Horse Head in Ha - Page 2

gregbradley · #21 07-12-2009, 04:30 PM

Your images continue to impress with this setup Paul.
A little bit more of fine tuning your setup and it should be a reliable
imaging machine.

Elongation in one corner and not the others to me indicates sag/tilt.
Collimation would be all corners wouldn't it?
I got a touch of this myself on the weekend as I had to space out an adapter
that screwed in too deeply into my filter wheel causing some slight tilt.

Are you using all screw adapters?

Modern cameras plus filter wheels plus OAG plus adapters adds up to a lot of weight which is a strain even on an expensive Tak focuser.
So if there was any slop in the focuser to start with it will add to the problem.

You can always use a guide scope. I use an Astrotech 66ED scope and an SBIG ST402ME (nice camera but cheap fittings like the power connector which often is "touchy" and the autoguiding cable won't disengage from its socket oh for a FLI guiding camera!). It works fine although I only do 10mins with it.

As far as not being able to have the image brighter because of noise;
you clean up background noise by either:
1) light gaussian blur on the background only.
2) use a plug in like Noise Ninja which does a really nice job and hard to beat
3) Use a Noel Carboni action

You can even blur the noisy areas manually by using the blur tool and rubbing it on the offending areas. Works well with noisy rim areas of dim galaxy shots.

Just moving up the black point is another way but you lose most of your detail as a lot of faint stuff is towards the black end of the histogram.

When you image LRGB on this use either no filter or a clear filter for the luminance. No need for UV/IR coated luminance filter which reduces a small amount of transmission on this dim object.

Greg.

Garyh · #22 07-12-2009, 05:37 PM

That`s a nice HH Paul.
Would love to see it again with more subs!

Paul Haese · #23 08-12-2009, 12:15 AM

Good points Greg. I checked my images from 50 seconds (the ones I used to setup framing) and the stars are the same shape. That certainly is not flexure, so it means something is not right on the image plane.

I just have to go through and check a few things now. One for certain is to ease off the collimation screws a bit and recollimate but keep the screws loose. I am thinking that the secondary might be warped a little, so just need to check that.

Greg I am not using screw adapter between the focusor and camera connection. The OAG is incorporated into the camera, so I need to get a handle on this I think. Other people have got that sorted. The spacer that I put in to get focus might also be affecting the stars too. It might need shimming.

Everything is an evolution and I thank you all for your comments and suggestions.

gregbradley · #24 08-12-2009, 04:43 PM

Ashley at Precise Parts in Miami is great for creating a custom made anodised aluminium adapter. He could make one for your camera to fit your focuser. Putting a nice camera like that in a screw tightened focuser is asking for trouble.

Yes 50 seconds shows no differential flexure but it would also still show tilt which affects any exposure no matter how short.

A heavy camera in a screw tightened focuser is unlikely to be square.

But as you point out it may well be something else but even if collimation is out tilt still appears to be present. Perhaps both problems exist.

Greg.

Quote:

Originally Posted by Paul Haese

Good points Greg. I checked my images from 50 seconds (the ones I used to setup framing) and the stars are the same shape. That certainly is not flexure, so it means something is not right on the image plane.

I just have to go through and check a few things now. One for certain is to ease off the collimation screws a bit and recollimate but keep the screws loose. I am thinking that the secondary might be warped a little, so just need to check that.

Greg I am not using screw adapter between the focusor and camera connection. The OAG is incorporated into the camera, so I need to get a handle on this I think. Other people have got that sorted. The spacer that I put in to get focus might also be affecting the stars too. It might need shimming.

Everything is an evolution and I thank you all for your comments and suggestions.

AlexN · #25 08-12-2009, 05:19 PM

Funny you should mention that Greg.. I was just about to say the same thing regarding Ashley at Precise Parts.. I received a few adapters a couple of days ago that he made up, all are brilliant.

I figured much the same thing.. Heavy camera setup with a 2" compression ring style focuser was probably a nightmare in the making... I got him to make solid screw in fittings for damn near everything, and the one push fit part of my whole setup now is the 2" nose that slides into the focuser, its 3.1" long so it sits firmly against the wall of the focuser tube and is very unlikely to sag about... the OAG screws onto that, flattener screws onto the rear of the OAG, CFW screws to Flattener and Camera screws to CFW... It all looks solid as a rock... If anything the only thing I see giving me grief is the actual focuser its all being put into

Paul Haese · #26 08-12-2009, 05:41 PM

Well as it turns out guys great minds think alike. Precise parts has machined up an adapter from the camera to the flattener. It is on its way to me as we speak. The problem with the stars is only recent. One of my early images (lagoon nebula) taken with the QSI showed only mild elongated of stars (see attached) caused from field curvature. It would seem therefore logical everything stems from something I have done in recent months.

