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Binocular sweeping

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#1 Mr. Bill

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Posted 04 June 2013 - 03:44 PM

Next time you are out observing the Milky Way, try slowly sweeping in an overlapping pattern. The eye is very good at detecting edges of low contrast objects such as dark nebulae against starfields when moving...especially peripherally.

Binoculars give you the advantage of superior contrast to monocular viewing and sweeping fields gives you the best use of that contrast.

Using this technique, given dark, transparent skies, clean optics with high quality coatings and correct baffling and blackening you will see detail in MW structure similiar to those CCD images you admire.

Oh, one last thing...complete dark adaptation (no red light) and practice, practice, practice.

:cool:

#2 guangtou

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Posted 04 June 2013 - 04:18 PM

Mr. Bill

Thanks for the tip and I look forward to trying it out. Can you share a bit more exactly how you observe? For example, do you study charts before observing to preclude use of a red light? Thanks .

#3 Mr. Bill

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Posted 04 June 2013 - 04:26 PM

After 30 years, I got a pretty fair idea of what I'm looking at (most of the time). :grin:

But seriously, even faint red light will have a negative effect so use judiciously. Try to minimize the brightness as much as possible. Remember, it takes 20 minutes to completely dark adapt, but only a few milliseconds to lose it.

Take a night out (say every other observing session) forget the charts and goal directed activity and just wander around looking at fields for their intrinsic beauty...compose "pictures"... sort of like spontaneous photography and think about the scales of what you're observing and your place in it.

Its humbling but also can be transcendental....

#4 GlennLeDrew

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Posted 04 June 2013 - 04:41 PM

For the study of Milky Way structure, the usual printed chart is not sufficient. A good image mosaic is vastly superior. The Cambridge Photographic Star Atlas is most highly recommended. It presents the milky way band at a level of contrast much like that seen from a decently dark site.

Some mosaics are processed so as to really boost contrast. This is still OK, as long as one does not develop unrealistic expectations.

A good approach is to start with an 8X40 or 10X50. Simply sweep about and note any particularly interesting bright patches (star clouds) or dark gaps and embayments (dark clouds). The reasonably wide field should allow to locate them with respect to the surrounding stars. Make a crude sketch, or mark it on your atlas. Then after the night is over compare with a photo.

A larger bino or RFT can then be used to ferret out more detail and structure.

After a time, you'll be able to know just where you're gazing based on milky way structure--no need to 'star hop' along this river of light.

This is rather different approach from most amateur sky gazing, where discrete targets--almost universally light emitters, and of small size--are sought out in telescopes. Great swaths of the sky are then overlooked. Familiarization born of consistent sweeping provides the bigger picture.

#5 Jon Isaacs

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Posted 04 June 2013 - 05:02 PM


A larger bino or RFT can then be used to ferret out more detail and structure.



Indeed.. This is one reason why I have a series of F/5 telescopes starting with an ST-80 with a 2 inch focuser.
Richest field viewing can be done over a variety of scales, these features exist in many shapes and sizes big exit pupils and wide fields of view are required...

Mel Bartel's built a 13 inch F/3 that with a Paracorr and a 21mm Ethos provides a 1.9 degree TFoV with a 6mm exit pupil. My own 12.5 inch F/4.06 does a fair imitation providing a 1.62 degree TFoV with a 6.6 mm exit pupil. Add the possibilities of an O-III filter or a UHC, there's a lot to see.

This is about my favorite combination for scanning the Milky Way, bigger scopes narrow the field too much.

Jon

#6 Mr. Bill

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Posted 04 June 2013 - 05:37 PM

IMO, no RFT can match giant binoculars for viewing extemely low contrast detail in MW structure....two eyes are 40% better than one.

My 5 inch f/5.5s BinoBox is amazing at 30x and 2.2 degree fov using 24mm Pans.

I use my 6 inch f/5 with 21mm Ethos for bigger fov and also my 10 inch for close ups but neither can match the BinoBox views for detail or the comfort of bino viewing without squinting through one eye.

YMMV, different strokes, etc. That's what makes the hobby fun..

#7 KennyJ

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Posted 04 June 2013 - 05:39 PM

< Its humbling but also can be transcendental >

At around midnight, away from city lights, at various locations around the Mediterranean and Canary Islands, and in Fiji, Australia and New Zealand, with temperatures still around 70 degrees F, I've experienced this with NAKED EYE, just lying on my back.

Location, location, location! - --

--- the right time in the right place ---

--- more important in my book than any type, size or magnification of any binoculars or telescopes.

