Various questions

[Jon (Jonathan)]

Originally Posted by wasyoungonce

Should be able to do live view FWHM focusing adjustments with BYEOS and APT.

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

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 (Dave)]

Originally Posted by lazjen

My current main goal is to take some good DSO images using a DSLR from my backyard.

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.

1. Polar Alignment.

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.

2. Focus.

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.

3. Errors and Limitations. how can I determine the maximum exposure length I can effectively do given the conditions to minimise problems?

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

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.

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

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 (Chris)]

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 (Dave)]

Originally Posted by lazjen

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.

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 (Chris)]

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 (Jonathan)]

Originally Posted by lazjen

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

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

Originally Posted by lazjen

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.

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

[lazjen (Chris)]

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 (Jonathan)]

Originally Posted by lazjen

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

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/~cvedel...mirrorlock.htm

[lazjen (Chris)]

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

[Jon (Jonathan)]

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

EDIT: and here they are http://www.iceinspace.com.au/forum/s...489#post981489

[lazjen (Chris)]

Yes, noticed them.

Ok, probably worth the money then.

[lazjen (Chris)]

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.