Various questions

[lazjen]

A poor subject title, sorry, but after last night's session with the gear in the backyard I've got a few questions to ask. Since I'm a beginner I'm posting here, but if the topic belongs elsewhere, feel free to shift this thread. If the wall of text is too much, jump to the end for the "TL;DR, questions listed" bit. :)

Background: My current main goal is to take some good DSO images using a DSLR from my backyard. My "sub-goals" towards this include learning to do good polar alignment; focusing; understanding and recognizing errors and limitations as they appear on the images.

1. Polar Alignment. This was interesting as I can't see SCP from my setup location. It's blocked by the house. I used the G11's PA assist routine (http://gemini-2.com/hc-English/E026.php) and while that was good, I found that when it slew to the star it was so far off that I could barely see it in the finder scope (sometimes it wasn't even in the field of view). To be thorough: I'm fairly certain I've set lat/long correctly. Time set is probably within 1 minute - does this need to be more accurate?

I did note that I was "generous" with my mount level when I set it up. I did note a significant improvement in the PA when I adjusted things further to a more rigorous level.

From this point I started taking longer images (about 30 sec to 1 minute) to check the alignment and attempt to correct errors found. I had issues with focus (I'll detail below), but by iteration the gross trailing in the images was soon (relatively) gone.

2. Focus. I had a lot of issues with this. I did the G11 PA assist with the eye piece in, so focus wasn't an issue. I then switched in the camera to check the results of the PA as I don't believe I have any other way to do so via the eye piece. I found it difficult to focus with the live view either on the back of the camera or on the computer screen. I think this was a combination of issues - it's quite a precise focus required and small movements either way could throw it out. The small screen on the back of the camera, even at 5x or 10x wasn't easy to see the differences. It was slightly easier on the computer screen - but a current limitation is the computer is inside, not conveniently near the scope. Then there was the to-ing and fro-ing between screen and focus adjuster. In the end, the best result I got was pointing to the moon and focusing on that before heading elsewhere.

I did some research and note the use of Bahtinov Mask to help focus. Does a Bahtinov Mask work well with the live view mode of the DSLR?

Although I may get a laptop in the near future to be able to bring closer to the scope, I think my manual fiddling with the focuser is error prone. What alternatives to manual focusing can I look into? Any recommendations for my setup (see sig)?

With the DSLR, I noticed that the focus got softer the more I zoomed in on the captured image, so while it might look ok at certain resolution/zoom levels, looking too "closely" is not good. I've read that this is something to expect with DSLRs, so I'm not overly concerned. For my Canon EOS 6D, how can I determine the quality of my focus for an image and/or how much zoom can I expect to be able to do and still have reasonable focus?

3. Errors and Limitations. After a couple hours of the above last night, I got to the point where I thought I could grab some images to process. I wasn't concerned at this point to be accurately picking a target - I just wanted to grab some data and see what errors popped up. I went to ISO 800 and 1 min exposures, and I was pointing somewhere around Eta Carina (ok, I was greedy and wanted some pretty colours :) ). Because the images were downloading to my computer, I could see what was happening after each shot. And the results were interesting and not consistent. I took 33 images in total over a few sets. Ignoring some soft focus issues, about 5 to 8 (I think) were acceptable to DSS to use. I think I know why most images were rubbish (e.g. needed to improve PA further for example) and I hope to post example problems in follow up posts to get specific feedback. Ignoring my skill level in the equation (as hopefully that will change :) ), how can I determine the maximum exposure length I can effectively do given the conditions to minimise problems? Given 5 or so images "worked" while others didn't, there's some variables I have not accounted for at this time.

Finally, how far can I possibly go for exposures without using guiding?

Thanks for any advice/assistance!

TL;DR, questions listed:

1. Time set is probably within 1 minute - does this need to be more accurate for PA and/or pointing to a location?

2. Does a Bahtinov Mask work well with the live view mode of the DSLR?

3. What alternatives to manual focusing can I look into? Any recommendations for my setup (see sig)?

4. For my Canon EOS 6D, how can I determine the quality of my focus for an image and/or how much zoom can I expect to be able to do and still have reasonable focus?

