Red dot finder or finder scope?

[Sirius_Starseed]

Which one would I be better off with. My 130P came with a red dot finder but I don't really like it that much. No matter how much I turn the two nobs the red dot just doesn't want to go in the middle - it seems well off centre when I look down the focuser at the red dot.

I've also read and heard that they're not that good anyway and to be honest, it seems a but cheap. Would you recommend going for a finder scope? If so, which one?

Thanks!

[Ben Ritchie]

Both.

A decent RDF is great for finding the general area of sky you want to be in, and a fair few objects can be found with just a RDF and a widefield eyepiece (e.g. M57's easy, just point the RDF between beta and gamma Lyrae and you'll see it in the EP). But when you need to hop around some fairly featureless constellation - especially in moderate light pollution - then a finder really helps. Especially a right-angle, correct image one - straight-through finders are a recipe for neckache!

Standard RDFs can be a bit rubbish, but the Telrad or Rigel Quikfinder are both great.

[Ogri]

Must admit I find the cheap, basic RDF that came with my ST120, to be very good. You are keeping both eyes open are you?

Also set it up during the day on something a few miles away.

I've got a straight through finder on the 200p, and I really don't like it one bit - especially perhaps as my lowest magnification eyepiece is 60 x mag, and 30 x mag along with the RDF work very well together with the ST120.

A Telrad soon I think.

[Doc]

Your RDF when properly set up is very easy to use and will get you almost exactly in the right area. It must be aligned with your scope and you must keep both eyes open when using it, one aimed into the finder the other out into the sky to see where the red dot is aiming for. It's a knack but once mastered is easy as riding a bike.

[Talitha]

I think a combination RDF and regular finder scope is the best way to go. The RDF gets you into the ballpark and the finder scope makes starhopping a breeze.

Regarding your problem... an RDF i bought a few years ago needed to be 'shimmed up' at the forward end with a small folded piece of paper in order to raise it high enough for the dot to be parallel with the eyepiece's sight line. If the red dot is always too far to the left or right though, you may need to re-square it with the OTA so the adjuster is able to get the dot on target.

TBH, i've had three different types of RDFs and found all of them to be lacking in craftsmanship (read: flimsy/cheap). The finder which came with my 16" LightBridge is outstanding, though. It was obvious from the instruction sheet that it was intended for use on a rifle, so i did a websearch on the brand name and eventually found out it had indeed been manufactured for use on firearms. The original price was about $150 but it's no longer available (as far as i could find) on gun supply websites. I'm guessing the company came out with a newer model and the astronomy sector bought up the surplus for a song.

This is it, although i'm not sure if it's available in the UK or not. The price is nearly twice what i'd been handing over for the less expensive RDFs but well worth it, IMO. It takes more turns to move the dot, which means the adjusters are a lot more sensitive. When i was centering the red dot for the first time, i was turning and turning and turning the little hex wrench and kept thinking "ok, pretty soon this puppy's going to get to the end of the leash" but it never did. Obviously there's a lot more 'play' in the adjusters than what's in my other RDFs, and that's a good thing.

[RichieJarvis]

Hi Sirius,

I am sure I am teaching you suck eggs, but you do know that the dot doesn't need to be in the centre, right? It will move about as you move relative to the finder. To setup, get a star front and centre in a wide-angle eyepiece, and then move the knobs until the red dot is on the star your scope is on. If you cannot bring the dot onto the star with the knobs, then your RDF needs to be adjusted on the scope until it can be.

You'll find that no matter how much you move about, the dot will stay on the star. This is called collimating the scope to the finder by the way.

Myself, I replaced my finders with RDF's a while ago, and use them to align my scopes for camera use - I find it much easier, because of the wide field of view and accuracy of RDF's. If the dot is on the star, then it is on the camera, and means I don't have to take the camera off. All the ones I have cost less than £20, so they are by no means expensive ones either!

Cheers,

Richie

[Chris H]

The RDF that came with my 130p is pretty good and I'm sure it must be the same as you have. Not sure what you mean by 'it seems well off centre when I look down the focuser at the red dot'.

