Hi
Joachim's advice is spot on. Most binos show some colour fringes (chromatic aberration) especially towards the edge of the field of view.
Binos are designed to be looked through the dead centre of the optical tubes and this is called the optical axis. Setting the distance between the eyepieces is therefore important. Measuring your IPD is one way to do it, another is to remember that the field of view should be perfectly round so if it is oval (ie narrow either side to side or narrow top to bottom) you need to adjust the binos until it is circular.
Bear in mind too that CA can be made worse if the binos are not fully focussed. The out of focus blur that affects the whole view also 'spreads' the CA a bit too and makes it look bigger than it really is.
Some people are very prone to noticeing CA and can hate it so much they don't enjoy binos that even have a hint of it near the edges of the fov. Lets hope you are not one of these, but if it turns out you are then binos like Zeiss's FLs (still available as 32mm) or Kowa's Genesis models are outstanding performers in this regard.
Lee
This thread isn’t very long but it’s already shown me the 2nd edition of BINOCULARS: ... needs to give more space to the discussion of aberrations. Here, I would like to address the thread as a whole. I will start with a bold statement followed with a few particulars. Cutting to the chase by nature, I’m often taken as being mean spirited. I assure all that is NOT my intention. I just believe getting to the punchline in short order, on certain subjects, is the best thing for all concerned.
Although the thread can create valuable camaraderie and nudge some observers into bettering their view of nature, overall, participating in it, is as productive as rearranging deck chairs on
Titanic. Unless one has the power to change physics, nothing short of buying a better binocular is going to solve the problem of chromatic aberration. You may roll it around the field and the super-thoughtful and kind are remaining with those chairs to instill a touch of hope in those who are about to drown in depths of optical realities. But, that leads to considerably more flutter than flight, as it has since bino forums came into being.
Hopefully, all observers want a better view. Many, however, are not willing to do what getting to that view will take. And, if I didn’t have some fine binoculars around the house, I wouldn’t miss the boat because of WON’T but because of CAN’T. For some, it’s a matter of casual priority. For me, it would be a matter of essential priority—3 month’s groceries are simply more important to my wife and me than a new Swarovski. Also, I would love to have 100 copies of my book to sell at birding events and star parties. But, until I get my first royalty check next month, that’s not a happening thing. Thus, I understand, completely.
So, What Are the Options:
1) Install blue blocking filters somewhere along the optical path—full-aperture filters would be easiest. Just the thought of that, however, may reduce “effective aperture” enough to drive some nitnoids to distraction. And it should be understood—although it never has been—that aberrations do not exist independently. In reducing one to a tolerable amount, you may have to increase two others by a tremendous mount. Only the armchair opticians and engineers can pull off any better. The engineers at Zeiss, Leica, and Swarovski don't have the luxury of living in the make believe world that haunts so many binocular forums.
2) Buy a new binocular—one you have personally checked for chromatic aberration before putting your money on the counter.
3) Realize that the “perfect” binocular does not exist, those even getting close are cost prohibitive, and your real hobby is about BIRDS and not BINOCULARS.
Lee said:
“Binos are designed to be looked through the dead centre of the optical tubes ...”
Unlike a couple I have encountered on BF in the last few days, I feel I can trust my friend Lee to understand my motivation as I take it upon myself to temper his comment. It speaks to the SPIRIT of the matter, but not to the LETTER.
“Binos are designed in such a way as to offer the most aberration-free image when the observer has his or her eyes positioned exactly in the middle of each exit pupil, with the eyepieces—and therefore those exit pupils—positioned at the observers exact IPD. On the best models, aberrations are seldom bothersome.”
There has been a great deal of talk about the observer doing just that. But, what is great in theory may not work at all in practice. Even, if the instrument were surgically implanted on the observer’s head, there would still be too much variance in alignment to eliminate all chromatic aberration. Even by those new to observing, CA can be measured. Even if not quantifiably by micrometrics, an observer could determine, by qualitative means, what level of CA he or she could tolerate in a binocular."
The good news:
We have the ability to make a bino that is relatively free of annoying aberrations, including CA. More elements, aspheric elements, and exotic and expensive glass types make it so.
The bad news:
As optical engineering now exists, only the very wealthy could afford such a specimen. And certainly, optical companies are not going to invest in a technology that is financially doomed from the start.
More good news:
The BBC reports that Amereican scientists have some up with an array of electronic sensors that may make conventional lenses obsolete. And with that technology, I expect aberrations to largely become relics of the past, as these arrays are smaller than the sensors on the back of our retinae.
Impossible?
It is also impossible for all the books in a large metropolitan library—complete with color graphics—to fit on a wafer the size of your little fingernail crammed inside a piece of plastic the size of your little finger. But, we use them every day.
“There was a demon in memory. They said whoever challenged him would lose. Their programs would lock up, their machines would crash, and all their data would disintegrate.
"The demon lived at the hexadecimal memory address A0000, 655,360 in decimal, beyond which no more memory could be allocated. He lived behind a barrier beyond which they said no program could ever pass. They called it the 640 K barrier.” — with my apologies to The Right Stuff… :cat:
Back in my hole, now.
Bill
