Starwiz

10 hours ago, vlaiv said:

1.5" - 2" RMS - poor performance suitable only for short focal length wide field shots with resolution 3"/px or lower.

1"-1.5" RMS - suitable for resolution 2-3"/px - wide field work

1" - most of stock mounts can achieve this as good result (on a good night) - suitable for work 2"/px

0.7" - 1" - good guiding, suitable for work at 1.5"/px

0.5-0.7 - very good guiding, suitable for work at 1.2"-1.5"/px

<0.5 - top tier mounts, suitable for high resolution work at 1" - 1.2"/px

Otherwise, I would recommend to deal with DEC backlash. You have very high DEC rms and this is because mount is "loose" in DEC. That level of slack in DEC axis can be felt by hand. If you reduced that with mount tuning, and bring DEC RMS to be equal to that of RA - about 0.55 - total RMS will then be ~0.78 and that is good guiding, on a better side of stock EQ6.

Thanks Vlalv, that gives me something to measure it against.

John

Can anyone tell me how I can qualify the performance of my guiding?

I presume it would be based on the focal length of the telescope, etc.?

I have downloaded the log file viewer, but don't know how to interpret the results.  How good is it and how good does it need to be for the imaging I'm doing?

Thanks

John

4 minutes ago, Davey-T said:

Usually mount the OAG in front of the wheel otherwise filters would reduce the light, especially narrow band ones.

Dave

OK, thanks.  That makes sense.

John

32 minutes ago, alacant said:

Unlike a short focus guide telescope, the oag camera focus must be exact

That's probably the point I'm missing.  I need to get both the main camera and the OAG in focus.  I'm using the standard focuser that comes with the SW200p, but I'm now wondering about the extra distance caused by the filter wheel, so would I need to mount the OAG between the wheel and camera?

Thanks

John

1 hour ago, ollypenrice said:

A reflector is, in principle, best guided with an OAG. Are you sure you have the backfocus? And, if using a coma corrector, can you maintain the right chip distance from it?

Olly

I'm not using a coma corrector at the moment.

I'm currently using a 21mm spacer with the 1600mm-pro, which leaves me with spare 15mm outward travel and 21mm inward travel on the focuser (as per the diagram below).

The OAG is 16.5mm thick, so would replace the 21mm spacer, leaving me with spare outward travel of 10.5mm once focused, unless I'm completely missing something (which hasn't been unknown in the past). 😀

Thanks

John

2 minutes ago, discardedastro said:

You may need a more sensitive camera for OAG - the 120MC is OK with a guidescope, but might be hit-and-miss on an OAG. https://www.talkunafraid.co.uk/2019/04/adventures-in-differential-flexure/ I ended up replacing my guidescope rings with some solid machined blocks of aluminium and that eliminated my flexure problems almost entirely as a cheaper fix.

Thanks.  An interesting article on the differential flexure, so I'll have a good read.

I scrolled down on the content of the link I originally posted and the example set-up shows a Zwo 120mc being used with the OAG, so I guess my question is, does anyone else use it with this OAG?  I'm also wondering if if makes a difference with what scope is being used (F-number) as the OAG is tapping in on the light from it?  I'm using an F5 SW200p.

John

8 minutes ago, Spaced Out said:

I have the ZWO OAG, it works fine for me. I have a fairly sensitive guide cam (lodestar X2) and I haven’t tried any other guide cams with it.

I use a Baader MPCC mkIII and I found it a bit of a faff getting CC spacing + OAG + filter wheel + camera all lined up and working well. The problem I had was CC spacing. At the correct spacing (I think I added about 1.6mm) the prism of the OAG was sitting over one corner of the imaging sensor, which I didn’t like very much ! To get it to line up nice and level with the flat side of the sensor I used 2 thinner spacers adding up to the total required spacing instead. I put one between OAG and camera and one the other side between the OAG and MPCC, then it lined up nicely. 

The only negative I can think of about this OAG is that the stalk with the prism on feels a little bit wobbly sometimes, not as sturdy as I imagined, doesn’t affect operation tho.

Thanks.

I'm using a Zwo ASI1600mm-pro plus filter wheel for imaging and a Zwo  ASI120mc for guiding, so I guess it should be compatible.

John

I suspect I'm getting a bit of flexure during parts of my imaging sessions.  There is slight star trailing despite the polar alignment and guiding data looking very good.

I'm thinking about getting an OAG.  Does anyone have any recommendations and is this one any good?  https://www.firstlightoptics.com/off-axis-guiders-oag/zwo-off-axis-guider-oag.html

Thanks

John

5 hours ago, ollypenrice said:

To step back for a moment, LRGB is faster than OSC because an OSC camera always has a colour filter in front of every pixel all of the time.

It's been almost a year now since I switched over to mono and don't regret it.  As Olly and others have said, the overall capture time is quicker with mono than it is with OSC.

I've found the processing time is longer with mono as you can have as many as 5 sets of data to process in the instance of HaLRGB, but it's something enjoy when the conditions aren't suitable for imaging.

John

Well done.  It just goes to show you can still get results with the full moon out.

John

2 hours ago, happy-kat said:

And I recall now picking the lowest score as the reference frame can help if stacking is reluctant to use all the frames.

This isn't working for me.  

I have a recent batch of Ha frames where it was only stacking 43 frames out of 118.  I've just tried using a lower scoring frame as the reference and now it says it's only going to stack one frame.

