MichaelBibby

I live under bortle 2-3 skies and I am often surprised by how well DSO images turn out with a bright moon. I would recommend doing your own comparison on the same target, one taken during the new moon and the other during the near full moon so you have a much better idea how much of a compromise it is for you under your skies with your equipment and using your methods of post processing. 

28 minutes ago, ollypenrice said:

Where is the artificial intelligence in all this? It is just a regurgitation of numbers already out in the public domain, with one vitally important number replaced by the adjectives 'average' and 'good.' Since these are the numbers which define everything that the system will produce, what are they and where are they?

I would rate this answer average to poor.

lly

I asked it:

Me: "give me the scientific definition of 'average' and 'good' seeing conditions."

Bard:

While playing with Microscofts generative 'A.I.' model called 'Bard' I thought I would test it with this question and see what it came up with:

Me: "if I were to compare images taken through each of those telescopes using a camera with a pixel size of 2.9um, and was guiding at a total error of 0.5 arc seconds, would I notice the difference in resolution under 'average' to 'good' seeing conditions?"

Bard: "Yes, you would likely notice the difference in resolution between images taken through a 150mm Newtonian telescope and a 200mm Newtonian telescope, using a camera with a pixel size of 2.9um and guiding at a total error of 0.5 arc seconds, under average to good seeing conditions.

The 150mm telescope has a theoretical resolution of 0.8 arcseconds, while the 200mm telescope has a theoretical resolution of 0.6 arcseconds. This means that the 200mm telescope can resolve finer details.

The pixel size of the camera is 2.9um, which corresponds to a sampling rate of 0.12 arcseconds per pixel. This means that the camera is capable of sampling the images from both telescopes at a high enough rate to capture the difference in resolution.

The guiding error of 0.5 arc seconds is relatively small, so it will not significantly degrade the resolution of the images.

Under average to good seeing conditions, the atmosphere will typically introduce a blurring of about 1 arcsecond. This means that the effective resolution of both telescopes will be limited to about 1 arcsecond. However, the 200mm telescope will still be able to resolve finer details than the 150mm telescope, even under average to good seeing conditions.

In conclusion, you would likely notice the difference in resolution between images taken through a 150mm Newtonian telescope and a 200mm Newtonian telescope, using a camera with a pixel size of 2.9um and guiding at a total error of 0.5 arc seconds, under average to good seeing conditions.

Here is a table that summarizes the expected resolution of the two telescopes under different seeing conditions (Please note that these are just estimates. The actual resolution of the images will depend on a number of factors, including the quality of the optics, the observing conditions, and the processing of the images.):

On 10/02/2022 at 02:16, Varavall said:

Hi

I'm a bit late to the party, but I have a the very same rig. As you can see in the photo it can be loaded with all the kit you may wish for. I have done the collimation,  Rowan Belt mod and adjusted the backlash out of the drives, and I made a pillar mount out of scrap aluminium to minimise risk of collisions with tripod legs. For guiding I started by using the 9x50 finder scope with QHY5L II C, but I have now bolted a TS optics 80mm finder/guider scope to the top which gives better pixel ratio for guiding. I can do 10 minute guided subs without problems. Of course the tube is a sail when the wind blows and it can rock a bit. All in all I am very happy with it's performance. I have only been into mono imaging for 6 months so there is still a lot to learn about the rig, but I attach a photo I took recently in LRGB SHO.  It's a scope that provides enjoyment without breaking the bank, well at least until you start mono AP!

I would HIGHLY recommend rotating the scope so that the focuser, and guidescope, is facing DOWN, and I would remove the finderscope too. Doing that should really help improve the guiding performance. You want to get as much weight closer to the axis of the mount to reduce the 'moment arm'.

As I understand it, there is also the effect of improved 'contrast' with the wider aperture, which in and of itself can have the effect of making an image look 'sharper'?

6 minutes ago, johnturley said:

Based on the optimum focal ratio being 3x the pixel size, the optimal focal ratio would be around f9, so at 750mm focal length you will be UNDER rather than oversampled with both the 6in and 8in telescopes, more so with the 8in if they have the same focal length.

You haven't stated whether you are talking about planetary or deep sky imaging, for deep sky imaging what is more important is being able to fit the desired object in the available field of view. For planetary imaging the theoretical optimum with both scopes would be achieved with about a 2x Barlow, but with a native focal length of just 750mm, you might find the resultant images a bit on the small size, and find a 3-4x Barlow gives more pleasing results.

 I think some people get too hung up about what should be the optimal focal ratio, and it might be worth doing a bit of experimenting to see what gives the best results. Some planetary imagers get excellent results with focal ratios as long as f20 or even f25.

John  

Sorry John, deep sky objects, not planetary.

Thanks everyone.

I understand that in a vacuum angular resolution is a function of aperture and wavelength, and although I understand the supervening atmosphere imposes limitations beyond those of the wave nature of light itself, am still getting my head around the relevant maths. 

I was looking at buying an 8" F4 but it looks like a cheap but good as new 8" F5 has landed in my lap, which I will be using with a Nexus CC that will bring it down to F3.75 at 750mm, so I should be able to make some direct comparisons, under varying conditions, with my 6" F5 which is also 750mm.

I'll post some comparison images in the coming months so that hopefully others can learn along with me (targets like m42 and the Horsehead nebula are rising on the East coast of Australia), but obviously the biggest confounding variables I'll have to find ways to mitigate or at least record is seeing conditions and integration time with different focal ratios.

To be clear, the question is: what kind of gains, in terms of resolution, can you reasonably expect from increasing aperture at these focal lengths?

An F5 6" Newtonian has a focal length of 750mm, and a F5 8" Newt with a 0.75x reducer (Starizona Nexus) also has a focal length of 750mm (i.e., at F3.75). My question is quite simply: will the increase in resolution going from the 6" at 750mm to 8" at 750mm be noticeable?

Obviously there are some variables to consider, like the pixel size of the camera and the seeing conditions. In my case I am using the 585 sensor with a pixel size of 2.9um which will be oversampled at 750mm. Will the difference in resolution only be noticeable in the very best seeing conditions, or would it be noticeable in average seeing conditions?

Another use case would be going from 6" F5 Newt with 0.75x reducer (about 585mm) vs a 8" F4 with 0.75x reducer (about 600mm). Obviously we would be comparing an F5 scope vs an F3 scope at the same focal length, but again the question arises: will the greater theoretical resolving power of the 8" be noticeable in real world conditions?

Any guidance here would be helpful (and what would be super helpful is a direct comparison of two different images taken under comparable conditions).

 

Hi all, quick question: when I bought the Uranus-C 585 about a year ago the HCG switch point was 180 (confirmed by sensor analysis in Sharpcap) but now I see they have changed the specs on this camera to make the HCG 210. My question is: can I update the driver to change the HCG to the new value? (The latest camera driver was released about a month ago.)

While I'm here I may as well share my latest image: This is the raw Sharpcap livestack image of the Lagoon nebula in Sagittarius made up of only 48 x 1 minute subs (gain was 250 in Bortal 2.5 skies) on an 6" F5 Newtonian (no post processing, slight crop in from the edges):

3 hours ago, ollypenrice said:

This is incorrect. There is no increase in the amount of light per unit time because the available light from M33 goes into the front of the telescope and cannot, therefore, be increased by a lens at the back. What the reducer does is put the same amount of light onto fewer pixels, exchanging intensity for scale and resolution. Your calculation applies when the aperture is increased so as to reduce the F ratio. When the focal length is reduced to increase it, all you get is a smaller, less resolved, but brighter image in the time.

This debate is an old one and is usually called The F Ratio Myth, which will Google.

