When doing high resolution work, a dirty diagonal does affect performance, so for planetary observing, a diagonal should be cleaned whenever one can see dust on it. I recommend dielectrics because the dielectric coatings are very hard and can stand up to regular and somewhat indifferent cleaning methods. I don't recommend a dielectric diagonal because it gives a better view than other types. To me, the primary reason for upgrading to a dielectric diagonal is that sooner or later, it become necessary to clean a diagonal, and planetary observers should clean their diagonals frequently. If the diagonal has some serious defect then changing it would maybe make a difference, but in most cases, the improvement that comes from replacing a diagonal is quite difficult to see.īut that does not mean that I would not recommend an upgrade. If you'd like a mechanically better diagonal, like one with a compression ring instead of a set-screw, that can be a reason to upgrade, however.Īgree. Unless there is something wrong with your current diagonal, you really won't notice much, if any, improvement. I don't (currently) have any intention of going to 2" So, staying with the 1.25" setup is there anything to be gained from a different diagonal? What do I need to know?īy improvement I guess I mean improved brightness or definition. I have a Celestron 9.25 SCT and I'm wondering, is there a significant improvement to be had by using a different diagonal? That is in comparison to the stock provided piece. If you stay with 1.25", a mirror increases the length by about 10mm but such a small difference won't affect the view.
If you install a larger diagonal, just make sure to minimize the length. The SCT is corrected and optimised to have its focal plane where it is with the provided visual back and prism diagonal (about 105mm from the back of a C8 and about 115mm for a C9 if I remember correctly). You know I'm going to try it though.Īctually, the spacing is critical so if you want to try without a diagonal, you'll need to replace the diagonal by an extension tube of similar focal length (about 67mm). If it is so close you really can't tell the difference, stay with what you have.I would have never considered this. If it's noticeably better without, you may benefit from a better quality diagonal. Then, with the same eyepiece, look at it with the diagonal and look for the same things. A good look noting detail, contrast and scatter. Pick an eyepiece that gives you good planetary views and look at Saturn without the diagonal. Saturn may be a little better since it's at a lower elevation. Put the scope on a target like Jupiter or Saturn. it may or may not work for you depending on how well its angles are made, but it would make it better in many s good thing they're only $40 so they can easily be replaced without a dent in the wallet. screwed the back plate on flush and it fixed it. but the celestrons get the job done at a decent price.Īs far as the collimation of the prism, I've found them easy to fix, I got frustrated with one of mine a few yrs ago, and took it apart, removed the flat spring and cut out three pieces of some craft felt and placed them behind the black cardboard backing thats between the prism and the back plate of the diagonal. I find the build quality good, certainly as good as any vixen prism and maybe even a takihashi prism, they all use this sorta thinner aluminum material for the body ( or have in the past, I haven't seen any new ones in person), so in that regard they are basically the same, but not the same quality as the machined aluminum diagonals that some companies are using like TV, AP, Baader and even Astro-Tech.
The celestron prisms are made from BK7 glass they have modern coatings and is a perfectly fine optical glass for diagonals such as the one that came with the scope and will provide a lifetime of good use if taken care of.
they have less light scatter than a mirror and are made to be used in long focal length scopes such as the SCT's, Mak's and long-ish refractors, (plus its just cool the way it bends the light.lol) I also like the celestron 1.25" prism, but I love prism's in general.