BrendanC

Hi all,

I just got a baffle to fit to the primary on my 130PDS, in an attempt to get my stars a bit more defined. It goes around the outside of the primary and hides the primary mirror clips - very much like this: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p12358_Wega-Primary-Mirror-Baffle-for-Skywatcher-Newtonian-130PDS.html

I've yet to fit it, but I just had a thought: if I do fit it, will it affect my focal length? And if so, will that mean data acquired after fitting the baffle, will be incompatible with data acquired before it? As in, will images acquired with the baffle fitted, register and stack ok in DSS with images acquired without the baffle fitted? I'd rather know either way before I fit it!

Thanks, Brendan

Thanks - that's why I was asking this, because I'm aware that the EXIF isn't from the sensor, it's from the processor.

I've discovered that just leaving it in the fridge for a few minutes gets rid of the issue. So, I guess it's as I thought: an object lesson in the difference between sensor temps and processor temps. I'm just glad I spotted this before ruining my darks library!

Hi all,

I thought it would be interesting to make a list of all the things I've had to learn along the way over the past two years or so, starting with scratching my head figuring out how to put my first scope and mount together (Sky-Watcher 130P Synscan) and now producing images I'm pleased with on a consistent basis.

So, I just jotted them all down, sorted them A-Z, and here they are - no attempt to categorise, it's a mix of techniques, hardware, software etc. This is without even considering mono shooting, filters, and all that jazz.

Align mount
APT
ASCOM drivers for DSLR
Assemble scope and mount
Attach camera to laptop
Attach camera to scope
Attach guide camera
Attach guide scope 
Attach mount to laptop
Bahtinov masks
Calibration
Collimation
Coma
Control everything from laptop
Control remotely
Dithering
Drizzling
DSS
EQMOD
Exposure times
Focusing
Guiding
Image formats CR2 and FITS
ISO
Mount handset
Magnitudes
Mosaics
PHD2
Photoshop
Planning sessions
Plate solving
Polar align
RA/Dec and Alt/Az
Registax
Sharcap
StarTools
Stellarium
'The sky'
Topaz DeNoise
Using camera
Visual - star alignment, finder scope alignment, eyepieces/barlows
What to do when things go wrong!

Just a little bump of this one cos I still don't really know what's going on.

I have a theory that it's evidence of how the Digic 3 processor, from which the EXIF temperature is derived, is demonstrably a different temperature from the sensor in certain conditions.

It would be great if anyone could confirm this one, ideally by having experienced this themselves. I know that in theory this could account for it, but whereas in theory, theory and practice should agree, in practice, they don't!

Hi all,

Just experimenting with Siril.

In DSS, I can use groups to match my lights and darks by temperature and/or exposure time.

In Siril, I can't see how this is done.

I've looked around online, inc the Siril forum, and can't find a definitive answer.

Any ideas?

Thanks, Brendan

Well, after leaving it in the fridge for a bit longer, I started getting the same as the darker darks.

So it could be something thermal.

If so, it would be an object lesson in how EXIF temperatures differ from the thermal state of the sensor.

Hmmmm.

I'm not - it's just that the dark came through at that temperature. I was hoping it would go down during the night, but I was testing it now.

Also, given that my camera typically is around 10 degrees above ambient when shooting, I can easily imagine an evening of 19C. I do have subs at 29C and above, believe it or not.

The problem still remains though. Why is one taken at 29C markedly different from another?

Hi all,

I decided to extend my darks library while the clouds are still rolling in.

I know, I know - I shouldn't be using a darks library with a DSLR but it seems to work for me.

Anyway, my past MO has been to put the camera in the fridge and build up the library for 60s, 120s, 180s and 240s exposures, all at ISO800. Then I group them according to temperature and build master darks from 50 subs for each temperature.

Here's an example of one at 29C that I took a while ago, stretched in APT to bring out the details:

I've used these darks for a while and they produce good images (or at least I think so).

