Strategy for getting my 40mm EP, exit pupil and scope to do fields etc.

[Tufty]

@Nightspore another great table! Never seen that before!  So my achro is just over 9 at 9.4 so maybe places me on the border or in the yellow which means filterable levels of CA? not sure what the black diagonals mean exactly - frightened to ask! Doesn't look good.  I shall look further into this.  A bit of purple/lime fringing on bright planets hasn't bothered me on the achro, it's only noticeable to any extent on the moon and sun but is very unobtrusive.  It seems more exaggerated in the plossl supplied with the scope, though again nothing obtrusive.  My worst case of it was over this last weekend looking at Jupiter but we are at air saturation point here and after 20 mins of viewing things got worse and when I looked the telescope was dripping and the objective was covered in dew like the eps and me.

 

The chart is a bit weird - it's for achros and I'm looking at the 152mm obj  - I actually had an opportunity to get 6" f/9 refractor but chose the 5" as the suggestion was CA would be better controlled in F1200.  Intuitively you'd think that a 6" would bend light more with greater CA at shorter tube lengths. But the table shows f9 and 10 ok but worsens at f11 beofre getting controllable again. Strange!

[Moonlit]

1 hour ago, Nightspore said:

 

Cyan fringing and chromatic aberration essentially depend on the quality of the doublet, triplet (or other) ED glass. CA is also very subjective. My 72 ED DS Pro can show 'purple hazing' on very bright objects

Aha, I've not really thought about which color the fringes are but I'm pretty sure magenta is one. Come to think of it I don't notice it as much with the new 2" Sky Watcher diagonal (not the dielectric one) with the new 32mm EP as compared to the OLD 1.25" SW diagonal with the old Plossls that came with the scope.

 

Tufty: My brother who lives a few miles away will get my achro when I get the Newt, so I'll be able to use it still! It only cost me $170 complete with an EQ4 mount 🙂 The 80ED I want is to keep where I live (Bortle 8-9) so I have something to take out on short notice.

The 10" newt I have coming is too big to move all the time so that will mostly live 70 miles away (Bortle 4) where we have a cabin where I spend a lot of time.

 

The SWA32mm is not the most expensive (around $150) but I love it for wide fields. I have ordered 19mm and 4.9mm Siebert EPs (they look wonderfully 'industrial') for better quality EPs at an OK price.

A TeleVue Nagler or Ethos EP might be in my future, but the road is long and winding and I am not in a big hurry 🙂

Edited November 16, 2022 by Moonlit

[Tufty]

1 hour ago, Moonlit said:

Aha, I've not really thought about which color the fringes are but I'm pretty sure magenta is one.

 

The 10" newt I have coming is too big to move all the time so that will mostly live 70 miles away (Bortle 4) where we have a cabin where I spend a lot of time.

 

The SWA32mm is not the most expensive (around $150) but I love it for wide fields. I have ordered 19mm and 4.9mm Siebert EPs (they look wonderfully 'industrial') for better quality EPs at an OK price.

A TeleVue Nagler or Ethos EP might be in my future, but the road is long and winding and I am not in a big hurry 🙂

 

Yes the magenta on Nightspore's chart complements lime so I suspect that was the 'green' you saw.

 

Wow a telescope cabin! Sounds great.  Norway was my very first work trip when I started my first main job after university.  I went to Trondheim and worked at the uni there with a research team.  One day they took us by bus to a place called 'Hell' (getting on a bus going to Hell is one of my dinner stories).  We passed through many very dark places and I thought it would be great to have a telescope in dark parts of Norway.  Hell was amazing, it was like a lunar landscape with weird scifi planet colours.  But right in the middle of this lunar landscape was a great, very bright hotel made of glass which must have been visible miles around.

