How to choose your next telephoto length...

[foxbat]

This is a screenshot of a spreadsheet that I put together to help me work out what length lens I should be saving up for.

It tells you how much bigger an object will appear to be when viewed through the lens that you want, compared to the lens that you actually have including any teleconverters that you may use. All figures are percentages.

For example, if I upgrade my 400mm to a 500mm then I can see that by reading off my 400mm from the left row and then going across to the 500 column that I will get a 56% increase in the size of the subject.

Similarly I can see that by adding a 1.4x TC to my 400mm then I'll get a 96% increase.

I hope you find this useful.

http://www.aprd31.dsl.pipex.com/tmp/percent.gif

[RbrtPtikLeoSeny]

Foxbat, first of all wow... well done!

This is pretty sweet! I have a 200mm max, would like a 400mm lens, and can see that'd increase the size of my subjects by 300%. Add a 1.4x t-con and it's 684%!!! That's so cool! 96% just by adding a 1.4x t-con to what I have. This is pretty helpful! Thanks for sharing this with us.

[Hellashot]

I think you have too much spare time on your hands.

[foxbat]

I think you have too much spare time on your hands.It's raining today and it's this or TV... ;)

[weasel]

How do you figure a 2X TC increases size anything but 2X?

[CorruptedPhotographer]

how did you figure out how much everything increases by? so say you have an EF 135mm and you want a 200mm for example, accordin to the above excel calculations. The image from EF 13mm increases by 119% when attaining the 200mm. Where did you get the 119% from ? :D lovely table.reminds me of my days studyin accounting.

[weasel]

Regardless of the focal legnth one works with, a 2X TC doubles that focal legnth. That means that both height and width are reduced by half. Overall area is now reduced to 25% of what it was before converting. This means the subject is doubled in size.

[foxbat]

Regardless of the focal legnth one works with, a 2X TC doubles that focal legnth. That means that both height and width are reduced by half. Overall area is now reduced to 25% of what it was before converting. This means the subject is doubled in size.I'm afraid that simplistic view is wrong. Image size is a function of the square of the focal length. The formula to calculate the increase in image size as a percentage from x millimetres to y millimetres is ((y*y)/(x*x)*100)-100. The theory is documented in many textbooks, I just plugged it into Excel.

[weasel]

It is just that simple. The angle of view for a 50mm lens is 47 degrees, of a 100mm lens-24 degrees. The 100mm takes in half the height and half the width of the 50mm lens but fills the format. Therefore the subject size is increased 200%. A 200mm lens has an angle of view of 12 degrees, a fourth that of the 50mm lens, therefore the increase in size is 400%. My gosh, it's not called a 2X TC because it's not 2X! Look, fill the frame of your camera with a 12" ruler using a 50mm lens. Now view it (same distance) with a 100mm lens. Bet it fills the frame at 6".

[grego]

Find out which lens will piss off your wife/gf/husband/bf, and what will empty your wallet, and then you will know which lens is best. :)

[LightRules]

This is the software I use; it's good and easy to set up: http://www.cpr.demon.nl/prog_plotf.html

[schmoelzel]

Buy a zoom........take many many many shots..........look at exif info and see which focal lengths you seem to use more often than not........buy appropriate primes or stick with the zoom and save lots of money!! This is what I did about 6 months ago and how I decided that I wanted the 35L, the 50F.14, the 85L, and will have the 135L again!! These seem to be where my 70-200L always seemed to end up..........

[schmoelzel]

oops......sorry, misread the telephoto lens it the title!! I guess the 35 and 50 wouldn't fit into the telephoto category until canon comes up with a 7.6 crop factor sensor!! :D

[Poco]

It is just that simple. The angle of view for a 50mm lens is 47 degrees, of a 100mm lens-24 degrees. The 100mm takes in half the height and half the width of the 50mm lens but fills the format. Therefore the subject size is increased 200%. A 200mm lens has an angle of view of 12 degrees, a fourth that of the 50mm lens, therefore the increase in size is 400%. My gosh, it's not called a 2X TC because it's not 2X! Look, fill the frame of your camera with a 12" ruler using a 50mm lens. Now view it (same distance) with a 100mm lens. Bet it fills the frame at 6".

You guys are both right, you just have a slightly different meaning of "bigger". On the one hand, when you double the focal length you double the width and double the height. On the other hand, when you double the width and double the height you make the area four times the size (an increase of 300%).

That 12" ruler with the 100mm lens fills the frame at 6", but it is also twice as wide so the area of the frame it occupies is 400% of the original size (an increase of 300%). Well, not really, since half of the ruler is out of the frame, but you get the idea ;).

Now I am going to have to agree that using the area that something occupies as some sort of useful measure seems a bit strange. When you are comparing lenses do you think "That bird would have been four times the area of my frame if I had a longer lens" or do you think "That bird would have been twice as tall"?

[weasel]

Photography has always been about linear measurements. From paper size to format size to the increase a TC gives.

[BearLeeAlive]

You guys are both right, you just have a slightly different meaning of "bigger". On the one hand, when you double the focal length you double the width and double the height. On the other hand, when you double the width and double the height you make the area four times the size (an increase of 300%).

