RDF annoyances

[JeremyS]

1 minute ago, John said:

It can be done. This is 50% better looking

Now take off the other 50%, John, and job done. Will trounce any beauty contest. 😀

Edited January 31, 2021 by JeremyS

[Dantooine]

1 minute ago, ScouseSpaceCadet said:

That's the correct posture. Of course this also needs to be done when aligning the red dot finder. Sometimes the simplest solution is the best... 😉

 

So if I cans strip one down and put some current resistance in there so the the lowest setting is the highest setting and move down from that things could be sweet. 

[Dantooine]

3 minutes ago, JeremyS said:

The Baader Skysurfer V is optically and mechanically far superior to the III. Much more expensive. And whilst not at the Telrad end of the ugly spectrum, it’s a big brute. 

I tried the baader V and didn’t like the shape of the dot, it just didn’t seem to be a round dot on the one I had. Maybe it was just a bad example but it put me off of them. 

[John]

I have read of people applying dark red nail varnish to the light source to dim it down.

It's not a colour that I wear though

[Dantooine]

I’m surprised nobody’s mentioned laser finders. 

[ScouseSpaceCadet]

1 minute ago, John said:

I have read of people applying dark red nail varnish to the light source to dim it down.

It's not a colour that I wear though

Red is too much of a statement colour and clashes with the beard. Go with biege.

[Dantooine]

5 minutes ago, John said:

I have read of people applying dark red nail varnish to the light source to dim it down.

It's not a colour that I wear though

A piece of film negative would probably work if you’ve run out of nail varnish. 

Edited January 31, 2021 by Dantooine

[Dantooine]

1 minute ago, ScouseSpaceCadet said:

Red is too much of a statement colour and clashes with the beard. Go with biege.

I think after my 12 hour shift I need to sleep as my kitchen light is getting dimmer than my red dot 🤣

[JeremyS]

On 11/01/2021 at 21:22, NGC 1502 said:

PS - please don’t let on that Ed from Essex uses red nail varnish 😁

 

8 minutes ago, John said:

I have read of people applying dark red nail varnish to the light source to dim it down.

It's not a colour that I wear though

I think it’s more of an Essex thing John

[Dantooine]

16 minutes ago, ScouseSpaceCadet said:

That's the correct posture. Of course this also needs to be done when aligning the red dot finder. Sometimes the simplest solution is the best... 😉

 

I’m pretty simple so that’s why this works well for me 😆

[JeremyS]

What about laser finders? 🤣

[Dantooine]

Just now, JeremyS said:

What about laser finders? 🤣

Apparently you can get them with undercuts.  

[Dantooine]

I’m going to bed and will see how this thread had progressed in the morning. 

[JeremyS]

Just now, Dantooine said:

I’m going to bed and will see how this thread had progressed in the morning. 

Regressed more likely 🤣

[wibblefish]

Honestly I leave you guys alone for one evening and this happens  

I have a Rigel coming so will hopefully solve all my RDF annoyances though you are welcome to continue the thread 🙈

In answer to a question I use both eyes when viewing the RDF but some zenithy angles were causing me struggles which I think I mentioned at the beginning way back. Of course the big question will be where to mount the Rigel on a short tube refractor! Thinking top of the scope mid / front copius blutac experiments will no doubt occur

 

Edited February 1, 2021 by wibblefish

[JamesF]

10 minutes ago, wibblefish said:

Honestly I leave you guys alone for one evening and this happens  

It wasn't us!  A big boy did it and ran away!

James

[AlexK]

3 hours ago, Dantooine said:

In the Uk we wouldn’t dream of putting any sight on a shotgun 🤣 there’s a brass bead on the end of the barrel. To be honest (and no disrespect to American shooters) it would be laughed at in Britain. 

Yeah, American skeet and trap-ers kinda laughed at me on the range too once with their rustic polished nearly with diamonds-incrustated receivers over-unders. But when I shoot 20/20 skeet 3 times in a row, and they've realized that was my first try with that modded Saiga-12 every single one came to check that wonder including from the club's booth. Surely I was banned with it ever after from any even informal competition 

Back to the subject: Telrad is indeed a very dated design. However its price is still too good for its functionality. The only modern rival to it is the QuInsight with its updated collimator optics. But it's nearly twice as expensive even though nearly 90% 3D printed.

