Rossco72

i use 2.8nm Antlia filters. 

Image processed in Pixinsight using Blur X and Noise X along the way. 

Friday night saw almost 3 hours of clear skies. The first 3 hour window this YEAR!!! for me.

Spent an hour getting new mount aligned and guidescope focussed and finally got 2 hours imaging.

So here it is, 2 hours with the 2600MM Pro across 2 channels.

Obviously more integration would be great, maybe even some SII but I was surprised how reasonable this turned out for first light and only 2 hours total!

Cheers for looking.

1 minute ago, saac said:

Ah so you are to blame for the weather, Feb has been poor so far across in Fife.  That AM5 makes for a good looking setup. Are you using the PoleMaster rather than the ASiAir for polar aligning.  My PoleMaster hasn't been used for some time, I quite like the way the ASiAir does the polar align even though I don't use it that much now. 

Jim

To be fair I use the ASIAIR polar alignment to check I'm close enough to guide. Once I get a pier installed I might take the time to spend on the pole master to get it locked in as close as I can.

Apologies for the rain and cloud folks, hopefully it will pass soon.

I have recently acquired a ZWO AM5 mount to replace my workhorse NEQ6 Pro which done a sterling job for many years (I might still use it in a second setup at some point!). 

I attached the ZWO pier to my EQ6 legs as although the carbon fibre tripod from ZWO is great, it is very light and we get some very windy days here. I also added my pole master to the RA axis on the AM5.

Rig now consists of:

William Optics 50mm guidescope with ZWO helical focuser and ZWO ASI220MM guide Cam

William Optics GT81 IV Scope

ZWO ASI2600MM camera, EFW and EAF with Antlia 2.8nm Filters for Narrowband and LRGB Pro Astronomy.

Protected under a Telegizmo 365 cover.

If only we now had some clear nights!!!!

Cuiv the Lazy Geek and Lukomatico are two of my favourites.

at 150dpi it should be ok at a reasonable distance but you will see pixelation close up. at 300dpi it should look pretty smooth. At 600dpi it would be like HD on a telly. Some photo printers will do more than 1200dpi

5 hours ago, michael8554 said:

Thanks. i have that, this was my starting point but i am way over 70mm now

Wouldn't you just take the resolution of your image in pixels and divide by the size you want out in inches and that's your number? The higher the better, although anything over 600 dpi will likely be lost on most printers.

Nice image, I like the colour balance and neutral background you have achieved.

@Stuart1971 I understand tilt may make it impossible to determine, but in your opinion do I still need to move the camera further back? The last set of images still appear to show stars radiating from centre.

Radio Silence on this since April, wonder if there is a problem with it?

Howdy wise and knowledgable imagers,

I have never been entirely happy with my stars, they aren't awful but they also aren't very good. I have a William Optics GT81-IV telescope with a William Optics Flat 6A mk3 reducer/flattener. These are supposed to be able to produce a 44mm flat imaging circle. I use a ZWO ASI533MM Pro camera which only has a 24mm or so diagonal and so I was hoping for pretty much excellent stars and flatness across the entire image.

 took a series of shots and used ASTAP and Pixinsight to try and assess the quality of the stars, the eccentricity and FWHM etc. but I could do with some help understanding where I am going.

Each shot is taken, assessed and then the adjustable field flattener rotated one turn of the very fine threads which is probably less than a mm. However I am now considerable further away than the recommended 62.1mm for the GT81 telescope. Am I going too far or do I need to keep going further?

Below are the series of FIT images followed by the ASTAP analysis images and then the Pixinsight analysis images. Each set is 1 turn of the reducer further away than the set before.

1_30.0s_Bin1_L_20230514-225148.fit

2_30.0s_Bin1_L_20230514-231103.fit

3_30.0s_Bin1_L_20230514-232039.fit

4_30.0s_Bin1_L_20230514-233632.fit

6_120.0s_Bin1_H_20230515-225159.fit

7_30.0s_Bin1_L_20230515-230931.fit

8_120.0s_Bin1_H_20230515-225817.fit

9_30.0s_Bin1_L_20230515-232831.fit

Anyway, apologies for the long post, but I would appreciate input from anyone with experience in setting the correct offset and whether I should continue to move further away to dial this in.

Cheers

5_30.0s_Bin1_H_20230515-224627.fit

Finally finished the 8 panels of Ha on this target. I have 3 OIII and 2 SII so long way to go yet and I will be doing RGB for the stars eventually.

