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 Oct 7, 2009, 3:38 AM   #1
Senior Member
 
Join Date: Jun 2006
Location: Rockingham Western Australia
Posts: 592
Default Tamron f2.8 90mm lens

After seeing recommendations by Tcav and MVASteve I have recently purchased a f2.8 90mm Macro Tamron lens. For use with my A200.

I have been playing for days and doing direct comparisons with my Tamron 18-250 lens.

My conclusions are that the f2.8 90mm does everything I asked for in close up (flowers etc) pictures that I was disappointed in when using the 18-250 which just wasn't sharp enough at the closer distances. The 18-250 lens will remain my main lens as I think it is great.

Using the new lens I was a little bothered that the photos were paler than I liked, so after a lot (and I do mean a lot) of practice using bracketing I concluded that the lens needed an negative AV of about 1 as standard for both distance and macro type work


This is contrary to the manual (leaflet) with the lens which suggest a + factor to compensate for the lack of light entering the lens.

Any comments

Fred

Last edited by Bootneck3; Oct 7, 2009 at 5:50 AM. Reason: addition
Bootneck3 is offline   Reply With Quote
Sponsored Links
Old Oct 7, 2009, 7:44 AM   #2
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,544
Default

Can you post some examples of images that have not been corrected for exposure?
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Oct 7, 2009, 3:53 PM   #3
Senior Member
 
Hawgwild's Avatar
 
Join Date: Mar 2006
Location: Pensacola, Florida
Posts: 3,525
Default

Please do, as I am about to buy this lens Saturday if I can find one in Orlando.. Robert
Hawgwild is offline   Reply With Quote
Old Oct 7, 2009, 7:18 PM   #4
Senior Member
 
mtclimber's Avatar
 
Join Date: Oct 2005
Location: Oregon, USA
Posts: 18,143
Default

fred-

The Tamron 90mm is well know for its sharpness and macro capability, but I have never heard of an exposure problems.

Sarah Joyce
mtclimber is offline   Reply With Quote
Old Oct 10, 2009, 7:57 AM   #5
Senior Member
 
antony's Avatar
 
Join Date: Mar 2007
Location: Sydney, Australia
Posts: 182
Default

Congratulations on your Tamron F2.8 90mm lens
__________________
AntBlog701 (blog) | SillyDog701 (website)
antony is offline   Reply With Quote
Old Oct 10, 2009, 8:20 PM   #6
Senior Member
 
Join Date: Jun 2004
Posts: 477
Default

Just wondering, is the rear element on the Tamron F2.8 90mm perfectly flat?

I have a Tamron F2.5 90mm SP, and the rear element is perfectly flat (as are some of the other Tamron Adaptall 2 lenses).

When I stop this lens down, say F16, you can see a bright "spot" on the image, where the light is reflected off the sensor, back onto the flat rear element and back onto the sensor. As you increase the aperture, the spot gets fainter and larger, and around f8, it disappears. However, I think the "spot" only disappears because it takes up the more of the frame, but I'm sure it just decreases the contrast, which is what might be happening to you.

e.g.
at F32:


At F16:


At F11:



Could this effect be tricking the light meter, or perhaps decreasing the contrast so it looks "paler"? (On Bootneck's lens)

Last edited by dnas; Oct 12, 2009 at 3:02 AM.
dnas is offline   Reply With Quote
Old Oct 11, 2009, 12:27 PM   #7
Senior Member
 
Tullio's Avatar
 
Join Date: Jan 2006
Posts: 7,370
Default

Have you tried the same exact experiment but with a different lens? I think you may find that this phenomenon occurs with every lens.
__________________

Tullio
Tullio is offline   Reply With Quote
Old Oct 11, 2009, 1:01 PM   #8
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,544
Default

dnas,

The flare you're seeing is probably the flare that results from light reflected off the image sensor back at the rear element of the lens, and then reflected off the rear element of the lens back at the image sensor. Digital image sensors are much more reflective than film, so this wasn't a problem with film. But most lenses produced since the advent of digital SLRs have additional coatings on the rear element of the lens specifically to prevent this problem.

Your Tamron 90/2.5 is from the film era so it doesn't have those additional coatings. Bootneck3's lens is almost certainly a new "Di" lens, which includes the additional coatings, so he's not likely to see that flare in his images.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.

Last edited by TCav; Oct 11, 2009 at 1:03 PM.
TCav is offline   Reply With Quote
Old Oct 11, 2009, 5:57 PM   #9
Senior Member
 
Join Date: Jun 2004
Posts: 477
Default

Quote:
Originally Posted by TCav View Post
dnas,

The flare you're seeing is probably the flare that results from light reflected off the image sensor back at the rear element of the lens, and then reflected off the rear element of the lens back at the image sensor. Digital image sensors are much more reflective than film, so this wasn't a problem with film. But most lenses produced since the advent of digital SLRs have additional coatings on the rear element of the lens specifically to prevent this problem.
Didn't I just say that?? You "explained" something to me that I just explained myself!!!
"you can see a bright "spot" on the image, where the light is reflected off the sensor, back onto the flat rear element and back onto the sensor."
dnas is offline   Reply With Quote
Old Oct 11, 2009, 6:09 PM   #10
Senior Member
 
Join Date: Jun 2004
Posts: 477
Default

Quote:
Originally Posted by Tullio View Post
Have you tried the same exact experiment but with a different lens? I think you may find that this phenomenon occurs with every lens.
No, that particular phenomenon does not occur with every lens.

1. It's not apparent with most modern lenses with the reflective coatings on the rear element.
2. Most lenses have either a convex, or in a few cases, a concave rear surface, which serves to diverge the reflected "flare" by the time it reaches the sensor for the second time. That means that the "spot" will be larger than the sensor, so you can't see it. It will however cause a decrease in contrast, if that is the case.

The Tamron that I have is an old lens, and has a perfectly flat rear surface, so it's ideal for re-reflecting the "spot" back onto the sensor.
dnas 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 4:39 AM.