RDF recommendation

[KP82]

Recently got a Baader sky surfer iii RDF along with a quick release finder shoe to replace the flimsy plastic 6x30 stock finder on my Bresser AR102xs. The problem is the adjustment of the red dot is very limited. The red dot can only be moved within the lower left quarter of the full circle before neither of the control knobs can be turned any further. As a result I haven't been able to get it aligned with the scope.

I thought Baader made good quality accessories (the quick release finder shoe is very well engineered), but it looks like either I've got a dud or the unit is not well designed.

Is the Altair starwave all metal RDF any good? Or can anyone recommend an alternative model?

[spillage]

Although not often used now I do like my telrads.

[John]

I've found some of the multi-reticule finders (the metal types) work well but their reticules tend to be over-bright even at the lowest settings. I guess that's because they were originally designed as rifle sights for daylight use ?

The Telrad and the Rigel Quickfinder are purpose designed for astronomy and have more appropriate brightness adjustment which does not drown out fainter astro targets. They also have a wide range of adjustment to align them with the scope optics.

I did used to have a Baader Sky Surfer III though and found it quite a good finder. I wonder if you could shim the finder base where it fits into the finder shoe to give yourself the range of adjustment that will enable finder-scope alignment to match ?

 

[Alan White]

I really like the Rigel Quickfinder as it adjust to very faint for dark skies and brighter for at home.

[emadmoussa]

Telrads work great but too big for what they do. Rigel Quickfinders can be an alternative. 

These are great as well: https://www.ebay.co.uk/itm/Opticstar-Red-Green-Dot-Finder-RDF-UK/323031693373?hash=item4b3630783d:g:k44AAOSwvktaazTe:rk:4:pf:0 

But they require a scope-specific shoe. In most cases, mostly for refractors, they're more or less standard. But the price adds up fairly quickly if you want to fit it on an SCT, for example. 

[Ricochet]

5 hours ago, KP82 said:

The red dot can only be moved within the lower left quarter of the full circle before neither of the control knobs can be turned any further.

By full circle so you mean the view through the eyepiece or the bit of glass at the front of the finder? If it's the latter you must have your head too close to the finder because the red dot doesn't move off the centre of the glass, the whole finder moves. 

[KP82]

2 hours ago, Ricochet said:

By full circle so you mean the view through the eyepiece or the bit of glass at the front of the finder? If it's the latter you must have your head too close to the finder because the red dot doesn't move off the centre of the glass, the whole finder moves. 

The eyepiece. I mean the RDF doesn't really have an eyepiece and I was just looking through it from the back as if I was using a straight-through optical finder.

As for the range of movement of the red dot I could get it to the very edge of the lower left part of the view but could not make it cross to the upper half.

[KP82]

The telrads and rigel are both too big for this compact scope. I may try the one suggested by Emad. It looks like the same as the Altair one but £15 cheaper.

[Ricochet]

9 hours ago, KP82 said:

The eyepiece. I mean the RDF doesn't really have an eyepiece and I was just looking through it from the back as if I was using a straight-through optical finder.

As for the range of movement of the red dot I could get it to the very edge of the lower left part of the view but could not make it cross to the upper half.

How have you fitted the finder to the scope? The Bresser uses a Meade style finder shoe but I don't see a Meade style foot in the stock finder images. Unless there is some sort of twist in the finder body itself it not being in line left-right suggests either your finder shoe or foot is not square to the OTA and a second finder will have the same issue.

[John]

9 hours ago, KP82 said:

The eyepiece. I mean the RDF doesn't really have an eyepiece and I was just looking through it from the back as if I was using a straight-through optical finder.

As for the range of movement of the red dot I could get it to the very edge of the lower left part of the view but could not make it cross to the upper half.

If you have not already done so, try actually putting it on the scope and aligning it with the scope optics. With this design of finder, the red dot does not actually move around the window of the rdf when you adjust it but the adjustment actually moves the whole finder body so that it aligns with the scope optics. The alignment of the red dot on the window of the finder is actually fixed as far as I am aware.