[AlexK]

9 hours ago, ScouseSpaceCadet said:

Interestingly, noone seems to have asked the OP how they look through the the red dot sight?

I ask because closing one eye will introduce a parallax effect. Positioning your head well back and opening both eyes keeps the dot where it's supposed to be.

Sorry, but that's a common misconception. RDF, Rigel, Telrad, QuInsight are leveraging the collimation of light principle to place their reticle image at infinity, so the parallax supposed to be completely eliminated (that's the whole idea of this sighting device type) and the dot, or rings, or other reticle should appear fixed to the sky. No second eye required at all. I'm using my Telrad single-eyed exclusively and enjoying the several arcminutes accuracy of pointing every time.

However, the user's eyesight and the optics used to create the collimator device is limited by its price. Thus the parallax can be easily detected in $50 RDFs due to the short focal range and severe spherical aberration of their air-blown spherical mirrors. It's much less prominent in Telrad due to the much longer focal range of the used collimator (that's why Telrad is so long) and especially good in the QuInsight due to the more expensive two-part wide field lens collimator. In military grade, 10x more expensive collimator, which I have displayed for fun above, they are also using a holographic reticle, which is compensating the collimator lens or mirror surface figure by providing a 3-dimentional reflective shape in the focal plane resulting in the much more flat collimated wavefront. They are still having some parallax, but it's already not affecting the performance and practically invisible (by the way, there are simple RDFs exhibiting a hand polished aspherical sapphire in the front, those are nearing the $1K price tag just for the starter.

I believe the "two eyes" technique came from the grim times when some reputable telescope maker rolled out a beginner telescope with the "innovative" RDF sight without any "curved optics" inside  I can't find any polite curse to describe that abomination, nor google for it's name and image...

In practice, to reduce the parallax of small RDF's (the venerable Rigel included) the "correct posture" would be to stay behind it as far as you practically can. That way the concave mirror will have a smallish AFOV so when you finally catch the red dot/reticle in it it will be reflecting from the certain point of it. After you have it aligned with the scope it will stay there every time and show no parallax anymore, just because if you move your head to the side you will simply lose the dot

Telrad would benefit from that trick as well, however its longer focal is les prone to the spherical aberration. That's why it is safe to sight from close proximity (I've been placing my nose side against the top edge of the mirror, as my Telrad was installed on the side of the OTA, QuInsight works by touching the edge with the eyebrow) and avoid the red dot hunting chore above completely. However, there are three factors making its parallax worse:

• the user eyesight (with any bad eyes asking for prescription optics to see stars as dots the collimation wouldn't work without glasses, you can refocus the reticle to your eyes but that's exactly what's causing the parallax, so you should focus in glasses too),
• the cyclic collimation pattern (collimator gets out of focus a bit due to the internal mirror gradually walking it out of perfect focal point as you change the length of the light path while aligning the reticle with the scope, using collimation screws in the same order each time, QuInsight doesn't have that issue by the way),
• and the ill installation angle (when the axis of the scope is at a significant angle from the optical axis of the Telrad's lens you have to align it a bit off center which is increasing aberrations).

Edited February 1, 2021 by AlexK

[Dantooine]

3 hours ago, AlexK said:

Sorry, but that's a common misconception. RDF, Rigel, Telrad, QuInsight are leveraging the collimation of light principle to place their reticle image at infinity, so the parallax supposed to be completely eliminated (that's the whole idea of this sighting device type) and the dot, or rings, or other reticle should appear fixed to the sky. No second eye required at all. I'm using my Telrad single-eyed exclusively and enjoying the several arcminutes accuracy of pointing every time.

However, the user's eyesight and the optics used to create the collimator device is limited by its price. Thus the parallax can be easily detected in $50 RDFs due to the short focal range and severe spherical aberration of their air-blown spherical mirrors. It's much less prominent in Telrad due to the much longer focal range of the used collimator (that's why Telrad is so long) and especially good in the QuInsight due to the more expensive two-part wide field lens collimator. In military grade, 10x more expensive collimator, which I have displayed for fun above, they are also using a holographic reticle, which is compensating the collimator lens or mirror surface figure by providing a 3-dimentional reflective shape in the focal plane resulting in the much more flat collimated wavefront. They are still having some parallax, but it's already not affecting the performance and practically invisible (by the way, there are simple RDFs exhibiting a hand polished aspherical sapphire in the front, those are nearing the $1K price tag just for the starter.

