Is aperture king?

[PatrickO]

I'm a newbie with lunar photography (and astrophotography generally.)

For detailed lunar imaging, i.e. 100-200km,  what are the most important elements of the equipment setup. As the title asks is aperture king?

This is a genuine question as I think about  my own setup.

Edited February 19 by PatrickO

[Elp]

Aperture provides more resolution to a point, you're then at the mercy of atmospheric seeing.

[rl]

Aperture is king. At least up to the point where the atmosphere starts to interfere. Doubling your aperture halves the size of the smallest lunar feature you can see; a 5" scope will resolve about 1 arcsecond which translates to just under 1 mile on the moon. (the wavelength of light also enters into the calculation; these numbers are for green light). Shadow effects can make the minimum visible feature even smaller. Doubling your aperture while keeping the focal length the same has the additional advantage of cutting down the exposure time by 3/4 (see below)

Seeing in the UK puts a limit of 0.5 to 2 arcseconds due to atmospheric turbulence implying that there is no point in having more than 10" of aperture on most occasions for detail. This is generally true for visual observations; very occasionally you can do better but it's single digit number of night in a year where I live.

But there is a trick for astrophotography of bright solar system objects called lucky imaging. If there is enough light that the exposures can be kept short (meaning a few milliseconds) then you can shoot a video of thousands of frames in a few seconds. Some of those frames will coincide with instants where the atmosphere behaved itself and will be unusually clear. There is free software available that will analyse the file and pick out just the good frames..say the best 20%..and add them up into a single more detailed image, throwing away the rubbish ones.  Virtually all the brilliant results you will see on this site are done this way. It's a result of modern PC hardware being able to move, store and process vast quantities of data quickly.

Generally speaking, virtually all amateur astrophotography relies on adding up multiple frames (called subs). The real detail adds up in proportion to the number of exposures, while the random noise adds up more slowly (technically as the square root of the number of subs) so you get an improvement in the contrast.

[vlaiv]

For lunar and planetary (lucky type), aperture is king.

[happy-kat]

From looking at images and posts camera too can add like a camera that's sensitive in IR as that can be more atmosphere stable it seems and mono gives extra filter options like UV

[PatrickO]

6 hours ago, Elp said:

Aperture provides more resolution to a point, you're then at the mercy of atmospheric seeing.

 

2 hours ago, rl said:

Aperture is king. At least up to the point where the atmosphere starts to interfere. Doubling your aperture halves the size of the smallest lunar feature you can see; a 5" scope will resolve about 1 arcsecond which translates to just under 1 mile on the moon. (the wavelength of light also enters into the calculation; these numbers are for green light). Shadow effects can make the minimum visible feature even smaller. Doubling your aperture while keeping the focal length the same has the additional advantage of cutting down the exposure time by 3/4 (see below)

Seeing in the UK puts a limit of 0.5 to 2 arcseconds due to atmospheric turbulence implying that there is no point in having more than 10" of aperture on most occasions for detail. This is generally true for visual observations; very occasionally you can do better but it's single digit number of night in a year where I live.

But there is a trick for astrophotography of bright solar system objects called lucky imaging. If there is enough light that the exposures can be kept short (meaning a few milliseconds) then you can shoot a video of thousands of frames in a few seconds. Some of those frames will coincide with instants where the atmosphere behaved itself and will be unusually clear. There is free software available that will analyse the file and pick out just the good frames..say the best 20%..and add them up into a single more detailed image, throwing away the rubbish ones.  Virtually all the brilliant results you will see on this site are done this way. It's a result of modern PC hardware being able to move, store and process vast quantities of data quickly.

Generally speaking, virtually all amateur astrophotography relies on adding up multiple frames (called subs). The real detail adds up in proportion to the number of exposures, while the random noise adds up more slowly (technically as the square root of the number of subs) so you get an improvement in the contrast.

 

2 hours ago, vlaiv said:

For lunar and planetary (lucky type), aperture is king.

Many thanks for replies.

Does the mount make a difference? Obviously with "lucky imaging" the the target only needs to stay on the sensor for 1-2 minutes. However, I would think that a stable mount with tracking would help?

[vlaiv]

8 minutes ago, PatrickO said:

 

 

Many thanks for replies.

Does the mount make a difference? Obviously with "lucky imaging" the the target only needs to stay on the sensor for 1-2 minutes. However, I would think that a stable mount with tracking would help?

No, it really does not.

While it is good to have the mount that can keep the target on sensor - I was able to do that with Eq2 mount with simple DC tracking motor that had potentiometer speed control (so I adjusted tracking rate in real time to keep the planet on sensor).

