Mars with 3 different scopes - comparison

I did some imaging of Mars last Saturday in fair seeing just after sunset with my 175 refractor, 250 Mak and 305 Mak. I started with my 175 refractor which seemed to give the best visual image, probably because the larger instruments had not settled due to the day's heat build-up. It has been quite hot during the day, around 90F inside the observatory, which then drops rapidly to about 70 when the roof is opened at sunset. The seeing was so-so, maybe 6 out of 10 with Mars changing shape rapidly but not tearing sideways.

After shooting Mars with the refractor, I went to the 305 Mak-Cass, but there were some tube currents. I opened the back of the scope to expose the quartz mirror and blew some air across the surface from an ordinary room fan placed some 4 ft away. This immediately stabilized the image and eliminated the plumes off the top of Mars. This actually worked better than an internal fan and added no vibration to the scope.

After some 15 minutes of imaging I switched the camera over to the 10" F14.6 Mak-Cass (back also open to get rid of the heat), and was surprised to see a very contrasty image of Mars with much surface detail. I was able to get some 8 video frame sets of about 1000 frames each before the seeing deteriorated (as it usually does after sunset).

The contrast of the 10" Mak-Cass is due to the very small central obstruction (23%) which makes it perform almost refractor-like. Both the 175 and the 10" were visibly more contrasty than the 12" Mak because this instrument was designed for wide-field imaging and has a 38% central obstruction. Theoretically it is much more affected by poor seeing, and you can see it in the comparison images.

The small central obstruction not only improves contrast, but also reduces the effects of seeing quite dramatically. This is quite easily seen when watching the videos taken with each of the 3 scopes.

Just for comparison I added a simulation of Mars from calsky.com, and sure enough the 10" Mak image clearly shows 3 of the volcanos as well as Olympus Mons to the right of middle. The albedos are different in the simulation (almost inverted), but you can clearly see the giant mountain and the trapezoidal area around it. Lots of other features are shown, with Mars being a puny 15 arc seconds in diameter and very low in the sky. I would love to see what this scope could do when Mars is at opposition, twice as large and high in the sky in excellent seeing.

http://www.astromart.com/common/imag...6.jpg&caption=

Camera is a cheap and cheerful QHY-5-II color camera

On Monday, 11 July 2016 18:09:27 UTC-4, Razzmatazz wrote:
I did some imaging of Mars last Saturday in fair seeing just after sunset with my 175 refractor, 250 Mak and 305 Mak. I started with my 175 refractor which seemed to give the best visual image, probably because the larger instruments had not settled due to the day's heat build-up. It has been quite hot during the day, around 90F inside the observatory, which then drops rapidly to about 70 when the roof is opened at sunset. The seeing was so-so, maybe 6 out of 10 with Mars changing shape rapidly but not tearing sideways.

After shooting Mars with the refractor, I went to the 305 Mak-Cass, but there were some tube currents. I opened the back of the scope to expose the quartz mirror and blew some air across the surface from an ordinary room fan placed some 4 ft away. This immediately stabilized the image and eliminated the plumes off the top of Mars. This actually worked better than an internal fan and added no vibration to the scope.

After some 15 minutes of imaging I switched the camera over to the 10" F14.6 Mak-Cass (back also open to get rid of the heat), and was surprised to see a very contrasty image of Mars with much surface detail. I was able to get some 8 video frame sets of about 1000 frames each before the seeing deteriorated (as it usually does after sunset).

The contrast of the 10" Mak-Cass is due to the very small central obstruction (23%) which makes it perform almost refractor-like. Both the 175 and the 10" were visibly more contrasty than the 12" Mak because this instrument was designed for wide-field imaging and has a 38% central obstruction. Theoretically it is much more affected by poor seeing, and you can see it in the comparison images.

The small central obstruction not only improves contrast, but also reduces the effects of seeing quite dramatically. This is quite easily seen when watching the videos taken with each of the 3 scopes.

Just for comparison I added a simulation of Mars from calsky.com, and sure enough the 10" Mak image clearly shows 3 of the volcanos as well as Olympus Mons to the right of middle. The albedos are different in the simulation (almost inverted), but you can clearly see the giant mountain and the trapezoidal area around it. Lots of other features are shown, with Mars being a puny 15 arc seconds in diameter and very low in the sky. I would love to see what this scope could do when Mars is at opposition, twice as large and high in the sky in excellent seeing.

http://www.astromart.com/common/imag...6.jpg&caption=

Camera is a cheap and cheerful QHY-5-II color camera

Very nice work, shots from all three are worthy.

