Revelation 8" Dobsonian

[AliMac]

Hello all.

I wonder if anybody has any experience/knowledge of the above. I just bought one on ebay for £120, and at the moment I'm feeling like it was a good buy. That said I havent seen it in the flesh, as I'm picking it up tomorrow.

I've been thinking of getting a Skyliner 200p, and I really wanted to know how the two compare. Does the Revelation have a parabolic mirror for example?

Also, apologies to anyone I pipped at the post for it...

Ali

[LukeSkywatcher]

I dont know this scope but have just googled it:

http://www.myforumab...or-other-255912

http://www.skyatnightmagazine.com/forum/revelation-8-dobsonian-telescope-feedback-t5791.html

Its seems like a good scope and £120 seems a good price.

I just hope it is in good nick. Have you even seen pics of it?

I cant find anywhere that says if the mirror is parabolic or not. I guess if it was, someone would have mentioned it.

[AliMac]

The seller provided four pictures, which seem to show it in good nick externally. One shot showed the primary, which the seller indicated may need cleaning. I think the shot confirms that, but I feel reasonably confident I can do that.

Hey ho! I'll find out tomorrow!

[LukeSkywatcher]

Just out of curiousity, can you post the pics?

[AliMac]

Hi Luke,

I can't seem to extract them from the Ebay page, but I think this link should take you to it;

I should have said thanks for googling it earlier!

Ali

[LukeSkywatcher]

Not a lot to go on with those images but overall it looks like a well cared for scope. If the primary needs a clean...........thats not a big deal.

[John]

I had a Revelation 8" dobsonian a few years back. It was a decent scope - very similar to the Skywatcher 8" dobsonian in performance. It certainly had a parabolic primary mirror. The only issues of concern that I noted with it were that the chipboard base was prone to absorbing moisture at the edges and swelling a little and that coatings on the primary mirror did not seem that durable - I think mine would have needed re-coating within a couple of years. They were sold by Telescope House quite a few years ago and I think cost £199 new at one point, which was a bargain.

[LeeB]

the revelation scopes i've looked through have been good and i'm sure they are parabolic, they are back again and currently available at telescope house. I love there cheap 2inch eyepieces , the 43mm version gets most use as my hunter eyepiece.

[AliMac]

Thanks for all your replies! I now have the scope safely in my possession. I've had a quick look through it at a neighbour's chimney pot, and the view seems ok. However, the mirror has quite a large blemish on it, as you'll see below. I have no experience of mirrors, so could anyone tell me if this is sufficiently dreadful as to warrant a clean, or even, heaven help us, a recoat?

I suspect I won't get a chance to test it properly for a while yet, given the clouds that are rolling in even now...

Ali

[LeeB]

please describe the mark, is it missing aluminium or just dirt, are there any scratches or chips and how shiny is the mirror surface in general, when doing this don't touch the mirror!!!

[dtr42]

looks like the aliminium is/has broken down and maybe someone has had a go at cleaninig it , however try it on ths sky at night when its clear as the mirrors can get suprisingly dirty but still produce decent results , good luck

[Hals]

I have a nasty scratch on my 6" Dob's primary but to be honest, I don't find the views any different to what I remember them prior.

I agree with dtr42, looks as if it's a scouring mark. Hopefully it's just dirt !

[LeeB]

if it is a recoat don't panic galvanoptics do it for around £68 plus post including flat, then as good as new.

[dtr42]

a recoat starts making the scope expensive if you can live with it then i would [at least till i got some use out of it

[AliMac]

Having spent the last couple of hours looking at it, I think you're both right about it being scouring marks. Also, from what John said above, and from other info gleaned from Google, it seems that the coatings on this model are prone to deteriorating. I guess someone saw the black dots, thought they were dirt, and had at them with a cloth causing a bit of scratching to the surface of the mirror. If it turns out that the scratches are too severe, will recoating the mirror solve the problem? I presume the process involves removing the reflective layer. Are telescope mirrors coated from the front or the back? What I'm getting at is whether the scratches to the mirror surface would be removed by recoating.

I've just had another try on a more distant chimney pot and the view seems fine. I'll give it a try on stars as soon as any deign to appear. I imagine that'll be in a week or two.

Thanks again for all your replies.

