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Teaser: The tension in the air is palpable.

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#51 GlennLeDrew

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Posted 05 February 2019 - 05:10 PM

Back in the late '90s I simply taped 2" UHC filters to a 10X50. The views of the larger emission nebulae were wonderful.

 

For folk who suffer heftier dew and frost, dew caps would be mandatory for more extensive viewing sessions. A reasonably snug slip fit over the exterior of the adapter, with an internal stop that is intercepted by the adapter's forward face, would be simple enough to make. Even a user-made craft foam thingie is more than sufficient.


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#52 paulh83

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Posted 05 February 2019 - 05:32 PM

Jim,

 

The sky is starting to clear down south of you. Hopefully, you will get a chance to use them tonight or tomorrow. Looking forward to your report. I might just have 2 OIII filters and the Fuji 10x50s to go with them. Glad I kept that second OIII filter....

 

Paul  


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#53 jrbarnett

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Posted 05 February 2019 - 08:39 PM

Jim,

 

The sky is starting to clear down south of you. Hopefully, you will get a chance to use them tonight or tomorrow. Looking forward to your report. I might just have 2 OIII filters and the Fuji 10x50s to go with them. Glad I kept that second OIII filter....

 

Paul  

Thanks Paul.

 

I've been onboarding a new employee and otherwise in meetings all day today at work, looking outside at crisp, clean, (cold), blue skies.  Now that I am winding up work for the day, I look outside and it's still clear (shockingly).  I think these adapter with filters will be soooooooo good, that it'll be cloudy by the time I get home.  :)

 

Best,

 

Jim



#54 jrbarnett

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Posted 05 February 2019 - 08:44 PM

Back in the late '90s I simply taped 2" UHC filters to a 10X50. The views of the larger emission nebulae were wonderful.

 

For folk who suffer heftier dew and frost, dew caps would be mandatory for more extensive viewing sessions. A reasonably snug slip fit over the exterior of the adapter, with an internal stop that is intercepted by the adapter's forward face, would be simple enough to make. Even a user-made craft foam thingie is more than sufficient.

Justin (CNer Enkidu) made a great observation.  With the filters installed on the sky side (rather than the objective side) of the adapter, there are female threads exposed on the filter itself.  The nosepiece from a cheap 2" diagonal or cheap 2" eyepiece will thread right into the filter creating a dew shade.  I have a GSO SCT diagonal for which I have the optional very lightweight aluminum "refractor" nosepiece.  I may just order a second GSO refractor noesepiece and, viola, have lightweight dew shades for the filters.  I'm just wondering how long is too long (i.e., will these shades vignette the FOV)?

 

Best,

 

Jim



#55 jrbarnett

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Posted 05 February 2019 - 10:42 PM

I have clear skies.

 

I have a couple of hours of family stuff to do, but after they're all abed I should get a wonderful first light opportunity.  In addition to the obvious choice, M42/43, I'm thinking Rosette and Cone.

 

- Jim


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#56 jrbarnett

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Posted 06 February 2019 - 03:02 AM

Hmm...

 

Bracing and clear.  Aculon 7x35s, Wild Man adapter prototypes and matched Orion Skyglow 2" filters.

 

I was out for almost an hour.  It was quite cold (for here at any rate) at 31F.   I used the filtered Aculons reclined in a zero gravity chair.  I also had the unfiltered 7x35 Action EXs on hand for comparison of filtered vs unfiltered views.

 

Preliminarily I'll say this.  The Skyglow filters do pass a fair amount of light.  I saw lots of stars and the adverse impact to my limiting magnitude was less than I expected.  I'd say the filter eliminated a full magnitude or a bit more when compared to the unfiltered binoculars.  Still the stellar context was pretty and rich.  This is a good thing.  The filters clearly suppressed sky glow that was seen in the unfiltered views, which is also good.

 

I do NOT like the blue-green hue applied to all stars by the filters however.  And the Oliphant in the room is whether nebular targets were enhanced enough to make the hue issue and dimming issue "worth it".  Limiting my review to these particular filters, I am on the fence.  For very bright nebulae like M42, the filtered view had slightly higher contrast making the wings slightly more defined than unfiltered.  But I think the unfiltered view was livelier (there are a lot of bright stars in the belt region, and those looked better in the naked binoculars).  I actually preferred the unfiltered views of M42.

 

Moving to the Christmas Tree/Cone complex, obviously no "cone" feature (it takes a 12" from my backyard to get a hint of the actual cone feature), but the contrast improvement of the filtered view vs. unfiltered did make the nebulosity involving the cluster slightly easier to see at the expense of making the cluster itself less engaging and less rich.  The filters mattered more on this target than on M42.  Moving then to the Rosette, the experience was similar to the Christmas Tree, but due to a greater uniformity of magnitudes in the central cluster the dimming was less objectionable.  That is even though fewer stars were seen filtered than unfiltered, the clusterretained it's basic shape and identity better than did the disparate brightness stars of the Chrstmas Tree cluster.  The Rosette nebulosity was enhanced by the filters again only slightly.  I did prefer the filtered view of the Rosette to the unfiltered.  Of the three targets for the session, this is the only target where I felt the Skyglows were "worth it".

