Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Sony Alpha dSLR / Konica Minolta dSLR, Sony SLT

Reply
 
Thread Tools Search this Thread
Old Aug 5, 2008, 4:41 PM   #71
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,544
Default

It's not hard to figure it out for yourself. I enjoy doing it (I have a background in metrology), but some might call it tedious.

I could explain it, but that would be off-topic. [suB]:-)[/suB]
TCav is offline   Reply With Quote
Old Aug 5, 2008, 4:53 PM   #72
Senior Member
 
Gardenwife's Avatar
 
Join Date: Sep 2002
Posts: 103
Default

You're so bad! LOL I had better figure it out soon, because I'm having shoulder surgery on the 14th and won't be able to do much with my Sony for many weeks. I'm on the hunt for a sub-compact camera, probably on older Fuji F-series.
Gardenwife is offline   Reply With Quote
Old Aug 5, 2008, 10:31 PM   #73
Senior Member
 
Tullio's Avatar
 
Join Date: Jan 2006
Posts: 7,370
Default

To find a lens sweet spot, you set your camera to Av mode, choose a well litstill subject, set the ISO to 100and take several pictures changing the aperture value, from wide open to the closest you can getw/o getting the camera shaking warning (you can actually go 1 1/2 f/stops lower due to the anti-shake feature). Do this for various FL (i.e. 28mm, 60mm, 90mm and 105mm). Then you upload the images, crop them 100%and analyze themone by one, noting the ones thatlook sharper. Then, look at the EXIF data to see which aperture the sharp ones were at andyou found the lens sweet spot.I went through most of this exercise for thisparticular lens and found that images are sharperbetween f8 and f11 at 105mm, f7.1 and f11 at 90mm, f 7.1 and f13 at 60mm and f6.3 and f13 at 28mm. Out of all these ranges, to my eyes f9.0produces the sharpest images always. So, I'd say that f9.0 isits sweet spot.Of course the down side of it is that you need a lot oflight if you want to shoot at f9 all the time. Now, that is not to say that you should avoid larger apertures (small f numbers). As long as you stay below 90mm, your images will look pretty decent, IMO.
Tullio is offline   Reply With Quote
Old Aug 6, 2008, 11:02 AM   #74
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,544
Default

Since Tullio brought it up, I'll add that the subject should be very detailed. A brick wall will do nicely. It will show you edge and corner sharpness, plus any geometric distortion.



I would modify Tullio's procedure by saying that you should use a tripod and turn off SSS. This will give you much more uniform views from shot to shot, and at some apertures, you may need to use slower shutter speeds, and why tempt fate? I would also suggest that you not crop the originals. You should view them at 100%, but cropping eliminates that info about edge and corner sharpness and the geometric distortion I mentioned.

These shots came from my test of an 18-200 that I used to have. It shows pincushion distortion at 35mm and barrel distortion at 18mm. (?)(!)

Attached Images
 
TCav is offline   Reply With Quote
Old Aug 6, 2008, 3:18 PM   #75
Senior Member
 
Tullio's Avatar
 
Join Date: Jan 2006
Posts: 7,370
Default

Those are certainly good suggestions, Tcav. The brick wall idea is very good speciallyif you are also trying to determine how much distortion your lens produces but, since it cuts down the light too much, using a tripod is a must. The last thing you want is to think that small apertures do not produce sharp images but the reason actually being camera shake due to slow shutter speeds rather than the aperture itself.
Tullio is offline   Reply With Quote
Old Aug 7, 2008, 10:41 AM   #76
Senior Member
 
Gardenwife's Avatar
 
Join Date: Sep 2002
Posts: 103
Default

You guys are the greatest. Thanks!

I picked up a Fuji F50fd to use as my every day knock around camera since it's very small and lightweight. After my shoulder surgery, I'll be limited in my movement for quite some time, but this new little camera should allow me to occupy my itchy shutter finger.

Before I next week I am going to do some test shots like you suggest. We just happen to live in a brick house, too. :idea:
Gardenwife is offline   Reply With Quote
Old Aug 7, 2008, 11:25 AM   #77
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,544
Default

And using a tripod makes it a lot easier to compare two shots. When the shots are taken from exactly the same vantage point, it's easier to see differences between the two.
TCav is offline   Reply With Quote
Old Aug 29, 2008, 5:46 PM   #78
Junior Member
 
Join Date: Jan 2006
Posts: 8
Default

Wow, that lamp shot and its 100% crop are simply amazing. Really seems like a great lens, especially for the price.

steefje is offline   Reply With Quote
Old Aug 29, 2008, 6:10 PM   #79
Junior Member
 
Join Date: Jan 2006
Posts: 8
Default

Wow didn't notice there were 4 pages here. But atleast it was on topic
steefje is offline   Reply With Quote
Old Aug 29, 2008, 6:39 PM   #80
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

We've got a 10 page thread discussing (mostly) the Tamron 28-300mm lenses. :-)

http://forums.steves-digicams.com/fo...=84&page=1

New dSLR owners like to look for a walk around lens with acceptable results at a bargain price (and this one was only $39.99 new in the box with free shipping from at least one vendor when this thread was first started).

JimC is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 5:04 PM.