HD Pentax-DA 55-300mm F4-5.8 ED WR Review

What's the Same - The Aperture

Because bokeh is such a critical feature of a telephoto lens, and we have quite a few sample photos to display, we wanted to give it the attention it deserved. Additionally, there has been a lot of demand to see if the starbursts have improved or at least changed with the new HD 55-300, so this page is designed to put any confusion pertaining to the aperture blades and their effects to bed. Now let's take a look.

The Aperture Blades Themselves

In light of some misinformation being shared around the forums, we'd like to set the record straight on two things. First, the new HD 55-300 WR does indeed have rounded aperture blades. The second is that this is not a change from the smc 55-300. It had rounded blades as well.

We'll let the comparison below do the talking for us, but before we get to that, we wanted to point out that the reason the 'bokeh balls' do not retain their circular shape for long (and instead have pretty clean edge lines, akin to straight blades) is because there are only 6 blades. Had they come equipped with eight or nine (the DA* 60-250 has nine), the story would be much different. The reason blade count matters is the more blades, the thinner they are with a more exaggerated curve. While not as dramatic, the difference could be compared to a rounded hunting knife blade versus a scythe.

So how does this analogy pertain to image quality? Simply put, its the more rounded the aperture stays before closing down to the point that the only part that doesn't overlap between the aperture blades (and thus creates the iris) is straight edges. Because of the 55-300's six blades, this happens very quickly. With larger manual lenses, for example medium and large format lenses, it wasn't unheard of to find apertures with rounded blades numbering 12, 14, or even 16 blades, maintaining perfectly circular openings well past F18. If not through the entire aperture range.

Electronically automated lenses do not have this many blades because it would take too long and require too much force to close them all down in the automatic, split-second manner that occurs today. In case you weren't aware, this is what happens automatically when you press the shutter on your Pentax DSLR's, to include with fully manual lenses because of the lack of an 'uncrippled' mount that would allow stop-down metering.

smc vs HD Highlight Bokeh Comparison

A wall of Christmas tree lights presented an excellent venue to compare the 'bokeh balls' of the two lenses, as the out of focus circular blobs are the most objective way to perform a bokeh test. Very stressful for the lens, imperfections in what are supposed to be perfect circles are realized very easily and quickly. The following comparison was conducted with the following settings:

For your analytical pleasure, we've included the entire aperture range for you to scrutinize. Clicking on any of the below images will allow for an enlargement.

	smc	HD
F5.8
F6.3
F7.1
F8.0
F9.0
F10
F11
F13
F14
F16
F18
F20
F22
F25
F29
F32

As you can see, there is absolutely no difference in bokeh between the two lenses.

smc vs HD Starbursts Comparison

Under the same auspices as above, we wanted to put the starburst question to rest because it has been asked if you can expect improved starbursts with the new HD lens. We did a quick comparison to show the handling of starbursts by the smc and HD models, and once again we found no difference at all, which is exactly what one should expect using the above bokeh comparison as the basis for that assumption.

We aren't going to post another aperture range full of identical images (as that's what it would be, just like above), so instead we'll show the below image. Shot by forum member noVICE using the smc version, it is an example of what you can expect from the starbursts to come from the new HD variant in real world use. Clicking on the below photograph for an enlarged view:

Pentax K-7, 78mm, 15 sec, F16, ISO 100

Again, we didn't feel the need to lengthen this page with yet another indistinguishable series of comparison photos, but fear not. There's a starburst comparison between the HD 55-300 and the DA* 60-250 later on in this review that shows many example photos so you still won't miss out on what the HD 55-300 (and thus the smc 55-300) can do in this respect.

Verdict

The bottom line is simply this: it is without any doubt that the smc and HD variants have the exact same aperture blades, both in number (six) and shape (rounded).

Enough of the old - let's see what's new.