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Old 17-09-2018, 06:59 PM
Cimitar (Evan)
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Eagle Nebula (DSLR vs ZWO 174MM)

I recently took a single test sub of the eagle nebula using my new un-cooled ZWO ASI 174MM and it got me thinking... how would it compare to my DSLR on the same target under similar conditions?

The image on the left is a single 3.5min exposure, ISO1600, on an un-modded Canon 600D DSLR. The image on the right is a single 60sec exposure (using the default settings in Firecapture) with the ZWO ASI 174MM. Sorry I don't have the actual settings, it was literally my first night with the camera.

Chalk and cheese in my opinion.
I think it might be time to start saving for a new imaging camera

The scope is an 8" SCT, approx f/7. I also took a 600sec exposure at ISO800 on the DSLR, however the end result wasn't that much better. I'll upload that image separately.

Cheers, Evan
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Old 17-09-2018, 07:34 PM
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ASI174 wins. The comparison would be a lot closer with a modified DSLR.
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Old 17-09-2018, 07:37 PM
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Atmos (Colin)
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It is an interesting comparison although not at all unexpected
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Old 17-09-2018, 09:57 PM
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Good to see, although completely expected.

This is not just a comparison between a DSLR and an astro camera but also a comparison between an unmodified sensor with a Bayer matrix vs mono sensor.

The efficiency will be several times lower for the DSLR sensor:
1. The missing IR (expecially Ha from the Eagle nebula) is blocked by the filter in an unmodified DSLR.
2. The Bayer matrix. Mono will be about 2x more efficient (depending on sensor, Bayer matrix etc) and also will have a better resolution.

Apples and oranges I would say
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Old 19-09-2018, 09:14 PM
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Here's the 600sec ISO800 exposure taken with a Canon 600D
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Old 19-09-2018, 09:22 PM
Cimitar (Evan)
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Quote:
Originally Posted by cometcatcher View Post
ASI174 wins. The comparison would be a lot closer with a modified DSLR.
Quote:
Originally Posted by Atmos View Post
It is an interesting comparison although not at all unexpected
Quote:
Originally Posted by luka View Post
Good to see, although completely expected.

This is not just a comparison between a DSLR and an astro camera but also a comparison between an unmodified sensor with a Bayer matrix vs mono sensor.

The efficiency will be several times lower for the DSLR sensor:
1. The missing IR (expecially Ha from the Eagle nebula) is blocked by the filter in an unmodified DSLR.
2. The Bayer matrix. Mono will be about 2x more efficient (depending on sensor, Bayer matrix etc) and also will have a better resolution.

Apples and oranges I would say
What really blew me away was the comparison between un-processed subs.
The 60sec ZWO image (attached below) is straight out of the camera. No processing whatsoever.
The DSLR images in this thread are also un-processed.
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Old 19-09-2018, 09:57 PM
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The ZWO is defiantly a lot smoother but here's an other comparison pic taken with a 1100d, 180secs at 800iso, unmodded camera pic cropped but otherwise unprocessed.
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Old 19-09-2018, 10:14 PM
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The ZWO is defiantly a lot smoother but here's an other comparison pic taken with a 1100d, 180secs at 800iso, unmodded camera pic cropped but otherwise unprocessed.
Oh wow!
It's vastly different isn't it. I just looked up the manufacturing date of the 600D vs 1100D, however, according to wiki they're both built in 2011.
Can the type of telescope or f ratio contribute to the difference in quality of the final image? I only ask because I use an SCT, which I've heard to be considered 'slow'.
What type of telescope did you use for that image?
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Old 19-09-2018, 10:21 PM
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Can the type of telescope or f ratio contribute to the difference in quality of the final image? I only ask because I use an SCT, which I've heard to be considered 'slow'.
Yes. A fast F4 system will capture nebula in much shorter time than an F10 system will. This is why fast scopes match DSLR's so well.
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Old 19-09-2018, 11:05 PM
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For example here's one I took years ago. 1100D 10x45secs ISO 3200. 8" f/5.
Very simple unguided imaging, and just stacked in DSS, no separate darks, flats, etc: Far better images of M16 than this can be obtained with a DSLR. Best viewed at 50% screen.
raymo
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Old 19-09-2018, 11:33 PM
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Hi Evan

There is no doubt that the Astro cam image is clearer. I concur that the fact that it's a mono cam would help with that considerably. It's a good comparison to see. Often, as we all have different equipment, it's hard to tell what is causing what difference. Good on you for posting it.

