pipnina

3 hours ago, Stu said:

That’s why I don’t go down the full AP route

Out of interest, have you tried stacking the 4 minute subs? I believe these eliminate hot pixels so I think you may get much better results?

It does produce a cleaner image for sure, but it also does cause some artifacts on stars (they tend to go odd colours) and it means you need to sit there with the phone hitting the shutter button every 4 minutes- deep sky camera lets you take about 30-40 mins worth at a time.

That said, I did find a way of controlling my phone from my pc indoors so it might be tolerable if I tried it again.

In the end these phones are impressive for jack-of-all-trades devices but I think you'll agree that we mostly image with them from curiosity or necessity and not because we expect greatness!

21 hours ago, Stu said:

I think this is as deep as I get! I don’t have any desire to get into flats/darks/stacking on a pc, so the convenience of the Google NightSight mode really suits me.

I have gone down this route, and sadly even if you go through the effort it's not worth it:

The camera in the pixel6 (at least the wide angle one, I only have the normal version not the pro) has terrible coma and concentric rings of distortion. It also suffers from internal reflections and has very strong dark noise and hot pixels. Mind this was when I attempted it when night time temps were still 15c, not freezing!

The end result is that you hit a brick wall fast, I'll find my attempt that took a lot of working out to get right, and even then it's not as good as I would have liked for I believe 2 hours of data!

Edit: Here's what I achieved using the p6 by itself and a star tracker, using deepskycamera app and pixinsight. This used several hundred gigabytes of hard drive space and hours if processing so I think the result is a bit disappointing. Best to stick to the inbuilt 4 minute timer I guess! 

3 hours ago, Mark68 said:

Hi all,

I live in Brentwood in Essex and have a few clear nights at the moment, I was wondering if I could have some help in knowing where a good place to go would be to try and see the milky way.

Is this a good time if the year, is there a particular direction I need to look.

 

Thanks in advance.

It's the wrong time of year right now, as the milky way core is more of a summer-autumn object.

I know that usually people refer to the core when they say "Milky Way", but of course everything our human eyes can see without assistance is the milky way (except for the megallanic clouds and andromeda) so really the core would be best specified as the outer milky way is also visible under suitable skies!

Based on your location however, visual observations of the milky way structure could be challenging. This is because the brightest part (the core) appears in the south, where you will be staring at london's light pollution!

The outer sections of the milky way structure are fainter, and so harder to detect. The outer milky way runs through Cassiopeia down just to the left of Orion. It's not easy to spot but if you can it's quite incredible!

In your case I would think you need to drive somewhere dark, but maybe someone more local to you will have better tips and experience to let you know how practical your aims are! I live in deepest darkest devon so the lack of life down here has made astronomical observations a bit easier. I have seen all parts of the milky way visible from the north only a short drive away from my host city. I appreciate I am raletively lucky in this way however.

Happy hunting! If you have a modern or higher end phone you might catch the core of the milky way in the summer via the long exposure camera mode? Even when I can't see it directly, the phone seems to be able to with a bit of teasing.

1 hour ago, Gumminess8083 said:

Hmm, interesting observation!

I'll try taking everything apart once again and re-tightening all the parts!

Am I correct in assuming that fixing this would require me to open up my scope?

In my case it meant tightening the flathead grubscrews that held the focuser onto the scope. These have always been external screws for me so I could just take a screwdriver to them and tighten them to remove the slop. Only my current focuser is tilt-adjustable though.

32 minutes ago, Stuart1971 said:

It could also be some sort of flexure in the imaging train or focus tube, as after the flip the weight will be shifted and so would the tilt….

Could be the front cell or the focuser aren't quite done up tight? I've had that issues before...

Something about this reminds me of a very old post here, I think by @ollypenrice looking for some sort of "andromeda shelf" that was not confirmed at the time but someone had claimed to detect.

Could this be the object in question?

