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What exposure time in each frame would you recommend for a Takahashi E-160ed and Asi6200mm ? I normally use 300 seconds for my FSQ85, and I wonder if would be a good idea to take shorter frames, due to the speed of the E-160ed
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With my QHY600 I've been using 180s for LRGB at 0 gain in extended full well readout mode (about 80000 e- well depth).
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Figure out what your sky-noise limit is. In my bortle (6) I expose for 120s for SHO and 30s for RGB. I prefer running shorter subs facilitate better image rejection.
Re the second point, nothing wrong with those settings, but you can significantly increase you dynamic range in Mode 1 Gain 56 at the expense of more subs.
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I might be weird but I usually use different exposures for different targets
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I might be weird but I usually use different exposures for different targets
Interesting, so do you mind sharing your criteria? Shorter frames for brighter targets, maybe?
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Most dso targets I shoot with 300s, but every now and then it's too much or too little.
My latest fail I mean example was the bubble nebula, I overexposed the core and no matter what I did in post, I was not able to fix it.
Even with masks after a light stretch, it just started to look weird at some point.
On the other hand, dark nebulae I sometimes go with 600s.
The concept of shooting at a given expore time depending on the scope is new to me.
Unlesst you meant exposure time suitable for most targets.
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Most dso targets I shoot with 300s, but every now and then it's too much or too little.
My latest fail I mean example was the bubble nebula, I overexposed the core and no matter what I did in post, I was not able to fix it.
Even with masks after a light stretch, it just started to look weird at some point.
On the other hand, dark nebulae I sometimes go with 600s.
The concept of shooting at a given expore time depending on the scope is new to me.
Unlesst you meant exposure time suitable for most targets.
But do you use this exposure in a fast telescopes like the E-160ed? Or only on slower APOs ?
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Depends on a lot of things -- local sky conditions, SNR to swamp the read noise, speed of the scope. What works for one person in their sky conditions may not work for another in other sky conditions. The E160-ED @ f/3.3 hoovers the light, so I expose shorter times than with my f/7 refractor.
Greg Crinklaw is currently adding exposure calculators to SkyTools (he presented his approach at NEAIC) that will account for all of the above. Interested to see what it recommends for my imaging system at my location.
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Rafael Sampaio:
But do you use this exposure in a fast telescopes like the E-160ed? Or only on slower APOs ?
I use it for my slow F7.5
Will be way too long for most targets with a fast scope like yours.
Usually I take a sub and check the histogram and data.
With a new scope I tend to take a few subs with different exposures, load it into Pixinsight and have a closer look after a quick stretch.
Got my F7.5 since about a year and I'm still unsure at times what exposure to use.
There's not one correct answer to your question it will take some trial and error.
If you just look at the numbers, your scope gathers roughtly 3x more light than mine, so I'd use 100 seconds as a starting point.
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Jeff Ridder:
Depends on a lot of things -- local sky conditions, SNR to swamp the read noise, speed of the scope. What works for one person in their sky conditions may not work for another in other sky conditions. The E160-ED @ f/3.3 hoovers the light, so I expose shorter times than with my f/7 refractor.
Greg Crinklaw is currently adding exposure calculators to SkyTools (he presented his approach at NEAIC) that will account for all of the above. Interested to see what it recommends for my imaging system at my location.
Perfect! So, based in your experience, what exposure time would you recommend for a Bortle 4 sky, with a IMX 455 sensor with medium gain (HCG on), and a E-160ed?
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Rafael Sampaio:
Jeff Ridder:
Depends on a lot of things -- local sky conditions, SNR to swamp the read noise, speed of the scope. What works for one person in their sky conditions may not work for another in other sky conditions. The E160-ED @ f/3.3 hoovers the light, so I expose shorter times than with my f/7 refractor.
Greg Crinklaw is currently adding exposure calculators to SkyTools (he presented his approach at NEAIC) that will account for all of the above. Interested to see what it recommends for my imaging system at my location.
Perfect! So, based in your experience, what exposure time would you recommend for a Bortle 4 sky, with a IMX 455 sensor with medium gain (HCG on), and a E-160ed?
I'm in Bortle 4 with E160-ED @ f/3.3 with QHY600M. For narrowband, I use readout mode 1 (High Gain mode), gain 56 (the point where the dynamic range jumps up and read noise drops to around 1.5) and 600 second exposures with 6 nm filters (S, H, and O). For wideband, I use readout mode 3 (extended full well), gain 0 (well depth 80k) and 180s exposures (LRGB) -- especially if there are bright stars in the frame (Sadr, gamma cass, etc.). If using high gain mode @ gain 56 for broadband, I'd probably shorten that to 60 seconds or so and take a look at the histogram.
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At Obstech Chile, moonless nights only, RGB at gain 100 with an ASI6200MM (corresponding to mode 1, gain56 on the QHY) : 120s.
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Spacetime Pictures:
At Obstech Chile, moonless nights only, RGB at gain 100 with an ASI6200MM (corresponding to mode 1, gain56 on the QHY) : 120s.
Thanks, what the telescope used?
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Rafael Sampaio:
Spacetime Pictures:
At Obstech Chile, moonless nights only, RGB at gain 100 with an ASI6200MM (corresponding to mode 1, gain56 on the QHY) : 120s.
Thanks, what the telescope used?
E160ed at f3.3
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So, if you have higher light pollution you need shorter frames, right?
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Rafael Sampaio:
So, if you have higher light pollution you need shorter frames, right?
Yes!
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a) You 'need' shorter frames, or b) Shorter frames are a more efficient use of integration time?
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a) You 'need' shorter frames, or b) Shorter frames are a more efficient use of integration time?
If I understood correctly, you will get too much noise with a long exposure in a light polluted area. The light pollution will cancel the extra signal you want to get. So it’s more efficient to get more frames , with short exposures.
Right?
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Light pollution is part of the signal. You want to collect enough signal to swamp the read noise. Since light pollution contributes to the signal, you will get there faster so can expose for less time, even though the target signal might be weak. In principle, you can expose longer, but at the risk of saturating your stars. This video is worth the watch: https://youtu.be/3RH93UvP358?si=Xl4_bJvbwsNWnPL5.
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Jeff Ridder:
Light pollution is part of the signal. You want to collect enough signal to swamp the read noise. Since light pollution contributes to the signal, you will get there faster so can expose for less time, even though the target signal might be weak. In principle, you can expose longer, but at the risk of saturating your stars. This video is worth the watch: https://youtu.be/3RH93UvP358?si=Xl4_bJvbwsNWnPL5.
Perfect!
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To proof my point that there is not one optimal setting for a scope, here ist the image of the day
300" @ F2.8
Tbf I assure he in like b2 or so.
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There's something to be said for erring on the side of shorter subs.
1. Allows you to cloud dodge more effectively (lol)
2. Allows for better rejection in processing at the expense of calibration time
3. Allows for poorer guiding and alignment issues
4. Avoids oversaturation of stars and brighter targets
*Technically* according to Robin Glover who is far cleverer than I, there are optimal sub lengths for filters, F ratios and SQM.
*Realistically* I throw out X% of my subs each night anyway, so I'd rather throw away shorter ones.
The E130/E160/E180 is a photon-guzzler to rival most of the astronomy market. CMOS doesn't need long subs like CCD's did. This scope and modern CMOS all point to the shorter sub. Honestly, I've been getting ridiclously good results with just 60 second subs.
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