pipnina

6 minutes ago, Franklin said:

Actually, Gerald North speaks in his books about his use of this telescope and I seem to remember him mentioning about stopping it down to help with the CA.

Yes I would expect it probably does suffer from CA quite badly, we really take our modern specialised glass types and curves and magics for granted! I don't think that scope will have had any fluorite lenses or asphericals!

I went to the observatory in 2018 as part of a kent/london holiday, and while my horrible vertigo on that hill prevented me from seeing the monster of a scope at the top (unusual I know, but these days I've been climbing cranes so if I go again, it should be no issue), I knew that in winter months they do still provide demonstrations visually and with a CCD.

Being such a monster of a refractor, I can only imagine the views in the center of field would be very good, but also very very limited in terms of off-axis quality given the era of design. I havent been able to find any of the images taken with the scope however, despite the scope's original purpose being for photography!

Has anyone here been fortunate enough to visit the scope when demonstrations and viewings were on offer?

13 minutes ago, alacant said:

Hi

No time to do it justice I'm afraid, but it looks fine to me. The flat frames are working perfectly:

But then if I abuse them (as I tend to by the time I am processing it, with the heavy stretching and bringing out of faint detail etc) it rears its head in at least some form!

Here's a stretch of the full master light (so multiple nights worth of lum data, all under a new moon so no interference there). It seems to manifest here in the form of a brightness plateau in the center of the screen. If I run DBE in pixinsight, the image is largely nicely flat but the central plateau is now almost pinched.

Now this could be boiled down to inconsistencies between nights perhaps, if it wasn't appearing in more of my images! this example is of only a single night.

I figure it's either reflections in the tube or the baader mpcc coma corrector?

I have no idea precisely.

12 hours ago, Bibabutzemann said:

If the cloth you are using for flats it too thin, then internal reflections could effect your flats. Daylight sky is already too bright for a normal shirt in my experience.

Maybe you could give us a unstretched single calibrated frame.  Then its easier to see what is causing your gradients.

I would use a flocked dew shield as first measurement to block out stray light . Its easy, riskfree and protects the 2nd mirror from dew.

Cloth I'm using is sort of flannel thickness- almost like a thin bath towel but much thicker than a shirt

Here's a calibrated image, although made of only 3 of the 40 odd flats, I had to remake them. Plus a raw flat and a raw light. star_Light_001.fitsFlat_001.fitsstar_Light_001_c.tif

I have the astro essentials flexible dew shield, which seems pretty black on the inside already, so I don't know if I need to flock it or if it's already suitably flocked?

6 hours ago, alacant said:

Hi

If you image with it in place, then you should take the flat frames with it in place. That will probably solve the issue. Otherwise...

The biggest improvements for us was a black shower cap over the 1º mirror end, uprated springs, matt black secondary spider+focuser barrel and removing the 1º mirror clips. 

Number one mirror end? Is this a mod or something you put in place for flats only?

I suppose removing the primary clips and glueing it could work, what glue should I use?

Is there anything you'd recommend for making the focuser barrel black? I can spray paint it or similar? And the sides of the secondary I was thinking about using a little strip of that stick-on velour I'm going to baffle the inside of the tube with?

How have you guys flocked your 130-pds? I have the flocking material (and lint roller) recommended from FLO and plan to take the primary mirror cell out this weekend to get good access to the inside of the tube. I am not sure if I should stop with the inside of the tube, or do other bits as well like the inside of the focuser tube (IIRC it's silver?) and the edge of the secondary (not blacked by default and faces the camera sensor...)

I have some bad reflection-like effects in the middle of all my images and have to work DBE in pixinsight HARD to get rid of it.

Doesn't seem to affect subs though, or maybe, at least not much (ABE applied to this single sub below, maybe some effects but maybe it's just ABE not correcting the vignette or background gradient properly?)

I'm using a Baader MPCC coma corrector, ASI EFW, chroma LRGB filters, RisingCam 571 with AR window. I also have a big lens hood over the front of the scope, but even bore I had that there were still issues with this sort of pinching effect in the center of the frame. I take my flats by smoothing out a white cloth over the aperture and kept it taught with a thick elastic band. Then exposed it to the sky opposite where the sun was at half peak (max ADU in my flat subs was 30k'ish out of 65k). (no lens hood at this stage since I found it made the vignetting much stronger and figured it would upset the correction)

Anyone else seen this effect?

Hello! I have been tuning my setup recently and got to thinking about why my mount would:

1: need to correct DEC error so frequentlyl if my polar alignment was as good as it should be

2: I get field rotation in my mosaics (at 2 deg by 1.5 deg image scale) when slewing in RA and after meridian flips.

