The "No EQ" DSO Challenge!

[Filroden]

1 hour ago, The Admiral said:

I've never been clear on whether read noise increases with gain or not!

Read noise reduces with increasing gain (you're amplifying the signal so the fixed read noise represents a smaller percentage) and dynamic range also reduces with increasing gain, so you're always is a trade-off. Jon Rista on cloudynights has put up a lot of information about CMOS chips (using the ZWO ASI1600) on read noise, gain, etc. I suspect the principles will apply to any CMOS though the read noise will be different.

[rotatux]

About read noise: yes for my cam it is about constant (and low) when varying ISO, just like sensorgen says.

I've also done my own tests and can confirm this, as those graphs show. I believe they would look the same on any modern CMOS sensor, apart from the data range (my sensor is 12-bits so 0-4095 only). What's more interesting for us is that the saturation capacity is not the same at all for each color (I don't speak of mono sensors of course), and it appears sensorsen only covered green capacity.

BTW intermediate isos are real steps in the amplification stage, so worth investigating, contrary to what many sites say about staying to "round" values.

You can also see that the E-PL6 has about max range at 800 iso in the reds where it's the weakest. So IMO there would be no point going to 400 or 200 iso, let apart to expose correctly for the chosen duration.

Additionally I generally prefer to raise ISO because 1/ IMO half to quarter of the data range is acceptable (sacrifices only 1 or 2 bits that will be gained back with stacking), and 2/ I want higher numeric values ("ADU") to average out to higher precision numbers (this is debatable and depends highly on my 16-bit limited software processing chain).

This is been debated here many times ;-) so I would prefer not to expand too much and come back with more actual results... i.e. DSO images

[dph1nm]

18 hours ago, Uranium235 said:

Its about finding what point your camera becomes "ISOless", which turned out to be ISO200 for my Canon 1000d...

I don't think the 1000D ever becomes "ISOless". The read noise at ISO1600 is half that at ISO200

NigelM

[Uranium235]

32 minutes ago, dph1nm said:

I don't think the 1000D ever becomes "ISOless". The read noise at ISO1600 is half that at ISO200

NigelM

Sensorgen DR graph for the 1000d:

Graphs for all canon cameras here:

http://dslr-astrophotography.com/iso-values-canon-cameras/

Im inclined not to go against the article that Christian wrote, so far its been very accurate and helped retain star colour that otherwise would have been burnt out very quickly at f2:

The read noise is an aside, and is dealt with by proper calibration. What works in real world use and retaining as much dynamic range as possible is what counts I think. Take a moment to read the article, then you can decide for yourself:

http://dslr-astrophotography.com/iso-dslr-astrophotography/

Whether you agree or disagree with it is entirely up to you, as there will always be differences in opinion when it comes to what works best

But, I think we are digressing too much as this thread is about non-eq imaging.

[Alien 13]

Just looked up my Camera (80D) and the graph looks totally different to all the others i.e. its a straight line, not sure what it means as I always shoot ISO 800-1600.

Alan

[Stub Mandrel]

The problem I have is that there are loads of different articles, each appearing as scholarly and well-worked out as the next, and they all end up giving different advice!

 

[rotatux]

As requested, plate solve of my previous image through astrometry.net:

(job)

[rotatux]

2 nights ago I managed to have another go at Markarian's chain, and tried different settings (mainly, higher ISO: 3200 instead of 2000).

I find it's much better than previous try, maybe except blobby stars typical of refractors and strange star colors (though I see it also in SDSS images on astrometry.net). Was also much easier to process, as I didn't have to go at the limit of stretching to get decent details. Of course still more frames wanted, but I had other targets within that available 2 hours window.

Details in my gallery.

And annotated with astrometry.net job:

Discovered Siamese Twins (left half-height) and strange NGC4299 (lower right border), going to read about them.

[SteveNickolls]

Hi Fabien,

Thanks for posting your latest image, well done there :-) Can I enquire as to the equipment used, settings etc. and any filters employed? I'd like to have an attempt at imaging that area of sky before it is totally out of my view but that's down to the weather which isn't co-operating at all this year.

Good luck too with further imaging.

Cheers,
Steve

[rotatux]

Hi Steve, thanks for comments. Absolutely no filter, as most of the time they remove too much wanted photons

Setup details are in my gallery page: follow the rabbit link just under the first image ;-) . I was trying a new way to not clutter posts too much, would you prefer / should I rather copy the settings in each post ?

[SteveNickolls]

Hi Fabien, Thanks for your reply. No that's fine thanks, just me being idle I guess :-)

I'm hoping to do more in the future with camera and lens and seeing the outcome of images at say 200mm FL is very helpful and inspirational.

Cheers,
Steve

Edited May 18, 2017 by SteveNickolls

[rotatux]

Let me share two more processed images from 2017-05-16' ~night~ with the OM-Zuiko 200/4.

First is Bode's galaxies, code M81 and M82. Two more NGC galaxies in the scene. Shows somewhat unexpected structure for that FL. Details in my gallery.

Second is America Nebula (NGC7000) and Pelican Nebula. The 200 FL fits almost perfectly that targets. Details in my gallery. I tried some HDR to detach the brightest stars and give some 3D look, but that masked the faintest parts under the Pelican, so I stayed with the traditional version.

