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DSLR Exposure Question

Acquisition Introductions Deep Sky M51 NGC5194
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Scott Deming avatar
Scott Deming avatar
Hello! I'm a new member and excited to be here! I've been viewing for several years and just recently got into astro imaging. I'm very familiar with standard photography and pretty proficient with a DSLR when it comes to day shots, studio and green screen. However, I'm curious about deep sky imaging and best exposures/ISOs when using a DSLR. I have a Panasonic GH5s, which is pretty remarkable for low light. I've taken a few images and typically average 90 seconds to two minutes, using ISO of 1200 to 1600. I tried attaching an image of M51 from a few nights ago, but can't figure out how to do it. I took twenty lights at 2 minutes, twenty darks at 2 minutes and twenty flats at whatever the aperture setting decided. ISO was 1600.

I feel like I'm missing a lot of detail. I do understand the Ha filter thing and the difference between DSLRs and dedicated astro cameras when it comes to that, but I'm wondering how limited I am with the GH5s and if I should consider a ZWO or another astro camera, or if I just need to learn some tricks with the DSLR to boost detail and color. Any help would be greatly appreciated!

Thank you!

Scott Deming
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Marc Agostini avatar
Marc Agostini avatar
Hi Scott,

First of all congrats, I have never seen such a great "first light" before, especially on a more demanding type of telescope ! You clearly know what you're doing.

One great resource fo knowing your perfect ISO setting is this site: https://www.photonstophotos.net/Charts/PDR.htm

If you select your GH5s, you can see the dynamic range vs. the ISO setting. At 1600, your camera already starts to suffer, you only have 6 stops of dynamic range left. You can tell this in the image, because the lights in the centre of the galaxy and all stars are burnt out, which makes you loose details. Also, the noise level is pretty high, which diminishes detail. Try lower ISO and longer exposure, telling by your perfectly round stars you can afford it!  But I'm afraid your camera hasn't much DR to begin with, even at low ISO its only arround nine stops.

Modern Astro cameras offer three main advantages compared to your camera:
  1. Higher dynamic range, in the range of 13 stops
    2. [/*]
  2. Higher quantum efficiency, which leads to a better use of the photons your Scope collects[/*]
  3. Lower noise levels, thermal and read noise will be much less, which gives you a much better SNR for every sub you take.[/*]
For a scope of your focal length, I would recommend something like the ASI 294 or a similar camera with the IMX 294 sensor. If you want to know why, read up on the subject of sampling or use this handy siteOne more thing: For ISO, use native steps, like 200,400,800,1600...... The steps inbetween usually happen on camera and not on chip, which can result in loss of information.

Clear skies, Marc
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Scott Deming avatar
Scott Deming avatar
Wow! Marc, thank you so much for this amazing information! I use my GH5s and GH5 for studio work, mostly green screen, as well as using the GH5 (higher photo resolution) for stills. I knew it wasn't meant for astro imaging, but thought I'd give it a shot.

Again, thank you for all this wonderful information. I will certainly consider it all.

Regards,

Scott
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Van H. McComas avatar
Van H. McComas avatar
Scott,

If you go looking for another DSLR you might want to take a look at this site:  https://www.spencerscamera.com/

I bought my Modified Canon T7i there but a lot of astrophotographers are going with CCD cameras which I know nothing about.

The only thing about a modified DSLR is they aren't any good in daylight unless you add back in a filter on the lens to remove the inferred.

Looking forward to your next images.

Van
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