We use a gravitational bar torque method to compare bar strengths ( the maximum tangential force normalized by radial force ) in B and H -band images of 152 galaxies from the Ohio State University Bright Spiral Galaxy Survey .
Our main motivation is to check how much the difference in the rest-frame wavelength could affect comparisons of bar strengths in low and high redshift observations .
Between these two bands we find an average bar strength ratio { Q } _ { B / H } = 1.25 which factor is nearly independent of the morphological type .
We show that { Q } _ { B / H } > 1 is mostly due to reduced bulge dilution of radial forces in the B -band .
The bar torque method needs an estimate for the vertical scale height of the galaxy , based on the radial scale length of the disk and the galaxy ’ s morphological type .
Since these two might not always be possible to determine at high redshifts in a reliable manner , we also checked that similar results are obtained with vertical scale heights estimated from the radii corresponding to the K -band surface brightness of 20 mag/arcsec ^ { 2 } .
Also , we made a simple test of the usability of the bar torque method at high redshifts by checking the effects of image degradation ( nearest neighbour sampling without any adjustment of noise levels ) : we found that the estimated bar strengths varied by \pm 10 \% at most as long as the total extent of the bar was at least 10 pixels .
Overall , we show that the gravitational bar torque method should provide a proficient tool for quantifying bar strengths also at high redshifts .