Hello all...
A couple of weeks ago while visiting Craig_L, testing out my Canon 1.4x Extender on his Tak 90, we hit upon a great idea - we both love those high contrast LRGB/HaRGB images but lacked the expensive high end gear (and locations) to produce the necessary H alpha images needed for their composition.
I suggested that it might be possible to fork out a little cash to acquire the Ha data via one of the easily available GRAS scopes... http://www.global-rent-a-scope.com/
This way we could obtain high quality Ha data taken on equivalent/similar focal length scopes to our own. We would then be able to merge/blend this data with the RGB images from our own setups - Simple!!!!
Operation and acquisition of images from the GRAS scopes is straightforward. They even give a discount for imaging under moonlit conditions - this proved very economical for Ha imaging!!
Craig_L is now hooked I believe!!!!! I'm sure he'll soon post a stunning Running Chicken Nebula done with this method which is excellent - almost time for it to come out the oven Craig!?
The alignment and rescaling of the FSQ Ha shot with my 280mm lens shot proved to be the biggest pain and processing in PS was a bit hit an miss too - stumbling around in the dark, finding my way with this method I'm afraid! Because of the disparity in the fields of view, I've cropped my original widefield drastically! Something I loathe to do!!! Viva Widefield!!!
Still not that happy with the result - stars take on ghostly blue halos, colour balance is tougher and I seem to have lost a bit of the finer background nebulosity on the edges of the image at the expense of gaining slightly more detailed contrast in the body of the neb...Still, it's been fun trying on these crappy rainy nights!!
I really can't afford to regularly go down the GRAS path for acquiring Ha data so I've been considering purchasing an Astronomik 13nm Ha EOS Clip In filter for the 40D - any thoughts/experiences?
Low Res images...
image 1: Ha Data
image 2: RGB data
image 3: Ha/RGB blended data
Good work Doug...and I thought I was the only insane individual that enjoys rental scopes around here. Hybrid composites, i.e. the matching of data from different focal lengths can be challenging, though it depends on what you're trying to achieve. At the focal lengths you're talking about 280mm for RGB and 530mm for Ha, the differences are not large so IMO not too difficult. Your woes of different FOVs can be addressed. I've matched RGB data against 5 to 6 times the focal length with good results i.e. 530mm RGB against 2900mm Luminance. I believe I've provided information in previous posts on these forums. Anyway, here are a few pointers;
I'm not sure on the tool you're using to align/register the data from the different images. Most image processing software will handle the task relatively well, but one tool stands out from the crowd - Registar. It only does a few things, but does them exceptionally well.
The quality of the data with dictate how far you can upscale it to match. Poor data upscaled delivers mottled noise, but usually can be handled with low frequency noise reduction techniques.
Don't upscale the luminance, you'll loose resolution in the process.
Down scaling the luminance to match the RGB is extremely effective delivering impressive resolution. This works really well if you've got a wide field RGB, but the extend object is lacking "punch". Down scaling a higher resolution luminance i.e. taken at a longer focal length of the extend object will improve its quality.
You'll probably find it easier if you match a low resolution RGB to a higher resolution luminance, if you down scale the luminance first, tweak and flatten to produce a "SuperRGB" layer, then reintroduce the luminance. This assists in managing the overlay of colours (and also provide the opportunity to performed additional colour tweaks such as dodging, etc.)
One of the biggest challenges of hybrid composites is matching the stars. Upscaled data causes the stars to bloat. For RGB data, this isn't a huge issue, but you can end up with halos. With an LRGB composite, all the details including star sizes are coming from the luminance, thus you can safely use the minimum filter on the RGB layer to control the halos. This will not result in nasty deformed stars as we're not applying it to the luminance. For large, bright stars in the FOV, the star pinch technique will do a better job. Though for wide field images, the minimum filter will suffice.
Conversely, depending on what data you're matching, it can also help to use the maximum filter to introduce more colour to the stars, giving them a more pronounced profile.
I admire your efforts on this. Thinking outside the square and pushing boundaries. I like what you've come up with. HaRGB blends can be complex even with data acquired at the same focal length. Keep at it and you'll nail it.
