Focal Length | Basics of Photography | Photo Forum

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Focal Length
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August 21, 2014
6:18 pm
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In Oxana’s Lesson 5 between 10:26 & 10:36 min, she explained that there are 3 ways to control the depth of field.

1. Apperture

2. Focal Length

3. Distance from the object

 

So far Lessons 1 thru Lesson 5 we haven’t learnt or heard this word “Focal Length”. That’s why I find it little confusing. What is Focal Length?

a) How can I read the current focal length?

b) How can I change its value (increase or decrease)?

Some one kindly explain.

 

Thanks

C1

August 22, 2014
1:36 pm
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Focal length isn’t a measure of how long or short a lens is physically, but the distance in millimetres from the optical centre of a lens to the imaging sensor when the lens is focused at infinity.

When you buy the lens, you look for specific focal length – 50mm, 85mm, 24-70mm. Lenses with only one number (like 50mm) are fixed lenses, which means you can’t change the focal length. Lenses with 2 numbers (like 24-70mm) are zoom lenses, which means you can change the focal length in the range between 24 and 70mm. 

The longer the focal length, the closer to the subject you’ll get (it is like a binocular). The shorter it is, the more of the scene you will be able to get into your photo. 

Please watch this video about lenses: 

list=UUchFM6wXty2IJXA9SiTVN4w

August 23, 2014
7:10 am
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cadone…

For the sake of this response, I’m assuming that you are using the 10-30mm kit zoom lens that comes with the J4.  

As you zoom the lens it’s focal length will change from it’s wide angle length of 10mm to it’s telephoto length of 30mm.  I do not believe that this lens has specific focal length markings between wide and telephoto, so it could very well be that you will not be able to “read” the exact focal length at the time of taking the shot.  The focal length of any image, however, should be available in it’s Exif data, which, of course, is less useful.

The crop factor of the J4 sensor works out to about 2.72, meaning that a 10mm focal length has approximately the same angle of view as a 28mm lens on an FX or 35mm film camera. The Nikon 1 Nikkor 10-30mm VR standard zoom is thus roughly equivalent to a 28-80mm FX (full frame) lens.

-- Mandrake --

August 23, 2014
12:47 pm
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Hello Mandrake,

Thank you for your response. Yes I am try out to explore and learn proper photography techniques with J4. Thanks for tip about the exif. I right away tried to read about it and even found a smartphone app. I am sure rest of the world already aware/use this, but i am just discovering. This app show exposure details of selected photo & I could read f, shutter speed & ISO values of the photo. I felt that its helpful while learning exposure.

The crop factor of the J4 sensor works out to about 2.72

I don’t understand this completely. I have completed 5 lessons. But I guess I will after watching all the videos.

August 23, 2014
12:52 pm
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Thanks Oxana,

I had not seen this video yet. This video gives a good idea about lens.

August 23, 2014
1:50 pm
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cadone said

I don’t understand this completely. I have completed 5 lessons. But I guess I will after watching all the videos.

You will learn about crop factor in Lesson 21. 

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