You will also find that the position of the red dot on the screen of the RDF, when peering through the back of the unit, appears to move around as your head / eye changes angles. The ret dot is not in fact moving at all.

I think you might not have a problem if you fit the finder to the scope and adjust the finder aim so that it matches where the scope optics aim.

The finder that emad links to is fine but it's reticule is too bright for astronomy under a dark sky, even at the lowest setting I found. I recently sold one for this reason. 

 

[JeremyS]

I bought a Baader 30mm SkySurfer III a few months ago also thinking the Baader name would bring better construction. But I found it pretty flimsy and with limited adjustment. I no longer use it.

[John]

In defence of the Sky Surfer III, which I quite like as a unit, while is is plastic, it does have a few advantages over the usual RDF's:

- The view window is larger than most and it's coatings render it pretty invisible (which is what you want)

- The view window is recessed in a hood which prevents dewing more than finders where the window is more exposed

- The "dot" is smaller and more precisely defined than many other single dot RDF's and is not too bright when adjusted low.

As a reasonably priced replacement for the stock low quality optical finders and entry level RDF's I think it's a decent option but there are plenty of others

I've tried many RDF's over the years and the Sky Surfer III is far from the worst IMHO.

[Carbon Brush]

I have an assortment of small RDF devices purchased a few years back.

One had deep tinted plastic that allowed you to see only bright objects - like Jupiter or Venus.

Another (possibly Skywatcher) had such a bright dot that it prevented you from seeing anything other than Venus or Jupiter.
Fortunately by modifying this I could make it usable.
A higher LED series resistor and a variable resistor made it usable under all conditions from daylight to dark adapted vision.

Somewhere I have some pics of the modification. If there is interest I will see if I can find them.

David.
 

 

[KP82]

2 hours ago, Ricochet said:

How have you fitted the finder to the scope? The Bresser uses a Meade style finder shoe but I don't see a Meade style foot in the stock finder images. Unless there is some sort of twist in the finder body itself it not being in line left-right suggests either your finder shoe or foot is not square to the OTA and a second finder will have the same issue.

I replaced the Meade style shoe with a Baader universal shoe which accepts the standard synta style bracket.

[KP82]

2 hours ago, John said:

If you have not already done so, try actually putting it on the scope and aligning it with the scope optics. With this design of finder, the red dot does not actually move around the window of the rdf when you adjust it but the adjustment actually moves the whole finder body so that it aligns with the scope optics. The alignment of the red dot on the window of the finder is actually fixed as far as I am aware.

You will also find that the position of the red dot on the screen of the RDF, when peering through the back of the unit, appears to move around as your head / eye changes angles. The ret dot is not in fact moving at all.

I think you might not have a problem if you fit the finder to the scope and adjust the finder aim so that it matches where the scope optics aim.

The finder that emad links to is fine but it's reticule is too bright for astronomy under a dark sky, even at the lowest setting I found. I recently sold one for this reason. 

 

I did have the rdf mounted on the scope.

You're right the adjustment knobs actually move the body of the finder relative to the fixed position of the red beam emitter. The only problem here is on this Baader the emitter gets moved as well albeit not as much as the rest of the finder body. I believe this explains why the range of the adjustment seems so limited.

I found a stock Celestron RDF that was given to me by a friend long time ago. I replaced the dead battery and put it on the scope. I managed to align this one easily and upon closer look I could see that its beam emitter didn't move at all while the body was being moved by the adjustment knobs. So it could be a QC problem with the Baader.

Since the other one linked by Emad might be too bright for night use, I think I still stick to the Celestron even though its aperture is slightly smaller (25mm vs 30mm on the Baader) and its beam is a little dimmer.

[Ricochet]

3 minutes ago, KP82 said:

The only problem here is on this Baader the emitter gets moved as well albeit not as much as the rest of the finder body.

That doesn't sound right. I would talk to your supplier about the issue.