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Elephants trunk problem - any ideas gang??


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Guys,

I'm wondering if anyone can assist me please??

I have recently 'upgraded' from a rather brill 130 PDS with Baader MPCC to a TS 65mm Quadruplet refractor which is smaller, lighter (just) and is a beautiful instrument to use.  However, I have a full spectrum Canon EOS 500D which before went straight into the 130 PDS and captured a good amount of light with 5 minute subs.

However, I now use a UV/IR blocking filter with the 'frac via a 2" nosepiece.  The camera and scope work well enough, but I have just last night taken 2 hrs worth of 600 sec guided subs with my rig and am in the process of stacking these for a third time in DSS as I'm struggling to drag any detail whatsoever out of the images, other than a rather nice looking star field!

My guiding was spot on, the framing spot on (I can just make out the trunk just off centre in the stacked images after I've fettled with them for ages) and my subs were (on the face of it) good.

x12 600 sec subs at iso 400 each with a histogram just right of centre and nice and bright when stacked, I just cannot tease any real detail, colour or filaments out of the stack.  I am most puzzled by the whole thing.

Seeing was excellent and I was shooting almost straight up, so LP not much of an issue (and this isn't bad anyway where we are).

When DSS has finished again I will upload a single CR2 sub and also a straight jpg from the autosaved Tiff from DSS, but in the meantime am I missing something??

Is IC 1396 a particularly faint object?  Are 10 minute subs inadequate?  Are there any good 'default' settings to use in DSS with full spectrum CR2 files from my Eos?

Any advice gang???

:)

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It certainly isn't difficult in a CCD camera but that's using an Ha filter to get the main nebulosity. In RGB only it's pretty slow. It really is an Ha dominated target so an Ha sensitive camera is a must, but you say yours is full spectrum so it should be OK in Ha. 

Do you take the linear data out of DSS and into a better graphics programme? You should. I wouldn't do any stretching in DSS.

You could always Dropbox the linear data for us to explore.

Olly

Edited by ollypenrice
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It certainly isn't difficult in a CCD camera but that's using an Ha filter to get the main nebulosity. In RGB only it's pretty slow. It really is an Ha dominated target so an Ha sensitive camera is a must, but you say yours is full spectrum so it should be OK in Ha. 

Do you take the linear data out of DSS and into a better graphics programme? You should. I wouldn't do any stretching in DSS.

You could always Dropbox the linear data for us to explore.

Olly

I have always processed images in DSS to at least introduce some contrast and colour and then finish the last 50% processing in Photoshop. When I was using the 130 PDS I just had a 2" LP filter screwed into the nosepiece but now have to use a UV/IR cut filter due to having a refractor.  I was thinking of removing this filter as I'm sure it is cutting a bit of the Ha out but I'm not sure even the quadruplet will handle this and star bloat will be just as bad as a lack of detail.

I'm currently trying Bilinear interpolation as opposed to AHD debayering with other adjustments in DSS.

As for Dropbox, tell me what you need and I can oblige.  (never used Dropbox).  Do you want the unprocessed TIFF after stacking before any adjustments?

Thanks for the help!!!  :)

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Do you want the unprocessed TIFF after stacking before any adjustments?

Yes please, that would be good! This is not a great object for RGB as Olly has said but 10 minute subs (say 10 or more) and a little post processing in PS should reveal something acceptable.

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post-22225-0-56799600-1407274630_thumb.jpost-22225-0-52347400-1407274656_thumb.jFor now, here is a straight jpg conversion of what my DSS output is, along with a processed version I've just finished in Photoshop.  I will see if I can figure out how to upload the original TIFF to Dropbox.

Thanks guys.....

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https://www.dropbox.com/s/mgc0hzi53cmc3t3/AHD%20Debayered%20third.TIF?m=

https://www.dropbox.com/s/0p5tay73v4fwmgg/LIGHT_600s_400iso_%2B20c_00689stdev_20140805-01h05m10s184ms.CR2?m=

These two links should work (hopefully).  First one is the unaltered output from DSS.

Second one is an original RAW file from the Eos 500d.  All my subs were like this. 

Good luck!! (see what you think).

Thanks......

Scott.

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https://www.dropbox.com/s/mgc0hzi53cmc3t3/AHD%20Debayered%20third.TIF?m=

https://www.dropbox.com/s/0p5tay73v4fwmgg/LIGHT_600s_400iso_%2B20c_00689stdev_20140805-01h05m10s184ms.CR2?m=

These two links should work (hopefully).  First one is the unaltered output from DSS.

Second one is an original RAW file from the Eos 500d.  All my subs were like this. 

Good luck!! (see what you think).

Thanks......

Scott.

Hi Scott,

May I ask what UV/IR filter you are using?

A.G

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Your over exposed for a start.

You really want your in camera histogram around the 25% mark, your way to far too the right.

For feint objects your may want to up the ISO, may be at least 800 and see if 1600 is any good

but keep the histogram around 25% or very maximum 40%.