5. Ignoring my skill level in the equation (as hopefully that will change :) ), how can I determine the maximum exposure length I can effectively do given the conditions to minimise problems?

6. Finally, how far can I possibly go for exposures without using guiding?

[lazjen]

Right, here's some images, straight jpg conversions of the raw files. Ignore the vignetting - I'm working on fixing that. Files are large in size, be warned.

ISO 800, 1 min exposures.

Ok Image (http://www.rymich.com/astro/problems1/2013_05_18_OK.JPG)

I suspect some of the following errors are related to each other:

Error 1 (http://www.rymich.com/astro/problems1/2013_05_18_ERROR1.JPG)
Error 2 (http://www.rymich.com/astro/problems1/2013_05_18_ERROR2.JPG)
Error 3 (http://www.rymich.com/astro/problems1/2013_05_18_ERROR3.JPG)
Error 4 (http://www.rymich.com/astro/problems1/2013_05_18_ERROR4.JPG)
Error 5 (http://www.rymich.com/astro/problems1/2013_05_18_ERROR5.JPG)

I think that's a fairly good representation of the error types I got. If not, when I sort these out the rest should become clearer. :P

[lazjen]

Upon closer examination of the images DSS thought ok enough to use (and a sample linked previously), I can see they've got problems, just harder to see at first. Zooming in shows little 'u' or 'crescent moon' shapes on the stars.

[multiweb]

The first goto you do is always likely to be off. So the trick is to mechanically move your mount azimuth and elevation to get the star back in the finder where it should be then synchronise or reset the alignment to your target. From there on do the alignment routine to close in the SCP. Your mount needs to be as level as possible or any change in azimuth will change your elevation as well and vice-versa.


Yes it will . I regularly use bathinov masks for my lenses from 200mm down to 50mm. Most DSLR will also zoom when you do a focus on a star so it's just a matter to focus in and out. Practice makes perfect.


Slew to a very bright star and do a 3-5s exposure with a bathinov mask.


This will be trial and error unfortunately. Star with 2min then 3, 5min max. ISO800 is ok to start with.



You need to get into auto-guiding asap.

[multiweb]

These are all tracking errors. You need to get into auto-guiding.

[lazjen]

Marc,

Thanks for your replies.



Right. And tonight's main focus will be to do this better. I think I would have saved myself a lot of wasted time if I had leveled the mount better in the first place. I've marked my position on the ground from last night as well, so I should be begin the process closer to correct.



I'll sort out getting or making one of these soon then.



Ok. It's a whole area I haven't researched much yet. I didn't expect to have to do so until perhaps a bit later on when I consider moving to using a CCD camera. Time to start googling. :)

[wasyoungonce]

Ok, perfect focus is best achieved using a computer connected to the DSLR camera and running a camera control software package like BYEOS (http://www.backyardeos.com/) or APT (http://www.ideiki.com/astro/). Also you may need to re-focus depending upon temperature changes over the imaging period.

Laptops give much bigger screens can be zoomed in much larger with much higher resolution than the rear camera LCD screen.

Also, these DSLR camera control programs have focus routines built into them and control of much more....focuser's, telescope mounts thru ASCOM etc etc.

Spend a few $ on a program and toss the EOS canon utility....you will be glad you did after first use! APT even has a freeware version that has most function enabled so give it a go.

[LAW]

I've got a canon DSLR setup and I've been using Backyard EOS, there's a free trial but I bought the full version because it's so useful. The program has screens to help with drift alignment, focussing, and also separate screens for DSO and planetary photography.

Just with good polar alignment I've managed 2 minute exposures on an old EQ6 but I have to throw out a lot die to tracking errors. Maybe 1 in 4 is good, which is why I'm slowly sorting out an Autoguider.

[lazjen]

Ah ok, I'm not adverse to spending the money where required and if something like one of these programs will help a lot then I'll grab one. As I mentioned previously, I hope to go to CCD camera one day so I was using DSLR as a stepping stone and not investing heavily in it for software. Still, I prefer to avoid needless pain, so I'll look into these programs.

[lazjen]

Have you narrowed your options for an autoguider at all?

