Eyepiece for "That Notorious Nag" :)

[scarp15]

This is my target for the coming winter.

I'm going to try an H-Beta filter and a good dark sky and see how I get on.

Rustysplit (Alan) managed it with a 27mm Panoptic and Hb filter last year in his 14" Dob. I'll try a 20mm Nagler in mine it gives roughly the same field as the pan.

I could be wrong Steve but I can recall that thread and I think it was Alan's 19mm pan that captured the Horse head, though I believe he has a 27mm Panoptic to. I once had a 19mm Panoptic though at the time made way for my 20mm nagler, but another credible contender. Mark has already commented that this eyepiece works.

[mert]

Some more info at the bottom of this link http://www.rocketmime.com/astronomy/Telescope/SurfaceBrightness.html

[scarp15]

That's good and following the link just re-read the Barbara Wilson Magic Eyepiece account, which in a nut shell puts it back into perspective.

Suppose that really it is about waiting for the winter sky and getting on with it,  hopefully on a night of good transparency.

[John]

The "Magic Horse Head Eyepiece" piece is good

I notice that she also mentions DSO observing experience as being a potential factor. At least we can get some practice in before Orion is nicely on show

Just need to identify some suitable practice targets now. How about a black Knight chess piece against a black background positioned about 30 miles away ? 

[mert]

That's good and following the link just re-read the Barbara Wilson Magic Eyepiece account, which in a nut shell puts it back into perspective.

Suppose that really it is about waiting for the winter sky and getting on with it,  hopefully on a night of good transparency.

It'll come around sooner than expected lol

[mert]

The "Magic Horse Head Eyepiece" piece is good

I notice that she also mentions DSO observing experience as being a potential factor. At least we can get some practice in before Orion is nicely on show

Just need to identify some suitable practice targets now. How about a black Knight chess piece against a black background positioned about 30 miles away ? 

I could stick a Knight chess piece on the top of the mountain "Buachille Etive Mor" in Glencoe, that's about 20 miles away but an easy target, I can just see the top on a clear day

[michael.h.f.wilkinson]

Some more info at the bottom of this link http://www.rocketmime.com/astronomy/Telescope/SurfaceBrightness.html

The equations used here assume a linear sensitivity of the eye, which is not quite correct. Many people find that objects stand out better at slightly smaller exit pupils due to the darker background. This highlights the key issue: we are not looking at maximising the surface brightness, we are looking at maximising the apparent contrast between object and background. If the visual system (as a whole) acted in a linear fashion, the largest contrast should correspond to the highest surface brightness, but in practice this is not always the case. I have often found that throwing a bit of extra magnification at a DSO helps, and that galaxies are spotted far more easily at a 2.2mm exit pupil than with 3.1mm.

There are many non-linear processing stages in the brain, and these could help explain these observations. For starters, the eye changes its sensitivity as a function of the brightness of the image, so a bright background can reduce dark adaptation, resulting in worse detection of faint edges. This is another issue: we are better at detecting edges than faint transitions (again due to non-linear processing in the visual system). I have found several faint nebulae by picking up the edges of dust lanes within them, rather than the faint outer edges. Rosette in my C8 was a prime example, the Cave another.  I spent something like an hour trying to find the Cave, and couldn't spot it. I grumbled that the background was too bright, probably due to LP, and then suddenly spotted this dark blotch dead centre, and realised why it was called the Cave. A bit of moving the scope in declination or RA revealed that the background was not that bright elsewhere, confirming the presence of a faint extended nebula.

[mert]

The equations used here assume a linear sensitivity of the eye, which is not quite correct. Many people find that objects stand out better at slightly smaller exit pupils due to the darker background. This highlights the key issue: we are not looking at maximising the surface brightness, we are looking at maximising the apparent contrast between object and background. If the visual system (as a whole) acted in a linear fashion, the largest contrast should correspond to the highest surface brightness, but in practice this is not always the case. I have often found that throwing a bit of extra magnification at a DSO helps, and that galaxies are spotted far more easily at a 2.2mm exit pupil than with 3.1mm.

There are many non-linear processing stages in the brain, and these could help explain these observations. For starters, the eye changes its sensitivity as a function of the brightness of the image, so a bright background can reduce dark adaptation, resulting in worse detection of faint edges. This is another issue: we are better at detecting edges than faint transitions (again due to non-linear processing in the visual system). I have found several faint nebulae by picking up the edges of dust lanes within them, rather than the faint outer edges. Rosette in my C8 was a prime example, the Cave another.  I spent something like an hour trying to find the Cave, and couldn't spot it. I grumbled that the background was too bright, probably due to LP, and then suddenly spotted this dark blotch dead centre, and realised why it was called the Cave. A bit of moving the scope in declination or RA revealed that the background was not that bright elsewhere, confirming the presence of a faint extended nebula.

Thanks for the explanation Michael, I'm hoping on a clear night we can all try various filter and eyepiece's to see what works, how dark is the sky where you are?

[michael.h.f.wilkinson]

Thanks for the explanation Michael, I'm hoping on a clear night we can all try various filter and eyepiece's to see what works, how dark is the sky where you are?

Not dark enough. I am in a quite dark patch in the suburbs, but for really good skies must travel further afield.

[mert]

I know Michael, the never ending hunt for perfect dark skies continues lol