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focal length

Started Nov 6, 2017 | Questions
srmdnadem New Member • Posts: 3
focal length

Hi Mester, how can I get a specific focal length from this lens? For example, how can I get focal length=40 mm or 50 mm? please

the answer will be

focul length will be 27-88mm (35 mm equivalent). So , if I do not move the lens to enlarge the view. Is that mean the focal length will be 27 mm or not, please?

that is my enquiry

ANSWER:
This question has not been answered yet.
Great Bustard Forum Pro • Posts: 45,641
Re: focal length
2

srmdnadem wrote:

Hi Mester...

"Mister" or "Master"? I like "Master" better.

...how can I get a specific focal length from this lens? For example, how can I get focal length=40 mm or 50 mm? please

the answer will be

focul length will be 27-88mm (35 mm equivalent). So , if I do not move the lens to enlarge the view. Is that mean the focal length will be 27 mm or not, please?

that is my enquiry

I'm guessing you want to know how do you get a 40mm or 50mm *FF equivalent* focal length with a 17-55mm 1.6x lens (27-88mm FF equivalent).

The way I'd do it is move and/or zoom to get the perspective/framing combination I wanted. However, if you are curious what the nominal focal lengths would be to get the FF equivalents, multiply the actual focal length by 1.6 to get the FF equivalent or divide the FF equivalent by 1.6 to get the actual focal length.

For example 25mm on 1.6x is equivalent to 25mm x 1.6 = 40mm on FF. 40mm on FF is equivalent to 40mm / 1.6 = 25mm on 1.6x.

Below is some additional related information which you may find helpful.  If not, don't read it. 

The same applies to the relative aperture with regards to DOF, light gathering, and diffraction.  For example, f/2.8 on 1.6x is equivalent to f/2.8 x 1.6 = f/4.5 on FF.

Putting it all together, we see that 25mm f/2.8 1/100 ISO 400 on 1.6x is equivalent to 40mm f/4.5 1/100 ISO 1000 on FF where by "equivalent to", I mean all will have the same perspective (if taken from the same position), all will have the same framing, all will have the same DOF, all will have the same diffraction (not that it matters at these wide apertures), the same amount of light will be projected on the sensor (resulting in the same noise), and all will have the same motion blur.

Hope that helps!

diness Veteran Member • Posts: 3,758
Re: focal length

srmdnadem wrote:

Hi Mester, how can I get a specific focal length from this lens? For example, how can I get focal length=40 mm or 50 mm? please

the answer will be

focul length will be 27-88mm (35 mm equivalent). So , if I do not move the lens to enlarge the view. Is that mean the focal length will be 27 mm or not, please?

that is my enquiry

I’m sorry, I really don’t understand your question?   Are you wanting to know the full frame equivalent of your lens on crop?  If so, what lens and the bigger question is why?  There really isn’t all that much use for that information unless you are really used to 35mm values.   But in any case, take the focal length times 1.6 and you will get the ff equivalent of that same field of view

 diness's gear list:diness's gear list
Canon EOS R Canon EF 135mm F2L USM Canon RF 35mm F1.8 IS STM Macro Canon RF 24-105mm F4L IS USM
Mike Maier Forum Member • Posts: 67
Re: focal length

diness wrote:

srmdnadem wrote:

Hi Mester, how can I get a specific focal length from this lens? For example, how can I get focal length=40 mm or 50 mm? please

the answer will be

focul length will be 27-88mm (35 mm equivalent). So , if I do not move the lens to enlarge the view. Is that mean the focal length will be 27 mm or not, please?

that is my enquiry

I’m sorry, I really don’t understand your question? Are you wanting to know the full frame equivalent of your lens on crop? If so, what lens and the bigger question is why? There really isn’t all that much use for that information unless you are really used to 35mm values. But in any case, take the focal length times 1.6 and you will get the ff equivalent of that same field of view

Some manufacturers made it simple for people and if you read the question carefully it says “27-88mm (35 mm equivalent)”. That is very simple 27 mm has same field of view as it would be on full frame 35mm sensor. Therefore if you want 50 mm equivalent set the zoom to 50mm, if you want 40mm set it to 40mm.

 Mike Maier's gear list:Mike Maier's gear list
Canon EOS 5DS Canon EF 70-200mm F2.8L IS II USM Canon EF 24-70mm F2.8L II USM Canon EF 16-35mm F4L IS USM
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