Gravitational Lensing

Gravitational Lensing
The Einstein Cross
Q0957+561
Time delays
Q0957+561 time delay
Modeling
But there is still a lot of variation in derived H0's:

Lens	H₀	Reference
FBQ 0951+2635	64 +/- 14	Jakobsson etal 2005
B0218+357	78 +/- 6	Wucknitz etal 2004
PG 1115+080 and RX J0911+0551	56 +/- 23	Tortora etal 2004
B1608+656	75 +/- 7	Koopmans etal 2003
B1608+656	61-65	Fassnacht etal 2002

Histogram of lens results (from Paraficz & Hjorth 2010, comparing to Saha et al 2006 & Oguri 2007)