Perhaps the stars just aren't good enough.

John

Congrats on an excellent first image.

Fast forward another 4-5 years into the future and you will be waiting for another 10 hours of Ha data to finish off an image that you can't shoot at the moment because the moon is too bright.

It starts off small, but then the desire increases.  😀

Thanks for the replies.  Here's a frame that's not stacking.

Has anyone tried manually stacking frames?

I have about 120 Ha frames of M82.  The galaxy data looks good, but DSS is only stacking about 40 frames - it doesn't seem to be detecting enough stars even though I've tried different thresholds.

Thanks

John

On 10/01/2020 at 13:34, almcl said:

That looks like coma.  

Can be corrected with coma corrector (!)  I use this one on my SW200P  but one draw back: it can create reflections on very bright stars.

Many thanks.  I did wonder, but don't remember it looking this bad before.

John

Under a near full moon last night, I ran some trials in Ha on the Heart Nebula.

On looking at the images this morning, I'm seeing some strange star shapes towards the corners of each image.  Image shows the magnified stars.

SW200p, ASI1600mm-Pro, EFW filter wheel & Zwo Ha Filter 31mm.

Any thoughts as to the cause.  I collimated the scope beforehand.

Thanks

John

On 14/11/2019 at 17:11, adoldesa said:

When making my choice of camera I concluded that with the weather in the UK and the useful time I can spend outside a colour camera with a Tri-Band filter was a much better option for me, since I will be able to capture all the important bands of emission nebulae in one shot.

Using a mono camera doesn't really take any more imaging time than a one-shot colour camera.  With each filter of RGB, the exposure time is around a third of the time for the one-shot colour camera as all the pixels are in play for each filter.  The bayer matrix  filter in the colour camera means the pixels in use for each channel is reduced.  I remember Olly Penrice posting about this in the past with a more knowledgeable description than I can give.

I have found, however, that mono requires a lot more processing time afterward due processing each channel separately.

John

6 hours ago, DaveS said:

I freed up some space on my boot drive and downloaded the latest version. Looks to do the job.

Good stuff!

51 minutes ago, MarsG76 said:

Monitor display differences are a big factor when color balancing photos.. astro or otherwise....  

to preserve the detail, try desaturating the image and use the gray scale as a Luma channel.. the color can be used as a color channel, (even gaussian blurred slightly), and you can easily adjust the hue without losing any detail, which will be preserved by the luma gray channel.

Thanks.

1 hour ago, MarsG76 said:

Very nice image.. personally I'd try to decrease such a heavy green hue.... but great image nonetheless.

Thanks.  Yes, I was a bit undecided about that.  When I tried decreasing the green, I started to lose detail in the Ha component, so I left it as it was.

I also have two laptops and it looks different on each and different again on my phone.  One day I'll work out how to calibrate the displays.

John

2 hours ago, DaveS said:

Thanks John, looks like I'll need a PS equivalent.

Gimp has the Healing Tool which should do the job for you.

John

9 hours ago, DaveS said:

How do you manage to get Stratton to do anything meaningful? When I've been trying it I get horrible halos where stars were, and trying to get stars only in Stratton is even worse.

I'm processing each Ha, OIII, SII separately in Straton.   Then for the stars, I'll also process each channel of RGB separately.

I too, get unwanted artifacts especially where the brighter stars were.  I use the PS spot healing tool or brush to clean these up.

For 'stars only', I use the Straton tool 'Subtract main image from reference image'.  In this case, it doesn't matter if there are some unwanted artifacts left over, because I'm going to use levels to saturate the black point, ready for when I reintroduce the stars as a separate layer.  However, if there are any that get through this process, such as brighter parts of a nebula, then I'll just clean these up with the spot healing tool or brush.

John

7 minutes ago, carastro said:

Very nice image.

Can you share this technique with us? 

Carole 

Thanks Carole.  Technique as posted above.

I used Stratton to remove the stars from the nebula, so I could process them separately as RGB, then used Stratton again to create a stars only image which I then used the technique on.  The stars only image, I used levels to saturate the black point, so there was no background other than the stars.   I added this to the nebula as a stars layer, setting its mode to 'lighten'.

John

29 minutes ago, alacant said:

Hi. Lovely image.

I don't understand the colours, but I'm trying.

I think however your idea for star processing is great; we're no longer limited by being forced to use old algorithms. Software seems the way to go. I'd be delighted to see the end of our coma correctors. Forever!

Cheers

Thanks.

I used this technique for shaping the stars:  

43 minutes ago, tooth_dr said:

That’s pretty special John. Any more capture details?

Thanks.

SW200p on NEQ6.

ASI1600mm Pro cooled to -10C.

Orion Mini Guide Scope with ASI120mc.

Ha = 90s x 32 (Bin 1x1), 180s x 61 (Bin 1x1), 300s x 50 (Bin 1x1).

OIII = 90s x 32 (Bin2x2), 200s x 21 (Bin 2x2), 300s x 21 (Bin 1x1).

SII = 90s x 31 (Bin 2x2), 300s x 21 (Bin 1x1), 600s x 11 (Bin 1x1).

RGB = 20s x 20 (Bin 1x1) each filter.

Imaged over several nights.  I'm still experimenting with the exposure lengths, hence so many different times.

Stacked in DSS, processed in PS.  Darks, Flats and Dark Flats applied.

John