chiltonstar

I can't imagine how you look and sketch as well! A lovely rendition.

Chris

With a DSLR taking images of the Moon, the exposure times that are usable generally give you problems from shutter shake and mirror slap. With my Nikon D750, I lock the mirror up and use a remote wire-less release to minimise this. Also, using a very heavy mount instead of a photo tripod will reduce vibration if you use a small scope. For example, using an ED80 (the original full resolution image is very sharp).. Don't forget, if you use a phone at the eyepiece, you are adding two extra optical components (eyepiece and phone camera lens) which can introduce distortion.

Chris

6 hours ago, alex_stars said:

Hi @chiltonstar

Those are exactly the views I am after. Since we have the same 180 Mak and I am on the lookout for some new EPs, may I bother you for some advice?

Currently I have a cheap 8-24mm Seben Zoom (Celestron and such quality) and I have an ADC which I plan to use visually. Now I am on the outlook for some EPs to extend my set.

I see you list the candidates I have in mind, Baader Orthos, Vixen SLVs and a Hyperflex zoom (I presume from the focal length). Unfortunately I can't get all of those at once so I thought I ask:

Having experienced such a great night recently, which of your EPs was the most useful in combination with the ADC during that night?

Clear Skies,

Alex

I've PM'd you an answer Alex.

Chris

...but how do I avoid the ringing visible ? The avi's were stacked in Autostakkert and all have slight ringing on the NW side of the planet.

Chris

Probably with this scope too, I think. 00:15 last night, best 1000 frames from 5000. The seeing was excellent despite the cloud bands, which prompted me to get the camera out rather than visual which I normally prefer.

180 Mak, ZWO ADC, ASI20 MC. Image rotated to correct orientation

Chris

23 hours ago, mikeDnight said:

 

 

 

I'm not sure if its of any interest but I've attached the grid I made from 2016 showing the features which match the BAA coordinates. Folding the map round to roughly show the CM at the time of the sketch, Syrtis Minor appears to the right. The grid is mirror reversed and so is only of use to refractor or Cass users, as it shows how features may appear through the eyepiece of a small aperture scope. Details are as exact as only roughly, almost, approximate allows, but useful to me all the same. If 129° were the meridian Olympus Mons would have been pretty much central. The cylindrical grid chart shows the polar regions as they appear through the telescope.☺

In 2016 the northern hemisphere was tilted toward us. Looking at my 2016 globe from roughly the same angle as Mars now appears in 2020, the same meridian shows the features in the sketch, with Hellas on the lower right limb and Syrtis Major on the limb just coming onto the disk.

I'm always impressed by your stunning sketches Mike - something way beyond me because in the words of my art teacher at school "you have the artistic skills of a carrot, boy!"

I see the BAA website has a collection of maps as well - very interesting. Browsing through a stack of old Astronomy Now magazines (on their way to the recycling bin) I also found a poster from AN with an observer's view of Mars on one side, and a much more detailed Explorer's view on the other. Might be a good one to work from at the eyepiece after lamination. It doesn't seem to be available from AN as a proper poster unfortunately.

Chris

Yes, Herschel on the SS map is the huge crater - by "zone", I was implying the region around the crater which is darkish. 

A large scale downloadable map of Mars with plenty of detail would be good - I for one prefer a paper chart at the eyepiece rather than a screen, but any flat projection struggles a bit with polar regions and becomes a bit difficult to interpret IMO.

Chris

Many of us are "getting old" Mike! Seems to be a fact of life unfortunately.

The 103 degrees is the azimuth scale from the SkySafari map, not Martian coordinates I think. What I could see at 23:30 - 00:30 matched what was shown on the screenshot almost exactly, although I thought the features on Jupiter were a wee bit in error when I swung across to Saturn and Jupiter. It was interesting to compare the frac and mak views, which were pretty much according to theory. The frac view of Mars was bright, contrasty and apparently sharp, whereas the mak view (obstruction) was hazier at first until I adjusted the ADC and let the scope cool a bit more (15 mins), which then showed finer detail. It was more obvious on Saturn where Cassini was very dark with the frac, lighter with the mak, but at higher magnifications you could see that the apparent width of the feature was less with the mak. Assuming that the true width of Cassini is 0.5 arcsec, then I presume the apparent width with a 100mm frac is 1.2 arcsec, and 0.86 arcsec with a 180 Mak if the seeing is excellent.

Clear(er) skies!

Chris

3 hours ago, mikeDnight said:

Hi Chris, 

I observed Mars early on and Syrtis Major hadn't yet come onto the disk, so I missed that.  You mention something I've never heard of, "the Herschel Zone".  I haven't been able to find anything about it during a brief search, so I thought I'd ask you where and what it is on the disk? Hope you don't mind! ☺

I use the Skysfari map (attached for the time I was observing) Mike, and the names are sometimes not quite the same as other maps I believe. I don't have a better one.

I had both my 102mm Vixen f13 frac and the 180 mak run up at the same time - an interesting comparison!