#8 Koala117

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Posted 04 June 2013 - 06:08 PM

I'm glad this thread was made. My new binos should be here in a day or two! While not exactly a pair of Zeiss, I'm still excited about them.

My first try with them will be a 'see what I can see' via scanning around. I've had some good suggestions for first-timer targets. Those will wait a couple of days. I think I will first try the advice in this thread. :D

#9 Koala117

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Posted 04 June 2013 - 08:38 PM

I wanted to add this question:

two eyes are 40% better than one.


Why is it 40% as opposed to 100% better/more? I am sure you're right, as I've seen others say this on CN recently! I'm just not sure I fully understand the reason that this is the case.

Regards

#10 Mr. Bill

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Posted 04 June 2013 - 08:54 PM

I wanted to add this question:

two eyes are 40% better than one.


Why is it 40% as opposed to 100% better/more? I am sure you're right, as I've seen others say this on CN recently! I'm just not sure I fully understand the reason that this is the case.

Regards


information theory....the signal to noise ratio = the sq rt of the number of sensors-1.....[sq rt 2]-1 = 1.414 or 41%.

#11 davidmcgo

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Posted 04 June 2013 - 09:20 PM

Great tip, Mr. Bill! My favorite summer viewing is with my 130mm f8 AP with an original style Celestron 50mm Axiom for 20x. This eyepiece has little to no angular magnification distortion and perfect contrast and sharpness. Sweeping with my DM6 makes the dark nebula and star clouds look curled or 3 dimensional. Several dark nebula show an almost brushed texture, very fine striations. Simply amazing. My Nikon 10x70s handheld work well for this, too. I recall having the impression of the area around Rho Ophiuchi looking ruddy in these from the Mojave Reserve a few years back where it was so dark Jupiter cast discrenable shadows.

Dave

#12 Jon Isaacs

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Posted 04 June 2013 - 09:37 PM

IMO, no RFT can match giant binoculars for viewing extemely low contrast detail in MW structure....two eyes are 40% better than one.

My 5 inch f/5.5s BinoBox is amazing at 30x and 2.2 degree fov using 24mm Pans.



We each enjoy this the way we enjoy it... I am sure the bino box is awesome.. But...

My math says that your 5 inch at 30x provides a 4.2 mm exit pupil. My 12.5 inch at 48X provides a 6.6mm exit pupil. The image in my single eye is 140% brighter than the image in your single eye.. You get 40% for using both eyes... My field of view of view is about 73% of yours..

Jon Isaacs

#13 Mr. Bill

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Posted 04 June 2013 - 11:13 PM

IMO, no RFT can match giant binoculars for viewing extemely low contrast detail in MW structure....two eyes are 40% better than one.

My 5 inch f/5.5s BinoBox is amazing at 30x and 2.2 degree fov using 24mm Pans.



We each enjoy this the way we enjoy it... I am sure the bino box is awesome.. But...

My math says that your 5 inch at 30x provides a 4.2 mm exit pupil. My 12.5 inch at 48X provides a 6.6mm exit pupil. The image in my single eye is 140% brighter than the image in your single eye.. You get 40% for using both eyes... My field of view of view is about 73% of yours..

Jon Isaacs


I find that it takes REAL dark skies to make anything over 5mm exit pupil effective....most of my observing in my green/blue backyard best seen at 4-5mm.

I found it takes Bortle Class 1 skies to appreciate 6mm ep....(when I owned Fuji 25x150 binos and observing at 10000 feet in the White Mnts.)OBTW....how big can your pupil dilate...a full 6.6 mm?? Otherwise, it's wasted.

I find two-eyed viewing to be much more relaxing than monocular regardless of the math and that goes a long way for an enjoyable observing session. I have 15 inch f/5, 10 inch f/4.7, and 6 inch f/5 at my disposal to use.

This is the Binocular forum.... :grin:

#14 Koala117

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Posted 04 June 2013 - 11:34 PM

I wanted to add this question:

two eyes are 40% better than one.


Why is it 40% as opposed to 100% better/more? I am sure you're right, as I've seen others say this on CN recently! I'm just not sure I fully understand the reason that this is the case.

Regards


information theory....the signal to noise ratio = the sq rt of the number of sensors-1.....[sq rt 2]-1 = 1.414 or 41%.


Mr.Bill,

Got it. Thanks kindly! =)

#15 RichD

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Posted 05 June 2013 - 03:37 AM

Yes, 6.6mm is really for the super dark skies only and even then I prefer 5mm.

