martin smith images Loc: Scotland

Hi all

I recently came in to possession of a tamron mirror lens as shown in the photos. I bought a tamron to canon eos adaptor and when I coupled it up I found that the lens would not focus 100% at the furthest distance. I also noticed a rainbow type pattern on the back lens as shown in the second photo. The lens is clean and without dust or mould but I cannot remove this rainbow pattern and I suspect that this may be the cause of the focusing problem. Does anyone have any sensible ideas as to whether I can buy a new back lens or other solution. The lens itself comes apart very easily but apart from this rainbow pattern I cannot see any other apparent problem that would cause this issue. Focusing close by is fine, it is only at the extreme distance where the problem lies. Thank you in anticipation of your assistance

Searcher Loc: Kent, England

I don't have the camera/lens combination you have, but over the years I have purchased several lenses not made for my cameras, and course the matching adapters. In order to focus at infinity, all my adapters contain a single lens which makes the lens focus as it should. Are you using a glassless adapter?

martin smith images Loc: Scotland

yes, the adaptor is glassless,

UtahBob Loc: Southern NJ

That probably is the issue. If you pull the adapter off, set the lens at infinity and then handhold the lens against the body without trying to mount it, can you achieve proper focus? Again, moving the lens physically and not the focus ring. If the distance that gets it happy at infinity focus on the lens is less than the thickness of the adapter then you need a different adapter or maybe this can't be done.

i.e. you can mount nikons on canons but not the other way
around is my understanding.

My mirror has a t-mount adapter. Maybe the mount on this is removable and there is a t-mount setup for it? Looks like there is a set screw in the photo you show?

martin smith images Loc: Scotland

thank you for your info, I'll try that. Can you explain in more detail what you mean about the set screw?

UtahBob Loc: Southern NJ

I added an arrow to what I am seeing and a photo of the back of my mirror lens. I attach a t-mount adapter to my nikon and then screw the lens onto that adapter. I can't find the t-mount adapter right now.

To me it looks like in your second photo that the inner ring area around the rear element is very similar to mine - are there threads on the outside of this inner ring? I'm thinking if you remove the mount from the lens you are left with that ring which would then thread onto a t-mount adapter for eos bodies. You'd have to google t-mount, etc to see what I'm speaking of - if someone else has one of these it would be easy to check it.

(Download)

martin smith images Loc: Scotland

thank you ever so much. I'll check it out later and get back to you. You've been a great help. thank you M :o)

chrisewers Loc: born UK. live in USA.

I did a lot of research on using lenses on different bodies. It depends on the original focal point of the lens and where your sensor is. for instance i have FD lenses for canon so thought i could use on my 70D. yes you can get the adapters but
A) even with the adapter your mirror might hit the lens.

B) you may need an adapter which contains a lens because the focal point of the lens is already behind the sensor. They correct for this but the glass is low quality leading to loss of some 2 f stops or more and the rainbow, softening etc you are seeing. Almost none of the adapters will focus to infinity, some might just and others will but the lens markings say it focused too early.
Good idea if you have lenses, and dont shoot at infinity and dont mind f stop loss. Maybe this is what you are seeing.
I gave up on the idea but some do get use out of the lenses. Other camera lenses like minolta also can be adapted (doesnt need glass in adapter just 2mm thick adapter) but focal length available is hit and miss as you dont have to be far out when you are making an adapter that has to be EXACTLY 2mm thick.

chrisewers Loc: born UK. live in USA.

oops i meant "already in front of the sensor"

hammer531 Loc: Fall River , Ma

I have a similar lens . The t-mount has no glass in it , it just provides the proper flange to mount on your camera . The set screw is there to lock the mount on the back of the lens . I noticed in your photo that the two green dots do not appear to line up . Try loosening the set screw , line up the two dots and then retighten the screw. Not to tight but just enough to keep the mount from turning .

martin smith images Loc: Scotland

thank you all, I'll try all these things tomorrow in the daylight and let you know how i get on M :o)

cthahn

You just discovered why you do not want a mirror lens.

martin smith images Loc: Scotland

Hi again everyone who replied to my post. I tried holding the lens to the camera without the adaptor and I could still not focus at infinity. I then, as an experiment took off the distance ring and removed the focus stopping piece to enable me to focus beyond the infinity point if that makes sense. In other words I could focus up to the subject and out of focus beyond the subject but I still cannot get a pin sharp image at the clearest focus point, I appear to get a double image, (see pic) which I know you agree is not good and I'm beginning to think it may be something to do with this rainbow mark on the back lens. Any suggestions would be helpful. Thanks again

UtahBob Loc: Southern NJ

When using the mirror, at least the inexpensive ones that I have seen I think you have to stay away from "pin sharp". I don't think that is a viable expectation. For the image you show ... is this handheld without the lens and the body connected or is this with the two connected with the adapter and the focus ring modifications you implemented? Also do you have it on a tripod? Just trying to eliminate shake which at this focal length is easy to create. You are not shooting through a window right?

I pulled up a mirror photo of mine with some out of focus tree branches and highlights. As you can see the highlights take on the characteristic donut shaped boken but the tree branches definitely start to look doubled which is not something that I really noticed before, but I really don't do much with the mirror. From this observation, I think the double image you are seeing if not from shake is another characteristic of the mirror lenses in the out of focus areas. I also added a 300mm nikkor shot of the same area from a 70-300 g lens which is very soft on the one side at less than f11 but these crops are from a pano so I don't know exactly what part of the frame they were from. Both shots were at f8. The 300mm shot is less out of focus because it would have had a greater dof at the same distance.

I find the mirror always needs a lot of contrast boost.

I think you still have focus issues and it goes back to what other have said is when you are focused at infinity or thereabouts the image is not falling on the point of the sensor but somewhere behind or in front of it and that's most likely the result of the thickness and/or composition of the adapter. I think some heavy googling is necessary to figure this one out.

Mirror at 500mm (750mm equiv)


Nikon zoom at 300mm (450 equiv)

martin smith images Loc: Scotland

thank you Bob for your very helpful comments. The image was with the adaptor and the lens fitted to the camera and outside on a tripod with a cable shutter release. as still as it was possible to get it. M :o)