[lazjen]

After some reading and searching, looks like APT is the way to go. It seems they're making progress with the WiFi mode to the 6D, and if I go CCD in the future, I won't have to relearn a package. I'll download it tonight and hopefully get to try it out.

[Jon]

Hi Chris,

I've got a very similar setup to yours - G11, with a Canon 60Da and a SCT10" (mines 2540mm focal length f/10, you are at 2000mm f/8). I started imaging about six months ago so I guess I'm a bit further up the learning curve. So some thoughts:

1) Polar alignment - I never found the polar alignment helper much help in the Gemini system. Do a good drift alignment and leave the tripod exactly where it is if you can. I keep mine on a balcony under a tarp. Obviously, I take the mount itself off the tripod!

One of the side benefits of getting set up for autoguiding is that you can use PhD to do a quick polar align. It's easy as pie. See here: http://njstargazer.org/PolarAlignment.asp at the bottom of the page.

Try to set the time as accurately as you can, but you've got plenty of leeway. If you have a field of view of 5 degrees in your finder scope, that equates to 25 mins of sidereal time; in other words, if everything else is bang lined up, the time you enter can be more than 12 mins off and the object should still be in your finder.

BTW, a word on finders: if I'm honest I have more than once been caught out cursing the "unpredictable GOTO alignment" or whatever, before I've realised that the finder isn't lined up with the main scope. It's easily bumped out of place, especially if you are packing the scope up every night. The very FIRST thing you should check, once you've got the first alignment star in the centre of an eyepiece, is that the star is also in the dead centre of your finder, and if not, adjust it. I have to adjust 4 night out of 5.

Finally, as you mention, once you attach the camera, the star that was nicely centred in your eyepiece/diagonal view is way off or nowhere to be seen in the camera live view. Move the scope back so the star in in the centre of the camera view and his Align->Synchronize on the Gemini handset. Or build the model using the camera from the start.

2) Focus

I'm a bit unsure what you mean by "zooming in" on the target. BackyardEOS, which I use and would heartily recommend, will allow you to select and view in close up any stars on your image, to help with focus. But I think you are doing the right thing by focusing on the moon or a bright star first, then going to your target.

I have a motorised focuser that is controlled via USB. It's not cheap ($300 for my focuser plus USB controller) but it is a boon. Allows very precise focus control without all the jumping about you get when you touch the focus knob. Plus, it means I can sit inside and control the scope and camera from the PC! The G11 is a breeze to control with the Ethernet cable.

3) Errors and limitations

Get into autoguiding! As all the others have said. It's not that expensive, and not that complex. Something like this: http://www.bintel.com.au/Astrophotography/Autoguiders/Orion-Mini-Autoguider-Package/403/productview.aspx is all you need. I have the larger version http://www.bintel.com.au/Astrophotography/Guidescopes/Orion-Awesome--br-Autoguider-Package/780/productview.aspx as the extra precision helps with the long focal lengths. You and I jumped in the deep end with our setups - starting off imaging with a $400 5" f/4 reflector or somesuch atop the G11 would be a *whole* lot easier. You could probably get 1-2 minute unguided subs with such a setup and an f/4 scope is going to collect a whole lot more light an that time than your big slow f/8. However good my polar alignment, I've not been able to comsistently get a usable unguided sub longer than 30" with a 10" SCT on the G11.

For your setup, there's really no choice but to bite the autoguider bullet.

The good news is, it's not that hard, at least to get going. With something like the Orion starshoot autoguider camera in the links above, you just fit the camera into the finder scope, plug a cable from the camera to the Gemini autoguider socket, plug a USB cable from the camera to your laptop, fire up PHD ("Push Here Dummy") free autoguider software, and four mouse clicks later you're off.

I'd also recommend you get a focal reducer when you can afford it. (see this thread: http://www.iceinspace.com.au/forum/showthread.php?t=103278 ). Not only do they create a larger field (without one you won't fit much of Eta Carina onto the image at 2000mm f/8!) they also effectively make the focal ration faster: you're getting more photons per pixel, so your subs can be shorter. So the larger field and smaller objects mean you can take loner subs without tracking/guiding errors showing up; but you need less time to get the same level of brightness. So you're getting a bonus both ways.