On Monday, July 11, 2016 at 3:09:27 PM UTC-7, Razzmatazz wrote:
I did some imaging of Mars last Saturday in fair seeing just after sunset with my 175 refractor, 250 Mak and 305 Mak. I started with my 175 refractor which seemed to give the best visual image, probably because the larger instruments had not settled due to the day's heat build-up. It has been quite hot during the day, around 90F inside the observatory, which then drops rapidly to about 70 when the roof is opened at sunset. The seeing was so-so, maybe 6 out of 10 with Mars changing shape rapidly but not tearing sideways.

After shooting Mars with the refractor, I went to the 305 Mak-Cass, but there were some tube currents. I opened the back of the scope to expose the quartz mirror and blew some air across the surface from an ordinary room fan placed some 4 ft away. This immediately stabilized the image and eliminated the plumes off the top of Mars. This actually worked better than an internal fan and added no vibration to the scope.

After some 15 minutes of imaging I switched the camera over to the 10" F14.6 Mak-Cass (back also open to get rid of the heat), and was surprised to see a very contrasty image of Mars with much surface detail. I was able to get some 8 video frame sets of about 1000 frames each before the seeing deteriorated (as it usually does after sunset).

The contrast of the 10" Mak-Cass is due to the very small central obstruction (23%) which makes it perform almost refractor-like. Both the 175 and the 10" were visibly more contrasty than the 12" Mak because this instrument was designed for wide-field imaging and has a 38% central obstruction. Theoretically it is much more affected by poor seeing, and you can see it in the comparison images.

The small central obstruction not only improves contrast, but also reduces the effects of seeing quite dramatically. This is quite easily seen when watching the videos taken with each of the 3 scopes.

Just for comparison I added a simulation of Mars from calsky.com, and sure enough the 10" Mak image clearly shows 3 of the volcanos as well as Olympus Mons to the right of middle. The albedos are different in the simulation (almost inverted), but you can clearly see the giant mountain and the trapezoidal area around it. Lots of other features are shown, with Mars being a puny 15 arc seconds in diameter and very low in the sky. I would love to see what this scope could do when Mars is at opposition, twice as large and high in the sky in excellent seeing.

http://www.astromart.com/common/imag...6.jpg&caption=

Camera is a cheap and cheerful QHY-5-II color camera

Looks like you have some money invested into this hobby?
I all ways found my 4" APO (Older Vixen/Celestron C102F Fluorite) model the best and stable visual images on planets.
Long time ago I even seen a large dust storm on Mars.

On Monday, July 11, 2016 at 5:17:06 PM UTC-7, StarDust wrote:

Looks like you have some money invested into this hobby?

Actually, he gets a GREAT deal on his telescopes... since he makes them :)

Razzmatazz wrote:
Just for comparison I added a simulation of Mars from calsky.com, and sure
enough the 10" Mak image clearly shows 3 of the volcanos as well as Olympus
Mons to the right of middle.

Well, if you happen to have an in with the maker of those 'scopes

http://www.astromart.com/common/imag...rums/828000-82
8999/828196.jpg&caption=

Camera is a cheap and cheerful QHY-5-II color camera

I am reminded of my first half-way decent image of Mars, made with a
Questar and Barlow a Point Gray color camera. Not quite up to A-P
large-aperture standards, but respectable. Anyway, Olympus Mons, or
rather, the CO2 clouds above O.M., were visible as a bright spot. I
thought this was an artifact in my image and I was going to remove it
in Photoshop‹Until I chanced to look at the Calsky simulation and found
the same spot in the same location!

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

StarDust:
Looks like you have some money invested into this hobby?

"Razzmatazz," aka , is Roland Christen, who founded
Astro-Physics with his wife Marj in 1975 (I think it was). See
http://www.astro-physics.com and
http://company7.com/astrophy/index.html. So yes, you may safely say
that he has "some money" invested in astronomy.

Mr. Christen frequently changes his Usenet handle for comedic effect,
but being a man of integrity and one with the courage of his
convictions, he displays a genuine identifying e-mail address in his
posts. The first part of his e-mail address is chris10 (chris ten, get
it?) but I don't get the "11" part, unless maybe he is Roland Christen
II.

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

Nice images! - and good for showing the advantages of aperture and the disadvantages of (large) central obstructions.

I seem to recall a 'rule-of-thumb' that says an obstructed aperture performs (on planets) like an unobstructed aperture that's equal to the obstructed aperture minus the obstruction diameter. Your images seem to provide evidence that "small" obstructions are less damaging and "large" obstructions more damaging than the 'rule-of-thumb' would imply - though in fairness other variables such as seeing and cool-down may have been factors as well.

