parallaxerr

10 minutes ago, Stub Mandrel said:

Try Noel Carbineris's actions his remove large/small blue violet haloes works really well on that. I've run both on it, but nothing else:

Thanks Neil, looks good.

Guys, whad'ya think. I should be using the ZS66 not the ST120 right? If I've got a doublet apo on hand why not use it. The ST120 probably grabs more photons in one go but surely not having CA in the first place is preferable.

Am I going to lose out with the smaller scope? The pixel resolution comes in at 2.04" with my camera so I'm unlikely to see any square stars but is 66mm "enough"?

8 minutes ago, The Admiral said:

Pity you've only got half of the 'running man'. If you did image it again it'd be worth seeing what a vertical format will do. Then again, if you use the '66 it'll have a wider FOV.

Yes, the running man fell foul to field rotation unfortunately, so had to be cropped out. The ZS66 should capture it and now I'm starting to get some idea of what I'm doing I may experiment with rotating the camera!

3 minutes ago, The Admiral said:

I'm getting lost amongst all these filters! Which one's the fringe killer, and how does it differ from the semi-apo?

This explains the Baader series best Ian...

http://www.baader-planetarium.uk.com/en/pdf/baader_contrast_filters_US_ATT_review_0414.pdf

Reprocessed with flats & dark flats which have got rid of the amp glow or gradient or whatever it was and left the colours a little more "natural". I stretched this image further and applied less noise reduction but the background has still come out pretty dark just using as simple ST workflow. The final conversion to TIFF then JPEG appears to adjust contrast slightly too.

I really don't like the CA. I tried the fringe killer filter but didn't get on with it. My next attempt (hopefully tomorrow night) will be with the ZS66 AND the semi-apo filter to cut back moon & sky-glow. I'll see how the histograms look through the different setup but hope to try ISO800.

50 minutes ago, The Admiral said:

I use my Nexstar with only about a foot of leg extension. I can't prove any benefit but it strikes me that it ought to be a little more rigid.

Ian

I was using less leg extension with the ZS66 but wanted the ST120 a bit higher, there's still a good bit to go, I never go full extension. Doesn't seem to have made any difference though to be honest, the most vibration prone part of the whole SE setup is the single fork arm.

6 hours ago, Nigel G said:

I hope you don't mind.

Not at all Nige, you've highlighted the gradient I was masking with contrast which obviously took away some fine detail. Just reprocessing with flats & dark flats, gradients gone...

1 hour ago, The Admiral said:

But of course what is important here is whether the stars are clipped at the top end, and I find it well night impossible to tell from my own histogram display whether that's occurring because they are such small peaks (though switching on blinkies might help)

Same here but I don't have the blinky option. I have a feeling I was nowhere near saturating the sensor at ISO400 which is why I didn't capture some of the higher end of the range, i.e. fainter stars.

1 hour ago, The Admiral said:

you'll probably think that the background is too noisy, but go with it because by the time you've performed all the other actions you'll find it'll quieten down considerably

I think this is where I made a mistake. I set the ISO low to quieten the background but lost detail, at ISO800 I should capture more data and be able to get nice backgrounds through ST.

1 hour ago, The Admiral said:

I think these mobile devices tend to make images look more vivid as it's perceived that's what the general public want/expect

Agreed, although my monitor at home is a 32" LCD TV so I think it needs tweaking. The image looks best here on my work PC, more natural, but looks saturated on my tablet/phone.

18 minutes ago, Filroden said:

I personally prefer to see a non-black background as there will be very feint detail which will be lost if you clip the shadows. It does mean leaving noise visible but that can be reduced. 

I think you're right. There was very little noise in the subs to start with and Startools has tried to reduce it further, so this is a litle too dark. Looks like I'll be trying ISO800 next tiime despite all the theory and specification of my sensor suggesting it's not a good ISO to use, it goes to show that the final image is what counts!

OK, I wasn't going to post this just yet but I have a question - in comparison to other M42's I've seen, there seems to be quite a lot less stars in mine. Probably a result of setting ISO to 400, but I really do like the dark background. What do you think? Stars vs noise?

Note: this is far from fully processed. I threw this together at 2am so there's no flats or dark flats, just 101x30s light frames and x50 darks. The image has 4 noise hot spots towards the corners which I think is amp glow, I tamed it by over adjusting contrast and colour. Also it appears my computer monitor colour needs calibrating as this image looks far less vivid on the PC than on my other devices!

Also to note, this was taken with the Baader semi-apo filter. It made processing infinitely easier without the sky glow - subs were captured between 20°-30° Alt! After Autodev in ST, the image was washed out a lime green colour instead of red/brown but the wipe tool handled it much better, less noise probably helped. A little disappointed with the CA still.

11 minutes ago, jimbo747 said:

Hibernation works! Why didn't I know about this before!?! For some reason I just assumed only fancy pants EQ mounts had it!

Yup, I put mine straight into hibernate when the clouds came in. Woke it up again 2hrs later no problem

Got over 100 subs on M42, darks in progress now, then it's bed time. Good job I have a half day in work tomorrow!

Well what a horrid night so far...Cloud, lots of cloud. Technical issues, more cloud and target (M33) now above max alt. D'oh. HOWEVER, I think I have carried out some valuable testing. Thanks to @Filroden's post re: ISO settings, I have experimented with mine...

