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Archive 2012 · Dust in a Contax 85mm F1.4, is it hard to remove?
  
 
MRosth
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p.1 #1 · p.1 #1 · Dust in a Contax 85mm F1.4, is it hard to remove?


Just bought a lens on Ebay and I noticed that from F10 to F16 I get a little black dot on the pictures and I can clearly see the dust between the front elements with my eyes when I look true the lens.

So to my question, is it hard to clean this by myself?
I have no experience at all with taking apart a lens.





Nov 13, 2012 at 11:10 PM
aleksanderpolo
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p.1 #2 · p.1 #2 · Dust in a Contax 85mm F1.4, is it hard to remove?


Have you use other lens to see if the dust is on the sensor?


Nov 13, 2012 at 11:22 PM
MRosth
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p.1 #3 · p.1 #3 · Dust in a Contax 85mm F1.4, is it hard to remove?


That was my first thought as well but it doesn't show up on any of my other lenses.



Nov 14, 2012 at 12:10 AM
thrice
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p.1 #4 · p.1 #4 · Dust in a Contax 85mm F1.4, is it hard to remove?


Sorry but you're wrong, there is NO WAY diffraction isn't obliterating that dust spec regardless of aperture, unless it's the size of an M&M.

Shoot a white wall at f/16 on a tripod with your contax, and then with another lens.



Nov 14, 2012 at 10:01 AM
d.o.k
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p.1 #5 · p.1 #5 · Dust in a Contax 85mm F1.4, is it hard to remove?


thrice wrote:
Sorry but you're wrong, there is NO WAY diffraction isn't obliterating that dust spec regardless of aperture, unless it's the size of an M&M.

According to my experience with dusty lenses (zooms particularly), there is definitely a way.



Nov 14, 2012 at 11:29 AM
thrice
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p.1 #6 · p.1 #6 · Dust in a Contax 85mm F1.4, is it hard to remove?


Mmhmm, show me the lens and the sample shot. The laws of optics simply don't support the idea of individual dust particles inside or on a lens surface showing up in the image.

If you put a thick layer of dust that obscured say 30% of one of the lens surfaces inside or on the lens you might see a veiling glare and lack of contrast.



Nov 14, 2012 at 11:53 AM
Fred Bruche
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p.1 #7 · p.1 #7 · Dust in a Contax 85mm F1.4, is it hard to remove?


The dust spec must be pretty large...
http://www.lensrentals.com/blog/2011/08/the-apocalypse-of-lens-dust



Nov 14, 2012 at 12:53 PM
Bifurcator
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p.1 #8 · p.1 #8 · Dust in a Contax 85mm F1.4, is it hard to remove?


Yes, dust in almost any lens over about 35mm will show up as solid black specs in bokeh highlights at apertures under f/22 or so - even relatively small specs. And the longer the lens the less the aperture is relevant. In fact a great way to tell if dust is significant enough to affect IQ is to go out at night with the aperture opened up, focus it to the lens's MFD and then shoot some distant street lights. If you see specs you can't say that the dust won't affect IQ. In such a case it will both lower the contrast in some areas when normally shooting and also show up as hard black specs in the bokeh highlights.

I dunno if that's what MRosth is seeing but it's certainly possible.






Nov 14, 2012 at 03:10 PM
MRosth
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p.1 #9 · p.1 #9 · Dust in a Contax 85mm F1.4, is it hard to remove?


Took the lens into a repair shop and they have now cleaned the front elements and the black dot is gone.

Will upload pictures before and after



Nov 14, 2012 at 04:51 PM
Dudewithoutape
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p.1 #10 · p.1 #10 · Dust in a Contax 85mm F1.4, is it hard to remove?


How much did it cost to clean it?


Nov 15, 2012 at 02:20 AM
 

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AmbientMike
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p.1 #11 · p.1 #11 · Dust in a Contax 85mm F1.4, is it hard to remove?


Im getting weird stuff in center, m4/3. 90 Tamron 49B gives white dot 135/3.5 zuiko gives purplish dot sometimes. Past f8. Both clean I think.


Nov 15, 2012 at 04:07 AM
AhamB
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p.1 #12 · p.1 #12 · Dust in a Contax 85mm F1.4, is it hard to remove?


AmbientMike wrote:
Im getting weird stuff in center, m4/3. 90 Tamron 49B gives white dot 135/3.5 zuiko gives purplish dot sometimes. Past f8. Both clean I think.


That sounds like an aperture spot from internal reflections. You'll probably only see it in bright conditions.



Nov 15, 2012 at 09:56 AM
thrice
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p.1 #13 · p.1 #13 · Dust in a Contax 85mm F1.4, is it hard to remove?


I look forward to these before and after pics!


Nov 15, 2012 at 10:01 AM
MRosth
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p.1 #14 · p.1 #14 · Dust in a Contax 85mm F1.4, is it hard to remove?


Heres how it looked like


DSC06289 by MRosth, on Flickr

and after


DSC06291 by MRosth, on Flickr



Nov 15, 2012 at 10:37 AM
briantho
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p.1 #15 · p.1 #15 · Dust in a Contax 85mm F1.4, is it hard to remove?


To make this test relevant MRosth, the after shot should be shot with the same aperture as the before shot. It appears you are comparing f22 to f1.4.


Nov 15, 2012 at 11:10 AM
Bifurcator
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p.1 #16 · p.1 #16 · Dust in a Contax 85mm F1.4, is it hard to remove?


And same subject with the same focus distance too if ya can.


Nov 15, 2012 at 02:42 PM
MRosth
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p.1 #17 · p.1 #17 · Dust in a Contax 85mm F1.4, is it hard to remove?



DSC06314 (1) by MRosth, on Flickr

Same background and shoot at F16.

There are still some small dirt/dust dots but not as big as seen on the first picture



Nov 15, 2012 at 08:19 PM
kosmoskatten
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p.1 #18 · p.1 #18 · Dust in a Contax 85mm F1.4, is it hard to remove?


In my experience particles and smudge on the back/rear element of a lens can be visible but even major particles are practically invisible if they are on the front element, exceptions are water drops and smear etc.

I have seen a telephoto lens with a crack in the front element where the chipped part had been painted with a black felt pen and nothing was showing up in photos. The owner said it was standard practice in sports photography.



Nov 15, 2012 at 09:25 PM
wfrank
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p.1 #19 · p.1 #19 · Dust in a Contax 85mm F1.4, is it hard to remove?


MRosth wrote:
There are still some small dirt/dust dots but not as big as seen on the first picture


With a quick look I see 3 remaining spots which to me look as typical sensor-dirt. Buy a 10 blower and they are likely to disappear, should have nothing to do with the lens.

Never seen anything like the first one, except for when I had dirt on the matte screen. But that would only concern the OVF, not the image.



Nov 15, 2012 at 10:08 PM
jotdeh
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p.1 #20 · p.1 #20 · Dust in a Contax 85mm F1.4, is it hard to remove?


MRosth wrote:
That was my first thought as well but it doesn't show up on any of my other lenses.


Did you test those other lenses fully stopped down, too? I agree with wfrank, all of this looks like sensor dust to me, and maybe by coincidence that big blob fell off (anti dust vibration) while you had the lens repaired.



Nov 15, 2012 at 10:17 PM
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