Contrast, brightness and vision - reality or optic

A question for those optical and vision experts out there . . .

I am an experienced observer and generally used Ultima eyepieces and an Ultima barlow for my planetary observing in my 6" f/5 Newt and 8" SCT. Thanks to another great Astromarter, I acquired a Televue 2.5x barlow several weeks ago for a head-to-head comparison test. Over the past two weeks, I have done side-by-side comparisons between the Ultima & Televue barlows at identical magnifications.

As has been noted many times on this forum and in reviews, both barlows performed well with excellent contrast. The Ultima is a little dimmer and imparts a slight tan tint, and the Televue brighter and truer in color - maybe even sharper.

Here's the pickle . . . brighter, truer and sharper means better, right? That's why Televue barlows are so highly lauded. So how come I feel that I can see "more" using the Ultima? It seems that with the slightly darker and tanner tint of the Ultima, I can actually see finer planetary detail, particularly in Jupiter's cloud bands, the GSR and Saturn's subtle banding.

Frankly, I've noticed the same thing when I have used orthos - they are sharper, truer in color and brighter, but I can see more detail in the slightly dimmer and tinted Ultimas and Lanthanums.

So, I'm confused. How can dimmer and tinted beat out truer, brighter and better contrast? Is this an optical illusion, a comfort factor or something that is perhaps unique to my eye's color receptors? I'd be curious as to others' experiences and insight.

First perhaps it might be helpful to point out that all conventional Barlows are variable to some extent, and the 2x Ultima Barlow is biased towards higher magnification (up to 2.2x in common practice). The point is that ensuring equal magnification requires some effort to achieve.

Secondly, what is "bright"? I mean this as a rhetorical question. Eyepieces do not transmit all frequencies of light evenly, so every eyepiece is at least a weak color filter. The eye is not very sensitive to blue, but eyepieces that transmit more blue/violet than yellow/red appear whiter, and in laboratory experiments I think it is very likely you could fool people into thinking that a dimmer view was the brighter one by manipulating the spectrum just a little bit if the difference in overall brightness was not large. For some reason, the view in Tele Vue eyepieces appear a little yellowish compared to eyepieces such as UO Konigs and orthos. Frequently this is intepreted as a brightness issue, but I suspect the transmission in the critical green area of the spectrum is on a par, and even if the Tele Vue eyepieces are disadvantaged in the blue/violet end of the spectrum somewhere, these frequencies are not very useful scotopically, anyway.

Peter,

Can you see any baffles inside the barlows? Is blackening equally good? Scattered light can reduce contrast without reducing brightness.

Dmitri

Peter, check out the article on planetary eyepieces on Cloudy Nights web-page. I've noticed the same thing concerning the TV/Ultima barlows that you have. the Cloudy Nights article points out that eyepieces (or barlows, for that matter) that have a slightly "warmer" tone can actually help make out details in the Jovian cloud bands, whereas eyepieces with a "cooler" tone give the same cloud bands a more bleached-out look. Hope this helps!
Larry Seguin
Taos, New Mexico

I've also found that Jupiter often benefits from a neutral-density filter -- maybe the 'darker' barlow has a similar effect: reducing glare, to the benefit of contrast. Jupiter would particularly benefit from this, being a rather bright, white, planet.

At 2.5X, do you mean a TV "Barlow lens" or the TV Powermate?? The Powermate is a large step ahead of "barlows" and I understand it works differently. I have owned and used/tested a 2X TV barlow, Celestron Ultima, Meade 140 "Apo" Barlow (junk) and a 2.5X Powermate. Of the Barlow lenses, the Celestron Ultima was by far the best in about 6 different scopes with 6-8 eyepieces tried.

The Powermate, however, had them all beat hands down for sharpness, contrast and anything else you could look for. Could even use it with long FL, wide-field eyepieces with no loss or darkening at the edges.

I kept and used the 2.5X Powermate and it was excellent with any eyepiece. If TV makes a 2.5X Barlow, it must have been discontinued since I can't find one listed on dealer sites, just the Powermate.

When I do the acceptance tests on the mirrors for VERITAS we use a white beam light source the passes through a variable narrow band filter and then onto a optical head that sends the beam down to the mirror surface. This head also contains a detector that converts the reflected light into millivolts that can be read on a voltmeter. We step through a light range from 260 to 700.

I wish that all optical components had to go through this test. Besides reflectivity for mirrors, it could also measure transmission for eyepieces. We then would be rid of a lot of the subjective B.S. that goes along with much of the amateur optical accoutrements of the hobby.

Darrell