kuvik

Thank you, also on behalf of the co-author and the club.

Thank you for your kind words!

Thank you! I`m glad you like it and find it useful.

Dear Forum Members! A friend of mine and I made a book about our Messier observations. Basically it is an album that contains our photos and sketches of the Messier objects including a short description of all of them. About the book: With the spread of astrophotography, and especially digital astrophotography, we get a very different picture of deep-sky objects than what our ancestors could have seen for centuries by peering into their telescopes. Fortunately, many people still observe visually today, but most astrophotos are taken with long exposure times and are published with strong post-procession. The result, although very spectacular, has little to do with what we can see in the telescope. In many cases, novice telescope owners are disappointed that the deep-sky objects seen in the eyepiece are not as bright as they saw in the photos, in addition, most of them appear completely colorless. With this album, we want to bring the objects of Messier’s list closer, to make them look in our photos and drawings as – with some perseverance – we can see them in amateur telescopes. It can be downloaded from the Vega Astronomical Association's website. http://vcse.hu/online-visual-messier-guide-online-vizualis-messier-kalauz-horvath-t-varga-gy/ I hope you will find it interesting.

Finally I have decided to make a RC, so I have figured the test plate to a little stronger hyperboloid. After several attempts, this is the best, that I can get out from this mirror. For the hyperbolization I have used a star lap and a full size lap. The mirror has a turned down edge, but the calculated optical diameter is 27 mm, so I have made a cardboard mask for the test, which works as a baffle too in the test tube. This evening I have observed the shadow of Ganymedes on Jupiter with this test tube. Star test shows undercorrection, but it is normal (the primary is currently a slightly undercorrected paraboloid). The next step is to get an aluminium coating on the secondary, and after that I will figure the primary to the correct hyperboloidal form. Thank you David and Nigel for your help!

Impressive! 😮

Thank you, Nigel! Theoretically it is possible to correct the defect of one optical component with figuring the another mirror with an opposite error. But I don't want to to that in this project Yesterday I have roughly hyperbolized the reference, and I have tried to match the surfaces. David, your advice worked. The relatively high rpm helped to work down the glass from the outer zones. Your project is very interesting! I think those small disks are polishing tools. I use small tools too for figuring larger mirrors, but in this case I'm experimenting with petal laps.

Unfortunatley I'm not well equipped, but I think star test will show any important problems. The secondary is a bit oversized, so a possible edge defect will not be a problem, and/or moving the secondary I will be able to tune the overall correction if it is necessary. Each fringe a half wave, as you said, David. If the deviation is 1 fringe, it means, the wavefront error will be lambda/2?

Hello David! Hello Nigel! Thank you for your replies. The primary mirror is a non-perforated 150/450 paraboloidal mirror. Originally I have made it for RFT purposes. I want to learn how to make hyperboloidal secondary, so I try to construct an OTA for a f/18 Nasmyth-Cassegrain. The secondary is 30 mm diameter and ROC=195 mm. If I'm correct, the conical constant must be -1.95. Now the secondarys edge has no defect. The reference has TDE, I want to fix it before hyperbolizing. The back of the glasses are just flash polished, they are not optically flat. I must hyperbolize the reference and use the fringe test. At this stage (polishing) I try to practice interpreting the fringe test and find out, how to fine adjust the ROCs and the figure. I think it will be a difficult and long project. The primary is around l/10. If I will achieve similar fringes with the hyperbolized glasses, will it be usable?

Hi! I'm working on a Cassegrain secondary mirror. It is the first secondary I make. Now it has still some pits on the edge, I try to keep it spherical. The concave reference is a good sphere but with bad edge. I have tested the mirror with interference test, but I have no experience to judge the result. Please, help me estimate the surface error (ignoring the bad edge).

Hi! I have had both of them. The BST is better mechanically. Optically they seemed equal for me in f/5 Newtonian.

Thank you! Yes, it is very hard to display the faintest parts of the nebula. Their visibility on the sketch are very sensitive for monitor calibration.

Hi! This time I have made an inverted sketch. I have tried to make it as realistic as I could. These nebulas are not easy target. The observations was made on two different nights. I think, UHC filter and 5-6 mm exit pupil works best.

Hello, thank you! Your drawings are awesome! 😮

Hi Mike! Nebula filters help a lot for me. Fortunately, skies are generally good from my observing site, so I can try even fainter nebulas.