magnification on DSO for 82mm bins

[bomberbaz]

Ok so hopefully someone with more experience can help here. 

I bought the TS 82mm astro binocular with the intention of low powered viewing on larger DSO such as M31, N/America neb, California nebula and asterisms etc but this query is more about magnification for galaxies. 

In a thread I was involved with earlier this year one thing came to my attention was I had been using insufficient power on many galaxy targets, someone gave a rule of thumb for at least 10x magnification per inch of aperture.

I pay attention to rule of thumb as there is often a lot of experience gone into these ROT's. In this case I found it very useful and wish I had been aware of this earlier. (see below)

On a recent visit to Galloway I was able to test this ROT out to it's fullest and confirmed I had on many occasion not been making full use of the aperture pull of my OTA. Since then I have born this rule of thumb in mind and even exceeded it with pleasant results.

Anyway, question concerns the ROT when applied to Bins. When using binocular do you double the magnification of the aperture you are using because you have double objectives, in my case 82mm. This gives circa 3.25" = 32.5 magnification x 2 = 65.

Or, and what I think it should actually be is the equivalent area of the two combined objectives viewed as one.  In this case two 82mm objectives are roughly the same in area as a 127mm, ergo 5 inch. So 50 times as a rule of thumb.

I hope this makes sense and I am not over thinking things,

Anybody have any thoughts on this?

TIA

Steve

[PeterW]

The rule will be to do with getting the size of galaxies bigger so your eyes can see them more easily. I’d start with the rule of thumb as it stands with 82mm or maybe a little more, certainly wouldn’t double it…. But tell us how you get on.

 

peter

[mdstuart]

Just to support Peters point. Small galaxies need magnification to see them. I often cannot see a galaxy at low power in my dob but it is visible at higher power.

I think higher powers also darken the background which helps.

There is a yellow book that goes in to the science behind this.

Mark

[bomberbaz]

17 minutes ago, mdstuart said:

Just to support Peters point. Small galaxies need magnification to see them. I often cannot see a galaxy at low power in my dob but it is visible at higher power.

I think higher powers also darken the background which helps.

There is a yellow book that goes in to the science behind this.

Mark

I notice you have 25x100 bins mark, what do you take them up to assuming they have interchangeable ep's?

[mdstuart]

Sorry used to have 25 x 100 mm bins . They were fixed magnification...so only good for the brightest and biggest galaxies

Mark

[bomberbaz]

35 minutes ago, PeterW said:

The rule will be to do with getting the size of galaxies bigger so your eyes can see them more easily. I’d start with the rule of thumb as it stands with 82mm or maybe a little more, certainly wouldn’t double it…. But tell us how you get on.

peter

The glass in my signature gives the following magnifications

Eyepieces mm

Magnify

AFOV

Exit Pupil mm

TFOV degrees

8.8	53	82	1.5	1.54
18	26	65	3.1	2.49
24	20	65	4.2	3.32
32	15	52	5.6	3.54

The 8.8 fits in with my total area idea and the exit pupil isn't too small.

I will let you know how I get on once I have chance for an in the field proper outing

 

[PeterW]

At, a Yellow Book… https://clarkvision.com/articles/visastro/index.html

Peter

[jetstream]

On 30/12/2021 at 12:32, bomberbaz said:

When using binocular do you double the magnification of the aperture you are using because you have double objectives, in my case 82mm.

Binocular summation comes in to play I think and I would up the mag until it becomes a detriment.

[jetstream]

@bomberbaz

https://www.cloudynights.com/topic/61467-binocular-vision-summation/

EdZ's excellent thread on the subject.

[Mr Spock]

For my 250mm Dob I use a 13mm eyepiece - x92. The objects are too small for less magnification. x92 also darkens the background significantly compared to lower magnifications.

[bomberbaz]

5 hours ago, jetstream said:

@bomberbaz

https://www.cloudynights.com/topic/61467-binocular-vision-summation/

EdZ's excellent thread on the subject.

Very in depth report and makes a lot of sense. In essence of the report and being an F5.8 pair of 82mm bins my thoughts, although wrong were giving results that are not that far away from what the true result is "likely to be" using the correct formula.

I think I will be fine with three of the eyepiece sets although the 8.8mm are being returned. Horrible kidney beaning, I can't work with that. 

A pair of 10mm apm uff will be used instead.