I am beginning to think that one possible cause is that my polar scope is telling me one story, while the RA bearings are performing another. I am worried that my RA axis is actually gyrating as it turns and effectively moving the polar alignment as it tracks and slews. But I have no way to measure this for sure.

I have performed the belt mod and as such I have tuned the belt tensions and worm gear backlash, and to be honest while it's a big improvement the mount would lock up completely in some places but have backlash in others, which may also be a sign that things inside are not as true as they ought to be!

I think using Ekos/NINA's polar alignment system to get a good polar alignment on the east side, then resetting to home and running it again on the west side should give me a good clue? What do you guys think?

2 minutes ago, wimvb said:

You need to select the guidescope. If that scope is 200 mm fl, then your guide rms is abt 3 x larger than what is reported when you have selected the imaging scope (650 mm).

Woops!

I guess I know what was wrong now then haha. I presume the guider was sending signals to the mount that were either too big or too small?

13 minutes ago, Same old newbie alert said:

Sorry I assumed you to be using PhD, but looking at the screenshot was you on the simulator?

The pulse values haven't been filled, so I'd assume you was guiding with the simulator..

 

Oh no no, this is me jkust bringing it up on my desktop in simulator mode, my kit is down in the shed so I can't load up what it was showing last night or what the kit shows in use atm.

I found a partial screenshot of what I was doing last night but sadly not the whole screen.

15 minutes ago, Same old newbie alert said:

What was the guidestar snr reading? 

The guide assistant will help iron out the tracking errors a little bit, it switches the guiding off and tracks the star to see how it performs then it calculates the min mo, aggression etc, in the tools tab.. the camera loop depends on how well the mount performs

I found a screenshot of what I was seeing in the guide preview screen

Also, just in case it turns out that this is the issue...

When I select the scope here, am I supposed to pick the guide scope or the primary scope? I figured it was supposed to be the primary since that would give me the arcsecond rms reading I was after... If I was supposed to pick guide scope it might explain why it thought my RMS was lower than my images showed?

41 minutes ago, wimvb said:

Differential flexure? The main mirror in a Newtonian can move relative to the guide camera. That's why oag is usually recommended for reflectors.

Have you tried imaging and guiding near Zenith? At this position, the mirror rests evenly on its support.

Last night I think M51 was transiting the zenith during my imaging, and it had similar star shapes to the image i took closer to the horizon the night before of the north america nebula. I heard that OAG was good for FL over 1000 and thought my 650mm/130mm scope would be good for a guide scope.

2 hours ago, Same old newbie alert said:

Check your focus on the guidescope, as you might be guiding on noise...next time get it up and running with the camera on a loop.. then manually move the mount.. if the stars don't move they're not stars.. any reason youre using such low camera loop?

2 hours ago, Same old newbie alert said:

Also do a dark library and bad pixel map.. run the guide assistant for at least a worm period and apply the settings

Dark library might be a good idea! I presume I'd be creating a big master dark for the guider to apply? Would it matter in this instance if the outdoor temperature changes since it could be as low as 0 in the winter and 15 in summer? They are pretty short exposures I suppose. Not sure what the guide assistant is though.

I used the lower camera loop because it was providing better RMS, while still tracking stars. I believe it wasn't tracking noise since my mount has always drifted much more considerably during longer-than-minute exposures, and it stayed put during a 7 min exposure (albeit with the star being oblong and fuzzy, can't find the image now though...) It also performed the DEC and RA star cross calibration fine which makes me think it was definitely detecting real stars.

Does a longer exposure (1 or 2 or even 3 seconds?) tend to result in better in-practice guiding?

3 minutes ago, symmetal said:

How good is your polar alignment? If it's too far off your images will exhibit rotation around the guide star. If  your guidescope isn't aligned with the main scope, and the guide star isn't in the image all the stars will show elongation in the same direction.

Alan

I'm relatively confident that it's at least close, since polaris was bang on the line in the polar scope, and in the right place on that circle when I set it (accounting for the visual error one expects at least given as the clock turns with RA in the HEQ5....) I didn't measure it but based on times I've measured it following polar scope alignment it's only been between 1 and 3 minutes off total.

4 minutes ago, knobby said:

Have you entered the guidescope length correctly ?

I've just checked the config and the scope's fl and aperture are correct - 200mm fl and 50mm ap

Hi!

