Colour in GRS

[Stu]

I had some lovely views of the GRS between around 8.45 and 9.30 this evening. This was after it had transited the meridian but it was still nicely placed.

I was observing with a 4" frac, and have never noticed colour before in such a small scope, but tonight the GRS was a lovely pinky orange colour. There was some nice detail following behind it and plenty more in other areas.

One thought I had was that observing before it is dark probably means that the cones in the eye are being stimulated more by the ambient light and are more likely to pick up the colour on the planet than when it is fully dark.

Is this theory complete hogwash or might it be along the right lines?

[Ags]

I do not bother with dark adaptation when observing planets, I too suspect that avoiding dark adaptation enhances color sensitivity.

But small scopes have a definite disadvantage when it comes to contrast and color. The reason is that the Airy discs of small instruments are really big - there is simply a lot of light bleed across the image: http://opticsandalgorithms.blogspot.nl/2015/04/refractor-diffraction-patterns.html

[John]

I have a feeling that dark adaptation is actually not ideal for planetary viewing. I get some my best views of Jupiter when there is still some light in the sky and it is against a relatively pale background.

[Ags]

My garden is always bright enough for color vision, so this is always the case for me. I did find that when I was fully dark adapted (at my old home in Wales) turning my scope to Jupiter was simply unpleasant, like staring into a colorless needle.

[Stu]

I do not bother with dark adaptation when observing planets, I too suspect that avoiding dark adaptation enhances color sensitivity.

But small scopes have a definite disadvantage when it comes to contrast and color. The reason is that the Airy discs of small instruments are really big - there is simply a lot of light bleed across the image: http://opticsandalgorithms.blogspot.nl/2015/04/refractor-diffraction-patterns.html

I'm far from being an expert on the theory of these things, but from a practical experience point of view I'm not sure I subscribe to the theory of light bleed across the image with smaller scopes. Is the increased resolution of larger scopes purely down to the smaller airy disk size?

Contrast in small refractors can be superb, with an ability to resolve details that sometimes elude larger scopes. I totally agree obviously that the resolution available in larger scopes is much higher but they can lack contrast, although I understand you are referring to refractors which don't have the secondary artefacts of newtonians.

Anyway, that's a discussion for another thread perhaps, I'd like to keep the focus on whether the colour detection on planets is better when observed under twilight conditions

Cheers

[chiltonstar]

Good to see you find the same! Certainly the view of the GRS is more intense with my ED80 than with my 5" Mak or through a mate's SW 200P - I put this down to the superior contrast of a 'frac compared with an obstructed scope, and possibly as well that with a larger scope, too much light may be hitting the retina for you to see mid-range colours well. Size of Airy disk with a smaller scope? Hmm - I dunno. It's still quite small compared with the size of Jupe's disk....

Chris

Posts overlapped.....

[cotterless45]

One easy way to check out colour and contrast is to choose a terrestrial target some distance away on a clear and bright day. I found my 90 and 102 frac certainly out smart my 150 frac.

This is very much the case with the GRS, where more colour is caught with the smaller contrasty scopes,

Nick.

[Piero]

One thought I had was that observing before it is dark probably means that the cones in the eye are being stimulated more by the ambient light and are more likely to pick up the colour on the planet than when it is fully dark.

Is this theory complete hogwash or might it be along the right lines?

To me this explanation makes sense, although I am not an expert on eyes, light or optics. If the eyes are dark adapted I would expect the cones to be less important than the rodes, and therefore this would cause a decrease in our ability to detect colours in the night. From an evolution point of view this could be the case for the simple fact that we don't need to discern colours in the dark, but just shades of grey for detecting things.

[mikeDnight]

I know that over the years the GRS has varied considerably in intensity and that its more easily seen during some apparitions than at others. I also think a small refractor has a distinct advantage over larger instruments as it doesn't gather too much light, which can actually hinder contrast. Mars is a fine example! It is small and extremely bright, so small, high quality optics tend to give better more contrasty views than larger apertures. In January this year the advantage of smaller aperture scopes was brought home to me after I'd bought an Equinox 80. Looking at Jupiter through the 80 ED I saw without any difficulty five belts, the GRS and a shadow transit as black as Indian ink. At the same time in a side by side comparison, my Equinox 120 only showed the equatorial belts and just hinted at the temperate belts. I performed similar comparisons over several weeks but each time the little 80 showed detail more easily.

The only fault with the 80 was that it lacked the resolution I needed to see the finer detail, but its contrast was perfect. I reasoned that if an 80 can give such great views while an equally top notch 120 struggles on some nights, then a 100mm scope should be the perfect compromise. I therefore took a gamble and sold both my equinox scopes, buying a top end 100mm. It paid off! The 100 is for me the perfect combination, giving high contrast and well defined views of the planets and moon, with excellent resolution.