Doug,
can't add to the advice already give, other than to suggest you try an Ha filter on the 40D. If it is anything like my QHY8 was, Ha was very good. I used a 48mm filter, and most likely you could "borrow" one of these to try first, just to see if it was you or not, and whether the 40D worked OK with it.
Gary
Doug,
can't add to the advice already give, other than to suggest you try an Ha filter on the 40D. If it is anything like my QHY8 was, Ha was very good. I used a 48mm filter, and most likely you could "borrow" one of these to try first, just to see if it was you or not, and whether the 40D worked OK with it.
Gary
Craig has offered to loan me his 48mm Baader Ha Filter, but I can't see a way to get it into my Camera/Lens optical path!! A quick google search for a 67-48mm step down filter ring was unhelpful - looks like they don't exist from a quick search!
May have to bite the bullet and order an Astronomik filter (and hope I don't get the halo I did with my clip in Hutech LPS filter!!)
Astronomik do a 13nm and a 6nm filter - the 13nm is cheaper and will let more light through I guess (a good thing for widefield work), but I wonder if the 6nm filter would be the better option!!
Aaaaargghhh my head hurts!
Doug
Ah, see your problem. In my case I was using the scope, with a 2" nose-piece, so screw on. Also used the Ha with a camera lens, but on the QHY8, and this time via an adaptor that was "hollow" enough to allow me to fit the Ha inside.
If you are using the Canon lenses straight on the EOS body, then yes the clip in sucker is likely the only way.
Mine is the Baader 7Nm and it is about right, if faced with the 13 Vs 6 dilemma I guess I would plum for the 6.
Gary
If you are using the Canon lenses straight on the EOS body, then yes the clip in sucker is likely the only way.
Mine is the Baader 7Nm and it is about right, if faced with the 13 Vs 6 dilemma I guess I would plum for the 6.
Gary
Talking to OPT about a 6nm filter - expensive gamble, but what's life without a little risk now and again!!??
I wouldn't be making a blind decision on the Ha filter bandpass. Plenty of info here in the forums (for instance).
Thanks jase - lots of information to process there.
After reading through I'm inclined to think the shorter subs afforded by the 13nm filter might be more user friendly initially but would I crave a 6nm filter as experience grew!!??
Given my location/setup/goals which filter do you think will suit my needs?
location: fairly dark skies, 10+ min subs no problem with LPS filter
setup: modded 40D and lens (no scope) 70-280mm FL, f4-f5.6, HEQ5 Pro autoguided.
goals: to blend high contrast Ha data with the RGB widefield image.
For lens work, I would recommend 10nm or greater. So go with the 13nm bandpass. While you'll still experience some shift, though it will not be severe. In fact, with a 13nm filter you could image at F/2.8 if desired.
While you don't have an astrograph operating at 8" - F/2.6, the concept with Ha filters remains the same. Take note of the 12nm Ha BPF graph detailing the shift in the URL (also posted below).
This aligns with what I mentioned in the other post - "...the shift results in a slight drop in transmission efficiency i.e. 90% to 75%, thus on a worst case scenario, you would need to increase your exposure time...however with fast optics, this would not be a huge disadvantage." Ultimately, the interference filter would still be operating fine, so you'll get the contrasty Ha emission line, its just that the transmission efficiency may not be as advertised. Having a larger bandpass addresses this issue.
Nice images Doug, But for me the end result does not show the value the GRAS hire would have cost. I would think it would be much more cost effective to purchase the Ha filter of your choise and have the ability to experiment with different target, exposre times and blends, all with a single outlay.
Nice images Doug, But for me the end result does not show the value the GRAS hire would have cost. I would think it would be much more cost effective to purchase the Ha filter of your choise and have the ability to experiment with different target, exposre times and blends, all with a single outlay.
Agreed Doug - but the GRAS experiment was a bit of fun and it cost me $36 for a few hours worth of imaging on a FSQ106. That's not too bad for a bit of indulgence!
The results are far from perfect, but have given me a hint as to the potential of this technique - so, yes I'll be investing in a filter to play around with at my leisure very soon.
