Trying the Tamron 28mm f/2.5

Orio · Expire: 2012-12-04

This evening I took the first shots with the Tamron 28mm f/2.5
Before I go on, I have to say that the light condition was really difficult. Certainly far from the best light to display a lens' qualities. The available light was so low that I had to confine myself to f 5.6 as upper limit, with only a couple of exception photos took at f 8, and always with no less than ISO 400, most often 1600 and sometimes even 3200!

Having that said, and saying beforehand that I want to retest the lens under better lighting conditions, I have to say that I was expecting something more in terms of optical quality after all the high comments I read about this lens. The sharpness is there, without doubt. The lens has remarkable clarity of detail rendition. Already from f/4, it is sharp and clear well above average. it is a little bit soft only wide open, but hey, of all the lenses that I have tried, only the Leicas can say to be really sharp wide open.

Unfortunately, sharpness is not everything in a lens, and that is where the problem is, because the Tamron 28mm suffers from serious corner light falloff. The falloff wide open (f/2.5) is certainly the worst I have ever found in a prime lens, and alas, I have to say that even many of the zooms that I have used were not as bad. At f/4, there is an improvement, but still below what I consider the acceptable level for a prime lens. At f/5.6 the falloff decreases ssensibly, and is finally at an acceptable level. In order to have it completely disappear, though, you must stop down to f/8.

Now, it's true that I seldom use wide angles at less than f/8. When I can. But sometimes, like today, you can not stop down too much and you have to use the lens at wider apertures. In these conditions, the Tamron 28 would produce images with a problematic quality, in spite of it's sharpness, which as I said, is excellent. But what good the sharpness wide open is, if you can not use it because of the light falloff?
So as far as the experience of today goes, I would say that the Tamron 28mm is a fantastic 28mm f/5.6. Meaning that you have to forget the larger apertures if you want to obtain a quality image.
Now, the fact is that at f/5.6, also my Pentacon lens gets very sharp, not to mention the Nikkor. So the sharpness advantage of the Tamron is really more theoretical than practical: by the aperture you can really start to use the lens, the other lenses have gotten to par too.
I can not support it with the price/quality ratio argument either, because it costed me 80 Euros (40 of lens + 40 of adapter), while I paid 65 US dollars for the Nikkor 28mm f/2 and around 20 Eur for the Pentacon 2.8/29. Only for the Distagon I have paid more (significantly more), but the Distagon is really a champion lens.

So for the moment, the idea that I have is that this Tamron 28mm 2.5 is an optical lens for the good weather. The excellent image clarity that it delivers, will really shine when you can shoot stopped down without problems. For cloudy days or dawn/twilight situations, however, I would leave it home and take with me the 2.8/28 Distagon or the Nikkor 2/28 instead.

Here's the image samples.

Rob Leslie · Joined: 20 Mar 2007 Posts: 1103 Location: UK Swindon

Orio am I right in assuming you are shooting with a Canon 5D?
of course on a crop factor DSLR one never sees this fall off and I have never been aware of it on film. My copy of the lens was bought by me new in 1975 so I took a few thousand film SLR shoots with it.
I am inclined to think that it may not suit the 5D.
It is a fact that the 5D exhibits fall off on all lenses to some degree and maybe the Tamrom worse.
My friend has a 5D and uses a photoshop plug in to correct the fall off. It seems to do a good job. Have you tried anything like that? He loves his 5D and like yourself finds the quality from the camera to be top notch but still admits you have to pick the right lenses for it but a tweak in PS can correct the light fall off problem with ease.
A bit of a mixed review you have written. I would certainly agree about the clarity and sharpness of the lens and note that that it was on a dull day. So it seems the only problem was the fall off? I would be interested to hear from Michael (SP Tamron) about this and I think Photodo has a test on the lens I will look up tonight.
Did you do a the same shot with the 2.8/28 Distagon or the Nikkor 2/28?

Orio · Expire: 2012-12-04

Rob Leslie · Joined: 20 Mar 2007 Posts: 1103 Location: UK Swindon

Hi Orio I just downloaded the two f2.5 shoots and put them in PT lens. It cleared them both no problem. I have to go out now but can post them tonight if you want.
The f4 Tamron shoots look the same as many examples of the 5D edge loss that I have seen posted in tests of the camera. The f2.5 are worse

Orio · Expire: 2012-12-04

Rob Leslie · Joined: 20 Mar 2007 Posts: 1103 Location: UK Swindon

Photodo rate the Tamron with a score of 3.2. They also list the 28 f2 Nikor and rate it a very good 3.9 however looking at the charts the edge sharpness of the Nikor falls off much quicker than the Tamron, especially a f8. It is only the wide open performance that gives the Tamron a lower mark than the Nikor. In the real world away from the charts I would be inclined to believe that the Tamron performs better than the Nikor. They also have the Distagon graded an excellent 4.3 As a comparison the Canon EF 28 f1.8 has a Photodo rating of 3.2 and the later AF Nikor D f2.8 28mm also rates 3.2
http://old.photodo.com/nav/prodindex.html

As for the Canon 5D it is a very good camera which I wouldn't knock.
As I wrote a good friend has one and does see the fall off, but he also calls the camera 'The Dogs Dangly Bits"
Here is a link and a few quotes from DPR review / test of the camera. They conclude it isn't a big problem and can be worked around however it does exist.

http://www.dpreview.com/reviews/canoneos5d/page24.asp

�It was my experience of shooting with the EOS 5D that it is certainly possible to see falloff in every day shots, although mostly only at large apertures."
"Prime lenses
Again the EOS 5D fully reveals the falloff characteristics of these lenses, although to be fair this probably wouldn't be noticeable on the 50 mm lens beyond F2.2 or the 100 mm lens beyond F3.5. However the comparison is pretty stark, you would get the same level of falloff on the EOS 20D with the 50 mm lens at F1.4 as you would on the EOS 5D at F2.5
As we explored earlier in this review and have discussed in previous 'full frame' digital SLR reviews such big sensors expose the weakest part of all lenses, the edges and corners. These limits occur most often at extreme wide angle and/or large apertures (even with the most expensive professional 'L' lenses)"

Me again.--It is questionable that the 5D has any light fall off problem or if lenses just aren't good enough for it. A few more qualified people than I have pondered the problem and the answer seemed to come from Leica. they wanted and tried for full frame on their M camera but gave up and went for 1.25 0r 1.3 (doing this from memory) even then they added 'Micro lenses' to the edge pixels of the sensor to cure the light fall off problem. They (Leica) said that on any sensor there will be light fall off as the angle the light hits the edge pixels degreases their sensitivity. With a FF sensor this angle is just too much, you would need a curved sensor to correct it. This is why they added those 'Micro lenses'
So that is the answer. the lenses have no problem it just that the extreem angle that image forming light from the lens hits the pixels. they just don't work so well if light doesn't strike them square on. This very real problem will one day soon be solved and then we will have some great FF digital cameras.