Julian0

Thanks all, no need to go into the specifics of the project, other than the optics challenge. I did some tests yesterday with a concave lens I have here and was able to get a telescope-like experience looking at my circular display in-tube, albeit at a focal length shorter than I would need. I hope my 250-500mm FL lenses coming in a few days will give me some more play, effectively replacing the objective lens with my 1080p circular display. I am enjoying learning about refractor telescope optics along the way. The project has to be done with a 120mm Sky-Watcher I have, for the overall format and look, adding an interesting layer of constraints!

A quick follow up that I've just ordered a collection of convex lenses of varying focal depth relative to the dimensions of the telescope to play with. They'll arrive in a few days, and I'll start playing around to see what can be done.

Some of you were very helpful with removing the objective lens on my 120mm Sky-Watcher 'Star Travel' telescope. Thanks again for that! I was able to do it without destroying my telescope. Now for a new thread relating to my project. I am not an astronomer by any stretch, however I am concerned with the loss of visibility in our night skies. In my lifetime I have seen satellites and night lighting (esp LED) reduce my own ability to view and marvel at the cosmos. I'm making a project that will tour internationally that in a large part seeks to draw attention to this issue. To do this, I am fitting a small circular screen into a refractor style telescope attached to a small embedded computer that shows an automatically generated starscape. By way of sensors, when moving the telescope on its axes, the generated starscape can be tracked as though looking at the real cosmos. I'd rather not go into any more specifics as to the project, so as not to derail, Rather, I'd now like to talk about the challenge I'm having regarding optics. I'm hoping that someone here that understands how refractor optics and the market for after-market lenses might be able to assist. In short, I would like the circular screen to be in place (or in the tube, as needed) of the objective lens in a refractor telescope, visible through the eye piece. It is clear simply replacing the objective lens at location with the screen will not work due to eyepiece and objective focal points. I am wondering if replacing the eye piece lens with an alternative, such that putting the circular display in place of the objective lens, might allow for clear in-focus view of the circular screen with a 'telescope-like' viewing experience. Does this sound feasible? If not, might there be another way to do it?

I was able to remove the lens cell, thank you.

Greatly appreciate the responses. This all makes sense. Yes the lens is in great shape. I am not removing it to replace it. As to why, that would derail this thread terribly! I will post my results when I have found another person to assist with grabbing the tube. Thanks again!

Thanks a lot for getting back. That seems like a sane approach. However, on my 120mm, I do not seem to have a detachable lens cell. There are no screws, and it does not seem to be turnable/unscrewable itself. I attach two photos to better explain. Please let me know if I'm missing something - not unlikely!

First post, hi all. To be clear, I know very little about telescopes, gulp! I need to remove the objective lens of my aforementioned telescope (no need to go into why). I see there is a threaded ring on the outside of the lens, holding it in place. It has 2 holes in it, diametrically exactly opposite each other. You can see one of them in the attached picture. I read somewhere (do not recall where) that these are used with a tool to grab and turn the ring, and that someone had done it with a piece of wood and two small nails. Before I make a mess, might anyone have some guidance as to the best way to remove this lens? I would like it to be able to put the lens back later, if possible - so a non-destructive strategy would be best if possible!