Converting reflector to refractor

[Jazza11 (Jeremy)]

i have a 114mm reflector and i want to convert it into a refractor that would make about 4.5" of refractor which i hear just 80mm is good so does anyone know if it is possible to convert a reflector into a refractor not nesseceraly the tube but the mirror (converting tube would help to) so can anyone help PLEASE!!!

[Rod]

Unfortunately this is probably impossible. Mirrors are usually made of pyex or plate glass which is unsuitable for making a high quality lens. Refractors normally require two glass types - a crown and a flint. Each of the four surfaces must be ground and polished to the right radius. Mirrors are cheaper because only one surface needs to worked.

If you want excellent images on a budget then a long focal length mirror is a good option, assuming you can mount it well.

Hope that helps,

Rod.

[Roger Davis]

Well said Rod.
Rod is well known for his instrument making techniques and knowledge.
It really has to be one or the other.
Your 114mm reflector should perform well enough to do planetary and some deep sky work. Why do you feel you have the need to convert it? Is the mirror coating coming off? Are the images not crisp? You can get the mirror recoated and collimation is a simple procedure.

[pmrid (Peter)]

Originally Posted by Jazza11

i have a 114mm reflector and i want to convert it into a refractor that would make about 4.5" of refractor which i hear just 80mm is good so does anyone know if it is possible to convert a reflector into a refractor not nesseceraly the tube but the mirror (converting tube would help to) so can anyone help PLEASE!!!

If you're talking about using your mirror as a grinding blank to make an objective lens, forget it. To make a decent objective you need at least an achromat to eliminate colour abberation and that means grinding 2 lenses, perfectly matched andf from materials with appropriately different diffraction ratings. You would be better off buying an objective lens assembly from Surplus Shed in the States. They have an excellent 127mm air-spaced achromat with a 700mm focal length giving a nice F/5.5 or so. It sells for US$139 and comes with a cage pre-made. But that's a lot of lens. They also sell a 90mm with a FL of 500 for about US$50 I think and other smaller as well.
Peter