I believe the "two eyes" technique came from the grim times when some reputable telescope maker rolled out a beginner telescope with the "innovative" RDF sight without any "curved optics" inside  I can't find any polite curse to describe that abomination, nor google for it's name and image...

In practice, to reduce the parallax of small RDF's (the venerable Rigel included) the "correct posture" would be to stay behind it as far as you practically can. That way the concave mirror will have a smallish AFOV so when you finally catch the red dot/reticle in it it will be reflecting from the certain point of it. After you have it aligned with the scope it will stay there every time and show no parallax anymore, just because if you move your head to the side you will simply lose the dot

Telrad would benefit from that trick as well, however its longer focal is les prone to the spherical aberration. That's why it is safe to sight from close proximity (I've been placing my nose side against the top edge of the mirror, as my Telrad was installed on the side of the OTA, QuInsight works by touching the edge with the eyebrow) and avoid the red dot hunting chore above completely. However, there are three factors making its parallax worse:

• the user eyesight (with any bad eyes asking for prescription optics to see stars as dots the collimation wouldn't work without glasses, you can refocus the reticle to your eyes but that's exactly what's causing the parallax, so you should focus in glasses too),
• the cyclic collimation pattern (collimator gets out of focus a bit due to the internal mirror gradually walking it out of perfect focal point as you change the length of the light path while aligning the reticle with the scope, using collimation screws in the same order each time, QuInsight don't have that issue by the way),
• and the ill installation angle (when the axis of the scope is at a significant angle from the optical axis of the Telrad's lens you have to align it a bit off center which is increasing aberrations).

You are correct but to simplify the physics..

the peep sight/aperture sights as used on the Lee Enfield .303 developed around a hundred (ish) years ago (one eye closed) and the single point sight developed I think in the 1970’s (two eyes open). 
Both of these put the aiming dot or marker at the furthest possible distance from the users eye cutting down the margin for error. 

[Dantooine]

8 hours ago, ScouseSpaceCadet said:

I'm quite happy with a solo RDF depending on what I'm about to look for, or if aligning a GoTo mount. Lunar and easy DSOs, a red dot is all you need. Harder stuff, then both a RDF and RACI finder.

Interestingly, noone seems to have asked the OP how they look through the the red dot sight?

I ask because closing one eye will introduce a parallax effect. Positioning your head well back and opening both eyes keeps the dot where it's supposed to be.

 

This is correct as the aperture where the dot is showing is reduced. For ease in finding the dot I start close then move away keeping it in view. I pick up the dot with one eye and open the second eye as I move back. 

[AlexK]

20 minutes ago, Dantooine said:

You are correct but to simplify the physics..

the peep sight/aperture sights as used on the Lee Enfield .303 developed around a hundred (ish) years ago (one eye closed) and the single point sight developed I think in the 1970’s (two eyes open). 
Both of these put the aiming dot or marker at the furthest possible distance from the users eye cutting down the margin for error. 

You are talking about the OEG ("occluded eye gunsight") requiring both eyes open (some sighting tools also using it, like survey compasses). But collimating sights we are discussing here are all a different thing utilizing a light beam splitter. The second eye is not needed AT ALL with all of the above discussed RDFs, folks. In fact, it's even counterproductive with these as sometimes the required "mental gymnastics" may play tricks on ya  Especially if pointing over a Dob's OTA. You can quit torturing yourself already!

[wibblefish]

Interesting but if I didnt use a second eye with my RDF then I wouldnt see anything to aim at as the reticule is darkened and the dot is very bright. If I just look through the sight with no dot on there are very few stars to be seen. 

Edited February 1, 2021 by wibblefish

[AlexK]

48 minutes ago, wibblefish said:

Interesting but if I didnt use a second eye with my RDF then I wouldnt see anything to aim at as the reticule is darkened and the dot is very bright. If I just look through the sight with no dot on there are very few stars to be seen. 

