Random cheapo Newtonian to try collimation?

[TiffsAndAstro]

Missed out on an Orion star blast 4.5 for £35 was wondering about the one below. Not bothered about the mount.

Just thinking about a cheap non bird Jones F5 ish Newtonian to try out collimation before maybe buying something better that won't needs lots of fixing to make it good, in the future.

This OTA weighs 4kg so not impossible for my current mount.

 

Apologies for worlds longest URL

https://www.ebay.co.uk/itm/116256865754?_trkparms=amclksrc%3DITM%26aid%3D777008%26algo%3DPERSONAL.TOPIC%26ao%3D1%26asc%3D20240315132637%26meid%3D9d7e1fe2c60c4db8bbf5485b08b19ca4%26pid%3D102055%26rk%3D1%26rkt%3D1%26mehot%3Dnone%26itm%3D116256865754%26pmt%3D0%26noa%3D1%26pg%3D4375194%26algv%3DRecentlyViewedItemsV2MobileWithMLRV6RankerPricelessTop50Features%26brand%3DCelestron&_trksid=p4375194.c102055.m146925&_trkparms=parentrq%3Af42a24fa1900ad993dea692fffff0868|pageci%3Ac1d5d29f-4c13-11ef-9343-e6e005883b3a|iid%3A1|vlpname%3Avlp_homepage

[pipnina]

Were you going to use a newt for imaging or visual observation? For imaging you might find they all behave with their own character and an f5 will be a doddle to collimate compared to an f4. For visual, you can get it "close enough" and it will look fine, maybe you could be picky at high power.

But all the newts I've used have behaved differently. Some barely held collimation at all (8" TS Photon f4 flexed under its own weight, while my 10" dob and 5" PDS were like bricks and easy to adjust, and even survived some transportation without need for adjustment.

If you want to look at a specific newt for imaging or observing, maybe if they sell it on FLO you could pick it up anyway, with a collimating tool (my preferred is laser for fast primary alignment and secondary squaring, cheshire for centering the secondary). That way you get to see if the newt you want to end up using works for you, with the safety of the 30-day return?

[TiffsAndAstro]

9 minutes ago, pipnina said:

Were you going to use a newt for imaging or visual observation? For imaging you might find they all behave with their own character and an f5 will be a doddle to collimate compared to an f4. For visual, you can get it "close enough" and it will look fine, maybe you could be picky at high power.

But all the newts I've used have behaved differently. Some barely held collimation at all (8" TS Photon f4 flexed under its own weight, while my 10" dob and 5" PDS were like bricks and easy to adjust, and even survived some transportation without need for adjustment.

If you want to look at a specific newt for imaging or observing, maybe if they sell it on FLO you could pick it up anyway, with a collimating tool (my preferred is laser for fast primary alignment and secondary squaring, cheshire for centering the secondary). That way you get to see if the newt you want to end up using works for you, with the safety of the 30-day return?

Could try that but I don't like taking advantage like that. I'd only return stuff that I had to.

I quite like the idea of finding a small newt just to try out. Might even be light enough for my mount.

Imaging only btw

I didn't bid on the above item in case it was a bad bird Jones.

ALso I like idea of trying out collimation to help me decide if I should get a decent one. Plus the mount upgrade it would need

[happy-kat]

Do you like defraction spikes on images?

[TiffsAndAstro]

22 minutes ago, happy-kat said:

Do you like defraction spikes on images?

yes i think i do. at least 'nice' ones.  i don't like them enough to want to add them to my current images though

[ONIKKINEN]

Collimation of cheapo newtonians will be significantly more difficult than with decent newtonians, so not sure this is a good way to learn collimation if that was your main goal with getting one for cheap at first. Its because if the scope is mechanically unstable proper collimation will be impossible to do consistently, especially with models that have plastic focusers and no primary mirror center marker. My first scope, an Astromaster 130 was all plastic and practically impossible to collimate accurately, so didn't learn much with that scope.

The smaller Skywatcher PDS (130/150) scopes are not too expensive or heavy, and there are a lot of them out there so you might find a good deal second hand which would be my suggestion for a soft landing to the world of newtonians.

[TiffsAndAstro]

3 minutes ago, ONIKKINEN said:

Collimation of cheapo newtonians will be significantly more difficult than with decent newtonians, so not sure this is a good way to learn collimation if that was your main goal with getting one for cheap at first. Its because if the scope is mechanically unstable proper collimation will be impossible to do consistently, especially with models that have plastic focusers and no primary mirror center marker. My first scope, an Astromaster 130 was all plastic and practically impossible to collimate accurately, so didn't learn much with that scope.

The smaller Skywatcher PDS (130/150) scopes are not too expensive or heavy, and there are a lot of them out there so you might find a good deal second hand which would be my suggestion for a soft landing to the world of newtonians.

Didn't even consider the lack of circle on the primary. I think 130mm ones just a bit too heavy.

Focusers will be rubbish I guess.

