Astrophotography - Improving technique and reasonable expectations

[Roysten]

Hi all, I've been reading quite a lot of threads about the basics of observing and imaging and think I'm getting a feel for the steps needed to capture images. Apologies if a lot of this is covering old ground, however I wanted to try and compare some of the approaches without hijacking someone else's thread. 

What I'd like to do is take a few of these concepts and get a few opinions on the best approaches, when you start getting diminishing returns for your efforts and how these things affect the images you try and capture.

I have a Skywatcher Explorer 150P with the supplied 2× Barlow. I am using a Logitech E3500 that I have modified (essentially ruined) and take pictures from. I have been using the Logitech image/film capture software (Sharpcap wouldn't let me capture at a higher resolution than 640×480) and I've been focusing mainly on Jupiter whilst I practice (please see attached image).

I appreciate that some of these are going to very open questions but here goes:

Cooling

I've read that ~1 hour for my scope is a reasonable amount of time to allow for cooling, I try and do this but it isn't always possible. What are the benefits of allowing the scope to cool for this length of time? Would 30min of cooling be much different from 60min? Does resting the scope of paving stones that have been warmed also make a significant contribution to these effects?

Electronic noise

My poor webcam has been taped to the metal tubing of an old EP, this masking tape goes straight across the back of the circuit board. Might this be introducing electronic noise that could be reducing the quality of my images or is this a hopeful excuse for other factors?

Light pollution/Seeing

I live a few miles from Hull City centre and have various street lamps that aren't as far away as I like. If I took my scope out to the country would the difference in light pollution make a significant difference to the quality of the images? Also with regards to seeing quality; if there a way to determine if a poor image is a result of poor seeing rather than other factors?

Stacking

I've seen that some people have talked about stacking 1000s of images to get the best images. I've found it difficult to capture more than 300 images with my setup (no motorised tracking), however I can manually track objects and then crop/centre images in other software before attempting to use Registax. In relation to my attached image would manually tracking objects in order to get 1000s of images help me improve my final images in a significant way?

Filters

Before I joined here I got a Celestron moon filter (with the dreaded plastic thread). I've taken images with and without it in the hopes that it would remove glare, some UV and some IR and not saturate the webcam sensor. But in order to use it I have to max out my gain/exposure settings on the webcam. Is this a good approach? Would a more dedicated filter that has a slightly higher transmission be a better compromise?

Finally... I imagine that all of these factors has their place, but does anyone have any opinion on what would be the best thing to try and tackle from this list (or something else entirely that I've missed)?

Thanks,

Roysten

[kens]

Cooling: The length of time depends on the temperature difference between the mirror and ambient. The mirror is a big thermal mass and cools slowly. When it is warmer than ambient the heat it gives off creates turbulent  air currents in the tube which affect seeing like any air currents. Warm paving stones can have a similar effect on the air outside the tube.

Electronic noise: unlikely to be significant. Insulating tape would be a better option though in case it gets damp and shorts the circuitry.

Light pollution: Dark skies make a big difference to contrast which is probably the most important factor in image quality. The local light sources affect your night vision but the collective light of a town creates scattered light all over the sky that puts a limit on how much contract you can achieve. There are many factors that affect image quality. The main ones are clearly different from seeing e.g. Drift from polar mis-alignment, periodic error, gross vibrations

Stacking: Without any tracking its hard to get any sort of decent run of subs. However, there's nothing to stop you taking say 5 seconds of subs, re-centre the object, then take some more and so on but its tedious and still makes it hard on the stacking software. Personally I don't do anything with the images prior to stacking. Registax or Autostakkert should be able to cope with some movement of the object in the FOV and adjust accordingly. If possible, use uncompressed frames. Post processing can also help up to a point. Disclaimer - I don't do much planetary

Filters: No idea.

General advice: Make sure your mount is stable. Get a motor drive if possible.Make sure the camera is securely mounted.

If you are doing mostly planetary I'd say light pollution is less of a problem than for DSOs. But since you are using high magnifications, cooling is important

My $0.02

[happy-kat]

I would use sharpcap as pushing the resolution higher is not going to get you a better image I don't think.

