kbrown

On 07/10/2020 at 11:43, Chriske said:

Indeed it as bit short.
But there is an easy fix.
I did a simulation and ended up with exactly the same optical(raytrace) result.
 

Lower the ROC  of the SecMir. to 595mm
Correct the CC of that mirror to -2.14
You'll end up with a distance of about 330mm instead of 250mm back focal length.
But : The telescope has a different end value now, it has grown now to f/25.5, so   F=6395mm.
This is just an example, you can play with these two figures as needed.

I entered your new focal length and back focus values to CassDesign and it gave me pretty much the same ROC and CC as you mentioned. Curious what did you use to do the simulations with?

Also I'd appreciate if anyone is able to explain how to read the raytracing graph shown below? I don't know whether this is a good result or not? All I know is that having a longer focal length (higher f-ratio) is beneficial due to the inherent coma and field curvature issues in these scopes. Surely F/25+ should be alright for planetary work?

Here's a magnified view of the above raytrace:

2 minutes ago, Merlin66 said:

Photographic negative copies of Ronchi screens were widely used when film cameras were the rage....

Have you tried a piece of fine fly mesh? That's generally my fall back.

 

Intriguing idea(s). Thank you. Hmmm

I've been trying to source a piece of a ronchi screen without much luck (in the UK). Either they'll cost an arm and a leg or are just not available. Just wondering if it would make sense to get some high quality laser printable overhead projector transparencies and print your own? I only have a mediocre black and white 2400x600 DPI laser printer. Wonder if that would be good enough say with 100 micron films for anything useable?

Greetings,

Ever since I was about ten (several decades ago) I have been fascinated by the prospect of making my own telescope from scratch including the optics after seeing a book about it in the local library. I've read and watched numerous videos on the subject and have a fairly good understanding on what is required to complete such a project. Most of the articles I've seen are concentrating on making a Newtonian telescope but since I already have one I'm not sure if I'd want to make another one. Recently I've been reading about Cassegrain telescopes and especially the Nasmyth variation that doesn't involve a hole in the primary mirror.

Here's the somewhat crazy idea I have in my mind at the moment which I'm not sure if it's worth pursuing. Feel free to shoot it down if it doesn't make sense since I lack the experience... To get my feet wet I was thinking cutting some corners and start by making the hyperbolic secondary and borrow the parabolic primary and maybe even the secondary from my existing newt to get it all working. Once I'm happy with the secondary I could then have a go at making a duplicate of the newt primary. Does this make any sense?

The primary I have is from a SkyWatcher 250PX i.e. 10" / 1200mm. My aim is to have a long focal length cassegrain for mainly planetary imaging. So maybe an effective focal length of 6000mm (5x) or so. I do realise this would still be a fairly sizeable scope but most likely nothing my NEQ6 Pro could not handle. I entered the numbers into the CassDesign.exe program I found by Mike I. Jones. I'm not sure what the units for the Unvignetted Field Width is so I left it at its default. Likewise I'm not sure how much of Back Working Distance I'd need. Other than that do these numbers make any sense?

1 hour ago, wormix said:

Out of curiosity, what scope is that on your setup?

 

cheers

Oh it's a DIY refractor I made some time ago. It's okay but I'm planning to improve it in the near future. More info here:

https://stargazerslounge.com/topic/319373-diy-refractor/

I decided to continue my experiments. The laser led without lens is a very small light source but it isn't round. I decided to go with a fibre optic cable route. Now I have a very round 50 micron daylight white (about 6000K) light source. Remains to be tested but I can already tell it's the best version so far. It looks bigger in the photo than it actually is as I wasn't able to focus  on the light properly.

18 minutes ago, kbrown said:

Apologies. I should have said the reticle has very very thin walls (0.3mm) and I printed mine with a 0.25mm nozzle. I'll add a thicker version of it which should be printable with bigger nozzles but they'll be more obstructive.

Here's a new zip file. I've added a thicker version of the reticle. Should be printable with a 0.4mm nozzle.

ChesireEyepiece.zip

3 hours ago, kimball wiggins said:

i could not print the reticle. am i doing something wrong?

 

Apologies. I should have said the reticle has very very thin walls (0.3mm) and I printed mine with a 0.25mm nozzle. I'll add a thicker version of it which should be printable with bigger nozzles but they'll be more obstructive.

Did some improvements on the main tube as I found it a bit fiddly to use. Now I can pop this into my 2" focuser without any adapters (still works with 1.25" focuser too). It also has flat flanges instead of angled ones so it's easier to secure flush against the focuser tube. The "plug" and the "reticle" are the same as before. STL files attached if you want to print one too...

ChesireEyepiece.zip

I'm thinking of getting one of these for planetary imaging purposes:

https://www.firstlightoptics.com/barlow-eyepieces/explore-scientific-2x-barlow-focal-extender-2.html

At the moment the imaging train on my 10" newt is a coma corrector in front of a filter wheel and zwo ASI 183mc pro on the other side. This puts the ccd at the required distance of 55mm of the coma corrector. What I'm not sure of is would the focal extender work between the ccd and filter wheel?

