Imaging Orion nebula DSLR only settings needed

[bendiddley]

Hi all. I want to start imaging the orion nebula. I will be using just my canon 1000d only (no scope) on an eq3-2 at 300mm using my standard 75-300mm kit lens. It will be tracked (unguided) and all I want to know is what settings would be suitable (ISO, aperture, exposure length etc) and the number of subs and darks etc I would need. Hope you guys can help.

[Bizibilder]

Try ISO 800 with an exposure of 30 seconds (unless you have a remote shutter release when you can use the "Bulb" setting and open the shutter for a minute or more).  I don't use camera lenses but I believe either full aparture or maybe one stop smaller would work best.  Take as many subs as you can - at the very least 30 but 100 would be better.  If you want to take darks (you could work without them to start with) take at least 24 with the same ISO and temperature as the light frames that you take of your target. (Light frames are the ones with your chosen image on them).

You may need to take a few trial exposures to get the focus spot on first.

[cosmojaydee]

At 300 mm and taking 30 sec shots , trailing will be visible , I would increase the ISO to 1600 reduce the time to 10-15 (you may even get tailing ) secs and take as many as you can . its a case of trial and error, as suggested take a few trial shots. 

Good Luck , look forward to seeing the images

[bendiddley]

Cheers guys

[The Admiral]

At 300 mm and taking 30 sec shots , trailing will be visible

As someone who is considering an EQ3-2 for "casual" astrophotography (not thinking about many hours of total exposure here) , are you saying that even with unguided tracking that you'd get star trails with an exposure of just 30 seconds, with a  FL of 300mm? What would one need to avoid star trails with this sort of exposure?

[brrttpaul]

This may help shows you how long you can take with different focal lengths, my 300mm would be less than 2 secs on my camera

http://www.sceneplanner.com/tool3.php

[Psychobilly]

If your polar alignments ok you shoul be able to get longer subs ... on the EQ3-2 You might have to throw a couple away . You will need to see how your particular mount performs.

My EQ3-pro would do 120s subs at 200mm fl unguided with hardly any subs being discarded and that was on a 1.6x crop sensor.. The NEQ-6 that replaced it can do 240s subs unguided... 

Peter....

[Alien 13]

An EQ3-2 with a 300mm lens will be limited to about 2 min exposures when the polar alighnment is spot on, 60-90 seconds will however be a more comfortable target but this is still long enough with a DSLR/fast lens combo to get some nice images.

Alan

[Rico]

You've mentioned that it'll be tracked but not guided, in which case you should be able to push 2 minutes plus, especially with a widefield image given by your 300mm lens.

ISO800/1600 seem to be the norm -  this is really down to your camera and possible your tolerance to noise.

The aperture setting is a funny one You could just leave it wide open which would improve the amount of light received by the sensor, improving your SNR, but it most cases this comes at the cost of extra coma, astigmatism, distortion and vignetting from the camera lens. Many people tend to stop it down until they get an image that looks satisfactory with respect to this list. You'll get diffraction spikes on the stars once you stop down because of the blades used to reduce the aperture ... some people like this, some don't.

Once you've chosen an aperture, and your focus is spot on, your exposure length is really down to how well you've aligned your mount. IMO, I would push it as far you can until you get star trailing and then adjust accordingly (all the while checking your histrogram looks ok). Once you've churned out enough subs (lets say 1-2hours worth), do some imaging by linearly reducing the exposure, this should give you a nice smooth gradient for the blown out core that you can blend in later.  So if you do 120s lights. Then do 60s/30s/15s lights as well. Check beforehand that the 15s light gets the detail your after from the core.  In terms of darks, I've always gone with the rule of doing as many darks as I do lights. Bias frames are super easy to do ... so no point in not doing them. In terms of lights, well if you leave the lens wide open, given the fact that you have a telephoto lens, you may need them.

Hope that helps

[kalasinman]

If you are tracking, this guide won't do. It's intended for camera on tripod. It also doesn't take into account that trailing varies with distance from the Celestial Equator.

[skysculptor]

If your eq3-2 is motorised and you have a polar scope fitted and you polar align well you should get upto a minute or so with out star trails maybe more if you polar alignment is spot on ! Drift aligned without auto guiding, try what the moderater said the better your polar alignment the longer you exposures can be.

[brrttpaul]

My mistake I genuinly thought it was on a normal tripod he was asking about (its still early) lol

[bendiddley]

Nice one, good advise from all, cheers.

You've mentioned that it'll be tracked but not guided, in which case you should be able to push 2 minutes plus, especially with a widefield image given by your 300mm lens.

