Is Extra Low Dispersion Glass worth the extra cost?

Today’s question comes from someone wanting to find out if their money is being well spent on binoculars that use ED Glass (Extra Low Dispersion Glass):

Question

I have read your reviews and all your notes on the web page and spend hours searching for a suitable and not least affordable binocular… I know a LOT ! about binoculars by now. I am intereste din the Barr & Stroud Savannah 8x42, however, how much better can I expect the ED version to be, compared to the regular Savannah model? Is it worth the money and the waiting for the ED verison? This is my first time buying a binocular and I have no clue. There are no shops dealing B&S in my town, so I have no option to try before purchasing. Can any one help?

Answer

Not so long ago ED glass was the domain of the super binocular, reserved for only the very best and most expensive binoculars, but now it seems that every other binocular that I review uses Extra Low Dispersion Glass and whilst they are still more expensive than the equivalent standard glass versions, the price has been coming down.

What does ED glass do?
The illustration above used by Vanguard shows basically what ED extra low dispersion glass (ED glass) does – Compared to standard glass, it gives the designer of a multi-element objective lens a wider range of options with which to control and minimise aberrations, especially chromatic aberration or colour fringing as it is sometimes called by concentrating and directing the wavelength of light more effectively towards your eyes.

What is Chromatic Aberration (Colour Fringing)
Chromatic Aberration is the failure of a lens to focus all the colours onto the same convergence point and it results in the edges of an image being slightly blurred and what you see through your optics is very well demonstrated on the image of the dove on the right.

The amount of Chromatic Aberration or Colour Fringing that you get on standard glass binoculars depends on the dispersion of the glass. Good quality standard glass binoculars will still usually use high quality “standard” glass and coatings and the amount of colour fringing will be very minimal. In these cases, it can actually be quite difficult to see any colour fringing even when you are looking for it – but if you carefully look around the edges of light coloured object that should have sharp edges against a dark background it will become noticeable, but you would generally not notice this when using your binoculars normally and not thinking about it. Colour Fringing is much easier to notice on cheaper binoculars that use poor quality glass with high dispersion.

To make things even more complicated, I have seen chromatic aberration on binoculars using ED glass but it has never been bad and only really noticeable when you are really looking for it.

I would go on to say that ED Glass does make a difference, but the amount of difference depends on the quality of binocular that you are comparing them against and you would only probably notice it, if you were to first look through a binocular that had very bad colour fringing and then look through the ED Binocular.

So is preventing colour fringing worth the extra cost of ED Glass?
Answering this question is a hard one and will depend on what you think is a lot of money and just how much importance you put down to getting the best possible view.

I think my general advice would be as always: Stay away from very cheap optics and get the best quality binocular that you can comfortably afford.

Being more specific and returning to your question on the Barr & Stroud Savannah Binoculars – The amount of colour fringing on the standard version was very minimal, whilst almost non existent on the ED version. On both you can only really notice it if you are actually looking for it and so won’t annoy you when using your binoculars normally.

So get the standard version if the amount of money you save is important to you, or get the ED version if you want the satisfaction of knowing that chromatic aberration has been reduced and therefore the quality of your view has improved.

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