So don't worry about zoom. If anything, you want to go in the opposite direction - make the image smaller. You've got 5472 x 3648 pixels to play with - do the "zooming" in Photoshop afterwards by just cropping the bit of the image you want.

I hope this is all of some use. Happy to follow up if I've not been clear.

Cheers

Jonathan

[lazjen]

Always good to hear from more people, especially those with similar situations.



I have no such luck. Although I have a reasonable sized backyard, I'm really constrained in my location due to street lights, roads, etc to a very small suitable area. And it's not a place I can leave setup permanently. Last night I got to setup again, and I "nailed" PA to a similar level very quickly. I've just setup again tonight and have already done some PA to probably close to the same level. I'm waiting for the camera battery to charge (because I forgot to recharge it earlier *sigh*) to check further.



I'll keep this in mind when I get to that point. I know I'll be referring back to this thread as I change/add things.



Checked the time tonight - it's certainly within a minute now, maybe 40sec.



Oh yes. Much cursing the first night I setup when I forgot to line up the finder scope with the main scope. I do a rough alignment just after I balance the scope by pointing off to some distance rooftops. Then, like you've mentioned, fix that up when I align the star.



I've got better with this part now and do a couple of alignments with the handset to help me out. Useful for helping with focus too.



Yes, it was just a but difficult to recognize the focus point vs what you see when there's a huge moon surface to see. I think I'm starting to get this a bit better, but the problems remain.



Ok, this sounds awesome. Is the USB controller connected to the Gemini unit?

And yeah, loving ethernet control of the G11. Played with the web page, plus I've messed around with Stellarium Scope/Stellarium.



:) I am convinced, do not fear. I will be looking into this in greater detail very soon!



As I was reading today I noted that APT can work with PHD, so that's cool too.



I have a focal reducer already - a 0.5 2" GSO - but I can't get it to focus with the camera. I think it's too far away from the sensor. I had troubles focusing with the eyepiece as well, until I put the eyepiece right up to the reducer.



Yes, I'll not worry about it for now until I see the effects of all the other changes I need to make.

Thanks again for the info.

[lazjen]

I think I spoke too soon regarding APT and 6D via WiFi. I may have had the wrong idea about it as the docs seem to suggest USB connection only to the DSLR. I certainly can't seem to get the 2 talking at this time.

[LAW]

Yeah, I picked an Orion StarShoot Autoguider up in the classifieds and I've modified a Celestron "firstscope" to use it as a guide scope. I just bought a $20 tripod with a "quick release" plate, dismantled it and fixed the head to the tube rings on my 8" and fixed the plate to the 76mm dob so it can be installed and removed without needing adjustment.

I started off with a Tasco 60mm (the infamous "525") which I also picked up for $20 but I found it cumbersome with the 700mm focal length at f/11. The little 76mm ~F/4 newt tube is much more compact, yields more stars and I was so impressed with it's perfomance I actually bought a second one to take hiking!

I only picked the Orion SSAG because it came up at the right time at the right price. Given my time again I'd probably go for the QHY5, which is basically the same camera but with less firmware restrictions. Simply put, the Orion is a dedicated Autoguider, the QHY5 can be used as a capture camera too. Given that I'm usually imaging with my 450D or 550D this isn't a huge restriction, but having options is rarely a bad thing.

[lazjen]

Well, it looks like the clouds are rolling back in for a bit, so I'll have to time to sort out some of these issues I think.

I'm sure the wife's going to be impressed that I'll be getting another scope already for this auto-guiding stuff. :P

A rough summary/list in no particular order:

1. Get Bahtinov Mask.
2. Sort out auto-guider gear.
3. Learn/setup APT. (Got an old netbook I'll setup to USB connect DSLR camera and run APT on for now to get started).
4. Motorised focuser.
5. Sort out focal reducer.

[Jon]

I'd prioritise 2, 3, 5 in that order. I don't know APT but if it's like Backyard EOS it will give you good feedback about focus. I suspect you are concerned about focus in your subs when in truth it's the guiding that's causing distorted stars. See how you go with the focusing with APT before throwing in the mask or the motorised focuser.

Just my 2c

[lazjen]

I think I agree with that priority list - because I have no real way of dealing with the errors that guiding and APT will solve, yet I have managed to get focus, even if it was fiddly work.

