Finder on Celestron Astromaster 70.

[Renato1]

I visited a friend tonight who had asked me to have a look at his Celestron Astromaster 70 refractor (70mm diameter, 900mm focal length), as he was having great difficulty with. The telescope was pretty average , but did yield some beginner views of Jupiter and Saturn that would wow newbies.

But the Star Point finder defeated me. It had two glass reticles about 40mm apart, and when I flicked the switch, the middle of the closest reticle had an illuminated dot on it. I couldn't locate anything with it, regardless of whether I used one eye, or two eyes as the manual states should be done.

The only way I can see this gadget working is if the front reticle was also illuminated, and having both front and back dots lined up with the object one is aiming at.

Could someone please advise whether there should be an extra illuminated dot on the finder, and thus that my friend's unit is not working properly? Or whether just having one dot on it is actually correct, and that I just don't understand how it should be used?
Regards,
Renato

[astro744]

I would think the Star Point finder is the same as any other basic red dot finder being a zero magnification pointing tool that uses a coated glass window to superimpose the image of a small red dot onto the night sky.

Make sure any brightness control is turned up to maximum and use both eyes. The dot will be at infinity. Move your head back a little away from the finder.

[julianh72]

As astro744 says, with any red dot finder, the only alignment necessary is to align the finder with the scope itself. The red dot just "hangs" in the sky, with almost no parallax - wherever the dot is hanging in the sky, that's where the finder is pointing, and assuming the finder is reasonably aligned with the scope, you should easily pick up your target with a low power eyepiece. It doesn't really matter whether you use your left eye or right eye, or whether your eye is close to or far from the finder - if you can see the red dot against the sky, you can target the scope.

The only comment I would make is that maximum brightness is fine for daytime terrestrial use or for finding the brightest planets and stars, but I use my red dot finder at close to lowest illumination, rather than maximum brightness, so that I can easily target fainter visual objects, not just the brightest ones. (At full brightness, the red dot can overpower the fainter stars.)

[Renato1]

Thanks, but I own four red dot finders and three Telrads myself, and they work just as you describe. That is why I am a bit mystified as to how this star point gadget is meant to work - there is parallax galore with the red dot on the first reticle.
Regards,
Renato

[Camelopardalis]

If it's anything like the red dot pointer on the Nexstar range, it's just a red dot....and gets in the way of anything else but the brightest of stars / planets :mad2:

I upgraded to a Rigel PDQ...makes a huge difference, likewise Telrad (but that's probably more than the scope is worth ;) )

[astro744]

Yes I should have clarified this statement a little by saying make sure the brightness is turned up so you can see the dot and then turn it down to a more comfortable level. Sometimes on my Telrad I struggle to see the reticle only to find my brightness was set too low. I do prefer it only just visible though.

[julianh72]

Hmm... Every red dot finder I have seen has only one optical element. I have a cheapie, and you do get a very slight double-image - I assume there is a secondary reflection off the second (sky-facing) face of the finder lens, but it's not too disruptive.

I don't suppose it's possible that there's some sort of protective film that's supposed to be removed before use?

[Renato1]

Thanks. I couldn't see any film on it when I examined it closely with a torch. But my friend lives over an hour's drive away, so I can't double check.

Both the reflector and refractor Astromaster have this weird finder on it. Curiously, reviews are positive for these scopes, which has me wondering if there is something else that should be happening with the finder, but that this one is defective.
Regards,
Renato