A bit like using a barlow is the bigger blurry image better than the smaller sharper one to look at.

Also the more you push it the more signal data might be dropped .

You could take several videos on the same evening process each one in registax and then combine the final images from each video. I think there are tips somewhere on handling rotation.

[Roysten]

Hi guys, thanks very much for your comments. 

Kens,

I think ultimately I'll have to get a new webcam and take more care when modifying it, heinsight is a wonderful thing but I think now I could take the lens off without having to remove the whole shell. Your comments on light pollution are quite illuminating (sorry for that), I haven't looked at many DSOs yet but I'll keep that in mind when I try. 

I'll try and take more time to cool. Normally I dno't have much time and just have to rush outside with the scope, maybe get 40 minutes then I have to be back in to get ready for work. I've definitely seen some big differences in image quality on nights are arguably very similar, be interesting to see if cooling is the source of that difference. Will have to dedicate more time to doing it properly. Why do you process the images after rather than before?

Happy-Kat,

I have wondered whether there's interpolation going on with the difference image sizes, I'll be able to better track the framerate in sharpcap I think as well and get more images to stack. The video files I get are very small, so it does make me wonder whether images are being dropped or whether the format of the files is quite low quality (or both!)

Does my attached image yell anything obvious to anyone?

[kens]

I'll try and take more time to cool. Normally I dno't have much time and just have to rush outside with the scope, maybe get 40 minutes then I have to be back in to get ready for work. I've definitely seen some big differences in image quality on nights are arguably very similar, be interesting to see if cooling is the source of that difference. Will have to dedicate more time to doing it properly. 

When you do that - look at the difference between indoor temperature (or wherever you store your scope) and the outside ambient. The bigger the difference the more time you need cooling. However, Newton's law of cooling is on your side to a degree (oh those puns)

Why do you process the images after rather than before?

With any form of image processing you are losing information. The exception is stacking as it is combining information from all of the subframes. For any individual subframe some information is lost but the resulting image has more information than any single subframe

So you want the most information to go into the stacking process first. That's why you should capture uncompressed video.

Once stacking is done you should have the maximum available information in the resulting image. That includes any imperfections which you then try to eliminate or minimise with post-processing.

[Roysten]

Cheers Kens, have got a clear(ish) night tonight so hoping to put some of this advice to good use!

When I sometimes take footage I separate the video from an RGB into 3 separate videos of each colour channel, which I recombine after processing later. Do you think there is any value to doing this or do you think it's better to just do all the processing after stacking?

[slim80]

Celestron have a new range of Neximage camera's.May be a wise investment.Checkout their Neximage Solar System Imager

http://www.firstlightoptics.com/celestron-skyris/celestron-neximage-5.html

[Roysten]

Thanks for that, have been wondering about cameras since reasonably priced ccd ones are hard to come.

You use the Neximage?

[kens]

Cheers Kens, have got a clear(ish) night tonight so hoping to put some of this advice to good use!

When I sometimes take footage I separate the video from an RGB into 3 separate videos of each colour channel, which I recombine after processing later. Do you think there is any value to doing this or do you think it's better to just do all the processing after stacking?

That's a good question. For imaging with mono camera you take RGBL images then stack each channel separately. You then have to align them before combining into a composite and post processing. That's because in the time between imaging each colour things usually move a bit. With a single colour image I believe the channels do need to aligned but I would have thought that the misalignment would be the same on every subframe so that could be done after stacking if indeed the stacking software does not do it automatically.

[Pr3tec]

I have made myself a mirror fan, that cools the mirror a lot faster. Great to have when you are short on time.

[Roysten]

That sounds pretty nifty, how does that work? Am guessing it's completely a custom design?

[Pr3tec]

I just used a pc fan, a pc fan regulator (potmeter) and a acrylic sheet. Very easy to make.

It also prevent light from entering from the bottom.

I nice video here:

[Roysten]

That's impressive, how much quicker do you find your scope cools down. Also is that the 200P?

[Pr3tec]

Little bit early to say, not so long since i made the fan. Looking forward to see the difference

[Pr3tec]

Its a SW 150p

[Roysten]

Ha, looked bigger, must be the angle!