[Jon]

Fiddly is right! I thought I could speed things up by slewing to a bright star, focusing on that with live view, then slewing back to my target and beginning to capture.

Sadly, I've realised that's not enough. So I do that, and once I'm back on my target I take a series of 3 or second, ISO6400 "snapshots" (Backyard EOS allows you to take a quick and dirty jpeg-only snap for this purpose). Between each one I adjust the focus a *tiny* bit trying to get the FWHM value as low as possible.

My experience with astroimaging so far is to remind me that, sometimes, there are no shortcuts :-)

[wasyoungonce]

Should be able to do live view FWHM focusing adjustments with BYEOS and APT (http://www.ideiki.com/astro/skinAstro/4_FocusAid.png).

Although to tell the truth I also do FWHM focusing then take a series shorter subs and adjust re-focus to get it right.;)

[Jon]

Oh, I do. Use live-view. But stars bright enough to show up on live-view aren't the easiest to focus with. For the shorter exposures I use a star that's moderately faint and small on the sensor, and adjust to get it smaller. Tends to produce more consistent FWHM readings.

[naskies]

Once you get your gear working smoothly, I highly highly recommend traveling out to a dark site at least once. You'll be amazed at the difference - e.g. a single 5 min sub at a dark site turns out better than a stack of 3 hours worth of data in my back yard. It's much, much easier to process without light pollution gradients to deal with.



Yes, it's normal if your initial PA is waaay off the second star won't be even close by. A zero power finder (e.g. Telrad) is useful for the first step when the star lands outside of your normal finder. (I use a CCD camera on top of my RC8 with a 6 mm C-mount lens that gives me a 60x40 degree view of the sky, and so I can re-centre the star from my computer.)

Having a mount that is level is really important - otherwise you'll tear your hair out in frustration (much personal experience). With good levelling (e.g. my iPhone's inclinometer reports 0.0 degrees in all directions) I can go from PA being 5 degrees out (no compass needed - just plonk the mount down on the tripod) to az/alt error being within ~1 arc min in just 3 iterations.

By the way - if you know that your mount isn't level, I find it useful to adjust az and alt separately during each iteration (i.e. adjust az in one iteration, re-slew, adjust alt, re-slew, adjust az) and only make 1/2 to 1/3 of the recommended adjustment each time.



When using LiveView (and nothing else) to focus, set your ISO to the maximum possible using ISO expansion and enable "exposure simulation" (or whatever it's called on the 6D). First look at a bright star and use the coarse knob to make it as small as possible. Next, use the fine focuser knob and again make the bright star as small as possible. Finally, with really slow movements - watch for the really faint stars that appear in the background as your focus gets better.

A Bahtinov mask makes life much easier - the long diffraction spikes are also useful for trying to centre a bright star when it's just off the edge of your chip. If you do get a Baht mask, be sure to use the free Bahtinov Grabber software to help with focusing.

The ideal approach would be to use a motorised focuser with software that analyses the star sizes automatically.



Shorter exposures are good because it limits the amount of thermal noise you get in the camera, it reduces the demands on polar alignment and tracking accuracy, and reduces the chances that something might ruin the sub (plane, satellite, car headlights, mount bumped, etc).

Longer exposures are good because you record fainter details (nebulosity, stars).

Too short, and you won't record any faint detail. Too long, and you'll lose dynamic range (blowing out parts of the image completely) and have fewer subs available to stack with.

For DSLRs under light pollution, you basically want to expose just long enough that your light pollution peak on the histogram detaches from the left side of the histogram by about 10%:

http://www.samirkharusi.net/sub-exposures.html

Each camera has an "optimal" ISO setting for deep space imaging - e.g. on my Canon 5DmkII and many other Canons it's around ISO 1600. Maybe ISO 3200 on the 6D?

The other limitation is getting round stars - if your ideal exposure duration is say 10 min at ISO 1600 but you get eggy stars, you may get a better result overall with only 5 min subs at ISO 3200 if that gives you round stars.



Not very long. If you take a look around here and elsewhere online, you'll find that the guys with the virtually perfect $20k mounts still autoguide (there are lots of reasons why it's necessary).

