There are generally 2 schools of thought on UV/protective filter. I called them the "pro" school and the "layman" school.

The pro school believes that since you spend so much money on a lens, putting any additional glass in front of it will just degrade IQ. So no filter + use hood and lens cap + more care. IQ rules, everything else is secondary.

The layman school believes it's a good idea to protect your investment and that the UV filter will protect the lens front element against damage and stuff. So they use filter. Resale value rules, everything else is secondary.

I'm the layman type. I spend about 10% of a lens cost on a *good* protective filter, knowing that it will degrade IQ but under my layman's eyes, the degradation is insignificant (if not invisible). But it gives me the peace of mind that (a) if my clumsy fingers/some random things scratch/damage/do something to the surface, my lens is still ok and (b) that signals good care to the market when I resell the lens.

Note that keyword is good. Cheap filters completely change the argument because IQ degradation is visible and significant. Genuine good filters have coating to reduce flare and good glass reduces light loss. Some like the Hoya HD series have reinforced glass to make it stronger.

LOL, I asked that same question several times and changed my mind several times. Considered manual 50mm f1.4 to DA* 55mm to DA* 50-135 to 70 limited + 100mm WR macro + FA 50mm to Sigma 50-150 to Tamron 28-75. I still have not bought any of them.

Basically, aim for anything that covers 50mm f1.4 to 85mm f2.8. Anything Pentax-made in that range should take good portraits.

Putting images on websites is an entirely different thing. A RAW file is like 10-20MB is size. You want website pictures to be about 0.1-0.5MB max because nobody wants to spend minutes loading a page. If you do pictures exclusively for websites then maybe it's a good idea to do JPEG (but maybe not - see flexibility below).

I understand why JPEG option is there (for example, higher speed, no need to invest in a RAW processing software, etc.) but I have absolutely no problem if it's not there. I don't invest in a DSLR to use 1/16th of what it is capable of because that is just a bad investment. All other things being equal, 1 > 1/16.

Lastly, I did switch from 12-bit RAW (Panasonic GH1) to 14-bit RAW (K-5). And IMO, there is indeed no end to IQ. Perfection is not attainable but people still pursue it.

It's not about speed. My point was that RAW gives you more flexibility. Like if you drive on a 200 mph limit, you have the flexibility of driving slow (and I use road, not highway!) or fast. On a 20 mph road, you don't have an option to drive fast (speeding not in the argument).

The sports car speed is meant to be an example of a certain desirable property you have in a sports car. Just like if you use the K-x, there are specific properties like wider DR, post-capture fixing of WB, etc.

If you do RAW, you can certainly do more RAW-specific adjustments (e.g. recovering highlight, pull up shadow, special noise reduction treatment, etc.). If you just want to mass-process a certain group a pictures, just mass-process and export to JPEG! But there are the RAW images right there when you want to do more than JPEG.

But if you do JPEG to begin with then there is zero chance you can do any adjustment to the full extent you can do with RAW. You can take perfect JPEG but there ought to be some occasions where you get the wrong WB on a priceless moment. Do you want to be stuck with the JPEG or have the possibility of fixing it with RAW?

Batch processing actually makes RAW versatility argument more valid. You can batch-process both JPEG and RAW. But if you want to (for example) recover 1 EV of blown highlight, you can't do it with a JPEG (all other things being equal).

And I would like to quote someone's signature I saw in one of the forums I read:

Think about this hypothetical situation:

You have a Ferrari F430 sports car and there are 2 roads you can take. One has a speed limit of 200 mph and the other has a speed limit of 20 mph. (In case you are not familiar with sports car, the F430 max speed is 200 mph). Which road will you choose?
If you choose the 20 mph road then you may be better off selling the F430 and get a scooter. What's the point of having a super fast sports car and limit yourself to a slow road?

Now replace the Ferrari with your K-x, the 200 mph road with RAW, the 20 mph road with JPEG and the scooter with a Point-and-shoot compact.

RAW is like a sports car maximum speed. It has everything that the camera can offer. You may not need it (like you may not drive at the speed limit) but there are cheaper alternatives out there which will save you a lot of money if you just want to do JPEG.

Of course, driving at 200 mph requires more care, skill, concentration - just like RAW will require more post-processing. Fortunately, sports cars have intelligent stability management, traction control, etc. RAW has... Adobe Lightroom (NOT photoshop!) or similar software.

I currently have a "quick JPEG" preset that apply automatic exposure adjustment, lens correction, tone curve, clarity, saturation and vibrance. The preset processed 800+ pictures in one of my recent session just by Ctrl-A and then choose the preset. 1 key press, 1 mouse click, a bit of scrolling (to go through the list of presets) and another mouse click for all 800+ pics.

That's without even discussing the fact that compression in RAW files is lossless whilst JPEG is lossy. And I chose my speed limit very carefully. A 12-bit RAW file has 16 times more data and an 8-bit JPEG.

So from my point of view, there are very few reasons to choose JPEG over RAW.

I stick with my previous comment re low quality filter. What brand is yours?

I'm guessing because the 300mm has very small field of view, it uses a very small section of the filter. So whatever imperfection is magnified.

In any case, try using a stable surface (instead of hand-held) to take out any possible effect of camera shake.

PM sent re UV filter.

I'm quite surprised when you say there isn't much difference between the K-7 and K-5. Did you try ISO 6400?

I personally do not want a FF Pentax. The K-5 is perfectly sized AFAIC.

If resolution is critical then Pentax has the 645D.

Do you mean the picture looks soft? If that's the case then it may be due to a low quality polarizer.

Why not Sigma 8-16? If using filter is a critical requirement then the Sigma 10-20 is another good choice.



Old Royal Naval College by Tùng béo, on Flickr



Old Royal Naval College Painted Hall by Tùng béo, on Flickr



Old Royal Naval College Painted Hall by Tùng béo, on Flickr

Just try my luck here to see if anyone has a Sigma 50-150 f2.8 to sell. Please PM me if you want to part with one.
Cheers.