Sigma 17-70mm f/2.8 - 4 DC OS HSM

My last lens were Sigma 18-200mm DC OS HSM. I've been use it for a while and I really enjoyed the lens especially its wide focal range feature. However, like many wide-tele superzoom lens, it's prone to produce poor image quality and unsharp image and this lens is not spared from the problem. And don't forget this lens is damn heavy and you need to have super stable hands to be able to stabilize it.

Recently, I've sold the lens and seeking for new lens to try. I'm eyeing for standard zoom lens now and two lenses are really captured my attention. First one is Tamron 17-50mm f/2.8 and another one is Sigma 17-70mm f/2.8-4. To compare:

Brand	Tamron	Sigma
Full Name	Tamron 17-50mm f/2.8 XR Di II LD Aspherical IF	Sigma 17-70 mm f/2.8-4.0 DC Macro OS HSM
Focal Length	17mm-50mm	17mm-70mm
Max Aperture	f/2.8 (fixed)	f/2.8(wide) | f/4.0(tele)
Autofocus	Yes (IF)	Yes (HSM)
Optical Stabilizer	No	Yes
Macro	No	Yes (0.22m)
Price	Lower	Higher by ~37%

Lets start with Tamron first. This one is non VC (vibration compensation). Tamron also got another similar lens with VC but with higher price tag. I really like the fixed maximum aperture on this lens. No matter wide or tele you go on it, the maximum aperture still at f/2.8 and that's really useful in low light condition. It also cheaper by around 37% from the competitor lens. The Sigma on the other hands, offers you extra focal length up to 70mm but at that focal length, the aperture is at f/4.0 ono.

Lets talk about autofocus. The Tamron has old-fashioned internal focus motor and it does produce quite load(but not disturbing for me at least) noise. Sigma however, implemented HSM (Hyper Sonic Motor) that resulting in quick and silent autofocus. In term of focus decisive, both is perform well. Image quality also more or less the same.

For the optical stabiliser, you can opt for similar Tamron lens with VC but I think you may not need it because the maximum aperture is fixed and you can easily snap with higher shutter speed. Just use the rule of thumb. At 50mm, use at least 1/50 shutter speed. I've tried both lens and Tamron really allow us to use this rules and minimizing blurriness. You get Optical Stabiliser with Sigma though. One thing with OS/VS on both lens is, you really need to wait until the stabiliser settle itself before actually snapping a photo. If not, the result can be uglier than not using stabiliser.

To make thing short, I chose the Sigma simply because I want the extra focal length, HSM and macro capability although it's not 1:1 macro. I don't want to have similar focal length as kit lens thats why I'm not very keen with Tamron. If you're on budget constraint though, choose the Tamron. You won't go wrong with it.

SIGMA 18-200mm F3.5-6.3 DC OS

Just got my hands on the Sigma all-purpose lens 18-200mm after been a while searching for it. This is by far the cheapest all-purpose lens available. I bought it at my local retailer.

The box

The lens mounted on my D3100

Things I like about this lens

• Cheap
• Good build quality
• Got optical stabilisation 
• Cover from wide all the way to telephoto in one lens
• Got zoom lock to avoid lens creep

Things I don't like

• Image a bit dark due to small aperture
• The zoom ring a bit tight especially at 50-80mm range..maybe just a while coz it's still new
• The stabilizer need some time to settle down especially at tele range

That's all. Thank you. Want to enjoy new lens..hehe

Photography: Depth-of-Field

Wow. Sibuk gilalah sempena amik intersesi ni. 2 subjek lagi tu. Memang hectic. Anyway, intersession dah pun habis and boleh rehat. XD Takut nak tau result :S

Anyway, untuk entry ni saya nak buat yang pendek je la..nak share about depth-of-field dalam bidang photography sebab recently ada rakan saya ni tanya:

"eh camane kau buat gambar belakang tu jadi kabur ea?"..and

"eh camane nak control brape banyak kabur kita nak ea?"..ha lebih kurang gitulah..

So, konsep yang dia tanya tu adalah berkenaan Depth-of-Field(DOF). Ia adalah term untuk menerangkan jarak antara depan dan belakang focus point yang relatively sharp. Untuk membezakan, kita guna term "shallow DOF" untuk jarak DOF yang pendek(means tempat yang dalam focus sikit je) dan "deep DOF" untuk jarak DOF yang besar(means tempat yang in-focus agak luas).

Source: http://images.cambridgeincolour.com/tutorials/dof_circleofconfusion.png

Apa yang penting sangat dengan depth-of-field ni? Penting sangat kalau:

• Nak buat bokeh
• Nak buat potraitization
• Supaya orang yang lihat gambar fokus pada objek bukan pada backgroundnya

Potrait - source: http://withfriendship.com/images/i/44403/Portrait-photography-image.jpg

Bokeh - source: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgoob7sSKLgYrrfOQcTO0qcSVcyB2GdyhxZh17koKRTbb2ouxkTOYZCq5auwb8VA4CFuE_6lSNKjL0r2p-Q0ETL3dkKSC17-39BjYZC76V5X3SPjWRVNPsuCi_JgxQsSEW_rE9arxuVYVw1/s400/awesome+bokeh.jpg

Macamana nak kawal depth-of-field??

Ada 3 cara:

1. Aperture
2. Focal length
3. Distance

But usualy, people only focus pada aperture dan focal length so saya akan cerita pasal dua factors ni sahaja ok.

1. Aperture

Aperture adalah luas bukaan iris/lubang pada lens. Ia diukur dengan menggunakan f/stop seperti f1.8, f2.8, f5.6. Makin besar nilai f/stop, makin kecil bukaan aperture dan juga sebaliknya. Ramai orang silap tentang prinsip aperture number ni bila mereka ingat f number yang besar, besarlah bukaan aperture. Wrong.

INGAT: f-number besar, bukaan kecil
              f-number kecil, bukaan besar

Aperture and its value

Jadi, untuk mendapatkan shallow DOF macam gambar potrait di atas, pakai aperture yang besar(f-number kecil). Kalau hendakkan deep DOF pakai aperture kecil(f-number besar). Tapi ingat, kalau pakai bukaan aperture kecil, anda kena matchkan dengan shutter speed yang bersesuaian sebab bukaan kecil hanya membenarkan sedikit cahaya masuk ke sensor camera/filem. So kena try-and-error ;-)

Shallow DOF

Deep DOF

To conclude:

• shallow DOF = wider aperture = lower f-number = lesser lighting entering camera
• deep DOF = narrower aperture = higher f-number = more lighting entering camera

2. Focal length

Kalau ikut wikipedia:

The focal length of an optical system is a measure of how strongly the system converges (focuses) or diverges (defocuses) light.

Tapi untuk layman term, focal length adalah berkenaan zoom. To cut it short, the more you zooming in, you'll get shallower DOF and vice versa. Simple.

Zoom more = shallower DOF
Zoom less = deeper DOF

Focal length comparison - source: www.freshdv.com/wp-content/uploads/2007/10/dof_explained_tutorial.jpg

Ok. Simple as that. Tu je lah nak cerita nak share. Skarang nak cari kerja. huhu..

Papai!!