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Astrophotography Evaluation:
Is Bigger Really Better?
Michael Ouzounian
Christian Liberty Academy
11th Grade
Category: Astronomy
Table of Contents
Page
Acknowledgements
1
Introduction
2
Purpose
3
Hypothesis
4
Review of Literature
5
Materials
10
Methods of Procedure
11
Variables Defined
16
Results
17
Conclusion
36
References
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Acknowledgements
I would like to thank my good friend Mr. Percy Mui, Observatory Director at Harper College, for
his supervised use of the following equipment: Canon EOS 1D Mark III digital camera, AstroPhysics Starfire 130 EDT telescope, Takahashi FSQ-106 telescope, and general use of the Karl
G. Henize Observatory facility at Harper College in Palatine, Illinois. I would also like to thank
Mr. Larry Pavell for his advice and support, along with the contribution of the Takahashi Epsilon
180 telescope for previous incarnations of this experiment. And, of course, I thank my parents
for their support, my mom for correcting my grammar, and my dad for checking my math!
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Introduction
This project is the third in a series of astrophotography experiments. My first project, titled
“Astrophotography Evaluation” was a comparison of image processing techniques, namely
combining multiple short-exposure images (that when combined produce a higher signal-tonoise ratio) and comparing them to a regular long exposure. The second project was “Film vs.
Digital.” The name for this project is fairly straightforward. In it I proved the distinct advantages
of using digital technology for astrophotography. Both of these projects deal with imaging media,
and both were based on subjective data. Before high school was over I wanted to do a third
project that was based on hard mathematical data. Therefore this project incorporates
computational quantitative data.
I arrived at this topic after thinking about two things I always hear about telescopes: 1.) that for
visual astronomy a larger aperture is better, regardless, and 2.) that for astrophotography you
want as fast a focal ratio as possible. This train of thought led me to form the purpose for this
experiment.
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Purpose
In astrophotography, will a telescope with a larger aperture really produce a brighter image and
out resolve an instrument with a smaller aperture when they have consistent focal ratios?
In formal physics it is a common known fact that a lens with a smaller aperture will out resolve a
lens of a larger aperture. It is also known that a larger lens will produce a brighter image than a
smaller lens. Do these truths hold water in astrophotography?
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Hypothesis
If two telescopes, both having the same focal ratio but differing apertures, are used to
photograph the same object, then the brightness and resolving power of both lenses will be
approximately the same.
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Review of Literature
This project encompasses many aspects of photography, physics and engineering.
Therefore, to comprehend it completely, a basic understanding of lenses, photography, and
their practical application in astronomy is necessary.
Part 1: Physics for Photography 101
The most important component of a telescope is the lens. Likewise, one of the most
important factors with lenses is their aperture. Aperture is quite simply the diameter of a lens
from edge to edge, in this case, expressed in millimeters. Generally, a change in aperture will
constitute several things: first, it will affect brightness, and second, it will affect resolution. All
things being equal, a lens with a smaller aperture will produce an image that is sharper than a
lens with a greater aperture, and a lens with a larger diameter will collect more light than a
smaller lens, resulting in a brighter image. This is because of Dawes law.
Of equal importance is the telescope’s focal length. Focal length is the distance from the
lens to the focal point, also expressed in millimeters. Why is this so important? Two reasons:
first, it determines the amount of magnification the lens will provide, and second, it plays a large
factor in determining the length and size of the instrument, which is very important when it is not
permanently mounted in an observatory.
In photography, longer focal length equals more magnification. Why? Because
magnification is a direct result of two values – the focal length and the diagonal of the imaging
area. When we divide the focal length of a lens by the diagonal of the imaging area, we get the
magnification. Expressed mathematically, the function is as follows: F/d=M, where F is the focal
length, d is the diagonal, and M is the resulting magnification. For example, let’s say a 500mm
lens is mounted on a 35mm camera. The diagonal of a 35mm frame is ~50mm, which is also
the value for the standard lens. Thus, a 50mm lens results in a magnification of 1x. A 500mm
lens provides a magnification of 10x on a 35mm camera. (500/50=10)
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Now that aperture and focal length have been defined, we move on to the next principle:
focal ratio. Focal ratio is a relationship between an instrument’s focal length and aperture, and
determines the amount of light that will reach the focal plane. The lower the number, the greater
the amount of light falls on the plane. These lower numbers mean that the system is “faster”
than a lens with a higher (“slower”) value meaning that, the higher the number, less light falls on
the plane. For example, an f 10 system is much slower than an f 5 system, meaning if two
exposures of equal length were taken using both systems (assuming they have the same
aperture), less light would be acquired by the f 10 system than the f 5. (Dickenson and Dyer,
2002)
Mathematically, focal ratio can be expressed in the equation F/A=f, where F is the focal
length, A is the aperture, and the resulting answer, f, is the ratio. For example, a lens with a
focal length of 1000mm and an aperture of 100mm would be 1000/100= an f 10 system.
Something else to consider: Which produces a sharper image, the lens with the slower or faster
ratio? Well, all things being equal, if a 1000mm f 10 and a 1000mm f 5 are compared, the f 10
should produce a sharper image because of the smaller aperture. (USCole.com, January 16,