Ty for the advice.

[TiffsAndAstro]

Er two more probably stupid questions sorry

Has anyone tried attaching secondary on a stick on end focus tube?

Also, do focus tubes always have to poke into the OTA so far or can they be cut down a bit once you know roughly where focus is reachable?

[PhilB61]

One additional thing to consider is that not all cheap "visual" Newtonian may have enough focuser "in" travel for a camera to reach focus. There are ways around this, longer collimation screws may help or relocating the primary mirror cell further in the tube. Yes, some do cut down the focus tube to reduce intrusion, but may not be required if one of the other options above is done. Lots image with the 130pds with good results.

[PeterStudz]

I see that the telescope in question has now been sold. @TiffsAndAstro did you get it?

Personally, I don’t think this is such a bad idea. And for that kind of price you can’t go wrong. I have a little SkyWatcher Skyhawk 1145p and for a visual grab-and-go/travel telescope it’s surprisingly good. Especially on a more solid mount & tripod. 

As a beginner, with only a few months experience, I restored a 200p Dob. I only fully understood collimation after I’d stripped it down and put it all back together. Before that time I thought I’d understood but I hadn’t. I can well remember taking a day off work to flock the entire OTA, which required stripping down to just a bare tube. I already taken the mirrors out before so had some experience and slight confidence. But I was surprised how quick I managed to do it. And I had the whole thing back together, collimation spot on, in time to look at the moon in the evening.

You could easily play around and do similar with a cheap secondhand Newtonian. take it apart, clean it, play around with the mirrors etc, and you will learn a lot. You’ll certainly learn how to collimate. All without fear that if you do completely mess up, you haven’t lost much.

Edited July 28 by PeterStudz

[TiffsAndAstro]

59 minutes ago, PeterStudz said:

I see that the telescope in question has now been sold. @TiffsAndAstro did you get it?

Personally, I don’t think this is such a bad idea. And for that kind of price you can’t go wrong. I have a little SkyWatcher Skyhawk 1145p and for a visual grab-and-go/travel telescope it’s surprisingly good. Especially on a more solid mount & tripod. 

As a beginner, with only a few months experience, I restored a 200p Dob. I only fully understood collimation after I’d stripped it down and put it all back together. Before that time I thought I’d understood but I hadn’t. I can well remember taking a day off work to flock the entire OTA, which required stripping down to just a bare tube. I already taken the mirrors out before so had some experience and slight confidence. But I was surprised how quick I managed to do it. And I had the whole thing back together, collimation spot on, in time to look at the moon in the evening.

You could easily play around and do similar with a cheap secondhand Newtonian. take it apart, clean it, play around with the mirrors etc, and you will learn a lot. You’ll certainly learn how to collimate. All without fear that if you do completely mess up, you haven’t lost much.

That was sort of my idea. Worst that can happen is I waste £30.

Didn't win it, but there might be others.

I even started thinking, I'll just build my own. After 5 minutes thought I decided not to

IM not entirely sure how to spot a bird Jones and avoid it, except they mostly longer focal length and bigger f numbers? 114mm primary  and 450 to 500mm FL and I should be safe ish?

not planning on refurbishing a 200p any time soon

Edited July 28 by TiffsAndAstro

[TiffsAndAstro]

1 hour ago, PhilB61 said:

One additional thing to consider is that not all cheap "visual" Newtonian may have enough focuser "in" travel for a camera to reach focus. There are ways around this, longer collimation screws may help or relocating the primary mirror cell further in the tube. Yes, some do cut down the focus tube to reduce intrusion, but may not be required if one of the other options above is done. Lots image with the 130pds with good results.

I see plenty of nice results from newts just wondered if cutting focus tube helped reducing instructions.

After dismissing my idea of using a super conducting levitating secondary, I decided might be best to stay traditional for now

I'll keep a look out for a 114mm f4 to F5 and take a chance if a cheap one turns up. Hopefully not a bird Jones.

[CraigT82]

You can spot a bird jones usually by the length of the OTA, overall it will be quite short for the advertised focal ratio. E.g. 125mm F8 (1000mm fl) but OTA is only about 500mm long. 

[PeterStudz]

Just now, CraigT82 said:

You can spot a bird jones usually by the length of the OTA, overall it will be quite short for the advertised focal ratio. E.g. 125mm F8 (1000mm fl) but OTA is only about 500mm long. 

That’s about it. 

Also make sure that the primary isn’t fixed. A few of the smaller and newer reflectors have a fixed primary. Obviously if you want to fiddle with collimation you don’t want that! Look for collimation screws at the end of the OTA. 

If unsure just ask on here. There’s some very experienced and knowledgeable people on this site! 

[happy-kat]

The ones with fixed primary mirrors tend to have adjustable secondary mirrors

[TiffsAndAstro]

1 hour ago, CraigT82 said:

You can spot a bird jones usually by the length of the OTA, overall it will be quite short for the advertised focal ratio. E.g. 125mm F8 (1000mm fl) but OTA is only about 500mm long. 

