A high quality telecentric 3X made by itself

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antonello
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A high quality telecentric 3X made by itself

Post by antonello » Thu Feb 08, 2018 12:29 pm

Do you need a very high quality 3.3X or 3X telecentric and do you have the ability to build it?
Here is my project for a telecentric suitable for a H-alpha Telescope f: 10 (I designed and built it for my 150/1500 mm h-alpha Istar).
There are two projects, one of a 3.3X (OSLO) and one of 3X (ZEMAX), both made with the 3 same catalog lenses (I have used Optosigma lenses, but Eksma lenses it is similar, but cheaper ).
In red there are distances between lens.

telecentrico_3.3X_SATTA.jpg
telecentrico_3.3X_SATTA.jpg (358.68 KiB) Viewed 583 times
telecentrico_3X_SATTA.jpg
telecentrico_3X_SATTA.jpg (970.31 KiB) Viewed 583 times

If someone wants to make a telecentric from 4X to 5X (with these same three lenses) for another telescope (f: 7.5 or f: 6) I can do the calculations.
I also send some pictures of what I have done.

1.jpg
1.jpg (456.62 KiB) Viewed 583 times
2.jpg
2.jpg (417.54 KiB) Viewed 583 times
3.jpg
3.jpg (70.97 KiB) Viewed 583 times

The projects are free for personal use.
Last edited by antonello on Thu Feb 08, 2018 2:52 pm, edited 1 time in total.

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marktownley
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Re: A high quality telecentric 3X made by itself

Post by marktownley » Thu Feb 08, 2018 2:17 pm

Interesting glassware! Thanks for this :)
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Re: A high quality telecentric 3X made by itself

Post by christian viladrich » Fri Feb 09, 2018 7:15 pm

Well done. Thanks for sharing !
Christian Viladrich
Co-author of "Astronomie Planétaire"
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antonello
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Re: A high quality telecentric 3X made by itself

Post by antonello » Mon Feb 12, 2018 6:57 am

Thank's.
I add only some useful information (they are written in the images, but if one does not know Oslo or Zemax can not interpret it): the first negative lens must be placed just before the telescope's focus. In a 150/1500 telescope this distance is 86 mm for 3X, 92 mm for 3.3X and 113 mm for 5X ...
These values are lower than the backfocus of commercial telescopes, so these telecentric can be used without "to cut" the telescope.

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Re: A high quality telecentric 3X made by itself

Post by marktownley » Mon Mar 12, 2018 6:05 am

Hi Antonello,

Is it possible to design a telecentric specifically for Calcium wavelengths - 393nm, configured for an f5 and f10 system? a range of magnifications?

Thanks

Mark
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Re: A high quality telecentric 3X made by itself

Post by antonello » Mon Mar 12, 2018 6:55 am

Hello Marktownley

1) Please note that this telecentric was born in the amateurs astronomers field for a telescope f: 10, to bring the focal ratio to f: 30 (3X), when the telecentric 3X Baader had not yet been released.
2) As someone else has already experienced, the focal ratio f: 30, for to make an etalon work properly, it is valid for etalon solid. The telecentric is not advisable for etalon in air, such as Lunt and PST, instead it is fine for etalon Daystar (which accept larger angles than the etalon Lunt and Coronado).
3) Of course, no problem to optimize the telecentric for 393nm. For the f: 10 (3X) I do not see any problem. For the f: 5 (6X) there will certainly be problems in the optical quality out axis and also in the excessive length between the two negative lenses (about 380 mm).

Can I know the focal lengths of the two telescopes f: 5 and f: 10?

After, give me one or two days and I check everything.

Greetings

Antonello

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Re: A high quality telecentric 3X made by itself

Post by marktownley » Mon Mar 12, 2018 8:12 am

Hi Antonello,

Ideally the scopes would be 100mm f10 and 100mm f5, but if you think the short scope is unfeasible that is fine. Hi-res CaK is going to be an interesting area to explore in the years ahead.

Many thanks

Mark
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Re: A high quality telecentric 3X made by itself

Post by antonello » Tue Mar 27, 2018 1:58 pm

Hello Maktownley
I have had the time to verify the quality of my telecentric in the Calcium line.
With Zemax in "optimization" mode I verified that the best scheme is the same as with H-alpha. Of course, the quality deteriorates slightly, but is always good for a field of 0.15 °, which corresponds to about 1 cm on the focal plane in a 150 mm f: 10 telescope.
Looking at the attached drawings, in Oslo for convenience and comparison with the reference image (3.3x H-alpha), it is possible to see, as is obvious, that for 0.393 nm the focus lengthens by 23 mm (image below), compared to the 200 mm focal length of the last positive lens. With these 3 simple lenses it is not possible to have more.
Of course, it is advisable to place the camera sensor at 200 mm, exactly as for the H-alpha
To obtain a larger field it is necessary to change the BK7 glass, but this leads to a different project ...
A similar speech is valid also for the 3x telecentric.
Bad news instead, as expected for 5X to f:6, where the quality is good only at the center of the field and it makes no sense to waste time.
confronto_telecentrico_3.3X_SATTA.jpg
confronto_telecentrico_3.3X_SATTA.jpg (671.32 KiB) Viewed 244 times

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Re: A high quality telecentric 3X made by itself

Post by marktownley » Wed Mar 28, 2018 5:12 am

Thank you very much Antonello, looks like this might be my summer project.
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Re: A high quality telecentric 3X made by itself

Post by allhoest » Sun Apr 01, 2018 8:08 pm

Hello Antonello,

Thank you for sharing your design.

I always wonder with these telecentric system the total length of the path, up to the CCD sensor: 350 to 400mm, depending on the design.
This induces torque on the focuser, especially if using a heavy Ha etalon close to the CCD.

Isn't possible to make the design shorter?
Daystar have a quite compact system with their quark filters.

Must the CCD be really positioned so far behind?
Sorry, I'm very poor in optic knowledge.

CS
Alex

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Re: A high quality telecentric 3X made by itself

Post by antonello » Thu Apr 12, 2018 11:28 am

Hello
I apologize for the delay...
Speaking of my telecentric, I had written to marktownley that quality decreases a little in the calcium line ... In reality this is not true, what happens is that it is the disc of difraction that in the wavelength of the calcium is half of that in H-alpha ... but the quality is similar, with the image points inside the difraction circles.
As for the message of allhoest, I understand her need for but for this purpose it is necessary to design a system with out-of-catalog lenses and an achromatic group. The work is long and expensive, and at the same time I have a thousand other projects in waiting list. I'm sorry.

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