Darkened??? Are you sure it's not a defect? Dirt/dust/grease/protective film? The bright dot is no good either, but that's rather easy to fix. Perhaps, you've got a really bad RDF (just looked through the thread and can't see you showing it or stating the model). As even on cheap airsoft gun RDFs the window is transparent enough for 3-4m stars. I had a chance to use a handful of various RDF's in the past and even though some were really flimsy, the window transparency was never an issue to even consider the OEG method. Now I see why it was hard for you. Two eyes into Zenith with one hunting for the red dot IS a torture!

Hmm. Just in case. Are you aware of general basic eyes darkness adaptation measures mandatory for observing from light polluted location? Like turning off lights in your house behind you? Avoiding looking into bright light with your observing eye (e.g. a computer screen)? Wearing the eyepatch on the observing eye? And definitely begin with reducing the dot's brightness to the barely visible (I don't believe your new optical finder would be sufficient for pointing, as it's still just a keyhole in the sky, but I see the Rigel is on the way, it should fix that).

Besides, how two eyes could fix the parallax existing for one eye already? If it's there it is there, move your head and the dot will shift over the sky one eye or two doesn't matter at all.

Edited February 1, 2021 by AlexK

[jock1958]

10 hours ago, John said:

It can be done. This is 50% better looking

I remember someone chopping one in half a few years ago but couldn’t for the life of me remember if it was someone on SGL or the other side of the house? 

[wibblefish]

55 minutes ago, AlexK said:

Darkened??? Are you sure it's not a defect? Dirt/dust/grease/protective film? The bright dot is no good either, but that's rather easy to fix. Perhaps, you've got a really bad RDF (just looked through the thread and can't see you showing it or stating the model). As even on cheap airsoft gun RDFs the window is transparent enough for 3-4m stars. I had a chance to use a handful of various RDF's in the past and even though some were really flimsy, the window transparency was never an issue to even consider the OEG method. Now I see why it was hard for you. Two eyes into Zenith with one hunting for the red dot IS a torture!

Hmm. Just in case. Are you aware of general basic eyes darkness adaptation measures mandatory for observing from light polluted location? Like turning off lights in your house behind you? Avoiding looking into bright light with your observing eye (e.g. a computer screen)? Wearing the eyepatch on the observing eye? And definitely begin with reducing the dot's brightness to the barely visible (I don't believe your new optical finder would be sufficient for pointing, as it's still just a keyhole in the sky, but I see the Rigel is on the way, it should fix that).

Besides, how two eyes could fix the parallax existing for one eye already? If it's there it is there, move your head and the dot will shift over the sky one eye or two doesn't matter at all.

Its a standard Skywatcher plastic one, maybe darkened is the wrong word but the lens at the end is tinted to some degree (its yellowish in the daylight) though I will double check for protective film in case I am being silly! Ultimately it works fine for bright stars or on clearer nights but if I get the purple soup washout I get fairly often in certain directions then I have no chance but I am getting better at guesstimating with my night sky app and binos (well the RACI now!)  Honestly I do wonder if I need to get over my contact lens aversion since having to swap from glasses (which inevitably steam up) to see the target then take them off for the EP as I find it more comfortable is annoying 😛 

My main trouble other than the large bright dot obscuring anything I was looking at was definitely the yoga positions even with a short tube as getting the right angle to even view the red dot was annoying into the zenith which is unfortunately where most of my gazing is due to the positioning of buildings / trees as explained at the start of the thread. The other night without the RDF I simply vaguely lined the top edge of the center of the tube up with the target star before fine tuning with the RACI which worked fairly well but I am hoping the Rigel will help alot as people speak highly of them.

Thanks for the kind suggestions but I think I am doing most of them (bar the pirate patch!). I am aware that light adaption is necessary though it can be tricky as I will sometimes get a temporary dazzle from either from the various bright street lights if I am not overly careful, security lights / neighbours window lights and my phone screen on occasion if I forget to unlock it first before accessing my skymap app. Its a bit of a balancing act normally but I manage fairly well mostly but have had to sit back and let me eyes readjust on occasion.  I turn off all the lights in my own house once I am out and only navigate by dim red LED torch if I need to check notes / EP / obstacles. I do try to shield at least one of my eyes (the better one) more than the other if I am moving about / switching EP by feel. My RDF on its dimmest setting is immensely bright and I haven't tried any of the mods kindly suggested to solve that as I decided to invest in a Rigel due to some birthday pennies (and the RACI)

 

 

Edited February 1, 2021 by wibblefish