The "No EQ" DSO Challenge!

[Stub Mandrel]

5 hours ago, The Admiral said:

We shouldn't be comparing f-numbers, but focal lengths and apertures. Perhaps that is what is meant by the 'myth'?

Exactly.

A La Palma M82 would cover nearly 100 times as many pixels... 1 arcsecond of sky to 19 pixels of my Canon 450D in fact!

My 80mm by 1.2 m Mak is pretty much optimal for the 450D at about 1 arc second per pixel.

Bin La Palma 19x19 and it will image a faint target a LOT faster at the same scale....

Interestingly the La Palma Liverpool scope uses a CCD with 15 x 15 um pixels - roughly nine times the size of those on the 450D and giving a scale of 0.45 arc seconds per pixel.

To properly compare my 130P-DS with it, it's important to realise the La Palma scope is giving twice the image scale so double the detail, but as the f-ratio is pretty much the same it is catching more than four times as much light per pixel. Bin La Palma 2 x 2 and it will give more or less the same image in 1/19 of the time. That's even without allowing for the La Palma scope being mono with filters and slightly higher QE.

 

[The Admiral]

4 hours ago, Filroden said:

As signal noise is proportional to signal

Ken, I've had a thunk . The noise associated with the number of signal (target and sky background) photons collected by a pixel will go as the square root of that number. If the number is increased, by whatever means, be it by using a reducer or by increasing exposure time, the associated noise will rise slower than the signal. In other words, the SNR from that source must surely improve with increasing signal, irrespective of any improvement due to dominating the sensor noise. If that wasn't the case, then surely there would be no merit in taking long duration subs, or taking many subs and stacking them? Am I talking sense? What a minefield!

Ian

[Filroden]

4 minutes ago, The Admiral said:

Am I talking sense? What a minefield!

Good point. I knew my logic had to be flawed. Back to head scratching!

[The Admiral]

1 hour ago, Stub Mandrel said:

Bin La Palma 2 x 2 and it will give more or less the same image in 1/19 of the time.

Now that's the sort of gear we want for Alt-Az imaging

Hmm, on second thoughts, a 20m focal length wouldn't work well with my Nexstar SE mount

Ian

Edited April 12, 2018 by The Admiral

[Manners2020]

Wish I'd kept my questions to myself now.

[Manners2020]

I was lost ages ago.

[alacant]

7 minutes ago, Manners2020 said:

Wish I'd kept my questions to myself now.

There's only one way out; we'll have to go back to taking photos of stars rather than talking about taking photos of stars. Much easier!

 

[The Admiral]

56 minutes ago, Manners2020 said:

Wish I'd kept my questions to myself now.

Oh I do hope you don't really feel that, we wouldn't want you to feel unable to ask questions. This sort of thing happens, and if anything just reveals our own uncertainty . Please, keep asking!

The best approach is always to give something a try, beats any theoretical discussion. In fact, we wouldn't be doing Alt-Az imaging if we had religeously followed what experts say 

Ian

[Manners2020]

No just kidding. I've taken enough bits from it to decide to try one anyway.  What's the worst that can happen.

[The Admiral]

9 hours ago, Manners2020 said:

No just kidding. I've taken enough bits from it to decide to try one anyway.  What's the worst that can happen.

Pleased to hear it and that you've decided to go for one, I'm sure you won't regret it. I bought mine not for any theoretical gains but purely because I wanted to be able to better image some of the larger DSOs. There's the added advantage of also flattening the field so I get stars reasonably sharp across the whole FoV. Without it, I'd have felt the need for a field flattener anyway. I've always used it for deep sky imaging, even for smaller objects.

Ian

[The Admiral]

11 hours ago, alacant said:

There's only one way out; we'll have to go back to taking photos of stars rather than talking about taking photos of stars. Much easier!

You might not say that if you were in the UK living with the incessant poor weather

Ian

[SteveNickolls]

21 hours ago, The Admiral said:

The best approach is always to give something a try, beats any theoretical discussion. In fact, we wouldn't be doing Alt-Az imaging if we had religeously followed what experts say 

I know you haven't set me up on this Ian but as regards understanding and carrying out Alt-Az imaging folks might well like to get a copy of Joseph Ashley's book, "Astro-photography on the Go-Using Short Exposures with Light Mounts" and available from our sponsors at -https://www.firstlightoptics.com/books/astrophotography-on-the-go-book.html

It does concern me that the popular, evergreen, "Making Every Photon Count", (specifically on page 44) states in my view quite wrongly - "With the mount, it can be seen that one type, the Alt-Az, can immediately be disqualified as being unsuitable for deep sky work..." For many people an Alt-Az mount is the ideal way to test one's toe in the very deep and expensive water that can become astro-imaging. An Alt-Az mount can be the real difference between someone wishing to try out imaging and sitting at home reading articles about it while saving up or waiting for a suitable second hand EQ mount etc., etc. to come along. I have to smile knowing that Joseph Ashley can compose his well thumbed 320 page book based mostly on the genre within the crack so quickly stepped over by the other book and which actually is testament to Joe's insight. This, 'No EQ Challenge' thread shows what can be done with such mounts and how much important learning goes off within its fertile posts. Above all have fun doing hands on astro-photography and be prepared to learn all the time (usual caveat-weather permitting).

