Back in late spring I got my first telescope, for free! Its a tasco 3" dob. However, it’s quite old. From what I can gather, it was made in the mid 60s.
I have been lightly working on it over the summer, getting the tripod in better shape, cleaning it, etc…
When I got it, I purchased a .95" → 1.25" adapter and got two eye pieces for it, 6mm plossl and a 23mm svbony.
My issue is whenever I use it all I can see is the arms attached to the secondary mirror as well as the secondary mirror. As I focus in to get the image clearer, it starts to get better. However, the focuser stops before it goes away. I know I need to collimate the mirrors, I am just tryibg to figure out how.
If the mirrors are collimated will this help with the issue or does the telescope need to “focus” more but can’t?
I have added pictures for reference.
Hi there, glad you here. I’m not the most experienced here, but this is the basics:
At the open end is the spider holding the diagonal mirror, it has 3 screws.
At the back end, thee will be 3 adjustment screws for the main mirror.
You need to get a laser collimation tool, it will sit where your eyepiece goes.
Get on YouTube and watch some videos on basic Newtonian telescope collimation techniques. Use whichever process you feel comfortable with.
With something that’s this old, be very gentle!
Hope this helps!
Thank you for the information! I’ll need to order a collimater, hopefully, after that it will look better.
I’ve been doing my best to be very careful. Especially because i do not know if there is any hidden value behind this. From what I had found, the 1964 version of this telescope was more used and that is still considered somewhat rare, though, valuable? I wouldn’t know. Either way, I’d like to keep this in as goid condition as possible, even if it’s just a little beginner scope from the 60s.
Another possibility is your focuser travel. Depending on the eyepiece you’re using, quite possible you may need to use an extender to put the eyepiece further out than you can currently move it.
Made me think of that because you said the image gets better as you focus, but you can’t move it out far enough.
You said it is you can’t focus In enough correct? We have this same issue on a 13” and 15” DOB with several eyepieces. This is a common issue when you use a DSLR camera. If the primary mirror can be moved up enough that might solve the issue. If not you will need to try different eyepieces to see what will work. If you can bring it out to some of the Club events you could try some of the members eyepieces to find ones that will work. A Barlow sometimes work but may make it to high power.
@CodyGossett Before you start on adjusting screws to collimate, let’s address the issue with focus: Please confirm: In which direction of focuser travel does focus seem to improve? As you move the focuser drawtube outward? 6Moving the eyepiece away from the image reflected in the mirror?)
I had that experience when I first began to use my reflector. Practice during the daytime on an object in the far distance…say, maybe a quarter mile away. (I used a chimney on a roof.) If moving the focuser outward does improve focus, carefully loosen the set screws holding the eyepiece and lift the eyepiece out some more, but leaving enough of the barrel to still be grasped by the set screws.
I didn’t initially understand why it would be designed that way but we can explain more when we get you in focus.
The image seems to get better as I move the focus towards the secondary mirror. I am wondering if perhaps the issue is the adapter I have on it. I will need to bring it with me to the next viewing night.
I haven’t adjusted either of the mirrors, and as far as i know this was sitting for a long time. From what I can tell the prinary mirror is as far back as it will go.
These guys are right and I believe your adapter may be the issue as well.
Do you still have any of the original eyepieces? You might try removing the adapter and just use the original .965" eyepieces. You can still find those on the Internet.
Just had a thought, if you do find it’s the adapter, look out for other older telescopes and accessories on Craigslist or classifieds, garage sales. Might even find some for free.
We can get you set up with a couple of original 0.965” eyepieces to start with, at least until you achieve focus.
As Joel mentioned, someone likely has 1-2 lying around. I’ve just checked Craigslist, FB Market and even CN. No luck!?
So, I’ve posted a separate thread here on our Swap area. If that doesn’t generate a reply in 1-2 days, please PM me here and we’ll find some very inexpensively on Surplus Shed. My treat!
Thank you so much for the help! Fairly new to the hobby so, just learning the utter basics right now.
Unfortunately, I do not have any of the original eyepieces. I actually got this telescope for free at a garage sale, I will definitly keep on the look out.
I am new to all of this too. I am really interested in seeing your old Tasco. I just got an old Tasco too. Different type but hopefully we can both learn with our old telescopes.
Here’s a little more information on reaching focus with your classic Tasco Newtonian reflector telescope:
When we add (almost) any component between the focuser and eyepiece, we are effectively “using up” at least part of the inward travel (“back focus”) of the focuser. In this case, the adapter for the larger barrel of the 1.25” eyepieces has also (unintentionally) served as an extension.
According to the specs here [link], the Alstar 0.965" to 1.25" adapter “adds about 30mm (1.2”).”
The adapter has served as an 30mm extension —preventing you from reaching focus. You weren’t able to reach focus because you lost that 30mm of travel to slide the focuser any further towards the telescope. Limited focuser travel is a common limitation of telescope focusers — even more inherent with the design with Newtonians.
Good news: By using the original 0.965” eyepieces, you should be able to reach focus.
These older style (0.965”) eyepieces are more simplistic (e.g., will have fewer glass lenses) and a smaller field of view* (can’t see as much of the sky at the same time.)
More good news: they are far less expensive than newer eyepieces. And the field of view will not be an issue for most all of the targets you’ll like be observing (such as the moon, Jupiter, The Pleiades, etc.)
By the way, from the plate on your telescope, we see that the Focal Length is 700mm.
Using these eyepieces (6mm, 12.5mm, and 20mm), you’ll have magnification ranging from 35x to >100x:
700mm /20mm = 35x
700mm /12.5mm = 56x
700mm/ 6mm = 116x