[dtr42]

think they strip it in a chemical bath [so it peels the aliminium of the mirror blank then they re aliminum it and seal it with an overcoat [think its quartz ] they may ask for a picture of the mirror and the scratch may still be there but the alumium will likely cover it [takes about 3-4 weeks £69 plus postage

[John]

Assuming the collimation is reasonably on song the scope will probably perform OK. It's amazing how bad the coatings have to be before the views start to suffer noticeably. The condition of the mirror will probably play on your mind though so getting it re-coated might be worth considering in due course to give you peace of mind that you are getting the full performance a decent 8" mirror can give.

[knobby]

As the others have said ... it takes quite a build up of dirt to make a difference to viewing, there's a thread on here somewhere about a filthy, and I do mean filthy mirror seen on TV in an observatory and that seems to work fine !

get some use out of it, I'm sure it'll be fine.

If you get the chance to look through another 8" to compare it, then worry if yours is not quite up to scratch.

Enjoy

[AliMac]

think they strip it in a chemical bath [so it peels the aliminium of the mirror blank then they re aliminum it and seal it with an overcoat [think its quartz ] they may ask for a picture of the mirror and the scratch may still be there but the alumium will likely cover it [takes about 3-4 weeks £69 plus postage

Thanks for that. I hope it won't be necessary, but it's good to know that the nuclear option is likely to have the desired effect!

Assuming the collimation is reasonably on song the scope will probably perform OK. It's amazing how bad the coatings have to be before the views start to suffer noticeably. The condition of the mirror will probably play on your mind though so getting it re-coated might be worth considering in due course to give you peace of mind that you are getting the full performance a decent 8" mirror can give.

I'm also very reassured to read the above! Is it a question of the amount of light reaching the eyepiece being diminished by a mucky/scratched primary, or should I expect visual effects as well?

[John]

Thanks for that. I hope it won't be necessary, but it's good to know that the nuclear option is likely to have the desired effect!

I'm also very reassured to read the above! Is it a question of the amount of light reaching the eyepiece being diminished by a mucky/scratched primary, or should I expect visual effects as well?

Reflectivity will be reduced so the views of dimmer objects might not be as good as they could be. Scratches / flaked coating can cause light scatter which could reduce contrast and sharpness.

As has been said, you may not notice any issues unless you compare the view through your scope with one with a pristine mirror or perhaps as you look at objects / features which are pushing the scope, performance-wise, eg: it might not be quite as easy as it should be to resolve the Cassini Division in Saturn's rings, the Great Red Spot on Jupiter, split a close binary star or detect one of the fainter deep sky objects.

[LeeB]

I'm just about to send my 8.5 for recoating, its at the point that a torch from the rear is very visable, but still works ok, I just like a shiny thing!!! its not done bad last recoat 1974!!!!!

[umadog]

Pull out the mirror and look at it carefully. Use a magnifying glass. If those are really scouring marks that have damaged the glass then that seller should be getting negative feedback. That would be more than just a cosmetic issue. He hasn't mentioned it in the advert. Clean the mirror properly (Google the cleaning procedure). Then look at it again. I'd consider a re-coat on that one.

[dtr42]

i always look at money being paid out is bad, if i can use something and it works reasonably then i live with it,but if the guy has taken a brillo pad to the mirror then would be opening a dispute with him as the mirror isn't just dusty ,but as has been mentioned the mirror can often be covered in dirt dust but is still useable ,again it would be good if you could get a similar 8" at an astro meet/starparty to compare it . I hope that you get great use and enjoy your new scope no matter what happens

[AliMac]

Well, first light. The images seemed just as sharp as with my refractor, and I couldn't make out any visual problems caused by the blemish on the mirror. I'll see how I get on with it over the winter, and I'll probably try to get a recoat next summer. I think it probably needs collimating as well, but I think I'll get by for a while at least.

I didn't have much time tonight, but got nice views of M13 and M31. With the former I feel sure I could make out some speckliness with averted vision, which is definitely a step up from my 90mm. I really need to look into getting a right-angled finder though; my neck is killing me....

So, sigh of relief, I'm reasonably satisfied that I've not wasted £122.

Thank you all again for your replies. I'm constantly amazed at just how helpful everyone is on this board.

Cheers,

Ali