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The Moon with 8''


astrolulu

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3 minutes ago, astrolulu said:

I would like to say hi by presenting some of my photos of the Moon - not necessarily taken in the last few days. I happen to be using two 8-inch telescopes, so I thought to start a thread devoted to photos obtained with such aperture. I think if other 8'' owners would join it, it could be an interesting reference material for people looking for information on what to expect from such diameters in the case of lunar photography.

Let me start by presenting a few photos taken with the 8 '' Meade LX200 ACF and the ZWO ASi 178MC camera:

TYCHO-2022-03-13.jpg

COPERNICUS-2022-04-12.jpg

MARE-CRISIUM-2022-03-10.jpg

MARE-IMBRIUM-2022-05-09.jpg

RUPES-ALTAI-2022-05-09.jpg

RUPES-RECTA-2022-05-09.jpg

Very nice work. I have a Skywatcher 200P and have used it on the Moon with my DSLR. I also have the monochrome version of your camera, the ASI 178MM. You have inspired me to see what I can achieve with the two together. I'll have to post my first stack taken at the last Supermoon in this thread. Not the best time to photograph the Moon, I know, but it was a clear night.

Thank you for the inspiration and let's hope we see many excellent efforts getting posted in this thread.

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Thank you very much. I am just finishing the processing of photos taken with my second 8-inch, i.e. quite old but still functional Celestron C8-N 200/1000 mm. It has the same parameters as your Sky-Watcher 200P, so we will have an opportunity to compare the results. I consider my Celestron to be quite good optically. Of course, as long as I use a small area of a few mm around the focus.

The Meade ACF has, of course, a great coma correction, but in the case of the Newtonian telescope, the smaller the matrix, the safer - that's why I use the 178 model with a small 2.4 pixel. In combination with a 2x Barlow lens (Newton) or without a lens (SCT) it gives a relatively optimal system of parameters.

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Thanks, this is the advantage of the camera, which simply gives a high resolution. With a focal length of 2 m, there is no reason to use an additional Barlow lens which allows me to cover a large part of the Moon's surface. For me, this is the most important advantage of this camera. I would like to switch to the 183 model - with a resolution of 20 mb and the same pixel size. At this resolution, capturing the entire Moon with the same magnification should be no problem.

Edited by astrolulu
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Here is my effort. Not the best time to photograph when the Moon is full, but it was the first time I had captured sufficient images to stack and actually stacked them. I have posted this photo before, but in colour. This one has been converted to greyscale in GIMP and I think it has improved the overall result.

Images were acquired with my D800 at prime focus of the Skywatcher 200P. Hopefully, I will soon be able to use the ASI178MM and get in a lot closer.

Moon_B&W_20220812.jpg

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Mandy, don't give up so quickly. Your photo contains the correct color information and will look great in color after correcting the purple tint and enhancing the color saturation. A certain problem is the discrepancy of colors in the upper part of the image, in which the coma effect was probably visible. This requires the same intervention as when eliminating typical chromatic aberration - you can try, for example, a color noise reduction filter.

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On 11/09/2022 at 00:05, astrolulu said:

Mandy, don't give up so quickly. Your photo contains the correct color information and will look great in color after correcting the purple tint and enhancing the color saturation. A certain problem is the discrepancy of colors in the upper part of the image, in which the coma effect was probably visible. This requires the same intervention as when eliminating typical chromatic aberration - you can try, for example, a color noise reduction filter.

Yes, I'll have another go at processing the colours. Can you explain a bit more about coma, as I really don't understand it fully. Is there anything I can do in processing or does it have to be dealt with during imaging?

I didn't realise who you were when we first started talking in here, but then I saw your link to the fantastic Moon map that I downloaded a long time ago. Thank you for that. It is so much easier to use than others I have seen.

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Mandy, thank you so much and I'm glad that my map is useful - it's very motivating for me!

I can see a similar effect myself when I take photos in the focus of an 8 '' newtonian. If I use low magnification (no Barlow lens) I notice that some of the outer parts of the photo are losing sharpness and blurring. I think the same is visible in your photo and that it is simply the coma that causes the pinpoint images of stars to turn into lines - the more clearly the further from the center of the field of view.

The truth is that the Newtonian telescope produces a coma-free image over a very small area, literally a few millimeters around the focus. In the case of larger sensors, especially in the case of DSLRs, coma may appear already in the area of the matrix. My guess is that this phenomenon deflects the rays slightly differently for each wavelength, hence the appearance of colored discoloration at the edges of contrasting details.

