Tamron Lenses - 2

Unfortunately not all the Tamron range are going to make the grade in Infrared, it's been amazing so far how good most are in comparison to most modern lens manufacturers, in general they are almost all usable in IR at all normal apertures, with hot spots only showing mildly stopped well down past f/11. 

Tamron 28-200mm f/2.8-5.6 Di III RXD [A071] Lens

The first possible casualty is the Tamron 28-200mm f/2.8-5.6 Di III RXD lens, it's problem is not that it has a bad hot spot, that looks to be fine in my initial assessment. The problem as shown below is immediately apparent as soon as the lens is mounted on an IR or Full Spectrum converted camera, there is a massive flare looking image contamination with the lens cap on. 

Tamron 28-200mm Lens 0.5s at f2.jpg

The rather impressive image above is taken on my 720nm IR Converted Sony A7RIV with the lens cap on the Tamron 28-200mm lens at 28mm for 0.5s at f/2.8 on 100iso, with little post processing, so that's how it looked in the viewfinder. The image would change considerably as you zoom and focus, but not changing aperture, it was worse at the wider end of the zoom range and near minimum focus distance. This is almost certainly due to some sort of optical encoder within the focus mechanism that uses an IR emitter and that IR light is leaking into the optical system and being picked up by the sensor in the IR sensitive camera.  It won't be a problem on a normal camera as the factory installed UV/IR filter pack will block all IR light, but for IR or full spectrum converted cameras it looks like this is going to be a problem. I will try the lens out in more normal conditions, but I have a suspicion this is going to start showing in images with some shadow detail.

Tamron 28-200mm Lens 15th at 28mm.jpg
Tamron 28-200 1s at f16 28mm.jpg

The good news is that it is very difficult to get the image contamination to show in an actual photo, partly because it appears much worse when the lens is focused very close at 28mm. The above image [Left] is taken in very dull overcast conditions with the stone work on the left getting full daylight and the darker area on the right in full shade [ It is my front porch ]. The exposure is 1/15th Second at f/2.8 on 100iso at 28mm and near minimum focus distance. It's not great, but I really had to try and find a situation where it showed at all even in overcast conditions. Although the contamination does not appear to be affected by changing the aperture set when a lens cap is on, that may not be the case in normal photography because as the aperture is closed down, the light hitting the sensor is reduced, so you would normally increase the exposure time or iso setting to compensate. Both of which will show the IR contamination more. As I suspected stopping down the aperture reduces the real image intensity, but not the contaminating image, so in effect the contamination shows much more as the exposure time is increased. The above image [Right] shows the same image at f/16 and 1 second exposure.

 

So the worst case scenario is 28mm end of zoom, stopped well down at minimum focus in low light levels especially with dark subject on the right hand side of the image.  

HOLD THE FRONT PAGE

The above images were all taken on lens firmware version 2.0, I contacted Tamron and asked if I could update the firmware to the latest Ver 3.0 as the release notes mention some noise on the right hand side of the image at long exposures. Sure enough and to my absolute amazement Ver 3.0 completely solves the problem, I can only assume the new firmware switches off the IR encoder during the exposure, which is genius - Hats off the Tamron for obviously finding the problem and solving it.  

Tamron 28-200 Ver 2 at 28mm 30s at 3200iso on  A7R with STC UV-IR Cut.jpg

Tamron 28-200mm lens Ver. 2.0 at 28mm

on FS A7R with STC UV/IR Cut Filter so like a normal camera. 30s at 3200iso

Tamron 28-200 Ver 2 at 28mm 30s at 3200iso on FS A7R.jpg

Tamron 28-200mm lens Ver. 2.0 at 28mm

on FS A7R. 30s at 3200iso

Tamron 28-200 Ver 3 at 28mm 30s at 3200iso on FS A7R.jpg

Tamron 28-200mm lens Ver. 3.0 at 28mm

on FS A7R. 30s at 3200iso

The above left image shows the image contamination at 30s and 3200iso shows even on a normal camera, which is why Tamron needed to address the problem for the majority of their customers. The middle image shows the same exposure on a full spectrum camera, the whole image is completely fogged at 30s and 3200iso, but Version 3.0 Firmware on the right hand image at the same 30s at 3200iso exposure shows absolutely no sign of any image contamination with a full spectrum camera - Problem Solved even for night or Astro work with a full spectrum or infrared converted camera.

N.B. My initial guess that firmware 3.0 switches off an IR encoder during exposure is incorrect, because the image contamination no longer shows in the viewfinder at all, I now suspect the IR encoder only operates very briefly during manual focus in Ver. 3.0, which will never affect the actual image.

Now that problem is sorted, lets have a more detailed look at the image quality in infrared;

Tamron 28-200mm with Ver. 3.0 firmware at 53mm f/9.0 on a Full Spectrum Sony A7R with an STC 720nm Clip In IR filter. No sign of any hot spot, sharp corner to corner, no strange artifacts from IR encoders, I think this is going to be a great all round lens for IR work.

Tamron 28-200mm at 53mm f9.0 720nm STC Clip In FS A7R.jpg

Click on image to open in new high resolution zoomable window.

Tamron 28-200mm with Ver. 3.0 firmware at 38mm f/8.0 on a 720nm IR Sony A7RIV. 

Infrared Image with Tamron 28-200mm lens with 720nm IR Converted Sony A7RIV

Click on image to open in new high resolution zoomable window.

Tamron 28-200mm at 43mm f7.1 720nm IR A7RIV Web.jpg
Roger Backhouse FS A7RII + Tamron 28-200 with STC 720nm Clip In Filter L.jpg

A couple more shots with the Tamron 28-200, above right is by Roger Backhouse, who has just bought the lens for his FS A7RII. 40mm f/11

Tamron 24mm f/2.8 Di III OSD M1:2 [F051] Lens

The final lens in the latest batch of lenses I have received from Tamron is the 24mm f/2.8, it looks and handles exactly like the 20mm lens I tested previously, again with the same very useful 67mm filter size. There is little sign of any hot spot at apertures upto f16 and the image looks sharp across the frame. Here are a couple of examples;

Tamron 24mm lens f7.1 720nm IR A7RIV Web.jpg
Tamron 24mm lens f7.1 720nm IR A7RIV 2 Web.jpg

Conclusions

My overall impression of the Tamron range of lenses in Infrared is extremely favourable, all the lenses tested are usable at almost any aperture for 720nm Black and White work, which is my personal favourite. I have now purchased both the 28-75mm and 17-28mm lenses for my own use and will continue to post images to the Full Frame Galleries, I'll also try and do more false colour work with them.