 

But this is only the beginning.  My gut feel is that a bit more aperture would help.  I also have a suspicion that less gentle narrower filters might do better on the strictly nebular aspects of these targets even at the small aperture of 35mm.  The other thing I want to try, given that my two eyes are mismatched, is to use just one filter (I'll try Skyglow, UHC and OIII) and try the single filter approach on each eye.  My right is astigmatic but brighter.  My left is much better but a bit dimmer.  I would also like to try mixing filters (example UHC right and Skyglow left).  I also want to move to a proper mount rather than using them handheld and reclined.

 

I'll reserve pursuit of the 50mm project for about a month, pending the outcome of more use of the 35mms filtered.

 

Best,

 

Jim   


Edited by jrbarnett, 06 February 2019 - 11:37 AM.

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#57 GlennLeDrew

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Posted 06 February 2019 - 04:13 AM

While we naturally desire to maximize light across the full field, the vignetting induced by even a 'skinny' dew shield of I.D. equal to the objective is less than one might surmise. And that includes wider bino TFoVs.

 

An example. Consider a 50mm bino delivering a 10 degree TFoV. Further, it offers the amazing characteristic of full illumination to the field edge. That is, it suffers no intrinsic vignetting. (Note that many real world binos have edge-of-field illumination in the range of 50-70%.)

 

Suppose a dew shield of 50mm I.D. is installed. How long must it be in order to reduce edge-of-field light to 50%?

 

The bino's semi field angle is 5 degrees, and objective semi diameter is 25mm. To a first approximation, half the light is clipped when the shadow of the front lip of the dew shield creeps inward to the objective center. This point is reached when the dew shield length equals

 

25mm / TAN(5)

= 25mm / 0.0875

= 286mm

 

That's 11-1/4 inches, or a bit more than 5.5 objective diameters. When the shield is of the (minimalist) same diameter as the objective, no less!

 

And because the typical bino already suffers mechanical vignetting, the *relative* contribution by our skinny dew shield is even less than it would be for a vignetting-free instrument.

 

Indeed, such 'excessively' long dew shields offer the signal benefit of more aggressive interception of out-of-field light. Particularly when the shield is not itself a source of scatter/reflection. A coating of fine sawdust, sealed and blackened with flat black paint, serves nicely. Or the shield can be increased in diameter, with a number of ring baffles installed. Why, a sufficiently long shield could intercept much or all of that light contributing to the false pupil segments, or 'fingernails, which bracket the principal exit pupil.

 

If such a measure were to realize tangible benefits as regards reduced intrusion of unwanted light, the payment exacted in the form of reduced outer field illumination would be worthwhile.

 

Contrast beats brightness! And besides, the central field brightness is never reduced, no matter how long the dew/light shield. Of course, some care in alignment of very long dew shields is warranted, else the region of full (or maximal) brightness moves off-axis.


Edited by GlennLeDrew, 06 February 2019 - 04:19 AM.

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#58 jrbarnett

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Posted 06 February 2019 - 11:38 AM

While we naturally desire to maximize light across the full field, the vignetting induced by even a 'skinny' dew shield of I.D. equal to the objective is less than one might surmise. And that includes wider bino TFoVs.

 

An example. Consider a 50mm bino delivering a 10 degree TFoV. Further, it offers the amazing characteristic of full illumination to the field edge. That is, it suffers no intrinsic vignetting. (Note that many real world binos have edge-of-field illumination in the range of 50-70%.)

 

Suppose a dew shield of 50mm I.D. is installed. How long must it be in order to reduce edge-of-field light to 50%?

 

The bino's semi field angle is 5 degrees, and objective semi diameter is 25mm. To a first approximation, half the light is clipped when the shadow of the front lip of the dew shield creeps inward to the objective center. This point is reached when the dew shield length equals

 

25mm / TAN(5)

= 25mm / 0.0875

= 286mm

 

That's 11-1/4 inches, or a bit more than 5.5 objective diameters. When the shield is of the (minimalist) same diameter as the objective, no less!

 

And because the typical bino already suffers mechanical vignetting, the *relative* contribution by our skinny dew shield is even less than it would be for a vignetting-free instrument.

 

Indeed, such 'excessively' long dew shields offer the signal benefit of more aggressive interception of out-of-field light. Particularly when the shield is not itself a source of scatter/reflection. A coating of fine sawdust, sealed and blackened with flat black paint, serves nicely. Or the shield can be increased in diameter, with a number of ring baffles installed. Why, a sufficiently long shield could intercept much or all of that light contributing to the false pupil segments, or 'fingernails, which bracket the principal exit pupil.