At that sky brightness your sub length will come down a lot, 10mins is way to much.

The RAW file was very red......LP?......are you using an LP filter?, if not get one and you can increase sub length.

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Hi guys,

OK, my filter is a Teleskop Service 2" UV/IR cut. Its a good quality filter.

As for the exposure, I generally try to make the subs bright to pick out the fainter nebulosity. It's worked for me so far with galaxies and I got some good detail in the Rosette earlier in the year but I guess this may not work for everything.  I had used my SW 2" LP filter screwed onto the UV/IR filter before but my subs were much darker than without the LP and my fear was they were cutting out a lot of detail. Although there were no internal reflections, so that was a pleasant surprise. I agree the subs are red and the histogram sees the red channel much further to the right than the green and blue - I assume this is normal given the sensor is now full spectrum.  It was even further to the right before with the 130PDS when I didn't use the blocking filter.

As for the iso, I have done a lot of testing with the Canon and although 800iso is ok, 400 iso is so much cleaner, I decided to use the lower iso and double the sub length.  Even with a lot of darks 800 iso images appear that bit grainier. 

Any thoughts?

Appreciate the input folks!

:)

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Hi guys,

OK, my filter is a Teleskop Service 2" UV/IR cut. Its a good quality filter.

As for the exposure, I generally try to make the subs bright to pick out the fainter nebulosity. It's worked for me so far with galaxies and I got some good detail in the Rosette earlier in the year but I guess this may not work for everything.  I had used my SW 2" LP filter screwed onto the UV/IR filter before but my subs were much darker than without the LP and my fear was they were cutting out a lot of detail. Although there were no internal reflections, so that was a pleasant surprise. I agree the subs are red and the histogram sees the red channel much further to the right than the green and blue - I assume this is normal given the sensor is now full spectrum.  It was even further to the right before with the 130PDS when I didn't use the blocking filter.

As for the iso, I have done a lot of testing with the Canon and although 800iso is ok, 400 iso is so much cleaner, I decided to use the lower iso and double the sub length.  Even with a lot of darks 800 iso images appear that bit grainier. 

Any thoughts?

Appreciate the input folks!

:)

Hi Scott,

I had a quick play with the DSS raw Tiff in StarTools, just a simple stretch and balancing routine. To me the LP has ruined the image as it has drowned  the low level signal from faint nebula, unbalanced the RGB colour balance and allowed the high signal areas such as the bright stars to bloat and dominate. I think that you'd need a very high quality LP filter with effective IR blocking. The choices as you may know are IDAS D1, Astronomik CCD Clip LP, Baader neodymium and the Baader UHC-S L booster. The Baader Neodymium is the weakest of the bunch but it may work if your LP is not severe. The Astronomik  behaves more like the Baader UHC-S L booster in allowing, Ha, Hb, Oiii and Sii lines and blocking most of the other stuff. The best one of the bunch is the IDAS and the most pricy but it is the most balanced with the least effect on exposure length and colour balance. Once you get the LP sorted you need to think about the exposure length. I am not familiar with the 65 Q but I believe it isa native F6.5, coupled to 1/2 of the aperture compared to the 130PDS I would increasethe exposure by 35~50 % but only after you taken care of the LP subject to some experimentation

Regards,

A.G

post-28808-0-78399800-1407316603_thumb.j

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Fine on the ISO.

My 60Da works best at ISO 1600 for nebs, it's rubbish at ISO 400 on galaxies, so I use 800 for them.

If you over expose and there is a large brightness range in the object you will lose the highlights.

Even though your sub length will come down you will still go for the same total exposure.

Depending on the target, 1 to 4hours is what your looking at, the more the better.

A really good LP filter will increase sub lengths by 2 to 3 times, so a good one is a must imo.

AG beat me to the LP filter part.......I regard the Hutech as the best I have,  the Astronomik clip second.

Edited by wxsatuser
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Sound advice, thanks guys.  I will be having a bit of a re-think with regards to my filter usage I reckon.  It is very much trial and error at the mo with the new optics and so on and I have to keep detailed notes of what works and what doesn't as it is often weeks between shoots what with cloud, work and more cloud :rolleyes2:

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  • 2 weeks later...

Am I losing the plot here? If the neb emits, even partly, in the IR, surely the IR cut filter will be blocking those extra photons?? Or is this a filter I don't understand?

Alexxx

Hi Alex

I think that one would want to avoid IR, especially with a frac as it won't focus on the same plane as visible light. Even if it was in focus it's not part of the spectrum we normally want to detect.

Louise

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Hiya

I don't think so - H-alpha is in the visible part of the spectrum - you can see through a 12nm filter. Of course, it's almost merging into the near IR but it's still actually visible whereas IR is not. That's how I 'see' it anyway!

Louise

Edit: this is quite a good article - http://www.astropix.com/HTML/I_ASTROP/DSLR_HA.HTM
Btw, Alex, did you sort out your haloes?

Edited by Thalestris24
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