12 replies to this topic

[natto_beer]

Dear CN members,

 

I have just purchased a SVBony SV179 Red Dot Finder, and it arrived today!

 

Upon trying it out, I am a bit concerned, though:

As I look through the finder and slightly move my head left and right, the red dot moves along.

(To illustrate, I am aiming the red dot at the center of my watch.

As I move left, the red dot wanders to the left as well.)

Thus, not knowing whether or not my eyeball is perfectly centered and aligned behind the finder,

I don't know the exact vector of the finder.

 

This is, of course, different from how my Rigel Quikfinder works:

I point it at, say, the my watch, and the red circles outline its center.

When I move my head, the red circles simple disappear.

Here, I know the vector the device is pointed and every time i look at it, I will see the same spot outlined.

 

Questions:

Is my SVBony finder defective, or are they all like this? (I realize this device is as cheap as it gets.)

How would such a device be useful in telling you where the telescope is pointed if the red dot can wander all over the place?

 

Thank you!

 

 

[insertnamehere]

I have a Baader Sky Surfer III Red Dot Finder and the dot moves like the SVBony you described. Try it on a star, you'll see how it works.

 

Chris

[Jon Isaacs]

Hi:

 

What you are seeing is known as Parallax error.  Are you looking at a star or at a nearby object?   If you are looking at a nearby object, there will be parallax error.  If you are looking at a star, ideally there will be no parallax error...

 

Jon

[PJBilotta]

Cheap red dot finders have a lot of parallax error. Their basic optical qualities and cheap components cause the dot to move a lot when you move your head. Almost all cheap ones exhibit significant parallax.

The Quickfinder is a very different animal, and has a longer optical path that helps reduce parallax. It's location rings also make finding objects significantly easier, though they still move a bit when you move your head. It's easier to reposition your eye, though, because of the larger projected rings. I think you will find it much easier and enjoyable to use than any red dot, with perhaps the exception of the Baader Skysurfer III, which is longer and has less parallax than most other red dots.

The Telrad has a longer focal path than any of these, resulting in a projected reticle that is very stable and exhibits very little parallax. It is, by far, the easiest to use, if you don't mind its bulky size and looks.

[Jon Isaacs]

Cheap red dot finders have a lot of parallax error. Their basic optical qualities and cheap components cause the dot to move a lot when you move your head. Almost all cheap ones exhibit significant parallax.

The Quickfinder is a very different animal, and has a longer optical path that helps reduce parallax. It's location rings also make finding objects significantly easier, though they still move a bit when you move your head. It's easier to reposition your eye, though, because of the larger projected rings. I think you will find it much easier and enjoyable to use than any red dot, with perhaps the exception of the Baader Skysurfer III, which is longer and has less parallax than most other red dots.

The Telrad has a longer focal path than any of these, resulting in a projected reticle that is very stable and exhibits very little parallax. It is, by far, the easiest to use, if you don't mind its bulky size and looks.

 

It is actually possible to null the parallax error in the Telrad and probably the Rigel.  These both are aligned by tilting the mirror.  

 

For a reflex finder to be free of Parallax error, the reticle must be at infinity focus.. The Telrad reticle can be focused by walking the mirror using the three alignment screws.. You have to look at a star and then test for parallax error.  If you see some, then you walk the mirror one way of the other.  You check to see if there is more or less parallax error.. It's an iterative process and somewhat tedious.

 

Jon

Edited by Jon Isaacs, 18 July 2024 - 03:59 PM.

[natto_beer]

I have a Baader Sky Surfer III Red Dot Finder and the dot moves like the SVBony you described. Try it on a star, you'll see how it works.

 

Chris

 

Thank you for responding, Chris. So even the Baader product exhibits this phenomenon.

It sounds like very long distances mitigate the severity of this problem. I will try it out on a star next time the skies clear up.

It's monsoon season where I live, so it'll be a week or two =)

 

 

Hi:

 

What you are seeing is known as Parallax error.  Are you looking at a star or at a nearby object?   If you are looking at a nearby object, there will be parallax error.  If you are looking at a star, ideally there will be no parallax error...

 

Jon

 

Hello Jon!

Thank you - you put a name on my problem. Knowing the terminology is incredibly liberating =)

I was indeed looking at a nearby object, and it seems that was my mistake. I'll try it out on something light years away as soon as the weather permits and see if that nullifies the parallax error.

 

 

Cheap red dot finders have a lot of parallax error. Their basic optical qualities and cheap components cause the dot to move a lot when you move your head. Almost all cheap ones exhibit significant parallax.

