- This topic has 28 replies, 3 voices, and was last updated 6 years, 5 months ago by
.
-
Posts
-
Hi everyone,
I hand a mirror pretty good, a 200 f9 Giacometti, I would autocostruirmi one newton for global recovery, I accept suggestions on how to achieve the body and the spider secondary door.
Thanks in advanceAndrea
Hi Andrea.
“To talk” I would say that the problem of intubation of a “long” 200F9, It is almost the only difficult and expensive retrieval of the tube to be used in order to achieve the necessary stiffness to such a focal length, mounted on a photographic purpose equatorial adequate to the size that it may come out in the construction.
Tube that probably could have a length of one hundred mm less than the focal length, It would be along just under 1 meter and 80, which is no small.
Ideally, the aluminum source. I guess in diameter around the 220 – 230mm, and in a thickness that would imagine at least 4mm, now that would weigh 13.5kg.
With other materials of a similar length there is the risk of decline. (The carbon fiber would certainly be a robust and lightweight solution, but personally I do not sizing and implementation experience).
All remaining 4 set off (constituted by vane spyder; by the secondary mirror and its support; the focuser; and from the primary mirror cell), They would be purchased ready for their installation on round tube.
In fact the construction of the vain spyder is not difficult, but it may be purchased for example like this:
https://www.teleskop-express.de/shop/product_info.php/info/p9317_TS-Optics-massive-Metal-Spider-for-8–Newtonian-Telescopes-D-223mm.htmlThe support of the secondary and the secondary same, (that of a focal ratio telescope F9, I suppose the smaller diameter of 35mm) It would cost less than 35mm diameter which currently look to be the smallest diameter purchased from the online catalog of the same company in the previous link.
The focuser is a precision particular that very rarely can be autocostruito, and whose cost is not high, however, it starts at around 80 euro to rise.
The primary cell for a tube of this kind could also be a simple wooden board with three collimation screws, but without articulated triangles. Or a cell “Orthodox” It may also be purchased, but these are a little more expensive than other parts.
objectively, a primary mirror 200F9 is a curiosity. This being essentially a realization “school”, that is very simple and successful even by a novice.
The ease of implementation is due to the fact that a focal ratio F9 uses in fact a spherical mirror, that is, perhaps not even technically parabolizzabile, He is the flaring of its theoretical parabola (taken as a constructive reference), practically confused in the initial ball that is the basis of any realization of Newton optical.
hello Giulio,
it is the very particular optical, I thought to realize a square tube in multilayer 6mm until I have not found and received as a gift a cardboard formwork often (those for concrete cast of the columns) long 3 meters with an internal diameter 250mm and thickness 5mm. It weighs 7,8kg then once a measure will weigh on 4,40kg, I thought to stiffen it with glass fiber and polyester resin, according to you could go? Considering that the tube is free (resins part) I thought to try and control the flexure then back to the maximum on the multilayer, definitely more robust. For the focuser I have an old rack and pinion (I love to the detriment of crayford) and the spider autocostruirei sheet metal along with portasecondario. The secondary on balance will be 28mm (minor axis)Hi Andrea.
It is from that tube formwork is a good solution…but probably it is not just good but excellent, why not think of a length of flex 2 meters, when it is hooked to the frame through the usual two bands not really very close to each other, that allow the sliding of the tube per'equilibratura.As size of the secondary, a 28mm would seem to me even so.
Which field of full light it will serve to cover the area of your photos?For curiosity, I tried to do the little drawing CAD here below link, putting the data of the 200F9, to see which side would come out for a telescope which can be done photo shoots, for example with a reflex camera provided with a CMOS sensor 23x15mm, as they had the machines to 6 until 8 megapixel up to some time ago.
The sensor of those machines had a diagonal contained in 27,45 mm, and therefore it required a field of full light CPL equal measure. Let's say 28mm. (Or even slightly less if you can tolerate a slight decrease in brightness from the center to the edge image).
Such a field of full light from 28mm through the wall of the optical tube with a diameter of 39,8mm, and it is compatible with a focuser 2″, which it has a light passing 44mm. So would not lead to any vignetting or decrease brightness at the edge of the frame.
