Flame Nebula - any hints?

[hjw]

Over the last month I have tried to capture the flame nebula in Orion. As usual, my setup is still a Pentax K-30, a 55-300mm DAL lens (f/5.8) and the O-GPS1 gadget on a tripod. My exposure time at ISO6400 is limited to 10-20sec. I have collected more than 200 frames with a total exposure time of >40min. Lately it seems that the picture does not really improve anymore with more frames. I am wondering therefore whether I have reached the potential of my setup and you just can't get better results without a proper mount and a modded camera. Am I too ambitious here?

[kalasinman]

Nice effort! Yes many have commented that the point of diminishing returns on subs is under 50. Yes a tracking mount makes a vast improvement, as the steadiness is improved, and the sub exposure time can be much longer. Getting away from high ISO really helps with the noise too. Longer exposures capture the faint detail, as those details may not have enough photons coming in in a short exposure to trigger a signal. 1,000 x 0 is still 0.--Jack

[Imd]

I think your image is really impressive considering such a low exposure.  I agree with Jack's comments.

[Uranium235]

What Jack said!

Think of it in this simplified way:

Your sub length can be considered as signal depth (x), and your sub count can be considered as your noise reduction factor (y). But as you can imagine, trying to increase x  can only be achieved with tracking or autoguiding. However, while y is more of a fixed number (I use 8, 16, 24 or 32)  - x is a bit variable according to the speed of your optics. For instance, using an f4 optic rather than your f5.6 will deliver nearly twice as much signal - but not twice as many photons (its more like a improvement in the signal/noise ratio).

Conversely, having a few long subs - but not enough of them is just as bad, because youre fighting the noise and theres not enough data to make sigma clipping work (for hot pixel removal).

[iksobarg]

You get an A+ from me for effort and the image.

Given the feedback here I'm interested in your take now.

[hjw]

You get an A+ from me for effort and the image.

Given the feedback here I'm interested in your take now.

Thanks! My take on this is... I give up for the time being - BUT I had plans for a HEQ5 mount for Christmas and Christmas as it is, was more expensive than budgeted for. However there is always the birthday in Feb and Christmas for me this year will be postponed .

[Knight of Clear Skies]

After about 30 subs the improvement in image quality begins to tail off significantly.

This is quite a result given the modest setup. You'd get better results with a wider angle lens which would allow you to increase the exposure time. Also, a faster lens would throw more light on the sensor, and there are plenty of easier targets than the flame and horsehead. Would be interesting to see what could be achieved with a 50mm or 135mm lens on a brighter target. Can old M42 and Pentax-K mount lenses be fitted to your camera? If so there are some cheap ones available which are good for AP.

[hjw]

After about 30 subs the improvement in image quality begins to tail off significantly.

This is quite a result given the modest setup. You'd get better results with a wider angle lens which would allow you to increase the exposure time. Also, a faster lens would throw more light on the sensor, and there are plenty of easier targets than the flame and horsehead. Would be interesting to see what could be achieved with a 50mm or 135mm lens on a brighter target. Can old M42 and Pentax-K mount lenses be fitted to your camera? If so there are some cheap ones available which are good for AP.

When I read the the initial replies I was thinking the same thing and went out to take some pictures of the large magellanic cloud again. I used the 55mm focal length and took 28 minutes worth with 30 to 60 second exposure time (f/4.0; ISO 1600). In DSS I got scores of 11000+ ( ) while I usually have ~3000 for a good frame. Coming from a terrestrial photographic background it is counter-intuitive to reduce the focal length when the object does not fill the frame. Nobody ever said it would be easy. Can't wait to get the mount...

By the way, I probably would argue the 30 frame limit (with all due respect of a blumming beginner!). I think for me the magic number is somewhere between 70 and 100 on the short exposures with 300mm focal length. 200 was definitely a waste of effort where "waste" is the wrong expression. For me it is important to experience things to truly have them sink in.

Thanks to everyone - and another lesson learnt.

[Knight of Clear Skies]

That's an excellent result.

By the way, I probably would argue the 30 frame limit (with all due respect of a blumming beginner!). I think for me the magic number is somewhere between 70 and 100 on the short exposures with 300mm focal length. 200 was definitely a waste of effort where "waste" is the wrong expression.