The Quickfinder is a very different animal, and has a longer optical path that helps reduce parallax. It's location rings also make finding objects significantly easier, though they still move a bit when you move your head. It's easier to reposition your eye, though, because of the larger projected rings. I think you will find it much easier and enjoyable to use than any red dot, with perhaps the exception of the Baader Skysurfer III, which is longer and has less parallax than most other red dots.

The Telrad has a longer focal path than any of these, resulting in a projected reticle that is very stable and exhibits very little parallax. It is, by far, the easiest to use, if you don't mind its bulky size and looks.

 

Hello, PJ. Thank you for answering.

Yes, I noticed my Quikfinder basically has no parallax error. If my line of sight strays off center, the red circles simply disappear. 

So either I'm on target, or I don't have a signal. I quite like that.

I haven't had the chance to use a Telrad yet. I am just getting started in the hobby, and I only own a couple of 3" refractors and a C90 Mak, all of which seem too diminutive to mount a Telrad on =)

The scope I bought the red dot finder for is an AT72EDii - size-wise, it's a great fit, I have to say.

Edited by natto_beer, 18 July 2024 - 07:00 AM.

[rigelsys]

Thank you for responding, Chris. So even the Baader product exhibits this phenomenon.

It sounds like very long distances mitigate the severity of this problem. I will try it out on a star next time the skies clear up.

It's monsoon season where I live, so it'll be a week or two =)

 

 

 

Hello Jon!

Thank you - you put a name on my problem. Knowing the terminology is incredibly liberating =)

I was indeed looking at a nearby object, and it seems that was my mistake. I'll try it out on something light years away as soon as the weather permits and see if that nullifies the parallax error.

 

 

 

Hello, PJ. Thank you for answering.

Yes, I noticed my Quikfinder basically has no parallax error. If my line of sight strays off center, the red circles simply disappear. 

So either I'm on target, or I don't have a signal. I quite like that.

I haven't had the chance to use a Telrad yet. I am just getting started in the hobby, and I only own a couple of 3" refractors and a C90 Mak, all of which seem too diminutive to mount a Telrad on =)

The scope I bought the red dot finder for is an AT72EDii - size-wise, it's a great fit, I have to say.

eye relief on the QuikFinder is 3 inches behind...  Too far behind (6-12 inches) and you will lose the circles if you move too far off axis. 
 

[Jon Isaacs]

eye relief on the QuikFinder is 3 inches behind...  Too far behind (6-12 inches) and you will lose the circles if you move too far off axis. 
 

 

With the Telrad, I can be several feet behind..  For most circumstances, that really doesn't matter.. If the finder is 8-10 feet off the ground and one is pointing the scope while standing on the ground.. That is Telrad country.

 

Jon

Edited by Jon Isaacs, 18 July 2024 - 04:01 PM.

[natto_beer]

eye relief on the QuikFinder is 3 inches behind...  Too far behind (6-12 inches) and you will lose the circles if you move too far off axis. 
 

Hello there and thank you.

 

I had never noticed. I simply practiced a bunch until I kind of got the hang of finding the red circles by feel. I front-mounted the Quickfinder onto my C90 - not sure why I did that (it was my first ever scope). Thus, I never thought of moving my eyeball closer to the finder. I just tried, though, and it is indeed much easier to find the red dot when moving right up close.

[natto_beer]

With the Telrad, I can be several feet behind..  For most circumstances, that really doesn't matter.. If the finder is 8-10 feet off the ground and one is pointing the scope while standing on the ground.. That is Telrad country.

 

Jon

Oh ~ interesting!
I had wondered what - beside the form factor - the difference is between Telrad and QuikFinder =)

[natto_beer]

So the rain has finally let up, and I had a chance to get the scope out to try out the new red dot finder under real conditions. As insertnamehere and Jon have indicated, parallax error is indeed not an issue when pointing at objects lightyears away. My only gripe is the fact that the red dot is quite massive and rather too bright even at the lowest setting. It completely blots out target stars and then some, which makes highly accurate alignment difficult. It does work as far as getting the star into the eyepiece, however, and at this price point, I really can't complain.

 

Thank you again, everyone.

 

natto_beer

[rigelsys]

Oh ~ interesting!
I had wondered what - beside the form factor - the difference is between Telrad and QuikFinder =)

Quikfinder is a "compact" reflex finder :-) 

[Jon Isaacs]

 

 

Quikfinder is a "compact" reflex finder :-) 

 

 

 

 

Jon