As mentioned in the other thread, it's worth looking at off-axis guiders with your scope. Separate guide scopes will just give you extra grief.

Hope this helps!

[lazjen]

I already have a dark site in mind. I was there in April before I had my gear and took short exposure fixed tripod images on my older camera. Even with fighting clouds, it was an amazing view - the detail that can be seen even with the naked eyeball was great.

Leveling: The mount has level bubbles on it, so now I get the bubbles closer to the centre instead of just within the lines. That seemed to work well.

PA: According to the process with the G11/Gemini PA assist, you do one thing at a time (Az or Alt) before iterating to the other star and doing the opposite - just as you've mentioned.

Focus: Since I wrote my post, I've become a bit better at using the camera's liveview to focus. I haven't wrapped my head around APT yet to see how it'll help, but that will come - mostly a matter of RTFM, watch videos, etc. Haven't had the time recently to do that.

Exposure times: Once I sort out the other problems, I'll work my way through this to determine what's optimal from my backyard. The link had interesting reading - and makes me want to sort out things even more so when I get to do my dark site trip(s) I get maximum value from them.

Auto Guiding: I'll leave the details to the other thread, but I'll say here that I'm looking forward to sorting it out and getting more usable data. :)

[naskies]

Have you double checked that the built-in bubble level is centred? The G11s are probably better, but the EQ5/6s are usually soooo far off from the factory that it's really not worth the bother.

I use my phone to level my tripod first, before the mount goes on. I find that very small differences in levelling - e.g. 0.0 versus 0.3 degrees - makes a huge impact on the number of iterations needed to get very accurate alignment.

By the way - another issue to consider is what you have sitting under the mount. Setting my tripod up on green grass usually gives me no end of grief, because the ground settles when I place the mount on the tripod, and the PA changes during the night. Using a few heavy bricks under the tripod usually does the trick.

[lazjen]

Well, shoot, no, I did not consider how accurate those bubbles were. I'll do some checking to see.

I actually leave the mount on the tripod and carry the lot back and forth. Good weight bearing exercise. :)

Currently I do setup on the sorry excuse called grass in our backyard. While the ground is fairly firm, I've been mulling over the idea of putting in "stepping stones" or pavers to more permanently mark the position.


In other news: APT and the 6D are not happy with each other - APT sees the 6D, but that's about it - no liveview, no status info, etc. I'm trying to contact the author about it. Got myself a rego key for BackyardEOS to try in the mean time.

[Jon]

I really am hoping you take the OTA and counterweights off ;-)



I don't know APT. But Backyard EOS just works. It's great.

[lazjen]

I do take the OTA and counterweights off. :) Although I think I'm getting close to being able to leave some of the counterweights on and still being able to carry it - the hassle is more balance than actual weight.

I'm working on a trolley system to be able to take the whole thing in/out without taking any bits off. While I can pack it all away in 10 min now, setting up takes a lot more time.

Well, BYEOS at least seems to work with the 6D with my indoor tests this morning - FWHM for my kitchen wall was a shocker. :p

Weather permitting tonight I'll get to use it for real.

[Jon]

LOL. I think I took an image of your kitchen wall last night. 12 x 3 min subs of something so out of focus it may as well have been. It certainly wasn't M53 :-)

In my defence I was trying out a brand new piece of kit - tuner out to be the best value for money I've ever spent ($3.15) http://homepage.isomedia.com/~cvedeler/scope/mirrorlock.htm

[lazjen]

Wait a sec, if you get out of focus images, how can it be the best value for money? :screwy: :)

[Jon]

Took a bit of fiddling :-) I'll post some before and afters ...

EDIT: and here they are http://www.iceinspace.com.au/forum/showthread.php?p=981489#post981489

[lazjen]

Yes, noticed them.

Ok, probably worth the money then. :)

[lazjen]

The clouds have rolled over again, but I did manage a bit of time tonight to try out parts of BYEOS.

I spent about 1 to 1.5 hr doing drift alignments. I think by the end of it I was starting to get the hang of it, although I need a good way of orienting the camera better to make things easier.

The focusing tool was great too. I hope to see the results of this more when I get a chance to take a few images.