torus_optic

In 1997, I decided to sell my 16" to make a larger scope. The next reasonable size was for me, a 22". The first thing to find was a good optician. When you are at the other side of the atlantic ocean, that's not an easy thing to choose. I order from torus. I received the optic in a good delay. The interfero looks good, about 1/8 according to the optician. I was happy, sure to find a very good optic. I install the primary in the scope and begin to use.

For sometime, I use it but was a little surprised not to be able to use more than about 250x magnification on planets. Doesn't matter I thought, that's because of seeing, bigger mirror are more sensitive that's all. The gap of lightgathering power between 16" and 22" made me happy but planets were never that good (less magnification than with the 16"). I decided to make the primary test, in case of a problem, because all the rest of the scope was apparently good.

An independant test was made.. bottom line, secondary is good but the primary was not at 1/8, it was at 1/2,7. Needless to say I was disapointed, strong spherical aberration. I was incredibly disapointed, those average to low quality image on jupiter and other sharp object was due to that problem, a comparo for the first time with a good optic at the same time show me all I was missed because of this primary. I thought it was a shame because I make a scope as good as I can, spend time to collimate carefully, made a good cell, and the point where I can't do anything is the bad link.

As many people who jump from a smaller to a bigger one, the lightgrasp is astonishing and that make your forget your judgment... On top of that, many ideas like "bigger mirror don't show good planetary images because of their seeing sensivity" or widely spread.

Since I have posted my problem on bigdob, some other people with the same problem contacted me, most in europe. So, a simple advice, try to have your primary tested by an optician, it's not always fun to hear the datas but it worth the effort.