The60mmKid

Here's the specific tripod: https://fotopro.eu/en/product/p-2-mini-p2h-2/ There are many similar tripods sold under different brand names. I think the main thing is to get any mini tripod that:

- has rigid, extendable legs since this provides stability and adjustability to suit different binoculars and bodies...

- includes a ball head if possible since these are small and light..

- doesn't include a center column since (I assume) this would get in the way.

The chair is a generic zero gravity lawn chair. I'd suggest using any zero gravity lawn chair that you find comfortable. I've owned a couple that were basically the same, but some are sold with different cushioning and various bells and whistles.

Also: Because the legs rest on your shoulders, not your chest, you don't get any movement from your heartbeat. There's may be a little movement from breathing, but this is minimized with a little practice.

I call it the London Method.

It's an £80 mini tripod/ball head (tightened into the shown position) with one leg removed. It provides a significant degree of stabilization for small- and medium-sized binoculars. With this method, the view through my 18x70 binoculars is steadier than it is through my 8x30 binoculars handheld. It works standing and sitting, and it's easy to compensate for the altitude by just slightly adjusting where the tripod legs contact your shoulders. With a little practice, you can pan around with the binoculars almost as fluidly as you can when simply holding them in your hands. It works for observing near/at zenith. It weighs less than 1 lb. and easily fits in carry-on luggage.

In my opinion, this is the best way to bridge the gap between handheld observing and using a parallelogram mount. It's a game changer for me, and I hope that others benefit from it, too.

In an era of polycrisis, I find it comforting to look up and know that life glistens elsewhere even while suffering permeates this little planet of ours.

A lovely book that evokes so much nostalgia for me 😊

Do you mean biblio.co.uk? If so, I think clarification is in order. Biblio is a platform that allows independent bookshops/vendors to sell (typically used) books. They have an excellent international reputation and track record of ethical practices, such as carbon-offset shipping (which isn't at all a perfect solution but that at least draws attention to the climate emergency). Although I haven't looked, my guess is that people who complain on Trustpilot are mainly upset about a specific vendor and are erroneously blaming Biblio, which is just a platform. I've bought from Biblio for years with no problems at all, and I wouldn't want to see their reputation incorrectly harmed... especially because they provide an alternative to the actually harmful businesses from which we can easily purchase used books.

£1950 pair of 70mm binoculars and a comfortable lawn chair.

On 08/02/2024 at 12:32, ollypenrice said:

One thing I liked about this instrument was that I didn't have to wait till night time to use it. A shadow transit of Jupiter was easy to see on a very bright, sunny afternoon. You need to bear in mind, though, that the 31mm Nagler in use there is the planetary eyepiece...

lly

I like this because it looks like a big Astroscan. Cute!

To remember what I am.

Another nice thing about refractors is that they often come in twos.

This is more challenging to accomplish with reflectors.

3 hours ago, paulastro said:

Personally, I don't care what anyone calls me.

 

 

 

Be careful... There are people out there who would be tempted to take full advantage of such an opportunity 😇

4 hours ago, Paul M said:

Me too!

There are a few things I take seriously in life, and they are all in the death and taxes categories.

Astronomy has been, perhaps, the only constant in my life. I first became aware of the stars at about 7 years old. By aware I mean inquisitive.  Since then I've dipped in and dropped out as life dictated, but always looked up and gazed at the stars when opportunity presented itself. Just gazing and wondering. No depth of thought beyond "Hi Orion, nice to see you again".

I do much more stargazing than I do astronomy.

Does anyone else talk to the constellations, or is it just me? 

I love this. Part of what thrills and comforts me about stargazing is the passage of time and the relationship with the night sky. There's nothing like seeing a constellation or favorite sight (i.e., "object") again after a couple seasons have passed. I regularly find myself saying, "Hello, old friend," and really meaning it. Then, I wonder if they're glad to see me, too. I can't help but feel they are, gazing back at me while my life passes so quickly in relation to their own.

There have definitely been some good points made about observing doubles in general... But again, the specific question was about the theoretical limitations of a 70mm instrument with 18x magnification to resolve equal magnitude doubles, only considering the variables of aperture and magnification (and, thus, assuming perfect conditions and eyesight for the sake of the theoretical exercise). Some of the responses related to aperture, but not magnification. Others related to magnification, but not aperture. And others introduced other variables. If we don't know how to calculate using these two variables, that's totally fine. But I think it's helpful to keep the actual question in mind.

I found @lunator's reply most relevant and am eager to observe an 8" equal pair and report back.

I don't want to be taken seriously, and I love the word stargazer 🙂 Part of what I love about it is the lack of seriousness.

25 minutes ago, vlaiv said:

 eyesight is not that important variable if one can change magnification. You select magnification that allows you to easily see what the telescope is capable of. There is seldom discussion (but it does happen) - what can you split with say x40 power or similar. Most of the time, recommendation is to go with very high powers, even higher than one would use for planetary for example. That removes eyesight from the equation as at those magnifications - eye has no issues resolving things. With binoculars - it is a thing since one is tied to certain magnification - and that magnification tends to be on very low side of things - which is not suitable for splitting doubles because of eyesight issues.

Helpful. Thanks 👍

32 minutes ago, vlaiv said:

Not sure if that is true.

I'm sure that sky conditions play major part when talking about visual separation of doubles as well.

