Anyone have a focal length calculator?

[foxbat]

I'm looking for a calculator that can take a distance to subject, height of subject and the desired height of the sensor that the subject should cover. It should return the focal length that will give that result.

Does anyone know where I can find one of these? I'm trying to decide on the right lens purchase.

[jbradc]

Try this site...
http://www.compumodules.com/image-processing/focal-length-calculator.shtml

[Scottes]

http://www.photo.net/making-photographs/lens
In the middle of the page...


This might not be what you're looking for, but it may be helpful and it's pretty darn cool:
http://www.liquidsculpture.com/DOF/DOF.htm

[pturton]

Before I purchased my 10D, I made an xls worksheet to help me decide which lens focal lengths that I required for the subjects that I wish to photograph.

This xls sheet calculates the diagonal, horizontal and height based on using a sensor the size of that used in a 10D. The spreadsheet was developed using Office 95 Excel.

http://www.iaw.com/~pturton/dpr/FOV_10D.xls

Paul

[jbradc]

That is a cool spreadsheet, very handy. I think you may have too much time on your hands though :-)

[Edgar in ATL]

I found freeware, which works great. I always have my Pocket PC with me when shooting. I am sure a similar product exists for the Palm OS. For download...

http://home.comcast.net/~jonsachs/

BTW Use 52.6 lines/mm for the DRebel resolution constant (ie 1/circle of confusion).

[CyberDyneSystems]

Oh.. this is an easy one.

Distance Y(to subject) * Height {of subject} X % [Frame cover "~ r2] = NO LENS I HAVE IS LONG ENOUGH. ......EVER.....

[Jon]

Oh.. this is an easy one.

Distance Y(to subject) * Height {of subject} X % [Frame cover "~ r2] = NO LENS I HAVE IS LONG ENOUGH. ......EVER.....

. . . except for the ones that are too long like the 16-35 L on my 20D :{(#

[foxbat]

I love the spreadsheet. Paul can you clarify how to read the units? In the sample box are you saying that the the subject would occupy 2.26x1.51mm on the sensor. Also would I read off the 400mm row for a 1.6x crop sensor or a 640mm row?

[ed2day]

Thanks, Edgar, for the link. I've been thinking a focal length calculator must exist for PocketPC. Even better that it's free! PocketPC can run Excel sheets so Paul's will also go in. Thanks again.

[pturton]

Foxbat wrote:
"I love the spreadsheet. Paul can you clarify how to read the units? In the sample box are you saying that the the subject would occupy 2.26x1.51mm on the sensor. Also would I read off the 400mm row for a 1.6x crop sensor or a 640mm row?"

Sorry for the slow response.

2nd things first; The focal length equivalent is given just as to show the FOV of the actual lens being used. Select the lens focal length that you wish to check from the left hand column.

Now the first question;
If the subject is 40 meters away, a subject of 2.26 meters wide x 1.51 meters high will be captured by the sensor.

If the subject is 40 feet away, a subject of 2.26 feet wide x 1.51 feet high will be captured by the sensor.

The width and height are accurate enough to give you a rough estimate of which lens you would need to use to capture a subject of known size. For example: Today I saw a perched Sharp-Shinned Hawk at a distance of about 85 feet from my window. Using an 800 mmm lens, the hawk should fit well in landscape mode since this bird is about 17 inches tall. To fill the frame in portrait mode, I would need to move about 40 feet closer.

Paul

[Bob_A]

Maybe not what you're looking for, but you can get a freeware application for Palm OS called DOFMaster here:

http://www.palmgear.com/index.cfm?fuseaction=software.showsoftware&PartnerREF=&siteid=1&prodID=46570

Bob