I am thinking of fork out $90 plus tax which is $100 for the William Optics Erecting Prism or Long Perng 1.25" 90º Correct Image Amici Prism Diagonal. BUT the thing is I don't like the "Erecting/Correct image", I am used to the flip left right view of the Dieletric mirror diagonal.
I have the LP 1.25" 90* correct image prism, and its a good/great diagonal, at low -medium power its just as good as my cheap $45 beloved Celestron 1.25" prism 94115-A, which is excellent, but at high power on brighter stars with the RACI diagonals there a very minor horizontal diffraction spike barely detectable at high power, but its there if you look for it, however its absent on faint doubles like the Double Double in Lyra. And its biggest "pro" is with star hopping and Lunar feature ID'ing as it can be a challenge to find features at high power when following a correct image lunar atlas with a mirror reversed diagonal, so in this regard its a great to have and the diffraction spikes that are common on amici prisms are not noticeable on extended objects like the moon, only on point sources like bright stars.
There is a easy way to fix diagonals that may be out of collimation like with the Celestron Prism, take the back off but first make sure the small hex key set screws in the side of the diagonal are gently tightened (these are not for collimation, but for not letting the prism fall out if the back plate is removed). then you can remove the leaf spring and leave it out, it will not be going back inside, and cut one or two pieces of craft felt by using the black cardboard backing as a template, then add them in the back of the diagonal after you first place the cardboard back onto the backside of the prism. Then screw the backplate back on all the way, this will hold the diagonal in better alignment usually, I never have to worry about my prism being out of collimation now.
Also collimation of the diagonal (if the diagonal is collimatable) can be done with a paper mask with a center (+) marked on the front and taped to the front of the scope, then point the scope towards a mirror and put a collimated laser collimator in the diagonal, now you can lock the clutches on the mount and while standing behind the diagonal you can manipulate the collimation screws on the diagonal until the dot of the laser is on the center mark +. this is much easier than not using a mirror in front of the scope and having to make a adjustment then walk around to the front of the scope to see if you made the right adjustment.
Don't let the $45 dollar price of the Celestron prism frighten you, they are usually very good to excellent, with their polish and coatings and transmission.
Edited by T1R2, 18 May 2025 - 07:55 PM.
