Problems in image

[Andrew*]

Could someone please have a look at this picture and suggest what may be going wrong?

This is a 100% centre crop of a single shot through an old manual lens 200mm at f/5.6. This is the BEST shot of a series I took at different apertures and exposures. Every other shot has these horrible triangular stars and blue flaring, but worse. Many also have a particularly bright flare towards the bottom right of bright stars.

Is the lens carp or the focus out, or is it something... more sinister? DUN-DUN-DUNNNNN!!

Cheers

Andrew

[Andrew*]

Another example...

[roundycat]

my guess, and it is only a guess, is that the 'old manual 200/5.6' is to blame. What make is it? Even if it is one of the top five it is not likely to give a good result on a star test.

Dennis

[Andrew*]

Hi Dennis,

The lens is called "Kestrel" - never heard of it. It's actually f/3.5 at its widest but I stopped it down. I've just looked through it and it seems that the iris blades aren't correctly placed. One is a bit further in which will probably explain the defect. I think it could work quite well if the iris was fixed. Is there any way to do this?

cheers

Andrew

[brianb]

Is the lens carp or the focus out

It looks to me like the lens has a considerable amount of both astigmatism and coma. Most likely it has been disassembled and reassembled with the elements badly decentred.

Maybe it wasn't much good even when new, but it should have been better than that.

Some old manual lenses do very well - try for example the Olympus OM 200mm f/4.