Olly

Thanks for the technical corrections, because it doesn't do anyone any good to be clumsy and imprecise with a technical language, every use of it should be a practice of it's precision, especially on forums were people augment so much of their knowledge (learning both good and bad habits).

On 07/08/2022 at 04:28, jhayton said:

M33 has been one of my favorites since last November. I had just gotten my 8" and didn't have much time behind it before M33 slipped beyond my viewing.  I've been wafting patiently for its return.   Now it is high enough above the horizon for me to catch it, I still needed to wait until after midnight for it to clear obstructions.  I still managed to capture ~4hr on target.

 

74x180s

ASI2600MC-P
Sky-Watcher EQ6-R Pro
Sky-Watcher 200P-DS
Starizona Nexus x0.75
SVBONY UV / IR CUT

Great image. Nexus .75x brings an F5 down to F3.75, 1.78x the amount of light per unit of time, great upgrade (you can almost halve your exposure times for the same gain settings). I do still see a bit of coma on the edges of your image, did you get exactly 55mm of back spacing?

Sorry to derail the thread, but can anyone tell me if this adapter (which allows you to screw a 1.25" filter into m42 thread on the ZWO camera body, but so that the camera can still be connected to an m42 imaging train) work for the player one camera's (specifically Uranus-C)? Any guidence here appreciated. I have an existing 1.25" uv ir cut filter and am looking for a way to connect it to my imaging train with a Starizona Nexus CC/reducer. I understand that if the filter is added after the coma corrector then the back spacing will have to be increased by about 1mm (to 56mm) to compensate for the change in focal length caused by the filter in the light path.

UPDATE: Looking at the thread on the camera body, there isn't enough room to fit both an adapter for the filter and another m42 extension so it looks like this adapter won't work.

https://www.testar.com.au/products/zwo-t2-1-25-filter-adapter?variant=38122570547392&utm_source=google&utm_medium=organic&utm_campaign=Google Shopping feed app&utm_content=ZWO T2 1.25" FILTER ADAPTER&utm_campaign=gs-2019-12-27&utm_source=google&utm_medium=smart_campaign&gclid=Cj0KCQiA8t2eBhDeARIsAAVEga1Nxrpms_1oa77naDzWPryX8W3HAqUoj1kPddcKIECSVOKETMOG0RIaAlJJEALw_wcB

3 hours ago, Paul M said:

ASTAP is multifunctional. Will blink, solve, stack, annotate deepsky/comets/asteroids. I don't think it has a GAIA plug-in data set so parallax isn't a thing I've come accross in ASTAP.

It will also do photometry, both data base and measured.Plus a load of other stuff, for free!!

Here is a zoom into a deep image of mine with measure magnitudes annotated. I've left the tools menu open so you can some some of the other function.

Can I ask what you'd be using the parallax data for?

 

Thanks, I'll have a play with it. The reason I want to get parallax information is to add the depth dimension to my images, just to explore them in more detail and get a better sense of what I am looking at.

9 hours ago, PeterC65 said:

I've not gone below a gain of 180 for DSOs and usually stick with 400 gain, but I'm using much shorter exposures than you, usually no more than 8s. This is partly because I like to see images quickly with EEVA and partly because with my AZ mount anything more than 30s ends up looking blurred, due to mount movement I assume.

  

I'm often impressed with the results that people like yourself are achieving with AZ mounts. I suppose if you pair a really fast optical system (imagine for example a F4 newt with a Starizona Nexus 0.75 reducer to turn it into an F3 system, or a RASA, or a SCT with Hyperstar) with a sensitive camera like the 585 you could achieve really great results with AZ mounts.
 

While I'm here I'll share an image I just took of the Orion Nebula using a gain of 0 with 120s subs. Its only about 10 minutes of data and straight off the Sharpcap live stack (so you can see satellite trails). Really its just a quick test of the full well depth and dynamic range on this target. (Obviously my stretch is a balance of core brightness and faint nebulosity, but its a bit too much of a stretch for my liking).
This is at F5, Bortle 3 skies, with the moon just past full.