The 100 does not seem to be hindered by the seeing conditions anywhere near as much as my 120 was and so I'm able to now have more fruitful observing sessions.

The colour in Jupiters belts and its GRS is quite intense in the 100 and the little scope easily picks out festoons, ovals and barges as well as numerous finer belts I could rarely ever be sure of in the larger instrument. It also shows the mild green colour I'm M42 and also the colour in comet Lovejoy without any difficulty.

Interestingly, in the 100, even the Galileans are shown as perfect little discs, each one a different size and each one a different colour, and without any spurious flaring or light scatter.

I know that colour perception can vary greatly from one observer to another, possibly due to a variation in the number of cones each person has, but for me the little 100 shows colour well and gives the most consistantly good views of the planets I've ever had.

Mike :-)

[Piero]

Nice report Mike! So, which 100mm did you get?

[mikeDnight]

Hi Piero

I eventually decided on the new version of the Takahashi FC 100.

The FC 100 DC version.

Mike

[Ags]

Regarding scope size and brightness... If the image from a large aperture scope is too bright, why not simply add a neutral density filter to the optical train?

[chiltonstar]

Regarding scope size and brightness... If the image from a large aperture scope is too bright, why not simply add a neutral density filter to the optical train?

I sometimes add a ND filter (or various coloured filters) with Jupiter to see more detail, even with a 5" scope. It doesn't seem to improve the colour contrast though.

Chris

[michael.h.f.wilkinson]

I think the planets are bright enough to switch off the dark adaptation of the eye, at least, if you take your time observing them (always better anyway). I find that I initially do not see much colour (if I am fully dark adapted), but that the colour returns very quickly. Mars is always red of course, the surface brightness is great enough to trigger the cones instantly.

[Piero]

Hi Piero

I eventually decided on the new version of the Takahashi FC 100.

The FC 100 DC version.

Mike

Superb! Very nice! There is something about refractors.. Dunno.. They are just beautiful! Have a lot of fun with it!

[Stu]

I think the planets are bright enough to switch off the dark adaptation of the eye, at least, if you take your time observing them (always better anyway). I find that I initially do not see much colour (if I am fully dark adapted), but that the colour returns very quickly. Mars is always red of course, the surface brightness is great enough to trigger the cones instantly.

Hi Michael,

I'm sure it is all down to individual's eyes, but I can often spend a number of hours observing Jupiter and have never seen much colour in it.

Using the 16" at SGLX, the colour was pretty vivid so I assume my cones need a little more than yours to fire.

My main point was that recently in the 4" from home, a scope I have never normally seen colour with, I was getting it pretty strongly. I assumed that was because I was observing during relatively bright twilight conditions due to Jupiter's current positioning, rather than more normally observing after dark. I am guessing my cones are reacting more strongly due to the background brightness level?

Stu

[jetstream]

Good observation Stu- I was watching Jupiter with the SW120ED last night and found the views at dusk very good. The GRS, splits in the bands, cap zones were all showing nicely. I also get good color with the dob and again my best views are at sundown.

[Pig]

It all makes perfect sense.... it just takes someone to notice & mention it  Nice new avatar BTW Stu

[John]

I think the planets are bright enough to switch off the dark adaptation of the eye, at least, if you take your time observing them (always better anyway). I find that I initially do not see much colour (if I am fully dark adapted), but that the colour returns very quickly. Mars is always red of course, the surface brightness is great enough to trigger the cones instantly.

I tend think you need the opposite of dark adaptation to get the best from Jupiter and Saturn and maybe Venus too. Some planetary observers deliberately look at a piece of white paper / card illuminated with a while light before observing these targets I believe.

[Stu]

It all makes perfect sense.... it just takes someone to notice & mention it  Nice new avatar BTW Stu

Thanks Shaun.

Avatar is hopefully appropriate for the day, you may have noticed some others.....

Won't be around long

[Pig]

Oh I see.... May the 4th be with you  LoL crazy people

[Stu]

Oh I see.... May the 4th be with you  LoL crazy people

We aim to please

[Pig]

Well I have to admit it did make me laugh

[Jimtheslim]

I always prefer looking at Jupiter through my 90mm refractor at twilight as opposed to 'dark'. Detail always seems a bit clearer and CA reduced. In fact I would love to visit the polar regions in their summers so you could have whole nights of just twilight.

[mikeDnight]

I tend think you need the opposite of dark adaptation to get the best from Jupiter and Saturn and maybe Venus too. Some planetary observers deliberately look at a piece of white paper / card illuminated with a while light before observing these targets I believe.

I've never tried the illuminated paper idea. I often leave the observatory white light on however when I'm making a sketch of a planet. The light is not bright and its source is shielded but it would be enough to kill dark adaption. The planetary views however are very contrasty and colour can often be seen without difficulty.

Mike