What can you do about it? First of all, check the collimation of the telescope, secondly, you can experiment with position the Moon within the frame to minimize this effect, and thirdly - use higher magnifications, i.e. in practice Barlow lenses 🙂

Edited by astrolulu
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11 hours ago, astrolulu said:

What can you do about it? First of all, check the collimation of the telescope, secondly, you can experiment with position the Moon within the frame to minimize this effect

A Coma corrector is a good investment, the flat field is especially good for the large DSLR sensor. 

https://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html

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Thanks, the triple Messier is one of my moon favorites 🙂 CA is inevitable if there's a piece of glass along the way - for example the SCT corrector. It will always appear in a rudimentary form, but luckily there are tools to deal with it, e.g. in Photoshop.

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@astrolulu I've had a bit of a play with the original stacked image and adjusted the colour balance. It looks a lot better than the original colour image.

Your image taken with the LX200 is fantastic!

@Laurieast thank you for the link to the coma corrector. I'll certainly keep it in mind for future reference, but I think I'll spend a bit of time perfecting my technique first, then go for kit upgrades. I just need some clear skies, now!

Thanks again, to both of you. Your advice is always appreciated.

Moon__Colour_Corrected_20220812.jpg

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Hi Mandy, thanks for posting your next version here. Although I do not use GIMP and I do not want to pretend to be a specialist in this field, let me share a few rules that are worth applying regardless of the software you use.

Rule one is to keep an eye on the full tonal range of an image. Please note how our eye works. Even if we move from a bright environment to a dark room, where we initially do not see anything, the eye tries to increase the amount of light and maximize the scale from dark to light - so as to "stretch" the brightness and tonal range of the image as wide as possible.

The "Levels" parameter (in GIMP Colors-> Levels) serves the same purpose. Darkest parts should be black, and the brightest parts of the image usually should be white ("almost white" sometimes works better). Our goal is to extend the tonal range of the image, visible in the form of a histogram, so that there is no empty space left (black) and right (white). Note that the adjustments can be made either on a full-color RGB image, or on the individual R, G and B components. Try to play with this dialog box, you will see that in a simple way you will greatly improve the effect.

levels.jpg.169808fb7da01bdb22cc734c783dd582.jpg

The second important issue is the selection of the scale to the image resolution. You have a great telescope and there is no reason why you should not get images comparable to those shown here, which were also taken with an 8 '' instrument. For some reason, however, the resolution of your photo is smaller than it could be. I suspect you might have used a DSLR with a large pixel sensor and you lost a lot of information about fine details. Regardless of the reason, however, it is always worth using such a scale of the image at which the blurring of details is no longer clearly visible. I tried to reduce your photo to 70%. In addition to the fact that these blurring immediately become less noticeable, such a reduction is always a good opportunity to further sharpen the image. If you compensate for such a reduction by adding a background that allows you to effectively display the object, the effect should be much better.

mandy.jpg.772bf0dd26d70488bf8b68b35e32821b.jpg

Edited by astrolulu
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@astrolulu Wow! Your results with my image are amazing. Thank you for doing this. I will have another look myself later and see if I can achieve similar.

You are quite correct about pixel size, as I used my D800 for this work, which has a pixel size of 4.88 um. I am planning to make my next attempt with the D3200, which gives 3.84 um, so a slight improvement. Obviously, my best option would be the ASI178MM with it's 2.4 um pixels, but I am not able to set up at present and I don't think the Moon's disc quite fits this sensor with my current telescopes, but it should give some nice close-ups.

I'll keep practicing!

PS, if you put an @ before the name of anyone you are replying to, they will recieve an alert. I have to look for your replies at present. 😊

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Thanks @Mandy D 🙂 I use the color version 178 model and I can recommend it. Of course, the monochrome version has a chance to pick out a slightly more precise detail, but it is worth remembering about the time limitations accompanying planetary photography. For example, Jupiter rotates so fast that if collecting material takes more than 2-3 minutes at magnifications we can afford with 8'', the image will simply be blurry. Meanwhile, depending on the size of the frame and the parameters of the computer used, these 2-3 minutes may be the minimum time required to collect a decent number of frames in order to avoid excessive image noise. In the case of a mono camera, photographing Jupiter, and even Mars rotating about twice as slow, might be a challenge, as the time of each session must be multiplied by 3 ...

Edited by astrolulu
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