A very stupid question

[spacegalaxy]

I went to Meade's site and saw Cemax eyepieces, which in their discription says that it is specifically designed for H-alpha viewing, which is also used for Nebulae, so does it improve nebulae viewing? Sorry for the really stupid question, I am new to the world of astronomy! Link: https://www.meade.com/eyepieces/solar-eyepieces/coronado-cemax-12mm-eyepiece.html

[johninderby]

They are just overpriced regular Plossl eyepieces marketed as HA eyepieces. Nothing Special. Same as regular GSO Plossl eyepieces I beleive.

You can find threads on CN about them

Edited January 30, 2022 by johninderby

[vlaiv]

It won't do much good for Ha nebula viewing.

Those eyepieces are meant for Ha solar observing where there is plenty of signal and image brightness is much higher than with nebula viewing. Magnifications are much higher - like when observing the moon and planets so it is the sharpness and contrast that is important to clearly see features on surface of the sun (but only with special filter - never turn telescope to the sun unless you have special solar filters!).

 

[vlaiv]

1 minute ago, johninderby said:

They are just overpriced regular Plossl eyepieces marketed as HA eyepieces. Nothing Special. Same as regular GSO Plossl eyepieces I beleive.

 

I think so too but description says that selected coatings are optimized for Ha usage - and that can be true as there are different types of coatings - some optimized for UV some for IR and some for visual.

for example look here: https://www.evaporatedcoatings.com/optical-coatings/ar-coatings/

you'll find several different reflectance graphs depending on type of coating applied.

[johninderby]

This thread on CN gives some interesting opinions and suggests that the Cemax eyepieces perform like a decent plossl in HA 

https://www.cloudynights.com/topic/388210-cemax-eyepieces/

[spacegalaxy]

26 minutes ago, vlaiv said:

It won't do much good for Ha nebula viewing.

Those eyepieces are meant for Ha solar observing where there is plenty of signal and image brightness is much higher than with nebula viewing. Magnifications are much higher - like when observing the moon and planets so it is the sharpness and contrast that is important to clearly see features on surface of the sun (but only with special filter - never turn telescope to the sun unless you have special solar filters!).

 

I didn't understand the difference in those two, can you explain?

[vlaiv]

31 minutes ago, spacegalaxy said:

I didn't understand the difference in those two, can you explain?

Sun is about the same size as the Moon is in the sky (apparent size). It is also extremely bright.

When you do solar Ha observing, you are in fact using extreme filtering - much more than with say Ha nebula filter. Good Ha solar filter will pass 0.5-0.7A where A is angstrom - or 0.1nm (tenth of nano meter). Ha filters for observing nebulae is usually around 7nm wide so we have one filter that passes 7nm while other has 0.07nm bandwidth - that is about x100 difference.

It has to be because sun is so bright and you can't normally observe it with a telescope unless you have some serious filtering to reduce amount of light - otherwise it can damage your eyes and cause skin burns. For that reason - never point scope to the Sun unless you have proper filter - even simple finder scope can cause serious burns.

We observe sun and moon at very high magnification - like x100 and above. This is because detail that we are interested in is often small. We can do full solar disk viewing and that is also interesting - but usually people do want to see tiny detail and use high magnification.

Nebulae are completely different. They are often much larger than the sun or moon (although there are some that are even smaller - like planetary nebulae) and they are very very faint. Using too much magnification can be counter productive - they often don't have tiny detail that can be seen and raising magnification makes view dimmer - which is problem for already dim objects.

We often use peripheral vision to observe nebulae as they are very dim and we can't see detail with peripheral vision.

What is claimed for these Cemax eyepieces is that they have special coatings that makes Ha image very sharp/high contrast at high magnifications used when viewing the sun. Not going to go into whether that is true and how much difference there is between such eyepiece and regular plossl - but thing is - what they claim happens with such eyepiece - will not affect views of nebulae because the way we observe them

- they are faint so we can't really see that much difference in contrast (there is something called JND - just noticeable difference and for humans JND for visual stimulus is about 7%-10% so we can see difference of 7% in signal strength. That is a lot of photons for bright target like sun, but that is just a few photons for dim targets like nebulae - and we can't see individual photons - there needs to be at least 7-8 photons for detection)

- we use low power to observe them - any difference in sharpness of the eyepiece is not critical at low power since we can't resolve it at low power

[Don Pensack]

I might also add to the excellent summary above that the dark-adapted eye at night (scotopic vision) does not see the H-α line in the spectrum with more than a completely minimal sensitivity, if at all.

Whereas our photopic, daylight, vison might extend from 400nm to 750nm in the spectrum, our sensitivity at night changes to primarily 425-550nm with very little vision, if any, above 600nm.

That makes the 656nm emission of the H-α wavelength pretty much outside the range of our vision.

An H-α filter can be useful for a camera, whose sensitivity extends into the infrared, but it is not a visual filter.

 

So H-α is only useful for daylight viewing of the sun through a special solar scope that confines the light coming through to an extremely narrow bandwidth of H-α light.

The Cemax eyepieces are, therefore, aimed solely at solar viewing in special H-α solar scopes.  They have been marketed as accessories for the Coronado Solar telescopes, hence the gold coloring.

 

However, in the field they perform exactly the same for astronomy as other inexpensive GSO Plössls.

For use at night, lots of other eyepieces are their equals.

[spacegalaxy]

13 hours ago, vlaiv said:

Sun is about the same size as the Moon is in the sky (apparent size). It is also extremely bright.

When you do solar Ha observing, you are in fact using extreme filtering - much more than with say Ha nebula filter. Good Ha solar filter will pass 0.5-0.7A where A is angstrom - or 0.1nm (tenth of nano meter). Ha filters for observing nebulae is usually around 7nm wide so we have one filter that passes 7nm while other has 0.07nm bandwidth - that is about x100 difference.

It has to be because sun is so bright and you can't normally observe it with a telescope unless you have some serious filtering to reduce amount of light - otherwise it can damage your eyes and cause skin burns. For that reason - never point scope to the Sun unless you have proper filter - even simple finder scope can cause serious burns.

We observe sun and moon at very high magnification - like x100 and above. This is because detail that we are interested in is often small. We can do full solar disk viewing and that is also interesting - but usually people do want to see tiny detail and use high magnification.

Nebulae are completely different. They are often much larger than the sun or moon (although there are some that are even smaller - like planetary nebulae) and they are very very faint. Using too much magnification can be counter productive - they often don't have tiny detail that can be seen and raising magnification makes view dimmer - which is problem for already dim objects.

We often use peripheral vision to observe nebulae as they are very dim and we can't see detail with peripheral vision.

What is claimed for these Cemax eyepieces is that they have special coatings that makes Ha image very sharp/high contrast at high magnifications used when viewing the sun. Not going to go into whether that is true and how much difference there is between such eyepiece and regular plossl - but thing is - what they claim happens with such eyepiece - will not affect views of nebulae because the way we observe them

- they are faint so we can't really see that much difference in contrast (there is something called JND - just noticeable difference and for humans JND for visual stimulus is about 7%-10% so we can see difference of 7% in signal strength. That is a lot of photons for bright target like sun, but that is just a few photons for dim targets like nebulae - and we can't see individual photons - there needs to be at least 7-8 photons for detection)

- we use low power to observe them - any difference in sharpness of the eyepiece is not critical at low power since we can't resolve it at low power

Thanks for the detailed explanation!