CurtPalme.com Home Theater Forum

[ecrabb]

[Tom.W]

Exactly. Not enough information was provided about speed, focal length,price range and sensor size and speed...

[Tom.W]

Gamma ray bubble...

http://www.nasa.gov/mission_pages/GLAST/news/new-structure.html

[seamaide]

Sorry for the delay, got caught up in coursework.

Thanks for all the advice! You've all been so good to me, I'm really suprised that a group this kind and helpful can exist on the 'net, but maybe I'm a lil'jaded.

The camera I will be using is a custom made from somewhere in Cambridge, but it has specifications to this model from Andor: http://www.andor.com/scientific_cameras/ixon_emccd_camera/. The detector size is ~8mm*8mm, with pixel size of 16um*16um, and can be run in photon counting mode. It's around 40cm*30cm*10cm, a rectangular box with a cylinder on top. The system needs to be run through the night, and as the expected flashes are very short and in the visible-range, it needs to have a fast response time.

The reason I'm using that lens, is that it has been sitting around the dept. for the last couple of years, since they didn't want to throw it out. As there is a limited budget to final year projects, so I can't really buy more lenses. We've got a big optics department (http://www.nuigalway.ie/physics/research_top.html)so there are other lenses around that I could use, but the project I think was originally designed to finally have found a use for the HD-8M, so I think I'll have to prove it is no good, before I can get another lens. At least it will give me useful experince, which is one of the points of these projects.

Also, the plan with the set-up of the system it to have a flat mirror reflecting the image onto the CCD sensor, but if the back focal length (or front focal length unreversed) is only a few mm there might be problems with that arrangement, but corrective elements could be added to change this.

[guger]

@ seamaide
Hi Seamaide, I wonder if you already managed to finish your project. And how successful and powerful your telescope has been made.

About five years ago I got a Delta³ HD-116D. I originally got this lens to build a video projector, but I gave up that project and the lens took it place in the basement.

Recently I was thinking about using the lens to build a telescope. To be honest, I have no idea how to modify it to increase the focal length, so I started google-ing for details and I found your post here.

Would you please provide me with informations or details in order to use the lens to build a telescope?!!

I'll be very thankful for any details.

With regards…

[gjaky]

If you read this topic carefully you can realize that none of the projector lenses can be used as a telescope -effectively (due to their low resolution) Plus I don't know your lens, but by the sound of it I guess it is an LC lens which means you can't achieve a fully focused image on any plain surfaces.

[seamaide]

Guger if you pm me, I'll send you a copy of my thesis, so you can see some of the issues I had and the methods I resolved some of them.

But in brief, the project was somewhat of a success. I had a working setup, but I only had time to do lab testing, no field-testing, so there were errors on my measurements due to the approximations on infinity in a lab setup. And there was no full quantification of aberrations with the system.

My setup was designed to be used for detection of a specific astronomical event, so for an amateur astronomer, my setup and the data I collected may be of little use.

I calculated an angular resolution of 400 arcseconds, and my field of view, with the extra glass added, was reduced from the 52 degrees of the CRT lens by itself to 16 degrees.

Now these were acceptable values for the intended application, but they may not suitable for yours. And whether you could even replicate these values is another thing entirely. I had professors specialising in optics and astronomy helping me, along with technicians, and expensive pieces of equipment.

The reason the CRT lens was used, was that my advisor wanted to get a student to design a wide-angled lens system on the cheap. So the setup was designed to keep that field angle of the delta lens as wide as it could be. Several roadblocks were in the way of this objective, the most problematic being the issue with the image plane.

When the object your are imaging is at infinity, which it would be for astronomical purposes, the image plane was inside the lens. There was 2 solutions, either place glass in front of the lens, so the object would appear to be at a finite distance, bringing the image outside of the lens; or using glass to the rear of the lens to take it out. The former was out entirely, would restrict the field of view too much, negating the whole point of using that lens. The latter was the method used, I had a relay lens, taking the image out the CRT lens, focusing it onto the sensor.

I didn't have time to design a relay lens, so I used one that was hanging around the department. This proved the biggest limiter on field of view. I had some time after experimental working ended to start working out the specifications a 2 element relay, and only managed to get the equations for the curvatures according the the raytracing of the axial marginal ray from first principles But this wouldn't have been that useful, even if I had worked out some concrete specifications, as I don't actually know how to correct abberations with design specs yet so the relay lens would have been aberrated to h***. (At least the HD-8 was somewhat aberration-corrected)

Umm, so for tl;dr, unless you want a wide-angled field of view, and have the resources to get the necessary equipment(good relay lens, and good sensors), I would say that you are better off buying a telescope.

If your curious, attached is a somewhat blurry photo(sorry) of my setup in the configurations i used. Note how small the relay lens is, which was of course the biggest limitator of the system.

[Revox]

Can you give me a "link" or an short explanation, why you get an immage out of a lens with a glas?
I noticed that the picture on the phosphor is really sharp when i got my glases on (they ore around 0,5dpt).

Stefan