5 replies to this topic

[Riaandw]

Pointed at the big search light in the sky last night. Rather fun from the usual deepsky. 

 

 

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[Riaandw]

14" Meade ACF on its forks and the ASI533MC at native focal length around 3800mm.

 

Looks a little dark. But feel like I'm over exposing while live stacking in Sharpcap. I'm in the first 30% of the histogram. Before throwing in the the VIP Barlow for a mosaic. Any tips to improve my result?

[jeffry7]

14" Meade ACF on its forks and the ASI533MC at native focal length around 3800mm.

Looks a little dark. But feel like I'm over exposing while live stacking in Sharpcap. I'm in the first 30% of the histogram. Before throwing in the the VIP Barlow for a mosaic. Any tips to improve my result?

The moon is a very bright subject. You can use this to your advantage to improve the quality of your data.

You can set the exposure such that you are using 2/3rds or 3/4ths of the histogram.

The tradeoff is wanting to keep exposure short, to prevent distortion from seeing, and wanting to keep the gain low so that you have less noise

Since you can collect many images quickly, you can stack out the noise. The moon being bright also helps keep the shutter speed short.

The reason to extend to higher portions of the histogram is so that there are more divisions between the brightest and darkest portions of the image. Why have a 12 bit sensor but only capture 8 bits worth of data by leaving the exposure so low? Or however many bits you are using at 1/3rd.

Some lunar photographers actually use ETTR techniques to make the most of the sensor.

You can then adjust the exposure in post to suit.

One thing to mention is that by using 3/4ths you leave room for sharpening later. Sharpening will make light areas lighter. If you already have bright highlights sharpening might cause the highlights to blow out.

There are ways to deal with that though

Tldr; yes you are underexposed. You can get better data by letting your histogram go up to at least 2/3rds. If you like the dark look, you can adjust in post with Exposure Compensation.

[Riaandw]

Thank you for that. Very useful and informative. Some tweaking then.

[Borodog]

You do not want to clip (saturate pixels) on the way in. Set your exposure and gain such that there are no pixels showing on the right hand side of the histogram. This will often leave the Moon overall looking dark, because the Moon has tiny but bright highlights. If you just increase the gain or exposure, you will clip these highlights. Instead, you should brighten the image via applying a nonlinear curve, either using the middle line of the Display Histogram, or by applying Gamma in the live stacker. Good luck.

Edited by Borodog, 15 June 2025 - 09:57 AM.

[JMP]

As Mike says, one of the challenges is trying not to blow out or saturate the bright spots. Exposure looks pretty good, actually. The 533 camera captures a linear image and a linear image will always look dark. Apply some gamma to bring up the background. A DSLR does this automatically, your eye acts in a similar way, bringing up the darker parts of the image.