Zoom Lens එකක උපරිම කාච ද්වාර (F) අගයන් දෙකක් තිබීමට හේතුව (උදා – 75-300 F 4-5.6)

කාචයක නාභි දුරේ සම්මත ඒකකය වනුයේ f අංකය වේ. එහි ගණිතමය අර්ථ දැක්වීම පහත පරිදි වේ..

fඅංකය =   කාචයේ නාභි දුර   /කාච විවරයේ විශ්කම්භය

මෙම සමීකරණය ඇසුරෙන් පෙනීයන්නේ කාච විවරයේ විශ්කම්භය වැඩිවන විට fඅංකය අඩුවන බවය.

aperture

උදාහරණයක්‌ ලෙස,

නාභි දුර = 70 mm

කාච ද්වාරයේ විශ්කම්භය = 17.5 mm ලෙස සලකමු.

fඅංකය =  (70 mm)/(17.5 mm)  = 4

දැන් කාච විවරයේ විෂ්කමභය නොවෙනස්ව නාභි දුර 105 mm දක්වා වැඩි කළහොත්,

fඅංකය =  (105 mm)/(17.5 mm) = 6

මේ ආකාරයට නාභි දුර වැඩිකරන විට කාචයක fඅංකය නියතව පැවතීමට නම් එම කාචයේ ද්වාරය විෂ්කම්භයද අනුරූපව වැඩි විය යුතුය.

105 mm හී දී f4 අගයක් පැවතීමට නම්,

කාච ද්වාර විෂ්කම්භය = 105mm/ 4  =26.25 mm

මෙසේ කාචයේ නාභි දුර වැඩි කරන විට ඊට අනුරූපව කාච ද්වාරයේ විශ්කම්භය වැඩි කිරීමේදී ප්‍රයෝගික ගැටළු මතු වේ. උදාහරණයක් ලෙස 300 mm වැනි වැඩි නාභි දුරකදී f4 අගයක් ලබා ගැනීමට කාච ද්වාරයේ විශ්කම්භය 75 mm විය යුතුය. එනම් කාචය ඉතා විශාල විය යුතුය.

එබැවින් දුර කාචවල නාභිදුර බොහෝ විට f4 හෝ ඊට වැඩි අගයකට සීමා වේ. සාමාන්‍ය මිලෙන් අඩු කාචවල දුර අන්තයේදී වැඩි F අගයක් ඇත්තේ මේ හේතුවෙනි.

උදා – Canon 75-300 f4-5.6 (රු.30 000)
Canon 75-300 is f4-5.6 (රු.70 000)

Canon 70-300mm f4-56

70 mm අන්තයේ f 4                   300mm අන්තයේ f5.6

Zoom කාචයක අන්ත 2 දෙක දීම fඅංකය නියතව පැවතීම සදහා නාභි දුරේ වැඩිවීමට සාපේක්ෂව කාච විවර විෂ්කම්භය වැඩි විය යුතුය. මෙවැනි කාච තැනීම ඉතා සංකීර්ණ ක්‍රියාවලියකි. එමෙන්ම මෙම කාචවල විශාල විශ්කම්භයෙන් යුත් කාච භාවිත කරයි.

උදාහරණ:-

Canon 70-200 f4 (රු.110 000)

Canon 70-200 f2.8 (රු.260 000)

images (5)

මෙවැනි කාච සාපේක්ෂව ඉතා මිල අධිකය.

Canon 70-300 f 4-5.6  , Canon 70-200 f 4  හා Canon 70-200 f 2.8  කාව විෂ්කම්භ වල වෙනස වටහාගන්න .

photo_70-200-compared

සේයා රූ කතා බහේ (https://www.facebook.com/groups/phototalks)  සිදුවූ කතා බහක් ඇසුරෙනි. 
අදහස් – ඉන්ද්‍රනාත තේනුවර මහතා, රන්ජිත් විජේකෝන් මහතා , ප්‍රමිත සුරියප්පෙරුම මහතා , ජනක බස්නායක මහතා හා උපුල් දයාවංශ මහතා..

