Lenses Info

Post date: Nov 09, 2010 8:52:14 PM

First the Background to this knoll. I noticed that the divali photos of friend were looking really good, specially the portraiture (the closeups). only the thing which was being captured seemed to exist and rest of the world seemed to sublimate in that immovable snap of time. The photo was moving before my eyes.

So i talked to him

Me: Gr8 work :) ye photos kaise li jarur bataiyio? do you have some new lens which you have mastered recently, ye same effect ( the sharp focus and everything else blurred kind of effect). aur photos me bhi hai. it looks really good in all the closeups. Ise point and shoot se kar sakte hai kya?

Him: Pappu: Thanks dost...haan ye 1 different type ka lens hai...jisme aperture kaafi jyada open ho jata hai...isse background wali cheezen out of focus ho jaati hain kam distance par...point and shoot mein ye effect utna prominent nahi hota kyunki uski lens assembly itna bada aperture nahi support karti. Baaki fireworks wali pics to standard lens se hi li hui hain.

Me: thanks for the info btw what's the name of this lens good to know for the future when i buy a good slr :)

Him: Nikon 50mm AF F/1.8...probably the most inexpensive lens in the market :)

So basically i started to search the net to understand that last line and this list is the resulting knowledge

1. 50 mm is NOT the lenses focal length. It is the distance between the lens and the sensor. The actual focal length is something different and usually not fixed for a camera lens

2. F/1.8 means that the aperture of the lens is  focal_length/1.8

3. F/1.4 is a very high value of aperture, such a lens would be very fast since the lens would have to be open for a very small time.

4. This is a picture of relative sizes by F number

1. This lens uses the DX format, DX format refers to the size of the sensor, it is equivalent to the size of retina, or the size of the photographic film. It is 2/3rd the size of 135 mm. Small film size means a small view angle.

2. F/1.4 is a very high value of aperture, such a lens would be very fast since the lens would have to be open for a very small time.

3. The 135 film format is the same as 35mm

4. The Nikon FX on the other hand is the same size as a 135mm film

5. AF means Auto focus. This lens also has a small view angle therefore it is a perfect match for the DX sensor size.

6. Its field-of-view crop is 1.54. The most common definition of FOV or Field of view crop is the ratio of a 35 mm frame's diagonal (43.3 mm) to the diagonal of the image sensor i.e., CF=diag35mm / diagsensor

7. Aperture Priority Auto Exposure, A mode, Av mode, or semi-auto mode : They are all the same thing where the photographer chooses the aperture setting and then lets the camera decide the shutter speed and ISO sensitivity

8. Here's a description of performance by varying aperture of this lens:

9. f/1.8: some light falloff. Some coma in the corners and a little less contrast all around seemingly due to spherical aberration

10. f/2.8: almost no falloff and the coma seems to be gone. Sharp all over

11. f/4: no falloff. Very sharp all over

12. f/5.6: great, same as at f/4

ALLRIGHT NOW LETS TALK ABOUT FOV, DOF, HYPERFOCAL DISTANCE 

1. One thing we havent talked about is the Closest Focusing distance: the nikon site for this camera says that it is 0.45 m/1.5 ft.

2. Why is Closest focusing distance so much greater than 50 mm ?

3. because remember 50mm is not the focal length

4. There are different categories of Macro Lenses but a macro lens usually only works best at a certain magnification. Now the further the lens is from the film or sensor, the closer the focusing distance, the greater the magnification. So a 50-60 mm lens needs objects to be far from the lens.  the smaller the mm number the wider the angle of view within a photograph

   1. 1. 50–60 mm range typically used for product photography and small objects

      2. 90–105 mm range the standard focal range used for insects, flowers, small objects

      3. 150–200 mm range gives more working distance — typically used for insects and other small animals

5. The smaller the mm number the wider the angle of view within a photograph

6. Depth of Field : (DOF) is the portion of a scene that appears acceptably sharp in the image. Basically the field is the space of sharpness. High DOF means you a lot of stuff appears sharp like in a wide angle lens. Tele Photo lens have a shallow depth of field

7. DOF is extremely small when focusing on close objects, so a small aperture is required to ensure sufficient DOF

8. The DOF and the focal length are two different things. Basically the Hyperfocal distance of a lens is that focal length of a lens at which the lens has the highest DOF. A camera focused at DOF can only clearly see nearest to that Hyperfocal_D/2. And most focus free lenses cannot accurately capture subjects nearer than six to eight feet from the camera

9. When the 35 mm lens is set to f/11 and focused at approximately 1.3 m, the DOF (a “zone” of acceptable sharpness) extends from 1 m to 2 m.

10. the larger the format size, the longer a lens will need to be to capture the same frame size as a smaller format. SO because the larger formats require longer lenses than the smaller ones, they will accordingly have a smaller depth of field.

11. If a photograph looks to be a wide angle image then it can be because it was taken with a 17mm focal length. On the other end of the scale, big mm numbers like 200mm or 300mm provide a magnified telephoto view. They are good for animal photography where you might want to zoom in on a bird yet not be too close and scare it away. 200mm helps in filling up the photo with the object

12. For a given format size, at moderate subject distances, DOF is approximately determined by the subject magnification and the lens f-number. 

• 1. For a given f-number, increasing the magnification, decreases the DOF; decreasing magnification increases DOF. 

  2. For a given subject magnification, increasing the f-number (decreasing the aperture diameter) increases the DOF; decreasing f-number decreases DOF.

All right now i have some more points that i would like to add here regarding shooting with a point and shoot

• If it's bright ( Set f numebr to lower value, ISO to lowest value and adjust shutter speed)

• For MAcro use a higher f number ( people say opposite but since i have a point and shoot and i need to focus on close stuff i would need a small hypefocal distance of .95

• High f number means almost everything would be in focus. and it basically reduces the aperutre area

• Dont Shoot slower that your focal length ( assume a 35 mm focal length, without zoom in simplest conditions)

• Also Rule of thirds

• The following is the info about the camera which i gathered using exiftool and snaps taken from my camera, then i wikied amd googled and compiled info here.

  • Xresolution : number of pixels per resolution unit

  • Resolutionunit : 1 inch for my camera

  • Circleofconfusion : .005mm in my camera

  • FOV = 50.7 degrees

  • focal length = 6.3mm / 35mm equivalent = 38mm

  • Hyperfocal dist = 2.85 when Fnumber  = 2.8

  • Hyperfocal dist = .95 when fnumber = 8.4

The End