Can you see what I mean?

Yes another screw in adapter is needed I think to attach the focusor to the camera, but I will need to think on this a little first as to how this will be done.

gregbradley · #27 08-12-2009, 09:06 PM

Interesting. The only thing I might add there is sometimes a sag or tilt problem can be slightly erratic as different angles of the scope for imaging different objects can cause different stress.

Hopefully your adapter sorts it out.

Greg.

Paul Haese · #28 09-12-2009, 01:51 PM

Greg its a matter of narrowing down the culprit. It could be something moving at one time and nto at another. Time will tell I suppose. Thanks.

Phil Hart · #29 09-12-2009, 09:55 PM

i am a fan of black and white images, particularly of this region so i really like this shot. and this is a great focal length for the region too - lots of promise for really attractive details (especially the complex area under the horse's chin). i agree that sharpening artefacts look like they're just starting to show at the top of the head.. but this could perhaps be masked out rather than reducing sharpening across the whole image.

on the topic of longer subs, i'm prepared to be a little contentious and say that i think you might not notice much difference going to 20 min subs, but then i'm biased by too much experience with DSLRs with low read noise. i know that with DSLRs, the read noise and therefore sub-exposure length becomes irrelevant even with greater than 1-2 minute subs. but don't take my word for it.. have a look at the middle row of images in this test:

http://www.philhart.com/canon_test

now i know that CCDs have higher read noise than DSLRs, but it's surely lower with modern cameras than it used to be. and the signal is low with HA so that also increases the desired sub-exposure length.

so in theory, yes longer subs will be better, but in practice i think the difference is so low that i'd go with paul on this one.. you'd only need to lose one 20 minute sub due to problems and you'd have lost more than you'd gained. ie a little increase in total exposure time is worth more than the increase in sub length?

having said all that, i'd love to see an objective test that does show a difference between 10/20 minutes subs with a modern ccd.

phil

Phil Hart · #30 13-12-2009, 01:18 PM

having spent the weekend surrounded by people imaging the horsehead, i should retract my comment about the sharpening artefacts.. the brightening around the edge of the horsehead is clearly a real feature. not the first time i've mistaken features for artefacts.. i was once cloning out bok globules from a nebula before i realised my mistake

anybody listening should also probably take my comments about sub-exposures with a grain of salt too. if you're chasing really faint stuff then photon statistics start to count against you with shorter subs.

i'll go and crawl back under my rock and hand back over to the experts..

AlexN · #31 13-12-2009, 01:24 PM

I did that the first time I imaged M16 Phil... The Bok Gobules just looked like random sharpening artefacts or maybe dust on the sensor, so I cloned them out

haha.. Yes the brightening behind the horses head an mane are real, and seen in many of the best photos of the area..

As for exposure lengths, I did think it was strange when you mentioned that 20 min subs wouldnt make a big difference over 10.. I thought "How does having twice the data per sub exposure not make a difference to the depth of an image? 60x10min subs may be 10 hours data, just like 30x20min, but surely 30x20min subs would give a deeper image"

How did you go imaging this weekend? got anything to post...

Paul Haese · #32 13-12-2009, 02:34 PM

There is an idea getting around the traps now that the background should have a weight of 1000 ADU. Most of my current images have something around 380. That probably would indicate that I need to capture my images for longer, but I need to balance this against saturating my stars. In reality I should have gone with a pixel size and well depth quite a bit larger.

So for now I need to keep the subs around 10 minutes. I think 20 minutes will saturate and flood the CCD too much.

Phil, that bright patch behind the head often looks like an artifact. There might be a star behind the head section that is illuminating the surrounding gas just enough to birghten that spot.

AlexN · #33 13-12-2009, 07:04 PM

Paul, for Lum/Ha data I wouldnt worry about saving the stars from saturation, worry about that in your RGB frames.. worst comes to worst take a series of 3 or 4 minute shots just for preserving star colours then selectively mask them if in you need to...

Lum and/or Ha should be purely as much data as you can get in order to give the target brightness and detail.. preserving star colours is another matter all together.

Manav (Yugant) · #34 13-12-2009, 07:59 PM

Beautiful image quite majestic in B&W

jase (Jason) · #35 14-12-2009, 05:33 PM

Looking good Paul. The first and second images, I think the highlights could be made to pop a little more, but data looks great. Will be good to see how you handle a RGB blend with such a data set.