More contrast with ED scopes? (1 Viewer)

[Hermann]

All else being equal there is no perceptible difference in surface colour rendition between ED and non-ED glass.

Not sure there, John. I found rather clear differences in colour rendition when comparing e.g. two Nikons (non-ED 60mm vs. ED), two Leicas (Televid vs. Apo-Televid) and few Kowas (TSN2 vs. a TSN4, 611 vs. 613).

The non-ED scopes always looked "flatter", in any kind of light, with less saturated colours. They also looked somewhat softer in direct comparison, even at lowish magnifications.

Hermann

 

[Tringa45]

Not sure there, John. I found rather clear differences in colour rendition when comparing e.g. two Nikons (non-ED 60mm vs. ED), two Leicas (Televid vs. Apo-Televid) and few Kowas (TSN2 vs. a TSN4, 611 vs. 613).

The non-ED scopes always looked "flatter", in any kind of light, with less saturated colours. They also looked somewhat softer in direct comparison, even at lowish magnifications.

Hermann

Hermann,
Perhaps I didn't express myself clearly.
What I meant was that one would unlikely be able to see any difference in colour rendition between ED and non-ED if the scope or binocular were directed at a uniform coloured surface, i.e little difference in spectral transmission.

John

 

[John goshawk]

I would have thought better contrast, means better colour saturation, which means purer colour.
I'm with Nethero on this one

 

[Tringa45]

I would have thought better contrast, means better colour saturation, which means purer colour.
I'm with Nethero on this one

On a uniform surface there can be by definition no contrast and there was a suggestion in post #17 that ED glass would somehow show "whiter" whites.
Non-ED glass will cause longitudinal CA and blur surface boundaries, i.e. result in a loss of contrast.

John

 

[Binastro]

I am not sure about this.

But consider a white background to be made of hundreds of thin white lines joined together.

With a short focus doublet that has chromatic aberration, each white line probably displays some false colour, which may mean the whole white background is not pure white.

With my Jaegers 123mm f/5.15 doublet refractor I tried to make intensity estimates on Saturn.
I could do this but the results were not very accurate and did not have the reliability of a planetary telescope.

With faint objects false colour is not a problem with this telescope.

In my opinion ED short focus scopes show whiter whites and have better contrast.

With a long focus doublet, say an 80mm f/15 false colour doesn't show.

With my Ross 100mm f/15 triplet the lack of false colour was disturbing for me, as it did not look like a refractor image, being totally false colour free.

I am told by somebody who probably knows, that even Newtonians have some false colour, but I cannot remember his explanation.

Regards,
B.

 

[John goshawk]

Agree with above.
I wouldn't association colour fringing too much with contrast loss. I would perhaps associate that more with a loss of sharpness.
ED scopes have more colour saturation and therefore whites are whiter in my experience. More colour saturation means more contrast.
Newtonians do have a very small amount of CA

John

 

[Tringa45]

But consider a white background to be made of hundreds of thin white lines joined together..

White lines on what background?
If of even spacing and thin enough, then the CA would merge to appear white again just like the red, green and blue pixels of a TFT merge to appear white.
The brightness would of course suffer due to the reduction in total white surface area.

Regards,
John

 

[Tringa45]

I wouldn't association colour fringing too much with contrast loss. I would perhaps associate that more with a loss of sharpness.

That is a contradiction. There can be no sharpness without contrast.
Chromatic and spherical aberrations will blur image boundaries and other aberrations will contribute to that off-axis.
I have conducted resolution measurements on my scopes using a backlit 1951 USAF glass slide. With increasing frequency (reduced spacing of the line pairs) the contrast diminishes until one only sees a grey blur.
With its standard eyepiece at maximum magnification the resolution of a good scope would exceed that of almost all viewers except those with oustanding eyesight.
I used a 3,5 mm astronomical eyepiece for 140x on my 88 mm Kowa and 130x on my 65 mm Swarovski. At 23 m distance the last elements where I could detect separation were 6,35 line pairs /mm with the Kowa and 5,04 line pairs/mm with the little Swarovski.

John

PS:- 6,35 lp/mm is a line width of 79 µm and 5,04 lp/mm a line width of 99 µm!

 

[jring]

Hi,

longitudinal CA is not color fringing. I means that different colors come to focus at different distances from the objective - thus there is no best focus point for the whole picture but rather different ones for different colors. This means, the whole image is a bit soft and you cannot really find a point of best focus - which is typical for very fast refractors at higher magnification.

I think the different color renditions of different optics are more due to the different coatings...

Joachim

 

[Tringa45]

I think the different color renditions of different optics are more due to the different coatings...

