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09-14-2019, 11:44 PM   #1
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Is this sharp? - Pentax DA 55-300mm f/4-5.8 ED WR

I recently bought a DA 55-300mm f/4-5.8 ED WR lens, but I'm not 100% sure that I've ended up with a good unit. I've read the reviews for this lens on the forum and I've noticed some people saying that they ended up with a dud lens that wasn't very sharp at 300mm. And after my first test run (just in the backyard) I wasn't satisfied with the images that I was getting. I thought maybe I just wasn't holding it steady enough (I'm more used to my Sigma 17-50mm which I'm really happy with).

So, what I've done here is zoomed the lens all the way to 300mm, sat it on a table, set it to a 2 second timer (stabilization off), auto focused on a K5 at f11 and took some shots of various objects in my yard with detailed textures as a test.

I'd love to get some opinions on the sharpness of these shots below. I'm not sure if it's just my eyes, or I'm expecting too much. I've uploaded them unedited to an image hosting site, so you'll find them to be clickable to see the original resolution.

I'm no photography expert, so if anyone has suggestions on a better way to test the lens, I'm all ears.







09-15-2019, 12:59 AM   #2
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None of them are sharp. Have you set the lens up using AF Adjust?

In any event, even using AF Adjust the critical focus point may/will vary depending on the fl youve zoomed to.

Search for advice on using AF Adjust.
09-15-2019, 01:27 AM - 3 Likes   #3
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I beg to differ.

The "feather" detail in the little bird looks pretty good to me.
The galvanised water tank at top left of the second image is tack sharp.
The in focus bits of the third image are a bit dark and low in contrast, but they look OK too.

Remember that at close focus at 300mm depth of field is still quite thin.

More testing is required - preferably using a flat subject perfectly parallel to the camera's sensor and focussed in live view on a tripod.
09-15-2019, 01:40 AM   #4
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At least in the first two of the three, things that are in focus are tack sharp - the moss left of and slightly behind the bird, the bluish paint - but possibly not those you intended to be in focus. So it could be both down to a slight back focus (likely adjustable) or shooting technique (familiarity/practice with the lens helps).

09-15-2019, 01:45 AM   #5
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You might find that f8 is sharper than f11. Diffraction starts to be an issue around f11.

09-15-2019, 02:42 AM   #6
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A little off

The first two I have no problems with, the third is hard to say, being a bit murky.

The contrast seems overall low, and so is the in-camera sharpening, and the third is underexposed, first and foremost.

Been so long since I used this lens, but it might be the camera that needs to use another set-up.
09-15-2019, 03:11 AM   #7
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These are tough images to evaluate. It would probably be a bit easier to take a photo of a wall or something like that and use live view to focus. I know that is boring, but it is a bit hard to say otherwise.

As others have said, the first image looks fine to me, not sure about the other two because I'm not sure where the focus was supposed to be.
09-15-2019, 03:24 AM - 2 Likes   #8
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There is something sharp in every picture. The lens appears fine.

A few points for the OP to consider.......

1. Autofocus will not automatically focus on what you intend it to. You need to be looking through the viewfinder and noticing which AFpoints light up. Experimenting with the different AF points the camera will use may help.

2. It is possible for the AF sensor to be slightly misaligned and this can be corrected in the AF/FA menu. But do not attempt this until you can demonstrate repeatedly that this is the case otherwise you will just end up down a blind alley. You need tripod, test chart and a rigorous testing protocol or you are wasting your time.

3. Depth of Field. I do not know how far you were from your subjects , but at 10 metres a 300mm lens has an acceptable DOF of 0.50 metres at f11. That means anything further than 25 cm behind or in front of the subject will not be in acceptable focus.

09-15-2019, 03:33 AM   #9
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Wow, this is all very interesting. Thanks for the replies everyone.