However for passing the CPL to me that would be necessary to install a secondary 52mm diameter, (or something more not to let it work with its edge that is potentially most critical point of the processing of a flat mirror).
(also put direct connection to the image can be magnified because):
https://s22.postimg.cc/579jvnbcx/Secondario_52_o_28_per_200_F9.jpgIf I have done something wrong, in the drawing it is seen that with a secondary diameter 28mm (In magenta) there is a CPL only point to the focus of the telescope generated by blue lines. Thus, the image also in a visual light will be at the center but subject to darken quickly towards the edge of the eyepiece field of view.
The CPL 28mm is instead determined by the green guidelines external those blue, that always starting from the perimeter of the primary (who is out of the picture on the left), agree to slash green 28mm mail orthogonal to the focal point at the far right of the drawing.
Turning then to 90 ° downwards that finger with its two green lines, it is seen that the crossing of the axes where was the diskette from the secondary 28, It forms a trapezoid outer green lines to those blue, you must be able to reflect the focus of the telescope the entire disk of the CPL 28mm.
So to do this, at that point you draw a circle with its center on the crossing of the axes, and tangent to the four sides of the trapezium generated by the intersection of the green lines.
Circle it designed that way is 52mm in diameter, as it should be the shorter side of the elliptical secondary necessary.Finally we see that the image will form in the CPL out of the tube, where you have to install a focuser that must lead the field diaphragm of the eyepieces, or the focus of the camera, to 118mm from the optical tube. And if you just have to see, otherwise you have to get off on the optical axis by installing a secondary a little longer.
What do you think? Did I do something wrong?
hello Giulio,
Unfortunately, the tube is often only 5mm then rinforzerò inside pasting 4 rings (one every 40cm) multilayer thickness 25mm diameter 220mm, so it should not flex. I thought then tighten 2 of these inner rings Vixen the bar so as not to have outer rings. With regard to the calculation of the secondary, I did put 6mm of field in bright light (the diagonal of my shooting Sensor) but that may be my mistake to make calculations, try to enter data with 6mm. The focuser will be a 2 inchCompletely redone the calculations, tube diameter 250, height 105mm focuser, field in bright light 6mm, result of 35mm minor axis.
With a secondary 28mm diameter ports CPL 6mm, out of the optical tube at a distance from it of 63,5mm, which will be the one that should be filled by the thickness of focuser more camera.
But in that case you must also check how to use eyepieces that are more easily “short” the set of extracted focus for the camera, and it could be forced to use the extensions, or vice versa normally use the eyepieces, extract but with a greater fire barlowil required by camera.
If the measure, which goes from the base of your focuser fixed on the optical tube until the sign of the position of the sensor of the camera, It was greater than those 63.5mm, You will need to further lower the secondary to extract greater fire. But you'll need a secondary mirror a little bigger.
If you want to be very sure you get yourself a paper drawing in which check your measurements.
In practice regarding the verification you can use all your eye, you should prepare a multiplication table using another any telescope, and focusing with each of them, with and without barlow lens, an object, measured with a caliper, and recording always for each of them, with and without barlow lens, the measure that elapses between the abutment of its barrel, and a common reference, convenient and fixed taken on the used telescope.
With this table would discover what the eyepiece of your park, which requires the greater introduction into the focuser.
AND THAT will be the most critical eye for which you will need to adapt the focal extraction of the new telescope. …(Given that all the others will be in focus in the extraction, that is gradually moving away from the telescope).Hello Giulio I simulated the newton Atmos free:
focale 1827mm
diameter 203mm
optical axis + the focal plane is given by the sum of the focuser (105mm) + the radius of the tube that is 250mm (then 125mm) total 230mm
field in bright light 6mm (sensor size of shooting)How can I upload the file?
Hi Andrea.
Sull'Upload (and use Atmos) Take me off guard.We ask the help of Massimo.
But I think Atmos is much better than my method “St. Thomas” based on the CAD drawing.
let's try this way…..eccoilfile
[/url]
- You must be logged in to reply to this topic.