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focus//sharpness (3 images)
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Very first shots with new tamron 28-75. the portrait was taken by the camera store salesman. I have always felt that this shot was sharp, vibrant and crisp. that is until I zoomed to 100%. the autofocus point is right on the face. there seems to be lots of detail and that impressed me with this lens.

The autofocus point on man from side is on the top of his head. again at 100% the shot is not sharp..

If something is not sharp at 100%, does it then fail the sharpness test..

I know that sounds like a duh!!!!!! kind of question but at regular view, all 3 shots looked in focus to me...

Comments (8)

The first shot is soft but sharpens nicely in Focus Magic.The second shows motion blur. Shook the camera.The third is also just a little soft and may show a small amount of motion blur..

I'd say that the focus is accurate from the lens but either the lens or the camera is just a little soft. Often the most detail is retrieved from post processing the image rather than in camera sharpening..

I'd also guess that the full size images will print nicely at 4X6 (A5)A member of the rabble in good standing...

Comment #1

1. first is sharp at focus point, you see some "unfocused" areas because of shalow depth. This image cound be done with everything sharp by using tripod and f/16 of diaphragm..

2..

Second image is blused by camera shake - Images stabilsed camera or lens could helt to some level, or another reason to use tripod..

1,2 applies to 3rd image too..

P.S. when we all printed 4X5 images they looked perfectly. Now, after looking at detail at high resolution monitors we see flaws undetected previously..

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Comment #2

If you will look at the meta data for the images, you will see that #1 was shot on a Rebel XT at 1/10th second. That slow a speed is not likely to be hand holdable by the vast majority of people, including camera store employees, who should klnow beter than to let you think this is anything but proof that the syhutter worked when the camera left the store..

Image #3 was at 1/30th and looks a bit sharper. My conclusion, use a faster shutter speed or use a tripod for impossiblly long exposures. It's not the lens.Van..

Comment #3

Harveyabc wrote:.

If something is not sharp at 100%, does it then fail the sharpness test.i know that sounds like a duh!!!!!! kind of question but at regularview, all 3 shots looked in focus to me..

These are not as sharp as they should be and for good reason. All were taken at 75mm focal length, 100ISO, f2.8 and were 1/10, 1/20 and 1/30 respectably..

There are potentially two factors there that impact on sharpness and focus - the very slow shutter speeds and the wide open aperture. You need a shutter speed at least 1/focal length plus a bit for the crop factor of the XT in order to eliminate camera shake - so at 75mm, that would give you 1/75 x 1.6 = 1/125. If you're going to be hand holding you need to up the ISO until you get that sort of shutter speed - which may vary a little depending on your personal stillness - I can hold very still, so at 1/20 etc. mine would have been sharp - but most people can't..

The second factor is the wide aperture - the wider open you are and the longer the focal length, the shallower your DOF. For arguments sake - if you were 5 feet from the subject at 75mm and f2.8 your DOF would have been about 40mm/1.5inches which leaves you little wobble room while framing and taking the shot - if you lock focus then either you or your subject moves a little, the focus can be off the optimal point in the frame and spoil the end result - it only needs both of you to move and inch each and your shot is potentially totally out of focus..

The XT has superb high ISO - so had you put the ISO at 400 you could have secured the shutter speed you needed straight away - and had you gone to 800ISO and f4 you would have got a better shot in all respects. A lens is potentially softest wide open, so stopping it down a little is also likely to sharpen up any resulting shots too..

There is nothing wrong with either lens or camera, you simply took the shots with far from optimal settings and not what the scenes needed. It's very unlikely that you'll get good clean shots at 100ISO indoors without flash - but don't be afraid to use the higher ISOs, they're excellent and will certainly give better results than relying on you and your subject keeping still enough with a slow shutter speed..

They appear to have been taken back in May, why only ask now?.

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Please do not amend and re-post my images unless specifically requested or given permission to do so...

Comment #4

All important questions on this subject have been answered.thank you!!!!!!!!!.

Shots taken in may- why ask now..

Just recently started to compare my shots with the very crisp, clear, vibrant images I see on this site and have realized that something was wrong ..

Have allowed myself to be completely lulled into sitting back, shooting auto and thinking everything would be just finewrong!!!!!!!!!!still gotta think before taking picture..

Spent 3 weeks in thailand with xt kit lens last year. happy with results then started reading all the terrible posts about that lens. wanted more reach and got the tamron 28-75. leaving for thailand next week and am taking both lens..

Still have this old film thing about lower asa giving finer image..

So just how high can I raise iso- 800?? is there any significant difference in image quality..

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Thailand shots taken with xt kit lens.couch shot taken on tripod..

Will make corrections as per suggestions and share results.hope that will solve problem.have this nagging feeling that maybe i'm just not a long lens photographer..

Comment #5

Wondering if I should buy the tamron 18-25 and take that instead of the kit lens...

Comment #6

There's nothing wrong with the 28-75 that using some thought beforehand won't cure..

You have 3 exposure variables, Shutter, Apature and ISO. For the mild telephoto end of the zoom you just need good light to get the apature into the 8-11 range with shutter speeds in excess of 1/100th (if there's only marginal light adjust the ISO up untill you can hit the target shutter speed and apature).

At the wide end of the zoom the same advice applies with the shutter speed in excess of 1/50th..

While your camera will generally do good work at higher ISOs (up thru 800 easily) always pick the lowest ISO that gets the job done. As ISO goes up the Dynamic Range goes down and noise in the shadow areas will start to intrude on the picture (though printed up to 8X10 you won't notice it.).

Personally I like wide angle lenses if what I'm taking pictures of lends itself to wide vistas, etc. But if my focus was on people in crowded streets I think I'd opt for a little longer lens. It just depends on your style of photography..

So sure buy the wide Tamron......it's called LAD (Lens Acquisition Disorder) the compulsion to have just one more lens ";^)A member of the rabble in good standing...

Comment #7

Update.

Playing around with the settings has significantly improved the tonal quality of my images as well as the sharpness and crispness..

Big difference!!!!!!!!!!!!!..

Comment #8

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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