor Dimensions (mm)

Recommended Barlow Magnification

C-11 HD

Sfr = 10

QHY128c

Cps = 5.97 um

36.03 x 24.05

Bx = 3.0x - 4.2x

C-11 HD

Sfr = 10

ZWO 174MM Mini

Cps = 5.86 um

11.3 x 7.1

Bx = 2.9x - 4.1x

 

 

ZWO ASI120MC-S $134

ZWO AZI120MM-S $161

Cps = 3.75 um

4.8 x 3.6

Bx = 1.9x - 2.6x

Questar 3.5"

Sfr = 14.4

QHY 128c

Cps = 5.97 um

36.03 x 24.05

Bx = 2.1x - 2.9x

Will it Fit?

References

 

Now that we know the Optimal Magnification and have determined what Barlow lens we need, we need to determine if the image will fit on our sensor, and what wiggle room we have, because as we are capturing the image, things tend to drift.  First consideration is the size of the object you are imaging.  While the sun and moon stay the same size throughout the year, the planets vary based on how close they are to the earth.

 

Apparent Size of common objects in the solar system

 

Object

Apparent Size

Sun

31.6' - 32.7'

Moon

29.4' - 33.5'

Mercury

4.5" - 13"

Venus

9.5" - 66.0"

Mars

3.5" - 25.1"

Jupiter

29.8" - 50.1"

Saturn

33.7" - 46.8"

Uranus

3.3" - 4.0"

Neptune

2.1" - 2.3"

Pluto

0.065" - 0.115"

 

 

 

Field of View

Configuration

F Ratio

Resolution

Field of View (deg)

 

Dawes Limit

Ideal Targets

Simulated Images

| C-11 | 0.7 Reducer | QHY128c |

7.0

0.63" x 0.63"

1.05 x 0.7

0.41"

Moon, Sun

,

|C-11  | 4x Barlow | Canon 60D |

40

0.08" x 0.08"

0.11 x 0.08

0.41"

Planets, Sunspots

,

|C-11  | 2x Barlow | ZWO 174MM |

20

0.22" x 0.22"

0.12 x 0.07

0.41"

Planets, Sunspots

,

 

|C-11  | 4x Barlow | ZWO 174MM |

 

40

0.11" x 0.11"

0.06 x 0.04

0.41"

Planets, Sunspots

,

|C-11  | 2x Barlow | ZWO 120MM |

20

0.14" x 0.14"

0.05 x 0.04

0.41"

Planets, Sunspots

,

|C-11  | 4x Barlow | ZWO 120MM |

40

0.07" x 0.07"

0.02 x 0.02

0.41"

Planets, Sunspots