The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Irix 45mm F1.4 and the Tamron 45mm F1.8 Di VC USD for their suitability to various photography scenarios:
Size and Weight Comparison
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Tamron 45mm F1.8 Di VC USD weighs 520g, 43% (405g) lighter than the Irix 45mm F1.4's weight of 925g.
Below you can find the dimension and weight table of the Standard Prime Lenses in Nikon F (FX) Mount for size comparison purposes.
Standard Lenses in Nikon F (FX) Mount for Size Comparison
Filter Threads
The Irix 45mm F1.4 has a filter size of 77mm whereas the Tamron 45mm F1.8 Di VC USD has a 67mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 77mm filters that we recommend you to consider for the Irix 45mm F1.4:
And these are the 67mm filters that we recommend for the Tamron 45mm F1.8 Di VC USD:
Lens Mounts
Both the Irix 45mm F1.4 and the Tamron 45mm F1.8 Di VC USD has the same Nikon F (FX) lens mount. Some of the latest released cameras that are compatible with the Nikon F (FX) lenses are Nikon D6, Nikon D780 and Nikon D3500.
Irix 45mm F1.4 is also available in Canon EF and Pentax KAF2 mounts.
Tamron 45mm F1.8 Di VC USD is also available in Canon EF and Sony Alpha mounts.
Focal Range
Both lenses have the same focal range of
45mm but while Irix 45mm F1.4 has the fastest aperture of
F1.4, the Tamron 45mm F1.8 Di VC USD's widest aperture value is
F1.8.