The difficulty using this method is getting the higher temperatures (dur, cos it's in the fridge, right?), which is where the dark files are most handy. So I decided to put the camera in a sealed box outside, with the lens cap on. I got this (ignore the square top left, that's just an APT thing):

It's the exact same exposure time - 240s - and EXIF again reports 29C.

Looks like light leakage maybe?

Realising the LED display was still on, I slapped my forehead, switched it off, thought that would be it. Nope.  So I draped a thick towel over the box. Nope, still there. So I wrapped the camera in a big hat, and then in the towel. Absolutely no way light's getting in there.

Still the same.

And now I just put it back in the fridge, exactly as per the, er, darker dark, and I'm getting the same result - a sea of purple noise. Nice title for a Prince song maybe, not so great for calibration.

So, I'm thinking this must be thermal noise, despite the EXIF reporting the same temperature. Is this the classic thing of the EXIF reporting the Digic 3 temperature, not the sensor temperature? In which case, am I stuffed?

Thanks, Brendan

No idea. Beats me. 

I have to say, the idea of a reducer somehow widening a field of view while keeping the aperture the same size has never made sense to me. I mean, I know it does. I just don't for the life of me understand how. 

That's exactly the route I took for exactly that reason, and my guiding is fine with a guide scope. 

4 hours ago, Jamgood said:

The best thing I did was give my laser to my cats for a toy. A collimation cap and a cheshire are all you really need. Maybe a concenter eyepiece if you're struggling with the secondary. Once the secondary is sorted, leave it alone.

 

Agreed on all counts (including giving the laser to the cat!). I was struggling, got a Concenter, sorted the secondary, never touch it now. Just a quick check with the Cheshire to get the primary centred. The Concenter was more than I wanted to pay for a pretty much one-off fix, but I would still be getting frustrated with collimation if I hadn't bought one.

Thanks - I use APT which doesn't have a mosaic feature, sadly.

I sorted it last night though, got to 89.7 degrees which I think is close enough!

Hey @vlaiv to the rescue again!

That's exactly what I'm going to do. Take one shot, plate solve, show in Stellarium, rotate, repeat until it's at 90 degrees. 

I was so certain I had the camera right before but obviously not. A check beforehand is definitely the right way to do this, especially with mosaics. And that's exactly why I did a trial run first. 

The geometry of RA, Dec and a camera beat me I'm afraid... 

Thanks again. 

Me again.

A sudden thought: when the camera is supposed to be rotated by 90 degrees, that's not at 90 degrees to the scope, is it?

It's at 90 degrees to the horizon. 

So I need to rake into account the angle of the scope - which, at 26 degrees, is about right for the veil nebula - and then rotate the camera by 64 degrees.

I've done mosaics twice before, not had this problem, and I can only assume it was blind luck that they worked out.

If someone could confirm I'm right about this, I'll have learned something! No such thing as failure, just a lesson learned and all that...

OK so I took a different approach - plate solved an image in APT and then used the Show function to see it in Stellarium. This shows that the image was at 64 degrees, not 90 degrees.

So my very first thought, that it's just the camera rotation, was right. But the camera looked to be exactly at 90 degrees. I cannot figure out for the life of me how I managed to be 26 degrees out.

Tonight I'm going to take just one shot, then do the same check: show the result in Stellarium and make sure I've got the right place and the right rotation.

Weird.

So, last night I did a quick test to check my veil nebula mosaic coordinates and camera orientation were right.

It came out like this, after running it through ICE...

According to Telescopius, which I used to create the coordinates, it should look like this:

/

Now, if I go through Stellarium and use the exact same coordinates, with the camera rotated by 90 degrees (which is what Telescopius says this would be), it works perfectly ie I can do a screen grab of the camera's FOV, copy and paste it into Photoshop, and manually rebuild the mosaic and it looks just like the above graphic.

