alacant

1 hour ago, fozzybear said:

Which ubuntu

Hi. This one.

3 hours ago, Dr_Ju_ju said:

Linux on a bootable USB stick,

Are we sure that kstars and siril are feasible from a usb?

3 hours ago, alacant said:

10Gb to try Linux

Not quite. To correct myself, Ubuntu quote 25Gb. Still a small chunk of say a 500Gb disk.

Cheers and clear skies.

3 hours ago, groberts said:

does it broadly 'feel' like Windows + intuitive to use?   

Hi. Intuitive, yes. Feel like Windows, no. Everything is different, from the way you install programs to the support you get online. HTH.

2 hours ago, JohnSadlerAstro said:

games I enjoy which only work with Windows

You only need about 10Gb to try Linux. You can free space either from within windows control panel or from the installation media e.g. a bootable usb memory. HTH.

Hi everyone

I thought this was going to be really painful; the last thing I expected was to get a first night image. The whole installation takes around an hour from a blank Ubuntu and for me included just indilib, kstars, siril and startools. It looks modern and is as intuitive as it gets.

I tested with a zwo120+oag, 700d and a sw250p on eq6: 90s snaps with full moon.

Recommended, especially if you're included in the windows update mess.

Cheers and clear skies.

53 minutes ago, RolandKol said:

bit too red for me

Hi. Not sure. I tried balancing it a bit but lost a lot of the nebula:( Great shot anyway:) Maybe do longer light frames? HTH and clear skies.

6 hours ago, John said:

Orion Optics, you can specify a different diameter secondary

Great idea. Get two? One for looking and one for snapping. Perfect. 

9 hours ago, John said:

I don't get any vignetting

You won't be able to see it, but a camera frame will. E.g. A flat frame with the 60mm secondary took 3.0s. With the 70mm and same light panel, it took 2.0s. That's a significant gain in light.

Another feature of the SkyWatcher was the alarming amount of light which simply misses the secondary altogether; point it at the sun and you can burn paper with the focused light exiting the open end of the tube with it. With the 70mm secondary, no light is allowed out of the tube unless via the focuser.

I'm sure it doesn't matter that much, but the OP wants DSOs.

Cheers and clear skies.

10 hours ago, 25585 said:

page about secondary sizes

This explains the problem with the small skywatcher secondary. The size of the secondary is smaller than its physical size; there's a bevel.

HTH

1 hour ago, John said:

Orion Optics use a 63mm one with their 250mm F/4.8

IIRC, not enough to get all the light reflected from the primary at the focal plane of a dslr. Not an issue if you're visual or don't mind vignetting.

Cheers and clear skies.

1 hour ago, Gerry Casa Christiana said:

some pictures done on your Bresser

Here's one with the 8" f4, the 6" f5 and the 6" f8. All white tube Bressers.

HTH

Just now, Gerry Casa Christiana said:

Do you have this scope

No, but I wish I did. I have a SkyWatcher 250. I needed to upgrade the -hopeless- single speed focuser to the -equally hopeless- dual speed Crayford, replace the 60mm secondary with a 70mm and I also needed a 50cm dovetail to prevent tube flex. The Bresser reflectors I have are head and shoulders above it.

Cheers and HTH.

You have the mount, yes? This one has a rigid aluminium tube, a decent fat focuser and a secondary sized for AP. The SW doesn't;)

HTH

Hi

Do you have stellariumscope installed also?

HTH

47 minutes ago, Atreta said:

 I'll make those adjustments

Your cap is fine. Better than mine. Does your Cheshire have cross hairs?

7 hours ago, Atreta said:

if i rack in the focuser and look through the cap, the position of the reflection shifts

Mine does that too. So also does a new one I bought for another project. They also slip unpredictably and change focus when you use the lock screw. Hopeless. YMMV but I've had no luck with sw focusers. Ever. Leave it locked in the focus position and collimate from there is your best bet. HTH.

7 hours ago, Atreta said:

This is how it looks like through the cap

OK. Can you post a shot of the cap? Is it a sight tube with cross-hairs? A Cheshire with cross-hairs maybe? IMHO best to forget that ATM and concentrate on the second shot you posted. Make a simple cap (see my shot here) so that your eye or phone are centred in the focuser tube. From the orientation you have ATM the secondary needs moving up the tube -away from the primary- and vertically -up relative to the orientation you have taken the photo-. Make it concentric. That will get you close enough for a star test or your other cap. Whatever your cap is is, I don't think you'll be able to see all three mirror clips using it as it has too small a diameter.

HTH and good luck.

30 minutes ago, Stub Mandrel said:

STL for a small 3D printed adaptor

Nothing as sophisticated I'm afraid. This is just brute force and ignorance 60x20 aluminium from the shed/door/window guy.

1 hour ago, Atreta said:

secondary viewed from a collimation cap

Here's mine. AFAIK -in Europe at least- a collimation cap is an old film canister with a hole in the centre. Maybe that's not it? Some confusing terms!

This snap is with the secondary positioned ready for the primary to be tweaked with a star test.

Post a picture of yours and we'll be able to help better.

HTH

Restoration project: sw 254 f4.7 dated 1999. Just look at it and it went out of alignment. Awful focuser (but not as awful as the dual speed Crayford!), awful tube, seized spider, tiny secondary, non springy springs, flexy dovetail... Loadsa frustration but all now tweaked and/or replaced

Major breakthrough with the collimation was the rigid box section along the top of the rings. It now holds at all angles. It's even lost that Skywatcher tinniness when you tap the tube. Reasonably sized galaxies at last:)

3 hours ago, moise212 said:

I believe they are thinner.

Hi. I don't think it matters how thick they are as the sensor is much closer to the camera connection than the 44mm of any dslr. Any OAG should fit in the 55mm distacnce you need for your coma corrector; get one with a large prisim e.g. this one has 16mm glass. The qhy needs only 18mm so you've loads to play with.

OTOH with a dslr, you really have only one choice to get the correct distance simply.

HTH.

2 hours ago, moise212 said:

upgrade to a 150 F/4

Hi. Be careful. I tried one but sent it back due to the (ridiculous) back focus. My dslr needed to be 18cm from the tube; impossible to hold rigidly and needing a long extension, even with the focuser racked out fully.

2 hours ago, moise212 said:

Perhaps a TS UNTC OTA

I think that's the sensible option as you can specify primary to secondary distances and specify a reasonably sized secondary. 

Here's a snap showing where the focal plane is located...

33 minutes ago, moise212 said:

I find quite easy to focus the OAG. Done once during daytime and then adjusted under the stars. Takes a minute to adjust

+1. There's a lot of misinformation on OAG focussing. I think this stems from years ago when they may well have been problematic. But modern cameras and focusers make them easy to manage; well worth the (not much extra and probably maybe even a bit less) extra cost for those pinpoint stars. Every time:)  Cheers.

9 hours ago, moise212 said:

a replacement primary mirror

Hi. Maybe you could re-aluminise it? Cheers.

2 hours ago, moise212 said:

replace this weekend the secondary mirror with a larger one

Ah, really? AFAICT it's the only sw Newtonian that doesn't lose light by missing the secondary. Admittedly, our test is crude. Hold paper at the open end of the tube with the telescope pointed at the sun. On the 130, nada. On all other sws we've tried, you get a nice focused point of light, enough to burn the paper where the light from the primary is not intercepted by the secondary. There are some details here.

Oh, and tremendous globular. Not much wrong with the secondary there!

7 minutes ago, Manners2020 said:

Wish I'd kept my questions to myself now.

There's only one way out; we'll have to go back to taking photos of stars rather than talking about taking photos of stars. Much easier!