Odd issue

[LewisM]

Out imaging M83 last night with the FSQ85 and OSC CCD. Focused before the run (Bahtinov magnified 400% and checked at 100%). Rechecked focus every hour (no shift - well acclimated). 600 sec subs.

Irrespective of this each sub seems to have large stars (perfectly round as tracking was sub-arcsec with no deviation and timed at 4 sec exposures) and halos. Detail in M83 is pretty sharp given the seeing. Oddly, each bright star also has a diffraction spike at 5 & 11 o’clock- checking shows no spiderwebs, no anomalies (I had a custom baffle made that eliminated the tiny spacer spikes).

Additionally, I was only using a uv/ir filter as I don’t use LP filters anymore. The subs upon debayer are VERY green (usually just a hint of green).

The temp dropped to 5.7 deg during the entire 3 hrs on M83. Severe vignette in the subs.

Does this sound possibly like a frosted CCD cover glass? (I baked the desiccant last week) or possibly frost/dew on my UV/IR filter? I checked the objective for frost, dew and foreign objects last night and this morning and all clear. Nothing obvious on ccd or filters either.

Considering to add a dew strip to the ccd nosepiece anyway but does this sound like ice/frost? CCD was running at -15 (my set point). I don’t think atmospheric ice.

[Wavytone]

Unlikely to be at the sensor if it affected all bright stars equally. Something infringing on the light path more likely.

[blink138]

sorry to butt in lewis and i cannot help with your problem, but can you tell me the advantage of your uv/ir cut filter instead of an lp filter?
i know you are in a severe lp affected area and so to am i
pat

[LewisM]

Pat, ALL LP filters remove colour to some extent, even the "good" colour you want. Software removal of the LP is a better solution than trying to filter it out.

The UV/IR helps with bloat of stars, especially with refractors. Helps get the "pinpoint" stars we all strive for.

[LewisM]

Here is what I am having trouble with - see image below.

Note the odd diffraction spike on the stars, the fuzzy delineation, the blue blotching right across the field (this is cropped - doesn't show much of the awful vignetting).

I took flats this morning (nothing moved), and they did not help much at all - it's like there was a transient issue - like frost - which cleared. The prior imaging run on NGC 3132 shown in the imaging section did NOT have these issues (yes, the seeing was average).

I can't so much more with this image (3 hrs), especially colour/saturation as anything further really starts showing up BADLY due to the odd blue blotching (this is all after DBE and BE in PI, plus some other tricks).

[Amaranthus]

So, just to get the question out of the way - it's definitely not blooming?

[LewisM]

Nope. This is an ABG CCD (OSC SBIG STF-8300C)

It happens in EVERY single frame of M83. Did not appear at all in the preceding target (2.5hrs)

[LewisM]

Here is my final edit of the data - you can see it had the potential - aftera LOT of fiddling - but the hazy stars etc really makes me think there was condensation or frost on the glass or chip. There was NO dew last night, but the temp did drop quite markedly from 1 am to 3 am.

There is still a LOT of red and blue blotching and noisy as frack despite 3hrs of data. The star fuzz/bloat was visible on the virgin subs straight off the CCD - I refocused again just to be sure too.

[LewisM]

Astrobin is down right now - need to upload a file to also show the extent of the vignette etc for a 3 hr integration with CORRECT flats, darks and bias.

Here at least is a 300% zoom of the bright spikes - notice the spectral lines etc - almost like a prismatic effect like an ice crystal (I keep convincing myself its ice :lol:). I checked ALL glass for potential cracks or chips - nothing.

[Slawomir]

Hi Lewis,

I looked at your Astrobin gallery and your image with the running chicken has a bright star with spikes as well. So it might be that only very bright stars bring up this issue.

Honestly such spikes do not bother me. To my limited knowledge, micro lenses also can cause spikes on bright stars, as well as an obstrusion into the optical path.

I wish I could offer a more useful advice.

Suavi

P.S. I was really tempted to suggest guiding issues...but resisted :D

[RickS]

Doesn't look like icing up to me, at least not the sort I've had in the past. That usually takes the form of small space invader like creatures appearing all over the FOV.

[iborg]

Hi

I think this is dumb idea, but, a strand of spider web? :shrug:

Philip

[ericwbenson]

Hi Lewis,

Funny the spikes in the 300% crop are not straight. Furthermore the micro lens flares that Suavi suggested are usually aligned with the axes of the CCD. Was the image rotated between subs?

