Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 1 NAME Name Group NAME Name Date Introduction to Telescopes 7 Lab Scopes Celestron CPC 800 SCT 11073 XLT (8 inch F/10) Research Scope: Meade LX200-ACF (14 inch F/10) Cassegrain Focus Telescope Ritchey-Chretien design Some Links on Telescope information Ritchey-Chretien Telescopes: http://en.wikipedia.org/wiki/ritchey-chretien Celestron Telescope Co: http://www.celestron.com/ New CPC 800 info: http://www.celestron.com/portal/celestron-cpc-800-gps-xlt.html New CPC 800 Telescope Manual: http://www.celestron.com/c3/images/files/downloads/1250207163_cpcmaster0809.pdf Old C-8 info: http://www.company7.com/celestron/products/sch4.html Old C-8 Telescope Manual: http://www.company7.com/library/celestron/celestar8.pdf History of Celestron Company: http://en.wikipedia.org/wiki/celestron Meade Telescope Company: http://www.meade.com/ Meade LCX200-ACF (14 inch F/10): http://meade.com/lx200
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 2 Part A: Real Image [Indoor] Each lab station will have one big lens (your objective ), and one or more smaller ones (your eyepieces ). To start, use a distant object (i.e. other side of room) and make a real image appear on a white screen. Probably we will need to darken the room and use desk lights to illuminate objects. 1. Measure Parameters of BIG Lens (a) What is the aperture (diameter of lens)? A = cm (b) What is the focal length (distance from lens to image)? F o = cm (c) What is the focal ratio? F/A = 2. Real Image: Take a look at your image on the screen, explore and discuss the following. Is the image erect, inverted, reversed, or both? How can you tell? [Hint see figure 4b in IT handout]. 3. Measure Parameters of small Lens (a) What is the aperture (diameter of lens)? A = cm (b) What is the focal length (distance from lens to image)? F o = cm (c) What is the focal ratio? F/A = 4. Aberrations: Discuss: Do you see any evidence of aberrations or distortions? Make sketches to illustrate the effects. [Hint, chromatic aberrations would be seen as rainbows at edges of lines, coma is when a the image of a dot looks like it flares out on one side. You might need to do some research on the web to figure out what these are!]
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 3 Part B: Aperture Stops [indoor] Each lab station will have one big lens (your objective ). Here use a fairly bright source as your object (e.g. desk light, or desk light illuminating an object). Again focus the lens to make an image on a white screen. You will then put aperture stops right next to your lens and see the effect. 1. Aperture Stop: Make a sketch of the aperture stop pattern used. 2. Predict: Before you do anything, try to guess how the aperture stop will affect your image. Describe briefly (sketch) your idea and logic behind it. 3. Apply the Aperture Stop and see how the image changes. Put the aperture stop right up against the lens. Describe how the aperture stop did affect the image [hint, is it brighter/fainter, different size? Clearer? Less/more aberrations? Does it matter if you move the aperture stop around?] Also, comment on whether your prediction was close to what you observed. 4. Use another stop: Describe (sketch) the pattern of the (second) aperture stop, and again summarize the results. Compare/contrast the affect with your first aperture stop.
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 4 Part C: Magnifying Glass: Virtual Images [indoor] 1. Use a big lens as a magnifying glass. When you look through the lens at a close object, is the image you see should be magnified. Note the object must be closer to the lens than the focal length else it won t work right. This is essentially the function of eyepieces in optical instruments such as microscopes and telescopes. (a) What is the aperture (in cm)? (b) What is the focal length (in cm)? A = cm F o = cm (c) Discuss: Is the image bigger or smaller than the object? Does the image appear to be closer or further away than the object? Is it erect, inverted, reversed or both? [Hint, make a drawing of your setup] 2. Use small lens as magnifying glass (a) What is the aperture (in cm)? (b) What is the focal length (in cm)? A = cm F e = cm (c) Discuss: Use your second lens as a magnifying glass. Compare what you see with question #1c above. How did the size and distance to the image change with the different focal length? [Hint: does a short focal length mean bigger magnification or smaller?]