I took 30s subs on Capella (the only star that seem to be dodging the cloud) at ISO's from 100 up to 6400 and Hi1 (12800) and checked the histogram peaks. Only ISO100 showed clipping on the left side but from 200 up, there was no clipping. The lower the ISO, the darker and smoother the background sky with grain starting to show at ISO 800. As it happens, with my sensor, there is a dip in read noise level at ISO400, sooooooo ISO400 is where I'm currently at. At this level I also have 50% more dynamic range available and a higher saturation capacity, although I'm probably not reaching it with 30s subs.

I think at ISO1600, despite marginally lower read noise, the reduction in dynamic range raised the noise floor and it was all getting amplified by the ADC. Scope is now on M42 clicking away, surprising amount of detail in the subs and a very nice dark background sky. Watch this space......

...Well I would if it wasn't for the 100% cloud cover that just rolled in

OK sounds like 3200 is OTT.

Now, the reason I have dismissed 800 is because the read noise for my camera is higher at 800 than at 1600 (not by much). I thought the noise I was getting in my images was read noise but my darks are absolutely jet black so maybe the noise was something else?  

I'll try a few 30s subs to see how the histogram shapes up.

Here's a comparison. These were 10 second exposures but I'll be using 30s later, will that affect things, ie: will the histogram shift with a longer exposure?

Hi guys,

I have a quick question hopefully one of you may be able to help with before I start imaging tonight...

I have just set the ST120 up ready to go. Focused with the new Bahtinov mask (turns out the focus was a good way off last time) and also fitted the new Baader Semi-Apo filter. I took a few test shots after alignment and I'm pleased to say that the sky-glow/LP is practically non-existent with the filter and CA, whilst still there, is significantly reduced

Based on my findings about sensor noise today, I took a few test shots at ISO 1600 and 3200 (supposedly 3200 has marginally lower read noise for my camera). At ISO 1600 the background sky is a nice deep blue but I noted the histogram spike is at about 1/4 from the left. At ISO 3200, the background sky is quite light grey/white but the histogram spike is nearly bang in the middle of the graph.

So the question is - which ISO setting? Does the histogram position tell a story and am I going to have problems processing with a lighter background sky if I set 3200?

TIA, Jon

What camera are you using Nige? It'd be interesting to see if your results correspond to the noise charts on sensor gen.info.

EDIT: Scratch that, just turned signatures back on saw your camera listed! Looks like 1600 is the sweet spot for the 1200D and lower than 800 is a no go.

This little bit of research may explain why I struggled with noise so much in my attempt at M33. My Nikon D3200 & ST120 combo gives a resolution of 1.32"/pixel vs 2.04"/pixel with the ZS66. Perhaps I should go back to the little apo but the bahtinov mask and Baader semi-apo filter for the ST120 just landed on my desk...decisions, decisions.

On the subject of noise, have any of you guys actively experimented with and defined meaningful results from trying different ISO settings? I read this article http://dslr-astrophotography.com/iso-dslr-astrophotography/ and went on to get my sensor noise info at http://sensorgen.info which suggests I may be better off at 3200 with my camera as the noise gets less at higher ISO! The only problem then is that the saturation capacity is reduced, but given the 30s exposures maybe it will work out OK?

Thanks for sending me on a half hour googling mission trying to understand pixel resolution Ian!!! A lot of information to absorb there and it seems the topic draws very different points of view. 

From what I can see, the fact that your sampling rates, with and without the reducer, are well bellow 2" which is probably the very best seeing we can expect, the only other factors to consider are target framing and SNR - the more oversampled the image is, the higher the SNR. I'd go with the reducer, but hey, I may be completetly wrong!

At least, that's what I can extract from this article...https://starizona.com/acb/ccd/advtheorynyq.aspx

Thanks for the encouraging words Fil. The green seems to be a problem for me, in both scopes. When I use the colour tool in ST the image has a heavy green tint to it, same with my M31 attemp. I cap green to yellow and reduce green further with the sliders but then then struggle to balance red an blue.

I just reprocess the same data in an attempt to remove more noise and address the ca, but I think the image is too soft now.

I also didn't drizzle in DSS and only binned 50% which I think has proven to remove the noise a bit better.

Just now, happy-kat said:

That's come out well.

Startools has great CA removal capability.

Thanks Kat, I have readt that ST is good at removing CA but I don't know how. Will have to read up on it!

Here's the result of Monday nights session with the ST120. M33, about 1hr of 30s subs, x50 darks, x50 flats and x50 dark flats.

The light frames suffered heavy LP so I'm not suprised there's still significant gradient in the image. I'm still learning startools so maybe more could be removed? Due to the noisy light frames I used x2 drizzle in DSS, which left me with a 12068x8024 image @ 1.08GB  I then binned to 25% in startools which did seem to smooth things out a bit.

The CA is there, as expected, but I don't find it overly offensive. Hopefully the semi-apo filter will help address it and the skyglow when it arrives.

Most of my attempts so far have been with about an hours worth of data, early in the evening. It's becoming clear I really need to capture more data, later at night, when the lights have gone off, target altitude allowing. Oh for a clear night on a weekend...and a new moon..and a target between 30° - 60°!!!!

1 hour ago, Nigel G said:

A comparison of  30s ISO 1600. With and without . .Different targets but same light pollution. 

 

 

Impressive NIge, thats's the result I'm after. Let's hope the Baader comes up with the goods with a bit of fringe killing added in.

That's one worth remembering alacant, thanks. If I can remove some of the orange/brown to start with, I'll be happy!

Oh well, impatience strikes again and I've ordered the 2" semi-apo. Below is an image showing the performance of the Baader neodymium on which the semi-apo is based, plus, based on my own experience with the 1.25" version, I should see less CA through the ST.