 

I'll be very interested to see how the Siebert's do - and I'm glad the achro will remain in the family. At $170 I'd suspect it would be difficult to find at that price again

[Nightspore]

2 hours ago, Tufty said:

@Nightspore another great table! Never seen that before!  So my achro is just over 9 at 9.4 so maybe places me on the border or in the yellow which means filterable levels of CA? not sure what the black diagonals mean exactly - frightened to ask! Doesn't look good.  I shall look further into this.  A bit of purple/lime fringing on bright planets hasn't bothered me on the achro, it's only noticeable to any extent on the moon and sun but is very unobtrusive.  It seems more exaggerated in the plossl supplied with the scope, though again nothing obtrusive.  My worst case of it was over this last weekend looking at Jupiter but we are at air saturation point here and after 20 mins of viewing things got worse and when I looked the telescope was dripping and the objective was covered in dew like the eps and me.

 

The chart is a bit weird - it's for achros and I'm looking at the 152mm obj  - I actually had an opportunity to get 6" f/9 refractor but chose the 5" as the suggestion was CA would be better controlled in F1200.  Intuitively you'd think that a 6" would bend light more with greater CA at shorter tube lengths. But the table shows f9 and 10 ok but worsens at f11 beofre getting controllable again. Strange!

 

I'm not sure what the stripey bits are either. I can't vouch for its accuracy. It's worth pointing out that CA doesn't help with resolution or definition either. It's usually at high magnifications that it gets intrusive.

 

 

Of course, there is the old 'fringe killer' stack trick. If you don't mind a bit of yellow lol. 

[Nightspore]

1 hour ago, Moonlit said:

Aha, I've not really thought about which color the fringes are but I'm pretty sure magenta is one. Come to think of it I don't notice it as much with the new 2" Sky Watcher diagonal (not the dielectric one) with the new 32mm EP as compared to the OLD 1.25" SW diagonal with the old Plossls that came with the scope.

 

Tufty: My brother who lives a few miles away will get my achro when I get the Newt, so I'll be able to use it still! It only cost me $170 complete with an EQ4 mount 🙂 The 80ED I want is to keep where I live (Bortle 8-9) so I have something to take out on short notice.

The 10" newt I have coming is too big to move all the time so that will mostly live 70 miles away (Bortle 4) where we have a cabin where I spend a lot of time.

 

The SWA32mm is not the most expensive (around $150) but I love it for wide fields. I have ordered 19mm and 4.9mm Siebert EPs (they look wonderfully 'industrial') for better quality EPs at an OK price.

A TeleVue Nagler or Ethos EP might be in my future, but the road is long and winding and I am not in a big hurry 🙂

 

If the SW diagonal is a prism it might be compensating the false colour.

[Tufty]

@Nightspore

 

I dropped into Widescreen once and bought some Baader things after chatting with someone in there on one of my trips, and this filter was recommended - I think I used it a few times in the ed80 but didn't seem to do much.  Maybe I havent put the time in enough yet.  In the achro I got *real green* with it and other stuff I didn't want!  During my 'learning journey' I think it's a 'contrast booster' I need for the achro, but never tried one as yet.  I do have a polarising moon filter for darkening tehe moon which works ok.

[Nightspore]

19 minutes ago, Tufty said:

@Nightspore

 

I dropped into Widescreen once and bought some Baader things after chatting with someone in there on one of my trips, and this filter was recommended - I think I used it a few times in the ed80 but didn't seem to do much.  Maybe I havent put the time in enough yet.  In the achro I got *real green* with it and other stuff I didn't want!  During my 'learning journey' I think it's a 'contrast booster' I need for the achro, but never tried one as yet.  I do have a polarising moon filter for darkening tehe moon which works ok.

 

That's the famous Baader Neodymium filter. Very useful for planetary at high magnifications. It's so useful for a lot of things, it's been referred to as the 'Swiss Army Knife' of filters.

 

 

The Fringe Killer, Semi APO and Contrast Booster filters roughly equate to Wratten #8, #12 and #15 filters, although they're more subtle. The Semi APO and Contrast Booster are possibly the best Mars filters.

 

 

Speaking of Mars filters, all these are useful.

Edited November 16, 2022 by Nightspore

[Tufty]

@Nightsporeoh crikey! I've never seen mars beyond a bright red disc. With all those filters I'd be spending the night going from one t'other! I'm very keen to see it with some or any detail but it's not really happened for me yet. I should reappraise my filter situation - all 2 of them! 

