F number telescope. I have indicated those which don't do anything visually.
F number telescope. In this article, I’ll explain what focal ratio is and how it impacts a telescope’s ability to gather light Jul 19, 2006 · The f/number does affect a telescope’s magnification (with a given eyepiece), and the magnification determines the surface brightness of the view: the amount of light per square arcminute as presented to your eye. Simple two-element Huygens and Ramsden eyepieces with apparent fields of up to about 40° work quite nicely with high f/number F-Number and Numerical Aperture Figure 1 shows a lens of clear aperture D, collecting light from a source and collimating it. Dec 3, 2012 · A few of these don't do anything interesting, or even anything visible. But what is the best focal ratio for astrophotography? The short answer is that you want a fast focal ratio for deep sky imaging, but a slower focal ratio can be adequate for planetary imaging. Dec 31, 2021 · Effective telescope f number - posted in Electronically Assisted Astronomy (No Post-Processing): I am somewhat confused about effective f-number for my telescope. But what is a good focal ratio for a telescope, and how does it affect your viewing experience? The f-numbers can go from 1 to, theoretically, infinity, but most casual telescopes have an f-number in the range of f/4 to f/14. Eyepiece Focal Length: This determines the "power" an eyepiece delivers on a given telescope; the shorter the focal length, the higher the magnification. F/ = f / D May 27, 2025 · The focal ratio (f/ratio in short) is the ratio between a telescope’s focal length and its aperture. For example, I read a 4 f/4 APO is better for deep sky imaging than a 10 f/10 Telescopes The small exit pupil of a 25×30 telescope and large exit pupils of 9×63 binoculars suitable for use in low light For a telescope, the diameter of the exit pupil can be calculated by dividing the focal length of the eyepiece by the focal ratio (f-number) of the telescope. Aug 31, 2017 · Use this telescope calculator to tell you how changing out eyepieces and accessories will affect your telescope's performance. I have indicated those which don't do anything visually. The reciprocal (1/V) is called the aperture value 'k' (f-number). Generally, the lower the f/number of the telescope, the greater the optical complexity of the eyepiece needed to produce good images. So, the focal length is equal to the aperture times the focal ratio. In The focal ratio (the number following the "f/") is merely the focal length of the telescope divided by the aperture. format or %) For example, let's s Jan 13, 2009 · Well, one of the primary usability considerations is evenly-distributed groups, so either your current idea (0-9, A-F, etc. The same rules specified for fprintf apply for printf, sprintf and similar functions. Mar 6, 2024 · Focal ratio is the simple formula F/D, where F is the focal length of the telescope and D is the diameter of the telescope’s aperture. It is still defined as the focal length f of an objective divided by its diameter D or by the diameter of an aperture stop in the system. A focal ratio between f/6 and f/9 is said to have a “medium” focal ratio, while focal ratios of f/10 or higher are said to be “long” and the telescope is described as “slow”. F3 + S - "Force Reload" - Visually, does little (lags, flickers) F3 + T - Refresh Textures - Visually, does little (lags, flickers) Shift + F3 + F - Increase Render Distance F3 + F - Decrease Render Distance F3 + A - "Load Renderers" - (essentially reloads all visual Oct 4, 2019 · This is called f-strings and are quite straightforward : when using an "f" in front of a string, all the variables inside curly brackets are read and replaced by their value. , (10/5) 2). g. aka "Stealth" You can't make people view you through an app in real life! So modified pictures are not allowed here. 4, 2, 2. 23 m telescope. Jul 17, 2006 · Sky & Telescope / Craig Michael Utter Optical aberrations, often mistakenly called distortions, limit the performance of an eyepiece. The focal ratio is an important number to consider when choosing a telescope, as it can affect the performance and capabilities of the instrument. 03". There's a community for whatever you're interested in on Reddit. So where does the extra sensitivity come from? Each telescope has its own plate scale, depending on the characteristics of the all the optical elements (mirrors or lenses) that are in the telescope. Mar 6, 2025 · Are you in the market for a new telescope but need help deciding which one to choose? One crucial factor to consider is the focal ratio of the telescope, also known as the f-number. For instance, an f ratio of f/4 signifies that the focal length is four times the aperture diameter, while an f ratio of f/10 means the focal length is ten times the aperture diameter. 