2008)
According to Dr. Michael Covington, “When you photograph extended objects – nebulae,
galaxies, the Milky Way, or objects on Earth – the brightness of the image naturally depends on
the f-ratio of the lens; the lower, the better.” He goes on to say, “Regardless of focal length, the
image of a star is a tiny point. Accordingly, when you’re photographing stars, what matters is not
the f-ratio, but the diameter of the lens.” He follows that up by saying that if both lenses have the
same diameter, they will both resolve the same amount of stars. However, the lens with the
faster focal ratio will show more nebulosity and faint detail, and of course, sky glow. This means
that, in theory, if you are looking to perform minor planet searches, planetary photography, and
viewing novae and clusters, you would preferably use a larger aperture lens, whereas if you
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were photographing extended objects such as star fields, nebulae, and open clusters, you
would chose a faster system.
One other thing should be mentioned. The lenses used in this experiment are
apochromatic, which means they bring all three primary colors to focus at the same point,
eliminating color fringing. This is very important when photographing bright objects, because it
eliminates the “purple halo” seen with achromatic refractors, which bring two colors to focus.
Part 2: The Ultimate Goal of Resolution
The ultimate goal of any imaging system should be resolution, which is the ability to
detect physical details by electromagnetic means. Optical resolution is measured by
determining how many lines per millimeter (lp/mm) that a lens can resolve. This is referred to as
spatial resolution. The amount of lines that can be resolved is dependent on two things, the lens
and the camera.
In this experiment, the “brightness” of a lens was determined by measuring the intensity
(brightness) values of different objects. Using the astro-image processing software MaxDSLR,
luminance, the sum of all the pixels in the analysis window (minus the background), was
measured. It is basically Maxim DL’s proprietary brightness measurement.
The Signal-to-Noise Ratio (SNR) is a ratio of signal to readout noise. MaxDSLR’s help
feature states that: “SNR is calculated as the ratio of intensity to the standard deviation of the
background times the square root of the number of pixels. When measuring a star, an SNR of 3
is usually considered the minimum necessary for detection.”
It should also be noted that all intensity and SNR values are measured in electrons.
Part 3: The Camera
When measuring resolution, the quality of the camera is as important as the quality of
the lens. This is because, when testing a lens you are really testing an imaging system. Having
a research grade optic connected to an inferior quality camera is like putting regular unleaded
fuel into a race car. The performance just won’t be there.
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The camera used in this experiment, the Canon EOS 1D Mark III, is a digital single lens
reflex (SLR) camera. All SLRs allow you to see exactly what will be recorded on the imaging
device using a reflex mirror. In a digital camera the recording medium is a digital silicon chip, in
this case, a Canon engineered and built CMOS (charged metal oxide semiconductor). The
CMOS in the Canon EOS 1D Mark III measures 28.1 x 18.7mm (APS-H size sensor) which
means that it has the same 3:2 aspect ratio as a frame of 35mm film, but is smaller by a factor
of 1.3x (that is, 1.3x smaller than a 24x36mm “full frame” chip). The logical reason for this “crop
factor,” aside from cheaper manufacturing costs, is because it gives a higher pixel density than
a larger chip with the same amount of pixels (more in a smaller space). This is a great
advantage when using this camera for critical work, such as testing resolution. The actual pixel
size of the Mark III’s CMOS is 7.2 microns square, which is relatively small. (Photo.net, January
14, 2008)
Part 4: Astronomy
Besides helping us record images of other worlds in all their beauty and splendor, deep
sky astrophotography is the ultimate real world test for any piece of imaging gear. To resolve
stars as perfect tiny points and resolve extended detail is no easy task. Every component must
function as required to achieve outstanding results. Perfection is to reproduce stars as round
points of light, to keep dead-on guiding accuracy for many minutes, even hours at a time.
In this experiment, four astronomical objects were photographed. Each one is identified
by its Messier Catalog number. (Charles Messier was an 18th century French astronomer who
created a catalog of bright, fixed celestial objects so that he would not mistake them for
comets.) With the exception of the Whirlpool’s companion galaxy, the New General Catalog
(NGC) 5195 is one of the largest catalogs of galaxies, nebulae and clusters of stars. Johann
Louis Emil Dreyer authored the NGC in 1888. It is still astronomy’s standard list of non-stellar
objects.
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The astronomical objects photographed in this experiment are as follows:
M44, the Beehive Cluster, is an open star cluster located almost right on top of the
elliptic in the constellation Cancer. It is very bright for a cluster, and can easily be seen on clear,
moonless nights. It is about 577 light years from Earth. For this project, the intensity of five
stars in M44 was plotted. The five stars can be seen in the photographic reference section of
this paper.
M51, the Whirlpool Galaxy is a spiral galaxy located 23 million light years (mly) from
Earth in the constellation Ursa Major (the Great Bear), located just south of Alkaid (the star at
the end of the handle in the Big Dipper). Its spiral structure is clearly defined because we see it
face on. For this reason, it was the first galaxy which was observed to have a spiral structure by
William Parsons, the Third Earl of Rosse, in 1845.
Messier 81 and 82 are two galaxies located in the northern part of Ursa Major. M81 is a
bright spiral galaxy, while M82 is a dimmer irregular galaxy. They both are approximately 12mly
from Earth, making them some of the galaxies closest to earth, and quite a spectacular pair
indeed.
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Materials
The apparatus and materials used for the astrophotography session were:
Lenses

