Print Page | Close Window

i'm new to optics: question about lens

Printed From: OpticsTalk by SWFA, Inc.
Category: Everything Else
Forum Name: Almost Anything Goes
Forum Description: Non OpticsTalk Talk
URL: http://www.opticstalk.com/forum_posts.asp?TID=14056
Printed Date: March/28/2024 at 12:53
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com


Topic: i'm new to optics: question about lens
Posted By: Almost
Subject: i'm new to optics: question about lens
Date Posted: December/16/2008 at 05:02
Hi there,

I found myself stuck to a simple question really. Trying to find a solution on my own doesn't guarantee a success. Therefore I would appreciate if any of you can offer me helps to solve the following questions.

1. how big a image a lens can see? You see, when you put the image at the focus of the lens, you get a collimated beam behind the lens, which is then focussed onto a ccd by another lens. Normally, I think this is determined by NA. I did  some calculation and found that the spot  size is much less than what the lens see. So, how can I know how big an area a lens can see. (given its focal length)

2. this is a related questio to question 1: how can I completely fill ccd? how to determine the focal length of the lenses necessary to fill completely the ccd area.


many thanks,
Almost



Replies:
Posted By: trigger29
Date Posted: December/16/2008 at 05:54
Hello? Dale Clifford.......Koshkin.......are you listening? This one is way over my head. We're talking sky scrapers here.

-------------

"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."


Posted By: pyro6999
Date Posted: December/16/2008 at 06:04
isnt this called field of view??

-------------
They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead"

343 we will never forget

God Bless Chris Ledoux
"good ride cowboy"


Posted By: Ed Connelly
Date Posted: December/16/2008 at 06:21
 
 
                                                                                                      Eat and Drink


-------------
Be sure to visit,

http://www.opticstalk.com/forum_topics.asp?FID=50 - THE ED SHOW

Ju Cucarachas!!!


Posted By: Kickboxer
Date Posted: December/16/2008 at 08:57
Go to the site below for a calculator:
http://www.videologyinc.com/lens%20focal%20length%20calculator.htm

You have to know whether you are optimizing on vertical or horizontal plane...CCD's, generally commercially available, use a 4:3 aspect ratio.  You are, in effect, trying to cover a rectangle with a circle (lens image) resulting in a constant situation of either incomplete image or too much.  Generally, the image is larger than the CCD to try to "fit" everything in.  To optimize you must pick one plane or the other because the focal length to completely fill the CCD vertically or horizontally is different.  



-------------
Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: rifle looney
Date Posted: December/16/2008 at 16:06
Shocked


-------------




Posted By: Almost
Date Posted: December/17/2008 at 02:51
Thanks Kickboxer, really appreciate.

However, my situation is slightly different. Like formulated in the question, although I might not have put it correctly, I would like to know how to choose a focal length of the lens in order to focus a collimated beam (coming from the objective lens; i.e., this is a two-lens system) onto a CCD to form an image. At this stage I want to make sure that the image fully fill the CCD, or as much as it can as you described.

cheers


Posted By: Almost
Date Posted: December/17/2008 at 03:00
One more note: I tried putting in 1000 meters as the distance from lens to object, to mimics infinity (or parallel or collimated beam). The value of focal length I got is absurdly high.


 


Posted By: lucznik
Date Posted: December/17/2008 at 09:39
I answered your question in the "spotting scopes" forum but, for the sake of continuity I will throw in the bulk of my response here as well since you posted in both places.
 
First, you still haven't defined the abbreviation "NA."  I realize that I'm probably the only person on the planet who doesn't know what it means but, if you could define it anyway, that might be helpful.
 
Second, although I admit to knowing only a very little (almost nothing in fact) about cameras, I am nevertheless unaware of any (digital) camera that allows for the kind of tinkering that it sounds like you are wanting to do - other than trying to find a specific lens for a given DSLR that would maybe offer some specific focal length that would "completely fill the ccd" - the value of which seems rather dubious.  How exactly does "filling the ccd" in the manner you describe help to create good photographic composition?
 
Furthermore, if you already know how to do the necessary calculations to determine that the "spot size is much less than what the lens see[s],"  then you already have the ability to answer your question about "filling the ccd."  


-------------
What if the hokey pokey really is what it's all about?



Print Page | Close Window

Forum Software by Web Wiz Forums® version 12.01 - http://www.webwizforums.com
Copyright ©2001-2018 Web Wiz Ltd. - https://www.webwiz.net