[Nightspore]

43 minutes ago, Tufty said:

@Nightsporeoh crikey! I've never seen mars beyond a bright red disc. With all those filters I'd be spending the night going from one t'other! I'm very keen to see it with some or any detail but it's not really happened for me yet. I should reappraise my filter situation - all 2 of them! 

 

You need at least around 200x to see detail on Mars. Magenta, yellow and orange good for darker albedo features (like Syrtis Major). Blue and especially light blue can reveal polar caps if they aren't easy to observe.  

[Tufty]

@NightsporeInteresting, interesting.  I don't think I've taken the ed80 much up to 200x mag - but that kind of mag seems to be meat and drink for the achromat.  To see Syrtis Major on my own scope is one of my life ambitions, the polar caps would be amazing.  Stupid question: are these colour filters like standard camera filters? I use yellow and orange lens filters on my camera for contrast.  Is there anything special about astronomical ones?  Another question: do you concur with what I've heard that the neodym ir cut is more appropriate for the apo but the contrast filter would be better for the achro?? I'm interested in increasing contrast for Jupiter at the moment, and possibly Saturn - all for the achro.  I'm going to try the IR cut again with the ed80 on brighter DSOs whenever I get the opportunity! Weather's pretty bad here at the moment

[Nightspore]

Personally, I wouldn't take a 102mm achromat to more than about 125x, and even that's pushing it. I doubt an *achromat would have the visual acuity to see any real detail on Mars at 200x, I've tried it. That's why they invented apochromats.

 

*An achromat f/7 or faster.

Edited November 16, 2022 by Nightspore

[Nightspore]

The colour filters are based on Wratten filters predominantly. Baader are derived from old Zeiss astronomical filters I believe.

[Tufty]

Mine is a 127 f9.4 fl 1200 , on paper they give x254 for max mag though conditions never seem to allow that. I have closeups of sunspots at around that.  But normally I don't go over x120, the detail has been good. I don't use it for anything other moon and planets really. I'm hoping the ed80 is going to help me out with other stuff.  Mags there I'm expecting x30 to 50.  As I say I tried it a while back on Mars but I hot a very bright disc which needed toning down somehow so I need to read the chapter on filters! 

 

On filters I will go with your suggestions, if I see syrtis major I'll be very happy.  

[Nightspore]

IDK, you might get away with f/9.4. Filters are more or less a sine qua non for Mars though. I tend to use a 127mm Mak', a 102mm ED doublet and a 150mm Newtonian for Mars. I've seen Syrtis Major with my 80ED, although it has a very high Strehl ratio.

 

 

In fact, the Syrtis planum was visible in October. The NPH should be visible as well. I've observed this almost reach the equator. The southern polar cap might still be visible.

Edited November 17, 2022 by Nightspore

[Nightspore]

In 1659 Syrtis Major was the first documented land mass ever observed on another world (Christiaan Huygens). He used it to calculate the length of the Martian day.

[Tufty]

There's just something about Mars. I shall try some filters. I believe we shall have to contend with some low altitudes for it this winter.  I have thought about a 127 mak a lot.  I've heard they are good on planets, and quick to set up etc. Also seen the SW 190 newt mak which has good reviews and may be more flexible for me in the long run. Anything to make observing simple and quick to go. I love the big achro but it is a palaver to fetch from garage etc.

 

Looks like Christiaan Huygens should get a national holiday! 

[Nightspore]

I had some of the best views of Mars ever, last opposition. With these:

 

[Tufty]

Very nice.  Looks like you have some ability to move scopes about as well. Theoretically then I shouldn't be too far off getting an OK view of mars with a 127 long and  80 short. Very tempted by the mak idea. I don't know omegon, or is that just the dew shield. Exciting stuff!

[Nightspore]

The Mak is a 127mm SW SkyMax. The doublet is an Altair Starwave ED-R. The dew shield is Omegon.

Edited November 17, 2022 by Nightspore

[Moonlit]

Back again!

@Nightspore The diagonal is a mirror, but not having been mishandled for 15 years like the 1.25" one I got with the scope must give some advantages!

 

@TuftyI've also been to Hell, just the train station though 🙂 Norway is cold, tonight was 20F/-7C but with good clothing it's not a problem comfort-wise.