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Buying a DSLR for your hobby– 01

I am writing this series of posts to help you in buying a DSLR camera for do photography as a hobby.I am no expert in this field but photography was my hobby for last 8 years. I only own a single DSLR. So I am writing this series based on my research on the internet and my opinion

DSLR to Quality Photos?

If you are watching for a good quality camera for your day to day photographic needs, DSLR might not be the best option. Replacing a day to day use small camera from a DSLR is not a good option. Caring a DSLR and shooting with is not simple as a small point and shoot cameras. Therefore the best candidates are high end compact cameras or pro-sumer cameras. There are many pro-sumer (or bridge or mirror less) cameras out there. they offer almost 80 % –90% picture quality and all (may be more) automatic functions for slightly less amount of money.

Nikon coolpix P series cameras –  (Ex Collpix P510)

http://www.dpreview.com/products/nikon/compacts/nikon_cpp510

Canon Powershot SX seris (Ex – Powershot SX40HS)
http://www.dpreview.com/products/canon/compacts/canon_sx40hs

Are some famous non DSLR super zoom cameras , which can provide quality photos and much smaller and light weight enabling day to day ease of use.

I like to do Photography as a hobby. so start with DSLR ?

surprisingly my answer is NO. Why ? In my opinion photography is not all about capturing photos or not about having a big camera. First of all you have to see the world in a different angle. You have to understand the art of photography. So if you wish to start doing photography as a hobby the best thing is to read some books and look at some artistic photos. Then start taking photos with a small camera.

When to buy a  DSLR ?

when you staring to see things better and feeling like you are ready to buy a DSLR then study about DSLR cameras, their features , accessories and expert reviews. Do some Research about DSLRs . Make a wish list and modify it.  http://www.dpreview.com is a good site to refer technological details and user/expert opinion about cameras.

In the next article I will be talking about DSLR technologies and accessories. So be patient or start your own research (at the end that’s what I really expect from you !)

Photography With Stage Lighting

Taking Photographs with stage lighting setups is one of most trickiest scenarios in photography.this article is about my photography experiences with stage lighting setups.

All photographs used in this article was taken by myself  using Nikon D90 digital SLR Camera at “Rhythm of the Maroons -2008 ” , musical event held at the Sugathadasa Indoor Stadium.  Stage lighting setup on that day included over 50KW of power cans, Color wash , Moving Head and scanner types of lights.

When we use regular flash lighting natural effects of background lighting gets cancelled due to high contrast of the flash light.if we turn off the flash lighting pictures will easily get underexposed and it will reduce amount of details in the photograph. lets look at following photograph

this photograph was taken with handheld camera.Therefore shutter speed was limited to 1/60s and aperture settings and ISO speeds  increased to maximum possible levels. As a reason of high ISO sensitivity , we can identify some noise in the picture. Even thogh we can use a monopod to increase shutter sped limitations but due to very dynamic nature of the objects in the stage that option was impracticable.

So far we identified following problems.

  1. Limitations of Shutter speed due to handheld camera and moving objects
  2. Noise due to High ISO sensitivity
  3. Low level of details due to under exposure.

to overcome these problems i have found some tips by my experiments. Those are

  1. Practice to held camera more stably and use some support (of walls etc) . this will provide opportunity to reduce shutter speed up to 1/30s . Lower shutter speeds than that can cause problems in capturing fast moving objects
  2. Wait till correct moment – most of the time we can identify moments with bright lighting setups. in those moments you can capture amazing photographs without any troubles
    also we can identify stationary moments in dances etc. capturing those moments are easy because we can avoid motion blur.
  3. Use Shutter Priority mode with automatic aperture and ISO settings  with these settings you can adopt changes in lighting quickly. all you have to do is select proper shutter speed for the lighting condition.
p.s – Hope this article will support you in dealing with stage lighting scenarios. For any clarification or further  information ,  please leave a comment or personal message.