Aligning images from two different cameras (HST)

[SHALMALEE KAPSE]

Hi everyone.

I want align two sets of images which I've downloaded from MAST Hubble Space Telescope (HST) portal. One set of images is from WFC3 and second is from ACS.

So far, I have tried using Drizzlepac (steps: Tweakreg, Astrodrizzle, Tweakback). However, when I do photometry on these newly aligned images to generate a color magnitude diagram (CMD), I am getting a slightly incorrect CMD.

I have also tried using astroalign, but it wouldn't work as my images have crowded field.

Does anyone know any alternate solution to this? Please let me know. Thanks in advance.