I tried out a new cloth shroud for the 120mm achro (pic attached) and a heated box to store EPs in to avoid dew and I think they were successes. Clouds rolled in so I packed up early to sit by the fireplace.

 

As a beginner I sit here with a selection of Wratten filters and I have yet to see Mars as anything but a red blob, as I've been more interested in DSOs and the Moon. Recognizing any feature at all on Mars is something I now will attempt to do with the 120mm f/8.3 achro so I will be able to tell the difference when the 10" f/6.3 arrives.

 

PS: One night this autumn I ended up looking at an almost full moon with the 120mm stopped down to 40mm (removing the smaller center hole in the cap) and a UHC filter through the 32mm EP and it was breathtaking. The green tint from the UHC and the added sharpness from the stopping down together created an image that will stay with me for a long time.

 

Thick cloth shroud to combat excessive cooling:

 

Edited November 19, 2022 by Moonlit

[Tufty]

On 11/19/2022 at 9:39 PM, Moonlit said:

Back again!

 

@TuftyI've also been to Hell, just the train station though 🙂 Norway is cold, tonight was 20F/-7C but with good clothing it's not a problem comfort-wise.

I tried out a new cloth shroud for the 120mm achro (pic attached) and a heated box to store EPs in to avoid dew and I think they were successes. Clouds rolled in so I packed up early to sit by the fireplace.

 

As a beginner I sit here with a selection of Wratten filters and I have yet to see Mars as anything but a red blob, as I've been more interested in DSOs and the Moon. Recognizing any feature at all on Mars is something I now will attempt to do with the 120mm f/8.3 achro so I will be able to tell the difference when the 10" f/6.3 arrives.

 

PS: One night this autumn I ended up looking at an almost full moon with the 120mm stopped down to 40mm (removing the smaller center hole in the cap) and a UHC filter through the 32mm EP and it was breathtaking. The green tint from the UHC and the added sharpness from the stopping down together created an image that will stay with me for a long time.

 

Thick cloth shroud to combat excessive cooling:

 

@MoonlitAh I didn't see this.  Yes observing makes one think about clothes.  I have a coat that works at -35C but not the socks and hat to match! but am looking into it.

Yes I am learning about telescope cooling and dew points etc. Still not sure how the sky sucks heat from the scope such that warmer ambient temperature leads to dewing of the scope.  I am looking into heater bands - nice idea about a coat for the scope.  I've heard that radiator insulation foil works well on scopes, so I will look intot that. 

 

I don't have a hole in my cap to stop down the aperture, guess I could make one, but I have used a rotatable moon filter which seems to work ok,  Yes the moon is something else! We're very lucky to have it!

 

Only my 80mm scope ever seems to be ready when both I and Mars are around. It shows nothing more than a very bright disc.  I haven't managed to get my 5" achro on it yet but my expectations are big.  I've been looking at people's images from a 5" SW skymax and they've been impressive.  Let us know what you get with the achro.

[Nightspore]

To see anything on Mars you're going to need at least 200x, whatever the scope aperture is. Although Mars (on opposition years) is much closer to us than Saturn and Jupiter it is not very large by comparison. Last opposition the best images of surface details I saw were with 5" and 6" reflecting scopes, with the very best images using a 102mm FPL-53/lanthanum ED doublet. I'm not convinced a 5" achro faster than about f/14 would achieve a stable image at 200x due to CA. My 80ED Evostar has a very good Strehl as well as FPL-53 glass. That is a reason why they can be so effective for AP. I've seen indistinct surface details on Mars, including the NPH and southern polar cap with my 60mm doublet. But again, it has very high quality glass and a good Strehl number.

 

Telescope objectives dew when the glass is cold enough to precipitate the atmospheric humidity into liquid water. Hence why heating can keep them dry. Oddly, this dew point temperature can vary during different times of the year. I've known it so cold that dewing is minimal. The other factor is the density of the humidity suspended in the atmosphere around the scope. 

Edited November 22, 2022 by Nightspore

[Tufty]

@nightspore I don't know how to tell how good the glass is in the equinox (the adverts say its Schott and fpl53 objective), but it doesn't strike me as the right kind of scope for Mars for visual observing. I expect it's better at AP but I'm a way off that kind of thing as yet- still working out where to put eps when changing them out!

