Pentax SMC DA 17-70mm F4 AL [IF] SDM offers the most attractive combination of range, speed, technology and price - on paper at least. It is a dedicated APS-C format lens with a field-of-view equivalent to 26-107mm (full format).
The DA 17-70mm f/4 features the new near-silent Supersonic (ultrasonic) Dynamic Motor (SDM) AF. Unlike the DA* 16-50mm f/2.8 SDM it does not offer the old AF drive screw for legacy DSLR support but that's forgivable by now.
This lens is using KAF3 mount which means only can AF with SDM support body. With non-SDM body, only manual focus available.
Specifications
| Image Circle | : APS-C |
| Focal Length | : 17-70mm |
| 35mm Equivalent | : 25.5-105mm |
| Max Aperture | : F4 |
| Min Aperture | : F22 |
| Diaphragm Blades | : 7 Blades |
| Lens Construction | : 17 Elements in 12 Groups |
| Angle of View | : 79 to 23 degree |
| Focus Details | : Internal, SDM with quick-shift focus |
| Front Element Rotation | : No |
| Zoom System | : Rotary |
| Closest Focus | : 0.28m/0.92ft. |
| Magnification Ratio | : 0.31x/1:3.2 |
| Filter Size | : 67mm |
| Dimensions | : 93.5mm x 75mm / 3.7 in. x 3.0 in. |
| Weight | : 485g / 17.1 oz (without hood) |
1. Build Quality
The build quality is really good and comparable with DA* series. It feel very solid in my hand. The weight is on the average side which is not too heavy and not too light. Zoom ring is quite bigger(approx 35mm long) and it is very comfortable. It is also tight and this prevent lens slip off or extend when camera facing down.
This lens extend when zooming. It is feature with Internal Focus[IF] which means the lens not extend and rotating while focusing. The picture below show the size comparasion of the lens when extend.
2. AF Mechanism
AF respond is very fast as expected since it use SDM focusing. But the AF speed not much different with non-SDM lenses. About the accuracy, this lens focus accuracy is good but sometimes it give up when no proper contrast detect and need to refocus. This lens also feature a quick-shift focusing mechanism means it can give you fully manual control and you can easily manual focusing without changing focusing mode.
During the focusing, this lens does not making any noise like screw dirven AF lenses. Thank you for the SDM feature which make this lens silent during focusing.
3. Image Quality(IQ)
IQ is comparable with DA* series. This lens reported use the same glass as the DA* series. Flare and CA control are very good and seems better than DA*16-50. This lens also quite good at macro at 70mm. Minimum focus 28cm at the whole facal range give this lens maximum magnification around 1:3.2 at 70mm. This sharpeness is good at whole range. Quite soft wide open at 70mm but good if increase 1 or 2 stop.
4. Distortion and Vignetting
Distortion is quite visible at 17mm but stil acceptable. At 24mm and above, distortion is nearly zero. At 17mm wide open, this lens show around -1EV vignetting but not really noticeble. It can be correct by using F5.6 and above.
5. Chromatic Abberations(CA)
This lens control CA quite well and it is acceptable. The weakest point is at 17mm which pronouced CA especially in wide open aperture. But it can be correct by step down one stop exposure. Beyond 24mm and above, the CA is very well control.
6. Conclusion
For overall this lens is very good for a daily use. The focal cover from 17mm to 70mm is very usefull for street shooting or travel.
Pros :
1. Better build quality, solid
2. Better CA control
3. Better accuracy
4. Fast respond and silent AF
5. IQ comparable with DA* series
6. Very good zoom ring
Cons :
1. Can only AF with SDM support body
2. Easy to give up(AF)
3. Max aperture F4
4. Price
7. Rating
| 1. Optical Quality | ★★★★ |
| 2. Build Quality | ★★★★☆ |
| 3. Value for Money | ★★★☆ |
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