Sigma IQ Expectations...

Hi, everyone!

Could you please let me know if this level of IQ is usual/acceptable, with the following exposure info.?

K7.
Sigma 150-500.
100th. sec.
F8
ISO200
Lens set to 500mm., OS off.
Tripod. mirror-up/3sec.delay

Focussed very carefully (auto., checked on manual) on the lower left insulator.


Jpeg straight from camera.



[IMG]http://i1021.photobucket.com/albums/af340/rogerhlane/IQTest002.jpg[/IMG]



Thanks,

Roger.

I wouldn't trust that particular exposure to give me an accurate indicator of the lens performance - tripod or not, 1/100th is a pretty slow shutter speed at 500mm on APS-C.

You're doing the right thing by not having the lens wide open, using mirror up, timer delay etc but you'll have to find a brighter day, brighter subject and probably also bump the ISO to get the shutter speed up. I'd suggest faster than 1/500th for starters

In my opinion, that picture is far too busy to get any idea of focussing accuracy. The insulator shown is such a small element amongst wires, branches and leaves, at all different distances. Try a test on a much simpler picture.

To test my lenses,I blue-tack coins on the garden shed and take photos of these from 12 feet distance.

You do need to increase your shutter speed to improve camera shake. I have the Sigma 150-500 and usually use it at 800 or 1600 ISO. I find mine performs very well at the 400mm setting.

Thanks to you both for that.

I'm aware of the rule-of-thumb re the reciprocal of the focal length is the longest shutter speed to be used, but presumed on a tripod with mirror-up & delay selected, the shutter speed would virtually be irrelevant...


Roger

Agree with above comments re shutter speed - I have just checked a number of my shots taken on my 150-500 and not one of them is shot at less than 1/500 and usually 1/1000 or faster. Although I seem to be able to manage decent levels of sharpness at ISO 100/200 between f/6.3 and f/11

In the right conditions - even at max length the 150-500 can deliver decent sharpness IMHO.

As an example - this was shot at 500mm range, f/6.3, 1/1600, ISO 200 - hand held with OS on and in camera shake reduction off



Carl

Nothing wrong with handheld at low shutter speed as long as the OS is engaged

1/80 sec for example


Why's that man lying on the ground by Blythman1960, on Flickr

1/20 sec is do-able, but definitely pushing it.


Fox by Blythman1960, on Flickr

Thanks again, all.

TBH, what I think I'm after is confirmation that it's the accessory behind the K7 that's faulty, not the (expensive, for me!) lump of glass in front of it!
I'm not expecting to get the hang of a new lens in minutes; I am, however, keen to know as soon as poss. what I can reasonably expect from the Sigma & adjust my abilities to suit.
(Bearing in mind I have the SRS guarantee period to sort it out!)

Thanks again for your advice & patience.

Roger.

Hi Roger

Bottom line is - so long as you do not (unlikely) have a duff version - you can expect good results from this lens.

Stick with it and you will not be disappointing - it is an excellent lens for the price

Carl

Am sticking with the testing, etc.
But I'm beginning to have more doubts re this lens/my K7 combination.
Particularly having seen David Robinson's Kestrel post on The Gallery & his other 150-500 images on his website).

Just a thought...
could the fact that the K7 is still on ver. 01 firmware have any effect on IQ with this lens....?

Sorry to go on about it but....!

Roger.

I also own the Sigma 150-500 and am very pleased with the IQ obtained with it. I doubt if the body used has any relevance, I have used mine on the K10, K20 and K5 with no discernable difference.
The sharpness of your picture is certainly not what I would expect from this lens but you do not say at what distance your point of focus was.
If say, it was about a hundred feet (or more), and at 100th sec. even on a tripod I would not expect any better result.
I had a similar problem a few weeks back with a Pentax DA300, I simply could not get one picture of acceptable sharpness from the lens. It turned out that the AF motor was faulty and was replaced under guarantee.
So a duff lens can escape occasionally....
But before returning the lens I did set up a series of tests using fixed targets at 20 - 25 feet which showed that that the AF was very unreliable and apt to produce quite severe back-focussing.


Roger.

Thanks, Roger.

This is from 10m away.
K7.
Tripod.
Manual focus (v. carefully!) on the junction of the post & the top rail.
OS off.
1/200th.
F6.3.
ISO 400.
Mirror-up.
Remote release F.




I don't believe this is sharp (enough).


Notwithstanding the noise, this is more what I would expect straight from the camera:





This was put through PSE9 unsharp mask, default settings FOUR TIMES!

Roger.

Do the same test but focus with live view.

Will do. Mike.
Thanks, what does this confirm?

Roger.

As my previous post, but focussed using live view.
(JPEG straight from the camera, no PP.)


[IMG]http://i1021.photobucket.com/albums/af340/rogerhlane/Liveviewfocustest001.jpg[/IMG]


Certainly not as easy to focus using l/v, since I always use the OME-35 magnifier when using the viewfinder.

I can't discern any difference.....

Can you, Mike?
Can anyone?
Am I any further on?
Shall I return it to SRS tomorrow?


Roger.

I always use contrast AF live view to check critical focus on a lens as you can zoom in to make sure you have it spot on.

Anyway, as to your lens question ... you are shooting wide open at 500mm so I wouldn't expect fantastic IQ (the big Sigmas prefer f8 ) but I would hope for something better than those you have posted here.