Astronomy: Field of View Concepts

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Questions and Answers

What is the true field of view (TFoV) of a 25mm Plossl eyepiece in Hadley?

1.4 degrees (correct)

50 degrees

36x

0.68 degrees

What is the approximate apparent field of view (AFoV) for a 25mm Plossl eyepiece?

50 degrees (correct)

36 degrees

1.4 degrees

68 degrees

Which eyepiece is considered the better option for budget high-power eyepieces?

20mm Plossl

15mm Goldline

6mm Redline (correct)

9mm Aspheric

What magnification does a 6mm eyepiece produce in Hadley?

150x Signup and view all the answers

How much does a 32mm Plossl eyepiece typically cost?

$25-30 USD Signup and view all the answers

Which statement correctly describes the 9mm eyepiece?

It produces a power of 100x. Signup and view all the answers

What is a significant disadvantage of using a 6mm eyepiece?

It has a smaller field of view. Signup and view all the answers

Which eyepiece is recommended as a minimum-cost option?

23mm Aspheric Signup and view all the answers

Which of the following eyepiece sizes does Hadley accept?

1.25 inch eyepieces Signup and view all the answers

What is the primary focal length of the mirror set recommended for the Hadley telescope?

900mm Signup and view all the answers

Which type of screws are specified for use in the Hadley telescope assembly?

#10-24 machine screws Signup and view all the answers

Which eyepiece focal length is recommended for producing low power magnification?

25mm Signup and view all the answers

What type of mirror is included in the recommended mirror set for Hadley telescopes?

Elliptical flat and spherical primary Signup and view all the answers

Which type of eyepiece should be avoided due to distortion at short focal lengths?

Plossl and aspheric Signup and view all the answers

How many #10-24, ½ inch long machine screws are recommended for assembly?

50 Signup and view all the answers

What is the approximate cost of a 'd114/f900mm' mirror set?

$30 USD Signup and view all the answers

What is a notable feature of the 82 degree 16mm UWA eyepiece compared to a 25mm Plossl?

It has a similar true field of view. Signup and view all the answers

Which characteristic makes the 82 degree 16mm UWA eyepiece a valuable investment for astronomy enthusiasts?

It has an exceptionally wide apparent field of view. Signup and view all the answers

What type of eyepiece design should be avoided due to poor focus and distortion?

Short Focal Length Aspheric or Plossl Eyepieces Signup and view all the answers

What is a common drawback of eyepiece kits?

They include a variety of unnecessary accessories. Signup and view all the answers

Why might someone consider deferring the purchase of the 82 degree 16mm UWA eyepiece?

Given the expense, it may be best as an upgrade later. Signup and view all the answers

What is the recommended adhesive size when applying silicone to the secondary mirror holder?

Roughly 5mm in diameter Signup and view all the answers

What should be done immediately after applying adhesive to the secondary mirror holder?

Press the secondary mirror into the adhesive Signup and view all the answers

How long should the adhesive be allowed to cure before mounting to the Upper Tube Assembly?

1-2 hours Signup and view all the answers

Which of the following practices should be avoided when handling the mirrors?

Touching the reflecting surface Signup and view all the answers

What type of screws are used to attach the spider and secondary mirror assembly to the Upper Tube Assembly?

3 short screws, ½ inch long Signup and view all the answers

What must be done with the screws after they are seated in the primary collimation cell?

Tighten them further to ensure secure seating Signup and view all the answers

Which component of the assembly ensures the smooth turning of the middle tube?

The crescent bearings Signup and view all the answers

What is the purpose of compressing the screws in the primary collimation cell?

To adjust the position and angle of the mirror Signup and view all the answers

What should be verified during the fitting of the crescent bearings?

That they are oriented with the curved surfaces aligned Signup and view all the answers

What can be said about the ends of the bolts in relation to the nuts?

It is acceptable for them to be below the end of the nuts Signup and view all the answers

What should be done first before assembling the primary knobs?

Insert the standard nut into the hexagonal pocket Signup and view all the answers

Which action should be avoided during the tightening of screws in the primary collimation cell?

Tightening them completely from the start Signup and view all the answers

What is indicated for the proper orientation of the crescent bearings during assembly?

The smooth side should face outward Signup and view all the answers

Study Notes

Field of View

"Field of view" encompasses "true field" (TFoV) and "apparent field" (AFoV).
True field (TFoV) represents the sky's arc size visible through the eyepiece, e.g., a 25mm Plossl offers a 1.4° TFoV in Hadley.
Apparent field (AFoV) indicates how wide the view presentation is for the observer; a 25mm Plossl has an approximate AFoV of 50°.

Low-Power Eyepieces

25mm Plossl: Priced around $20 USD, recognized for sharpness and versatility.
23mm Aspheric: Available for $12 USD, softens images and has a tendency to misstate FoV around 50°.
32mm Plossl: Costs $25-30 USD, ideal for wider views to easily locate celestial objects.

High-Power Eyepieces

Redline/Goldline series: Available in 6mm, 9mm, 15mm, and 20mm; the 6mm and 9mm are superior options.
9mm: Delivers 100x power with a 0.68° TFoV.
6mm: Provides 150x power with a 0.44° TFoV, favored for planetary and lunar observations while demanding more frequent adjustments due to a narrower field.

Advanced Eyepieces

82° 16mm UWA: Costs around $99 USD; provides an exceptionally wide AFoV and sharp images likened to high-end eyepieces.
82° 7mm UWA: About $99 USD, similar power to 6mm or 9mm eyepieces, allows for a larger field and easier planet finding.

Eyepieces to Avoid

Short Focal Length Aspheric or Plossl Eyepieces: Poor focus and distortion due to their use of acrylic lenses.
Eyepiece Kits: Often include poor-quality eyepieces and unnecessary extras, compromising overall viewing experience.

Telescope Assembly

Mirror Requirements: A mirror pair (primary and secondary) is essential, with the Hadley telescope only accepting 1.25" eyepieces.
Low-Power Options: A 25mm Plossl is superior for clarity, while a 23mm Aspheric is more affordable but less sharp.
High-Power Options: Consider "66°/68° UWA" or "TMB Planetary" in 6mm or 9mm, avoiding short focal lengths that distort viewing.

Assembly Steps Overview

Primary Knob Preparation: Standard nuts are used with screws in mirror cell assembly, ensuring easy adjustment.
Middle Tube Assembly: Houses bearing wheels for smooth mount pivoting.
Mirror Adhesive Application: Essential for securely attaching both primary and secondary mirrors, requiring caution to avoid touching reflective surfaces.

Final Steps

Following mirror and optical tube assembly, mirror alignment and focus adjustments are crucial for effective telescope use.

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Description

Explore the key concepts of true field and apparent field as they relate to eyepieces in astronomy. This quiz covers important definitions and calculations for understanding how magnification affects views through telescopes. Perfect for students and enthusiasts looking to deepen their knowledge of telescopic observations.