Personally I've based my opinions around printing materials on this guy's tests:

He tends to do a variety of tests that show tensile, impact, and other kinds of strength. So in general I feel it's good enough for us amateurs!

6 minutes ago, Peter Drew said:

I've made several Schmidt cameras and was halfway through making a 18" F3.5 photographic telescope with just a Newtonian primary similar to what you are proposing.  I have to ask you the same question as I eventually asked myself before I abandoned the project, "What was I hoping to achieve?"  My initial thought was to avoid the cost of a secondary and also to increase the light throughput.  Further research showed that, for a photographic instrument. the light gain was not enough to warrant the mechanical complexity.  Regardless of this, a single Newtonian mirror will still have the optical characteristics of a Newtonian, nothing like the corrected RASA or its variations.

If you do decide to continue I would recommend a primary mirror adjustment for focusing.  This can be achieved by fitting a 2" plug to the rear of a backplate of the mirror cell and fitting it to your focuser.  The focuser itself would be fitted in a fixed position on the telescope backplate.  Compression springs between the cell

and the backplate would take up the weight of the primary mirror and produce a light focusing action.    🙂 

   

I found it rather hard to design a newt in the online newt calculator tools that had good illumination across a good FOV, plus by removing the 90 degree light path turn you make it easier to baffle the tube and remove stray light from entering from the side of the focuser.

It's also just something interesting to work on regardless haha. A fair few correctors work with f3 mirrors which would be quite a good setup, something like a 10" or 12" F3 mirror and camera style focuser might be a bit better regardless of not exactly being a RASA.

But if I find like you did that it's not all that, I won't have spent much money to find out!

1 hour ago, Dr_Ju_ju said:

The one thing I'd recommend is not to use PLA but either ABS or, my preference, PETG ...   They will both give you a much stronger/resilient print.   

52 minutes ago, vlaiv said:

When you say stronger, what exactly do you mean in this context?

ABS/PETG is more flexible so it will flex more easily under load - which is bad for holding camera

Those also have higher impact strength - but I don't see it being important in this application. They are however somewhat weaker in load bearing applications (not too much and I would not dismiss them on account of that) - and have nicer failure mode that might be of some importance for this use case - but again, if properly designed I don't see mount failing under weight.

This is something that I consider a lot lately, and to be honest, I've been surprised by results people get when testing different material ability to bear weight.

For example - this guy does very interesting (maybe not very scientific) tests:

https://www.youtube.com/watch?v=E3WRBp-T42o

I've seen numerous videos where he is able to hold his own weight with 3d printed M8 bolt

In above video - M8 bolts printed in horizontal orientation fail at about 180-200Kg of load. I would trust such bolts to hold 20Kg for short periods of time (PLA is susceptible to creep, so might not be a good idea to put it under such load permanently).

Or how about car park / stop in 3d printed version?

https://www.youtube.com/watch?v=JSWtzMzZp9w

 

For now, I think I can only print with PLA anyhow as ABS requires a warmed containment for the printer to avoid warping, and PETG/Nylon etc filaments require hotends that run much hotter than my Ender3 can handle (above 235c I think is unsafe as the hotend has PTFE tubing running all the way up to the nozzle, which fumes up and can even burn above 240c)

PLA+ seems "stronger" than normal PLA, but only because normal PLA is very brittle, while PLA+ tends to accept a lot more bend. I think tests do show normal PLA to take more force before total failure however.

I expect creep to be the big problem here. A test part I made for a catflap cover has warped and all I did was leave a plate on top of it. I am thinking that steel spiders might be a necessity, but the holder for the focuser seems rock solid even with this PLA+ so I don't expect to need to change that material.

I am planning on making the spiders out of plastic first, and attaching them to the focuser holder and seeing what weight they handle. I may put some weight on them and wait a few days, see if they move... I also plan on making them quite tall, as I think they can be any depth without impacting the image... Not 100% sure about that though. I always assumed only the thickness impacted diffraction. I guess eventually i'll find out!