Talking with other observers I have noticed some people don't seem to notice the huge jump in contrast that happens when I use a bino over a scope. The difference for me is very significant and is a big reason why I love binos so much.

I wonder if the binocular summation effect varies among the population. My anecdotal evidence suggests it does.

#16 GlennLeDrew

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Posted 05 June 2013 - 04:02 AM

I find binocular summation to be a most significant factor indeed. I can eak out in a 60mm bino low contrast nebulae which are seemingly invisible to users of 12" cyclopean monoscopes. Two eyes do indeed rule!

#17 Jon Isaacs

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Posted 05 June 2013 - 06:20 AM

IMO, no RFT can match giant binoculars for viewing extemely low contrast detail in MW structure....two eyes are 40% better than one.

My 5 inch f/5.5s BinoBox is amazing at 30x and 2.2 degree fov using 24mm Pans.



We each enjoy this the way we enjoy it... I am sure the bino box is awesome.. But...

My math says that your 5 inch at 30x provides a 4.2 mm exit pupil. My 12.5 inch at 48X provides a 6.6mm exit pupil. The image in my single eye is 140% brighter than the image in your single eye.. You get 40% for using both eyes... My field of view of view is about 73% of yours..

Jon Isaacs


I find that it takes REAL dark skies to make anything over 5mm exit pupil effective....most of my observing in my green/blue backyard best seen at 4-5mm.

I found it takes Bortle Class 1 skies to appreciate 6mm ep....(when I owned Fuji 25x150 binos and observing at 10000 feet in the White Mnts.)OBTW....how big can your pupil dilate...a full 6.6 mm?? Otherwise, it's wasted.

I find two-eyed viewing to be much more relaxing than monocular regardless of the math and that goes a long way for an enjoyable observing session. I have 15 inch f/5, 10 inch f/4.7, and 6 inch f/5 at my disposal to use.

This is the Binocular forum.... :grin:


As I said, I am sure your binobox is amazing and I do enjoy scanning the night sky with a variety of instruments, binoculars included. And as noted in another thread, someday I hope to build twin telescopes with 2 inch focusers, a 18 x with a 5.3 mm exit pupil and a 3.2 degree TFoV is definitely enticing.

Glenn points to seeing things in his binoculars that elude some observers with 12 inch scopes. I am sure that is true. However, I have to think that the opposite is far more common...

As far as utilizing a 6.6mm exit pupil, it does take an eye that opens that far, mine apparently do. I find that large exit pupils are particularly advantageous when using O-III, HBeta and Ultrablock filters.

Jon

#18 Michael Rapp

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Posted 05 June 2013 - 08:32 AM

Familiarization born of consistent sweeping provides the bigger picture.


There is much insight here in Glenn's statement.

I experienced this during my last visual night with the scope. I was finding objects and, sure, I knew their location in the sky from the charts and using the Telrad, but it felt a little disjointed or disconnected.

I spent last half of the night exploring the sky in binoculars and the larger field of view coupled with the relaxed viewing position really gave me that feeling that I was becoming familiar with the sky at some requisite high-level.

For example, in my mind I can visualize Perseus in fairly decent detail and I know where in the constellation some of the more interesting fields are. I don't have this same feeling with say, Scorpius, even though I have logged far more objects in the telescope in that constellation than Perseus.

#19 Mr. Bill

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Posted 05 June 2013 - 02:20 PM

I have a pair of TV 32mm Plossels that I occasionally use with the BinoBox, but the 5.8mm ep really washes out the contrast under anything but the darkest skies.

As far as filters, the added contrast of bino viewing makes their use unnecessary most of the time.

Last night I observed the Cocoon nebula (a notorious low contrast object) with the 24 Pans unfiltered quite easily.

#20 Jon Isaacs

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Posted 05 June 2013 - 03:04 PM

I have a pair of TV 32mm Plossels that I occasionally use with the BinoBox, but the 5.8mm ep really washes out the contrast under anything but the darkest skies.

As far as filters, the added contrast of bino viewing makes their use unnecessary most of the time.

Last night I observed the Cocoon nebula (a notorious low contrast object) with the 24 Pans unfiltered quite easily.


A few comments:

- Contrast is independent of the exit pupil..

- I typically observe the cocoon nubula unfiltered but filters really do increase the contrast by large factors for those nebulae that primarily emit in narrow band.

- This is the binocular forum. I enjoy scanning the Milky Way with a variety of instruments that include both binoculars and telescopes. Enough has been said.. it's best to leave it at that.

Jon






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