Upgrading a Tasco 33TR

[xvariablestarx]

I have started to upgrade my old childhood telescope. It is a 75mm Focal length 700mm Tasco refractor. I have already put a modern red dot finder on it, to replace the "toy" 9x finder scope that was on it. I will be attempting to put it on a better mount than the flimsy thing that it comes with; I have some tube rings and a dovetail plate coming on Tuesday. Also coming soon is a .965 inch to 1.25 inch adaptor for the focus tube.

I also will be attempting to replace the existing spherical primary mirror with a new 76mm Focal length 700mm (the closest I could see to my original mirror) when it eventually arrives from China. The scope has an existing square secondary mirror on a single stalk, so I may keep that out of simplicity sake, instead of trying to find a way to mount the more modern secondary mirror coming from China. The primary and secondary show some corrosion around the edges, I can take the primary out and show if you are curious, but the secondary is hard to get a good view of down the eyepiece

If anybody has any comments let me know. This is mostly an experiment, I could never see too much with the scope as a kid, so I wonder how far I can improve it.

 

[Dave Lloyd]

18 hours ago, xvariablestarx said:

I have started to upgrade my old childhood telescope. It is a 75mm Focal length 700mm Tasco refractor. 

 

Reflector 🙂

[xvariablestarx]

1 hour ago, Dave Lloyd said:

Reflector 🙂

Yeah I meant reflector lol

[xvariablestarx]

 

If anybody is interested, my 8 inch dovetail and 90mm tube rings arrived. I was able to mount the scope on something more secure.

 

 

[xvariablestarx]

Next thing to tackle is the optics. I have a 1.25 inch adaptor arriving in the next couple of weeks, then a primary mirror, and a secondary which I hope I can avoid having to use.

[xvariablestarx]

Got my adaptor, tested it on the Moon, and it seemed to focus with the 21mm setting on my zoom eyepiece, so I guess the adapter works. Next thing is the primary mirror, but that replacement wont be here for weeks (if it gets here).

[xvariablestarx]

This is the condition of the mirror. It is very noticeable when you look through the eyepiece.

[xvariablestarx]

Haven't updated this thread in a while. I put the scope on a new Sparta mount, it can now point at zenith, or any place else using slow motion controls.

I got a new mirror in the main today. It is a bit wider than the original mirror, and a lot thicker, so I can't use the original mounting hardware, so I am attempting to glue the mirror in place.

There are disadvantages to doing this, but I have little choice I think.

 

 

[xvariablestarx]

Not updated this in a few weeks. I ordered a 0.965 inch Plossl, but because of some unknown issue, it never fully got to my local post office and was shipped back to the shipper. So I took drastic measures, I cut down the scopes focuser, to allow it to focus properly with the 1.25 inch to 0.965 adaptor which I put in it. I was partly successful, in that it could focus on stars at low magnification, but now an ugly thing about the scope, which I never was able to fix, reared its head; the views with the scope are very dim, and inferior by far, to those given with my 70mm/900mm refractor. I think the issue is with the existing square secondary mirror it has, and while I could possible mount another oval secondary mirror I have in the tube, I still would have the issue of having a primary mirror I cannot collimate, and a secondary which I can only collimate by twisting the stalk it is on.

I have learned a bit about mirrors and backfocus from my DIY attempts to fix the scope, but I have come to an end of what I can do with my abilities, so the scope will retired, improved, but not improved enough.

[xvariablestarx]

I am making one final attempt, putting in a new secondary mirror and moving the secondary mirror slightly towards the opening of the scope.

[Merlin]

Put your secondary mirror on the end of a thin rod, the existing one must be causing a massive deffraction effect.

[xvariablestarx]

4 hours ago, Merlin said:

Put your secondary mirror on the end of a thin rod, the existing one must be causing a massive deffraction effect.

I may have to attempt something like that also.

[xvariablestarx]

I moved the secondary mirror stalk, a few millimetres towards the tube opening, and installed the new secondary mirror. I also center spotted the primary mirror, so I could get some indication of what was happening inside optically. Next I need a clear night so I can test on some stars. I am hopeful some improvement has been done with the scope.

[xvariablestarx]

I got strange results with the Tasco. I can get good focus on a star, but trying to focus on something like the Moon ends up with muddy or blurry results.  I am putting the Tasco aside for now, until I get a brainwave about how to fix it.

 

One positive thing is that the star seemed brighter than with the old mirror, so perhaps I am on the right track.

 

[xvariablestarx]

I moved the mirror as close as I could to the center of the tube. With the zoom eyepiece I could get the magnification to the maximum without the image dimming, at about 9mm, no sign of bands on Jupiter though

 

 

[Pixies]

Is the focuser draw-tube protruding that far into the tube when you are focused on a star?

if it is, I'd say that your blurriness is a contrast issue caused by the size and shape of the secondary plus the draw-tube, too.

Can you aim it at the sky (away form the sun) and, with it focused, take out the eyepiece and take a quick picture down the focuser?

[xvariablestarx]

On 16/09/2021 at 10:26, Pixies said:

Is the focuser draw-tube protruding that far into the tube when you are focused on a star?

if it is, I'd say that your blurriness is a contrast issue caused by the size and shape of the secondary plus the draw-tube, too.

Can you aim it at the sky (away form the sun) and, with it focused, take out the eyepiece and take a quick picture down the focuser?

I will need to experiment with this later, I need to get a better alt-az mount and tripod for the scope instead of trying to use the eq1 I have it mounted on at the moment. I am starting to accept the scope optical limitations. I have been away from the hobby for months now, doing other things, I need to get back into it.