Do ASME/ASTM standards allow the use of optical enhancement (e.g. magnifying glasses) to view radiographs?

Yes. ASTM E 1742-08a stipulates that 'magnifiers shall be available to provide magnification between 3x and 10x to aid in interpretation and determine indication size, as applicable'. ASME V B22 SE-94 is less prescriptive: 'optical magnification can be used in certain instances to enhance the interpretation of the image'.

ASME V Article 2 Appendix IV appears to allow digital image storage and subsequent magnification. For welds, in particular, ASTM E 1032-06 says that 'where applicable' digital image enhancement 'may be used in an effort to resolve questions regarding the nature of the indication'.

References

1. ASTM E1742-08a Standard practice for radiographic examination, Para 5.4.7.
2. ASME Boiler & Pressure Vessel code, Section V (2010) - Nondestructive examination, B22 - Radiographic standards, SE-94 - Standard guide for radiographic testing, Para 27.3. Also ASTM E94-04
3. ASTM E1032-06 Standard test method for radiographic examination of weldments (Para 7.3 - Note 1)