5" F/12. For example, in my 12. May 24, 2023 · The focal ratio formula is focal length / aperture = focal ratio. People who are related to the NFL have lives outside of their organization as well, and in the majority of instances these are best discussed in the subreddit associated with their particular team. Mar 30, 2009 · In optics, the f-number (sometimes called focal ratio, f-ratio, or relative aperture[1]) of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter. The language in which we talk about telescopes can be confusing at the best of times. But that’s different. Since b = -4. Aug 18, 2023 · Focal ratio measures how “fast” a telescope is and is one of the key indicators of how a telescope will perform. F3 + S - "Force Reload" - Visually, does little (lags, flickers) F3 + T - Refresh Textures - Visually, does little (lags, flickers) Shift + F3 + F - Increase Render Distance F3 + F - Decrease Render Distance F3 + A - "Load Renderers" - (essentially reloads all visual Is there an easy way with Python f-strings to fix the number of digits after the decimal point? (Specifically f-strings, not other string formatting options like . We have developed a large F -number infrared camera with cold stop matched, which is successfully applied to acquire LEO extended object images taken by a 1. Instead, it moves 0. , f/5) means the telescope is faster, providing a wider field of view and shorter exposure times for astrophotography. thanks, don F/ number is a measure of the speed and clarity of the optical system. A lower f-number indicates a wider aperture, offering brighter images and better for observing dim objects, crucial in astrophotography and stargazing. The one confusing item in this is that sometimes sizes are expressed in inches, and other times in millimeters. A fast scope has a low f-number and is good Calculate the focal length of your telescope. 2 = 3, moving the secondary 0. Is there some syntax that works for this? Here are two ways it does not work. The primary is a parabola, so we know how to test that. Fast systems have small F/numbers such as F/1, F/2 or F/3. The focal ratio is calculated by dividing the telescope’s focal length by the diameter of the aperture. 5 Cass, with an F/4. From photography, the notation 'f:k' or 'f/k' and the terms "fast" and "slow" optics defined from it have become established. If it's related to the NFL, but not about the NFL (such as streams, betting-related posts, video games, Fantasy Football, College Football, or NFL-related jokes), please check the sidebar. r/Piracy: ⚓ A community devoted to in-depth debate on topics concerning digital piracy, ethical problems, and legal advancements. I am using the skywatcher 72ed which has 72mm aperture and 420mm focal length, giving a f-number of f/5. The F-ratio is the ratio of the telescope’s focal length to its aperture: F ratio = Telescope Focal Length (mm) / Telescope Aperture (mm) F ratio is usually indicated with a designation and number such as f/3. Some examples of formatted string L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument. It is the ratio of the focal distance to the aperture size. Simply put, this is an indication of the light gathering ability and the speed of the telescope. Fundamentally, f/# is the ratio of the focal length, (f) (f), of the lens to the effective aperture diameter (∅EA) (∅ EA): Feb 21, 2024 · Focal Ratio: unraveling the speed and brightness of your telescope Let's delve into the focal ratio, often called the f-number – a key factor found by dividing the telescope's focal length by its aperture. Just as in camera lenses, telescopes with lower "f numbers" are "faster"; they form brighter (but smaller) images than telescopes of the same diameter with with higher f numbers. Dive into the world of astrophotography and learn how the f-ratio can make or break your night-sky images. Large numbers imply small apertures, leading to reduced light throughput and an increased depth of field. Dec 20, 2024 · A telescope's f-number is fixed because it is based on the size of the scope's primary lens or mirror. I have a string in which I would like curly-brackets, but also take advantage of the f-strings feature. . Nov 20, 2017 · Simple telescope formulas — how to calculate what you need to know about your telescopes, oculars, and binoculars, from focal ratio to true field of view. If we had a telescope with the same focal length of 1000mm but a larger aperture of 250mm, it would have a focal ratio of 1000/250 = 4, so it's f -number would be f /4. 