As far as F ratio goes, lower f, lower required exposure time for the same data. That being said, I have an f10 SCT which is " slow " by AP standards and I live under skies that literally look like daylight when it's cloudy. The trick there is to trade in a good f ratio for some good old fashioned perseverance.
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Old 20-09-2018, 07:14 AM
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Quote:
Originally Posted by Cimitar View Post
Oh wow!
It's vastly different isn't it. I just looked up the manufacturing date of the 600D vs 1100D, however, according to wiki they're both built in 2011.
Can the type of telescope or f ratio contribute to the difference in quality of the final image? I only ask because I use an SCT, which I've heard to be considered 'slow'.
What type of telescope did you use for that image?

Hi Evan, the 1100d and 600d might be of similar vintage but have different sensors. I also have a later model 1300d but this is far more noisy than the 1100d so I stick with the 1100d.
I use a 10" f4.8 newt, capture times might be lower but noise is noise and in the end the sensor with the least noise wins.

Rick
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Old 20-09-2018, 02:45 PM
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Just another thought about the difference between unmodified 1100D and 600D.
I could not find the numbers but the AA/UV/IR filters in each camera could have quite different transmission rates for the Ha wavelength. And this target is very Ha rich.
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Old 20-09-2018, 07:46 PM
Cimitar (Evan)
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Quote:
Originally Posted by cometcatcher View Post
Yes. A fast F4 system will capture nebula in much shorter time than an F10 system will. This is why fast scopes match DSLR's so well.
Thanks Kevin, that might explain why I've seen so many DSLR images on the cloudy nights forum taken with fast newts

Quote:
Originally Posted by raymo View Post
For example here's one I took years ago. 1100D 10x45secs ISO 3200. 8" f/5.
Very simple unguided imaging, and just stacked in DSS, no separate darks, flats, etc: Far better images of M16 than this can be obtained with a DSLR.
raymo
Cheers Raymo, that's a great image you've got there!

Quote:
Originally Posted by RyanJones View Post
Hi Evan

There is no doubt that the Astro cam image is clearer. I concur that the fact that it's a mono cam would help with that considerably. It's a good comparison to see. Often, as we all have different equipment, it's hard to tell what is causing what difference. Good on you for posting it.

As far as F ratio goes, lower f, lower required exposure time for the same data. That being said, I have an f10 SCT which is " slow " by AP standards and I live under skies that literally look like daylight when it's cloudy. The trick there is to trade in a good f ratio for some good old fashioned perseverance.
Thanks Ryan, absolutely! Based the information contained in this thread I've now realised that it's not as simple as comparing the cameras. The telescope, f ratio etc. is also an important component.
I often find myself shooting at either f10 or f7. My favourite targets are galaxies so I prefer the longer focal lengths
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Old 20-09-2018, 07:59 PM
Cimitar (Evan)
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Quote:
Originally Posted by doppler View Post
Hi Evan, the 1100d and 600d might be of similar vintage but have different sensors. I also have a later model 1300d but this is far more noisy than the 1100d so I stick with the 1100d.
I use a 10" f4.8 newt, capture times might be lower but noise is noise and in the end the sensor with the least noise wins.

Rick
Thanks Rick, that makes a lot more sense now. In my mind it was initially just a direct comparison between cameras, however, I now realise that it's not as straight forward as that

Quote:
Originally Posted by luka View Post
Just another thought about the difference between unmodified 1100D and 600D.
I could not find the numbers but the AA/UV/IR filters in each camera could have quite different transmission rates for the Ha wavelength. And this target is very Ha rich.
Thanks Luka, you're right - that could also be having an affect. Makes you wonder if the filters may differ between models or whether its just between manufacturers.
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Old 20-09-2018, 08:50 PM
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The filters vary between models from the same manufacturers. This page has few graphs showing transmissions for various models for several manufacturers.
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