Help please!

[Steve1976]

Ok here are 2 photos of Cassiopeia. The first is wide open at F1.8 with the canon nifty-fifty for 30 seconds, the second is the same but for 217 seconds. Both are obviously without tracking. My question is this - if I wanted to do a star trail photo obviously I would need an even longer exposure time than both of these photos. But if I did this the sky would appear even lighter than that shown in my second photo. How to get round this? Is this just an inevitable result of light polluted skies which only post processing can fix?

Also if I took multiple shorter exposures and stacked them would Deep Sky Stacker 'ignore' the fact that I hadn't used tracking and resolve the slight movements over time of the stars?

Appreciate any help and advice folks!

[steppenwolf]

Post processing will help enormously but so too will a good light pollution filter like a Hutech IDAS LP filter.

[LukeSkywatcher]

You can download a program called "Startrails" for free online. It allows you to take short exposures and then run them through the program and it fills in the blanks for you so that you end up with dark skies (as dark as your sky is) and nice trails. I have tried it a couple of times by using about 20x8s exposures. The program edited them all together and kept the same colour sky as if just using a single 8 second exposure.

Obviously the more exposures you take the better the image. But even a few exposures gives pleasing results.

Here's a link to the program:

http://www.startrails.de/

You want to download the english version........unless you are a fluent German speaker.

[Steve1976]

Thanks for the response guys and Luke I will definitely check out that software. So even a little light pollution will be hugely magnified by longer exposures. Just what I thought.

[LukeSkywatcher]

Thanks for the response guys and Luke I will definitely check out that software. So even a little light pollution will be hugely magnified by longer exposures. Just what I thought.

Basically YES. I have found that from my location the longest exposure i can take is about 8-10 seconds. The sky is still nice and dark at this setting ans stars are bright. If i go as long as 15-20 seconds the whole image is just orange (similar to yours above but WORSE).

Its a fine balance between exposure time and ISO settings. Its pretty much just trial and error til you arrive at a happy medium for your location.

[JB80]

I have read some varying ISO numbers for trails, I guess it's different for everybody just have to work a bit to find whats right.

I like the look of the software too, I originally thought you just took the one really long exposure but I like the idea of not having to do that.

I'm not sure why I haven't tried doing startrails before but it's first on my list when skies clear.

How long of a break between exposures can you take or does it have to be fairly close to each other to get the software to join it up?

Also I just got a CLS clip filter for my camera so I'm assuming that will give me more time, how long can I set the exposures for or use manually with the bulb setting? Could I go in make dinner for 5 minutes and then reset it or could I go longer than that even?

[LukeSkywatcher]

How long of a break between exposures can you take or does it have to be fairly close to each other to get the software to join it up?

Good question.

From my experience with the software it really doesnt matter too much how long between exposures you leave. The software fills in the gaps. Obviously the most important thing is not to move your camera or telescope in between exposures. The same stars should be centered in every view. So a bit of tracking is needed. Nor should you change the magnification,ISO etc.

You can change the exposure time but its best just to leave everything the same.

The idea of the software is to take LOTS of short exposures and essentially stack them rather then spending hours on one single LONG exposure. The more short exposures you take the better.

Ive never used it with a scope. I have only ever taken images with my camera on a fixed tripod.

[LukeSkywatcher]

I'm starting to make it sound complicated. Sorry about that. It really isn't.

Its a simple case of taking many short exposures and "stacking" them. The more shots you take the longer the star trails become in the final image.

[JB80]

No, no. It doesn't seem too complicated, at least not the way you have explained anyway.

It's very informative, thanks.

Infact it is good advice because I was under the impression you had to use long exposures but now I will try it using lots of smaller ones. Plus if I can stop for dinner and it wont be too much of an issue that's a bigger bonus.

[jgs001]

The simplest option for star trails as has been said is lots of short exposures. You need a lockable remote shutter release. Set the camera to continuos shooting, shutter speed to 30 seconds iso to 800, and aperture to about f/4, the nifty distorts at the edges quite badly open more than that, although it might not be an issue for star trails, shoot in jpg, the software can't deal with raw anyway. Lock the shutting button on the remote and do something else, use some binos, jar dinner etc. Later release the shutter lock and let that exposure finish, or when your card or battery run out, and let atartrails do the work on the jpg's

[LukeSkywatcher]

The simplest option for star trails as has been said is lots of short exposures. You need a lockable remote shutter release. Set the camera to continuos shooting, shutter speed to 30 seconds iso to 800, and aperture to about f/4, the nifty distorts at the edges quite badly open more than that, although it might not be an issue for star trails, shoot in jpg, the software can't deal with raw anyway. Lock the shutting button on the remote and do something else, use some binos, jar dinner etc. Later release the shutter lock and let that exposure finish, or when your card or battery run out, and let atartrails do the work on the jpg's

Thanks John. I failed to mention that for ANY astro images that a lockable shutter release cable is also a good idea.

It makes life a lot easier and means you dont touch the camera as much thus eliminating any shake caused by touching the camera.

[Steve1976]

Great advice folks. I'll be trying all this tonight if the weather holds

[Steve1976]

Another question - do you need tracking in order to successfully use Deepsky Stacker or whatever you call it? For example, if I took multiple short exposures without tracking and then stacked them all together obviously there would be some changes to star positioning. Would DSS reposition and overlap all the stars so that it would look like a nice balanced non-startrailed type photo?

Not sure if that question made any sense!

[jgs001]

DSS will deal with the rotation between frames and combine the images. There is a limit to how many you can combine before you start to lose the corners, but I never worked out, for me, what that was.

Have a look at http://stargazerslounge.com/imaging-tips-tricks-techniques/73737-basic-widefield-camera-tripod.html there's a couple of example images there. I can process them much better now... but don't have the originals anymore...

[Steve1976]

Thats such a help thanks guys, its really answered all my questions (at least for now!). Love the photos too John.

[LukeSkywatcher]

I have stacked about 20 exposures of 8 seconds long in DSS. My target was just a widefield. To my amazement the final image even showed the Andromeda galaxy below Cassiopeia. No tracking involved. It was my first attempt at stacking. I stupidly moved my camera hence the blurred trees etc.

[Steve1976]

Like it mate, loads of stars in there and as you say the A Galaxy. Did you take any dark frames?

[LukeSkywatcher]

Like it mate, loads of stars in there and as you say the A Galaxy. Did you take any dark frames?

No darks,flats or anything just normal exposures. I'm only really starting to mess around with imaging. I havent even hooked my camera up to my scope yet. I just use it on a fixed tripod.

Here's a few good examples of what the Startrails program can do.

http://stargazerslounge.com/imaging-widefield-special-events-comets/124302-star-trails-wales.html