You're right. Sorry the images aren't better suited for testing purposes and/or under exposed. It was a bit random this afternoon. Here's a couple more at closer range though (more like 6' instead of 25'). All of them were focused on the centre spot.





I'll try to get some better ones tomorrow.
09-15-2019, 03:45 AM - 1 Like   #10
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I think your lens is fine.
09-15-2019, 03:49 AM - 1 Like   #11
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I agree with @Sandy Hancock and @pschlute.

It would be helpful if we could see the EXIF data. I'd like to know which camera it was, as well. Most importantly, would be to know exactly which spot you're focused on (you are using spot-focusing, right?).

As to the first picture, there are three areas on the bird that look good to me, the bridge of the beak, part of the tail and the feathering on the side. In the third, there's a pan-head slotted machine screw behind and to the right of the center of the flywheel apparatus that looks like the most sharp in that picture, at least the threads. So it looks to me like the problem could well be that the lens is back-focusing. Or I should say that the camera's not calibrated to the lens properly.

The reason I think that is that my guess is that you're focusing on something in front of the sharper parts, so the camera thinks it's focused on the springy nest thing, but what's actually in focus is behind it; same thing with the machine - the camera's thinking "flywheel" but what's in focus is the screw in the feeder-gizmo behind it.

If you look at the lug wrench in the second picture, that's telling because it's at an angle to the camera, and you can see that it's out of focus more on the near end than the far end.

Look at how to do "lens fine adjustment" in the instruction book that came with whatever camera you're using, then search PentaxForums for "how to calibrate your lens". I suggest that you do all that first, then take more pictures to show us, with more information about what you're doing and how you're doing it. It would be best to put something on the subject, like a sticker or binder clip to show exactly what point you're focusing on. Use a subject that provides more consistent variation in depth (e.g., the way the lug wrench is angled with a continuous stretch on either side of the area that's in focus).
09-15-2019, 04:23 AM   #12
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All 55-300 should improve quite a bit going from 300mm to a little bit less... it's probably the lens' weak point, and I only go there if absolutely necessary... you still have an advantage over the, say, 55-200.

Try to do some tests with a close and a distant target at different apertures (test charts are ideal... high contrast and fine detail), and manual focus in magnified LV, so you get a feel for the DoF at each distance, how the lens performs (also center vs. sides vs. corners) and which aperture is the best tradeoff between sharpness/DoF/diffraction.

I've found f/9.5 to be just about the sweet-spot on mine, at 300mm and, say, 5-10m, but of course YMMV.
09-15-2019, 04:45 AM - 1 Like   #13
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QuoteOriginally posted by Vital-Blurs Quote
Here's a couple more at closer range
Something sharp in both of those. I think you need to understand how DOF works and how to use it to your advantage, and how to achieve focus on what you want the camera to focus on

---------- Post added 09-15-19 at 12:50 PM ----------

QuoteOriginally posted by dlh Quote
Look at how to do "lens fine adjustment" in the instruction book that came with whatever camera you're using, then search PentaxForums for "how to calibrate your lens". I suggest that you do all that first,
Sorry, but I disagree totally with this. He needs to understand how a camera focusses first. Then if he is getting FF/BF he needs to scientifically establish what the problem is and correct it. Sending a newcomer down the AF/FA route straight away is just wrong.
09-15-2019, 05:31 AM - 1 Like   #14
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Hello,

I have the DA-L version of this lens. I haven't used it that much recently but I've found in mine that it performs better at around 250-270mm and below. So I try to stay away from pegging it to 300mm. Also, the sweet spot in mine is around f8, or between 5.6 and 8 at the lower end of the range.
As others have said, Your samples seem to be sharp at the focus point. But controlling DOF in a long lens is quite a challenge.

Thanks,
09-15-2019, 06:08 AM   #15
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I have that lens also. As esmaelg said, it's a bit weak at 300, also at 55. About 60-250 works best for mine at f8. Sharpness can be realitive and subjective. Your images look fine to me.
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