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Cons: - 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. I have a feeling the lens would be faster in screwdrive mode as well. - 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.

Pros: - 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. - Topnotch 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 Kenko teleconverter.

Summary: More information and sample photos here: http://photographybanzai.com/2010/11/24/lens-review-pentax-da-300mm-f4-sdm/

Cons: build quality nice colors and contrast

Pros: no apenture ring

Summary: my best lens