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05-16-2014, 05:23 AM   #1
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Just bought a used Tamron 70-300mm and...

The lens seems to be in good condition, but I have some problems with exposure at different aperture settings. At 300mm wide open (f5.6) the exposure seems to be fine, but at f35-45 it's way overexposed, pretty much all white (that's using aperture priority mode,I can get it to look ok in manual mode, but I'm guessing the lens should be able to do this by itself).

I've also noticed the lens seems sharp only from about f20-40, which seems a bit odd IMO...

Also, whether I use aperture wide open or tiny, there doesn't seem to be any visible DOF difference in the photos I took so far.
Seeing as this is my 1st telephoto lens, and also my 1st non-pentax lens, I'm not sure if the lens if faulty, or I'm doing something wrong.
Any help with this is appreciated.


Last edited by Rayn; 05-16-2014 at 05:32 AM.
05-16-2014, 06:05 AM   #2
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Hi and welcome.
I had the sigma brethren of the 70-300 as my first auto focus telephoto
It was a real blast !
You will find no lens likes being closed to the small aperture with the big f numbers like 20
A physical effect degrades the image.
That lens will be really happy at something like f 8 if there is enough light
05-16-2014, 07:07 AM   #3
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Just bought a used Tamron 70-300mm and...

Here's the thing; if I was using a tiny aperture and got a dark image, that I'd understand, but the fact I got an overexposed image leads me to believe something is wrong with the aperture on the lens. The camera naturally increases ISO and lowers shutter speed when using a smaller aperture setting (f35, for example), to compensate for less light... Right?
So either the lens/camera is not calibrated properly, or the aperture isn't really moving. That would explain the fact that when using manual mode, and keeping ISO and shutter speed the same, f5 and f35 give pretty much the same image/exposure.

Am I way off base here?

That's the only explanation I could come up with for this very odd behavior of the lens on different aparture settings..

I really like the lens and macro mode, but the only way of using it and getting consistent results right now is manual mode.. So I'm seriously considering returning it, unless ofc I'm missing something?
05-16-2014, 08:58 AM   #4
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I had an issue on a copy of the Tamron 70-300 where it had sticky aperture blades that sometimes got stuck at certain apertures. Perhaps that is what's happening with yours?

Try shooting in manual aperture, using the aperture ring. And even check to see if the aperture is closing right when you adjust the ring (before you shoot)

Good luck!

05-16-2014, 09:13 AM   #5
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Tried it out and you might be right; the blades are getting stuck, they won't close all the way after opened, and somewhere around 200mm they just snap close and won't move at all (?!?).
Damn it.. I was just starting to like this lens. Back to the owner it goes I guess..
05-16-2014, 09:18 AM   #6
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Take one or more photos at full auto. If these are OK then everything should be fine, and you need to work on your manual technique. If not, take the lens off the camera and gently move the aperture blade adjustment lever against the spring tension, while looking through either end towards a light. You should be able to see the blades open and close. When you release the lever the blades should move back to full open.














whem you
05-16-2014, 09:24 AM   #7
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QuoteOriginally posted by wsteffey Quote
Take one or more photos at full auto. If these are OK then everything should be fine, and you need to work on your manual technique.
That's what I did, using aperture priority mode. And exposure was all over the place, depending on the aperture I used.

QuoteQuote:
If not, take the lens off the camera and gently move the aperture blade adjustment lever against the spring tension, while looking through either end towards a light. You should be able to see the blades open and close. When you release the lever the blades should move back to full open.
When I move the adjustment lever the blades get stuck at around f12 (just a guesstimate, half way open) at 70mm. Then I start moving towards 300mm, still looking at the ring. At around 200mm the ring snaps back (closes) and after that, the adjustment lever DOES NOTHING. Like it's broken beyond 200mm (?!?)
05-16-2014, 10:56 AM   #8
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Busted?

Hello Rayn, welcome to the Forum!
It sure sounds like the aperture-setting mechanics are in need of adjustment or perhaps complete replacement. In either case, it may not be worth it, money-wise. For the price of a repair, you could probably get another one.
But, let's run through another possibility first, OK?
Is this the older series zoom, with a real aperture-setting ring? If so, the little drop pin near the smallest aperture (highest number, like f/22.0 or f/32.0) must be depressed while turning the ring, so it drops into place and locks. Then, the ring doesn't move manually, the camera controls it in Auto.
Similarly, this must be disengaged to shoot in full manual.
If that function is working (or, it's a newer version with no pin), you may have a bad one.
Good luck!
Ron

05-16-2014, 11:17 AM   #9
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QuoteOriginally posted by rbefly Quote
Hello Rayn, welcome to the Forum!
It sure sounds like the aperture-setting mechanics are in need of adjustment or perhaps complete replacement. In either case, it may not be worth it, money-wise. For the price of a repair, you could probably get another one.
But, let's run through another possibility first, OK?
Is this the older series zoom, with a real aperture-setting ring? If so, the little drop pin near the smallest aperture (highest number, like f/22.0 or f/32.0) must be depressed while turning the ring, so it drops into place and locks. Then, the ring doesn't move manually, the camera controls it in Auto.
Similarly, this must be disengaged to shoot in full manual.
If that function is working (or, it's a newer version with no pin), you may have a bad one.
Good luck!
Ron
Hey Ron,
Unfortunately, even though the lens is the older version and does have the ring, it's already set to auto. I tried playing with it, but it didn't fix anything.
Thanks anyway. It appears I'm gonna have to return it after all. Shame, as I loved all the shots that actually worked as intended... both of them.
05-16-2014, 03:11 PM   #10
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QuoteOriginally posted by Rayn Quote
....

Am I way off base here?
nah you are right as confirmed by other replies
was just trying to get you away from f20
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