1st DSO attempt

[aGreyarea]

Hi all,

I've just got a new (to me) goto and got my first ever pics of a DSO (wooohooo!)

I think I know where to start, but as there's nothing but cloud I wanted to clarify and get some further advice.

This is M42, a DSS stack of 12 x 30secs + 1 x 90 secs all iso100, from an unguided Omni 150 Newt and a canon 1000d prime focus. The laptop packed up hence only a few images in the stack. I've done some levels and curves in Corel photo Pro X3.

The first thing is the bright bit I can't get rid of. I thought it was a gradient(?) but read another post about vignetting on a 1000d, if it is vignetting, how do I make a lightbox (and why do you need as many flats as lights?)?

Would sorting that out also get rid of the vertical banding, or is that something else?

What else does it need?

Also in terms of form, how do I decide the right colours for an image? I understand the preference to look 'natural', but is there an 'Ideal' colour or do we accept that I might like it looking blue-er than someone else?

Sorry if these are a bit silly but I'm still finding my feet (and will be for a while I think!!).

Mnay thanks,

Liam

[Bizibilder]

It looks as if you have light getting to the camera sensor that shouldn't be - hence the "stripy bright light" effect. Could it be a house/street light getting into the end of the scope tube? Maybe a long "dew shield" would help? Otherwise that's a pretty impressive M42!!

[GrantEb]

Congrats on a very good first image.

Do the 30sec and 90sec subs both have the vertical banding?

[aGreyarea]

Hi,

Thanks for your replies.

I have a kendrick dewshield on the end already, but was trying to shoot it just over some houses a little way off. I had thought about flocking the inside, would that help.

Thanks Granteb, if i stretch the 30s I can just make a couple of verticle lines but not at all in the 90 sec sub. That doesn't even sound right to me.

Thanks

Liam

[GrantEb]

I think it is something to do with the amount of signal you are getting.

Next time try at iso400 or iso 800, should help.

[Photosbykev]

iso 100 is very low so my guess is you are pulling out more noise than signal in the image. Personally I use 800/1600 and shoot upto 300+ seconds on some images. Plenty of darks and flats will also significantly help you

[aGreyarea]

Hi GrantEb,

OK Thanks very much, I'll do that. I thought I read somewhere about always keeping the iso as low as possible but now that I think about it, that might have been for webcams.

Bizibilder, just been looking at your blog, Thanks for the comments but mine isn't even close to your M42! Wow! Is it much longer exposures to get the detail?

Thanks again both.

Liam

[Bizibilder]

My M42 was around 4 x 2min subs with 20 darks and 17 flats and really is "rough" - it needs far more data! - I just havn't had a clear sky where M42 has been visible - I have two trees blocking my southern aspect with around a one hour "photo opportunity" between them!!

[GrantEb]

Just did a quick experiment. I have found it very interesting.

These two shots are with my 1000d with the lense cap on(darks)

First is 30sec iso100, then 30sec iso800 at room temp.

Both were taken RAW, then stretched in PS, and converted to JPG's.

Notice the banding, and brightness on the right of the iso100 image.

Then the difference between that and the iso800 image.

Cheers

[GrantEb]

And here's 90sec iso100

[aGreyarea]

Hi GrantEb,

Wow, now I'm really showing my inexperience but why would the image show more/brighter noise on a shorter exposure?

I see why exactly you needs darks now, why would the image be brighter to the right? are most/all sensors like this, or is that why my 1000d is £200 and a similar size sbig is £2000?

Is that also vignetting in my image? I thought it was and it was off to the top corner because of poor collimation.

Photosbykev

Thanks, I don't have any way to guide it at all at the moment but will have to start taking darks and flats, I'll definately go at higher iso though, particularly after GrantEbs demonstration.

Thanks again all.

What about deciding on colours?

Is it just about taste or is there a form? I'm looking at you Bizibilder! Re your comments on your blog about the unmodded camera, if it should be redder, why were you not just a little more aggresive on the red curve, are there 'the right' curve to use? I say this because I think I prefer the colours in your image.

Thanks to all.

Liam

[GrantEb]

Not your inexperience, youré learning just like me.

I have no idea at the moment, but I am busy shooting darks at all different exposures and iso's to see what happens.

I am so glad that you posted this picture. It's all cloudy outside, but I now have something to work on.

I will keep you posted.

[Bizibilder]

"Should have more red" - The 1000D (and all other unmodded cameras) have a filter that blocks the red end of the spectrum - so the image does not have much red signal. Specifically this is the red from Hydrogen (Hydrogen alpha) that is emitted by nebulae such as M42. The unmodded camera simply doesn't record it - hence the image appears "weak" in the red colour. A "modded" camera has this filter removed (actually replaced with one that lets the red through) and therefore records the "red" from the object being imaged.

Posh (ie expensive!!) CCD cameras (which are designed specifically for astro-photography) don't have the filter installed in the first place and therefore don't need this modification!

[aGreyarea]

Bizibilder,

Sorry, I should have said I know and understand about the filter mods for standard DSLRs and using Ha filters, I think I meant to ask how you know it should look like that?

If it should have more red in it why weren't you just more aggressive with the red curve?

Have I gone wrong by applying curves to the RGB individually, should they all have the same curve to protect the balance?

Sorry if I'm starting to wear on you!

GrantEb

If it helps, all the images had the 'Long exposure noise reduction' set to 'auto' and the 'High ISO speed noise reduction' set to Enable.

I just took the camera out, let it cool down and shot a 30s dark at iso400 with the above and this is what I got.

its converted from RAW to TIFF, the histogram is stretched in Corel Photo Pro X3 and then saved as a jpg

[Bizibilder]

Trying to "push" the red when there is little red in the image won't achieve much - you just have to settle for what you have, in this case a "typical" unmodded DSLR "pallette".

I think you may have created a problem for yourself by having noise reduction ON/ENABLED - your camera will be taking and processing a "dark" for each picture you take. You will end up with JPEG's that are already processed! If you then process your own (processed!) darks as well you will not get a good result at all !!

When you take shots with the 1000D turn off noise reduction etc and operate the camera with the "M" setting. Set the image capture for RAW + L. This will save your images as RAW - these you process, and JPEG - these you can inspect but don't bother to process them.

Hope this helps

[Sierra Golf Mike]

Well impressed with your photo, pity about the banding though. Sorry if this sounds like a stupid question but when you say you used un unguided scope does that mean there was no drive at all hence the 30 second subs?

Steve

[aGreyarea]

Hi Steve,

Sorry, the mount is driven but not guided at all, i.e. no auto guider or guiding eyepiece so I could not correct for the periodic error. I actually got 16 subs but had to reject some from DSS because the stars had streaked. I was just lucky that the 90s sub was ok.

The banding is from the iso being set too low and we have come to agree that the bright bit is from light leaking into the camera from the viewfinder! The laptop was setup behind the front of the scope but next to the camera that had the viewfinder uncovered!

Best of luck!

[Sierra Golf Mike]

Thanks for the info.

Steve

[pwalsh61]

The lighter bit bottom right may be a bit of "amp glow" from the sensor warming up. I've just taken a few shots with my unmodded 1000D (30s at each ISO setting, lens cap on) and notice that when I ramp up the exposure and saturation there's a slight lightening bottom right.

Using a higher ISO setting means a shorter exposure time (so theoretically you should pick up as much with 30s at ISO1600 as you woould with 60s at ISO800) which in turn means the chip has less time to heat up. The trade-off is an increase in noise. As with most things it's all a matter of trial and error to find the combination of ISO, exposure time, ambient temperature etc which works best.