[Sirius_Starseed]

Hi Sirius,

I am sure I am teaching you suck eggs, but you do know that the dot doesn't need to be in the centre, right? It will move about as you move relative to the finder. To setup, get a star front and centre in a wide-angle eyepiece, and then move the knobs until the red dot is on the star your scope is on. If you cannot bring the dot onto the star with the knobs, then your RDF needs to be adjusted on the scope until it can be.

You'll find that no matter how much you move about, the dot will stay on the star. This is called collimating the scope to the finder by the way.

Myself, I replaced my finders with RDF's a while ago, and use them to align my scopes for camera use - I find it much easier, because of the wide field of view and accuracy of RDF's. If the dot is on the star, then it is on the camera, and means I don't have to take the camera off. All the ones I have cost less than £20, so they are by no means expensive ones either!

Cheers,

Richie

Oh shucks, in that case then I HAVE had it aligned up properly before What got me total confuzled and thinking that the red dot should be in the centre of the finder is because I was standing either more to the left or right, and I was thinking to myself that surely I should be standing central and seeing the red dot in the middle of the finder. Hmmm, so basically as long as the red dot has got a star covered and you can see that star down the main eyepiece you're OK?

I really am pants when it comes down to this whole setting up business

I will re-align it again then I still might buy a middle of the range finder scope just to see which one I prefer (I like to have all my options available) even if I do go bankrupt in the meantime

Thanks for your help!!!

[Sirius_Starseed]

This is it, although i'm not sure if it's available in the UK or not. The price is nearly twice what i'd been handing over for the less expensive RDFs but well worth it, IMO. It takes more turns to move the dot, which means the adjusters are a lot more sensitive. When i was centering the red dot for the first time, i was turning and turning and turning the little hex wrench and kept thinking "ok, pretty soon this puppy's going to get to the end of the leash" but it never did. Obviously there's a lot more 'play' in the adjusters than what's in my other RDFs, and that's a good thing.

I will keep an eye out for this. Thanks!

I know what you mean about turning those damn things. I was at it all last night. In fact in the end I got pretty damn sick of it. I was sending myself dizzy lol. Not to mention it was bringing back awful memories of me turning the screws on my secondary and seeing it come crashing down and chipping. Heck, it still makes me feel funny now

[brantuk]

Yup - the adjusters on the RDF are for aligning with the main scope - not for centering the dot on the screen. To use it simply position your eye so the dot is in the middle - use your other eye to look at the sky and confirm the general area you're looking for

[sammiefields22]

The general impression I get is that red dot finders are really good for finding what you're looking for. Since they don't magnify, they give a wild field of view. Also the fact that they don't give you an upside down image. It takes ages to get used to moving things in the opposite direction.

As long as your RDF is aligned properly with your telescope, I don't see why there should be a problem. I suppose the one major complaint I've heard about is the fact that the light tends to be too bright for many of the celestial bodies, esp the deep space ones, and its lowest brightness is just not dim enough.

I have a EZ finder II reflex sight which came with my Dobsonian. I'm very happy with it. I don't quite understand why it had to be made of flimsy plastic though. It looks so cool in the pictures.

[garyscott]

I used to use RDF's a lot when i used to target shoot competitively. The way to use them successfully for a telescope is to keep both eyes open, and move your self until the red dot is central in the ring, hold yourself in that place, and keep yourself there relative so that the dot remains central, then move the scope to your selected target whilst looking with one eye at the dot, and with the other at the "target", when the dot appears to be over your target, the scope should be aiming at it too. REMEMBER to move like you are fixed to, and part of, the scope. Imagine the scope as a rifle!. PROVIDED that you have adjusted the RDF to coincide with that which you are aiming at, i set mine up by finding POLARIS in the scope, get it dead centre, then whilst the scope is on Polaris, adjust the windage on the RDF until - using the technique described above - the red dot appears to be over Polaris.(both eyes open remember!). Its easier to do than to type i assure you!.