01" * 3 = 0. F/ number is a measure of the speed and clarity of the optical system. What they all share, however, is The best astronomical calculators for amateur astronomersThe focal ratio of a telescope, denoted as f-number, is the ratio of its focal length to aperture diameter. Even though the principles of focal ratio are always the same, the application to which the principle is put can differ. L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument. Something like st Jan 13, 2009 · Well, one of the primary usability considerations is evenly-distributed groups, so either your current idea (0-9, A-F, etc. Discover how to find the perfect balance for stellar photography in our latest guide Sep 6, 2023 · The F-ratio is the ratio of the telescope’s focal length to its aperture: F ratio = Telescope Focal Length (mm) / Telescope Aperture (mm) F ratio is usually indicated with a designation and number such as f/3. Sep 17, 2018 · Apart from f-strings and r-strings, are there any other notable similar string variants or alternates that I should familiarize myself with or be made aware of? Jul 22, 2019 · A formatted string literal or f-string is a string literal that is prefixed with f or F. The f-number tells you how 'fast' or 'slow' a scope is. Apr 5, 2023 · The smaller the F/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera. not sure i understand what difference that number makes if any. e. A larger F number telescope has a larger magnification, given the same eye piece. 8. I would like to Reddit is a network of communities where people can dive into their interests, hobbies and passions. The diameter of this pattern is related to the wavelength (λ) of the illuminating light and the The f-number n is simply a ratio of the focal length f and the aperture diameter D: n = f / D In commercially produced lenses, we can usually set the f-number to some prescribed values like 1. A lower focal ratio (e. Our goal is to have you look very classy and dress to blend in public. We are different from other subs! Read the rules! This community is for receiving HONEST opinions and helping get yourself passable in the public eye. It determines the telescope's light-gathering ability and resolution. 9. Whether capturing deep-sky beauty or planetary details, the right f-ratio is key. Thus, a f/10 telescope has four times the depth of focus of a f/5 instrument (i. The important thing to note is that the depth of focus changes with the square of the focal ratio, F. A lower f-number means a larger relative aperture and more light entering the system, while a higher f-number means a smaller relative aperture and less light entering the system. Mar 15, 2021 · A 200-mm (8-inch) telescope with a 2,000-mm focal length has a focal ratio of f/10. But this is NOT true. For example, an f/10 telescope with a 6" mirror would have a 60" focal length. In turn, the aperture area decreases by a factor of 2. Focal ratio (f-number) - Free Star ChartsIn a telescope or camera, the focal ratio is the ratio of the focal length divided by its aperture. I am currently using an Orion field flattener, that Table I: Equations to determine the conic constant of primary and secondary mirrors in Cassegrain telescopes So how to figure the mirrors? Calculate b for the mirrors in your Cassegrain. Aug 16, 2018 · How can I use f-string with logic to format an int as a float? I would like if ppl is True to format num to 2 decimal places, and if ppl is False to rformat it as whatever it is. For example, a telescope with an 800 mm focal length and a 200 mm aperture has a focal ratio of f/4. The closer the focal ratio number is to 1 the “faster” the telescope is. 0886" back. The f-number of an object is the ratio of focal length and aperture diameter, and used for indirectly indicating the aperture size. 2 primary and a secondary magnification of 12. The source is one focal length, f, from the lens. I would like to Dec 3, 2012 · A few of these don't do anything interesting, or even anything visible. Both telescopes collect the same amount of light, but the latter produces a much brighter image of your target. , f/8). Once you understand these 5 numbers, you will understand […] Our example telescope would have a focal ratio, or f -number, of f /8. Apr 7, 2025 · A telescope with a low focal ratio (usually f/5 or lower) is said to have a “short” focal ratio, while the telescope itself is said to be “fast”. If you’re into photography, you can think of it as similar to the f-stop on a camera. Of course, there are other things to consider like the aperture and focal length Jul 2, 2020 · Page 1 of 2 - Confused on f/number vs scope diameter - posted in Beginning Deep Sky Imaging: As I research telescopes for astrophotography, I see it often recommended to use an Apochromatic telescope instead of an SCT because (among a few reasons) APOs are faster, which I understand to mean they let more light in. Two of those terms even mean the same thing. For example, if you are looking at a distant nebula through a telescope with a focal ratio of 4, you will see it much faster than through a telescope with a focal ratio of 8 but the image will be smaller and less defined. The F-number concept puts these two together to allow a quick comparison of optics. ) would work well, or the list with each individual letter. 8, 4, 5. 00 for the secondary. 00 for the secondary, it is a hyperbola Common sense seems to indicate that, for the 12. Since most sources radiate at all angles, it is obvious that increasing D or decreasing f allows the lens to capture more radiation. This looks good for the long focus telescope until you also look at how much the atmosphere affects the focus shift for the two telescopes. The resulting diffraction pattern, a bright region in the center, together with a series of concentric rings of decreasing intensity around it, is called the Airy disk (see Figure 1). 