Sometimes talk about theoretical resolution of the telescope is had in context of planetary imaging for example. There we don't really entertain these variables as they are effectively excluded by the process of planetary imaging (lucky imaging where we discard subs that are too distorted by atmosphere).

Many of the conversations on splitting doubles that I've seen online make claims like, "___ telescope can theoretically split ___ doubles," while taking for granted that atmospheric conditions and eyesight are uncontrollable and important variables. (For example, I don't mind claiming that my FOA-60Q can split 2" equal doubles, and I don't feel the need to offer  caveats about seeing and eyesight since I assume most of us know about that already.) So, I anticipated a similar reply when asking about binoculars. I figure most people asking such questions on such a forum know about the impacts of seeing, etc., so that's partially why I'm surprised that we seem to be considering binoculars in a different way than we do telescopes in this instance.

Why is that we talk about theoretical limits of telescope resolution all the time but uncontrolled variables suddenly plague us when it's binoculars 🤔

Am I missing something?

2 minutes ago, lunator said:

There is a simple relationship in my experience..

The Dawes limit means you will not cleanly split the pair. If you want to cleanly split the pair the Raleigh criteria is more relevant. For white stars e.g 5500nm light it is 138/D.

From experience if you substitute the magnification M for D you will get a pretty close result.

So it becomes 138/18 ~ 7.5" 

Also from experience you can split pairs with a delta M of upto 2 magnitudes. 

I hope this helps.

Cheers

Ian

This does help! Based on my observing experience, that seems like a realistic split with the given aperture and magnification. I will observe a relatively equal ~8" pair with my 18x70s and report back.

Just now, Zermelo said:

Perhaps you are looking for a single formula that takes all the parameters into account? I've not seen one. The capabilities of the instrument and of your eyesight both impose limits on the resolving power, and either may be the limitation in practice. Usually, it's the instrument (aperture) that is relevant, and the usual formulae assume perfect instrument optics, normal visual acuity, and the absence of other limiting factors. If you're splitting doubles, then it would be more usual to be employing higher magnifications.

I'm looking for a way to account for aperture (70mm) and magnification (18x) and that assumes perfect eyesight and optics, which is usually what we do when we talk about telescopes' theoretical ability to split doubles.

I'm aware that we usually use higher magnifications for splitting doubles 😉 I have experience with that. But sometimes one wishes to use a certain instrument!

1 minute ago, Zermelo said:

The aperture is relevant to the initial answers you received. It sets a lower limit on the tightness of doubles that can be split, irrespective of eyesight. Then you need to take account of the limits of your eyes, and if the instrument is operating at a low magnification, the retinal cells may not be close enough to take advantage of the resolving power of the instrument. An eagle might be able to see finer splits with your binoculars than you can.

Ok, but here magnification and aperture (i assume, perhaps incorrectly) are both variables, in addition to the others mentioned (i.e., eyesight, optical quality). So where does that leave us?

17 minutes ago, vlaiv said:

I think that you won't come close to theoretical resolution of 70mm aperture for several reasons.

First is quality of optics, but more important is magnification - that is too low.

If we assume perfect optics, then it's down to visual acuity of observer.

https://en.wikipedia.org/wiki/Visual_acuity

There is table on above page that lists MAR for different grades of visual acuity that is important factor - it is minimum angle of resolution measure and is expressed in arc minutes in said table.

20/20 vision equates to 1 MAR of resolution - which means that 20/20 person needs to see two equal doubles at one minute of arc separation to be able to just resolve them (see the gap).

Since you have binoculars that provide x18 magnification - that angle will actually be 1 minute of arc / 18 = 60 arc seconds / 18 = 3.33' separation.

This is for person having 20/20 vision and perfect optics.

Binoculars are often fast achromats that suffer from spherical aberration which will somewhat soften the view so the actual figure will be larger, and if you have less than 20/20 - this will add to separation needed.

For example 20/30 vision adds 50% to separation so you'll be able to resolve around 5'.

 

After further reflection, my confusion has returned. You mention 3.33' (arc minutes) here, whereas @Mr Spock mentioned 3.3" (arc seconds). Based on my observing experience, the former strikes me as quite wide, and the latter strikes me as quite close.

Also, is aperture not a variable in this calculation? Would there not be a difference between the resolving ability of a 18x70 binocular and an 18x35 (hypothetically) binocular? That's surprising to me since aperture plays a clear role in the resolving ability of telescopes.

1 minute ago, The60mmKid said:

Perfect! Not to brag, but I have excellent vision and a magnificent pair of binoculars 😏 3.33" doubles: Here I come! 

But maybe I'll round up to 3.34" to play it safe.

Perfect! Not to brag, but I have excellent vision and a magnificent pair of binoculars 😏 3.33" doubles: Here I come! 

I appreciate the replies, but I don't think they address the question unless I misunderstand. The formula and tool calculate for a 70mm instrument, but my question also involves the fixed magnification of 18x. There's no way my 18x70 binoculars are going to split 1.7" doubles... as cool as that would be 😉

There's a reason I became a social scientist 😞 My mathematical abilities are hopeless to the extent that I often forget how old I am. Please help me. I want to know the minimum separation between equal magnitude doubles that is resolvable in 18x70 binoculars. I understand how to figure this out using aperture alone, but when magnification becomes a variable, I feel like I'm 15 years old again, sitting in physics class praying to various premodern deities for answers.

This, of course, depends on how we theorize existence. https://plato.stanford.edu/entries/existence/