I’ve always liked Tamron SP lenses as I think they give a lot for the money. SP, Super Performance, means they perform on a high level, more or less on the same level as first party lenses, without the same price tag. I’ve owned Tamron SP lenses for more than ten years and have been pretty happy about them, so when Tamron announced their updated version of the already very good 24-70 f/2.8 VC, I actually sold my Nikkor 24-70 f/2.8 VR to get the new Tamron. I’m not saying that the Tamron is better than the Nikkor, but it freed up some money that I could use on something else without sacrificing much of the performance (if any).
If you wonder about the Tap-In Console, I made a short article about it HERE.
This lens was my second Tamron lens to be able to use the Tap-In Console, and I would call it one of the most ingenious gadgets in the photo world, it’s also source of head-scratching. Why head-scratching? Because you might learn something about your lens that you haven’t thought about if you weren’t deep into lens design.
According to the Tap-In Utility, the 24-70 G2 should be calibrated at closest focus distance, medium distance and infinity (medium distance means half travel of the focus ring from closest to infinity), and at 24, 35, 50 and 70mm focal length. How to perform the actual calibration procedure is nowhere to be found in the documentation with the lens or the Tap-In Console, so I expected it be done at largest aperture as this is most common.
During this time period I sent an e-mail to Tamron in Japan, Europe (Germany) and USA if they had a step by step guide on how to do it, and also how far away is enough for calibrating at infinity with both of the mentioned G2 lenses (24-70 and 70-200). Japan responded first, by forwarding it to the European department as the request was outside of their area (maybe the Tap-In Console works differently in Japan?)! Got only one response from Germany telling that: “The distance is 0,95 meter, 5 meter and by infinity more than 20 meter.” That’s it! Nothing more! Obviously, this is for the 70-200 lens, but what about the 24-70 mentioned in the same e-mail and the other questions? Only useful information was “more than 20 meters”, which doesn’t appear in the Tamron utility and I find it strange as the furthest distance reported in the image file is 35.48 meters at 70mm focal length and 100.00 meters at 200mm!? From USA I got a couple of answers but in general they were just ramblings with no useful information and in the end, I didn’t even get an answer any more. I mean, the Tap-In Console was announced in the beginning of 2016, so I expect Tamron Customer Service knows what it is or are able to dig up an answer to provide some useful information?!
When I first got my 24-70 G2, I noticed considerably back focus at longer focal lengths that was easily visible in the viewfinder, but I just dismissed it in my mind as user error with a new lens, still the memory was lurking in the back of my head. This back focus was confirmed when I started the process of calibrating the lens late autumn last year.
I mounted the camera and lens on my Manfrotto tripod and illuminated the focus target with good light, and measured 38cm from the focal plane to the target and started the calibration with Reikan Focal 2. 24 and 35mm appeared to be not so bad (+2 and +7), but at 50 and 70mm I came quickly to +20 on both! Hm, that was unexpected, and I started thinking about the whole setup if I’ve overlooked something. The setup looked good but then I started to question the focus distance, is it the real measured distance that should be correct, or is it the distance the camera and lens think is the right one? This focus distance is embedded into the image file and can be read by an exif reader, so I found there is definitely not any accuracy in the embedded distance, but on the other hand I’m pretty sure it’s this distance the camera and lens are using.
If you want to know more about Reikan FoCal, I’ve made an article HERE.
So, after this somewhat revelation, I went back to doing another run of calibration where the camera and lens thought 38cm was (actual measurements was 41,5cm) and ended up with more or less the same at 24 and 35mm, but 50mm changed from +20 to 0, while 70mm wanted slightly more than the possible +20! Ok, didn’t see that one coming.
At 1 meter, the next focus distance, the lens behaved more predictable but still massive plus values needed to get it corrected. This, together with somehow similar results from the SP 70-200 f/2.8 VC G2, made me contact the store where I bought them, explaining the behavior of the lenses and ended up returning both of them! After about a month I got a brand-new copy of both lenses, more about the 70-200 G2 in another post.
And guess what? Indeed, the new copy behaved slightly different, but still quite similar! Head scratching, what is going on?! Could it be my camera? As it was a recall because of the shutter problem last year, I sent the camera to service and asked them to take a look at the auto focus at the same time. When the camera came back I noticed that the calibration values I’ve added earlier was consistently a couple of values off, so I’m pretty sure they have serviced the auto focus too. The camera out of the way, I continued to search for other explanations and I looked through some other calibration values I’ve done with other lenses. My 200-500 VR is pretty consistent at short and medium focus distance, the same with the Tamron 10-24 VC (in crop mode) gave me a variation of ± 2. Even the superzoom Nikkor 18-300 VR (also in crop mode) had only ± 1 throughout the zoom range. This doesn’t mean it initially was dancing around zero, simply indicating the difference between largest and smallest number throughout the focal range, all had some values into the plus side.