I had been thinking of this for a while, but until I got my 3D printer it was a bit of a non-starter.

Learning the ins and outs of printing and using FreeCAD has been quite challenging, but last night the first "finished-looking" prototype for the focuser-holder for my newtonian conversion came off of the build plate! And it fits very nicely.

My next step is to design the way to support it. EsunPLA+ may not be strong enough to support several kilograms of camera and focuser, so I may have to look into a hybrid approach with sheet steel vanes fixed into the PLA supports... Work ongoing!

For now, i'm happy I managed to design and produce a working holder for the focuser. While I could have bought a 2" rotating focuser as suggested by @vlaiv, which would reduce the obstruction and weight, I wanted to see what the minimum conversion cost would be for someone who already has a printer, so replacing the focuser isn't my intention at this time.

I intend to post more updates in this thread as my project progresses. And eventually find out if it's a worthwhile re-configuration for newt imagers!

So far this setup gives a central obstruction of 95~ mm diameter. Which is about 2-3mm more than the obstruction created in the RASA8's optical train. Perhaps I will work on a way of removing the focuser adjustment knob and replacing it with a printed part that can be slid on and off the shaft so it need not interfere with images...

Thoughts welcome!

10 minutes ago, doublevodka said:

Not just you, I'm not a fan of the tighter eye relief on shorter focal length eyepieces, I mostly prefer to barlow where possible, so instead of a 10 I'll use a 20mm and a 2x barlow, just find it suits me better.

I bought an 8mm BST because they are highly rated on here, but prefer a barlow and a basic 20mm plossl, although the seeing has been rubbish for months where I am so jury is still out a little as it's slightly more magnification

Thing is, my 24mm I think has LESS relief than my shorter EPs! Both the Vixen SLV and Stellalyra UWA have 20mm whereas I think the maxvision is around 17 or 18. Yet the shorter lengths feel harder to use somehow.

I don't know if it's just me, but I've noticed that even the medium-to-high quality EPs I have seem to be rather challenging to observe through.

For instance, my vixen SLV 10mm and stellalyra uwa 6mm both seem very hard to get a proper look through. I find as I get closer to the eyepiece, the field of view widens, but by the time I get close enough for it to widen to above say 40 degrees afov, the edges blacken as if I am now too close?

For my maxvision 24mm/82deg EP, I find it's quite hard to see the edge of the afov too, but I can definitely see much more of the afov in that EP despite not having as much eye relief as the 10mm and 6mm, it also lets me move my eye around much more than the other two, which seem very fussy about my eyes pointing straight forward all the time.

Could it just be that the small exit pupil makes them more challenging, the EPs genuinely aren't as good as I thought they were (mismatched expectations) or maybe the clouds have gotten me too far out of practice haha. 

Am I alone here with this struggle? I'm not a newbie by any means but I do seem to be struggling.

Something I noted was that PHD would fail to calibrate if too close to the north pole. Because 60 seconds of RA movement covers a far smaller star movement at +80deg DEC than 60 seconds of RA movement at +60deg DEC.

What was your target?

My small 130PDS did very nicely (with the exception of its known design flaws, primarily the focuser tube protrusion). But of course this is a fairly small scope compared to what you're thinking of, it still did nicely on small-ish galaxies:

I also used a scope more in the realm of your considerations: A TS-PHOTON 200/800. That made nice images... When behaving. It also seemed to suffer more from not producing a flat background, maybe the tube walls were not black enough or somesuch. It also NEVER kept collimation, it required modifications to be usable at all for imaging as the collimation shifted just by changing where the mount was pointing... I also never got it to dial in perfectly, all of my images with the scope have some coma or astigmatism somewhere.

The images I *did* get, I was mostly happy with. It wasn't easy to gather them though!

My advice: If buying a smaller newt, go cheap and do things like put flocking material on the inside of the tube and blacken the secondary edges. If buying a bigger newt (i.e. larger than 150mm) you need a more expensive model to have any ease of use. For some reason the step up from a 5/6" mirror to 8" increases the hassle involved massively unless the scope is better mechanically designed.

