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Using a Red Dot Finder properly


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Hi all...

My next stupid question! I now have a working RDF (the first one I got was DOA). Of course, the fog is hitting the ground outside so I haven't got to align it or anything yet, though that process is easy to follow, and I'll hopefully do it tomorrow during the day.

However, just from testing it I can see that the red dot moves around a lot, depending on my eye position. Which leaves it rather open to error. How can I reduce this error? Is there a preferred distance to how close my eye should be to it, right up close or fairly far away? Do I just try my best to always centre the dot in the middle of the finder when using it to locate something, knowing there's always going to be some leeway?

Any advice appreciated, thanks!

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If it moves about you're too close to it; move your head back so that you're seeing it with both eyes and you should see that it stays in the same position with respect to the far field. 

When I'm using a RDF (or a finder scope), I prefer to set up the scope and before moving to the first alignment star I go to the most distant street light, centre it with the telescope and then adjust the RDF so that it is pointing in the same direction.  

When it's (more or less) aligned I can then be pretty sure that it'll be good enough to get the #1 alignment star in the eyepiece field of view. I then centre the alignment star and put some fine tuning on the RDF. 

 

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13 minutes ago, Gfamily said:

If it moves about you're too close to it; move your head back so that you're seeing it with both eyes and you should see that it stays in the same position with respect to the far field. 

 

That's my experience too, both eyes open, maybe 20-30cm back from the RDF and once the dot is reliably lined up with the 'scope it stays lined up.

This is the somewhat tacky skywatcher bundled RDF I'm using, which I assume is the same as yours.

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If you stay far enough back, the RDF window will subtend a very small angle on the sky limiting any parallax error due to your head bobbing about.  However, it can become more difficult to find the dot in the first place when at a distance.  If this becomes a problem for you, get up close to the RDF, locate the dot, and then carefully back off holding the dot in your vision.

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I'm glad to hear I'm not the only one struggling with the RDF.

I find it doubly difficult when the scope is at an acute angle, requiring bending or crouching to see through it. I also have the problem of sometimes seeing double, ie two objects. I'm thinking of swapping it out for a finder scope, more expense of course - like a lot of hobbies one thing leads to another!

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1 hour ago, Aquavit said:

I'm glad to hear I'm not the only one struggling with the RDF.

I find it doubly difficult when the scope is at an acute angle, requiring bending or crouching to see through it. I also have the problem of sometimes seeing double, ie two objects. I'm thinking of swapping it out for a finder scope, more expense of course - like a lot of hobbies one thing leads to another!

No, I get the same with my Telrad.

I wouldn't replace your RDF with a finder, having both is ideal.

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I managed to finally get my new telescope out on Saturday night for a couple of hours (thanks for including the clouds in the box FLO! :D) and I had some trouble with the Red Dot Finder at first. I had setup the scope and aligned the RDF in the daylight the week before on a distant tree (that took several goes, I would definitely pick a more obvious landmark next time!) which helped immensely than trying to do it in the dark as well as learning how to work the telescope! 

I think it took me majority of the 2 hour session before I got a bit more comfortable with the RDF, I found as others have said that you have to sit back from it a little (which can be awkward even with the short tube refractor I have!) and use both eyes. I found myself trying to use a single eye at first but the sight is mostly opaque so you can't see to many light points through it, it definitely took my brain a while to work out how to "see" the red dot in my right eye overlaid with the stars my left eye was seeing so it definitely feels like a practice thing! 

I appreciate I am a total newbie but it was definately a little frustrating, hoping it will become easier over time :)

Edited by wibblefish
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Thanks for all your replies, I appreciate it.

At first I was thinking that I hadn't explained myself properly, as no matter what distance I looked at it from, the red dot still moved. But then I finally stopped just looking at the dot, and actually pointed the red dot at a target far away, and when I moved my head the red dot moved, but so did the target, so the red dot stayed on target. That was the bit I was missing/didn't understand!

Thanks again! :)

 

Edited by Jasonb
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4 hours ago, Aquavit said:

I'm glad to hear I'm not the only one struggling with the RDF.

I find it doubly difficult when the scope is at an acute angle, requiring bending or crouching to see through it. I also have the problem of sometimes seeing double, ie two objects. I'm thinking of swapping it out for a finder scope, more expense of course - like a lot of hobbies one thing leads to another!

