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Old Nov 5, 2006, 2:08 AM   #1
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I've had this lense for a while now and have always had problems with photos being blurry when focused on infinity and when using a wide aperture.
I've finally gotten around to testing it properly.

All shots were taken on a tripod with the 2sec timer so camera shake is not an issue here.
The focus ring was turned all the way to the end (Infinity) and everything that should have been was in focus. The camera also beeped to let me know.

The first set are just resized from the original RAW files. No PP.



The second set are crops to show the sharpness (or lack of!). Again no PP, except f22 which had some exposure boost in ACR (forgot to press AE-L?)



I realise most lenses are a bit soft wide open, but with this lense nothing is in focus when at infinity and f1.7
Surely this can't be right??

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Old Nov 5, 2006, 4:07 AM   #2
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I think you got it completly wrong. 1.7 has very narrow DOF and you try to focus at infinity (meaning very far away) which means nothing will be in focus. when the aperture goes up more and more foreground details become sharp, like they should.

thats what I think, maybe I'm wrong


greg
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Old Nov 5, 2006, 4:47 AM   #3
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gfurm wrote:
Quote:
I think you got it completly wrong. 1.7 has very narrow DOF and you try to focus at infinity (meaning very far away) which means nothing will be in focus. when the aperture goes up more and more foreground details become sharp, like they should.

thats what I think, maybe I'm wrong


greg
My understanding is that the narrow DoF will be wherever the focal point is. So, focus at infinity should be sharp at distance and blurred in front.

I would suggest actually focussing on something that is close to infinity on the lens barrrel and check the sharpness. If you have a specific reference point then you can more accurately assess the sharpness (or lack thereof).



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Old Nov 5, 2006, 5:12 AM   #4
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nadnerb wrote:
Quote:
I've had this lense for a while now and have always had problems with photos being blurry when focused on infinity and when using a wide aperture.
I've finally gotten around to testing it properly.

All shots were taken on a tripod with the 2sec timer so camera shake is not an issue here.
The focus ring was turned all the way to the end (Infinity) and everything that should have been was in focus. The camera also beeped to let me know.


I realise most lenses are a bit soft wide open, but with this lense nothing is in focus when at infinity and f1.7
Surely this can't be right??

It looks to me that it is right. Do not drive yourself crazy with this issue.

Assuming you have **spot** focusing (not centre wt), you were actually focusing on the scrub at the dead center and at least 10 ft away from the triangle sign or the street sign.

Do another set of the pix for the street sign which is easier to tell if it is in focus or not. You will still find that 1.7 is behind 2.8 or the ideal 8 in focus.


It is simple physics

Daniel
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Old Nov 5, 2006, 5:47 AM   #5
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Darren: you right, I just put it wrong. I meant nothing will be in focus on this photo because this sign or house is too close than infinity. it'd be better to try ladscape scene where the horizon is really far and try on some trees far away.

if you look at second crop ( f2.8 ) you can see that roof tiles are in focus and everything closer is blurred. I think that the focus point is even behind trees behind this house, that's why everything is blurred. I think to test it properly you need more space than on this photos.

btw: I don't think there's anything wrong with this lens

greg
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Old Nov 5, 2006, 6:04 AM   #6
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I see what you guys are saying, I'll have to try again tomorrow at a different location.
The thing is, the sign was definitely in focus in the viewfinder but the photo came out like that.
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Old Nov 5, 2006, 6:34 AM   #7
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try this
http://photo.net/learn/focustest/

or
http://www.focustestchart.com/chart.html

roy
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Old Nov 5, 2006, 7:42 AM   #8
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Setting the focal lengthto infinity is fine for landscape shots but this shot probably requires the focus to be set on the street signs.

That aside, the f8 shot doesn't look that bad - I've readjusted the histogram (darker shots look sharper) & added a touch of USM.
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Old Nov 5, 2006, 8:17 AM   #9
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Let me add my 2 cents worth: focusing on a subject at infinitiy is typically very forgiving considering that what is considered infinity is usually anything in excess of 25-30 feet. From the looks of the sample photos, nothing is in sharp focus. I do not believe DOF is an issue here since DOF is a funtion of focal length and aperture.Longer focal lengths have a shallow depth of field as do larger apertures.

I had a similar problem with a tamron lens (blurred images at infinity). I returned the lens to Tamron (under warranty) for servicing. They re-calibrated the lens and it solved the problem. Jay
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Old Nov 5, 2006, 12:36 PM   #10
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The series of photographs provided demonstrates the point of depth of field or view. Right off the top on the first series, just scroll down the series, with your eye on the flower branch sticking out of the left side, and also the pylon just right of center.

F1.7 - both are blurry
F2.8 - the pylon is better defined
F8 – both the flower (right) and pylon are better defined
F22 – again both the flower and pylon are even better defined.

With the focus being on infinity, this is just what you would expect. You have to understand that at f1.7 and infinity, the very thin (extraordinary narrow) focal plane (given the complex neighborhood setting that you used) that will actually be in focus is way off in the distance (somewhere), and will be extremely thin. As you progressively close down the aperture, the thickness of the focal plane will enlarge tremendously coming back to the camera, including more and more of the field of view.

If you go to the close up, cropped images, take a look at the following…

F1.7 – the only items in focus are the trees in the background above and to the left of the f, of the f1.7
F2.8 – the tile roof immediately behind the f1.7 is now in better focus along with the trees behind it.
F8 – now the trees in the distance, along with the tile roofs just below the f8 and the tile roofs off to the left are in much better focus. You can even read the street signs better.
F22 – Actually I think the F8 is better, you might have had some shake from a breeze or traffic when comparing the street sign NUMAWADING 4 between f8 and f22. Also, when considering the green fence down at the bottom of the crop.

Daniel, with the question of spot focus not center weighting probably asked the correct question. With this complex field of view with the multiple sets of items layered within the image, center weighting would be different each time, and you would have a difficult time to really determine what is going on. Or it certainly could be a calibration problem as Jelpee pointed out

Possibly a better setting for a test would be somewhere with a clear field with buildings several miles away – a city view from a ridge or something.


f1.2 f2.8 f8 f22
____________________ ____
////////////////////////// |
____/////////////////// Area in focus progressively
____////////// | enlarges with the f stop value
////////// |
______ ____

-^^^^^^-Camera-^^^^^^^-

Anyway, that's what the Navy taught me when I went to photo school so as to be able to take good pictures of ship antennas, since I was an electronic warfare specialist. Also, from my physics classes in optics at shcool – I have a few engineering degrees.

However, with all of that being said, there is nothing that is perfectly razor sharp in the series of images – at best - its the f8 image, with the street signs and the green fencing, however the street signs show a bit of blur around the letters (that could be from the angle that they were shot from, but they still should be sharper).

Anyway, just my guess….
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