This is a total of 44.75 hours just on the Ha....

Can't wait to add the other channels.

You could try colour masks and also when you do histogram changes, hold the bottom left down to keep the background from brightening.

I haven't done any real processing on this yet, just ran BlurX, stretched and NoiseX for sake of putting this up, will process fully once I have the other channels and panes completed. (If we ever get clear skies again!). This is around 24hours of capture just for these 4 panes and probably would benefit from even more...

As it has been a while since I posted, I thought I would show progress to date on my ongoing mosaic. This is the first 4 of 8 panels and only the Ha channel. This is the Soul Nebula, Westerhout 5, in Cassiopeia.

TIFF file

Soul_Ha_Pub.tif

PNG File

How does that apply to narrowband SHO filters?

1 hour ago, vlaiv said:

You have 3 hours of LRGB each.

Does not make sense to add up integration time of components - unless you just want to compare your previous attempts on same target or something else, and then you say, I have total of 12h of integration time.

You might just want to record total imaging time - in that case, it makes sense to note down that it took total of 12h of exposure to make that image.

That is what got me started on my thought process. So if I need say 84 hours to achieve a given SNR with my gear/skies etc. do I actually need 84 hours per channel? I just didn't know if there was some form of averaging going on when channels are combined that improves SNR

25 minutes ago, ollypenrice said:

I would call that 12 hours of exposure. I'm sure that's pretty much a universal convention.

Olly

I was just thinking about it and although it took 12 hours, with it being 3 hours per channel surely the SNR is based on 3 hours?

I stumbled across a SNR prediction tool that could estimate the exposure time needed to achieve a given SNR and for example I got say 84 hours was needed based on my 5 minute sub. Then I was thinking, is that actually 84 hours per channel, or does something clever happen to the individual noise when you combine channels?

I know I can get "decent" images without 84 hours, but I am curious to understand the maths of it.

Question for the brain trust:

If i take 3 hours each of LRGB and combine them, do i have 12 hour’s integration time or 3 in my image?

looking forward to finding out more about this!

15 hours ago, Fegato said:

Yes, but the speed of the scope (focal ratio essentially) has a big impact. My RASA 11 is F/2.2.  This has roughly a 5x exposure "advantage" over F/5 for example and 10x over F/7. Obviously camera, target, sky conditions, and filters all come into play as well. Certainly narrowband will generally need longer exposures - I'm usually around 60s -180s when using a dual narrowband filter, depending on conditions.

All true, I am at f4.7 so quick rather than fast lol. That RASA11 must suck in the light mind you...

There may be better tools if you connect a power pack, mini pc, NINA etc. but the sheer simplicity of ASIair and the fact it just works has totally transformed my imaging time.

Made even better by leaving the mount, scope, camera, ASIair etc. all out in my garden under a 365 Hood so i can be imaging in just a few minutes!

Love it.

5 hours ago, Fegato said:

It partly depends on your set up and how long your subs are, but you really want as many as you can use, as it's all about reducing SNR, and the more subs the better. I certainly wouldn't take the approach of only picking the "best" ones. I find I reject less and less. I use Pixinsight, and the pixel rejection algorithms allied to the improved weighting capabilities mean that it can pretty much sort it out for itself. I do like to blink through all the subs to see what I've got, and I will reject ones with very clear cloud impact or trailing stars, but I've largely stopped bothering about FWHM and eccentricity - I just let the software sort that out based on the weightings.

I have a RASA and it's a bit of an extreme instrument, so 30s is a max exposure for me in broadband. I'll normally be looking for at least 120 subs to stack, but can get good results with less that that. But I'll rarely count something as finished with less than 60 or so. As well as the need to get the best SNR, the pixel rejection algorithms just work better with lots of subs.

Interesting. Mainly i find I am doing Narrowband and either 5 minute or increasingly 10 minute exposures. Age old question I suppose, your 60 x 30s is only 3 of my 10m exposures in terms of photons, but I am not expert enough yet on understanding the impact on the noise. I only get 1 or 2 nights a month clear skies and I am loathe to spend one testing things out!

It appears to have a build in rotation device, I wonder if it might even be motorised??

The guide chip doesn't float my boat, but how cool would it be to be able to frame your target remotely without an expensive rotator in the imaging train.