Astro-Physics Starfire 130EDT refracting telescope

Takahashi FSQ 106mm refracting telescope with matching “Extender Q”
Mounting

Astro-Physics 1200GTO German equatorial mount

Bogen 3047 head and Gitzo 1325 tripod

SBIG STV auto guider
Camera

Canon EOS 1D Mark III Digital Single Lens Reflex (SLR) camera equipped with Canon
Remote timer TC-80N3
Software

Canon Digital Photo Professional V. 3.4

Diffraction Limited MaxDSLR

ImageJ scientific analysis software
Test Target

5mm Koren 2003 lens test chart with gamma 2.0 printed on Brilliant Luster paper
Specifics: Lenses
All lenses used in this test are world-class high performance optics. They are clearly
superior to anything from a major manufacturer, like Canon, because of the higher quality
control. They are designed first and foremost as a lens/mirror, and the rest of the telescope is
built around that. There is no compensation for anything on these telescopes. Let’s have a
closer look at each.
The Astro-Physics Starfire 130EDT is a long-focus apochromatic refracting telescope
with a lens diameter of 130mm and a focal length of 1040mm. This ratio rounds to
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approximately f 8. It employs synthetic ED (extra low dispersion) glass to reduce chromatic
aberration (color fringing). The advantage of ED over a natural crystal (such as fluorite) is that it
does not flux in adverse conditions; in other words, its expansion factors remain constant, no
matter what the temperature. (Company Seven)
The Takahashi FSQ-106 (Fluorite Super Quadruplet) is a short focus apochromatic
refractor having a natural focal length of 530mm resulting in an f 5 system; however, when
mated with the matching “Extender Q” conversion lens, it becomes an 850mm f8 system (as
was used in this experiment). Its optical configuration is a modified Petzval design employing
four optical elements in two groups. The optical structure can be best described by David A.
Novoselsky in his review of the FSQ on www.CloudyNights.com: “… a Petzval design. That
design employs a 'slow' doublet lens cell at the front, but uses a second 'doublet' at the back of
the tube to reduce the focal ratio. Potentially a much shorter scope overall and potentially also
one as well corrected as a triplet.” (Cloudy Nights, January 16, 2008)
Telescope Mounts
In astrophotography, a good mounting is essential to track the movements of the
heavenly bodies. Both mounts used in this experiment are of the German equatorial (GEM)
type. The GEM is essentially an alt-azimuth (normal) mount that has been tilted to the local
latitude and has its right ascension axis pointed towards the North Star, Polaris. What this
means is that the mount can rotate on the Earth’s polar axis, allowing it to counter the apparent
movement of the sky.
On both nights at the Karl G. Henize Observatory the facility’s Astro-Physics
AP1200GTO mount was used. The ‘1200 is a research grade mount, capable of loads up to
approximately 63kg. These mounts are literally used in research facilities in Antarctica. No
information is given on the Astro-Physics Website as to the guiding accuracy of this mount.
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Test Target
The Koren 2003 lens test chart is designed to assist in determining a lens spatial
resolution in lines per millimeter. Developed by Norman Koren, it consists of a series of black
lines that gradually get closer together. By photographing this target with your imaging system
and evaluating in ImageJ software, you can plot the lens the separation of the lines as a sine
wave, and determine the lens spatial resolution.
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Methods of Procedure
The following outlines the procedure followed for taking astrophotographs using a digital SLR
camera for this experiment:
Procedure for Digital Astrophotography & Image Analysis
Step 1
Digital Astrophotography:
Have camera loaded with a compact flash (CF) card, and attach to telescope using
appropriate adapters.
Step 2
Have the Astro-Physics 130mm telescope mounted, and aim it at the first object
(M44 was the first object photographed in this experiment). Calibrate the STV auto
guider, then begin tracking.
Step 3
Set the exposure length on the remote timer (in this case, three or five minutes), and
set the camera’s ISO value to 320. Then open the camera’s shutter. It will stay open
for the desired amount of time. You are now taking the picture. The shutter will
close automatically when the set exposure time is up.
Step 4
