How does one stack lunar image?

Started 3 months ago | Discussions thread
Lyle Aldridge Senior Member • Posts: 1,101
Re: Ummm ... are you using a tripod yet?

OutsideTheMatrix wrote:

Lyle Aldridge wrote:

I'm hesitant to ask, but your earlier post revealed that your images to that point had been hand-held, and I still haven't noticed any mention of a tripod in your posts. Also, your post in the other forum seems to say you're having difficulty keeping Jupiter in the FOV, which makes me wonder even more.

Yes I am now with manual focus mode, when I was shooting with AF-S mode, I was doing them handheld. Even handheld I had no problem keeping Jupiter and Saturn in the FOV in AF-S mode even with the camera zoomed all the way in (4zx/84x), but with manual focus mode when I zoom in somewhat, the planets seem to get dimmer and blurry, as if they are going out of focus. This wasn't happening in AF-S mode but in that mode when I snap an image it looks like a bloated star with none of the banding or rings that I see from other people who have the same camera. I was thinking of using the AF-L button to lock focus when they start to blur, but doesn't that mean if I zoom in further the focus will become unlocked again?

There are perhaps some exceptions, but for most cameras and astro targets, manual focusing is absolutely essential. It requires a steady hand and a steady tripod. Lots of cheap tripods aren't up to the task. I have zero experience with your specific camera, but it sounds like the zoom lens on your camera is not parfocal, so you're just going to have to focus and zoom in steps. Your may find it helpful to use auto-focus while you're zooming in on the target, then switch to manual.

The lens on your camera is only 135mm at its longest, but you will be using a level of magnification that demands extreme steadiness. If you have a way of activating the shutter without touching the camera, that would be preferred, but at least use a shutter delay, so any vibration will have dampened before the exposure is made.

Even in lunar imaging, and especially in planetary, you need to be aware of the limits imposed by atmospheric turbulence, and by the fairly small (33mm) aperture of your lens. At present, for example, Saturn's disk has an angular size of about 18 arc-seconds, and the theoretical limit of resolution for a 33mm aperture, using the Dawes formula, is only about 3 .5 arc-seconds. With your 1.39u pixel size, each sensor pixel is covering about 1.6 arc-seconds. You will need unusually good "seeing" to get the kind of detail I think you're seeking, and the atmosphere doesn't behave that nicely very often. I'm sure the people who produced the images you're admiring have a lot of others that don't show so much, either.

Finally, I took a look at the HS50EXR manual, and notice that it has an "advanced" function that I believe can produce a four-image stack of images. I own an EXR model that also has that feature, and have found that it does produce some improvement in sharpness of some of my own low-light (but not astro) images. It might be interesting to see whether it provides any benefit once you have the focus nailed down.

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