Tamron 90mm F2.5 macro problem

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Xaveryptak

Active member
That's my second T 90mm lens (old version F2.5) that I am having trouble with. At higher F stops (I think starting from around F5.6) I get a round light reflection right in the middle of the lens. I am using an original hood. I am using it with the ciecio7 FD adapter. The lens has an adaptall2 system with the Canon FD mount. I've returned the first lens but the second one shows the same artifact, perhaps a bit smaller size. I don't have this problem using the ciecio7 adapter with the Canon FD 50mm.

I am wondering if there is a leakage between the adapter and the mount and what I see is the light reflecting through the aperture. However the size of the reflection doesn't seem to change with the size of the aperture opening. (I don't see it though when aperture is open wider than 5.6)

Anybody is using this lens with the same or different adapter?
 
Are you using a filter on the lens? If so, have you tried removing it to see if the reflection goes away? A sample photo of what you're talking about would be helpful, as well as a description of the shooting scenario(s) that bring up the problem.
 
I've tried with filter on and off with the first lens but it didn't make a difference. The second lens has no filter on. At first I though thaat it was a dust particle since the lens #1 had few of those. But the lens #2 shows the same problem.

Here is a freeze frame:
1285017623.jpg
 
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This is only a suggestion and it will probably take a bit of trial and error to establish what the problem is. I wonder if this is caused by light reflected from the sensor back into the lens. The reason "digital" lenses were developed for DSLR systems was because of this problem i.e. digital sensors are far more reflective than film, and so this is more of a problem with digital than it was with film. The fact that 2 lenses of the same type both display the same issue points to something to do with the design of the lens, rather than a particular fault with a lens. Also the appearance of the bright spot looks far more like lens flare (which is internal lens reflections) than the effect of dust. I have noticed with my old lenses that have accumulated a fair bit of internal dust, that the effect tends to be a general all over lack of contrast, rather than specific marks or reflections.

It might be possible to counteract the problem by making a baffle similar to that found on 4/3 lenses. The Tamron 90mm f2.5 is a full frame lens and it provides a far wider image circle than is needed to cover the 4/3 sensor. This wide image circle can itself be the cause of internal reflections and I think this is why the 4/3 lenses were fitted with these baffles, so as to reduce internal reflections in digital cameras.
 
My first thought when I saw this photo was some kind of dust particle or even dried up liquid (errant spittle perhaps?) directly on the imaging sensor. I would verify the cleanliness of the sensor first and go from there. You might have to look real carefully to see it 'cuz it'll be a small spot, maybe slightly transparent.
 
htinla said:
My first thought when I saw this photo was some kind of dust particle or even dried up liquid (errant spittle perhaps?) directly on the imaging sensor. I would verify the cleanliness of the sensor first and go from there. You might have to look real carefully to see it 'cuz it'll be a small spot, maybe slightly transparent.
Click to expand...

I thought about it too but then I should've seen the same effect with my other lenses: stock, my pancake and Canon FD 50mm. Those lenses work perfect. Just in case, I went through a sensor cleaning 5x to no avail.
 
SteB said:
I wonder if this is caused by light reflected from the sensor back into the lens.

This wide image circle can itself be the cause of internal reflections and I think this is why the 4/3 lenses were fitted with these baffles, so as to reduce internal reflections in digital cameras.
Click to expand...

I think you're probably right. That's what I was afraid of - that it is a design problem. I though that maybe addidng an adapter changed the physics of the lens but your suggestion could be true too. That's why I also hoped to hear from someone using this lens.

SteB said:
It might be possible to counteract the problem by making a baffle similar to that found on 4/3 lenses. The Tamron 90mm f2.5 is a full frame lens and it provides a far wider image circle than is needed to cover the 4/3 sensor.
Click to expand...
SteB, how would you go about that?
 
Hi Xaveryptak

I have never tried making one of these baffles myself. However, I have seen quite a few articles on it on the internet. It is often used on older manual focus lenses adapted for 4/3 or m4/3. Basically you just use a circular piece of matt black card, which has a horizontally aligned rectangular aperture - this is placed in the lens throat or adaptor. If you try a Google word search using something like "4/3 lens baffle", or a similar combination of words, you will find lots of article and forum threads about this. I think the most important thing is getting the size of the rectangular aperture right. If the rectangular aperture is too small it will vignette, and if it is too large, then it will not provide enough protection.
 
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