 

Hmmm if the best images of mars came from 5/6" reflectors I am curious. I'd have though the shorter focal lengths would reduce magnification opportunity?  Somehow in my head I have planet+long focal length refractor or mak = happiness. Though I guess if you are imaging in a short focal length scope it's a different matter. The more ivread the less certain I become. 

 

Yes good point about humidity around the scope.  This ruined my session the other night when the sky looked clear.  Still a bit mysterious though that the scope will lose heat 'to the sky' but dew up from the air around it. How cones the sky impacts the scope but not the air around it! 🤔 

 

I'm warming to the idea of radiator insulation foil, extended dew caps and heating bands, though it looks to add to the palaver! 

 

 

 

 

 

 

[Nightspore]

1 hour ago, Tufty said:

@nightspore I don't know how to tell how good the glass is in the equinox (the adverts say its Schott and fpl53 objective), but it doesn't strike me as the right kind of scope for Mars for visual observing. I expect it's better at AP but I'm a way off that kind of thing as yet- still working out where to put eps when changing them out!

 

Hmmm if the best images of mars came from 5/6" reflectors I am curious. I'd have though the shorter focal lengths would reduce magnification opportunity?  Somehow in my head I have planet+long focal length refractor or mak = happiness. Though I guess if you are imaging in a short focal length scope it's a different matter. The more ivread the less certain I become. 

 

Yes good point about humidity around the scope.  This ruined my session the other night when the sky looked clear.  Still a bit mysterious though that the scope will lose heat 'to the sky' but dew up from the air around it. How cones the sky impacts the scope but not the air around it! 🤔 

 

I'm warming to the idea of radiator insulation foil, extended dew caps and heating bands, though it looks to add to the palaver! 

 

 

 

 

 

 

 

The best views of Mars I had were with an f/7 102mm Altair Starwave. The 127mm Mak is f/12 and the 150mm Newt' is f/6. It's not the focal ratio that's the problem. An achromat f/10 or under will produce far too much CA for Martian features to be seen with any acuity at magnifications around 200x. I tried with my ST102 and it was too indistinct. Achromats of around f/14 can work but they are very long. Just because CA is minimal at lower magnifications doesn't mean that the CA won't be a problem at 200x. You might get away with decent views of the Moon, Saturn and Jupiter, but Mars is a very different animal.

 

BAA on dew

[Tufty]

1 hour ago, Nightspore said:

 

The best views of Mars I had were with an f/7 102mm Altair Starwave. The 127mm Mak is f/12 and the 150mm Newt' is f/6. It's not the focal ratio that's the problem. An achromat f/10 or under will produce far too much CA for Martian features to be seen with any acuity at magnifications around 200x. I tried with my ST102 and it was too indistinct. Achromats of around f/14 can work but they are very long. Just because CA is minimal at lower magnifications doesn't mean that the CA won't be a problem at 200x. You might get away with decent views of the Moon, Saturn and Jupiter, but Mars is a very different animal.

 

BAA on dew

Yup this is why I signed up here, to find out how more experienced people do it and pick their brains!  Many thanks.  I guess the CA seems to me to be so well controlled in the f9.4 achro on moon Jupiter and Saturn, and other objects,  that I was having high expectations of Mars - but haven't had the opportunity to put the two together yet.  I take what you say as I have used the Equinox on Mars a few times. I do experience some bizarre CA on Mars (even at x50) with it but not on other things.  The Altair Starwave, I just looked, is a triplet apo and advertises as CA-free.... I can see myself starting a telescope arsenal!

 

Hmmm, I've got Mars on my list as something I want to keep coming back to.  Given what you say I will probably have to rethink my scope 'strategy' again. Something to show some Martian detail will be one of my essential (as opposed to merely desirable) tick boxes.  Still, I'll be keeping the 5" achro as nothing else I've ever wanted that I've finally got has delivered as well as this (except maybe a film camera I bought some time ago).

 

Thanks for the BAA link, very interesting and I'll be on it like a car bonnet now I've had a 'clear' night spoiled by dew!  I was thinking of joining the BAA at some point funnily enough.