Pompey Monkey

I was idly getting lost in the YouTube rabbit hole last night when I came across this clip of Star Trek Voyager. https://youtu.be/FyyMPIuXrqw

In one scene, the view outside the window caught my eye:

"That's nice attention to detail", I thought.

Until I rmembered they were supposed to be stuck on the other side of the Galaxy, 70,000 light years away...

2 hours ago, tooth_dr said:

Acquisition is (relatively) easy, it's the processing.  I was going to ask about processing as they have posted a few 6-7 hours images on the website taken with the scope. But upon reading more, apparently the scope can process the data too.  What is there left for the user?

I'm not 100% convinced that those pictures were even taken with that device. All it says on the Vaonis site is 150 mm scope, integration time, and IMX 455 sensor...

I can't  think why not.

I've been thinking about re-purposing (or even multi-purposing) an e-bike battery for the same reason. 48 V 840 Wh should keep an HEQ5, TEC cameras, dew-heaters, and all the other bits going for a whole night.

At around £300, they are not the cheapest, but don't  half pack a punch!

There's  no harm in getting focus on a bright star and then slewing to your target.

However, you should ideally re-focus when on target in case anything in the optical train shifts slighty with the scope in a different attitude. Especially if you are using a reflector or catadioptric ota.

If you are polar aligned but your gotos are out out in elevation, this suggests that the star alignment is incorrect.

Are you definitely syncing to the correct stars when you do your alignment?

7 minutes ago, nephilim said:

Thanks for the reply 😊, luckily I'm Bottle 3-4 so that's not a problem. I also need to change my signature gear as that's well out of date. I've now got the Explore Scientific EXOS II PMC8, ZWO asi 533 with Samyang 135ED f2 & guiding with SW Evoguide 50ED & ZWO asi 120mm-s guide camera, all controlled withe the ASIair Pro, so I think I'll be fine with 10min subs. 

Regards 

Steve

I also forgot to say that the 3 nm Ha also blocks a lot more of the light pollution from the Moon, meaning that you can image for a larger part of the month, whatever Bortle skies you have!

The OIII and SII filters are not so good at blocking the moonlight.

I'd advise based on your light pollution conditions:

If you work from a good dark site, then the 6.5 nm versions will do you fine.

However, if you are suburban/city based, then the 3.5 nm will reduce the effects of light pollution a lot more, improving contrast and making your processing much easier.

I'm in a Bortle 7 (6 on an exceptional night) location, and when I changed to 3 nm from 7 nm nb filters, the difference was very apparent.

Having said all that, nb imaging does require long exposures (10 minutes+) and you need to be sure that your EQ5 mount can consistently do that, or you will be chucking out lots of subs...

Even if I do get stung for VAT, at least there is no import tariff

https://www.trade-tariff.service.gov.uk/commodities/8525801900#import

18 minutes ago, whipdry said:

Recently contacted RisingCam about imports into the UK, in reply they stated the price did not include VAT or any Import Duty payable... seems UK customers would also face currency conversion charges as payment is either in the Dollar or Euro!

If anyone on here living in the UK has recently had an actual experience of a purchase please post a reply... BTW they offer stating a lower price on the customs paperwork, not sure that's a good idea!

Peter

Hmmm, I was under the impression that Aliexpress was bound to include the VAT on sales to the UK by government agreement.

https://www.moneysavingexpert.com/shopping/buy-from-china-aliexpress/

My order has been placed. Looks like there is only one left for now:

This price includes UK VAT!

9 minutes ago, tooth_dr said:

We also have to remember that there is a significant price difference too - an entire set of Baader UNB 2" filters is cheaper than a single 2" Chroma Ha filter (£960 versus £1199).

I can see it says FWHM, but also HBW further down.  What does this mean?  A typo or 2 different specs?

Now I'm really confused!

Here: https://www.omegafilters.com/resources/glossary#:~:text=The width of the band,and shorter than the passband. it says that HBW and FWHM are the same thing....

Maybe I should get me coat....

Interesting.

I've had my eye on a set of 36 mm unmounted filters from the UNB range but now I'm not so sure.

Baader states a HBWs of 3.5 nm (H-alpha) / 4 nm (O-III / S-II): https://www.baader-planetarium.co.uk/shop/baader-cmos-optimised-h-alpha-o-iii-s-ii-3-5nm-4nm-ultra-narrowband-filterset/ I can't find any more details than this.

On the other hand, Chroma specifies a FWHM  (with measurements) of 3 nm: https://www.chroma.com/products/parts/h-alpha-3nm-bandpass#tabs-0-main-2 and https://www.chroma.com/knowledge-resources/about-fluorescence/fluorescence-applications/glossary

This implies that the passband of the Chromas is only half that of the Baaders.