Cheers,
Steve

 

 

Edited April 13, 2018 by SteveNickolls
Black text anomaly in some settings removed.

[The Admiral]

Well, I know we share the same sentiments Steve, and your interjection comes as no surprise . But alas I guess you are preaching to the converted in this thread.

Ian

Edited April 13, 2018 by The Admiral

[Stub Mandrel]

In its defence MEPC does dare to state that you can do AP with an EQ3.

[Manners2020]

Damn  good point about going against what the experts say ian.  If I'd have listened to all those in the beginning  I would have not even been discussing this.?

[happy-kat]

M101 Pinwheel and many friends.

Yey it was clear last night and not working today so could stay up a bit later.

Imaged from 10pm to 11pm,. a bit of time lost trying to align as the street lights make it so hard to see stars. I can choose and align the first star but the second star I just accept where the telescope slews to as I can't see the star. Red dot finder aligned live on first star using tablet screen to centre the star and then adjusted RDF to point to it.

Virtuoso Canon 1100d vintage Q200 200mm lens at f4 (wide open) ISO 800

21 x 30 seconds + 1 x 20 seconds 1 x 45 seconds (felt the stars were just a smidge too elongated so stuck with 30 seconds) just over 12 minutes of data (I know just not enough!)

Flats, dark flats and bias files from session in February.

DSS 4.1.0 beta

StarTools using deconvolution to squash the chromatic aberration on the blue channel (can't wait for my Evoguide) and a final histogram squash of the red channel (light pollution) and HLVG in PaintShopPro saved as png.

This is the platesolve, over 20 DSO in this small area in Virgo.

This is a resize of one raw showing the street light got into my 10inch flocked bazooka (all subs are like this).

[SteveNickolls]

3 hours ago, happy-kat said:

This is a resize of one raw showing the street light got into my 10inch flocked bazooka (all subs are like this).

You have my thoughts soldiering on through all the local light pollution you have to contend with happy-kat. I hope you have a few more clear nights now the weather has turned (tonight is now looking promising). The last time I was imaging was around 9 weeks ago-almost unbelievable.

Best Regards,
Steve

[happy-kat]

Thanks Steve.  Last time for me was the.15th February!

[happy-kat]

The Pinwheel shows very clearly on my monitor but looks barely visible on my tablet viewing this post again.

[SteveNickolls]

3 hours ago, happy-kat said:

The Pinwheel shows very clearly on my monitor but looks barely visible on my tablet viewing this post again.

I've often found a similar issue, it's likely down to your monitor brightness setting. Others find my images dark while I see them fine.

Regards,
Steve

[happy-kat]

I've fine tuned my monitor to show variation at both the white and black end. 

[Stub Mandrel]

4 hours ago, happy-kat said:

I've fine tuned my monitor to show variation at both the white and black end. 

I've spent ages tuning my monitor and setting everything to the same colour profile, so at least my own images are consistent between applications.

I still worry that my images look awful on other people's monitors...

If you and @SteveNickolls see the same image differently it could well be because you are using different colour profiles, even if both monitors are perfectly adjusted.

FWIW I can barely see a fuzzy dot at the middle of the pinwheel, but it leaps out if I do a stretch on the data.

Edited April 21, 2018 by Stub Mandrel

[happy-kat]

I've just stacked it again with last night's data giving just over 42 minutes up from just 12, I'll give it a more robust stretch to make it much more evident when viewed on other screens (hopefully).

[happy-kat]

This is now 81 lights as I was out last night, so the total time went from 12 minutes are to 42. Focus was ever so slightly different as last night it must have been spot on as I got red and blue CA. I am going to whittle a few more subs out maybe as stars are not quite as round as I like.

I will be processing again wit a few more subs ditched and to see whether it is decon that is loosing my red/warm stars. Getting rid of CA and LP is a challenge.

Edit: reprocessed image added. I have managed to keep the star colours in this process (use of masks) and the pinwheel centre has much more detail. I am confused why adding so more lights has made the background so much more noisy! Hopefully you can see M101 this time. Will try again tomorrow but with no bias files and one with a bias master as a dark master.

Edited April 21, 2018 by happy-kat
replaced with a further process

[Stub Mandrel]

1 hour ago, happy-kat said:

Hopefully you can see M101 this time

Yep, nice one