When is a lens bad?

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Archive 2008 · When is a lens bad?

Daniel Goller
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p.1 #1 · When is a lens bad?

Quote is from another thread i no longer feel like hijacking (after realizing how much i typed), the quote is regarding the manual sanding of the Rokkor 58/1.2 shim.

tootalew wrote:
If you follow cogitechs instructions as far as using a glass plate, and using the old mount as handle/spinner there should not be a problem. That is pretty text book to achieve a level plane of flatness. I had my calipers and micrometer and measured all the way around as I went and wound up with no more than .2mm differance all the way around. Now if you have a granite inspection plate like used in machine shops, all the better, but a good piece of glass does just fine.

.2mm is quite huge when it comes to say adapter thickness and achieving infinity focus. (i mean evenly around .2mm too thick and bye bye inifinity from my experience with a CZ 35-70/3.4)
Now you have an mount that is .2mm off and no complaints.
Which helps enforce the question i had, how bad does a lens have to be that people do complain?

And a glass plate ensures maybe flatness of the surface worked on, less than perfect rotation, and you end up with a loss of parallelism that you should see, which again, how bad does a lens have to be that you can see it?

Using your .2mm as a measure, and seeing how big of a difference .2mm can have on achieving infinity on adapter thicknesses, and how none of it matters, it shows a few things. I think.

Wide open, even if anything but a less than perfect focal plane alignment exists, in real world use, it will not matter (as any happy Rokkor 58/1.2 would attest), and once stopped down, the aligment problems will become insignificant, or else manually worked on 58/1.2 lenses would have a reputation of not being sharp across the frame (and they don't)

So i wonder, are lenses that have a bad reputation misused? (Should we expect everything in focus on a 16/2.8 shot based on the numbers on a DOF calculator and the distance to the brick wall?)
Do we have unrealistic expectations? (Do we expect zooms to beat primes all the time?)
Do a few real instances of bad lenses of a series make us all measurebators and as mostly we find what we look for? (Because we look with unrealistic "test setups"?)

Just wondering mostly [insert favorite excuse why i post and not shoot stuff here]

Daniel

Aug 06, 2008 at 01:41 AM

tootalew
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p.1 #2 · When is a lens bad?

Daniel,
You made me realize something about that post, it should have read .02 mm. I apoligize for the confusion. I will stick by Pauls methods, they are sound, as long as you are geting rotation as you sand, and keep the sand paper clean. But even it was .2 mm (about .008" for those imperial only people) would it really effect much? I truely don't know, I am sure it would effect something but to what degree?

Aug 06, 2008 at 02:40 AM

Daniel Goller
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p.1 #3 · When is a lens bad?

tootalew wrote:
Daniel,
You made me realize something about that post, it should have read .02 mm. I apoligize for the confusion. I will stick by Pauls methods, they are sound, as long as you are geting rotation as you sand, and keep the sand paper clean. But even it was .2 mm (about .008" for those imperial only people) would it really effect much? I truely don't know, I am sure it would effect something but to what degree?

And i ran with your .2 not realizing it either.

It still is sanded by hand (and i wonder how many were able to measure theirs), and most people drill the mounting holes by hand w/o even using a proper center.

The base idea is the same, how bad does a lens have to be before you notice problems, and how many of the found problems are pixelpeeping measurebator induced "findings".
Compared to a lens that is so "poorly" modified yet satisfies.

And i am sure every particular brand has their own xx-xx/x.x lens with a bad rep. because we read about problems and instead of using it, unpack and test it.

I think looking for flaws, and flaws we find.

I think if we lost our warranty if we unpack and test instead of unpack and use (realistically), we would find a lot less problems with lenses.

Go out, enjoy taking pictures, don't test. <- i think that's what i want to say, not sure i'd have many listeners though.

Aug 06, 2008 at 05:21 AM

Glassbottle
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p.1 #4 · When is a lens bad?

Sure, perhaps testing is done to excess, and by people who don't really know what they're doing.

However, since every lens in human hands will produce a good number of dud images, I prefer to do some testing on a new lens so that I know whether the duds are my fault or the equipment's.

Usually the equipment is absolutely fine. But it's nice to know.

Aug 06, 2008 at 07:45 AM

mh2000
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p.1 #5 · When is a lens bad?

the good enough 0.02mm number comes from rumours of the Leica spec on rangefinders I think... so if it is good enough for the best rangefinders at all distances, it is certainly good enough for a D/SLR which will only matter at infinity.

Aug 07, 2008 at 06:18 AM

Cableaddict
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p.1 #6 · When is a lens bad?

tootalew wrote:
Daniel,
You made me realize something about that post, it should have read .02 mm. I apoligize for the confusion.

Well, that definitely does make a difference! Thanks for the correction.

Edited by Cableaddict on Aug 08, 2008 at 02:34 AM GMT

Edited on Aug 08, 2008 at 07:34 AM

Aug 07, 2008 at 07:00 AM

Ariithka
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p.1 #7 · When is a lens bad?

Daniel Goller wrote:
tootalew wrote:
Daniel,
You made me realize something about that post, it should have read .02 mm. I apoligize for the confusion. I will stick by Pauls methods, they are sound, as long as you are geting rotation as you sand, and keep the sand paper clean. But even it was .2 mm (about .008" for those imperial only people) would it really effect much? I truely don't know, I am sure it would effect something but to what degree?

And i ran with your .2 not realizing it either.

It still is sanded by hand (and i wonder how many were able to measure theirs), and most people drill the mounting holes by hand w/o even using a proper center.

(You can google about the reputation of the Pentax 16-50/2.8 to get an idea what my rambling is all about.)

"Is this a good one or should i send it back?" threads are just too much.

Ok, i vented, i let it out..

Myself and someone else from here were going to do a weekend "Battle of the Fifties", with Zuiko 1.2, 1.4, 1.8, Canon 1.4, 1.8, Pentax 1.4...but we decided to just take photos and not waste the time.

I agree with you, and looking at photos other people have taken, and deciding what is sharp out of them at f1.2 or 1.4 is a bit silly I realize now.

IMO, even if the lens is "crap" or worse than others you can get, wanting to take photos with it and how it feels to use are more important.
Just like the best tripod is the one you have with you, the best lens is the one you WANT on your camera body.

Aug 08, 2008 at 03:03 AM

Daniel Goller
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p.1 #8 · When is a lens bad?

Ariithka wrote:
Just like the best tripod is the one you have with you, the best lens is the one you WANT on your camera body.

The best lens is the one you HAVE on your body

Aug 08, 2008 at 04:04 AM

mh2000
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p.1 #9 · When is a lens bad?

I just bought a Vivitar Ultra Wide & Slim for $1 at the thrift store... I think maybe that will be "bad" hahaha! but maybe so bad it's good?

(plastic camera with f=22mm, f11 & 1/125th... in case you aren't up on crappy cameras)

Aug 08, 2008 at 05:58 AM


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