That 12" ruler with the 100mm lens fills the frame at 6", but it is also twice as wide so the area of the frame it occupies is 400% of the original size (an increase of 300%). Well, not really, since half of the ruler is out of the frame, but you get the idea ;).

Now I am going to have to agree that using the area that something occupies as some sort of useful measure seems a bit strange. When you are comparing lenses do you think "That bird would have been four times the area of my frame if I had a longer lens" or do you think "That bird would have been twice as tall"?
Was reading through this thread and wondered when someone would finally explain what I thought was obvious.

Yes, most of the time things are expressed in linear terms (i.e. twice as big instead to 4 times the size). Probably the only time I refer to the increase in area is something like landscape as opposed to subject photography where I do look at it as 4 times the viewing area instead of 2 times the height.

[genewch]

I still don't understand how the figures in % increase in size come up. For example, by naked eyes, an object shot by 200mm doesn't look like 119% of the size shot by a 135mm.

[foxbat]

genewch, it's a 119% increase in the area covered on the sensor not an increase in any one direction. Poco explained the difference quite nicely. When shooting birds that are so small that the resulting crop won't yield the dpi that I want then it's useful to know the % increase in pixels that I need to make the print. Basically I need a 500mm f/4L with a 1.4x ... or the sigmonster ;)

[Lester Wareham]

It is just that simple. The angle of view for a 50mm lens is 47 degrees, of a 100mm lens-24 degrees. The 100mm takes in half the height and half the width of the 50mm lens but fills the format. Therefore the subject size is increased 200%. A 200mm lens has an angle of view of 12 degrees, a fourth that of the 50mm lens, therefore the increase in size is 400%. My gosh, it's not called a 2X TC because it's not 2X! Look, fill the frame of your camera with a 12" ruler using a 50mm lens. Now view it (same distance) with a 100mm lens. Bet it fills the frame at 6".

You are both right: weasel is using linear dimension and foxbat area or pixel count.
:p

Also foxbat is using the increase in area rather than a ratio; myself I find linear ratio more useful, so 2X TC gives double (200%) the image height. But this is the same as 400% of the area or a 300% incease of area.

[CorruptedPhotographer]

Ok so from 300mm to 400mm there is an increase by 78% because

% increase = ((y*y)/(x*x)*100)-100.
where : x= 300 , y=400

= [(400*400) / (300*300) * 100] - 100
= [(160,000) / (90,000) * 100 ] - 100
= [ ( 1.8 ) * 100 ] - 100
= ( 177.8 ) - 100
= 78 % increase from 300mm to 400mm

So where is this 78% increase? As others mentioned, a subject @ 400mm does not look 78% more larger than a 300mm.

[BearLeeAlive]

So where is this 78% increase? As others mentioned, a subject @ 400mm does not look 78% more larger than a 300mm.
It sure does, in area it takes up. Again, not linearly.

[CorruptedPhotographer]

JIm, would you elaborate on " in area it takes up" and "not linearly" . thanks

[BearLeeAlive]

Another way to look at this that might help is to take a 1'x1' (1 square foot) piece of glass (or whatever). Double it's size (area) it would only be 1.414 x 1.414". Multiply 1.414 x 1.414 and you get 2 square feet (twice the area). If you double each dimension by 2 to 2'x2' you would get 4 square feet.

As another example, if you took an arial shot that covered one city block. If you put on a lens that was half the focal length you would get a shot of 4 city blocks, thus 400% the size or 300% bigger.

Sorry, I am having trouble conveying a concept that my mind is having no trouble with.

BTW, linear means in one direction, area is 2 dimensional.

[lordjim]

Buy a zoom........take many many many shots..........look at exif info and see which focal lengths you seem to use more often than not........buy appropriate primes or stick with the zoom and save lots of money!! This is what I did about 6 months ago and how I decided that I wanted the 35L, the 50F.14, the 85L, and will have the 135L again!! These seem to be where my 70-200L always seemed to end up..........

Great advice. I fully agree that this is probably one of the best way to choose your next lenses.

[Poco]

Ok so from 300mm to 400mm there is an increase by 78% because

% increase = ((y*y)/(x*x)*100)-100.
where : x= 300 , y=400

= [(400*400) / (300*300) * 100] - 100
= [(160,000) / (90,000) * 100 ] - 100
= [ ( 1.8 ) * 100 ] - 100
= ( 177.8 ) - 100
= 78 % increase from 300mm to 400mm

So where is this 78% increase? As others mentioned, a subject @ 400mm does not look 78% more larger than a 300mm.

Blast! I had typed up a long response and promply hung when I clicked "Submit Reply". I have to remember to copy-paste my replies before I submit - just in case.

Anyway the short version is that a 300mm to 400mm will make everything look 33% taller and 33% wider (400/300 = 1.333333 = 133% = 100% + 33%). If you have something that is 33% taller and 33% wider then it is 78% larger by area (width * height).

1.33333... * 1.33333... = 1.77777...
133% * 133% = 178%.

[Tapeman]

It's easy: GO LONGER AND LONGER STILL

[CorruptedPhotographer]

Poco, you explain splendidly. You should be a teacher(math!) .

thank you!

[BearLeeAlive]

Poco, you explain splendidly. You should be a teacher(math!) .

thank you!

Absolutely, if I could use Poco for speaking to my wife what I mean to say maybe she won't misunderstand me..........lol