Good luck!

28 minutes ago, ollypenrice said:

I've found the dedicated ones from astro suppliers to be disgracefully unreliable. I had several failures with Aurora panels which use thin, essentially rigid cables which break at the joints. And I've just had a large (hundreds of euros) Geoptik panel peg out, just out of warranty. They do work, when they work, and make life easier but I've spent enough on them and am done. I'll make my own, as I did before they appeared on the scene.

Olly

That's pretty shocking! I bought an A3 paper sized £35 panel from amazon intended for artists to illuminate their paper/canvas. It isn't perfectly smooth but has allowed me to take good flat frames, on my DSLR it was spotless, leading me to think irregularities with my flat calibration are more to do with my astrocam or telescope optics rather than the flat panel.

How "proper" astro companies can sell something that is less relaiable than a random cheap amazon purchase, for 5 times as much is beyond me...

23 minutes ago, vlaiv said:

Depends how linear fit is implemented.

I created my own version (needs aligned and cropped subs to work properly). It is a bit more advanced as it also handles first order background gradient - it corrects the "tilt" or gradient direction between subs so it makes gradient look the same in two subs.

If you choose sub with minimum gradient as reference - all others will have their gradient minimized as well.

It also makes gradient removal much easier on the whole stack as gradient direction will be aligned and the same - so it will look linear in the final image as well.

My version works quite well. Not sure how PI or other software have this implemented.

I suppose in PI you might do background extraction before the fit? I don't know, I tried it but maybe some small residual gradients were left (the scope was a bit dodgy in that regard)

10 minutes ago, vlaiv said:

Linear fit is extremely useful tool but it is being misused here.

It is actually very useful tool for preparing subs for stacking. Over the course of imaging session as target changes position in the sky - two things happen:

target changes brightness and level of light pollution changes from sub to sub.

Target changes brightness as it changes altitude while earth rotates and "atmosphere number" changes. This part is multiplicative in nature.

LP levels also depend on part of the sky in question and as target "tracks" across the sky - LP levels change.

In general sense, image signal can be written in form:

a * target + b

where a is constant that depends on atmosphere thickness and sky transparency and b is constant that represents average level of light pollution - or background signal.

It is easy to see that above equation is linear (ax+b) and linear fit changes a and b coefficients in one sub to match those of other sub - thus making them stack compatible (same signal strength and same background level).

This is misused as color calibration when linear fit is performed on 2 other color channels against selected one (like fitting R and B to G). It leads to "gray world" type of artificial white balance and also tries to make background color gray as well. "Gray world" white balance algorithm is based on premise that average color in any image is gray (there is as much blue as red and green so that average pixel value is really gray) - but that is flawed assumption.

Also - assuming that background LP is gray is also flawed. In most cases it is orange in color and should not be scaled like that - but rather removed altogether from the image.

 

I've noticed it can be a bit dodgy though- assuming it's valid for use in mosaic images. I could often get two images to linear fit together, but quite often when you stretched the merged linear-fitted images, one would get a black background before the other anyway...

It also couldn't handle one of my panels that accidentally had 768 offset instead of 0 (before i knew what offset to actually use). Linear fit just could not correct that and i got my python-coding friend to make a script to just subtract 768 from each pixel of a fits file, which did work. Sadlly the mosaic was impossible for me to complete regardless as I couldn't balance each panel's brightness... Not sure why linear fit wasn't working. I even tried the DNA linear fit script too I believe.

6 hours ago, 900SL said:

Thanks Pipnina. The spider vanes are pretty thick, I see some owners have milled them down but that seems a bit of a headache

 

The TS ONTC appeals but once you add on all the parts it gets expensive fast. I have had a couple of TS scopes though (live in Europe) and generally happy with their products.  I like the look of the f5 series, should be easier to correct, focus and keep in order

 

Cheers!

