PLT OF AN ATX BN2; ISLANDER; MISJUDGED THE ACR TFC AND MADE A QUICK TURN TO AVOID AN MLG ON DSCNT PASSING THROUGH RPTR'S FLT PATH. VISUAL SEPARATION IN USE.

Narrative

I DEPARTED CMA AT XI00 LCL ON A VFR CLB TO 5000 FT EBOUND TOWARDS VNY VOR. ALTHOUGH THE WX IN CMA WAS CLR WITH GOOD VISIBILITY; I HAD OPTED FOR AN IFR FLT PLAN BECAUSE I KNEW I'D BE FLYING WITH THE SUN IN MY EYES AND IT WAS LIKELY TO RESTRICT MY VISIBILITY. AFTER REACHING 5000 FT I WAS CLRED DIRECT VNY VOR. NOT LONG AFTER THAT TFC WAS CALLED AT MY 9 O'CLOCK AS (B737 OR B757?). I RPTED IT IN SIGHT AND WAS INSTRUCTED TO MAINTAIN VISUAL SEPARATION WITH IT. SOON AFTER; ACR X RPTED ME IN SIGHT AND WERE GIVEN THE SAME INSTRUCTION TO MAINTAIN VISUAL SEPARATION. (I HAD BEEN TOLD THAT ACR X WOULD BE DSNDING.) I WAS INDEED KEEPING THE OTHER ACFT IN SIGHT BUT I MISJUDGED THE CONVERGENCE COURSE THAT WE WERE ON. IN AN INSTANT THE SIT SEEMED TO CHANGE FROM NORMAL TO DO SOMETHING QUICK! IN THE SECOND AS I WAS DECIDING WHICH WAY TO TURN TO AVOID THEM; A VOICE FROM ACR X SAID THAT IT LOOKED LIKE I WAS TURNING RIGHT INTO THEM. IN FACT I HAD NOT YET INITIATED A TURN BUT AN INSTANT LATER I STARTED A TURN TO PASS BEHIND THE OTHER ACFT. A VOICE FROM THE ACR X ACFT INDICATED I SHOULD HAVE STARTED MY TURN MUCH EARLIER. INDEED I WOULD HAVE IF I HAD NOT MISJUDGED THE CLOSURE RATE. I HAD FULLY EXPECTED THEM TO PASS WELL E OF ME AND AT A LOWER ALT. HOWEVER; THE ACR X CREW HAD RPTED ME IN SIGHT; WERE ALSO INSTRUCTED TO MAINTAIN VISUAL SEPARATION; AND WERE ON 'THE L' IN A CONVERGING SIT. WE OBVIOUSLY BOTH MISJUDGED TO DISTANCE. IF I HAD JUDGED IT BETTER THIS WOULDN'T HAVE HAPPENED. AS TO FACTORS AFFECTING THIS SIT -- I WAS NOT OVERLY TIRED; THE ACFT WAS FULLY FUNCTIONING. IT WAS A HUMAN PERCEPTION ERROR.