[Ukvegas]

On 2014-10-30 at 12:17, JGM1971 said:

I do. Newcastle, UK. It was part of the reason I started this thread, as I wanted to see just what targets were potentially possible when not tracking EQ - I presumed that if you were an Alt As user, then part of your reason was that due to location, light pollution would rule out having a much higher spec set up.

I generally look to see if it's clear, then quickly set up in the back garden, using part of my house to block as much of the lamp posts in the street. Hence, I have no views West!

Great to see experimenters still around and making the best with what they have. Well done, love your shots. To me this is the best sort of astrophotography

[Stub Mandrel]

13 hours ago, rotatux said:

Let me share two more processed images from 2017-05-16' ~night~ with the OM-Zuiko 200/4.

First is Bode's galaxies, code M81 and M82. Two more NGC galaxies in the scene. Shows somewhat unexpected structure for that FL. Details in my gallery.

Second is America Nebula (NGC7000) and Pelican Nebula. The 200 FL fits almost perfectly that targets. Details in my gallery. I tried some HDR to detach the brightest stars and give some 3D look, but that masked the faintest parts under the Pelican, so I stayed with the traditional version.

If you have PhotoShop it might be worth getting this (formerly known as 'Noel's Actions'):

http://www.prodigitalsoftware.com/Astronomy_Tools_For_Full_Version.html

It can do a good job of getting rid of those blue/violet haloes which are caused by blue/UV overspill and achromatic lenses.

[rotatux]

2 hours ago, Stub Mandrel said:

blue/violet haloes which are caused by blue/UV overspill and achromatic lenses

Thanks Neil. I don't have Photoshop (no Windows, no Mac). If you know of a Gimp plugin then I could try something else...

Actually if you look carefully there's both blue and red rings around bright edges (check that moon image where the red ring is obvious), but with different size and intensity. That's a type of CA (I think "color dispersion") which I have no plugin to handle; That's neither Directional CA nor Lateral CA, which I already have a plugin for.

I'm ready to accept it as the price to pay for using the lens at full-aperture. Though I *can* reduce or get rid of it by using a DIY mask to reduce aperture to F/5 or F/5.6, but I'm just reluctant to use them because that fault is very uniform up to the edges (kind of artistic, one would say) and makes star colors more obvious.

Edited May 20, 2017 by rotatux

[Stub Mandrel]

Shame, I think 'Steve's Actions' which you get access to with 'every photo counts' has a red halo removal tool.

Have you astro-modded your camera? If so you might find that adding an IR/UV cut filter reduces the haloes. When I modded my 450D I retained the UV/IR filter, although for the 10D I had to remove both as they are joined together.

[rotatux]

No, never astro-modded either the PM1 or the PL6. Currently I don't intend to, as IMO I'm unable to do it and would just detroy the sensor if trying.

What would you think of the red sensitivity of the stock PL6, based on my image of America ? Intuitively I find it's much better than PM1, when I compare with e.g. that previous try.

[Stub Mandrel]

I found astro-modding hugely increased what I got from the NAN, and brought out the Pelican.

It's not as hard as it seems (OK I did destroy a 10D sensor on my first try...)

How do you do that 'mouse over' index thingy? - it's great!

Edited May 20, 2017 by Stub Mandrel

[Shaun_Astro]

Crystal clear last night. And they turn the lights off at midnight now.

 

Edited May 24, 2017 by Shaun_Astro

[Filroden]

2 minutes ago, Shaun_Astro said:

Took this, but my flats don't seem to work half as well with some shots, the camera is orientated the same way, I don't understand how sometimes they only remove less than half the vignetting; hence the clipping in the corners.

That's a nice result. Lovely star colours and you're just picking up the reds in the outer parts of the nebula.

Do you take new flats after every session. Whilst you can re-use flats if you're certain camera and scope remain oriented, this usually applies if you're using a fixed set-up. If you're tearing down the equipment each session i would recommend trying with fresh flats.

You're showing some trailing. What exposure length are you using? You may be able to take shorter exposures and integrate more of them to get the same total integration time. This might help reduce trailing and loss of exposures. I would never use an exposure that gave less than 80% results. We have far too few clear nights to be throwing away subs!

[Shaun_Astro]

**Removed**

Edited May 24, 2017 by Shaun_Astro
See next post.

[Shaun_Astro]

So I messed up, and used a load of bad subs and a set of bad flats. It looked terrible compared to this version, which is only 16 mins instead of 30, but notice the difference...

 

 

Edited May 24, 2017 by Shaun_Astro

[Filroden]

I liked the first version but this is amazing! And only 16 minutes? We're your subs 30s or less? If so I'd put that into the competition. 

[Shaun_Astro]

1 hour ago, Filroden said:

I liked the first version but this is amazing! And only 16 minutes? We're your subs 30s or less? If so I'd put that into the competition. 

Thanks man! 33x30 sec subs, darks and flats. What competition? 

[Filroden]

5 minutes ago, Shaun_Astro said:

Thanks man! 33x30 sec subs, darks and flats. What competition? 

Competition details: 

Forum to post images: https://stargazerslounge.com/forum/226-imaging-challenge-3-30-second-exposures/