(Very) High Resolution Lunar Images – September 23, 2019

This post features some of the best lunar images I’ve ever acquired until now. They were all taken in very good seeing conditions, with some excellent moments that allowed for a few Green-filter shots. This means that my 355mm Newtonian was pushed to the maximum, and after performing some calculus and comparisons with other amateur images, I’ve concluded that no better resolution views are possible for the imaged areas using a similar sized scope. I must go forward in telescope-size at some point…at least a 450 mm one.

The processing of these images was performed not once but about three times for each of the images, in order to get the least amount of artifacts on them; this was paramount as these series were acquired specifically with the goal of making resolution measurements onto them. They are significantly over-sampled from the acquisition process in order to increase the number of pixels for the smallest details. This results in some not-so-nice looking images, but again, this was not the reason for acquiring them. However, for each of the original sized image I have an 80% resized and re-sharpened version, so a “better looking” shot.

Interestingly, while processing the original sized images, I’ve realized that part of the processing is similar to processing techniques of Deep-Sky images, and this is due to the noise levels that affect the large-amplification low-light images in general.

Now for the images…

Each lunar formation has two image versions: one slightly smaller but processed for a nicer view of the entire area, and the original-sized image, showing the slightest contrast differences at the pixel scale. This original-size images are the ones that resolution measurements were performed onto, comparing my shot with the data offered freely via the LROC QuickMap and its measurement tool. The virtual map can be found here: (https://quickmap.lroc.asu.edu/?extent=-90,-26.443275,90,26.443275&proj=10&layers=NrBsFYBoAZIRnpEoAsjZwLrc0A)

All images were acquired with a 355mm diameter Newton telescope, 1600mm focal length, 2.5x and 2.7x Barlow lenses, ASI 174MM camera and Baader CCD Green filter.

Image scale is approx 0.08 arcsec per pixel for all images, while telescope theoretical resolution is about 0.33 arcsec. This means that smallest details, considering perfect seeing conditions, should be around 4 pixels in length. I know, the details are over-sampled, and some image noise was unavoidable, but again, the motivation for this was to see just how “small” the “smallest” can be in terms of resolution.

Crater Pythagoras.

Smallest detected craters (due to the shadow inside their wall) are about 800 meters wide for this area, but this is largely affected by perspective at which the crater is viewed (they are strongly elongated, so the minor axis of the ellipse is far beyond the theoretical limit of the scope used).

Pythagoras small size version:

Pythagoras original size version:

2. Crater Gassendi.

Smallest detected craters are about 600 meters wide, but the crater is not that far from the lunar limb, so again there is a perspective factor to be take into account.

Many small rimae are also observable around the area.

Gassendi small size version:

Gassendi original size version:

3. Vallis Schroteri and crater Aristarchus.

Smallest detected craters are about 650 meters wide. The resolution is also slightly affected by the perspective.

One interesting feature and very rarely imaged is the small sinuous rima to the right of Aristarchus. It is around 650-700 meters wide in some parts.

The long rima that actually starts where Vallis Schroteri begins near Aristarchus, is also around 600 meters wide towards its tail (to the left of the image).

This image was also slightly affected by dew forming uneven on the secondary mirror of the telescope; the lower left corner of the image is smeared.

Aristarchus small size version: