So you got your new SONY DSLR ... now what?

[DonSchap]

The subject of PRIME Lenses was brought up and this really can be a real "mine field" to navigate, because there are various advantages to the different focal lengths and apertures.

The most dynamic aspect of a PRIME lens is Depth of Field (DOF). Having a short focal length PRIME lens with an ultra wide aperture (f/1.4 - f/1.8) provides a lot of light, but also a relatively deep DOF at close range. The same aperture and distance on a medium prime length PRIME tightens up that DOF considerably (shallow). On a telephoto PRIME lens, the DOF at wide aperture becomes very thin.

A couple of DOF examples:
f/1.8 @ distance of 10-ft

Focal length → DOF

20mm → 5.8-ft

24mm → 3.8-ft

35mm → 1.8-ft

50mm → 10-inches

85mm → 4-inches

135mm → 1.5-inches

Now, increasing the distance between you and your subject does have large effect, but the subject is reduced in size. Increasing to 20-ft, the subject is half as large. That can be a real problem with a wide angle lens, as the subject gets kind of 'lost' in all of the background:

Focal length → DOF

20mm → 30.6-ft

24mm → 17.5-ft

35mm → 7.3-ft

50mm → 3.5-ft

85mm → 14-inches

135mm → 6-inches

While this is hard to envision, without the accompanying images, you can kind of get the feel for the problem if you have a typical 17-50mm, 18-50mm, 18-55mm, 24-70mm or 18-70mm "kit" lens. Ignoring the DOF for a few moments, focus on your subject (10 feet away), then simply watch through the viewfinder as you zoom from 50mm down to 24mm. Now, step back 10 more feet (to a total distance of 20 feet) and do the same thing. Yeah, a lot more background to fight the "framing battle" with.

So, as you can probably tell ... picking the proper PRIME lens depends almost entirely on the situation. The low-light struggle with DOF has to be reconciled, before you spin wide open to f/1.4 or f/1.8, otherwise ... everyone may be bright, but they are going to look a little fuzzy around the edges.

So which PRIME lens to own? Well, generally speaking, the 50mm f/1.7 would be a place to start, because it is a relatively low-cost choice and splits the difference between wide and telephoto. The next one is a bit more difficult to choose, because the cost goes up considerably and kind of depends on whether you have a APS-C (α100, α200, α300, α350, α700) or a Full Frame (α900) sensor camera.

Note: The new α230, α330 & α380 DSLRs may NOT have motor drive in them and using screw-driven AF lenses (currently ALL non-SSM/non-HSM lenses) may not be an option, because autofocus (AF) will not be operational. This still remains to be seen, at this time. A new 50mm f/1.8 is being developed at this time, for this reason. Yeah, the ground is a little shaky on these new offerings. If you thought "lens selection" was bad before ...

Here is a "short list" of available prime lenses w/ filter diameters* (non-MACRO despite description)

Non-fisheye Wide Angle PRIME
TAMRON SP AF 14mm f/2.8 LD Aspherical Rectilinear (no filter ring)
SIGMA 20mm f/1.8 EX DG ASPHERICAL RF ø82mm
SONY 20mm f/2.8 ø72mm
SIGMA 24mm f/1.8 EX DG ASPHERICAL MACRO ø77mm
SIGMA 28mm f/1.8 EX DG MACRO ø77mm
SONY 28mm f/2.8 ø49mm
SIGMA 30mm f/1.4 EX DC HSM ø62mm
SONY 35mm f/1.4 G ø55mm

Normal PRIME
SIGMA 50mm f/1.4 EX DG HSM ø77mm
SONY 50mm f/1.4 ø55mm
SONY DT 50mm f/1.8 ø55mm
Minolta 50mm f/1.4 ø49mm or ø55mm
Minolta 50mm f/1.7 ø49mm or ø55mm


Telephoto PRIME
SONY 85mm f/1.4 CZ ø77mm
SONY 135mm f/1.8 CZ ø77mm
SONY 135mm f/2.8 [4.5] STF ø72mm Manual Focus
SONY 300mm f/2.8 G SSM ø42mm (internal)

* Some folks pick and choose their lenses to have similar filter-ring diameters to reduce filter costs, so I included it.

[Biomech]

Thanks, you have been a great help

[DonSchap]

Concerning PRIMES (fixed focal length lenses) vs. ZOOM (variable focal length lenses):

Almost ALL zooms are limited to a maximum aperture of f/2.8. To understand roughly what this means ... consider the f/stop scale:

Consider source light has a value of 1

Therefore, an aperture setting of:

f/1 = ½ source lighting
f/1.4 = ¼th “ “
f/2 = 1/8th “ “
f/2.8 = 1/16th “ “
f/4 = 1/32th “ “
f/5.6 = 1/64th “ “
f/8 = 1/128th “ “
f/11= 1/250th “ “
f/16 = 1/500th “ “
f/22 = 1/1000th “ “
f/32 = 1/2000th “ “
f/44= 1/4000th “ “
f/64= 1/8000th “ “


So, as you can see ... you are rapidly losing light as you "tighten"up" the aperture. As such, back to the zoom lens. At f/2.8, you are only getting 1/16th of the available light. In daylight or a well lit room, that is probably fine. But in the evening, when the lights grow dim ... f/2.8 becomes a challenge. If you only have an F/4 lens? Forget about it, without a flash, unless the subject is very still and you have a tripod.