That's interesting. I believe the 30 number is well supported by theory but perhaps using such short exposures might change the equation? The stack will limited by read noise. Have you tried kappa-sigma clipping, and have you tried taking dark bias frames?

By the way, the scores in DSS seem to be related to star count, so you generally get a higher value with wider fields of view. FWHM is probably a better indication of sub quality.

Coming from a terrestrial photographic background it is counter-intuitive to reduce the focal length when the object does not fill the frame. Nobody ever said it would be easy. Can't wait to get the mount...

Hope you can get your mount soon, that will certainly open up your skies. In the meantime have you considered a lens upgrade? Prime lenses generally outperform zooms for AP due to lower complexity (all optical designs are a compromise). At the same focal ratio light transmittance will be higher and there should be less coma in the corners. There are some cheap options available, this image was taken with an £18 lens for example. With your setup I'd consider a 50mm lens.

[hjw]

@Knight of Clear Skies: Nice images there. I tried to find rosetta the other day and didn't even get a hint. A modded camera is another one of those desirable pieces of gadgets... As to my equipment I think I will stick with what I have for the time being and play around with it. I am waiting for the mount and I still have a old newtonian lying around (115mm aperture and 900mm focal length). I have already talked to an engineer at work to get it shortened once I figure out by how much. Once I get a feel for the mount and saved a bit more I am looking at a SW 80ED scope (alternatively a GSO RC astrograph - but that will be question in the distant future). There you go - the path to better astrophotography is laid out and waiting for my first step on it. Until then I think there are plenty of parameters I can play with with what I am doing now to keep me entertained. For Australians the best skies are coming - hot summer nights with wind coming from the desert - crystal clear skies and no jacket needed .

By the way I just noticed the forum has a auto-censor function. I was referring to myself as a beginner leaking red body fluid which got translated into "blumming"?! That's an expression I had to look up (even after 25 years in a country you don't know them all) and it doesn't quite fit the bill.

[steppenwolf]

I think that with the equipment limitations you have, this is a remarkable image.

Although it isn't written in stone and so much depends on the objects in question as this has a huge affect on the signal to noise ratio, I have always worked on the basis of a minimum of 10 subframes and an upper limit of between 20 and 30 subframes - after around 30 subframes, I don't really think that it is worth capturing more of the same data. This is really such a balancing act but you're having fun and achieving some good results so just keep at it.

[kalasinman]

I'm a beginner too. One thing that amazed me when going from a tripod to an EQ mount, is the vast reduction of noise with 2 minute subs as opposed to 30 second. I just ordered the filter fpr a do it yourself mod of my D5100. After seeing the before and after pictures , I just have to do it. As it is, I get next to nothing from North America, Heart, etc.

[hjw]

I think that with the equipment limitations you have, this is a remarkable image.

Although it isn't written in stone and so much depends on the objects in question as this has a huge affect on the signal to noise ratio, I have always worked on the basis of a minimum of 10 subframes and an upper limit of between 20 and 30 subframes - after around 30 subframes, I don't really think that it is worth capturing more of the same data. This is really such a balancing act but you're having fun and achieving some good results so just keep at it.

I don't really want to argue, especially not with you Steve. Is it possible that you guys with proper mounts can chose you exposure time for each sub by the amount of light you get? So when you look at one of your subs you see your DSO nicely but the frame is noisy. So with each sub you increase you signal to noise ratio but keep the brightness of your target more or less constant? I am guessing here, because I never had this luxury. The closest I might get is with M42 which I can clearly make out in my subs. When I look at one of my subs of the Flame Nebula, it's black with stars and maybe a hint of the target. I would really have to increase brightness and contrast ridiculously to see something other than stars. I did stack the 30 best frames of my 200 but the result is inferior to the picture above. I guess the morale of the story is: You DO need a mount! But in one thing you are definitely right, I do have fun with it !

This is the result of the 30 best frames:

[kalasinman]

One step ahead, into the quicksand. OK got the mount (thrilled), but.....guiding, proper scope, camera mod??   Sigh...

[hjw]

One step ahead, into the quicksand. OK got the mount (thrilled), but.....guiding, proper scope, camera mod??   Sigh...

I can imagine your excitement... and your pain