 

If such a measure were to realize tangible benefits as regards reduced intrusion of unwanted light, the payment exacted in the form of reduced outer field illumination would be worthwhile.

 

Contrast beats brightness! And besides, the central field brightness is never reduced, no matter how long the dew/light shield. Of course, some care in alignment of very long dew shields is warranted, else the region of full (or maximal) brightness moves off-axis.

Thank you Glenn.  Very clear and it makes perfect sense when you lay it out so clearly.

 

Regards,

 

Jim



#59 jrbarnett

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Posted 10 February 2019 - 10:52 AM

Still waiting for a break to try some different filters, mixed filters, filtered/unfiltered eyes, etc.  It rained much of the night and when we gt up this morning we were greeted by snow across the valley on Sonoma Mountain (it's not really a mountain, it's a "hill").  The snow line looks to be only about 50-100 feet above our elevation on the hill on the opposite side of the valley.

 

But unlike yesterday this morning I see a mix of clouds and sun.  I would like to set up my observing table and lay out my filters in the order I'd like to test them with the adapters, but I'm sure  being so defiant in the face of the weather deities would trigger swift retribution - a hail storm, localized "sun" shower or similar.  :grin:

 

Justin's adapters have enjoyed an unexpected  Caribbean holiday.  From Miami they traveled parts of the Caribbean, vising Jamaica, before making their way back to the continental US to a logical transoceanic flight departure point en route to the Netherlands.  Very odd these logistics companies.

 

Best,

 

Jim



#60 Crow Haven

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Posted 10 February 2019 - 02:03 PM

My namesake winter storm hasn't made for any observations here other than the rare snowy kind...

--kitchen window view up to the observatory for the last few days--

Hope you have better weather soon.

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#61 charlesgeiger

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Posted 12 February 2019 - 02:10 AM

I suppose it doesn't matter much weight wise but couldn't the adapter be made of delrin , ABS or PVC?...I know threading the filters in plastic might be problematic after several uses.  The adapters appear to be aluminum and 'thick' but I would think that custom dew shields could be made of the same material, fit over the adapters, possibly again with compression fittings?  So one would take the adapters, screw in the filters, and then slide over the adapters with compression fitting....then attach to binoculars...so you have both adapters and dew shields from same manufacturer.  Just a thought.  Metal is probably the best substrate but the same idea...

Charlie


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#62 PJ Anway

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Posted 12 February 2019 - 06:20 AM

I suppose it doesn't matter much weight wise but couldn't the adapter be made of delrin , ABS or PVC?...I know threading the filters in plastic might be problematic after several uses.  The adapters appear to be aluminum and 'thick' but I would think that custom dew shields could be made of the same material, fit over the adapters, possibly again with compression fittings?  So one would take the adapters, screw in the filters, and then slide over the adapters with compression fitting....then attach to binoculars...so you have both adapters and dew shields from same manufacturer.  Just a thought.  Metal is probably the best substrate but the same idea...

Charlie

I agree. When I made a set of filter adapters for my 10x50's out of Delrin, I press-fitted aluminum threaded inserts. This works well (I suspect much better than threading the Delrin) and they are very light.

 

DelrinAdapters.jpg


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#63 terraclarke

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Posted 12 February 2019 - 10:25 AM

Thanks for the tip on the Optolong filters Simon.
 
I like these super-gentle light pollution filters in 77mm.
 
https://www.optolong...lear-sky-filter
 
It sounds like they'd produce relatively natural coloration but also very effectively eliminate the streetlight bands.
 
They'd be adaptable for 70mm or 80mm (if you don't mind losing a little aperture) binoculars pretty easily.
 
Best,
 
Jim


Sorry for being late to the party but I’ve been thinking along similar lines. I’m strongly considering ordering the Oberwerk 20 x 65ED binoculars and have been mulling over ways of blocking extraneous light and reducing skyglow whilst using them in my urban backward. I really like the idea of these Optilong 77mm skyglow filters and the really nice thing is that since they are a standard camera lens size, you can get standard photo lens hoods that thread into the front of the filter ring. I really like these metal ones from eBay and they are quite reasonable:

https://www.ebay.com...741bb76fff07e81
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#64 Loren Toole

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Posted 13 February 2019 - 09:51 PM

Jim

I've tried a variant of your original idea, use a filter only on the tube that is seen by

your dominant eye. The other tube is unfiltered, so there's brain processing going on

that reduces the coloring and odd light intensities resulting from filtering on one side.

I predict you'll like this combination as opposed to filtering both tubes.

 

I am not convinced this yields spectacular improvements in objects but it does yield

a reduction in LP and modest contrast gain.  I haven't done much filtering because

I lacked a practical filter holder, in fact I used a wide rubber band on my 8x40s, this

works (just barely) to hold the 2" filter.

 

Loren


Edited by Loren Toole, 13 February 2019 - 09:52 PM.

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