So, let's pop on an f/1.8 lens. Does not sound like a lot of change, but consider this ... you now are working with 1/6 instead of 1/16 of the available light. That is an amazing difference in the number of photons that are going to strike your camera's sensor.

So, why PRIME? Because, now, your camera can actually detect something, indoors, at a reasonable shutter speed, where before you would have had to have a tripod and prayed that NO ONE MOVED. That can be all the difference in your images ... and play a terrific part in photographing an orchestra (with all those moving arms and fingers) or a dance recital (as the subject gracefully moves, instead of a motion blur of some kind.). Some venue where a flash simply cannot be used.

The neat part of one of these wider-aperture prime lenses is that they work very effectively on the intro-DSLRs ... allowing these cameras to operate at a much lower ISO, reducing the "noise" that you probably would encounter at ISO-800 or 1600. You can get a lot more mileage, per se, out of the intro-DSLR with a good lens on it. When you are ready to move up to a more advanced camera, that great lens goes right along with you, where it can be appreciated even more.

Camera bodies come and go ... but, great glass is ... well, always great glass.

[DonSchap]

Some of the special prime lenses are the MACROs and Fisheyes.

MACROs allow for a very close-up shot, with a very wide aperture (usually f/2.8), allowing for exceptional clarity, detail and extremely shallow depth of field, effectively "fuzzing out" the areas in front of and behind the subject.

Below is a listing of the "currently" available lenses:

MACRO PRIMES
SONY DT 30mm f/2.8 Macro (ø55mm)
SIGMA 50mm f/2.8 EX DG (ø55mm)
SONY 50mm f/2.8 (ø55mm)
SIGMA 70mm f/2.8 EX DG (ø62mm)
TAMRON SP AF 90mm f/2.8 Di 1:1 MACRO (ø55mm)
SONY 100mm f/2.8 Macro (ø55mm)
SIGMA 105mm f/2.8 EX DG (ø58mm)
SIGMA 150mm f/2.8 EX DG (ø72mm)
SIGMA 180mm f/3.5 EX DG (ø72mm)
TAMRON SP AF 180mm f/3.5 Di LD 1:1 MACRO (ø72mm)


Fisheye lenses offer a distorted aspect to your image, forgoing the rectilinear correction of the standard optic. Normally, because of the rather eccentric shape of the first element, these type of lenses cannot accommodate filters and therefore have no filter ring on the front of the lens. Many do have a gelatin-filter ring in the rear of the lens to add various "style" elements to the image.

Fisheye PRIMES
SIGMA 4.5mm f/2.8 EX DC Circular Fisheye HSM
SIGMA 8mm f/3.5 EX DG Circular Fisheye
SIGMA 10mm f/2.8 EX DC Fisheye HSM
SIGMA 15mm f/2.8 EX DG Diagonal Fisheye
SONY 16mm f/2.8 Fisheye

[Amrou-A]

Thank you Don for that full knowledges ..

Much appreciated.

[DonSchap]

The mission of these boards should be to get the information out there ... in as good and acceptable a fashion as can be presented. We all need to contribute to our hobby, to keep it growing and progressing.

Photography got kind of stale back around 1995-2004. These boards and the impact of digital really got things moving, again.

Enjoy!

[sdecker]

I'm just wondering in what respects the 18-70 has such a poor performance? Is there a site where I can find side-by-side comparisons with other lenses? For me it seems to do a pretty decent job in decent lighting, and I can live with some minor CA and light falloff. It doesn't seem spectacular, but is it really toss-worthy for an entry-level DSLR user like myself?

[DonSchap]

Here is a relatively fair side by side of the SONY 18-70 "kit" vs the SONY CZ 16-80 lens, to give you some idea what is lost in your photography when you opt to use this rather extraordinary poor lens.

Also, a civilized discussion concerning this lens choice.

[Didds]

Originally Posted by DonSchap

Here is a relatively fair side by side of the SONY 18-70 "kit" vs the SONY CZ 16-80 lens, to give you some idea what is lost in your photography when you opt to use this rather extraordinary poor lens.

Also, a civilized discussion concerning this lens choice.

Isn't there a similar lens that would come somewhere between the two?

[Didds]

Originally Posted by DonSchap

Multiple lens approach[/B]

1) (Normal zoom lens) SP AF 17-50mm f/2.8 XR Di-II LD or
Attachment 12694

1a) (Normal zoom lens) SP AF 28-75mm f/2.8 XR Di LD MACRO
Attachment 12692
[B]

What's SP (as in SP AF 28-75mm.......) - and AF presumably is autofocus?

Thanks for this thread, very informative!