Widening my approach

[DonSchap]

I made the decision to go with a wider/brighter lens, as I had hinted at earlier this month. My eye had been on either the 24mm f/1.8 or 20mm f/1.8 from SIGMA. I finally decided to go as wide as reasonable and it is the:

AF 20mm f/1.8 (D) EX Aspherical DG DF RF (ø82mm-filter)

It is a little bit more money than the 24mm and definitely has a bigger filter-ring, so that cost will be higher, also. That, coupled with the fact that I already have a 24mm f/2.8 ... going a bit wider seemed the better "capability" decision.

Again, from my earlier discussions, this lens allows for a much wider Depth of Field (DOF) at f/1.8 than the 50mm f/1.4, at the same distance.

Subject distance or Center of Focus (CoF) is at: 10-feet

Lens . . . Aperture . . . . DOF
50mm . . . f/1.4 . . . = 0.68 ft
50mm . . . f/1.7 . . . = 0.81 ft
50mm . . . f/1.8 . . . = 0.86 ft
50mm . . . f/2.8 . . . = 1.36 ft

20mm . . . f/1.8 . . . = 5.82 ft
20mm . . . f/2.8 . . . = 10.5 ft

24mm . . . f/1.8 . . . = 3.88 ft
24mm . . . f/2.8 . . . = 6.51 ft


Bump the whole shebang out to 20 feet!

Subject distance or Center of Focus (CoF) is at: 20-feet

Lens . . . Aperture . . . . DOF
50mm . . . f/1.4 . . . = 2.75 ft
50mm . . . f/1.7 . . . = 3.28 ft
50mm . . . f/1.8 . . . = 3.47 ft
50mm . . . f/2.8 . . . = 5.58 ft

20mm . . . f/1.8 . . . = 30.6 ft (that is, near: 13 ft, far: 43.6 ft)
20mm . . . f/2.8 . . . = 131.4 ft (that is, near: 10.8 ft, far: 142.1 ft)

24mm . . . f/1.8 . . . = 17.5 ft (that is, near: 14.5 ft, far: 32 ft)
24mm . . . f/2.8 . . . = 37 ft (that is, near: 12.5 ft, far: 49.5 ft)

As you can see, that 20mm at aperture f/1.8 is really going to be quite handy for getting those school plays and recitals in low light ... when you can get close, w/o obscuring the entire crowd, lost in an "outside the DOF" fog.

If you do not understand this presentation, that's okay ... as you really have to have a wide-aperture to truly appreciate it and what is happening. A 50mm lens is just not going to work close-up.

In fact, to get the same effective DOF the 20mm gives you @ f/1.8 at ten-feet away ... with the DT 50mm f/1.8 you would have to back up to 25-feet.

Doing the same thing at 20-feet (20mm @ f/1.8) ... the DT 50mm f/1.8 lens would have to be 57-feet away. The subject is getting pretty small at that point.

My UWA, the SIGMA AF 10-20mm f/4-5.6 DC EX is quite a bit darker, as you can tell ... nearly 3 f-stops worth! Zooms always are. It is quite excellent for outdoor work, but indoors ... it can take a beating with low light and the resultant "noise" at higher ISOs. The wide PRIME eliminates that to a large degree.

Anyway, that is what this lens brings to the party. Low light capability and ... some real room.

Below is a rough diagram to demonstrate the 20mm @ f/1.8 DOF at the two different subject (CoF) distance:



Let there be ENOUGH light, eh?

[dr4gon]

Uh oh, it's another Sigma again!

So, I guess you don't want to use the 70-200mm to get in on the action and would rather take a step back and capture everything?

[DonSchap]

At least, now ... I have a real working choice in the matter.

You also have to consider that the choices are rather limited, as Tokina does not manufacture a "SONY" mount (EDIT: Apparently there is some word that Tokina will have the SONY-Mount on their lenses by the end of this year. Guess we shall see.), and TAMRON gave up its wide primes (SP AF 14mm f/2.8) in the SONY-mount, also, last year. SIGMA is all that people have left to use, so there is that. at the manufacturers, not you Ryan.

The one thing I do dread, is finding out, after it arrives, it has to be "tuned." Man, that is so annoying!

Yes, I am aware that SONY has the "left-over" five-contact Minolta SONY re-brand 20mm f/2.8 lens (the SONY actually costs $30 more for less lens), but as per the chart in the first posting ... I want truly wide-aperture for indoor use. I believe that I have outdoors pretty well covered.

[DWessel]

Don,

Looks like a great acquisition, especially for indoors. While I'm enjoying my 50mm f1.4, I've experienced the DOF problem your post discusses when in close quarters and low light. Step back, step back, step back ... damn.

Now you can be close, wide and fast!!!

[Rooz]

The one thing I do dread, is finding out, after it arrives, it has to be "tuned." Man, that is so annoying!

dare i say it...AF fine tune. lol

[DonSchap]

@ 'Rooz': No ... let us do it right ... IN THE FIRST PLACE! QC to the rescue. It's morally correct.

@ Darin: It is a DG lens, which means you can slap it on the A900 and get the real wide angle (94.5-degrees) out of it. The APS-C sensor cameras only get 63.8-degrees out of it (effectively 30mm). I'll see what I can post that will really point out the advances a lens like this can offer.

Here's SIGMA description:

DG (DG Lens)
These are large-aperture lenses with wide angles and short minimum focusing distances. With an abundance of peripheral illumination, they are ideal lenses for Digital SLR Cameras whilst retaining suitability for traditional 35mm SLRs

[Rooz]

AF fine tune takes the angst out of the equation.

[jimr-pdx]

At least, now ... I have a real working choice in the matter.

You also have to consider that the choices are rather limited, as Tokina does not manufacture a "SONY" mount (EDIT: Apparently there is some word that Tokina will have the SONY-Mount on their lenses by the end of this year. Guess we shall see.), and TAMRON gave up its wide primes (SP AF 14mm f/2.8) in the SONY-mount, also, last year. SIGMA is all that people have left to use, so there is that. at the manufacturers, not you Ryan.

The one thing I do dread, is finding out, after it arrives, it has to be "tuned." Man, that is so annoying!

I picked up a Tamron 14/2.8 for a song recently (and I'm a lousy singer!) - wonderful images, and yes: back focus. If they ever accept this warranty registration (it failed online and came back 'wrong address' by postcard.. but it does ask how many rolls I shoot per year ) I will have to have mine tuned too.

Images at http://picasaweb.google.com/alphaPDX/SP14

[DonSchap]

That SP AF 14mm f/2.8 Rectilinear should be a super lens to work with, once you get it tightened up.

A good demonstration of the lens flair in your picsaweb postings. Something that definitely needs to be watched and corrected.

If you tire of the SP 14 ... let me know.

[bigw00dy]

What a coincidence.
On my lunch break today, I stopped into a camera shop I was told about from a friend of mine. I was looking a Sigma 10mm-20mm wide angle lens they had there.
I did not have my a100, so the owner took down a loaner a100 and snapped the lens on. I like it of course. For anyone in the tri-state area, this shop is not bad...Not your typical 'Ritz' camera shop. They have a ton of product on hand and they don't hound you. Toward the end of my break, the owner threw the offer out there to trade in my a100 for an a350.

For anyone interested:
http://www.lecameraonline.com/