Chriske

...si on tire non pas seulement au centre mais sur toute la surface on pourrait obtenir la forme désirée ?....Correct, that is what you see on the images above. The thin glass disk and the neopreen together are spreading the pulling force over a very large (and correct) area of the primary. That's why it works..! And there is no visible astigmatic error at all..! In fact the pulling force of the unit is far bigger than any 'possible' astigmatic error. So because of that force I'm pretty convinced that there is no possible way an astigmatic error can occure in the first place, that is if all the componets are correctly constructed, glue is correctly use, etc..I'm not going to start a debate wether it works or not, I gave the info Olivier asked for, that's all. All we know is the darn thing works...!Good luck anyway, Chris.

Hey,me again...No problem to flex a mirror into a hyperbola. We've already done it. We've pulled several mirrors from sphere to oblate sphere, to parabola and even to hyperbola. Although we've flexed and measured mirrors to a parabola we did not measure the hyperbolic one. I'm pretty convinced it would be a correct figure. To be shure you have to test it for yourself. If you do, keep us informed...;-) We pulled the mirror into a hyperbola just to test how far we could go to test the strenght of the glue we were using. Once under heavy tension we left it for a few weeks. No problem there, the glue we use for flexing (Araldite) is doing the job very nicely. In fact if you ever want to remove the glue(for whatever reason) you'll need chisels and that sort of tools to remove it from the mirror. Even with strong acid it will not loosen from the mirror.Chris

Some more info about the images above. I have the impresssion not to be clear on this matter. Sorry about that...;-)Puller plate :1- Spherical mirror ; We use 19 mm thick glass up to mirrors of 250 mm diameter. Starting from 300 mm diameter we use 25 mm thick glass. 2- Layer of neopreen (the same material they use to make wet-suit (diving-dress) The neopreen we use is 8 mm thick. Dimensions of this part are calculated with Flex software. 3- Glass disk 6 mm thick. This glassdisk has the same diameter as the neopreen disk, but has no central hole..! 4- Small aluminum disk. We use a disk about 40 to 50 mm diameter, thickness about 5 mm. 5- Threated rod or fine threated bolt.Additional info on the puller : Our mirrors are all made out of plate glass. I started building telescope/grinding mirrors early 80', made some 30 telescopes myself and helped constructing about 350 scopes during course. Most of these mirrors are made out of plate glass : float or borrofloat. Never had problems with these mirrors at all. Easy to grind/polish and easy to flex to. The neopreen disk is glued to the mirror, then 6 mm thick glassdisk is glued to the neopreen, at last the aluminum disk is glued to the 6 mm glassdisk. Before glueing that aluminum disk to the glassdisk you have to attach the threated rod to it. Diameter of that aluminum disk is not important at all. The combination neopreen/glass will spread the pulling action so the pulling force is spread evenly all over the mirror. The 6 mm glassdisk has to be flat but not 'optically' flat. See to it no glue is running over the edges of the neopreen because you will loose the flexing effect. Instead of that 6 mm glassdisk you could use a steel plate, or aluminum, but see to it it is very flat. Whe tested other materials but at the end glass was the best option because of it's flatness. If it's not flat you will end up with astigmatic errors, like we once did. Use the best glue you can find, we've tested different brands of glue but at the end we used Araldite. It's a two component glue, it's very strong...!!! Also see to it the entire disk is glued and no empty spots are there because you'll end up with optical errors. To prevent the parts sliding sideways while glueing/drying make a small stand to secure it's position because some glues need 24 hours and even longer to dry.Pusher plate :These parts we do not glue. 6- A neopreen ring, again the dimension of this ring is calculated with the Flex software. 7- This ring can be made out of any material but we make (pour) them out of resin. The advantage of this resin ring : very fast to construct and it can easely be machined. The ring has to be parallel to prevent optical errors. We use a lathe to do this. 8- Pusher plate, again you can use any material but we prefer to use MDF = very flat. Here one could use a metal or aluminum disk, but you should machine it be very flat. 9- Washer and wingnut. These days we use a nut instead of a wingnut because in some situations our hands are to big to reach the small wingnut.As I explaned before once assembled, no need to do a Foucaulttest, just go outside with it and pull until you have a perfect starimage. It is also possible to pull yourself an ellips instead of a parabola. Just pull the mirror in the shape you want to, very fast and easy.Whatever you do, always keep in mind flexing is deforming the mirror mechanically, that is clear. This is done in a controlled way and very accurate. This flexdevice is handeling 1/50 wave and even even less. So whatever you're doing while constructing all the part keep this in mind. No errors are allowed al all. Once you have made one, it'll be fun and making the second one will go very fast, you'll see...!This is our latest project : A telescope for handicapped. The 250 mm f/8 mirror is a flexed one. This is a scale model. Planning to make the same one with a 400 mm primaryStill need some more info, just let us know. Good luck... ...and keep us informed how you progress.Chris

....la personne responsable m'avait donné l'impression d'être assez classique....What a pitty and what a waste of time!!! ...there are lots of new things to discover, techniques to try out. We as amateurs here in Belgium(Hove near Antwerpen) always pushing our limits again every day. This flexing techniques works perfect. We're going to flex one of these days mirrors even thinner than the ones that have been adviced by the inventor of Flex (Mr. Adler) I think it is possible to flex mirrors 12 mm thick and maybe even thinner. I also will try to make resin mirrors. I know there are opical limitations but why not just try it. Maybe, just maybe, in a few decades no one will use a heavy mirror made out of glass ever again in his telescope. This all sounds weird I know, but would you have believed in 1968 they would walk on the moon 1 year later...?Greetings, Chris [Ce message a été modifié par Chriske (Édité le 09-04-2007).]

Robert,I do not know if a f/4 system would work with this flexing device. I myself would try it if I was planning to make one. Problem is I can not guarantee it.Try it and let me know...;-)Just testing to add an image. This is the 420 mm f/6.2 mirror. Ignore the durt on the surface of the mirror. Greetings, Chris.[Ce message a été modifié par Chriske (Édité le 08-04-2007).][Ce message a été modifié par Chriske (Édité le 08-04-2007).][Ce message a été modifié par Chriske (Édité le 08-04-2007).]

Hello,Sorry to post in English I understand and even speak very fluently French but I can not write it down, so sorry. Maybe someone on your forum will translate my message...?Olivier Durant asked me to explain some more about flexing mirrors.Flexing mirrors is quit simple, In fact we will never again parabolize our mirrors the old fashion way (with pitch) ever again...!!You need two parts, The puller part and the pusher part The nice thing about flexing, you do not need a Foucaulttestingdevice at all..! You only need to perform a startest to see if the device has the correct tension. You just pull the device until you have a perfect starimage. On the Foucaultstand we measured better than 1/20 lambda. It all depends on how well the spherical mirror was finished. I'm planning to flex in the near future two 500 mm disks into a parabola, we already flexed a 420 mm so these big disks should not be a problem. I did not buy these 500 mm mirrors, I grinded and polished them myself. These two mirrors will be used to make myself a giant binocular. It'll be my second bino. If you're planning to flex mirrors do not use thick glass. The thickest glass we've used until now is 25 mm and had no problem with it. Second advantage of this flexing-thing : you do not need to support your mirror with these special mirrorsupports like the ones used in PLOP( 6 point, 9-point, ..etc...). Even when looking at a very low altitude there is no trace of optical deformation at all.If you want some more info about building a flexingdevice just let me knowChrisHow do I add pictures on this forum..?[Ce message a été modifié par Chriske (Édité le 08-04-2007).]