I finally got my guidecam (ASI 120mm mini) and performed the belt mod on my HEQ5 pro, and tuned my worm gear spacing. The last two nights I've gotten the chance to test it out and at first I was astounded: Once I had the guidecam at 0.5s exposures it was still picking up plenty of guide stars and my RMS was measuring at 0.2-0.3 arcseconds! But I was experiencing a different story on the main camera that showed very oblong stars and signs of wobbling on a 7 minute test exposure of the leo triplet. Even on 2 minute exposures of my NGC7000 mosaic (on my profile) the stars were still not round despite the guide chart showing error far below my pixel scale.

I suppose there are two reasons I can think of why this may be happening already, but I figure I'd ask here to see if any of the more experienced people around have their own ideas for what might be wrong.

Currently I think it could possibly be flexture, though I don't know how since the guidescope was as tight to the tube ring as I could make it. I have now however affixed it to a dovetail bar that is itself connected to BOTH tube rings, so maybe that will help. I have also made the guide scope align with the main scope's FOV, which in my mind might reduce the effects of turbulence in the guiding (star moves left in main scope, but moved right in guide scope as a result of turbulence??)

I'm also considering that maybe I need to tweak the guider settings? I am using Ekos at the moment and (almost) everything is on default (0.75 aggressiveness, min error 0.1 which I tweaked from 0.2, etc.)

Little sample of my stars after a 4 min sub, with guiding error peaks rating consistently below 0.5 seconds: They're almost sort of becoming square (left-right is ra and up-down is dec, or near enough) I'm imaging at 1.2 seconds per pixel.

Any help appreciated!

Just got around to making a mosaic with the Ekos planner and Pixinsight. This is a 2x2 mosaic with about 30 mins of luminance per panel. Stitched in Pix using platesolving and then co-ordinate based mosaic framing and mosaic blending. Then I colourised it in red using a layer mask in gimp so I could have red nebula and white stars.

Sadly I had an off-frame reflection in the lower two panels, but I don't know what from. I have a big lens hood over the front of my scope now so I don't know what exactly caused it, but i experienced something similar in another image I made of the horsehead, so I don't think its a terrestrial source, maybe a bright star somewhere?

I'm quite pleased with the result! Sadly it took me a long time to work out how mosaics should be done in pix, but every day is a learning day after all?

If only milky way season had longer nights for us up in the north! I would love to do core mosaics when its at its highest in the summer.

1 hour ago, PeterW said:

The following link may help provide some info as to where it might be worth looking and where not. https://www.climate-policy-watcher.org/climate-dynamics/the-atmospheric-absorption-spectrum.html Although water absorbs a lot au can clearly see the moon with my 10micron thermal scope (resolution is too poor to see details).

 

Peter

What kind of thermal system do you have? Very cool to get images in UK skies at that wavelength!

44 minutes ago, wimvb said:

Remember that NASA’s IR imaging telescope pre JWST was airborne, to exclude most of atmospheric influences. Silicon devices could, in principle, detect wavelengths longer than 1 um, but internal losses increase with increasing wavelength.

36 minutes ago, riklaunim said:

Depends how long wavelength you want. 1100-1600 nm is often done from standard ground observatories.

The VLT can capture up to 20µm, albeit in the middle of a desert and at great altitude haha.

38 minutes ago, Cosmic Geoff said:

A lot of CMOS astro cameras are sensitive to infrared. Check out the specs of the ZWO ASI224MC, for instance. I have used mine to image planets in near infrared, with an IR-pass filter.

All DSLR cameras have an IR-cut filter, which some astro users are keen to remove...

Even the 224 only has 10% QE at 1µ, which is 1/3 the sensitivity it has at 900. Following that trend, by the time it is trying to capture light at 1.1 (the first IR hydrogen line) it would have 0.03% QE!

No doubt more experienced imagers have thought about the poor quality of the typical blue subframe, and how the red subs always seem to have the highest contrast and lowest LP intrusion. And of course how the sky is blue in the daytime, and when objects in the far distance fade into the fog, they fade to blue.

I wondered recently: "Just how far into the IR does this effect hold true?" only to realise that if amataur IR cameras and filters were available, it could be a whole new world of possibility!

First off, not only would the sky be FAR more transparent, but the negative effects of seeing are actually reduced considerably! Just have a look at the comparisons avialble on this website with an unfortunately not astro friendly product: https://www.infinitioptics.com/technology/nir-near-infrared

And on top of that, hydrogen has THREE emission lines at 1.09~, 1.2~ and 1.8~ microns. Beyond what our full-spectrum CMOS cameras can see, but no doubt impressive and fascinating structures. And to make things better.... No light pollution outside of the visible light range either!

