Here is a pic I took last night using a 10 inch LX200, ASI1600 mono pro. the subs were 50 frames at 4 seconds each, binning was 4 and the gain was set to 164. How can I make the stars look sharper and not so round?
Good advice Glenn. I was using a CLS filter with my modified camera and the stars were “ unnatural “ so I swapped to the CLS CCD which has a I/R cut and the difference was amazing.
Thank you for the advice, Glenn, Ryan, Marc and Bojan. Yes I do have a IR cut filter it is 1.25 and my filter wheel is two inch. so where on the line would the IR filter go or do I need to buy a two inch IR filter? My filter wheel only has the RGB filter but I don't have a Luminance filter yet.
its a common question and not always hardware related. besides you have the data captured and want to correct/improve this aspect. take a look at this Light Vortex Tutorial. Its for PixInsight but if you can read you can learn how/why to do what you want hopefully with similar tools in the software you use.
its a common question and not always hardware related. besides you have the data captured and want to correct/improve this aspect. take a look at this Light Vortex Tutorial. Its for PixInsight but if you can read you can learn how/why to do what you want hopefully with similar tools in the software you use.
LX200 is SCT, it should not have a problem with IR..
Not meaning to hi jack this thread but can you please explain why an SCT wouldn't have issues with I/R ? I’ve literally just bought an adaptor to use my CLS CCD on my C5 and C9.25 for that reason. I was hoping to see the same improvements as I did with my Newt.
It is reflector system, and only element that could contribute to CA is corrector plate.
Being relatively thin. it's effect is negligeable (also according to my experince).
However, if you have other optical elements in a train (like focal reducer, field flattener) then you may need IR filter, because they may not be corrected for IR (at least cheaper models).
As to improvement you noticed with your Newt, the problem was in those additional correctors. IR filter can help there, but if you are using Newt in prime focus, IR is not needed.
IR Spectrum bleed is a factor in Astrophotography irrespective of what type of telescope you use. Despite my limited experience I cannot think of a single telescope design (other than one specifically designed for IR use) that would correct for IR spectrum bleed. This would not be an issue in visual use as your eye is not capable of detecting IR spectrum without technological assistance (ie: NVG), it only becomes a factor in imaging as a sensor is sensitive enough to pickup a small amount of IR spectrum bleed, right at the end of the red end of the visual spectrum. Additionally, a sensor is sensitive enough to pickup minute quantities of the UV spectrum too, hence why regular daytime use cameras are factory fitted with a UV/IR cut filter as standard. When imaging with a camera that does not have a UV/IR cut filter, you will get small quantities of UV & IR spectrum bleed into your image which, causes star bloat & a small wash out in colours ; the only way to eliminate this is by using an UV/IR cut filter in front of the sensor..
I'm happy to be corrected but, most, if not all commercially available telescopes (other than an achromat) correct, or attempt to correct for CA in the visible light spectrum only, ie: RGB, they do not attempt to correct for UV or IR spectrum bleed at the extreme ends of the visual spectrum. I'm pretty sure the corrector plate on an SCT, no matter how high the quality does not correct for non visible light spectrum bleed..
I own a ZWO ASI224MC, the instructions specifically recommend the use of a UV/IR cut filter, I have personally seen the difference, particularly through my SCT.. no filter = star bloat, with filter = less star bloat.. not as noticeable through a refractor but, still there.. cannot comment on a newtonian but, I suspect the results would not differ...
Cheers
Quote:
Originally Posted by bojan
It is reflector system, and only element that could contribute to CA is corrector plate.
Being relatively thin. it's effect is negligeable (also according to my experince).
However, if you have other optical elements in a train (like focal reducer, field flattener) then you may need IR filter, because they may not be corrected for IR (at least cheaper models).
As to improvement you noticed with your Newt, the problem was in those additional correctors. IR filter can help there, but if you are using Newt in prime focus, IR is not needed.
I'm with you Carlton . CA has nothing to do with I/R. CA is caused by the different angles of refraction through the lenses of REFRACTORS. Better lenses or more lenses in order to bring the wavelengths back in line can correct that. I/R is there regardless and is a glow around bright objects where I/R wavelengths are emitted from the object such as stars. Without I/R cut, all naked sensors will pick up this glow regardless of the optics causing bright I/R emitting objects to " bloat " in the image.
Guys,
Mirrors do not have problem with IR (CA), because they reflect IR (and UV) the same way they reflect visible light (reflection coefficient may be lower if appropriate coating is not used). Of course, resolution is lower for longer wavelengths, but the saturated image of the bright (and overexposed) stars obtained by sensor is actually way larger than the theoretical size of the Airy disk, partly also due to scattering inside the sensor.
However, lenses are different from mirrors, due to different refraction indexes for different wavelength. Therefore the focal length of refractor lens for IR may differ quite a lot from that for visible light. That is called CA and it is the main cause of star bloating, and this where the IR filter is sometimes a must.
IR emitted from stars is emitted from their photospheres just like the visible light (and UV, and X and gamma and so on) - so stars are point light sources for all practical purposes.
If IR is emitted from spread objects, then capturing that light is not the problem per se, you are capturing something that is really there.
Of course, if you are into NB, IR (or UV) filter may help to eliminate spurious pass bands of NB filters.
BTW, have a look at this discussion on CN on the subject - it may be interesting for some of you.
As for lenses (Canon 400mm f/2.8L in particular) and star bloating caused by excessive IR (CA in principle), have a look at what I have done in terms of IR filter.
And, to reiterate one more time - my Newt (mirror system) and my C11 (SCT) do not show bloated stars even when used with modified camera (which is expected).
If the corrector plate eliminated/corrected for IR then it would be useless for spectroscopy.. it's not... it would not allow me to use an IR pass filter for planetary IR imaging... it does...
Sorry but, IR spectrum bleed is a completely different beast.. it is a factor for imaging using refractors for CA leading to star bloat & it can be a factor for star bloat using other telescope designs; it is also a factor in colour washout.. hence why a filter is used on those camera's which do not have a native UV/IR cut filter. The difference between an Astro modded camera & a full spectrum mod is in fact, whether the IR cut filter is left in place...
Star bloat in an SCT (in fact in any imaging scope) can be caused by many, many other factors.. field curvature, focal length, tracking inaccuracies.. the list goes on. Is an IR filter going to fix all of these... NOPE.. but, it will eliminate factors caused by spectrum bleed... it will help but, it won't fix everything...
This is why people who are really, really, really good at this use all sorts of additional gear to achieve spectacular images... field flatteners, guiding, plate solving... to name but, a few...
