How long ... oh Lord???

matt · #1 06-03-2006, 01:45 PM

Not sure if this is the right place for a question of this type so mods... do your thing if you have to.

I'm just keen to get some idea of what's "normal" in our wonderful hobby for a situation I've encountered.

I've ony been imaging since late last year and have carried out most of that imaging between, say, 10pm and 1am.

In about 4 months I've yet to capture what I would consider a crisp, well focused image. Even though collimation appears fine and focus on the screen looks as best as possible under the conditions.

I'm putting it down to bad seeing and poor tranparency, due to summer conditions.

So .... finally ... here's the question/s for imagers everywhere:

What's the longest run of bad seeing and or transparency you've ever had?

I'm honestly keen to see your responses and thank you in advance for posting.

CS ... truly ... CS

Robert_T · #2 06-03-2006, 02:01 PM

Hi Matt, this one really depends on how often you go out to image regardless of the conditions. I generally have a go any night the sky is clear or looks likley to be. In the last year I had one extended period of good seeing 8/10 and better in the evening hours that lasted nearly a week, that immediately preceding CHristmas. Apart from a few week long breaks in cloud last Christmas it's been pretty dismal cloud-wise. The one and only one good steady piece of seeing 8/10 or better I've had this year (06) was one morning a few weeks back when I stubbornly refused to acknowledge the ubiquitous cloud and by some miracle it had cleared before I imaged.

Point I'm getting to is that good seeing is rare and is often missed unless you image a lot. Dennis's best image of Jupiter was taken from Brisbane on a morning that I got up but decided not to bother because the sky was 90% cloud.

cheers,

matt · #3 06-03-2006, 02:08 PM

If it's possible, discount cloud cover.

I mean nights where it looked clear but the images you end up with are very ordinary. Bad seeing. Humidity.

How long, with fairly regular nights of imaging, were you out there before a "good" night finally came along? Days... weeks... months...decades?

cometcatcher (Kevin) · #4 06-03-2006, 02:36 PM

Discounting cloud, I forget but it was many weeks. The planets looked like viewing them underwater, which was kinda what was happening I guess.

[1ponders] (Paul) · #5 06-03-2006, 02:59 PM

Those perfect evenings come along only a couple of times a year. You should be able to get a couple of weeks of above average seeing during the year with the rest of the year being ordinary to poor. Of course this will depend on where you live, local topography, prevailing weather conditions yadda yadda.

Longest run of poor conditions. I've been able to image only about 8-10 times since last sept (Lostock not included). Plenty of times I've setup and then packed it in 3 hours later. And in that time I had one night that I would have considered good conditions. But even prior to that seeing had been terrible for ages, but I put alot of that down to my specific location and the prevailing microclimatic conditions (sea breezes early followed Katabatic winds later at night during winter)

Robert, Striker and Dennis are in Brisbane about 100 km away from me and they seem to get less cloud cover than I get, or they are more persistent and stay up longer. But when I do get a good night I have less light pollution than them to worry about.

Now I gather you're talking about imaging with the NexImager, and not a DSLR? Conditions need to be much better for planetary imaging than say for wide field to semi-wide field DSO imaging. Another thing to consider it how long are you leaving your sct to cool down before imaging?

If you've not already done this, as an experiment, set your newt out at the same time as your sct, late in the arvo/early evening (protect from sun to prevent heating up

). Hopefully is is a fairly good night. If it turns out not to be, try this again another night. Check that collimation is as good as you can get it.

Let them sit for an hour and check the seeing through each, using eyepieces to give the same or similar magnification (high mag) and the same star. Defocus to see the diffraction rings an notice any movement then focus to try to see the airy disc (check collimation again while you're at it) and again check for image disturbance. Do the same thing each hour and see if there is a difference in the patterns between sct and newt. The open tube newt should equalize with the ambient temp quicker and show less diffraction disturbance than the sct. Doing this I'll be surprised if your SCT mirror is close to ambient in 5 hours, particularly in Canberra. Remember to your trying to equalize internal/external temps, not necessarily trying to lower your mirror temp. A mirror temp that is lower than ambient has it's own problems as well. Here in Bris and the surrounds we're fortunate to not have really larger day/night differentials most of the year. I reacon this is why bird likes to come up to Rockhampton in May. Most stable time of the year for us here.

Anyway, after trying this a few times you'll soon be able to tell the difference between poor seeing conditions and tube turbulance inside the SCT. Hint: instead of being irratic sharp scintillating movements it will look more like leasurely boiling movement (though the greater the differential the more active the boiling).

Hope this ramble has been of help. The best seeing in the world won't do any good if your scopes not settled.

matt · #6 06-03-2006, 03:14 PM

Paul

Thanks for that terrific response. Nothing rambling about it. Just very thorough.