Repeat this process until the desired objects have been photographed at the
appropriate exposure times, and with different telescopes.
Technical Data of Objects Photographed
Object
Messier
Number
Magnitude
Celestial
Coordinates
Beehive Cluster
44
+4.7
RA 08 : 40.1
Dec +19 : 59
Whirlpool Galaxy &
companion NGC 5195
51
+8.4
RA 13 : 29.9
Dec +47 : 12
M81 and 82
81&82
6.9 and 9.3
RA 05h 41m
00.0s
Dec 02° 27' 12.0"
Magnitude is the scale on which stars and astronomical objects are rated for brightness; the lower the
magnitude, the brighter the object, and the higher the magnitude, the dimmer the object. The ancient
Greek astronomer, Hipparchus, developed this magnitude scale, also known as the Hipparchus scale.
In essence, the scale ranges from negative 30 to positive 30.
Celestial Coordinates are measured in right ascension (RA) (east west movement equivalent to
celestial latitude) and declination (Dec) (north-south movement equivalent to celestial longitude).
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Step 7
Once all the desired pictures have been taken, download them to your computer.
Process the original Canon CR2 RAW files in Canon Digital Photo Professional and
save them as 16bit TIFF files.
Step 8a
Image Evaluation:
[Photographic evaluation was performed with Diffraction Limited MaxDSLR software.
This software is designed for astronomical image processing. It is similar to Adobe
Photoshop, but is designed exclusively for astrophotographers.]
Open up MaxDSLR, and load the selected image. Then open up the Information Tab
and using the cursor, select the star for evaluation. While evaluating the galaxies,
set the cursor to “large rings” by right clicking and selecting “large rings.” Otherwise,
for evaluating stars in M44, right click and select Ring Size>5.
Here is an illustration:
You should also have set the pointer aperture to “large rings.” This is done by simply right
clicking on the image and selecting “large rings.”
Step 8b
Locate the star you want to evaluate, center it in the analysis aperture, and double
click. This locks the cursor in that position. You can now take readout
measurements from the Information Window. Repeat the process on each target in
the field. It is applicable to all images.
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Procedure for Determining Resolution
The software used for evaluating resolution (in lines per millimeter) was ImageJ, a cross
platform program written in Java by the U.S. National Institute of Health. It is designed for
medical uses, such as evaluation of images taken through microscopes, however, with a little
thinking outside of the box, it was used for this comparison.
Step Procedure for Evaluation in ImageJ
Step
1
Taking the Photos:
Mount the 5mm Koren 2003 lens test chart up against a flat, evenly illuminated surface. In this
experiment, a garage door was used. Mount the Takahashi FSQ telescope on the Gitzo tripod
about 55 feet away. With the camera attached to the telescope, take the photograph. Repeat
the process for the 130mm Astro-Physics telescope, except move the telescope to a distance of
67 feet from the target. This is to compensate for the 1.2x longer focal length of the AP.
Step
1
Step
2
Open up ImageJ, and load the selected image.
Using the line tool, draw a line across the top sine pattern on the Koren 2003 test chart, as
shown.
The accuracy is not overwhelmingly critical, just so much at that it goes from end to end.
Step
3
Now, click Analyze> Set Scale, and enter "known distance" as "25" and "units" as "cm," as shown.
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Step Procedure for Evaluation in ImageJ
Step
4
Then go back and click Analyze>Plot Profile. A sine wave appears plotted on the graph, like this:
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Step Procedure for Evaluation in ImageJ
Step
5
Now, find the midpoint of the Gray Value (i.e., Y=30,000 on the 60,000 scale), and begin
moving the cursor in the positive X direction until the cursor touches the low point of the sine
wave, as shown.
The X value (in this case, 19cm) is how many centimeters down the test chart the lens can
resolve.
Step
6
Using the X value (19), find that value on the Y axis of the 50% MTF chart. Trace a line on the Y
axis until you intercept the MTF slope function. Then draw a line down to (Y=0). The resulting X
coordinate is the lens approximate spatial resolution. This lens has an approximate spatial
resolution of 70lp/mm.
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Variables Defined
Independent Variable

