[normhead]

I can't speak to the DA*300, but I own the DA*60-250 which is a highly regarded lens, and for good reason (it's one of the best lenses I own). Whilst it has a constant f/4 aperture and therefore has the advantage for lower light work and subject isolation, even the humble screw-drive HD DA55-300 is capable of remarkably comparable results when stopped down just a little, unless viewing images at 100% reproduction. That plus the compact size and light weight make it an extremely versatile lens. I understand the newer PLM is even better optically...

Given the flexibility of the DA 55-300, the DA* 60-250 in 1.4 TC, is the more likely replacement. But it's going to have the same dust sucking issue. Zooms just do that. Only Internal Focus [IF] primes don't. I've had my DA* 60-250 for going on 8 years now and the dust still doesn't bother me.

[SSGGeezer]

I have both and they are both amazing tools on my KP. I have not compared them on my recently acquired K-5IIs, but the flexibility of the PLM along with the light weight and fast focus are what make it a winner. I have it mounted more than any of my other lenses and have not seen any dust accumulation in over a year of constant use. The IQ of the DA*300 is even better than my copy of the PLM but as Norm notes, it is slower to focus and it is noticeably heavier. You cannot go wrong with either!

[MetalUndivided]

My guess is both out resolve any current APS-c sensor

If you're referring to the PLM, I don't think so. It definitely doesn't outresolve a 24MP sensor.

What more do we need for sharpness?

I'm not sure what you need, but anyone who shoots birds needs as much sharpness as possible. Sure, if birds in your area rub their snouts against your forehead, you probably don't need it. That's not the case for most people, though.
There's no way a photo from a PLM will look no worse than the same photo from a DA* with shutter speed being equal at least due to higher ISO, let alone actual optical performance of the lens. Sure, if you downsample a 6000x4000 photo to be shown in web at 1500x1000 that difference will likely walk out the window. Once you start cropping a 1500x1000 image out of a 6000x4000 image, the difference will be very pronounced.
The DA* trades some flexibility at the shorter end in exchange for flexibility in cropping.

[mikesbike]

I also have & use both for different purposes...what jddwoods said. Becoming my mainstays for outdoor use!

Exactly. No one can tell you which of the two lenses is "best". Best for what purpose? Best for keeping out dust? Your own photographic needs are what determines which lens to use.

[Rondec]

If you're referring to the PLM, I don't think so. It definitely doesn't outresolve a 24MP sensor.

I'm not sure what you need, but anyone who shoots birds needs as much sharpness as possible. Sure, if birds in your area rub their snouts against your forehead, you probably don't need it. That's not the case for most people, though.
There's no way a photo from a PLM will look no worse than the same photo from a DA* with shutter speed being equal at least due to higher ISO, let alone actual optical performance of the lens. Sure, if you downsample a 6000x4000 photo to be shown in web at 1500x1000 that difference will likely walk out the window. Once you start cropping a 1500x1000 image out of a 6000x4000 image, the difference will be very pronounced.
The DA* trades some flexibility at the shorter end in exchange for flexibility in cropping.

I would think for birders the more common decision would be between the DA *300 (with a TC) and the DFA 150-450.

[MetalUndivided]

I would think for birders the more common decision would be between the DA *300 (with a TC) and the DFA 150-450.

If the budget allows so.

[Rondec]

If the budget allows so.

Sure. But the OP asked the question of a DA *300 (an 1100 dollar lens) versus the DA 55-300 PLM (a 400 dollar lens). There is no doubt that at 300mm there isn't going to be a comparison between these two lenses in terms of pure image quality -- there is a reason for the price difference. There certainly could be plenty of reasons to use the DA 55-300 or even to own both, but I would think most birders would gravitate towards faster (and longer) glass.

[normhead]

If you're referring to the PLM, I don't think so. It definitely doesn't outresolve a 24MP sensor.

Based on what? Have you actually compared images?

I regularly shoot a K-3 with both lenses. I've been quite impressed with the DA 55-300 PLM. I no longer take the DA* 60-250 for quality, I take it for ƒ4. The IQ is close enough.

The DA 55-300 was redesigned after the K-3 came out. The original 55-300 is 12 elements in 8 groups. The PLM is 14 elements in 11 groups. It's definitely been redesigned for the 24 MP sensor. Meanwhile the AF speed of the 60-250 can only be describe as pokey, where as the PLM is as good as it gets.

[MetalUndivided]

Based on what? Have you actually compared images?

Based on how the photos out of my PLM+K-70 look. It definitely doesn't outresolve the sensor. Frankly, I don't think the DA* does either.
Have I compated the images? Yes, although not in an accurate way as I don't have the money for a DA* 300. The DA* looks plain better, except for maybe bokeh, but that's a matter of preference.
Like I said, compare 1:1 images, not 4x downsampled ones.

[normhead]

Based on how the photos out of my PLM+K-70 look. It definitely doesn't outresolve the sensor. Frankly, I don't think the DA* does either.
Have I compated the images? Yes, although not in an accurate way as I don't have the money for a DA* 300. The DA* looks plain better, except for maybe bokeh, but that's a matter of preference.
Like I said, compare 1:1 images, not 4x downsampled ones.

Well you and I are going to have to disagree, although, I was recommending the DA*60-250 with TC as a better compromise than the DA 55-300, I wasn't discussing the DA*300.

Don't assume anything. I always compare 1:1 images, not downsampled.
Amazing how many people think I'm an idiot.

By the way, there's a very easy test for this. Put a 1.4 TC on the lens in question. If that increases image detail, the lens has extra resolution compared to the sensor. If the lens is just the same level of detail only bigger, then the sensor out resolves the lens.

Only one of my tested lenses, an old Vivitar M 135 2.8 was actually out resolved by a sensor. I suspect the whole concept is pretty much a marketing myth. That doesn't mean one lens can't be sharper than another or that it makes no difference to the sensor. But to be out resolved by the sensor would mean you get the maximum subject resolution possible using that lens on the given sensor.
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/321890-und...re-detail.html

When I did a test DA* 60-250 against the DA 55-300 PLM with the 1.4 TC on both , the PLM was not as good. Not as good but of course with a 1.4 on the PLM you're at ƒ9.3 and diffraction is setting in, so I don't actually know if the difference I was seeing was a lack of sharpness in the lens or diffraction.) But, that doesn't prove the PLM without the 1.4 TC is out resolved by the sensor.

I like this comparison, because you can see exactly what you're paying the extra for. And as some noted, you wouldn't care unless you were seeing both images. You don't get a lot for your extra $600 unless you need ƒ4. And of course, it's only of interest for use with the 1.4TC. It doesn't resolve the issue of how good the lens is without the TC.
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/365761-hd-...ml#post4617614

Based on my general observation and testing, the reason for buying the better lens would be one of 2 reasons, you want to shoot a faster aperture to keep your shutter speed up in low light or for cleaner bokeh, or you want to shoot with a TC.

If you're happy with what the DA 55-300 PLM does, because you always shoot in good light with no TC, the light weight and super fast AF make it a no brainer.