A few years back I happened upon a used Takahashi 128mm f8 fluorite doublet lens ( a few sleeks in the coating from over zealous cleaning). I had planned to eventually buy the tube, focuser rings etc. from Texas Nautical.
However after getting the lense cleaned by one of the opticians at work, he decided to do a cross polarizer test on the lense. I had seen annealed optical glass under this test and wasn't expecting much, but we saw a velvety pattern suspended inside the lense, and also the shadow cross shown the picture. I have heard the shadow is not unusual, but the velvet pattern was unexpected.
Does anybody have some thoughts on this type of effect? The Tak fluorite doublet gives crisp pinpoint stars and of course nearly zero color error.
However after getting the lense cleaned by one of the opticians at work, he decided to do a cross polarizer test on the lense. I had seen annealed optical glass under this test and wasn't expecting much, but we saw a velvety pattern suspended inside the lense, and also the shadow cross shown the picture. I have heard the shadow is not unusual, but the velvet pattern was unexpected.
Does anybody have some thoughts on this type of effect? The Tak fluorite doublet gives crisp pinpoint stars and of course nearly zero color error.
Attached Image:
David Simons