Different apertures and focal lengths

Standard of deviation (in image analysis)

Different glass elements of multiple types

Different optical configurations (triple and quadruple element refractors)
Dependent Variable
Data ranked in four categories:

Luminance measured in electrons

Signal-to-Noise ratio

Resolution in lines per millimeter
Controlled Variables

Same mounts and tracking systems

Camera

Exposure times

ISO Settings
Control Group
Resolution data that was acquired by testing each lens resolution in lines per millimeter.
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Data
Note: Although photographs of all objects were taken on all four nights, the data from April 1623 is sketchy because of the hazy conditions. Therefore only the best photographs were chosen
for evaluation. This also is why there are three nights of data from one telescope, and only one
night of data from the other: April 14 was the only crystal clear night.
Session One
Date:
April 14, 2008
Time:
21:14:53 to 23:13:59 CST
Weather:
Clear, 10* Celsius, with only slight breeze
Location:
Karl G. Heinze Observatory at Harper College, Palatine, IL
Telescopes:
Astro-Physics Starfire 130EDT
Session One, Starfire 130
Image
Number
Object
1
M44
2
3
M81&82
M51
Time
Exposure Started
21:09:11
Exposure Length
(Seconds)
178
21:23:15
21:36:38
300
21:33:24
M44, Beehive Cluster with 130mm
Object
Intensity
SNR
1
2
3
4
5
4471501
4475595
4500000
4336194
4029848
111.854
107.411
117.728
272.471
372.961
M51, Whirlpool Galaxy with 130mm
Object
M51
NGC 5195
Target A
Intensity
SNR
507585.8
457887.5
93721.18
115.44
103.345
30.397
Object
Intensity
SNR
M81
M82
37949140
19640450
324.732
81.968
M81 & 82 Data with 130mm
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Session Two
Date:
April 16, 2008
Time:
21:09 to 23:00 CST
Weather:
Clear, -5.5* Celsius; hazy, wind gusts of 14kmhr
Location:
Karl G. Heinze Observatory at Harper College, Palatine, IL
Telescopes:
Takahashi FSQ-106
Image
Number
1
M81 & 82
Session Two, Takahashi FSQ
Time
Object
Exposure Started
21:04:36
Exposure Length
(Seconds)
300
M81 & 82 Data with 106mm
Object
Intensity
SNR
M81
M82
12375240
6217313
327
64.9
Session Three
Date:
April 20, 2008
Time:
20:30 to 23:00 CST
Weather:
Partially clear, hazy, 10* Celcius, wind gusts of 10kmhr.
Location:
Karl G. Heinze Observatory at Harper College, Palatine, IL
Telescopes:
Takahashi FSQ-106
Session Three Takahashi FSQ 106
Time
Object
Image Taken
Image
Number
1
M44
22:31:27
Exposure Length
(Seconds)
178
M44, Beehive Cluster Data with 106mm
Object
Intensity
SNR
1
2
3
4
5
4361941
4427450
4346386
2761373
2192096
658.053
600.645
670.541
642.62
526.398
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Session Four
Date:
April 23, 2008
Time:
14:00 to 15:30 CST
Weather:
Thin haze, 6.2*Celsius, wind gusts of up to 12kmhr
Location:
Karl G. Heinze Observatory at Harper College, Palatine, IL
Telescopes:
Takahashi FSQ
Image
Number
1
M51
Session Four, Takahashi FSQ
Time
Object
Exposure Started
22:03:17
Exposure Length
(Seconds)
300
M51, Whirlpool Galaxy Data with 106mm
Object
M51
NGC 5195
Target A
Intensity
SNR
898680.3
798545.6
262377.2
40.866
40.31
13.522
Session Five: Resolution Data
Date:
April 23, 2008
Time:
14:00 to 15:30 CST
Weather:
Overcast, 7.2*C, wind gusts of up to 17kmhr
Location:
North Barrington, IL
Telescopes:
Astro-Physics Starfire 130EDT, Takahashi FSQ
Image
Number
1
Object
5mm Koren 2003 lens test chart
Telescope
Astro-Physics 130mm f8
Exposure Length
(Seconds)
1/250 sec
2
5mm Koren 2003 lens test chart
Takahashi 106mm @ f8
1/320 sec
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Telescope
Approximate Maximum
Resolvable Lines Per
Millimeter
Astro Physics Starfire 130EDT
70
Takahashi FSQ-106
51
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Graphs:
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Results
The results of this experiment are lop-sided. On the one hand, the 130mm does produce
brighter objects in two of the photographs (M44 and M81&82), however, it is bested by the
106mm on the Whirlpool Galaxy (M51). This is an interesting observation, however it still is a
two to one victory for the 130mm.
Conclusion
The results of this experiment disprove the hypothesis that the two lenses will perform
approximately the same. As proven, a larger lens is not as sharp as a smaller lens, however,
the larger lens does produce brighter images.
there are some things that we do learn from this experiment, such as:

