Lens Review: Pentax DA* 300mm F4 SDM

In the current land of Pentax, the DA* 300mm F4 SDM is as long as new lenses get unless you have the time, money, and connections to custom order something longer directly from Pentax Japan. Even then I’ve only heard that is possible from what people say on Internet forums.

Until around a half year ago, I managed with a Tamron AF 75-300mm f/4.0-5.6 LD telephoto zoom lens. Eventually I was looking for that Pentax SMC coating as well as weather resistance and presumably higher sharpness, so I started my research to see what was available. I made the big purchase and can now say I’m happy that I did.

Technical specifications for the lens:
Lens Mount: PENTAX KAF2
Lens Construction: 8 elements in 6 groups
Angle of View: 5.4 degrees
Aperture: F4
Number of Diaphragm Blades: 9
Minimum Aperture: F32
Minimum Focusing Distance: 55.2 inches (1.4m)
Filter Diameter: 77mm
Maximum Magnification: 0.24X
Dimensions: 3.3 x 7.2″ (83 x 184mm)
Weight: 37.7 oz. (1,070g)
Case: S120-210
Objective Cap: O-LC77
Hood: PH-RBK 77mm
Lens Aperture Ring: N/A
Tripod Adapter: Included, demountable w/coin
Diaphragm Control: Fully Automatic
Focal Length: 300mm (equiv. 450mm)
Notes: Supersonic motor, Quick-shift focus, SP (Super Protect) coating, Filter window, Detachable tripod mount

A quick overview of the lens on Youtube:

General talk about the lens and its features:
The DA* 300mm is a super-sonic drive motor 300mm prime lens designed for digital SLR cameras. For its focal length, it is physically quite compact. Fitting in Pentax’s idea of having comparatively small durable weather resistant pro level lenses. The obvious drawback is that the lens has a maximum aperture of f4, which isn’t really that much of a drawback considering the physical trade off necessary to get that extra stop of light on such a long lens. The exterior is completely metal (besides the rubber grip material and focus measurement window) and a real beauty of a lens in all respects. It’s the type of quality feel that spoils you and makes you not want anything lesser after handling it. The lens is comparatively small next to existing 300mm F4 Canon and Nikon designs (around 0.2 inches in width, 2 inches in length from both) and lighter by around 100 – 400 grams. The distance scale marks are inside the barrel and visible through a clear plastic window, so the manual focus ring respectively does not rotate when the camera is in auto-focus mode. The lens also has a convenient toggle switch to flip between auto and manual focus. The focus ring itself is large at almost 2.5 inches long making it easy to access and use. The focus throw is pretty long taking around 4 single handed turns from end to end. Once you hit the end of the focus scale, you can still turn the ring, but there is a noticeable increase in resistance after a slight “thud” sound. There is a built-in tripod mount that allows the lens to be rotated to allow the camera to be orientated vertically or horizontally with two registrable clicks for perfect orientation, although that depends on how tight you have the thumb-screw. The actual tripod mount part itself can be easily removed with a coin, which is a thoughtful yet strong and convenient mounting mechanism. The specifications and serial number are engraved into the metal manual focus ring, which I thought was a nice touch. Some of the older and cheaper Pentax lenses used stickers for the serial number, which is a bad idea as in regards to theft protection. As I mentioned before, the lens is weather sealed and is probably one of the most weather resistant lenses from Pentax or any company for that matter. The lens has a 77mm filter thread and objective lens approximately the same size, which is pretty standard for this class of lens and good enough for almost anything you can throw at it including astrophotography.

What I like about the lens:
- While I have not scientifically tested the lens, I feel that it is sharp enough from it’s widest aperture and have never found an image that was was not good enough due to optical quality.
- It follows the tradition of Pentax rendering with vivid contrast. This lens is also very strong at controlling chromatic aberrations such as purple fringing.
- Seems very good at controlling flare, but I almost always use the lens hood.
- The bokeh can be beautiful (at times), especially in combination with a sharp subject producing a strong 3D effect.
- The lens seems bright throughout the whole frame event at the widest aperture (it is a full frame lens by design and has been confirmed “good enough” on pentaxforums.com with film cameras).
- The construction is top notch and one of the best lenses I’ve personally owned.
- SDM is quiet in focusing compared to screw-drive lenses.
- Quick-shift focus with a nice feature to have.
- Top notch weather sealing.
- Small and light for it’s abilities relative to similar lenses.
- The lens is very versatile considering how long the focal length is, which is partly due to the short minimum focusing distance.
- I can easily hand-hold this lens and pan-focus on moving subjects.
- The lens is still very sharp and usable with a 1.5x PzAF Kenko teleconverter I have, but not perfect. The teleconverter can add visible aberrations depending on the situation.

What I’m not too fond of:
- Maximum aperture of f4 is challenging at times with my K-7 because I like to keep the ISO low, but I’m not sure how much having f2.8 would really help…
- The lens isn’t cheap hovering around $1100, but good lenses hold value well.
- Pentax SDM hasn’t had the best track record, but my lens has been problem free. I did have two instances when I first got the lens where I needed to slightly rotate the screwdrive screw on the camera body after seeing that the lens locked up of sorts when I tried to auto-focus. For whatever reason the screw-drive connection wasn’t complete and held up the SDM from functioning. I’m guessing the screw drive connection in the lens was just a bit stiff initially (especially since the screw-drive bit isn’t used but on the oldest of camera bodies).
- Focus isn’t “lightning fast” with the K-7 and K10D, but it works fine. I think the K-5 might be better in this regard.
- Not specific to this lens as I have not had SDM issues, but I feel Pentax should allow users to select either SDM or screw-drive focus mode in the camera body.
- Bokeh can be wavy depending on the scene and conditions, which is most likely due to having sharper more contrast-y background blur or possibly just a property of the glass elements in how they handle the light and how you are facing a close background. I always use a lens filter, so I can’t say if it’s caused by that or just a property of the lens design.

Images with a bit of analysis:

This lens handles strong light sources quite well to avoid flare (bright 2 watt LED light-source).

ISO 200, 1/20th, f4.0
Chromatic aberrations are not much of an issue (bright 2 watt LED light-source).

ISO 400, 1/400th, f4.0
The lens is able to produce lovely bokeh and sharp subjects at f4.0

ISO 1600, 1/250th, f4.0
Here is an example of the wavy bokeh. From what I can tell it happens when the background is high detail and close to the subject (downward angle in this case).

ISO 320, 1/400th, f4.0

A few additional images:
Early Mist.
IMGP8403
Midori.
Intense Light.
IMGP8038

Conclusion:
One of my best lens for sure. Although it’s also my most expensive lens to date, so quality should be high. If you are in need of a long telephoto and want to stay with Pentax and not buy a used lens, this is it. Your only other option is the 60-250mm, but I feel the DA* 300mm provides some positives to make up for not having the ability to zoom. Such as better weather resistance by not having an extending barrel, 50mm more millimeters in focal length, ideal long telephoto lens for people who prefer primes, and most likely a bit cheaper than the 60-250mm. Either lens would be a good buy though… Your other options for new lenses would probably be in the Sigma and Tamron line-ups, but those currently don’t have weather resistance, which I feel is important in these “slow-ish” long lenses that are designed for being used outside.

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