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First light with 16mm Nagler Type 5's (2)

Started by tomhole, 07/06/2003 02:53AM
Posted 07/06/2003 02:53AM Opening Post
With respect to the Naglers, I'm getting a pair. I know that binos make less expensive ep's better. I have been using plossls for the last 3 weeks. They do look good in the binos. But, the Naglers are in another league. I felt the difference between the Nagler view and the plossl view was as dramatic as it is in cyclops mode. That tack sharp, 82 deg AFOV is simply remarkable in the binoviewers. I could not get the entire FOV at once with the Naglers in cyclops. I could with the binoviewers. One big round field of stars. So, I'm gonna stray from the pack a bit and say that the Naglers are worth the $$$ for the added performance. THe same benefits that binoviewers afford plossls are afforded the Naglers, and the Naglers win.

With respect to the brightness and sharpness, I don't think I've discovered anything new. This has been my experience all along with the binoviewers. The image is slightly softer and noticeably dimmer. I thought it might be the extra glass that I was using to get to high powers, but I saw the same thing at 150x with just the 2x corrector on the binos.

I might still find myself in cyclops mode when I am at a dark sight and want everything I can get wrt to light throughput and sharpness on DSOs. But for right now, I can't stand to look at anything with one eye, so I may just end up with a bigger telescope.

The end.

Posted 07/06/2003 11:29AM #1
Hi Tom,

That pretty much agrees with the experience I have had with my 9NT6's (71x, 1.15°) with one exception. I cannot see the full 82° AFOV with direct vision in two-eyed mode, while I can see it in "cyclops" mode because I can turn my head that extra bit relative to the EP.

Have you accurately measured the fields you are seeing? I used both the drift method and pairs of objects spaced just inside my calculated TFOV. In both cases I had to be looking straight ahead and use peripheral vision to pick up objects at the field edges when using both eyes.

This has also been discussed over on the Astro Binoculars forum, and the general consensus seems to be that most two-eyed observers can only see 65°-70° with direct vision.

Still love those Naglers,

Posted 07/06/2003 01:26PM #2
Hi Tom,

"brightness" and lightloss has been a subject of contention using binos. Just last week at RASC Vancouver Jack Newton was asked about light loss through binos, and he shot back " There is no effective light loss through binos...", and implied that two eyes receiving data resulted in an effectively brighter image, independent of any light loss through the optic chain of the bino. ( I.E. you've got twice the rods/cones picking up twice the hits of a single eye, even if 15% more light is coming through the single eyepiece, you've got 200% of the the receptors to get hit! )

Empirically, this is what some other folk are seeing and claiming! ( Weird, huh? )

This also matched my experiences ( using Siebert 2" ) in that the "light loss" after hours of testing seemed to be darker, more contrasty images due to the higher power magnification. The problem was that more, and fainter stars, were visible through the bino than through the eyepiece itself... that wouldn't imply reduced light through the binos?

Surprisingly, I've also noticed a "weak eye" effect with some people trying out the bino. They really aren't seeing bino, one eye was taking precedence and they see a darker, fainter image..tricky! This apparently isn't the same as daytime binocular viewing!

Another use case I've run into: after a lot of work, a visiting viewer will suddenly go "OH!".. they twisted their head, or angled differently, or somthing.. the image gets brighter, and they REALLY bino. I tested this by asking them to close one eye, and then the other... and they said one view was entirely BLACK! It turned out that they didn't know what to expect and assumed everything was fine, cuz they could "see" something.

Yet another cause of "faintness" is something out of whack with the light chain... a filter not screwed on with planes parallel and tight... a diagonal not collimated dead on with the binoviewer...

I now make it a habit to periodically close one eye and then the other to make sure I'm really binoing, if the image is fainter than I expected.

Or was it an increase in contrast afforded by two eyes and the bino? Or the increased magnification bring out better contrast and the fainter stars ( like trying to pick up the central star on the Ring with higher magnification? ).

Unfortunately, I've yet to figure out a good test for this. Sensors based on % throughput through each eyepiece and adding 'em together doesn't correctly mimic the EYES, in that they are the weak link in the chain?

And Testing equal magnification doesn't seem possible without screwing up the test, since I'd have to use different eyepieces of different focal lengths to compare ( ie. a Single of one high powered eyepiece, vs 2 of a lower powered eyepiece using the binoviewer. ). Apples to Oranges.

When I get totally confused about this, fortunately I can just pop out the binoviewer and just enjoy the view!