Old topic I know but I had another go at and another approach to this after reading some posts using a weak laser diode without a lens under its lasing threshold instead of a regular light source and a pinhole. I got a bunch of cheap laser pen lasers with lenses from fleabay. Removing the lens was super easy. Just pull it out carefully. Turned out the laser modules had a 330 ohm series resistor on them. Bit of calculating and experimentation I decided to add a 2.2k resistor in series with the module. The torch has 3xAAA batteries so this results in just over 1mA current flowing through the diode. Well under the lasing threshold. I could go higher if needed but at the moment I don't know how bright this needs to be. Seems bright enough already but I haven't done any tests with it yet.

There is a bit of a glow around the diode itself due to reflected and scattered light in and on the PCB where the diode is mounted. Might try to do something about it but it will be difficult without breaking the hair thin wires going into the laser diode.

You're right guys! I did some 3D mock-ups and 1.6m square would be way too tight. 2.2m looks more comfortable. I haven't got much space to play with nor the greatest skies above me either so I don't want to go too crazy. I consider this as a practise run before I retire somewhere away from cities

Thanks,

Kari

I'm thinking of building a small ROR obsy with a warm room in our back garden. I have a Skywatcher 250px at the moment. Just wondering how much space I need for it. Been thinking about 1.6x1.6 metres floor for the scope room. Does that sound OK? The OTA is about 115cm long. Trying to keep it as small as possible but yet comfortable enough for doing maintenance work. 

Finally got around completing this mod. Wasn't easy to enlarge the existing holes on my old SW counterweights without a pillar drill. I managed to do it with a step drill bit to get a clean start for a 27mm HSS cobalt twist drill and plenty of WD40. My arm still aches though 😕

I then 3D printed bushings to bring the hole sizes down to the required 25mm for the new shaft. Not sure how long those will last but so far so good.

2 hours ago, Davey-T said:

Where does the T ring enter into the setup ? the camera should fit straight into the Quark.

Dave

The T-Ring is on the ASI so I could put the 1.25" nosepiece on it. This is the closest I could get the ASI to the Quark with what I have. I tried unscrewing the 1.25" receptable off the Quark but that revealed a thread that I couldn't recognise or use with anything.

Maybe I'll try imaging with my QHY5L-II instead. Smaller sensor but at least it's mono...

Hi,

I'm not new to astroimaging per se but I am new to solar imaging and could use some help to get my rig set up correctly. I've recently bought a Daystar Quark Chromosphere  "eyepiece" but have had very few opportunities to actually use it. I'm using it with a 72mm F/6.9 achromatic refractor. I was testing it the other day with my ZWO ASI183MC Pro (I know, mono would be better), but wasn't able to achieve focus. This was probably mainly due to clouds always obscuring the sun a bit but still I was disappointed not to be able to see more than a blurry white blob no matter what I did. I had the Quark after my diagonal and the camera attached to it using the 1.25" nosepiece together with a 11mm T-ring. Does this sound correct? I haven't been able to find information on how close/far away the sensor should be from the Quark. Any insight on this would be appreciated.

Thanks,

Kari

5 hours ago, silverdb said:

I just bought a 3D printer.  I've been building telescopes for 20 years and am looking for astronomy related projects to print on my new printer.  Are you willing to share the models for your cheshire eyepiece?

Of course. I've attached the models here. You shouldn't need to use any supports if you print the "plug" and the "tube" upside down.

ChesireEyepiece.zip

I know this isn't directly helping you but I thought I'd still point this out. You can get a cheap USB GPS module such as Stratux Vk-162 which will work with gpsd in Linux. INDI has a driver that talks to gpsd (indi_gpsd). This is what I'm using with the indiserver running on my RPi3. Works well with Kstars/Ekos as the client on my laptop.

Search for "D C FIX Velour Black Velvet". That's what I used...

1 hour ago, m.tweedy said:

They were on mine. I suggest you contact the supplier

Thank you! I did yesterday. Still waiting for an answer 😕

My PETG prints have been alright although it doesn't get much colder than 0C here. I still wouldn't use them for anything that requires heavy duty structural strength. Print orientation matters as layer separation can be a problem even if it doesn't get cold.

On 09/03/2020 at 12:20, Chriske said:

Your life will never be the same again...😁

Why did I read this as "Your wife will never be the same again..."

I got it from ebay (item 152427520030). Took a while to arrive as it came from China. 

On 16/02/2020 at 13:11, m.tweedy said:

The Orange collar is fitted permanently to the NEQ6 but the counterweight shaft unscrews. It is easy to remove but does not slide in to the body of the NEQ6. I have to say it is a nice solid counterweight shaft-much more sturdy than the stock one.

Went ahead and ordered the 5kg version in the view of enlarging the bores of my old weights so I can add them onto the new shaft too. 

Couple of questions though. Is the kit supposed to come with a safety screw that goes onto the end of the shaft? Mine didn't. Also is it supposed to come with scrub screws for locking the collar in place? These are missing too 🤔