Thanks for the great images! My last decent look at Mars was made with Excalibur shortly after watching "The Martian" ;-)

Sketcher,
To sketch is to see.


On Monday, July 11, 2016 at 4:09:27 PM UTC-6, Razzmatazz wrote:
I did some imaging of Mars last Saturday in fair seeing just after sunset with my 175 refractor, 250 Mak and 305 Mak. I started with my 175 refractor which seemed to give the best visual image, probably because the larger instruments had not settled due to the day's heat build-up. It has been quite hot during the day, around 90F inside the observatory, which then drops rapidly to about 70 when the roof is opened at sunset. The seeing was so-so, maybe 6 out of 10 with Mars changing shape rapidly but not tearing sideways.

After shooting Mars with the refractor, I went to the 305 Mak-Cass, but there were some tube currents. I opened the back of the scope to expose the quartz mirror and blew some air across the surface from an ordinary room fan placed some 4 ft away. This immediately stabilized the image and eliminated the plumes off the top of Mars. This actually worked better than an internal fan and added no vibration to the scope.

After some 15 minutes of imaging I switched the camera over to the 10" F14.6 Mak-Cass (back also open to get rid of the heat), and was surprised to see a very contrasty image of Mars with much surface detail. I was able to get some 8 video frame sets of about 1000 frames each before the seeing deteriorated (as it usually does after sunset).

The contrast of the 10" Mak-Cass is due to the very small central obstruction (23%) which makes it perform almost refractor-like. Both the 175 and the 10" were visibly more contrasty than the 12" Mak because this instrument was designed for wide-field imaging and has a 38% central obstruction. Theoretically it is much more affected by poor seeing, and you can see it in the comparison images.

The small central obstruction not only improves contrast, but also reduces the effects of seeing quite dramatically. This is quite easily seen when watching the videos taken with each of the 3 scopes.

Just for comparison I added a simulation of Mars from calsky.com, and sure enough the 10" Mak image clearly shows 3 of the volcanos as well as Olympus Mons to the right of middle. The albedos are different in the simulation (almost inverted), but you can clearly see the giant mountain and the trapezoidal area around it. Lots of other features are shown, with Mars being a puny 15 arc seconds in diameter and very low in the sky. I would love to see what this scope could do when Mars is at opposition, twice as large and high in the sky in excellent seeing.

http://www.astromart.com/common/imag...6.jpg&caption=

Camera is a cheap and cheerful QHY-5-II color camera

On Tuesday, July 12, 2016 at 4:33:14 AM UTC+1, Davoud wrote:


Mr. Christen frequently changes his Usenet handle for comedic effect,
but being a man of integrity and one with the courage of his
convictions, he displays a genuine identifying e-mail address in his
posts. The first part of his e-mail address is chris10 (chris ten, get
it?) but I don't get the "11" part, unless maybe he is Roland Christen
II.


Integrity indeed !, when you post in the same thread under two different pseudonyms it is sockpuppetry lite and that is fatal no matter how good his magnification images are.

On Monday, July 11, 2016 at 8:33:14 PM UTC-7, Davoud wrote:
StarDust:
Looks like you have some money invested into this hobby?

"Razzmatazz," aka is Roland Christen, who founded
Astro-Physics with his wife Marj in 1975 (I think it was). See
http://www.astro-physics.com and
http://company7.com/astrophy/index.html. So yes, you may safely say
that he has "some money" invested in astronomy.

Mr. Christen frequently changes his Usenet handle for comedic effect,
but being a man of integrity and one with the courage of his
convictions, he displays a genuine identifying e-mail address in his
posts. The first part of his e-mail address is chris10 (chris ten, get
it?) but I don't get the "11" part, unless maybe he is Roland Christen
II.

--
I agree with almost everything that you have said and almost everything that
you will say in your entire life.

usenet *at* davidillig dawt cawm

Uh! Sorry, I didn't know that. I heard of Astro-Physics, but never owned any of their products, too rich for me.

On Monday, July 11, 2016 at 7:26:36 PM UTC-7, palsing wrote:
On Monday, July 11, 2016 at 5:17:06 PM UTC-7, StarDust wrote:

Looks like you have some money invested into this hobby?

Actually, he gets a GREAT deal on his telescopes... since he makes them :)

yes! his employees make it for him! I worked for 10 years making laser optics,
machining/polishing/bonding YAG, doped YAG and Sapphire materials, mostly using diamond powder/slurry. Nor easy, all most as hard as real diamond.
All government contracts!
Had enough!