Orion Optics make the CT8, which is f4.5, carbon tube and still cheaper than the vixen, I have hard of people getting good results with these, but I am not an orion optics connoisseur so sadly I can't give first-hand impressions 😕

I have looked for the vixen and it seems like it could be out to cost you about £1600-1700 already, so the Orion option is most likely cheaper. The TS I can see is probably more expensive as you say however, but from what I hear the TS ONTC scopes and the Orion AGs are about as good as it gets for newtonian imagers.

IMO it's a choice between the vixen, which you know will have excellent optics and rigidity but also have very very chunky diffraction spikes, against the more expensive TS ONTC and the cheaper Orion CT. I might be missing a brand somewhere but afaik mid-high end newtonians are actually not easy to find, but the budget/low-end market is flooded.

Also: In theory the wynne corrector will work with any newtonian, as they all have parabolic mirrors, and as such are all the same shape, if the diameter and f ratio are the same.

I have looked at it myself before and seen a lot of people complain about the super-strong diffraction spikes (you can see in the pics of the scope that those spider supports are very thick!). But if you like strong spikes you might consider that a positive.

I think vixen are quite highly regarded so the optics are likely very good. However: I don't have much more knowledge about them sadly as it's not a popular model!

I do know that the TS carbon tube scopes are highly regarded for imaging: https://www.teleskop-express.de/shop/product_info.php/info/p6119_TS-Optics-8--f-4-ONTC-Carbon-Tube-Newtonian-telescope---fully-customizable.html

A bit expensive though, but I don't know how it compares in price to the vixen. I would personally avoid reflector greater than 6" unless they're of a premium (vixen, TS ONTC, etc) as my own experience shows they do not hold collimation at all. My 8" TS PHOTON was atrocious, but my cheaper built 130PDS was rock solid, for example.

Hope you find the one that's right for you, and I hope this helps!

7 minutes ago, ONIKKINEN said:

The RisingCam camera body is only 80mm in diameter, so shouldn't be any more extreme than your average F4 newtonian obstruction. T2 inline focuser and should work nicely, will need some DIY hardcore steel spider though.

Indeed! The focuser i took from the side of the scope has a square connection that is only 75x75mm already. The diagonal in the scope is 70mm minor axis too, so I shouldn't be seeing too much increase in obstruction!

8 minutes ago, vlaiv said:

I like the idea and have contemplated that on several occasions.

One issue that you might have is with any idea of motor focuser. In fact - you might want to look at this for focusing:

https://www.teleskop-express.de/shop/product_info.php/info/p9360_TS-Optics-2--Non-Rotating-Helical-Focuser-with-M48-connection.html

Alternative is to use primary mirror focusing - but designing good mechanism would probably be nightmare-ish to say the least.

Maybe synced lead screws (much like some CoreXY printers have) to move primary up and down the tube?

Certainly the mirror cell for this scope is of poor design. I had to use the technique Alacant told me where you remove the mirror, put silicon sealant on the cork pads, and let the mirror weight squash it down. Before, the mirror would slop in the cell and the collimation would move when tilting the scope in the mount. If I did up the brackets even a little, the issue persisted but then there were signs of pinching. So sealant it was.

It doesn't hold colimation either, I had to adjust it near every time I moved it, which was not the case with the cell used in the 130PDS, which held nicely even if i moved it.

The  rotating focuser might be a good idea though, but maybe only if my initial attempts at getting it to "just work" go well first!

I need to devise a way to keep dust out of it too while I'm at it, as the dust cap it came with won't fit after the new bits im designing  go into place, and there's a hole where the focuser USED to be. It's already got stuff on the mirror (a healthy coating) so I will need to break out the cotton buds and clean water before I do an optical test!

I am thinking about how I will do the focuser-tilt adjustment though. I have a CAD part for the focuser and its 230mm diameter curve to sit on and be bolted onto, next I need to design the tilt and then the spiders it will attach to. Then likely re-deisgn and re-print in matte black when my current first spool of white runs out haha.