Individual subs are so short that mount simply does not have time to make impact - it is virtually stands still for duration of ~5ms (actually - we can calculate it roughly if sidereal tracking speed is 15"/s then in 5ms - mount moves for 1/200th of that or about 0.075" - there is simply no "room" for it to make error or any sort of jitter that would show in single frame).

[Mandy D]

@PatrickO In addition to @vlaiv's comment on tracking, I would add that it can be advantageous to not track or to allow the Moon to drift through the FOV. If you have any dirt or defects on the sensor, these will automatically and magically disappear when you stack your images, since the stacking software will not see them as features to be stacked. I have a dark mark on the sensor of my camera and it never causes a problem if I am stacking.

[woldsman]

There’s no substitute for aperture in the sense that it sets a limit to resolution. Your mount (and your muscles!) have to be able to manage the load but for planetary and lunar, tracking differences are going to be minor. There are some other considerations to bear in mind though. For example, cooling down time, ease of collimation, level of optical aberration, and £££. These create trade-offs. For example, a F5 150mm reflector will cool down much faster than a 150mm F12 Maksutov but requires accurate collimation. Additionally, you can see DSOs more easily in the reflector than the Maksutov.

Edited February 20 by woldsman

[Bivanus]

Also a newbie , still playing with DSLR and  an ASI 120mms. What I have come to realize is that for lucky imaging the king is quite likely of the software kind while the queen is the camera. By no means does it mean aperture is un-inportant, however, if you are thinking about where to put the big bucks on a new rig , consider buying a good camera even if this would mean rounding down the inches on the OTA. My opinion , and I totally agree with people to disagree.

EDIT: I have an EQ6 ,however, most imaging for moon & planets is done from the AZ6. And yeah, the Secret Spymaster of the Astro Court is ...The Seeing...

Edited February 20 by Bivanus

[JOC]

I have long since dismissed the thoughts that (telescope) aperture is king unless you are in the business of chasing feint fuzzies where the light gathering ability of (telescope) aperture seems to trump all.  For viewing the heavens the key seems to be the apparent magnification from the EP.  In the UK they say that pushing x250 is probably not possible.  Telescope aperture undoubtedly let's you push the magnification up a bit, but if you are going to top out at x250 you don't need a huge scope unless you are chasing low light objects from what my own experience has shown.  I get almost as good a view of things like Saturn from my tiny grab and go as I do from an 8" Dob.   I think all more aperture in a telescope gives you is more hassle in setting up it up!!  I already don't bother to use my 8" Dob much for that reason.

[dweller25]

I tend to match my scope aperture to the average seeing conditions where I live which is around 1 arc second. So I have a 120mm refractor with a resolution of 0.96 arc seconds.

But I do mostly planetary viewing.

IF I did DSO I would buy a light 10” Newtonian for the light grasp.

Edited February 20 by dweller25

[Flame Nebula]

9 hours ago, JOC said:

I have long since dismissed the thoughts that (telescope) aperture is king unless you are in the business of chasing feint fuzzies where the light gathering ability of (telescope) aperture seems to trump all.  For viewing the heavens the key seems to be the apparent magnification from the EP.  In the UK they say that pushing x250 is probably not possible.  Telescope aperture undoubtedly let's you push the magnification up a bit, but if you are going to top out at x250 you don't need a huge scope unless you are chasing low light objects from what my own experience has shown.  I get almost as good a view of things like Saturn from my tiny grab and go as I do from an 8" Dob.   I think all more aperture in a telescope gives you is more hassle in setting up it up!!  I already don't bother to use my 8" Dob much for that reason.

I think aperture matters for planetary astrophotography, especially saturn. This is based on images on astrobin, where for example a C9.25 or C11 gives better resolution of the encke gap, than a C8. Similarly images taken with a C14 or larger dobsonian 12-16" are far superior to 8".

 

[Ags]

Aperture is King, but Takahashi is Takahashi.

[dweller25]

6 minutes ago, Ags said:

Aperture is King, but Takahashi is Takahashi.

They are not magic enough to overcome big high quality mirrors 👍

Lights touch paper and steps back 🤣

Edited February 20 by dweller25

[Elp]

So what is Astro Physics?

[astrolulu]

Quality optics and a good logo can be valuable during visual observations. When stacking hundreds or thousands of frames, they become meaningless - what matters is the aperture.

[Elp]

Well, also the quality of the engineering. But I suppose you can get decent results with not the best engineering.

Edited March 24 by Elp

[ollypenrice]

On 20/02/2024 at 10:54, JOC said:

 For viewing the heavens the key seems to be the apparent magnification from the EP.

I wonder if the active ingredient here is the exit pupil?

Olly