The acute angle yoga positions got to me after a couple of months, I was starting to think maybe I ought to do some warm up exercises and stretches to get myself prepared while the 'scope cooled down ... I also found it difficult to get lined up with something I knew was there, but couldn't see with the naked eye . I bought one of the smaller, cheaper RACIs ,(SW 6x30) and added it to my little dob using a £5 shoe from FLO. I wasn't confident of precisely where it would go for convenience , so used some sticky pads to fix it so I could change my mind. I've found the good spot (on the heritage , only having half a tube limits the choices, best place seems to be near the pivot) and just need to psych myself up to drill holes to mount it properly. Can't quite bring myself to do this yet, think I'll procrastinate until the sticky pads give way and force action !

My mak has the same shoe, and the RACI went straight on instead of the bundled RDF, but .... sometimes an RDF is easier and quicker , so I find after a few short sessions with the mak  I want both there too ! The mak is not a simple. drillable tube like the dob, so I did some research and saw that the telrads and Rigel quickfinders both offer extra features and (being lightweight compared with the mostly metal RACI) come with bases you fix on with sticky pads . Telrads have many vocal fans, but crucially it is quite a long thing for a small 'scope, and is low to the tube. The quickfinder has some of the same features (principally one red circle of known size around the red dot) has a a smaller footprint, but is quite tall, and a bit cheaper. I think the height might make it easier to use, not needing to get my face quite so close to the scope. It comes with two bases as well, which means I can install them on both 'scopes to swap it back and forth if it is a huge improvement over the RDF.

I'd put the quickfinder on my wishlist for after the festive madness period, but then one came up in the FLO black Friday sale for £30 and it seemed rude not to buy it  ... I'd love to report how it compares with the stock RDF,  but the weather since then has alternated between fog and heavy rain !

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3 hours ago, wibblefish said:

I managed to finally get my new telescope out on Saturday night for a couple of hours (thanks for including the clouds in the box FLO! :D) and I had some trouble with the Red Dot Finder at first. I had setup the scope and aligned the RDF in the daylight the week before on a distant tree (that took several goes, I would definitely pick a more obvious landmark next time!) which helped immensely than trying to do it in the dark as well as learning how to work the telescope! 

I think it took me majority of the 2 hour session before I got a bit more comfortable with the RDF, I found as others have said that you have to sit back from it a little (which can be awkward even with the short tube refractor I have!) and use both eyes. I found myself trying to use a single eye at first but the sight is mostly opaque so you can't see to many light points through it, it definitely took my brain a while to work out how to "see" the red dot in my right eye overlaid with the stars my left eye was seeing so it definitely feels like a practice thing! 

I appreciate I am a total newbie but it was definately a little frustrating, hoping it will become easier over time :)

Hello wibblefish,

I see that is your first post on here

There's plenty of very helpful and kind people on here who are happy to help relative beginners like me. Do make a new topic in the 'welcome' section and introduce yourself, you will be made to feel very welcome.

As you've found, this hobby has a steep learning curve,  to my surprise I can't just set up, look through a telescope and see everything easily, But that means that the most valuable accessory isn't some £200 eyepiece or £2000 telescope, but totally free patience, persistence and a willingness to learn . Keep at it, the rewards are well worth the effort.

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Tiny Clanger, your reference to Yoga antics made me smile!

Do report back on your finder "findings". I would like a 6 x 30 scope with a right angle so it mimics the main scope, like this one here: https://tavcso.hu/en/product/6x30a but Zermelo recommends to keep the RDF which means fitting another shoe, either by self adhesive tape which may not be secure or (horror of horrors) drilling the Mak tube. That would presumably mean a disassembly job to remove the swarf. My little Mak hasn't got a huge amount of real estate either.

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28 minutes ago, Tiny Clanger said:

Hello wibblefish,

I see that is your first post on here

There's plenty of very helpful and kind people on here who are happy to help relative beginners like me. Do make a new topic in the 'welcome' section and introduce yourself, you will be made to feel very welcome.

As you've found, this hobby has a steep learning curve,  to my surprise I can't just set up, look through a telescope and see everything easily, But that means that the most valuable accessory isn't some £200 eyepiece or £2000 telescope, but totally free patience, persistence and a willingness to learn . Keep at it, the rewards are well worth the effort.

Hi! 