This 3D printing business is a lot of fun so far, I could definitely see myself annoying my family members with yet more machinery and equipment in the house haha.

Since we're talking about budget achromatic scopes here- I figure this might be a good time to mention my plans to revive my 8" TS PHOTON.

I have gotten an Ender3 3D printer this last week and I've been dialing it in and getting to terms with the CAD -> Slice -> print process. I have plans to replace the secondary mirror in the photon with a 3D-printed support for the 2" focuser- turning it into what I think is called a "camera newtonian"? Although Sir Isaac created the design that used the diagonal, so maybe his name shouldn't be attached to it.

But on an 8" scope the obstruction shouldn't be too severe, and as long as my prints are strong enough the flex shouldn't be bad either. I might need some chunky spider vanes though...

In such a configuration the collimation might be a little easier, as only focuser tilt is consequential and primary collimation (while not EASY on the PHOTON) should be able to make it a nice fast design with minimal/no vignetting, as the focuser and diagonal lost a lot of the light in the original design.

If it works as-is, I may get a corrector that reduces the FL and have a "poor man's RASA8" haha. I am sure reality will catch up to me however...

54 minutes ago, vlaiv said:

If we really want to go budget friendly on newtonian - we should be looking for 1.25" sized coma corrector. There are few very affordable scopes that are 4-5" class.

I don't mind 130PDS - I just wonder once you add 2" CC is it still a budget option?

Compared to other AP scopes, I think the 300 I spent on my 130PDS + Baader MPCC was pretty budget! The mount (HEQ5) cost more than twice as much in 2017 prices, and I don't think the HEQ5 can handle too much more than the 650mm fl / 1.28" pixels that scope gave me with my DSLR.

I think it's a bit pricier today, but I'd still struggle to find a scope + corrector that beats it on a value perspective! A 1.25" corrector will probably be sub-optimal for a lot of beginner / budget minded people- a lot of them will use APS-C or 4/3 DSLRs or mirrorless cameras that they may already own or buy second hand off ebay.

6 hours ago, ollypenrice said:

As Peter says, above, a Newtonian is an inexpensive choice and will trounce an achromatic refractor for imaging.

An achromat really is not a good option.

Olly

From my own experience, I can say that a 130-PDS (about as cheap as they come) is very good for the price. Once you learn how to handle collimation yourself it's pretty rock solid and trouble-free. Mine paired with the Baader MPCC did let some out-of-frame reflections through but for 350 for scope and corrector you can't complain.

I did find that it wasn't very suitable for a mono setup though, as the focuser is weak and the cost of upgrading it didn't make sense for the scope. All-in-all it is a strong recommend for someone on a tight budget!

I will say though that for some reason, even the step up to an 8" newt is probably a bad move on a budget. For some reason even though it doesn't sound a lot on paper, that weight and size creates a huge amount of flex. My TS PHOTON 8" F4 was a nightmare that I eventually ran from light-speed. I guess that larger than 6" newts are best left to more expensive, higher-quality models...

My 2p anyway. Adding this for any newbies reading the thread.

8 hours ago, Peter Drew said:

Sanity check for an imager?  Whatever next!    🙂

Tell me about it!

I used about 1500 worth of kit until march this year. HEQ5 + pre-owned D3200 + 130PDS+BaaderMK3 CC.

I used that from 2017-2022. Then in february I bought a risingcam 571. Then I bought £3000 woth of chroma filters... Then I replaced the 130PDS with an 8" f4 TS newt, which I never got to work as I liked... Then spent money on a second hand 130mm triplet... Oh no oh no.

I looked up how much I spent in total this year... I felt very guilty... After 3 years of saving money and living with my dad to save for a "house deposit" i blew a lot of that in 9 months chasing better images haha. I'd been looking at even just the astrocam upgrade til then going "One day, but man they are expensive!"