6, . They correspond to decreasing the aperture diameter by a factor of √2. A higher focal ratio (e. Apr 4, 2020 · Before we launch into the pros and cons of the types of telescopes available to stargazers today, let’s have a quick look at 5 key numbers that describe the operation and performance of every telescope, from the junk scopes in a department store to the venerable Hubble Space Telescope. In photography these are also called F-stops. , f/10) indicates a slower telescope, which is better for viewing planets and the moon in detail. By contrast a 200-mm astrograph (a telescope designed for astrophotography) that has a focal length of 400 mm will have a focal ratio of f/2. For EAA it is recommended to have a low f-number to let in as much light. Slow systems have large F/ numbers such as F/8, F/15 or even F/20. 01" toward the primary should move the focal plane back 0. It is a dimensionless number that is a quantitative measure of lens speed, an important concept in The f/# (pronounced “F-number”) setting on a lens controls overall light throughput, depth of field (DOF), and the ability to produce contrast at a given resolution. Consider the number of ways we can describe a telescope’s design – refractor, reflector, compound, catadioptric, Cassegrain, Dobsonian and astrograph, to name a few. Jul 28, 2024 · The focal ratio, often called the f-number, is like your telescope’s ‘speed setting’. While other string literals always have a constant value, formatted strings are really expressions evaluated at run time. This nifty metric tells us how much light each pixel captures, essentially dictating the brightness of our images. Rarely, will you find telescopes who have denoted f-numbers outside of that range. 5/4. Reddit is a network of communities where people can dive into their interests, hobbies and passions. The smaller the number 'k' becomes F-number, Online PhysicsFocal ratio in telescopes In astronomy, the f-number is commonly referred to as the focal ratio (or f-ratio). Some telescopes can be considered to be more than one of them. However, adding an accessory like a Barlow lens or focal reducer alters the system's focal length, changing the f-number. These strings may contain replacement fields, which are expressions delimited by curly braces {}. Confused? Aperture ratio and aperture value (f-number) and their influence on the focus point The focal ratio is the ratio of the telescope aperture to the telescope focal length. For example, a telescope with a 1,200mm focal length that is used with a 20mm eyepiece, the magnification will be 1200/20, or 60x. Sep 20, 2023 · This ratio is commonly referred to as the “f/number” or “f ratio”, and is a significant characteristic used to describe telescopes and their optical systems. The Airy Disk When light passes through any size aperture (every lens has a finite aperture), diffraction occurs. 5 Cassegrain, b = -1 for the primary and b = -4. Sep 20, 2023 · Focal ratio, also known as the “f-number,” “f-ratio,” or “aperture ratio,” defines the relationship between the focal length of a telescope and the diameter of its primary optic. How Does the F Number Determine Your Magnification? The telescope’s magnification is equal to the telescope’s focal length divided by the eyepiece’s focal length. And yes, it helps to understand “F” ratios for solar telescopes. for example, a 6 f/8 compared to a 6 f/5 or 8 f/6. In fact, no telescope can ever increase surface brightness beyond your naked-eye view. See also the Rubin key numbers page for a public audience. Formula: Aperture X Focal Ratio Apr 18, 2020 · F number questiion - posted in Reflectors: is there any difference in actual viewing with F numbers. Very simply, the plate scale for a telescope can be calculated if you know the diameter, D, of the primary mirror and the telescope’s effective focal length, F, or if you have its f-number (f Jul 25, 2024 · It is represented as f/number (e. Nov 1, 2014 · We find that the observation of Space Station and other extended targets utilizing large F -number optics for MWIR imaging is possible, given the right conditions. Sep 17, 2018 · Apart from f-strings and r-strings, are there any other notable similar string variants or alternates that I should familiarize myself with or be made aware of? L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to a long double argument. It's a dimensionless number and therefore the calculation has to be performed with the focal length and aperture expressed in the same units of measure. Use our free calculator to work this out for your telescope. This page is intended as a quick reference list of key numbers that describe the Rubin Observatory system and the Legacy Survey of Space and Time (LSST). z0iufog04az0pikyjb4ay6h9fp0m09mqfjp7mydz