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A cluster and a bubble

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M52 and NGC 7635 (the Bubble nebula)

16 18 x 10 minutes exposures at ISO 200

SW 150PDS on AZ EQ6GT, Pentax K20D (not modified)

The camera picks up some Ha. Enough for the bubble to show, but not enough for the background Ha. I'm not sure if I should keep the faint red or get rid of it and get an even background.

Comments welcome.


Edited by wimvb
note to self: learn to count
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Hej Wim

nice shot!

Just wonder why you run the camera on ISO200? Is the Pentax that noisy? I can usually set my Canon 60Da to ISO1600 before I notice an increase noise with the natural cooling in wintertime Sweden. At ISO1600 you could have got 128 exposures in the same time with the same light intensity (or go for more signal in each sub). I am in Australia right now and tried some AP with my wife's Canon 70D last night. I have no EQ drive so I limited it to 20 s exposures at ISO1600 and the result was terrible due to noise so I have given up, but down here it is 30 °C at night.

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My camera is so noisy that anything higher than iso 400 is a waist of effort. I tried the Iris neb last month with iso 1600 and yesterday with iso 400. The lower iso in combination with the lower temperature made all the difference. Besides, iso in modern dslrs (or in my case, even ancient), is basically the same as gain in astro cameras. It just amplifies the electric signal. With low noise, this can better be achieved by stretching during post processing.

I can dig up the two images of the Iris, and post for comparison.

To combat noise in my images, I now use a combination of Olly's technique (bad pixel map and aggressive hot pixel filter) and darks. I found out that with the longer exposure times that come with guiding, just using Olly's technique isn't enough anymore. During post processing, I heavily rely on PixInsights noise reduction methods.

In short, I need to save up for a new camera.

Which part of Australia are you in? Doing marine biology, I guess you are at the Small Barrier Reef?

Ha det bra, och gott nytt år

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Here's a comparison image of my camera's performance at ISO 1600 and ISO 400.

It's a crop from a single frame. Debayered in PixInsight and stretched using STF as a permanent stretch (also in PI). Saved as jpeg.

Scope: SW 150PDS + Baader CC, camera: Pentax K20D (not modified)

Like I wrote before, anyting over ISO 400 isn't worth it, unless the temperature is in the negative numbers.


Edited by wimvb
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yes, that is much more noise than my Canon 60Da, so saving up for another camera sounds like a good plan - you clearly deserve it. My next one will probably be one of the cooled ZWO-ASI cameras - clearly a lot of bang for the buck.

Good guess, I am on Lizard Island Research Station on the northern part of the GBR. Fantastic dark sky. Nearest city is Cairns 200 km south so no light pollution whatsoever even at the horizon - next time I go here I should bring some AP gear to keep me up at night!

I attach a cropped sub from one of my last images from back home (November), so ca 0°C. It is from the centre of the Pacman Nebula at ISO1600 and I have a hard time even finding a hot pixel. I do not bother using darks. The final stacked image is here:


IMG_2371 crop to show noise.jpg

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I noticed the much lower noise level of Canon cameras when I did some processing for other people. It's nice to be able to process an image and not needing to start with noise reduction. At the moment, TGVDenoise and MultiscaleMedianTransform are my best friends. And Dynamic Crop is a close relative. Here's my starting point for the above image (stacked, DBE applied and colour calibrated)


ZWO is also on my list, the ASI1600 mono cooled has started to prove itself. But by the time I can afford a new camera, maybe a mono version of the ASI071 will be available (APS-C, dslr size sensor). Otoh, I also have Atik on my wish list. Smaller sensor, but proven track record.

Enjoy your stay "down under".

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my sometimes very understanding wife says I am allowed to buy the ASI1600MMC and I have my finger on the trigger. The first plan is to use it to collect Ha to add to my DSLR RGB images, but the chip is just a bit too small to be perfect so like you I think that I should probably wait and see if the ASI071 comes out in a mono version (I would be very troubled if that happened a week after I bought an ASI1600MMC). Even the colour ASI071 seems a fantastic option compared to most DSLRs since it is chilled.

By the way, I see on amazon.co.uk that you can get a 60Da used for around 400 GBP - 1/3 of the price of the ASIs. I really like my 60Da, both for the low noise and the increased Ha sensitivity. Here you can see the extra Ha that I managed to get out of the bubble with that camera:


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The problem with the asi071 mono (if it will come) is probably going to be a need for larger filters. I haven't done the math, but likely even 36 mm filters may be on the small side. The filter set will be more expensive than the camera.

I have considered getting a cheap canon, but  I believe it was @ollypenrice who put it wisely "buy once, cry once". With my light pollution (not too bad, but enough to be a nuisance and a limit to what I can image), I am taking the step to Ha-RGB. I have also thought the colour asi to be a good alternative for cooled and modded dslr. The asi071 will fill a gap in the market. That would take care of the noise, but not the light pollution problem.


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