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

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.

"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.

Hi, Charles,

Charles L Webster said:

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

Click to expand...

Oh, of course. Thanks.

Best regards,

Doug

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

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