refurbish Helios 8" newtonian reflector?

[pellgarlic]

Hi all. I'm hoping to get a bit of guidance as to how the more knowlegdable and experienced folk on this forum would recommend I progress with a dilemma I have...

Having recently gotten into astronomy, and having used a pair of Lidl "Rocktrail" binoculars for the past couple of months, I decided I wanted a telescope for christmas. I have had a go of my girlfriend's dad's Helios 8" newtonian reflector, which seemed ok, but he said he didn't think it was very good quality. Recent views of Jupiter on quite a clear night were good but not great, and not as good as I remember it being when I had a go of the same scope when he first got it about 10 years ago. I couldn't get a sharp image, but don't know if this was just down to lack of knowledge about how best to use the scope, and how to ensure it's collimated etc.

Having researched a bit, as far as I can tell, his Helios 8" newtonian (on an equatorial mount), bought in "Black & Lizars" in Edinburgh around 2000, has been superceded (the producers of the scope having changed the product name) by the scope known as the "Skywatcher Explorer", both of which (having the same or very similar optics) are well regarded "budget" scopes. I had all but decided I wanted the Skywatcher 8" Dobsonian before I discovered that the Helios was essentially the same scope (optically at least), so now I'm not sure it's worth getting a new one, as I have access to the Helios whenever I want really, although it will need some "fixing up".

The main factors making me unsure are:

1. I've read that the mirrors in reflectors need re-plated/re-coated over time. I'm not sure how to discern whether this is required on the Helios or not, and how much it would cost to get done if required, and how practical it is to do if required (i.e. would I have to send the whole scope away, or is the mirror easy to remove and send away separately?). A cursory glance appears to show the mirror in good condition, but I don't really know what I'd be looking for, or if it's even possible to tell with a cursory look.

2. The finder scope on the Helios isn't very useful at present, as the mount fittings are quite loose, so it wobbles about, and I think that would need to be repaired, possibly even moved to a different position (don't know if that is possible) as the screw holes have become too large for the screws holding it on to be able to achieve a tight grip. So this would add to the cost of refurbishing the scope.

3. I've read that although the optics are generally the same on the Helios and the Skywatcher, that the Skywatcher has an upgraded "focuser" - a Crayford, as opposed to the R&P (rack and pinion) found on the Helios, which was said to be "sloppy". This may be a minor factor in relation to the previous two issues.

Any input on these issues would be greatly appreciated. =)

[Chris H]

Was the Helios collimated correctly? If not this could seriously reduce the quality of the views. What magnification where you using? Was it high? It may have been the atmosphere that was causing the poor view.

Does the mirror look clean and shiny? If so its most likely its ok if not it may just need a clean. There are plenty of threads on the forum about how to clean a primary mirror.

The finder could easily be moved or better still buy a Telrad or Rigel finder and just stick it where you want it.

The focuser might just need to be dismantled, cleaned and lubricated, this may remove the slop. If not you could buy a new focuser. But if your going to clean the primary, replace the finder and buy a new focuser it might just be easier to buy the 8" Dob. The decision is yours.

[spaceboy]

I had a Helios 200P and even after a botched cleaning of the mirrors couldn't distinguish optical difference between the Helios and a new SW Explorer 200P. The finder sounds like you could get away with using larger washers. The R&P isn't too bad if you strip, clean and make adjustments. The only down side may be the tripod as I'm guessing it is aluminum and with the 200P sat on top you may experience excessive vibrations during focusing and in breezy conditions. I would stick with it as it will give you many nights good viewing for nothing. Leaving spare cash for EP's. As others have mentioned you may want to get a Cheshire and check the collimation.

[steelfixer]

Hi Pellgarlic

I own exactly the same scope as you are talking about and I would rate it as first class.

I have stripped, cleaned and adjusted the focuser as suggested by Spaceboy and find it is a lot better.

I would also suggest you get yourself a laser collomater.

To give you some idea what it is caperble of I have attached a photo of Jupiter taken through mine with a Phillips SPC 900 web cam.

[pellgarlic]

Hi. Thanks for all the replies, they're very encouraging and helpful =).

I decided to have a look at collimating the Helios, as it seemed a prudent step and potentially a large part of the problem. I've ordered a cheshire collimator from FLO, which should arrive in a few days, but have been doing what I can without it in the meantime, and I think it's highlighted the problem I had with poor views recently:

WHen looking through the focuser tube with no eyepiece inserted, I can see the secondary mirror squarely positioned in the middle, but the reflection of the primary mirror in it is off-centre (I can just see the circle that marks the centre of the primary mirror at the very edge of the secondary mirror, closest to the primary mirror). I can also see that on that edge of the secondary mirror, there is a "chip" missing, as if something has struck it. (As the telescope was temporarily stored at a "fried of a friend" of my girlfriend's dad, because he had no room for it, it may not have been treated with as much care as it should have been).

Adjusting the 3 "hex screws" on the secondary mirror's mount doesn't provide enough movement to bring the reflection into line (it hits the physical maximum short of alignment). If I lightly press the secondary mirror into the position it needs to be in, it does move, reaching a physical stopping point where the reflection in the secondary shows the primary centred exactly, but when I let go, it moves back into its "wrong" position. Is it normal to be able to move the secondary mirror like this? Or does it indicate that some damage has been done to the secondary mirror's mount (or indeed the mirror itself)? I notice that there is a small screw on the tube that the mirror is mounted in, near the edge which has the chip, but I'm not sure what it does.

The other concerns I had about this scope in comparison to its newer Skywatcher relative:

- The primary mirror - it looks a bit dusty, but still quite shiny, and I can't see any damage on it, so it's possibly fine. I just thought that the mirrors needed "redone" regularly.

- The "loose" finder scope - on closer inspection, it's not actually the mount that's loose, it's the scope itself within the "band" that holds it. I could probably just pad it with something to keep it steady.

- The focuser - I can't actually say I've had any issues with it, I was just repeating what I'd read about it from others, and as I have no experience of the Crayford focuser, I can't really say if it would make any difference to me. This focuser seems to work ok in actual fact, so I guess that was a bit of a non-issue too =)

Additional points that were raised:

@spaceboy - yeah, the tripod is a little wobbly tbh. It has been repaired in the past (the centre "tray" that goes between the legs), but I don't think that will have made much difference to it. I may investigate replacing the mount.

@steelfixer - that image of Jupiter is cracking =) That's kind of how I remember it looking when I first looked through this Helios about 10 years ago (excpet maybe not with as much detail as your image), so I hope I can get it back to full working order again.

[pellgarlic]

actually, i've figured out why the secondary mirror was moving - i removed the end-piece (secondary mirror, vanes and all), so i could get a better look at it, and found that the mirror is attached to its mount by 6 sticky "pads", two of which had become detached (likely incurred at the same time that the mirror received the chip on its edge), allowing it to "swing free". i've affixed it back in place now, so that should take care of that... =)

now i'm working on the panel at the other end (half of the hex screws are really tight, and i broke the alan key trying to remove them, so i'll have to wait til tomorrow to buy a new key), so i can give the primary mirror a clean as well.