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 5 Part D: Refracting Telescope [indoor] Using your big and small lens, you will construct a small telescope (see figure 6 in IT handout). Use big lens as your objective Use small lens as your eyepiece (ocular) 1. Parameters of lenses (a) What is the focal length of the objective? (b) What is the focal length of the eyepiece? F o = cm F e = cm 2. Observation (a) What is your target object? (b) How much bigger does it look through the telescope? (c) Summarize: is the image erect, inverted, reversed, or both? Any aberrations seen? 3. Theory (a) Calculate the expected magnification: M=F o /F e = (b) Compare your observed magnification [#2b] with the theoretical one [#3a]. How close are you? 4. Second Eyepiece: Use a different eyepiece, and comment on the changes. (a) What is the focal length of this eyepiece? F e = (b) Calculate the expected magnification: M=F o /F e = (c) Comment: does image appear bigger or smaller? Is it what you expected?
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 6 Part E: Telescope Magnifying Power [indoor prep] For information on our telescopes consult equipment manuals available either on blackboard or at website. This is done indoor Calculations are done for both the 8 inch and 14 inch scopes. 1. Telescope Objective Mirror Parameters (a) Aperture (inches): 8 inch 14 inch (b) Aperture (cm) [hint 2.54 cm = 1 inch]: (c) Focal length (in cm): (d) Focal Ratio: (e) Summarize: What type of focus is the telescope (hint: Newtonian, Coude, Cassegrain)? How do you know which it is? 2. Eyepieces [8 inch] [14 inch] (a) Assuming eyepiece of Fe= mm calculate magnification power: (b) Assuming eyepiece of Fe= mm calculate magnification power: (c) Assuming eyepiece of Fe= mm calculate magnification power: 3. FINDERSCOPE Parameters (for C-8 telescope) (a) Lookup the expected magnification of the finderscope: M = [Note this will be printed on the eyepiece of finderscope, e.g. if it says 9x50mm it means the eyepiece is a 50 mm, and the power is 9x.] (b) Summarize: The finderscope is a small telescope. What type is it?
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 7 Part F: Outdoor Telescope Observation If it is clear, we will go outside and do some observations. The actual targets may change on spur of the moment due to obstructions, sky conditions and availability. 1. Magnification View an object at low power and then at high power and experience what magnification does. View Jupiter using 40 mm eyepiece. Make a sketch of what you see in the eyepiece. Switch to a higher magnification (what mm eyepiece?). Again sketch what you see. Comment: How does the higher magnification affect what you see? Try to be quantitative. 2. Light Gathering Power Observe Comet Lovejoy using a 40 mm eyepiece. Note the intensity of the image. Switch to a much higher magnification (what mm eyepiece?). Comment: How does the higher magnification affect the brightness of what you see? 3. Resolving Power Use the 40 mm eyepiece Target: point telescope a close double. Possibilities (Winter 2015) are: Wide: iota Cancri (31, mag 4.2 and 6.6) Medium: Polaris (18, mag 2 and 9) Narrow: Gamma Andromedae (name Almach ) [10, mag 2.3 & 5). Look at star in finderscope. Does it appear to be one star, or can you see two? Look at star in the 40 mm eyepiece, again, does it appear to be one star or can you resolve it into two stars? Look at star with higher magnification (what mm eyepiece used?), and again see if you can resolve it. Comment: How much magnification was required to resolve the double? Is this consistent with a calculation of the limiting resolution of that eyepiece? [ 120 divided by the magnification power].
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 8 Part F Object Observations Name Group# Date Name Telescope Name= Aperture= Focal length= Object Information Name= Magnitude Catalog # Constellation RA Dec Notes/Description: Finderscope View Power Field Notes: Eyepiece Focal Length Eyepiece Focal Length Magnification Power: Magnification Power:
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 9 Part F Object Observations Name Group# Date Name Telescope Name= Aperture= Focal length= Object Information Name= Magnitude Catalog # Constellation RA Dec Notes/Description: Finderscope View Power Field Notes: Eyepiece Focal Length Eyepiece Focal Length Magnification Power: Magnification Power:
Printed: Jan/13/2015 Intro to Telescopes Activities Page IT- 10 Part F Object Observations Name Group# Date Name Telescope Name= Aperture= Focal length= Object Information Name= Magnitude Catalog # Constellation RA Dec Notes/Description: Finderscope View Power Field Notes: Eyepiece Focal Length Eyepiece Focal Length Magnification Power: Magnification Power: