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09-19-2013, 06:31 AM - 1 Like   #1
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New Lens Inspections?

Hi Everyone;

Like many of the people writing in, I've sprung for a couple new lenses. About a year ago, I did the same and basically I just shoved the lens on and started firing away. I'm betting there are more than a few of us that have done it. But, it got me thinking. Is that the best way to do it? Depending on who you buy from there can be no return or some sort of 14 to 'X' day return policy in effect on the purchase. After that it is through the warranty. So, identifying problems early is important.

I'm wondering if there is anything systematic that people are doing to inspect their new lenses? I see many posts where people are asking if they have a bad copy or they have already identified that they have a bad copy and exchanged it for a second. It dawned on me that unless it had a giant crack in the glass I wouldn't really have a clue what I'm doing. Of course, if the lens couldn't even focus on my couch in broad daylight then I would worry.

So... What is it that you do when you inspect a lens? I've been doing a little looking around and can find some suggestions, but I do think a really nice checklist would be good to have for those aiming to move beyond their kit lenses. Many of us are ordering on-line. I don't have a bricks and mortar show within 4 hours drive from me so inspecting before hand isn't possible.

I'm thinking something like:

(1) Look for any obvious sign of physical use (did they sell it as open box?). e.g. are there scratches on the rear mount. Any sign of damage to the glass when you open it. Do all the parts and rings appear to be solid? No early signs of nicks and cracks. If any of this then contact the seller. Should it have been priced differently? or be returned?

(2) I'm curious whether anyone cleans the mounts before they attach the lens to the camera? I didn't and I'm wondering based on my internet wanderings whether I should have. (As an aside, when or how often should they be cleaned?)

(3) Get a good look at the lens in light... Questions: How much dust is too much dust in a new lens? Should there ever be dust in a new lens? Some people talk about oily blades on both used and new lenses. Ummmm... I'll be honest, I don't know what an oily blade looks like so... Pictures anyone? How much is too much? Also, I can see stuff about looking for pieces of plastic in your lens. I'm assuming that means loose in your lens floating around... I vote for that probably not being a good thing...

(4) Ok, now so far we have done the appearances. So, I think we can shove it on our camera now. I'm wondering if there are a few really basic easy test scenarios that we should all try with our new lens to very quickly know if we have to move it up a notch? I can see that people have already written about how to test front and back focus:

https://www.pentaxforums.com/forums/pentax-dslr-camera-articles/167547-how-fi...ack-focus.html

But that seems excessive to me when I've just pulled my new lens out of the box. I really only want to get to the fine tuning if I'm pretty sure I need it. So any simple recommendations of quick and dirty tests we should do with a new lens? If there are, please let me (us) know what we are looking for and what we should do about it. e.g. if you shoot this and it seems a bit soft then do the front-and-back focus. If this, then the lens needs to be returned in the 14 days or is this something that we should do via warranty?

Finally, many people are using Pentax lenses and there have been concerns on occasion about their SDM. Is there any early warning signs that there is something wrong that people should be listening for?

Or is this all really unnecessary? And, like last time, should I just shove the suckers on and start firing?

Many thanks!

Eric

09-19-2013, 06:51 AM   #2
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Eric, let me just address one of your questions:

QuoteOriginally posted by EricG Quote
Some people talk about oily blades on both used and new lenses. Ummmm... I'll be honest, I don't know what an oily blade looks like so... Pictures anyone? How much is too much?
Oily blades show up (almost always on old used lenses)
by the camera over-exposing at narrow apertures
because the blades can't shut down fast enough
when the photograph is being taken.

So just check that the lens is exposing correctly.
Don't worry about a visual inspection for oily blades.
09-19-2013, 07:19 AM   #3
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It depends on what kind of lens you are talking about.
With oily blades, for example, I remember reading that some Soviet m42 lenses need much oilier blades than Pentax lenses from that era.

Here is what I try to check, if I don't forget:
a) aperture ring and aperture blades. Check if it stops down properly and correctly.
b) mount and contacts. You dont have to clean them with shampoo (in fact, you shouldn't), but just make sure there isnt grease on there. Maybe ipe them gently with a soft, dry cloth. Something that doesnt leave trails.
c) focus - does MF work, does the focus ring turn smoothly throughout or are there resistances? Do the distance scales show proper values? If the lens is AF, does AF work for near and far objects?
d) element decentering - is the photo equally sharp across the frame? If you take a photo of a wall at f8, straight at the wall, parallel to it, is one side of the frame noticeably less sharp? is the CA much stronger in one side than the others? But don't confuse edge sharpness with decentering. Older lenses often have poor edge performance. Decentering means the elements aren't aligned properly and causes optical problems across a big part of the frame (for example, the whole side left of center)

Front and back focus correction can help you a lot if you are using AF, but only do it when you suspect there is a problem, if the focus often seems to be wrong, with no explanation. Then print out a chart, get a measuring tape and put it the correct distance away from the camera. The camera should be on tripod and level. The light should be natural light.
09-19-2013, 07:51 AM   #4
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Road Test?

Hello Eric,
I do the same things mentioned so far, give the aperture lever a couple thumb flicks, wipe the contacts (I find an old well-washed hand towel is good for this) and spin the focus ring, whether it's an AF or MF lens. Always use my Rocket blower to blast the front and rear elements, this is more to keep possible unseen dust off my sensor than anything else, just a precaution.
But last, I road test every new (new to me, that is) lens. My regular trip is a 10-block walk to a neighborhood bakery, stopping to try a couple shots wide-open, stopped down, close-focus, infinity, a few of the same subject with exposure compensation (manual bracketing, in other words) and anything else that seems useful. With 'A' series lenses and newer, it's all being recorded on the EXIF data, so no need to keep notes. I'm also seeing how the AF works during this time and may try a shot or two using MF.
Then I stop and have a tasty fresh-baked treat and a cup of coffee, chimp my photos and head home. Usually between 35-50 photos each time.
These are loaded to Lightroom and scanned closely, checking the EXIF info, histograms, flare control, highlight and shadow results and some moderate pixel-peeping. I might even get a 'keeper' out of the bunch, but usually not. That's not the purpose anyway.
Overkill? Maybe. But it gives me a slightly more comfortable and familiar feeling for the newbie and some idea of the capabilities and limitations.
Ron

09-19-2013, 11:44 AM - 1 Like   #5
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QuoteOriginally posted by EricG Quote
Some people talk about oily blades on both used and new lenses. Ummmm... I'll be honest, I don't know what an oily blade looks like so... Pictures anyone? How much is too much?
When the blades are fully closed, oil will trail behind them like this, leaving darker wet spots:


Preset lenses are sometimes meant to have oil on the blades, but other lenses aren't. It causes the aperture to close slower than it should. You can use an M42 lens with slow blades, as long as they move eventually. The K-mount design holds the blades fully open while focusing and stops them down just as you press the shutter button. Slow blades cause overexposure, usually getting worse as you try to stop down more.

This lens still works fine. I've seen much worse. Oil migrates and often gets worse over time. I would not buy a lens that looks like this unless I knew how to take it apart. The blades are in the middle of everything so getting to them is the issue; cleaning is not that hard.

QuoteQuote:
Also, I can see stuff about looking for pieces of plastic in your lens. I'm assuming that means loose in your lens floating around... I vote for that probably not being a good thing...
Some lenses rattle a bit because of the aperture lever mechanism. I haven't seen loose plastic pieces but maybe I'm just lucky.

QuoteQuote:
(4) Ok, now so far we have done the appearances. So, I think we can shove it on our camera now. I'm wondering if there are a few really basic easy test scenarios that we should all try with our new lens to very quickly know if we have to move it up a notch?
My recent experience: I bought a used DA 50-200mm f4-5.6 WR lens. I wanted to see if it was as good as my SMC Pentax-F 70-210mm f4-5.6, so I did an extensive comparison. They seemed very close to me so I was happy. Then I started taking some distant shots and they were soft. Also, autofocus didn't lock very well at a distance, even at noon on a sunny day. It turned out that the lens didn't focus quite to infinity. It was fine up to about a mile, and that's where all my detailed comparison shots were. It was almost certainly built that way. I fixed it and it's great now. So I can recommend checking infinity focus.

I wouldn't drag out test charts, at least at first. That's really boring and the most likely issue you'll discover is that you've made a testing mistake.
09-19-2013, 12:42 PM   #6
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For me, and this opinion will vary from person to person

What you have outlined is a good start. Dust is inevitable, so look for a lot of dust , a little does not matter. Look for cleaning marks on the elements, indication of aggressive cleaning

As to cleaning mounts, I have been shooting pentax for 30 years and using AF lenses for 20+ since I got a PZ 1, I have never cleaned my mounts, so I think that if needed is sign of a hard life,

What's important to me, is exposure accuracy. I test every new lens using a tried and true method. I shoot a block wall at every aperture and check the exposure using a photo editor , measure the changes in greyscale value with aperture. For example, manycameras don't meter well with MF lenses, I have characterized how each lens works on each body known, Modern l
Else's may not have linear apertures, my sigma 70-200/2.8 is great. Greyscale is plus minus 2 greyscale over F2.8-F22 but F32 overexposed bu 1/2 stop. My tamron 28-75 is spot on at F2.8 but gradually drifts to +1 stop at F32. Therefore I adjust each time I change shooting aperture

Know yur gear For AF lenses I have never used focus charts , shoot the lens, of the r exults a ok don't gomlooking for problems, you will find them even of a lens is within tolorances.

One last point, check for some performance issues, lateral CA and susceptibility to urplemfrnging come to mind
09-20-2013, 05:27 AM   #7
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Thanks for responding all. Some really handy things in the responses that I can use.

I must admit the bakery test sounds rather promising... Close focus on sausage roll, gingerbread man, butter tarts... Portrait photo of the server... Picture of the sky while dreaming (too infinity right?). But point well taken, get out take a quick 50 shots of varying types and distances and look on the big screen at home to quickly see any easy identifiable issues.

I'm glad to know what oily blades look like now. It's one thing to read about it, but another to see it. Yes, I have a rocket blower. I just need to make a point of using it. Every time, I pull it out my kids eyes go wide and they try to thieve it and one still thinks it is something to chew on. So rocket blowing happens in secret at my house.

I'll definitely try the wall test suggested because that seems quick and easy to see. There is a huge painted mural on a wall near my work and I have an industrial cement cinder block wall near work too so I can easily get some pictures which should identify de-centering. Thanks for that, never thought about it and it would seem to be a clearly identifiable problem and easy to test for. I've usually adjusted EV based on the picture that I was taking, I never really thought of seeing if their was a drift through the f scale of various lenses and adjusting right there and then. I'm using Aperture so I tend to tweak some of the grey scale issues post processing and usually by taste. But you are right, I clearly don't know my lenses well enough yet and really I should get as much right in the field first versus waiting to do it via software. I'm learning slowly, but it sure is fun when I get out there.

Thanks again for the great info!
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