I'm usually pretty good about the amount of time I leave the scopes outside to reach equilibrium. Although I've never set them up side by side. That's a great idea and I'll be doing that. I'll let you know how they compare.

Your words have convinced me even more that I've simply not had a night of good seeing so far since Oct 2005. At least not on the nights I've set up to image. Also, Canberra does seem particularly afflicted as far as seeing goes. I'm sure Bird has made comments to that effect.

Persistance. Get out there night after night, if you can. Leave the scope set up and out overnight and do more pre-dawn capture if possible. That's the plan.

But honestly, this lark should come with some kind of warning for your state of mental health

acropolite (Phil) · #7 06-03-2006, 06:50 PM

Matt, try the wee small hours of the morning. I've forund that the seeing improves dramatically in the last couple of hors before dawn. Do the DaveP trick and put the scope out to cool, set the alarm get up at 4AM.

matt · #8 06-03-2006, 07:25 PM

Yep. As I expected the 3-30-5-30am shift looks to be where the gold is.

It's a shame that Mon-Fri that's exactly the time I'm already at the office

asimov (John) · #9 06-03-2006, 07:30 PM

Here's my take on this.

I bought the toucam mid October 05' & that's basically when I thru myself full-on into imaging. I was available every single night without fail until 4 weeks ago, when I finally scored a job.

In that time I've seen 2 really good (8.5-9/10 seeing) nights...possibly 3.

I was most annoyed on those nights because I was only starting out & even with good conditions, I managed to stuff things up. I could have got better images had I known then what I know now.

Yes, the wee hours before dawn seem to be the best.

matt · #10 06-03-2006, 07:35 PM

2, maybe 3 good nights in about 130-150 nights?

hmmmmmm

Doctor. Come quick. I don't feel well at all!

asimov (John) · #11 06-03-2006, 07:47 PM

Yeah, it's certainly enough to make any astrophotographer sick...VERY sick!!

My phyco-analyst reckons 'it's only a matter of time'......time before WHAT doc??

I keep asking!

matt · #12 07-03-2006, 07:38 AM

Update .... update ... update

Left the scope out all night. Ventured out between 3 and 3-30 this morn.

Shocking. Absolutely disgraceful

Defocused Jupiter looked like it was being held under a constantly running tap. The good news? That's left it sparkly clean!

Good seeing, folks.... don't live here.

But don't fear. I won't quit. Never, ye weather Gods. Never!!!

asimov (John) · #13 07-03-2006, 07:53 AM

Don't live here either guys....My scope is still out there lol.

You must have the jetstream directly over head Matt?

matt · #14 07-03-2006, 08:03 AM

Is it ever anywhere else, Asi?

asimov (John) · #15 07-03-2006, 08:22 AM

I'm starting to get paranoid about all this! Take last night for instance: No jetstream within 500 miles of my joint (according to the map) & no wind.

A wee bit of what I call 'fast' star twinkle, but I setup anyway. I get Saturn on the screen & it looks like crap! IE: In & out of focus & with that damn red hazy ring around the planet, that I see on occasion & put it down to moisture in the air? not certain though.

I take an AVI at my usual toucam settings for Saturn & bung it thru registax. The final image was nice & sharp.......With a nice bright purple fringe on the planet limbs & rings with the red halo around it!

Many would suggest it's the achro refractor causing this, but have a look at my many saturn pics posted in here.

I'm wondering A: high altitude winds were present, causing this fast star twinkle...(4/10 seeing) & B: moisture in the air causes this red haze around objects.

Hhhhmmmm.

matt · #16 07-03-2006, 08:28 AM

I'm pretty sure we're onto something in regards to atmospheric moisture Asi.

All my images of late have a red tinge on one limb and blue at the opposite limb. It appears we're seeing the same phenomenon ... and that's borne out by the fact we're seeing it with both refractor and reflector?

asimov (John) · #17 07-03-2006, 08:46 AM

Yes, the simple..yet crucial fact we're both using totally different scopes & seeing the same phenomenon suggests this.

Re: my saturn pic. I tried to process this red halo out, which I did easily but the catch is I destroyed the image quality by doing so, damn it!

Canberra & Cummins both start with C!

matt · #18 07-03-2006, 08:50 AM

and I'm happy (sort of) to report that Bird has just confirmed the same lousy seeing this morning at his place.

That feels better. Thought I might have been going insane there for a moment. Or getting worse

asimov (John) · #19 07-03-2006, 09:24 AM

I've taken the day off (due to an incident at work yesterday) & gonna re-collimate anyway....just to be on the safe side

iceman (Mike) · #20 07-03-2006, 09:51 AM

Last few mornings i've got up at 4am to find clouds.. so I get ready for work and have left by 4:45am, and it's starting to clear up.. by 5am it's clear

I hate to think how many times 9+/10 seeing has been missed due to clouds, or becuase you were too lazy and slept in that morning