Hi Joachim,
Agreed on the influence of coatings, particularly the mirror coatings on S-P prisms, though they are seldom used nowadays on straight scopes.
Glass material may even have some influence where glass paths are long as in prisms. The transmission of BaK4 is not very good at the blue end of the spectrum.
As regards colour fringing, here are some interesting depictions in Henry Link's 2014 test of the Zeiss 8x54 HT:- Tests of the Zeiss 8x54 HT.
In post #4 lateral colour near the cetre of field can be seen, which is pretty catastrophic.
In post #16 there is uniform green fringing in the centre, which Henry interpreted as spherochromatism.

John

 

[John goshawk]

In my opinion a slight blurring of image boundaries isn't the biggest cause of contrast lost, especially not at low magnifications.
That is just my opinion and the real answer to contrast loss with non ED glass may lie in quantum physics.

Believe it or not, I do have a right to my own opinion.

 

[Hermann]

In my opinion a slight blurring of image boundaries isn't the biggest cause of contrast lost, especially not at low magnifications.
That is just my opinion and the real answer to contrast loss with non ED glass may lie in quantum physics.

Can you please explain why and how quantum physics may explain the contrast loss with non-ED glass? Thank you.

Believe it or not, I do have a right to my own opinion.

You sure do, but it always helps if someone can explain how he/she arrived at that opinion.

Hermann

 

[John goshawk]

I arrive at my opinion through observation and experience. In the same way I can easily tell the difference between a chiffchaff and a willow warbler.

 

[John goshawk]

Furthermore I find a recent private message I come home to by someone above quite disturbing .
A horrible thing to receive after spending most of the day birdwatching, with a very dear friend who has very poor health due to advanced dementia.
Just trying to have an interesting discussion. I don't have any fixed views on this topic. I have an open mind.
But I'm hardly going to listen to people who can't show basic respect.

 

[tenex]

Is the chroma aberration not very local/fringing.How does it spread throughout the entire white area.
This was actually the point of my question.

Does it at all? Let's get back to this. Whether ED glass improves contrast depends on what you mean by "contrast". It should improve fine detail and edge definition. But as John said it's not going to affect overall color, so those talking about the creaminess of white or overall contrast are referring to something else, likely resulting from a difference in coatings. And when comparing scopes, more expensive ED models will tend also to have better coatings. So we need to get clear on what's the result of ED glass and what's not, in a complex optical system.

 

[John goshawk]

My friend is letting me borrow his opticron HD66. Exact model/year as my own HD66 ED. There is a white wall opposite my house.
I will do some comparisons on this and other locations. Like I say I have an open mind.
There is a likelihood that the final image at the focal plane of a spotting scope is effected by every point of focused light/airy disc. It is a cumulative effect - hence the influence of quantum physics. This is true for Newtonians, however not entirely sure if is true for refractors.

 

[Hermann]

Does it at all? Let's get back to this. Whether ED glass improves contrast depends on what you mean by "contrast". It should improve fine detail and edge definition. But as John said it's not going to affect overall color, so those talking about the creaminess of white or overall contrast are referring to something else, likely resulting from a difference in coatings.

Agreed.

And when comparing scopes, more expensive ED models will tend also to have better coatings. So we need to get clear on what's the result of ED glass and what's not, in a complex optical system.

Well, yes. Probably, even though it's probably more costly to set up different coating runs for different lines of scopes. Probably more efficient to use the same process for everything (provided the glass types can be coated in the same way). But then you never know what the manufacturers do, especially not those somewhere in China.

In my comparisons I referred to scopes made by the same manufacturers at the same time (Nikon IIA and the EDIIA, the two 77mm Kowas and the two Leicas). I think that's a more valid basis for comparison than comparing totally different scopes when trying to see what difference ED glass makes, especially because these are well-known, "good" manufacturers.

Hermann

 

[tenex]

In my comparisons I referred to scopes made by the same manufacturers at the same time...

Yes, I did notice that. As you say, we don't know whether they differ only in the presence of ED glass in the objective, and thus what comparisons of overall contrast between them mean.

There is a likelihood that the final image at the focal plane of a spotting scope is effected by every point of focused light/airy disc.

I can't understand what you said here or how it applies, which makes me fairly sure that you don't either. But if it helps, consider that false color would not make white objects look "creamy". And if some sort of mysterious blending were going on, their color cast would vary depending on other colors in the field.

 

[John goshawk]

I can't understand what you said here or how it applies, which makes me fairly sure that you don't either

Why you being so rude? Would you say that if you sat opposite me?

 

[John goshawk]

I've given up with this website. There is some clever people here that could help me with developments of my theory. And I could help you.
However as soon as you engage in an indepth discussion you get your intelligence insulted straight off. Or something jumps down your throat with a wild assumption that you are making something up. Or you get abusive messages for daring to think out the box for one second.
How are we going to advance our learning if we don't firstly understand the concept of respect?