I mentioned the mirror I just finished in the testing thread, and rather than divert that thread I figured I would start a new one. My mirror is a 10" f5.3. I started grinding in 6/03, polishing 10/03, and finshed figuring in 10/04. I figure I spent at least 100 hours with the pitch lap and the mirror lost almost four inches off its focal length from the time I started polishing till completion. All this polishing time went towards fixing two badly turned edges and many figuring attempts.
I have attached a composite image of the nine sets of foucalt data I have. The horizontal axis is the distance from the center of the mirror to the edge, and the vertical axis is the wavefront error. The vertical scale is different for each graph, but in each case the red line indicates a height of 1/10 wave (measured from the bottom of the chart). The first test I took is in the small graph at the bottom middle. I used a quick and dirty testing aparatus in my living room (it uses dental floss to measure the knife edge movement). After seeing this result, I figured I had better go to the mirror class that night (I was planning to skip it). At the class we took the remaining six sets of data at the top of the picture. The instructor and I each took one set of readings along three different diameters. My readings are on the left and his are on the right. The two readings taken at chabot are at the bottom.
The mirror star tests slightly undercorrected (bright outer ring inside focus and vice versa.) I find this somewhat puzzling as the center is clearly too deep and the majority of the tests suggests that the edge is also low. If I compare the star test images to Suiter's book, I can easily see that it is better than his 1/4 wave undercorrected image. However, it is hard for me to objectively rate how my images compare to his 1/8 image. My wishful eye is a big problem here, but I am also very green with the star test. I also have not had a chance to star test under favorable conditions.
Since I am leaving for two weeks on wednesday morning, today was my last (realistic) chance to get first light. I rushed out to the first semi-dark site I could find, but the moon was already starting to rise. I was not able to push the power due to the seeing, but I could easily tell that the light grasp simply blows away my current 6" newt. Given the amount of moonlight flooding the sky, I had some fairly impressive views of the veil and the orion nebula. I got a peek at saturn before I left, but the seeing was just too crappy to see much (anything below a 15mm EP was a waste of time.) Unfortunately my trip lasts just past the next new moon, so my next observing session will probably be under similar conditions. My first chance to really push this sucker will probably happen around the new year.
I have attached a composite image of the nine sets of foucalt data I have. The horizontal axis is the distance from the center of the mirror to the edge, and the vertical axis is the wavefront error. The vertical scale is different for each graph, but in each case the red line indicates a height of 1/10 wave (measured from the bottom of the chart). The first test I took is in the small graph at the bottom middle. I used a quick and dirty testing aparatus in my living room (it uses dental floss to measure the knife edge movement). After seeing this result, I figured I had better go to the mirror class that night (I was planning to skip it). At the class we took the remaining six sets of data at the top of the picture. The instructor and I each took one set of readings along three different diameters. My readings are on the left and his are on the right. The two readings taken at chabot are at the bottom.
The mirror star tests slightly undercorrected (bright outer ring inside focus and vice versa.) I find this somewhat puzzling as the center is clearly too deep and the majority of the tests suggests that the edge is also low. If I compare the star test images to Suiter's book, I can easily see that it is better than his 1/4 wave undercorrected image. However, it is hard for me to objectively rate how my images compare to his 1/8 image. My wishful eye is a big problem here, but I am also very green with the star test. I also have not had a chance to star test under favorable conditions.
Since I am leaving for two weeks on wednesday morning, today was my last (realistic) chance to get first light. I rushed out to the first semi-dark site I could find, but the moon was already starting to rise. I was not able to push the power due to the seeing, but I could easily tell that the light grasp simply blows away my current 6" newt. Given the amount of moonlight flooding the sky, I had some fairly impressive views of the veil and the orion nebula. I got a peek at saturn before I left, but the seeing was just too crappy to see much (anything below a 15mm EP was a waste of time.) Unfortunately my trip lasts just past the next new moon, so my next observing session will probably be under similar conditions. My first chance to really push this sucker will probably happen around the new year.
Attached Image:
