Open Photography Forums  
HOME FORUMS NEWS FAQ SEARCH

Go Back   Open Photography Forums > OPF Welcome Hall > Layback Cafe

Layback Cafe Let's chat!

Reply
 
Thread Tools Display Modes
  #1  
Old April 16th, 2008, 03:21 PM
Ray West Ray West is offline
Senior Member
 
Join Date: Jun 2006
Location: UK - Somerset
Posts: 1,703
Default Really Cheap - a bit of a blog

I thought I may buy a telephoto of some sort. I've looked at the Canon 100/400 , studied the specs etc, of the sigma 500 and the 400 zooms, but I thought I could not justify the expenditure, at the moment, some household replacements taking higher priority.

I mentioned 'telephoto' to a friend of mind, and he said he had an old 500mm I could try. I was dubious of its quality, it was an unknown brand, and seemed rather lightweight. However, I found myself surprised at how good the images were, and certainly could see the potentials for a cheap second hand lens, which in the uk would cost about 15.00

Anyway, it led to other thoughts, details of which have dissuaded me from buying anything for a while.
But I thought I would play a bit with this lens.

My general local telephoto test shot is something like this. I am not looking for any comments re composition or anything on this image, it is just to explain the following. The tower, on the skyline is known locally as 'Curry Rivel Tower', and just below, that, and to the viewers left, about two thirds towards the transmission tower, is Burrow Mump, with its 'church'.






So, out of curiosity, I decided to see if I could do some calculations, to see if it was possible to estimate the height of these two buildings, if I know the distance from me to there.

Having digital maps of the area I can measure distances reasonably accurately, but there is nothing of a known height in the image. The maps show contour heights, but not heights of structures.

Anyway, my wife takes the dog for a walk most days, and I know her height, so I took some photos, from more or less the same location, of swmbo in the distance, and using the map, got the measurement to her location too.

There is some handy bits of free software out there, for example charten.com, has a pixel distance measuring one, or I could have used a ruler, I guess

So, I have some figures - albeit approximate, based on the number of pixels of an 'actual size' image, taken with the same lens, and simply shown on screen in photoshop.

subject, distance, object height, height above sea level

tower, 10.4 miles, 197 pixels, 243 feet
church, 6.93 miles, 88 pixels, 91 feet
shmbo, 0.817 miles, 92 pixels, 23 feet

my location is 137 feet above sea level, and shmbo is 5.2 feet tall

so, ignoring the different sea level heights, I can apply some simple proportions, based on shmbo pixels height/actual height, with the tower and church pixels, perhaps converting to 'virtual' feet,

we get

tower (197/92) * 5.2 = 11.135
church (88/92) * 5.2 = 4.97

and then multiplying by the distance, we get

tower = 11.135 * (10.4/0.817) = 141.7 feet
church = 4.97 * (6.93/0.817) = 42.12 feet

time to check the calculations -

http://www.follytowers.com/curryrival.html gives the tower height as 140 feet,

Amazing, considering the errors that could have crept in, and did creep in, I expect, except they probably cancelled each other out, this time.

http://www.follytowers.com/burrow.html does not show the church height (talking about height of St Michael's Church not ground level above sea level) - and I can't find it in ten pages of googling....

Well, I would guess its about 40 foot high, I may make a phone call or two tomorrow.

Now, their are other identifiable items in that image, or in other photos on which I've used that lens, so, having 'calibrated' the lens, it is easy to estimate the sizes of objects, knowing their distance..... or is it? ;-)

(I am aware of where this can lead to - a three dimensional head ache;-)

Best wishes,

Ray
__________________
All images posted in OPF are assumed to be for Comment & Critique, unless otherwise designated Comment Only or Edit and Repost.
Reply With Quote
  #2  
Old April 17th, 2008, 04:53 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,517
Default

Hi, Ray,

Nice example of the principle of "stadia measurement".

But I think the best part is "Burrow Mump" - just the name!

And it would be nice to know the decoding of "swmbo/shmbo".

Note that this same data suggests that the focal length of the lens in use is 496 mm, a nice verification of the entire process (assuming that the original image was taken at the "large" resolution of the 20D).

Thanks.
Reply With Quote
  #3  
Old April 17th, 2008, 09:17 AM
Charles L Webster Charles L Webster is offline
Senior Member
 
Join Date: Oct 2006
Location: Silicon Valley CA
Posts: 596
Default

"swmbo" generally translates to "she who must be obeyed," a reference to "Rumpole of the Bailey."

A perfect example of an engineer with time on his hands. "I've got a tool, what problem can I fix with it?"

Thanks Ray, I had forgotten how to do that stuff.
__________________
<Chas>

Everything in the frame must contribute to the picture.
http://www.charlesLwebster.com
Reply With Quote
  #4  
Old April 17th, 2008, 09:26 AM
Doug Kerr Doug Kerr is offline
Senior Member
 
Join Date: May 2006
Location: Alamogordo, New Mexico, USA
Posts: 8,517
Default

Hi, Charles,

Quote:
Originally Posted by Charles L Webster View Post
"swmbo" generally translates to "she who must be obeyed," a reference to "Rumpole of the Bailey."
Oh, of course. Thanks.

Best regards,

Doug
Reply With Quote
  #5  
Old April 17th, 2008, 09:30 AM
Ray West Ray West is offline
Senior Member
 
Join Date: Jun 2006
Location: UK - Somerset
Posts: 1,703
Default

Hi Doug,

swmbo = she who must be obeyed - (yours has red hair, and a foxy fur, iirc.)
shmbo = typo for above. (typo = typing error)

Somerset, has a number of such 'mumps'. They are at the edges of villages, usually, being the place where the field workers, over the thousands of years, kicked the mud from their boots.

The link I referred to, interestingly, can not decide if it is 'burrow', or 'barrow'. I think the confusion is that a 'barrow' is an ancient burial hill, generally man made, and can often look like this.

Best wishes,

Ray
__________________
All images posted in OPF are assumed to be for Comment & Critique, unless otherwise designated Comment Only or Edit and Repost.
Reply With Quote
  #6  
Old April 17th, 2008, 10:11 AM
Ray West Ray West is offline
Senior Member
 
Join Date: Jun 2006
Location: UK - Somerset
Posts: 1,703
Default

I Phoned the owners, they do not have a record to hand of the height of the church, but they will be meeting the local warden tomorrow, and have said they will get back to me. I can see myself having to go over there, and measure it for them.

Charles, it takes one to know one ;-) ;-);-)

Next stage, possibly, a ten yard length of string, and dispense with the maps. (and I'm not measuring it out ten miles or so.)

Best wishes,

Ray
__________________
All images posted in OPF are assumed to be for Comment & Critique, unless otherwise designated Comment Only or Edit and Repost.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 05:14 PM.


Posting images or text grants license to OPF, yet of such remain with its creator. Still, all assembled discussion 2006-2017 Asher Kelman (all rights reserved) Posts with new theme or unusual image might be moved/copied to a new thread!