Can anyone recommend a good finder scope for my 8" Celestron CPC,the 9x50 that came with it has to be re-ajusted every time I pull the dust caps off it...I was considering a red dot finder as I only need it to do my 3 star alienment.
Go for a telrad. With that and a low power eyepiece you should be able to find what you are looking for through the main scope and do without a finder. Thats how I used to do it. Finders are just too much trouble to look through on a SCT...
Wow – that is bad news. How far do you need to adjust it? If the alignment of the 9x50 Finder is only “off” by a small amount, such that you can still see the object in a say, 32mm eyepiece, then I suspect a red dot finder isn’t going to provide you with any better accuracy?
I’d look at options on fixing the finder – does the misalignment occur in the mounting bracket, the finder stalk or the adjustment screws?
Do you really need to remove the finder? I modified my OTA packing so I could leave the finder attached to the OTA. Of course, mine isn't the CPC but the SGT so it may be different. If you can work out a way to package your OTA complete with the finder then it simplifies all your setup and breakdown of the scope.
Wow – that is bad news. How far do you need to adjust it? If the alignment of the 9x50 Finder is only “off” by a small amount, such that you can still see the object in a say, 32mm eyepiece, then I suspect a red dot finder isn’t going to provide you with any better accuracy?
I’d look at options on fixing the finder – does the misalignment occur in the mounting bracket, the finder stalk or the adjustment screws?
Cheers
Dennis
I think it's in the finder stalk,because when I remove the dust caps I can feel the whole finder tube move and then I have to re-adjust it with the screws..The finder tube has a o-ring on it that seats it into the mounting bracket and it seems the tube slides in the mounting bracket a little bit as I'am pulling the dust caps off. I leave the view finder attached to the ota all the time. I don't know if it is just a poor design of the view finder or if I'am doing something wrong when I remove the caps. I try to hold the tube from moving when I take the caps off,but it always needs to be re-adjusted...Thankyou very much for taking the time to help a newbie...
It looks like a spring-loaded finderscope mount as used on many scopes. There are two adjustment screws that allow you to apply pressure to the fiinderscope housing at two points on the periphery - and that pressure is opposed by the spring-loaded third side which lets you adjust the angle of the finder which swivels around an O-ringed pivot at the front end. Is the O-ring seated properly between the finder housing and the mount housing? Is the tension on the opposing spring strong enough to hold position after adjustment? I've found that by sticking a self-adhesive felt pad on the end of the spring-loaded surface it gives better tension.
I usually find that I have to do a minor adjustment every time I go to an observing site by aiming the scope at a distant terrestrial object (such as the peak of a house roof, or the tip of a flag pole or something) and then after centering the object in the eyepiece, I align the crosshairs of the finder to the same part of the object. That sets me up for the evening's viewing.
I also uncap the finder prior to this setup so that the alignment isn't bumped by that action, and remove the finder from the OTA when I'm done.
I think it's in the finder stalk,because when I remove the dust caps I can feel the whole finder tube move and then I have to re-adjust it with the screws..The finder tube has a o-ring on it that seats it into the mounting bracket and it seems the tube slides in the mounting bracket a little bit as I'am pulling the dust caps off. I leave the view finder attached to the ota all the time. I don't know if it is just a poor design of the view finder or if I'am doing something wrong when I remove the caps. I try to hold the tube from moving when I take the caps off,but it always needs to be re-adjusted...Thankyou very much for taking the time to help a newbie...
Sorry want a be, I think I misread your original post. Have a look at the finderscope bracket. When I got mine, the manual described assembling the findersope with the adjustment screws to the front (pictures and all!) but this doesn't work. You will have greater success with the bracket turned around so the adjustment screws are at the back. The rubber o-ring then fits quite snugly in the front ring. Maybe this is your problem? If not, sorry, I'm out of easy fixes I think...
It is a spring loaded one, I'll try the felt pad as u said and see if that helps,do you put the pad between where the spring load screw makes contact with the tube? I'll also check to see if the o-ring is properly seated..Thanks for the advise.....
do you put the pad between where the spring load screw makes contact with the tube?
Yep - use a sticky one and stick the pad to the spring-loaded post, not the tube - so that it can slide and sit anywhere it likes on the tube. It you stick it to the tube itself you'll have to constantly make sure that the spring-loaded post is lined up and sitting on the pad properly.
...the manual described assembling the findersope with the adjustment screws to the front (pictures and all!) but this doesn't work. You will have greater success with the bracket turned around so the adjustment screws are at the back. The rubber o-ring then fits quite snugly in the front ring.
Al makes an excellent point. Mine has the screws as the rear of the whole assembly and the o-ring towards the front. There is a beveled o-ring seat for it to engage into if it's the correct way around.
I agree with Shredder, Throw yours away and get a Telrad. Nothing else comes close. I have had my Telrad for 12 years and am on the second set of AA batteries
I agree with Shredder, Throw yours away and get a Telrad. Nothing else comes close. I have had my Telrad for 12 years and am on the second set of AA batteries
Refracting finders give wide field magnification - Telrads don't.
I'd use a either a red dot or Telrad in addition to a normal finderscope - but I'm not sure I'd use one to ever replace it alltogether.
I have used a TelRad for 15 years or so. Can't remember changing the batteries.
I am trying a Rigel QuickFinder on my latest scope as it has a 4 deg circle and a 0.5 degree circle like a TelRad. It is smaller and neater but I am finding it more difficult to use. I think it is because the long body of the TelRad gives a good clue as to where to position the eye and the short body of the QuickFinder doesn't.
The QuickFinder has a ghost image about 20 deg away from the main circle which initially confuses but eventually helps when you realise that it is in a predictable position in relation to the main circles.
The big advantage of circles over dots is that they allow you to offset or step by a known amount. This is enormously important when aiming for objects not visable to the naked eye where you have to offset from a nearby star.
I have actually used both, red dot, telrad, and finder on my SCT (which I have recently sold). I found the telrad by far the easiest to use (and align for that matter).
While the red dot and telrad are essentially the same thing, the telrad is (in my opinion) easier to sight through, possibly its the physical size (as mentioned about) or the lack of a ghost image (which you get on the red dot finders). I personally think its just it has a bigger plate of glass to see through, and so easier to use. Note I have a new dot style finder on my new scope and miss the telrad (a lot).
As for the traditional finders. I personally gave up on mine, and just went with the telrad. The reason being that while the telrad doesnt give any magnification, you generally dont need any. Usually you can visually put the telrad in the right direction, and then using a low power eyepiece line it up fully through the main scope. In short if you cant find it in a low power eyepiece through the main scope (after roughly aligning with the telrad) then you probably arent going to find it with a conventional finder anyway.