EB

[Peter Ward]

When you say "OSC" camera...is it a CCD or CMOS sensor?

Spikes are a hallmark of CMOS readout architecture...( simply put...the nature of the beast....I gave a talk on this
at the CWAS/Astrofest a number of years ago )

If it's a CCD...bugger...much harder to nail the cause down...but I'd be cleaning all optics that close to the sensor for a start :thumbsup:

[doppler]

I had the same issue with my reflector last year. I took some more subs the following night and the spike was not present. I thought it might have been caused by a dust bunny or by some random reflection but after cleaning the camera sensor and coma corrector it was gone so I guess it was just a smudge somewhere distorting the light path.

[LewisM]

It's an OSC SBIG STF-8300C CCD Peter..I know you don't read checklists :lol:

Suavi - the baffle I had made removes the spikes. It chokes the light path down to 83mm just in front of the objective, so the foil spacers are not ever any longer "exposed" to the light path. THis was installed AFTER Running Chicken. I tested this setup on Betelgeuse and on Canopus to see if it removed it, and indeed it does, so no, it is no longer the foil spacer issue.

What concerns me is it appears to bee a combined effect - the poor readout is what worries me the most, with SEVERE vignette, bad colour blotching etc. The prior ones on NGC 3132 seem just fine, then bang - off it goes with odd spikes, "hard" blue and red blotching etc etc, almost like the electronics had a heart attack.

So the issues are:
1. odd spikes
2. odd halos/fuzzy edges
3. severe vignette (never been seen in prior 10 min subs)
4. colour oddities/blotches.

Here's a jpeg of the full combined frame - forget the noise, it's the vignette I'm showing here and the fact the specifically produced flats did nothing. Also shown is the prior run of 3132 - you can see flats removed just about all issues and very little vignette present (not counting the red sky glow). All mere screen transfer stretches in PI.

[Octane]

Wasn't thin high cloud by any chance?

H

[LewisM]

Gawd H, I said that (or ice) back int he original post, but it seems 99% of respondents did the usual Aussie - don't read the effing question :)

I am putting it down exactly to that - extremely thin upper level cloud or ice in the atmosphere.

[Camelopardalis]

Wonderful advertisement for Tak this thread :thumbsup: :P

[LewisM]

I've tried EVERYTHING I can think of in processing to clean it up, but not happening (the fluffy stars get a ring of dots all around them and the colour really doesn't want to come out). So, about to hit Shift-Delete on that file batch. 3hrs down the gargler...

[Camelopardalis]

Are you sure you didn’t get a hair or an eyelash on the sensor window?

Back in my cold-fingered DSLR days I had frosted it over a couple of times and the stars get much more diffuse. Yours shows a much more distinct halo. :shrug:

[LewisM]

Wonderful advertisement for the idiocity of push-onitis - imaging through bad atmospheric phenomenon.

The NGC 3132 stuff came out just fine :P

[Camelopardalis]

:thumbsup:

[LewisM]

Dunk, RTFQ :lol: - the camera was not removed or disturbed from the prior 2.5hr run on 3132, so no way ANYTHING got in there.

As I mentioned WAAAAAAAAAY back in post No1 (I think), the temp SUDDENLY dropped to 5.7° (was 8°, and that is why I rechecked focus), so I suspect the front that came through was happening just then and I was getting pre-frontal atmospheric disturbance/ice/vapor...

The SBIG cooler percentage was 78% prior to this change, and during the change, it dropped to 54% cooling - so, the cooler atmosphere was aiding and abetting the cooling.

If anything it's a bad advertisement for SBIG :lol: Anyway, another EP size dew strip on the way to preheat the camera nosecone...

[Camelopardalis]

What was it? Push-onitis:lol:

[LewisM]

That's a prime example of $hitty Lewis Processing - aka The SLP Method

[Octane]

haha, sorry, was at work so quickly skim read.

I ask as I've seen this before in my own images when there's high-level thin cloud usually not perceptible to the eye.

H

[LewisM]

All good H. Just funning with you.

Def stealth clouds/ice

[xelasnave]

Five nova all at once?
alex

[LewisM]

Nova Glacies Alex (I am sure you learnt Latin at school) :lol:

[multiweb]

I occasionally get that on the odd star with my old Q. Bright stars that are about half way between the center of the field and the edge. Mostly yellow will do that. One bright line going through. Maybe it's a TAK thing.

[xelasnave]

No latin ..it was all Greek to me.
alex