On 03/01/2023 at 07:38, bottletopburly said:

Using the zwo585mc for imaging is there a recommended offset ? or does it not matter currently I have it set at 3 offset .

I usually use 25. Its something that I am confused by as well. All I really know is that you should ensure your histogram is off the left edge, and that its not so far right of the left margin that its clipping on the right hand side. I would be curious to hear others with much more expeirence than myself have to say.

While I am here I may as well share a little mosaic I did with the Uranus-C with my 150p of the Carina nebula:

All I know about this scope is that it is branded OPTEX and its 210mm. It looks like an F4/3.8 (to my untrained eye at least). The focuser looks to be 1.25" rack and pinion. It comes in a box (a wooden trunk) marked 'Astro Boy' and contains an equatorial mount and tripod (though I'm not sure if it is the original case). Can anyone tell me anything more about it, especially the optics? Would it be GSO mirrors? My guess is that it is probably over 30 years old. Would converting it for astrophotography present any obvious problems, or would it be a pretty 'simple' matter of replacing the focuser with a two speed one?

There doesn't seem to be much information out there in the wilds of cyberspace.

 

Just to confirm that adjusting the screws on the spider veins did indeed fix the problem with my diffraction spikes, thanks guys! (I do love pristine spikes...)

I took a couple of photos of my spider vein, making sure that the camera sensor was the same height as the centre of the spider, and tried to line up, first, the secondary mirror so that it was concentric with the primary, and then, second, the hub of the spider with the primary. I'll take a closer look later when I get some time, but are any problems evident to others? A twist in one or more of the veins? Are the angle's between the veins perfect right angles? It looks like the vein's perpendicular to the axis of the focuser are not quite straight but pulled towards the focuser, so I'll correct that and do some testing.

So maybe this is the situation I am facing (thanks to @inFINNity Deck for the graphic). Though I'd doubt it would explain my reflection problem, but its good to at least sort this out. Thanks @AstroMuni.



 

3 minutes ago, AstroMuni said:

I dont believe tilt will cause this effect. It could certainly cause some stars to be slightly out of focus in corners where the tilt is highest. But I am no expert here, and I came to know cause of my flare just yesterday. See my post on diffraction spikes in this channel.

Ah, I see. I'm not sure how I got it in my head that it was the effect of camera tilt (a trouble I have been having). I'll look into it.

18 minutes ago, AstroMuni said:

Any possibility that its reflection from the spider itself? One of your spider vanes is not exactly perpendicular to the light path causing the flare at the end of the spike pointing downwards. I have same problem with my spider but havent seen a reflection like yours (yet).

I'm pretty sure that the reason the diffraction spikes on Alnitak are splitting on the vertical axis (but not on the horizontal one) is because of a slight tilt in my optics train. Last time I checked, the spider veins were nice and straight.

 

40 minutes ago, barbulo said:

If not reflections of a very bright star, cables/ropes in the line of sight?

Interesting. I can't exactly remember, but I think that I waited for the target to clear some powerlines before I began imaging. I suppose one argument against that possibility is that the 'reflection' is in the exact same orientation as the spider-veins/diffraction spike in both images where it appears. I have seen the effect of powerlines in my images before, in the form of an extra diffraction spike (at least I am pretty sure that it was caused by the powerlines).

At this stage I am assuming its reflection from the inside of the OTA, but as Clarkey pointed out, not really a problem with any other targets.

 

I should also mention that my focus tube is completely extended for critical focus so that there really isn't any part of it protruding into the light path, which would be another possible source of reflection.

The back and sides of the secondary mirror are naked (besides the side of the secondary facing the focuser which I blackened with a sharpie), as is the side of the primary (I have completely blacked out the back end of the OTA to prevent any stray light getting in from outside).