The closest I have found to amateur astronomy IR-capable cameras... Are professional IR-capable cameras... One of which is a 92x92mm sensor. Something tells me even if they would sell to us peasants, we wouldn't be able to afford any of them. https://www.teledyneimaging.com/en/aerospace-and-defense/products/sensors-overview/infrared-hgcdte-mct/

Of course we would suffer a penalty to our diffraction-limited seeing, as 2µ would be about 1/3 the optical resolution of 700nm. But for the new things and possibilities I think it would be a worthy sacrifice for those interested in what lay mere nanometers and microns beyond our reach!

What do you guys think? I feel we're missing out here.

Hi

I've read a good starting point is to match time on L with time on RGB, which I presume means 3L + 1R +1G + 1B. I gather that the primary benefit of using luminance is that dark stuff can be brought into view, but in monochrome, while brighter stuff can still have nice colour data. Does this mean that if I am targeting a very deep image (IFN levels deep) I can capture a certain amount of LRGB with the 3:1:1:1 ratio, then stop collecting colour once I can get colour in the darkest parts of the bright objects I'm imaging? I also hear people talk about blue being a noisy band in astro and my initial experiments seem to support that, would it be worth intentionally capturing more B than G and R frames to bring out blues more easily?

Wondering what other people do here. Maybe even advanced techniques like blending RGB highlights into the L highlights to reclaim detail in bright parts of the image or something?

7 hours ago, Zummerzet_Leveller said:

Unfortunately this hasn't resolved my issue.  A bit of internet hunting (cloudy nights) and I've found similar issues related to reflections in the imaging train.  Potentially related to the reducer, so took the reducer apart and DIY flocked the internals.  I'll take some more flats and see if it improves things.

Also be aware that DSS will use the already calibrated master files once they've been made, so if you re-stack flats or bias or dark frames it may not actually recreate the master file it uses to stack, but just use the one it made previously.

Try deleting your old master files and re-stacking with all settings set to average (no median)

Flat_001.fitsFlat_003.fitsFlat_002.fitsM_81_Light_001.fitsM_81_Light_003.fitsM_81_Light_002.fits

Here's some samples, when I added my darks that matched my lights it didn't change anything so I dunno if it's worth including them.

Bias_002 - Copy.fits Bias_003 - Copy.fits Bias_001 - Copy.fits

13 minutes ago, ONIKKINEN said:

What does a single flat frame and the flat master look like?

Did you use all calibration frames? You have over correction, which to me looks like you might have skipped darks or bias, or both. Depending on the camera and flats exposure time you may need to use darkflats to calibrate the flats too. If you used one of the newer low thermal noise cameras then bias works just fine for that (i do this, no issues).

This image does look like the skyflats had some gradient to them with one corner much better than the other, but the over correction is what bothers me most.

I'm using bias brames, and these ones match the settings of the lights (same iso, same exposure etc)

I use them as darkflats and bias but I get the same result sadly. Other flat frames overcorrect all over the place. perhaps I have an issue with my baader MPCC causing a reflection, from my sensor to the MPCC and then back towards my camera? And now that I have changed my system, the new flats don't suffer it so badly?

This is what a single stretched flat looks like for the image at the start of the post, pretty normal I'd say.

I've been strugling for a while to get my flats to work as expected, and while this seems to be properly correcting my vignetting and dust bunnies, with the major gradient probably being my light pollution (tho it's an odd shape....) I have this ugly dark donut in the middle.

I have been taking daylight flats, with the scope pointing opposite to the sun in the sky and a thick white cloth over the opening of my 130-PDS, rubber band holding it taught with no wrinkles. Focus hasn't moved since I literally went out the morning after capture finished, and put the cloth staight on and took snaps. I target a peak of about half of full on my sernsor (around 30-34k out of 65k).

These flats were taken as the sun was setting, so maybe the gradual decrease in sky brightness is affecting them? Is it because of the secondary mirror blocking light too close to the front aperture? Some quirk of newotnians in general? given as this correction is much better than with no flats at all, can programs like PixInsight remove the complex gradient without destroying potential IFN and other faint detail currently invisible due to the gradients in my image?

This was merely a small sample stack of my nearly 6 hours of lum data, and I genuinely believe I caufght a fair bit of IFN in it but with these gradients it's impossible to draw out! : (

I had this recently! Vlaiv helped me work out that it was caused by using Median-kappa-sigma averaging in my lights. I suggest what he suggested- use "average" for all your files, light, dark, bias, flat etc. Then try other methods. I find normal Kappa-sigma (as opposed to median kappa sigma) works quite nicely.