Cheers
Doug
You can also use the transform function in Photoshop. Not that easy to use but with patience it will do it. Get the RGB as base image. Now make a new layer and paste the Ha into it. Now hit control T to turn on the transform mode. Now you will see little arrows that show the directions you can manipulate the image. I think if you right click you get a menu and you want all directions enabled. I zoom in and then you can see what you are moving. Change the blend mode to something like lighten so you can see the 2 images. Photoshop I think seems to "click in" when you are close but I could be imagining that! It can be difficult to get it right but with patience you can. Perhaps alignment in CCDstack or Images Plus first would be far easier. I sometimes use it if I forgot to align an layer like Ha and it is close to being aligned.
Send me a PM and I'll let you in on a Ha blending approach I developed.
Otherwise blending Ha can be a pain and not well written up and you'll get odd colours with little control over the result. Even the approaches in well known books are inadequate.
As far as nm of Ha I was under the impression smaller nm was better as less "other" light gets in. Downside was longer exposure times but more detail when you did. For example Fred's 3nm Ha images which show detail not seen in other Ha images. Also Don Goldman's 3nm Ha images of Helix etc show detail not seen before. But it was hard work I believe.
I use an Astrodon 5nm Ha and I think its very nice indeed.
Not sure if using a 40D makes a difference in that regard, I am talking about CCD cameras. Don't see what difference it makes though.
Even with 5nm Ha I find I get nicer contrast when no moon compared to moon although the results are still very good with a moon.
Change the blend mode to something like lighten so you can see the 2 images. Photoshop I think seems to "click in" when you are close but I could be imagining that! It can be difficult to get it right but with patience you can.
Use the "difference" blend mode in PS. When the stars align they'll turn black i.e. indicating there is no difference between the layers. This is much quicker than changing the opacity and/or guessing if they are accurately aligned. If a difference exists, you may need to resample/re-register the data to make it match. Once aligned, change it to normal, luminance or whatever blend you're trying to achieve.
Using 10minutes as a rough starting point for my proposed Ha exposures and using Eta as an example, would I be likely to record enough detail with the 6nm and 13nm filters in this time?
Im about to drop a 12nm Ha EOS clip I got from Bintel into my modded 40D for a laugh, be interesting to see how it goes.
Even with a 90% QE Astrocam, 3nm needs long exposures, at least double the 15nm I had before, so I think that with a 40D would be marginal indeed, if not impossible. 3nm sure does bring out the detail tho , and cuts right through moon and sky glow, the background ADUs last night were only 120 (saturation at 65k) with 10min exposures.
I think the 13nm you want would be about as narrow as you can reasonably go, and youll be supprised at the results even with urban skies and moon, its the next best thing to dark skies..
Noticed some patches of stars were blue. Is this an artifact from the processing of the Ha with the RGB data? If so, maybe you could try removing the stars from the Ha as was suggested. Not sure sure how you do this though?
Im about to drop a 12nm Ha EOS clip I got from Bintel into my modded 40D for a laugh, be interesting to see how it goes.
I think the 13nm you want would be about as narrow as you can reasonably go, and youll be supprised at the results even with urban skies and moon, its the next best thing to dark skies..
Thanks Fred - that's 2 votes for the 13nm! Keep us posted how you go with the 40D
Quote:
Originally Posted by Craig_L
Hey Doug,
Noticed some patches of stars were blue. Is this an artifact from the processing of the Ha with the RGB data? If so, maybe you could try removing the stars from the Ha as was suggested. Not sure sure how you do this though?
Craig
Yeah Craig probably my dodgy processing - as to removing stars from the Ha hopefully one of the gurus will suggest something but I would try using the Colour Range tool to select the stars then Minimum filter to remove 'em to taste!
Any advance on that
The H alpha/ RGB Experiment - Eta
I'm sure he'll soon post a stunning Running Chicken Nebula done with this method which is excellent - almost time for it to come out the oven Craig!?
Hybrid composites, i.e. the matching of data from different focal lengths can be challenging, though it depends on what you're trying to achieve. At the focal lengths you're talking about 280mm for RGB and 530mm for Ha, the differences are not large so IMO not too difficult. Your woes of different FOVs can be addressed. I've matched RGB data against 5 to 6 times the focal length with good results i.e. 530mm RGB against 2900mm Luminance. I believe I've provided information in previous posts on these forums. Anyway, here are a few pointers;
