The Tamron AF 17-50mm f/2.8 SP XR Di II LD Aspherical IF lens has received some good reviews (see review by PhotoZone.de) and appear to be a nice low-cost alternative to more expensive offerings from larger camera and lens manufacturers like Canon and Nikon. However there have been quite a few complains (including myself) of the lens overexposing in flash photography, especially in Nikon TTL-BL mode. Here are some threads I found on the Internet.
- 1st thread on Nikonians 3rd Party Lenses forum
- 2nd thread on Nikonians 3rd Party Lenses forum
- 1st thread on DPReview Nikon SLR Lens Talk forum
- 2nd thread on DPReview Nikon SLR Lens Talk forum
- 3rd thread on DPReviwe Nikon SLR Lens Talk forum
- Article Tamron vs. Sigma Macro f/2.8 by Mihail Popov
My copy over exposes upto ~1.5 stops. The following photos illustrate the issue.
Tamron 17-50mm f/2.8
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Tamron 17-50mm f/2.8 with -1.5EV
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Nikkor 50mm f/1.8
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Nikkor 18-70 f/3.5-4.5G
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All test shots were taken at 50mm, f/7.1, and 1/60s using the same camera and settings. The photo taken with the Tamron lens is over-exposed compared to other lenses used in this test. The top-right photo is the top-left photo with -1.5EV exposure compensation in post-processing. I also did tests with both Nikon D200 and D70. Same over-exposure issue happened to both cameras.
The interesting observations are: It works fine in regular TTL mode, no over-exposure issue at all. You can force the camera into regular TTL mode by simply selecting center weighted or spot metering mode. It also works if you use the FV-lock function when the camera and flash are kept in TTL-BL mode. By “works” I mean that the shots will look similar to the ones taken with other lens at the same focal length, aperture, and shutter speed.
I sent my lens to Tamron for repair in the summer. It took them almost two months to work on it. At the end, Tamron sent me an replacement that has the same issue. I wrote an email to their service manager but got no reply.
Just recently, I wrote an article about EXIF information embedded in the photos. While I was examining the information extracted from Nikon NEF raw files using ExifTool, I found the that Nikon DSLR cameras have the focus distance recorded in the photos. This is nothing new. All D and G type lenses from Nikon can report the focus distance data to the camera. You might have not seen it because not many software or EXIF reader reports the data. What surprised me was the focus distance data from the test shots above. As shown in the following table, the Tamron lens sent an incorrect distance!
| Lens | Focus distance |
|---|---|
| Tamron 17-50mm f/2.8 XR Di II | 3.35m |
| Nikkor 50mm f/1.8D | 1.78m |
| Nikkor 18-70 f/3.5-4.5G | 1.68m |
It is now very clear to me why I got the over-exposed photos in TTL-BL mode. The TTL-BL mode on digital SLR bodies such as D200 and D70 is the so-called “3D Balanced Matrix TTL” or “3D Multi-Sensor Balanced Fill-Flash”, in which the focus distance data from the lens and the metering data (ambient and pre-flash) from the camera are combined to determine a proper flash output. The Tamron lens in question sends an incorrect focus distance that is much longer than it actually is to the camera. The camera is then fooled to ask the flash unit to put out more power to compensate for the longer distance, causing the over-exposure. In regular TTL mode, or when FV-lock function is used, the flash amount is determined mainly by measuring the reflected pre-flash intensity without involving the distance information. Therefore no over-exposure occurs.
This issue is quite common and since Tamron cannot do anything to fix it, I suspect it might be a design flaw. The lens does have a very short focus path: a quarter turn gets the lens from the shortest focus distance to infinity. It could be the inaccuracy of the distance information that is causing the problem.
The technical details behind Nikon’s 3D Matrix TTL-BL flash is quite complex. I will be writing an article about it in near future. For now, I am pretty sure this is the cause of the issue. If you have the same issue, you may want to check the focus distance data recorded in the photo and compare it with the data from a lens that doesn’t have the same issue by shooting the same scene at the same settings.
Update on November 20, 2007:
I have seen some follow-up posts on an old DPReview thread after one of my users posted the link to this article there.
Keywords: Exposure, Flash photography, Tamron, Tamron 17-55mm f/2.8
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Thanks for the research on this subject. I’ve been looking at the Tamron, Sigma and the Nikon 2.8 in that range. Do you have any thoughts on the subject??? I found this at Dp and will be bookmarking this site for further reading.
Thanks
Tom
Tom,
Thank your for commenting. It is not difficult to find people who love all of the three lenses. If you can afford one, the Nikon 17-55mm is probably the best. The Tamron is 1mm wider than Sigma.So the best suggestion is to test all of them and choose the one you like the most.
Max
I used to have the Tamron 17-50mm and ended up selling it. It did over-expose frequently with flash and also, I noticed the images always had a slight orange tinge to them…as if the white balance was overly warm. Yes, colour correction could be done, but I prefer minimizing post work. I ended up buying the 18-70mm Nikon which is obviously less fast, but the image quality is considerably better and for some reason I find this lens incredibly easy to hand hold. (1/5th at 18mm and 1/15th at 70mm is possible for some odd reason, perhaps I have very stable hands or something)
I have the Nikkor 18-70mm from the D70 package a while ago. It is a very good value. I was curious why Nikon was no able to squeeze out a f/2.8 DX lens since both Tamron and Sigma also have the same 67mm filter thread size. However I found f/2.8 to be very valuable especially for low light situations.
when will the article you reference below be available??
The technical details behind Nikon’s 3D Matrix TTL-BL flash is quite complex. I will be writing an article about it in near future
Ed,
Thanks for reminding me! Hopefully I will have time during the holidays to work on it.
Max
Really nice discovery and analysis. I found out that my nikon 18-135 lens also gives incorrect distance information. For distance less than 3.98m, it reports correctly. For distance more than 3.98m, it always reports 3.98m.
I have checked some pictures taken by other people using this nikon 18-135 lens. They share the same problem. If fact I haven't found out any sample taken by this lens with recorded focus distance larger than 3.98m.
Very interesting.
Do you have flash exposure problem with this lens? I'd expect it to under-expose for subject more than 3.98m away in TTL-BL mode.
Max
No, I haven't noticed any under-exposure because I bought SB600 just recently. Before that, I used the D80 build-in flash which has a guide number of 13. Given the max aperture f/3.5 of the lens, the built-in flash only reaches 3.71m. So 3.98m is beyond its capacity anyway.
I will do some test using my SB600, and let you know the result.
If you increase ISO on the camera, it can reach further than 3.71m. So 3.98m is not necessarily its limit.
Max