More head scratching. Then I started thinking, what if I was able to calibrate at other apertures? Would it make a difference or would it stay the same through the aperture range? My calibration software, Reikan Focal was able to set desired aperture, so I run through the calibration at f/2.8, f/4, f/5.6, f/8 and f/11 at closest and medium focus distance, and at all focal lengths mentioned above. Couple of reasons why I haven’t done at infinity, is partly that I haven’t found out how far away is enough, and also here in Norway it’s not much good daylight in the middle of the winter combined with cloudy and cold weather.
Below is a print screen of the results and I really didn’t imagine that it would be like this, referring to the beginning of the post when I wrote you might learn something new. As we can see here at focus distance of 38 cm, quite good at 24mm, but from 35mm and on there is a massive swing from plus to minus values, especially at 70mm.
Further we see more or less the same at focus distance of 1 meter, very good at 24mm, but from 35mm and on, a large swing from plus to minus. Although not as much as at 38 cm focus distance. I will post results for infinity when numbers are ready.
Honestly, I’ve never imagined that the plane of focus would move so much and for so many reasons. Not only does it move at different focal lengths, it moves at different focus distances and with different aperture too! My first thought would be, is this normal, does all or most other lenses behave like this too?! Unfortunately, I don’t have any of Nikon’s f/2.8 pro zooms available anymore, so I took my next best thing, the Nikkor 16-35 f/4 VR and here are the results from this lens.
And here the still popular Nikkor 50 f/1.4D
A short explanation of the letters after the values. I’m using Reikan Focal software to help me determine the correct value, and Focal are using four words to tell how good or the quality of the final value is. The best is Excellent, then Good, then Acceptable, and finally Poor. If I get an Acceptable or Poor result, I normally do another run to confirm the first one, and sometimes even a couple of more runs if there is a big difference in the values and in the end calculate the average value.
I won’t say that this is normal behavior of all lenses based on only those mentioned here, but at least it looks like it’s not so uncommon? Later I will do similar tests of the 24-120 f/4 VR and the 200-500 f/5,6 VR to see if it’s more prone in shorter or longer focal lengths.
Update; here are the numbers from the Nikkor 200-500 VR at 5 meters. I’m not sure if this revealed much of a pattern though.
So then comes the big question, how to choose witch value to add in the lens when it varies from huge plus to massive minus values? Well, that’s a very good question! For me though, I buy f/2.8 zooms to use them at large aperture, so I will aim the final calibration at f/4 and then it will be close enough at f/2.8, f/4 and f/5.6. If there is something like the 24-70 G2 at 70 mm at 38 cm, I will probably make a compromise between f/2.8 and f/4, and keep that in mind when wanting to use the lens at smaller apertures and close to 70 mm (like using live view could be a solution).
I guess when you’ve read so far you have a feeling the whole story is somewhat negative, and I agree. But remember what this is, a post about calibrating the lens, not about how it perform in daily life. So I think this slight negative angle is justified, I think Tamron could have provided better user manual on how to do the calibration. In their tech pages online they could also have explained the behavior of the lens at different lens designs without giving away any design secrets.
As mentioned this is not a post to talk about the performance of the lens, but I will say I really love Tamron lenses and how they make the photos look, so don’t let this post scare you away from any of the fantastic SP lenses from Tamron. I will not hesitate to buy another Tamron lens in the future.
Equipment in use for the calibration:
Reikan FoCal 2 calibration software on my PC.
Reikan focus chart printed in highest quality on 120g non glossy paper.
Tamron Tap-In Console and Utility.
Tamron SP 24-70 f/2.8 Di VC USD G2.
Manfrotto 475B tripod.
Kirk BH-3 ball head.
2x Dynaphos soft-boxes with total about 450 watts of low energy lights for illumination of the focus chart.
NB, the values mentioned throughout this post is only valid for my lenses together with my camera, do not expect they will fit your lens and camera, they will most likely do it worse! So, do your own calibration and find your own values. I posted those values only to prove the point, not to give the final answer.
In the end I have a few questions to our readers, if you know a rule of thumb, or how to calculate how far away is enough at different focal lengths to calibrate at infinity, I would love to hear from you. If you’ve done similar tests at different apertures and got the same results or not, I would love to hear from you. If you know why some lenses behave like this, I would love to hear from you. Or if you just have some comments or questions, so, come on, let me hear from you in the comments below!
Thanks for visiting!