Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
Calculating arc-seconds per pixel Question
|
I used CCDcalc from new .?
its old but still works....I think. It¡¯s free and I think a few amateurs ?have made update packs for the images?
|
|
Hi Tom I'm not sure what you mean by actual vs apparent. Often the actual focal length is slightly different than the spec of the focal length if you have two cameras with the same pixel *size*, they will have the same resolution (arcsec/pix), but if the sensors are physically different (i.e., larger or smaller compared to each other) you will have a different field of view (fov). Imagine looking through a small window in your house at a nature scene outside. it's a small window so you only see a little bit. then the window is "magically replaced" to become a much larger window. you see so much more. has your ability to see detail changed? no, you just see more of the scene. that's resolution vs field of view (roughly :) ) On Thu, Dec 31, 2020 at 11:36 PM Tom & Barbara Coverdale <tcoverda@...> wrote: I found the formula for calculating this value but have a question. When using focal length, is it the actual focal length or is it the apparent focal length? I have two different cameras with different size sensors but get a very similar arcsec/pixel. What ?am I missing? --
Brian? Brian Valente portfolio |
|
There are multiple online calculators for determining this.?
e..g.: The focal length you use is your telescope focal length multiplied by any reducer or barlow you may be using. Arcsec/pixel is determined by pixel size, so you could have two sensors giving the same ratio. But different sensor sizes would give you different field of views. Bigger sensors = wider FOVs. |
|
Probably not missing anything. But to be sure to check out the calculators at the www.astronomy.tools site. They are the best.?
toggle quoted message
Show quoted text
On Thu, Dec 31, 2020 at 11:35 PM, Tom & Barbara Coverdale wrote:
I found the formula for calculating this value but have a question. When using focal length, is it the actual focal length or is it the apparent focal length? I have two different cameras with different size sensors but get a very similar arcsec/pixel. What ?am I missing? ? -- Chip Louie Chief Daydreamer Imagination Hardware? ? ?Astropheric Weather Forecast - South Pasadena, CA? |
¿ªÔÆÌåÓýDo you mean ¡°effective focal length¡±? That term is used in relation to SLR cameras and lenses, to indicate the field of view relative to a full 35mm frame. For example, a 200mm telephoto lens on a camera with an APS-C sensor has a field of view of about 6.5¡ã. To get that field of view on a full-frame 35mm sensor would require a 320mm lens, so the 200mm is referred to as a ¡°320mm effective focal length¡± on an APS-C camera. But the effective FL has nothing to do with image scale; it¡¯s just a convenience for photographers who are used to thinking in terms of the view of various lenses on 35mm cameras. For calculating image scale and other astronomical purposes, you want the actual FL.?? -Les On Dec 31, 2020, at 11:36 PM, Tom & Barbara Coverdale <tcoverda@...> wrote:
|
|
Thanks Les, That is what I was trying to figure out. --- les@... wrote: From: "Les Niles" <les@...> To: [email protected] Subject: Re: [Losmandy_users_io] Calculating arc-seconds per pixel Question Date: Fri, 1 Jan 2021 11:39:01 -0800 Do you mean ¡°effective focal length¡±? That term is used in relation to SLR cameras and lenses, to indicate the field of view relative to a full 35mm frame. For example, a 200mm telephoto lens on a camera with an APS-C sensor has a field of view of about 6.5¡ã. To get that field of view on a full-frame 35mm sensor would require a 320mm lens, so the 200mm is referred to as a ¡°320mm effective focal length¡± on an APS-C camera. But the effective FL has nothing to do with image scale; it¡¯s just a convenience for photographers who are used to thinking in terms of the view of various lenses on 35mm cameras. For calculating image scale and other astronomical purposes, you want the actual FL.? ? -Les On Dec 31, 2020, at 11:36 PM, Tom & Barbara Coverdale <tcoverda@...> wrote:
|
Chip Louie
to navigate to use esc to dismiss