Top tip tyvm

[TiffsAndAstro]

34 minutes ago, happy-kat said:

The ones with fixed primary mirrors tend to have adjustable secondary mirrors

I assumed every newt even bad ones would have both mirrors able to be adjusted. I should avoid ones where primary can't be adjusted then?

[pipnina]

2 hours ago, TiffsAndAstro said:

I assumed every newt even bad ones would have both mirrors able to be adjusted. I should avoid ones where primary can't be adjusted then?

Definitely avoid ones where the primary is fixed in place.

I saw you mentioned a 130mm being too heavy? I'd say that's the absolute smallest I'd want to go for a newt since the ratio of primary mirror size to secondary size + sensor illumination coverage gets progressively worse as you go smaller (for the same focal length)

But 130 is a good sweet spot, and most of the good cheap newts are found in 130 or 150mm sizes. People have a lot of success with the TS Photon 6" (maybe not the 8", which I tried and found it too heavy for its own strength to support), and people also find a lot of success with the 130-PDS however it will have slightly odd star shapes unless you very carefully trim the length of the focus tube as it intrudes quite far into the optical path for imaging.

I would not recommend a mono cam for either, as it will be too heavy and apply too much torque on the focuser and thin sheet metal tube once you add a filter wheel.

[TiffsAndAstro]

2 minutes ago, pipnina said:

Definitely avoid ones where the primary is fixed in place.

I saw you mentioned a 130mm being too heavy? I'd say that's the absolute smallest I'd want to go for a newt since the ratio of primary mirror size to secondary size + sensor illumination coverage gets progressively worse as you go smaller (for the same focal length)

But 130 is a good sweet spot, and most of the good cheap newts are found in 130 or 150mm sizes. People have a lot of success with the TS Photon 6" (maybe not the 8", which I tried and found it too heavy for its own strength to support), and people also find a lot of success with the 130-PDS however it will have slightly odd star shapes unless you very carefully trim the length of the focus tube as it intrudes quite far into the optical path for imaging.

I would not recommend a mono cam for either, as it will be too heavy and apply too much torque on the focuser and thin sheet metal tube once you add a filter wheel.

appreciate the advice, i was really looking for a 4.5" / 114mm just for lightness, im not expecting to do anything more serious than break its collimation

[Clarkey]

On 28/07/2024 at 16:00, pipnina said:

People have a lot of success with the TS Photon 6"

For the F5, maybe. I have the F4 version and it is not too impressive. At very least needs a new focuser, shower cap, mirror mask and ideally a new spider. Once up and running it is OK, but you are better off buying a good one to start.

[TiffsAndAstro]

2 minutes ago, Clarkey said:

For the F5, maybe. I have the F4 version and it is not too impressive. At very least needs a new focuser, shower cap, mirror mask and ideally a new spider. Once up and running it is OK, but you are better off buying a good one to start.

there's almost no chance me doing all the stuff cuiv did to 'fix' his newt(s) so if i did ever buy a proper one after practicing on a cheap ebay special i'd want it to not need most of that doing to it

[Astronomist]

1 hour ago, TiffsAndAstro said:

practicing on a cheap ebay special

I'd go for a used Skywatcher Skyhawk 1145P (not the 1145ps, that has a non-collimatable primary). Yeah it's no good for imaging and has a nasty focuser, but you can get one dirt cheap and it'll work just fine for learning collimation.

[TiffsAndAstro]

57 minutes ago, Astronomist said:

I'd go for a used Skywatcher Skyhawk 1145P (not the 1145ps, that has a non-collimatable primary). Yeah it's no good for imaging and has a nasty focuser, but you can get one dirt cheap and it'll work just fine for learning collimation.

Ty for the suggestion will have a look

Edited July 29 by TiffsAndAstro
god knows why i typed meat

[bosun21]

For that sort of money it's a good idea. I would definitely stay at the f5 or higher for ease of learning collimation. Even when I went down to f4.7 with my 250mm go to dobsonian I definitely noticed it was more difficult and finicky to set collimation on as opposed to my previous 12" f5. Good luck.

[TiffsAndAstro]

So a very kind but misguided friend wants to buy me a Ty gift for helping with some stuff.

Does a new very cheap Newtonian exist that is light enough with accessories for my mount. Officially 5kgs but traditional half that which I'm sure I'm  already weigh (geddit?) over?

6" Stella Lyra on Flo is £280 which looks a bargain, but 5.3kgs alone.

Can't seem to find any 4.5" f4.5 500mm Newtonian new in the UK. Should be lighter though?

Ta for any suggestions.

This might be ok if I could get it sans eq1 mount?

https://www.opticalvision.co.uk/beginners-telescopes/skyhawk-1145p-eq1.html

Skyhawk has a non collimattable primary it seems

Edited July 31 by TiffsAndAstro