DSO Imaging on a budget

[vlaiv]

While we are on the topic of budget scopes, I'm building two very budget scopes at the moment. In fact - I'm building one as the lens for it is in the mail, I haven't ordered lens for the other yet but focuser for it is in 3d printer as we "speak".

80mm F/7.5 and 70mm F/6.9 achromats.

Both will cost less than £100 (in fact, 70mm might end up costing less than £50) and I will try imaging with those - just for fun.

With a bit of trickery, achromats can be made into color free scopes for imaging. Especially smaller and slower lenses.

[ONIKKINEN]

2 minutes ago, vlaiv said:

You are probably right. Using DSLR body on such scope is probably not recommended - but why not use mirrorless camera?

In fact - we might be expecting too much of a beginner. Perfect flats for mosaic?

Yep, that is no flats mosaic on ST102 (notice lack of chromatic aberration, who said fast achromats can't be used for OSC imaging?) taken from Bortle 7-8 skies with ASI185 - uncooled.

I think that while image is not perfect, many beginners would be satisfied with such result?.

Most beginners would do backflips from joy if they got this as one of the first attempts, so you are right i thought a couple steps too far ahead.

Pretty sure i have seen this image before, if i recall correctly you had a wratten #8 and an aperture mask? And binning of course, to counter the loss in aperture.

These dust spots and edge artifacts would actually be not that difficult to remove in Photoshop with some clone stamp tool, content aware fill, healing brush etc, especially if the image is turned starless with starnet++ first. Not sure if GIMP has similar tools but would imagine it does. Probably not something a complete beginner would know or figure out how to do but not that difficult either so perfect flats more of a luxury at that point (and if the sensor were bigger).

[Ian McCallum]

6 minutes ago, vlaiv said:

You are probably right. Using DSLR body on such scope is probably not recommended - but why not use mirrorless camera?

In fact - we might be expecting too much of a beginner. Perfect flats for mosaic?

Yep, that is no flats mosaic on ST102 (notice lack of chromatic aberration, who said fast achromats can't be used for OSC imaging?) taken from Bortle 7-8 skies with ASI185 - uncooled.

I think that while image is not perfect, many beginners would be satisfied with such result?.

Can I ask what the strange repeating square and dot pattern is, looks like a domino?🤔  Not the usual dust bunnies...

[vlaiv]

1 minute ago, Ian McCallum said:

Can I ask what the strange repeating square and dot pattern is, looks like a domino?🤔  Not the usual dust bunnies...

Just artifact of using mosaic to compose image.

This is 3x3 mosaic. Each panel has slight light drop off at the edge (correctable with flats) - and dust shadows are in same position - so they repeat.

[ollypenrice]

2 minutes ago, vlaiv said:

 

Both will cost less than £100 (in fact, 70mm might end up costing less than £50) and I will try imaging with those - just for fun.

 

Be reasonable, Vlaiv!  Where is your Christmas spirit?  I'll offer you £25 and pay half the postage. Yes!

🤣lly

[vlaiv]

5 minutes ago, ONIKKINEN said:

Pretty sure i have seen this image before, if i recall correctly you had a wratten #8 and an aperture mask? And binning of course, to counter the loss in aperture.

I later took this one as well, just few weeks later- same gear, same method, but instead of doing 3x3 mosaic, I dedicated more time per panel and did 2x2 mosaic - this one goes deeper, and I might have even recorded the flats (not sure would need to check data from 2016)

 

[pipnina]

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...

[vlaiv]

2 minutes ago, ollypenrice said:

Be reasonable, Vlaiv!  Where is your Christmas spirit?  I'll offer you £25 and pay half the postage. Yes!

🤣lly

These achromatic pairs are seriously cheap on AliExpress - check it out:

https://www.aliexpress.com/item/1005001460681644.html?spm=a2g0o.store_pc_groupList.8148356.17.43db7e76OOAAuK&pdp_npi=2%40dis!EUR!€ 26%2C95!€ 24%2C26!!!!!%402100bdcf16720872632597890ec378!12000016213390335!sh

All I need to do is get some aluminum tubing (80x2 mm costs something like 10 euro per meter) and to do some 3d printing - for lens cell and focuser (ok, some bits as well like linear rods and bushings).

Here is what I've designed for that 70mm version:

It is 1.5" non rotating helical focuser with T2 thread at the eyepiece end and M72x1 at telescope side. It has 40mm of focuser travel and 8mm/turn precision

Material for focuser is probably around 20 euro total

[vlaiv]

4 minutes ago, pipnina said:

turning it into what I think is called a "camera newtonian"?

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?

[ONIKKINEN]

28 minutes ago, pipnina said:

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...

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.

[pipnina]

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.

[pipnina]

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!