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Anonymous
Hi /p/,

I've got this 70-300mm lens from Sigma that I bought a couple of days ago. I bought a Circular Polar and a UV filter both from Marumi.

I noticed that when I'm using the polar and shooting at 300mm, focussing at almost infinite to infinite, the image is blurry. I don't dont have that problem when using the UV or no filter at all.

I tried my friend's 70-300 from Tamron with his polar and he had the same problem (just never noticed it). So it seems it's not a bad/broken lens or filter or something.

See picture. I took both at the same focal length etc.

Anyone else had this problem?
>> Anonymous
handheld at 300mm

there's your answer, junior..
>> Anonymous
>>219864

Both photos were taken on a tripod.
>> Anonymous
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what you need is the $10 CPL by Targus from Walmart

it makes things sharper and more in focus

oh and in before 0/10 lol

Camera-Specific Properties:Equipment MakeCanonCamera ModelCanon EOS DIGITAL REBEL XTiCamera SoftwareAdobe Photoshop CS2 MacintoshPhotographerunknownMaximum Lens Aperturef/1.8Image-Specific Properties:Image OrientationTop, Left-HandHorizontal Resolution240 dpiVertical Resolution240 dpiImage Created2008:06:02 18:38:06Exposure Time1/1250 secF-Numberf/10.0Exposure ProgramManualISO Speed Rating100Lens Aperturef/10.0Exposure Bias0 EVMetering ModePartialFlashNo Flash, CompulsoryFocal Length50.00 mmColor Space InformationsRGBImage Width500Image Height666RenderingNormalExposure ModeManualWhite BalanceAutoScene Capture TypeStandard
>> Martin !!ve2Q1ETWmJH
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>> Anonymous
>>219880
Is there really a 10$ Targus at Walmart and is it actually decent?
>> Anonymous
Shoot at the same aperture, for starters.

Also, are your filters clean or encrusted with some nonoptical crud?
>> Depressed Cheesecake !wFh1Fw9wBU
Use AF, shoot at the same aperture.
>> Anonymous
>>219902
>use AF

Why? AF can vary; if you set it to infinity manually it'll stay the same.
>> Depressed Cheesecake !wFh1Fw9wBU
>>219903
Shouldn't set it to infinity, since the focus goes past infinity to account for heat expansion and other factors. I'm not sure if the polarizer affects the focus, but why risk it? Try AF and focus on the same point.
>> Anonymous
>>219904
Again, AF can vary.

AF lenses do go past infinity, but they have an infinity mark on them and you can set it there.
>> Depressed Cheesecake !wFh1Fw9wBU
>>219908
Well, MF can vary too. You're shooting through another imperfect piece of glass which may cause interference and misfocus.
>> Anonymous
OP here.

I used AF to focus it, then set it to MF and took both pictures, so it's focussed at the same point. Took some other pictures with and without filters all with AF to make sure, but I got the same problem.
>> Anonymous
Mirror Lock up+2 second timer.
>> Anonymous
>>219898
This may actually be the case if he's shooting in auto or shutter priority mode.
Without the polarizer, the camera chooses a less than maximum aperture and the image turns out OK. When the polarizer is put on, it eats a stop or two of light, and the camera opens the aperture to the max. Then lesser DoF combined with a slight focusing error softens the image, or the lens is just inherently soft at max aperture.
>> Anonymous
>>219913

Whoah whoah whoah wait a second here...
F/5.6
1/1000 sec
Without Polarizer

F/7.1

1/400 Sec
With Polarizer

The aperture isn't more open, it is more closed. Shouldn't it be even sharper then?
>> Anonymous
OP here;
>>219913

I'll try that. brb
>> Anonymous
>>219914
Depends on the lens.

Pretty much lens improves as you go away from wide open, then hits its peak sharpest aperture, then gets less soft from diffraction.
>> Anonymous
>>219915

OP here again.. tried both at same aperture and still getting the problem.
>> Anonymous
>>219919
Do you have any other filters to try this with? millions of photographers use CPLs. I think if this was really the CPL's fault they wouldn't be as popular as they are.
>> Anonymous
>>219920

No. Only the UV one. The other CPL ones aren't of the correct size.

As I mentioned, I tried my friend's Tamron 70-300 with his own CPL, and he had the same problem. I doubt it's even the filter. Must be something with refraction or someshit, though I dont get why the camera would focus on a blurry image, and not just focus back and forth like it would normally do on a subject it cant focus on.
>> Anonymous
>>219924
Is it possible that that apartment is really blurry? Maybe the first shot is actually "out of focus" on a truely blurry apartment, and with the help of the CPL the camera was able to accurately focus on the blurry apartment building.
lol : P
>> Anonymous
>>219925
2/10