Please excuse the length of this post, but i am wondering if anyone is able to help.

I have an adaptall SP90 2.5, a lens that I love using. Perhaps I am sad, but even looking through this lens gives me great pleasure, never mind the images it is capable of capturing.
I purchased the lens predominantly for macro, but I am increasingly using it as a portrait lens and for candid shots. It is for this purpose that I am having problems with a well documented property of this lens...Sensor flare.

The rear element of the lens is flat and in certain higher contrast situations, light reflected from the surface of the sensor is reflected back onto the sensor and produces a blueish haze spot in the centre of the image. This spot is evident when the lens is stopped down. wide open it isn't there, but shows from about f8.
There is rarely (if ever) a problem in the macro range, but it becomes an annoyance at greater distances. The particular pain of the problem is that since it is sensor flare, rather than lens flare, it is never obvious throught the view finder that there will be an issue on the final image. Lens hoods, direction of light etc have little impact.

There are several ways to reduce or eliminate the problem. Using the 2 x teleconverter prevents the sensor flare as does using wider apetures. It also seems that only certain levels of contrast in an image will cause a problem, in particular if the centre of the image is darker with lighter areas towards the edge. Obviously a darker region in the centre of an image will show the flare more readily, but it is more than this. A property of the problem seems to be ( again well documented else where) that with a lighter or mid-tone centre to the image the flare is non existant rather than less noticeable.

Thats a poor summary of the problem, now for my question. The rear element is flat on the surface facing the sensor, but convex on the other face. What would happen if this element was turned around, ie surface 1 from the sensor was the convex face and surface 2 was the flat surface? Would this affect image quality? More specifically:-
1. Does switching the orientation of one element impact on the optical properties of the lens.
2. Would having the flat face lens as surface 2, reduce reflection back to the sensor and hence reduce sensor flare?

An obvious answer might be to try it and see, but I do not have a lens spanner or the will to try if it is pointless.
As far as I can see, appart from any change in basic optical properties that might occur, there are other reasons why this might not help.

A. Presumably the rear element is coated. Would a coating on surface 2 be a problem?
B. Suface 2 would still be flat, would it still reflect internally in the element and cause the same problem? ( I am aware that some have experienced sensor flare cuased by reflections from the flat face of a filter on certain lenses/conditions)

I appologise for the ramble, but are looking to you for your collective expertise and perhaps the experience of a lens tinkerer who may have played with a problem like this.
thanks in anticipation.
neville

I thought you were going to reveal that the guy in the 4x4 did the wedding shoot as well.

Would there be any way to append a heading with "sold" or change text colour to indicate a completed deal?
I guess admin could do something like this, but it would be a heavy burden. It would be great if the OP could do this.

All pms responded to.
Wow, what a fantastic response. thanks to everyone.
lens now purchased from smc

PM replied.

Mat:- His is a students budget!!!!!! £30 max for used.

Park cameras have new ones from split kits for £29 +delivery, but are minus the hoods.

thanks

Looking for a standard DA 18-55 AL or variant. Required 'urgently' for my son. Probably will need to order new, but thought I'd try here first.

PM sent

Might be barking up the wrong tree, but isn't this a 42mm screw mount? If you have just lost focus at infinity, it could be due to the k to screw adapter.

These are exactly the kinds of things that I have found Rocky Cameras brilliant for.
Very low prices, typically £2.50-3.00 each and with a filter. I found his service good. I am aware that others have had mixed experiences with poor descriptions of lenses and other higher value items, but for these kinds of bits and bobs you can hardly go wrong.
link

The attached filters may or may not be any good, but the hoods alone are well worth the price. Regard any useful filter as a free bonus.

I have a set of 3 manual tubes available, as I have acquired a set with contacts.
PM if interested.