I will do that thank you, I have been lurking on the forums for a little while now reading up on lots of telescope opinions and various sticky topics :)

Yes definitely steep but a good learning curve as I haven't had a proper hobby for a while now and this has caught my imagination so far! I have been voraciously reading a few good books and loving the few nights I have managed to get out (eye, binos then telescope finally!), hopefully enough to keep it all going longer term.

 

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13 minutes ago, Aquavit said:

Tiny Clanger, your reference to Yoga antics made me smile!

Do report back on your finder "findings". I would like a 6 x 30 scope with a right angle so it mimics the main scope, like this one here: https://tavcso.hu/en/product/6x30a but Zermelo recommends to keep the RDF which means fitting another shoe, either by self adhesive tape which may not be secure or (horror of horrors) drilling the Mak tube. That would presumably mean a disassembly job to remove the swarf. My little Mak hasn't got a huge amount of real estate either.

It's one of those things you read about, but think , nah, I can get by with just the provided RDF ... then experience tells you different !

I definitely think it is an advantage to have both : on the dob where I have RACI and the original RDF it didn't take long to get an idea of which finder to best use for types of objects. Because the RACI view is right way up and right way round, I could seamlessly switch between it and the RDF , which is obviously the same . That it differs from the actual 'scope view doesn't matter in the slightest, any more that the RDF differing from the 'scope does. And my neck is not feeling stiff after an hour of observing!

I have seen a 'Y' shaped bracket which goes in a finder shoe and has another shoe at the top of each 'Y' , and versions with 3 shoes, but they seem ridiculously big and heavy for a small 'scope and like so many astro accessories , the things are expensive ...

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2 hours ago, Tiny Clanger said:

Telrads have many vocal fans, but crucially it is quite a long thing for a small 'scope, and is low to the tube. The quickfinder has some of the same features (principally one red circle of known size around the red dot) has a a smaller footprint, but is quite tall, and a bit cheaper. I think the height might make it easier to use, not needing to get my face quite so close to the scope.

I recall reading somewhere that despite their looks and shape, there isn't that much different in height between the Quickfinder and the Telrad? In fact, FLO has the Telrad at 127mm high and the Quickfinder at 114mm high? Do let me know how you get on with the Quickfinder though, I'm curious about it...

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14 minutes ago, Jasonb said:

I recall reading somewhere that despite their looks and shape, there isn't that much different in height between the Quickfinder and the Telrad? In fact, FLO has the Telrad at 127mm high and the Quickfinder at 114mm high? Do let me know how you get on with the Quickfinder though, I'm curious about it...

The quickfinder stands upright though , and its footprint on the 'scope is small, the included bases are about 50mm x 55mm. The Telrad is horizontal. lying along the 'scope, and it is 215mm long, which would take most of the length of the solid tube of the heritage, and nearly all of the mak ... I got a tape measure out when I was fantasy shopping for my wishlist (don't tell me the rest of you  don't do fantasy shopping , I won't believe you. 😀 Granted it may be dignified as careful consumer research in advance of planned purchases  😀 ) and measured the tubes upto get an idea of where the telrad might fit.

The quickfinder does seem as if it would stick up/out like the proverbial sore thumb, but it's pretty much the same height as the RACI on its little stalk . Somewhere I saw a site where a chap had cut slots in the quickfinder base, added a bit of rubber to stop any slipping/scratches, and strapped the thing on his scope with some nylon webbing and a buckle . I don't think I'll try that, it would be a pain to realign every time you put it back on .Unless you marked the tube in some way, in which case, you might as well just stick the base on !

Heather

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Yeah, I do think the Quickfinder is a lot smaller, most of its size is its height, whereas the fact that the Telrad is the same height as it gives some idea how bloody big it is all over, and like you say, would look huge on a lot of scopes, mine included. Out of curiosity, I just measured the height of my RDF, and it's 100mm high on its own, and 110mm high on its base, so basically the same height as the Quickfinder too. It's just the shape of them that makes them stand out more I reckon.

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Managed to get outside for a minute when there's still some light and aligned the RDF with the Scope using a distant tree top. Went easily enough. Whenever I get any decent clear skies at night I'll do it on a star as well to make sure.

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The Quikfinder has 2 illuminated reticule rings, marking 2 degrees and .5 of a degree against the sky. The Telrad has 3 rings, the extra one is at 4 degrees.