ISO800/1600 seem to be the norm -  this is really down to your camera and possible your tolerance to noise.

The aperture setting is a funny one You could just leave it wide open which would improve the amount of light received by the sensor, improving your SNR, but it most cases this comes at the cost of extra coma, astigmatism, distortion and vignetting from the camera lens. Many people tend to stop it down until they get an image that looks satisfactory with respect to this list. You'll get diffraction spikes on the stars once you stop down because of the blades used to reduce the aperture ... some people like this, some don't.

Once you've chosen an aperture, and your focus is spot on, your exposure length is really down to how well you've aligned your mount. IMO, I would push it as far you can until you get star trailing and then adjust accordingly (all the while checking your histrogram looks ok). Once you've churned out enough subs (lets say 1-2hours worth), do some imaging by linearly reducing the exposure, this should give you a nice smooth gradient for the blown out core that you can blend in later.  So if you do 120s lights. Then do 60s/30s/15s lights as well. Check beforehand that the 15s light gets the detail your after from the core.  In terms of darks, I've always gone with the rule of doing as many darks as I do lights. Bias frames are super easy to do ... so no point in not doing them. In terms of lights, well if you leave the lens wide open, given the fact that you have a telephoto lens, you may need them.

Hope that helps

You say check the histogram, what should I be looking out for with that and why?

[Roy Challen]

As someone who is considering an EQ3-2 for "casual" astrophotography (not thinking about many hours of total exposure here) , are you saying that even with unguided tracking that you'd get star trails with an exposure of just 30 seconds, with a  FL of 300mm? What would one need to avoid star trails with this sort of exposure?

Hi Admiral,

I have an EQ3-2 pro, and I can safely say that you will not get trailing with 30 seconds exposure, provided that your Polar Alignment is good. Concentrate on that, and 2 mins is easy, 4 possible, and 5 not totally unreasonable. This is with focal length of 420mm. Personally, I think this mount is probably the minimum requirement for AP, but it does do the job well if you set it up well.

[jimbo747]

Didn't want to start a new thread but re the max exposure for unguided, is this different from untracked? I have a 127 make with fl 1500, so going by the 500 formula I'll have a max exposure time of less than 1/2 a second and even with a 0.5 reducer its still under a second. However this is on a goto alt az Mount so does that make a difference as I'll just get star rotation rather than streaks across the sky? I've seen a thread if here with someone using a 127 make with 0.63 reducer and taking subs of 30s with no noticible star trails. I know that in different areas of the sky and different altitudes it varies so how does it work in my case?

[jimbo747]

I mean mak not make, stupid phone autocorrect

[Rico]

If the histogram is too skewed to the right you may be clipping a lot of data - however this may not be too much of an issue of you're taking many exposures. In light polluted skies this can easily be done, so you just need to make sure that this isn't happening. I tend to use an LPF with mine, and sometimes I do end up clipping star colour data, but I find that the galaxy/nebula data looks much better since you're improving your SNR. I've been under the impression that a group of longer exposures are better than a group of shorter exposures that make up the same total time. If you intend on doing a set of different exposure lengths, this may not be an issue as you'll filling those blown out cores with different data sets. I think the same can be done to stars, where data may be clipped ... essentially you're trying to improve your dynamic range ... may be somebody with more experience can chime in?

[Roy Challen]

Didn't want to start a new thread but re the max exposure for unguided, is this different from untracked? I have a 127 make with fl 1500, so going by the 500 formula I'll have a max exposure time of less than 1/2 a second and even with a 0.5 reducer its still under a second. However this is on a goto alt az Mount so does that make a difference as I'll just get star rotation rather than streaks across the sky? I've seen a thread if here with someone using a 127 make with 0.63 reducer and taking subs of 30s with no noticible star trails. I know that in different areas of the sky and different altitudes it varies so how does it work in my case?

I once got a 90s exposure with NO trailing from an ETX 70 (alt-az). But yes, it is different from an EQ mount, and it makes a vast difference guided to unguided (not that I have experienced that personally as I have only really just got started with imaging myself). As to how it'll work in your case - try it and see. You have a long focal length so it'll be harder...

[Rico]

Tracked refers to having motors that rotate the mount about the RA/DEC axis. Some mounts don't have any motors at all but they can be manually tracked using knobs in both axes. Guided means that there is an additional camera monitoring a single star. Software can be used to ensure that the mount doesn't stray from this star by small adjustments in the motor during imaging using small pulses. So that while its 'tracking' it's also being guided using an additional ccd. The formula for maximum exposure times relates to untracked and thus unguided mounts - essentially a fixed tripod.

[jimbo747]

Ah thank you makes it clearer.