Chris

Never apologise for enthusiasm! There's a distinct shortage of it about.

I know what you mean about Mars - I spent an hour just immersing myself in the view last night, even through wispy cloud. The S. polar cap was distinct and the dark markings inc. the Herschel zone in the centre and Syrtis Major (?) just visible at the edge. Beautifully clear and rendered even sharper with the "cloud filter"!

Scope was 180 Mak, ADC, 7.2 - 21mm zoom and Nd filter.

Chris

8 minutes ago, Pixies said:

First ortho with some green writing.

Thanks to Saganite

I have his 9mm cousin - enjoy!

Chris

Interesting - worth keeping an eye out for. Bizarrely, it looks rather like Io transiting!

Chris

I'm thinking of witness statements describing an event, which may differ a lot - why the Court tends to believe the CCTV footage...

Chris

2 minutes ago, jetstream said:

The camera might not but the processing might embellish a squeak😀

Just as the brain does.... at least sharpening is only recovering information that is actually there?

Chris

46 minutes ago, mikeDnight said:

The trouble with that is that its about the human eye and how it sees the detail. Camera's can't answer that, because how the eye and brain sees and distinguishes detail isn't the same as how a camera and computer records detail.  When I've compared images of Jupiter and Mars with visual sketches I've made at the eyepiece, although the features are in the same position, the detail I visually recorded was at a different level of subtlety. With Mars, where I see dark albedo features, I also see the subtlest hints of mists and clouds that are rarely ever shown in an image. It's as if the camera sees at a different level of intensity and isn't as sensitive to the subtleties of detail. What's seen by a camera isn't what's seen by the eye/brain.

But surely Mike, the camera never lies....

Chris

2 hours ago, vlaiv said:

Either doubles or if one wants different type of feature, we could take two small craters on the Moon next to each other to be resolved as two features or maybe two mountain peaks - what ever needs to be actually resolved - or determined there are two things.

 

 

I've used 36 And in the past:-

Chris

What an interesting and informative thread this is!

Maybe the only definitive way to consider this issue of whether expensive refractors can "beat the laws of physics" would be from images of bright, close (eg 1 arcsec), similar magnitude double stars with different scopes, or maybe using an artificial star pair? This would remove the human subjectivity factor. I agree with @vlaiv above that linear features are something else, doubles are a better test.

Chris

7 hours ago, John said:

Is it because a quality objective lens puts a very high % of the energy into the airy disk and very little elsewhere ?

 

...but if that Airy disk is large and easily visible at the mag used, does this make any difference?

Chris

I think you made the point Stu about how large the Airy disks are with a small refractor (looking at doubles). How then do we see sharp views with a small frac at high magnifications when the Airy disks are so large at eg x300 and are blurring detail to that extent? Are we fooling ourselves.....?

Chris

58 minutes ago, John said:

Top quality optics = top quality high magnification performance, when the seeing allows.

It's not rocket science

...but of course within the limits imposed by the size of the Airy disk for that aperture, I presume?

Chris

Well, I got up to 75x per inch last night with my classic (ie old) 4" f13 refractor and it was still pretty sharp. Saturn was glorious with a lot of detail, ditto Jupiter with I think a transit taking place, and even Mars at quite low altitude (23:30) was sharp enough to show the S polar cap well and a good bit of detail on the disk itself. A tribute to the seeing I think, odd really because the weather forecast was dismal with lightning flashes everywhere.

Chris

14 hours ago, andrew s said:

 

PS I still prefer reflectors. 😜

Therapy, or buying another scope can cure this addiction.😼

Chris

46 minutes ago, rl said:

John...You have taken the exact phrase out of my brain that I was going to post! 

Reminds me of the quote...."youth is wasted on the young"

Chris

I think the issue of seeing the Encke division with a smaller scope can be looked at in a different way, as used in my "day job" as an atomic spectroscopist. Many features seen by eye or recorded with an imaging system are of course below the Dawes limit for the aperture, even Cassini. What we see is actually a convolution of the actual true appearance of the object with the instrument function (here Dawes, but in my area of work slit profile). A large, high resolution scope will broaden the feature a little but not degrade too much the intensity of the feature, but a small scope with low resolution will broaden the feature a lot and reduce its intensity a lot. In this latter case, the feature will only be seen with a scope delivering high contrast that can see the slight darkening produced by a convolution of eg Encke with an eg 1 arcsec Dawes function. My small Mak (127) has certainly shown Encke up on occasions when Saturn was high above the horizon, but the width of the feature as seen would have been very close to the 1 arcsec or so dictated by the Dawes limit for the scope (120mm).

Chris

10 minutes ago, JeremyS said:

Aren't we getting off track here? I thought we were trying to understand visual acuity at the eyepiece, not monitor resolution and performance....

Indeed - isn't the fundamental point essentially (pin out of grenade) can paying lots of money for an expensive refractor really beat the laws of physics?

Chris