A larger aperture does produce brighter stars, if brightness is measured in number of
electron counts

A faster focal ratio does show more extended detail. This is not represented in the data,
but clearly evident in the photographs
Things I would have changed about this experiment include:

Shoot on clearer nights

Shooting later in the evening at a darker location

Shoot with more lenses of varying apertures

Perform tests with scientific CCD cameras for increased resolution and sensitivity
Future plans: I completely plan on following up this project in the near future. I feel that it is not
thorough enough, nor conclusive enough. I truly want to know the real answer to my purpose,
and be able to prove it through my own data.
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References
Analog Photography User Group Forums; 4x5 Astrophotography [Online] APGU forums.
Available: http://www.apug.org/forums/forum44/38061-astrophotography-4x5.html [January 19,
2008]
Arnold, H.J.P (2003). Astrophotography: An Introduction to Film and Digital Imaging. Buffalo,
N.Y.: Firefly Books Ltd.
Canon USA consumer products website. [Online]. Canon USA Inc. Available:
http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&fcategoryid=139&modelid=1
4999, [January 21, 2008]
Company Seven Consumer Lines. [Online]. Company Seven, Inc.
Available: http://www.company7.com/astrophy/refractors/130sf-f8.html [2004, Dec. 14].
Covington, M. (2002). Astrophotography for the Armature. Cambridge, U.K. Cambridge
University Press
Dickenson, T. (1998). Nightwatch: A Practical Guide to Viewing the Universe. Buffalo, N.Y.:
Firefly Books Ltd.
Dickenson, T., and Dyer, A., (2002). The Backyard Astronomer’s Guide. Buffalo, N.Y.: Firefly
Books Ltd.
Hedgecoe, J. (1992). The Photographer’s Handbook. London WC2: Dorling Kindersley Press.
ImageJ. [Online]. National institute of Health.
Available: http://rsb.info.nih.gov/ij/ [January 16, 2008]
Mendel, D. (1964). Field Guide to the Stars and Planets. Boston, M.A. Houghton Company.
TakahashiFSQ106Review. [Online]. www.CloudyNights.com . Available:
http://www.cloudynights.com/item.php?item_id=747 [January 16, 2008]
http://photo.net/equipment/canon/1DIII/
http://www.uscoles.com/fstop.htm
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