The Quickfinder has a variable reticule pulse option which some like and others don't. This is available for the Telrad as an extra I believe. I don't use that myself.

I've owned a few Telrads but with my 12 inch dobsonian I wanted to keep the nose weight down to a minimum so I went for the Quikfinder and find that it works well for rough aiming. Most of my more detailed "finding" is then done with the 9x50 RACI optical finder:

 

dob12topend.JPG

Edited by John
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14 minutes ago, Jasonb said:

Managed to get outside for a minute when there's still some light and aligned the RDF with the Scope using a distant tree top. Went easily enough. Whenever I get any decent clear skies at night I'll do it on a star as well to make sure.

It was a dry afternoon here, clear sky patches even (forecast to vanish with the Sun, naturally ) but rather than playing with the astro kit i was fighting with a Nordmann fir xmas tree rather taller than I am . I bought it nearly 2 weeks ago, and it's been stood outside in a bucket of water ever since getting a good rinse from the rain. Today was the first chance I've had to deal with it without it being sodden , so sawed a slice off the base, trimmed the lumps from the trunk where it goes in the stand, set up the stand, staggered into the house with the fir, and plonked it in the base. Coffee break now, then secateurs to the odd sticky-out branch , then the decorating fun begins .

Well, it's something to do while the clouds roll in ...

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4 minutes ago, John said:

The Quikfinder has 2 illuminated reticule rings, marking 2 degrees and .5 of a degree against the sky. The Telrad has 3 rings, the extra one is at 4 degrees.

The Quickfinder has a variable reticule pulse option which some like and others don't. This is available for the Telrad as an extra I believe. I don't use that myself.

I've owned a few Telrads but with my 12 inch dobsonian I wanted to keep the nose weight down to a minimum so I went for the Quikfinder and find that it works well for rough aiming. Most of my more detailed "finding" is then done with the 9x50 RACI optical finder:

 

dob12topend.JPG

Thanks for that: all I've done with the quickfinder so far is, just after the postie delivered it, stand in the kitchen like a loon with a towel over my head to check the thing lights up ! I've discovered it is possible to change the 'telrad' circle size in stellarium, which should come in useful for planning star hopping.

When eventually the star light manages to fight its way through the clouds ...

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The nice thing about the Telrad and the Quikfinder is that they were designed for astronomers by astronomers. Most of the other designs of illuminated reticule / RDF finder I've used were a bit too bright even at their dimmest setting. 

 

 

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Got a chance to go out for a few mins with clear skies to see what I could see and test the RDF. I picked easy targets, and it helped me focus on Jupiter, Saturn, Mars & Vega. It was close enough that my 25mm EP could do the rest with a very small adjustment. I did find myself sometimes seeing two stars through the RDF and having to choose which one to aim at, not sure what's causing that, something to do with each eye seeing it differently I'm guessing?

As a proper test I saw a satellite moving along and used the RDF to judge its flght path and managed to find it. So I'm viewing that as a success! :)

Also found that I was a lot less fingers and thumbs with all the equipment, got into a routine of loosening the clutch knobs, moving the OTA where I wanted it to go using the RDF, tightening the clutch knobs, using the slow motion controls to be more accurate and then over to the EP, and it seemed to work quite well. It probably helped that it wasn't completely dark outside yet!

Am not really getting a 'perfectly' clear pinpoint image, but I'm not sure how much of that are conditions (not fully cooled down OTA, heat rising from the concrete in the back garden and other houses etc. etc.). Looking at Saturn at x65 I could definitely distinguish the planet from the rings, with areas of black in between them, and the more I watched, I got moments of more clarity and moments of less. As I'm so new to this, I'm not sure just how clear/sharp the image should/could be! :)

Edited by Jasonb
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25 minutes ago, John said:

The nice thing about the Telrad and the Quikfinder is that they were designed for astronomers by astronomers. Most of the other designs of illuminated reticule / RDF finder I've used were a bit too bright even at their dimmest setting. 

 

 

I think I read that the simple RDF was invented as a gun sight ? Therefore presumably best for daytime use ...

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55 minutes ago, Tiny Clanger said:

Coffee break now, then secateurs to the odd sticky-out branch

It's rare I get hit with a word I've never heard before, but today was such a day.  I had to look up secateurs, what we Americans would call pruning shears.  Do Brits prune unwanted growth with secateurs or is there a verb version of secateurs as well?

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