Having a job that requires a good appreciation of systems engineering, I'm always on the lookout for specification discrepancies like this.

Are we being mis-sold/misled, or is it that the marketeer for Baader just doesn't understand the difference between FWHM and HBW?

Does anyone know the truth?

Post deleted

This may not be the answer you were looking for, but for the price of a new EQ3 Pro, you could pick up a second-hand HEQ5 with Go-to.

This has twice the capacity of the EQ3 and will give you much more future-proofing.

Edit - Second-hand prices are stupid at the moment due to shortages of new kit.

That is amazing.

The PN is approximately the same angular diameter as Jupiter!!!

Edit to post the Astrometry result:

https://nova.astrometry.net/user_images/4450663#original

I tried to use AutoPEC with my AZEQ6GT a few years back.

It failed miserably, basically because there is no worm position information coming from the mount.

The encoders only "tell" ASCOM where the telescope is pointing, not what's happening to the worm.

You are on a hiding to nothing and, as other have said, the guiding is OK without the AutoPEC.

16 hours ago, Allinthehead said:

 

Thanks, I think the mono version will be on another level but 7k? What filters are you thinking? Who needs double glazing, you can just cuddle up to the Tak for warmth.

Whoops! I got the camera mixed up. I was thinking of an ASI6200, and a set of 2" Chroma filters...

On the other hand, I already have a set of 36mm Chroma nb filters.... hmmm

It's a stunning image. I cannot say more than that about it!

Now I just need to find £7k+ to buy the mono version of the camera and the required 2" filter to stick on the Tak that's sitting in the bedroom that's waiting for the Covid to be under control...

I have no idea which will happen first (unless I put off the double glazing for another year) 🤣🤣

1 hour ago, Phillyo said:

Hmmm not really. A shade just directs the light in the 'wanted' direction rather than up or outwards thereby wasting light/energy for no reason. Also adds to sky glow and light pollution. I don't think taking them all down is really the same as putting a shade on them do you?

This is exactly what they do in La Palma, and the effect is a bit surreal:

All the streetlights are shaded to direct the light down (by law), so if you are near, or in a village, it is quite possible to get dazzled when in line of sight to one. However, turn a corner into the shade and it's dark enough for you not to see where you are. The sky is absolutely incredible, so directing the light downwards actually really improves things.

This looks like an excellent start.  With all that thought and planning, it's bound to go wrong somewhere! (joke)

The only thing I can see that may cause you issues is the mounting of the guide-scope and computer to the stand-off plate. This could cause you an issue with differential flexure between the guide and main OTAs, especially as you are imaging at a little over 1" per pixel. On the other hand, it  might work just fine. If you do have this problem, maybe beef up that aluminium plate a bit. Double the thickness feels about right to me.

Basically though, you look good to go

What camera are you using?

60 (or 45) 60 second subs won't get you a lot of nebulosity at all with a DSLR.

If you have poor data to start with, then you are already facing an uphill battle.

That thing is really, really, faint. 

Good work.

18 hours ago, Mcwaffles2003 said:

Specs as I understand them:

Full well depth: The amount of electrons each pixel can store before becoming saturated. Higher numbers lead to greater levels of dynamic range

ADC: The degree of accuracy to which the fullness of a well is read. Higher numbers lead to greater dynamic range capping out when capable of reading per electron

Quantum efficiency: The chance when a photon hits the sensor that it will be read. Higher numbers lead to more brightness in the image and that brightness has hyperbolic scaling (a 60% sensor exposed for 8 minutes is equivalent to an 80% sensor exposed for 6 minutes or a 40% sensor exposed for 12)

Sensor size: Literal size of the sensor. Larger sensor gives a greater field of view limited by the image circle formed by the telescope.

Pixel size: Literal size of a pixel. Large pixels will gather light more quickly according to their area while smaller pixels will increase angular resolution up to dawes limit (if seeing allows)

Read noise: The average amount of noise, in extra electrons, per pixel per second. Higher noise leads to reduced contrast.

 

Please correct any inaccuracies in my understanding, or point out any nuances that I have missed.

 

Spot-on, apart from the Read-noise. This is a constant for all exposures relating to the electronic process of converting the charges on the sensor into an output signal. This is also known as Bias.

The noise component measured in electrons per pixel, per second, is the accumulated charge on the sensor (hence "per second") for each exposure. his is known as Dark current. Dark current is a lot lower in the newer CMOS cameras compared to CCD. There are other differences, but That is for someone more knowledgeable than me to answer!  

What @ollypenrice said: dithering will really help you with the noise.