•  Previous
  • 1
  • 2
  • 3
  • 4(current)
  • 5
  • 6
  • 7
  • Next 
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Tamron 70-300 VC exposure issues
#31
[quote name='_sem_' timestamp='1289230559' post='4051']

Certainly it does, but that's effective aperture, it decreases at close-focus normally ("bellows factor"). The nominal aperture (physical hole) is probably the same throughout the range. Can't tell for sure due to the lenses between my eyes and the aperture diaphragm, but the aperture blades surely do move at least approximately as expected at both focus ends.

[/quote]



Yeah, i am aware about this. I have a sigma 150mm macro that behaves this way.



I asked this because I also read somewhere about firmware bugs in some lenses related to effective and nominal aperture, not only with canon but with nikon too.



Does that happens in any aperture?



Sorry mate, I do not have enough knowledge to help you.
#32
[quote name='mst' timestamp='1288185934' post='3817']

According to my tests so far, it doesn't seem so.

[/quote]



I stand corrected. I have just finished a few tests and can happily confirm now that after its latest trip to Tamron Service Europe the Di 60 meters as expected. Sorry for saying otherwise first, this was based on some shots in the field only, combined with ... uhm ... user error. A layer 8 issue <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/rolleyes.gif' class='bbc_emoticon' alt='Big Grin' />



I will update the review accordingly. Probably also do a quick retest of the MTF values.



So, one down, one to go. On to the 70-300 VC metering issues ...



-- Markus
Editor
opticallimits.com

#33
[quote name='mst' timestamp='1289429540' post='4095']

I stand corrected. I have just finished a few tests and can happily confirm now that after its latest trip to Tamron Service Europe the Di 60 meters as expected. ...

-- Markus

[/quote]



Great news! I'm very interested in the MTF results (well, and whether it does produce a brighter image at F/2.0 than at F/2.4 at inf focus).

Btw, while you're at it it may be worth checking if AF works on D7000 if you happen to have one around, especially in Live view and the movie mode. Seems like many 3rd party lenses are incompatible.

Sem
#34
[quote name='hackmann' timestamp='1289257223' post='4058']

I asked this because I also read somewhere about firmware bugs in some lenses related to effective and nominal aperture, not only with canon but with nikon too.

[/quote]

Got no experience with Canon but AFAIK they show the nominal aperture which normally does not change with focus. Older lenses give nominal aperture on Nikon too; I guess you then have to compensate exposure manually (watch the RGB histogram and roll the EC wheel...). I got used to compensating exposure a lot with the Tamron 60 and Nikkor 18-200VR ;(



[quote name='hackmann' timestamp='1289257223' post='4058']

Does that happens in any aperture?

[/quote]

Yes, the whole aperture range is shifted by 2 stops at close focus compared to inf focus. The name "bellows factor" because old macro lenses would shift the whole lens away from the camera to achieve high magnifications just like bellows or extension tubes. With modern IF designs this is not so simple anymore; there still seems to be the same 2 stops difference at 1:1, but there may be a different curve in between; there are also considerable differences among different IF designs regarding what happens to the effective focal length and the working distance at close focus (compare the Nikkor, Tamron and Canon 60mm IF macros).
#35
[quote name='_sem_' timestamp='1289569733' post='4128']

Got no experience with Canon but AFAIK they show the nominal aperture which normally does not change with focus. Older lenses give nominal aperture on Nikon too; I guess you then have to compensate exposure manually (watch the RGB histogram and roll the EC wheel...). I got used to compensating exposure a lot with the Tamron 60 and Nikkor 18-200VR ;( [/quote]

???



The metering system should take care of this, unless these lenses indeed suffered from incorrect exposure problems at specific diaphragms. Stopping down manually should correct this in those cases.

Quote:Yes, the whole aperture range is shifted by 2 stops at close focus compared to inf focus. The name "bellows factor" because old macro lenses would shift the whole lens away from the camera to achieve high magnifications just like bellows or extension tubes. With modern IF designs this is not so simple anymore; there still seems to be the same 2 stops difference at 1:1, but there may be a different curve in between; there are also considerable differences among different IF designs regarding what happens to the effective focal length and the working distance at close focus (compare the Nikkor, Tamron and Canon 60mm IF macros).

Actually, the aperture doesn't chaneg at all. What changes is the image circle. At 1:1 th eimage circle is 4X as large, area wise, as it is at infinity, which means the saem amount of light is now illuminating 4X the area (of which only an area the size of the sensor is captured), In short, thi smeans 4X less light per area size, and therefore effectively 2 stops loss of light, even if those are not aperture stops.



The only reason why this is often equated to 2 stops is that diffraction also hits 2 stops faster. Unfortunately, popular belief has it that now F/2.8 suddenly becomes F/5.6, which is totally incorrect. It is indeed, as you mention, just the "bellows factor".



BTW, this is no different with IF lenses: the light loss as compared to infinity is purely determined by aereal magnification factor expressed in f-stops.



Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....
#36
[quote name='_sem_' timestamp='1289568409' post='4126']

Great news! I'm very interested in the MTF results (well, and whether it does produce a brighter image at F/2.0 than at F/2.4 at inf focus). [/quote]



... at the same shutter speed, I guess? I'll check that.



[quote name='_sem_' timestamp='1289568409' post='4126']

Btw, while you're at it it may be worth checking if AF works on D7000 if you happen to have one around, especially in Live view and the movie mode. Seems like many 3rd party lenses are incompatible.

[/quote]



No issues here, works as expected both in normal AF mode (phase detect) as well as in contrast AF (Live view) on the D7000.



-- Markus
Editor
opticallimits.com

#37
[size="3"][/size]



I would just like to say that my tamron 70-300VC USD lens is spot on exposure wise. If anything It tends to be a bit towards the left on my histogram compared to my other lens.
#38
[quote name='manny' timestamp='1290029804' post='4223']

I would just like to say that my tamron 70-300VC USD lens is spot on exposure wise. If anything It tends to be a bit towards the left on my histogram compared to my other lens.

[/quote]



Which mount do you use?



-- Markus
Editor
opticallimits.com

#39
[quote name='mst' timestamp='1290075991' post='4237']

Which mount do you use?



-- Markus

[/quote]



I have a Nikon D90. I have 8 lenses. My tamron compared to all of my other lenses has the histogram slightly shift towards the left and you can see it in the pics which turn out slightly underexposed . The crazy thing is that it does it only in Matrix Metering . In center or spot it's just like my other lenses. IQ wise the lens is exceptionally good , especially for the price.
#40
Strange. I just did the first vignetting measurements with the D7000, including the 70-300 VC. The lens clearly shifts towards overexposure, especially stopped down at the short end.



-- Markus
Editor
opticallimits.com

  
  •  Previous
  • 1
  • 2
  • 3
  • 4(current)
  • 5
  • 6
  • 7
  • Next 


Forum Jump:


Users browsing this thread:
4 Guest(s)