I have literally spent all afternoon scratching my head to figure out what's wrong here. The coordinates are right, I'm sure. The camera is rotated by 90 degrees. So why are the subs in the mosaic all out? Is it really a camera rotation issue?

I've been through everything several times and that's all I can think has gone wrong here. But I just don't know for sure.

I'll be running it again tonight. I've redone this in Telescopius and rebuilt all the plans, but I don't see anything radically different and I don't expect a radically different result tomorrow.

Any more suggestions?

Thanks, Brendan

Finally managed to get the imaging from the eclipse sorted.

Hi all,

I just watched this. Highly recommended!

https://www.netflix.com/gb/title/81343342

Hi all,

Just thought I'd share some DIY.

I've had a couple of occasions where I got big light spikes across images, probably due to internal reflections, which flocking might fix. I didn't want to flock the whole scope, which would involve taking it apart. Nor did I want to permanently change it, in case I wanted to reverse the procedure.

So, I got some magnetic paper, stuck some of the 'fluffy' side of some old velcro I had lying about on it, and then inserted that behind the focus tube simply by rolling it up, putting it between the spider vanes, and letting it unfurl and stick to the scope. Looks pretty good, comes out and back in very easily. Not tested it yet, but I thought I'd share it.

4 hours ago, cloudsweeper said:

Never mind AP, visual only can be a bit bonkers.  I've got FIVE telescopes and TWENTY EIGHT EPs.  And you know what? - it's still not enough!  🤪

Doug.

Personally I'd sell the wife and invest the money in some really tasty astro equipment. The kids too if you have any. But keep the dog. 

The best thing I ever did for collimation was to replace the horrible screws on the secondary with some decent thumb screws. I got these but they're currently out of stock (isn't everything?): https://www.amazon.co.uk/Set-Thumbscrews-Secondary-Mirror-Collimation/dp/B00UJUOXA4

You might have more luck at Bob's Knobs - see http://www.bobsknobs.com/

They're so very much easier to manipulate because you can move more than one at a time without worrying about Allen keys falling out or dropping onto the primary etc.

Then yes, as others have said, use a collimation cap and/or a Cheshire, not a laser.

And follow this guide: https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

Good luck. I hate collimating. Or, rather, I hated collimating until I also got a Concenter which helped sort out the secondary, and now I just have a quick check with the Cheshire to align the primary - about a minute, and I'm done. Very occasionally I'll check the secondary with the Concenter but it's always spot on. It was more money than I wanted to spend, but I'm glad I spent it. I also developed a solution using my mobile phone in case you'd like to give that a go, see https://stargazerslounge.com/topic/360299-interesting-collimation-technique/

Actually, come to think of it, I still hate collimating.

It's a big step, but the right one. I was very reluctant to take it because I'd become very used to using the handset as a relay with my old AZ mount. Then I got a second-hand NEQ6 (funnily enough through this forum) and wanted to do the same, but whenever I flashed the handset to be in relay mode, it wouldn't have it. Wouldn't work in PC Direct mode either (although relay mode is supposed to be better). Then, when I got an EQDIR cable, that didn't work either, with the default Sky-Watcher drivers. Then, on advice from this forum, I went the EQMOD route, instead of the Sky-Watcher drivers, and never looked back. EQDIR and EQMOD is absolutely rock-solid, and you can just let it all work in the background with no problems. So yes, forget the handset, get the EQDir cable, set up EQMOD via that link I shared (you don't need Stellarium and Stellariumscope but they come in handy sometimes - even though Stellarium now supports ASCOM, I think Stellariumscope offers a quick, easy way to align your scope if you're not plate-solving), and you won't look back.

Agree with the above. I could not get my NEQ6 handset to play ball so took the the plunge with EQDirect and never looked back. This tutorial is excellent: https://www.lightvortexastronomy.com/tutorial-setting-up-an-equatorial-mount-on-ascom-with-eqmod-stellarium-and-cartes-du-ciel.html