pitfalls in buying a used dob (are there any ?)

[mikebee]

after weeks & weeks of deliberation on what to buy I have finally concluded that aperture is king & the way forward is to buy the largest dia that my frail arthritic frame can manage, I have a max of £300 in the budget for my first scope & initially considered a 90 or 102 mak or even  a skywatcher heritage 130p & some extra lenses,  I don't want a "go to" & have finally decided  a 10" dobsonion would be a good choice to own, however this would mean going down the used route with the words "buyer beware " ringing in my ears, I would only buy something that I could inspect & collect so that may restrict an auction site purchase, what sort of things could go wrong with a used dob, I have seen some advertised with the words , mirror may soon require recoating, how do you spot this or is this something that happens to all scopes at some time, any advice on this or anything else that could go wrong would be appreciated, it has taken me a couple of months to get to this stage & I am happy to bide my time until the right thing comes along, thanks, mike b.

[Joseki]

Mirror coatings do fail eventually but you don't want to buy one that needs that doing unless you've already know how much it's going to cost to get done (plus a bit for the hassle IMO).  The mirrors should be shiny and without any obvious flaking of the coatings - dust on the mirror is not anything like the same issue and can be cleaned at home (assuming you're happy removing the mirror).  Shining a light behind the mirror should show if there are patches where the coatings have failed (if you can see the light coming through on the other side).  For dobs this size you'd find it difficult to buy replacement mirrors for much less than the price of the whole scope - which should tell you something about it's value with bad mirrors.  Other issues I can think of are the condition of the dob mount (has it gone crumbly, cracked etc) and whether the mount moves smoothly (fixable with a bit of effort).  The focuser should also move smoothly (since you won't want the hassle of fixing or replacing that).  Actually looking through it is also a good idea 

hope this helps

[red dwalf]

there`s not too much that can go wrong with a dob, just looking at the mirror you`ll see any defects but to be honest the modern day ones are robust, mirrors are very good, check the focuser works ok and smoothly and thats about it, you could buy a new 8" dob from First light optics for £279 and a new 10" for £435, a bit over budget but worth it.  

[Laurie61]

I would echo the words above, if you have not discovered it already this site specialises in second hand astro equipment.

http://www.astrobuysell.com/uk/propview.php?titlechoice%5B%5D=For+Sale&minprice=&maxprice=

[valleyman]

after weeks & weeks of deliberation on what to buy I have finally concluded that aperture is king & the way forward is to buy the largest dia that my frail arthritic frame can manage, I have a max of £300 in the budget for my first scope & initially considered a 90 or 102 mak or even  a skywatcher heritage 130p & some extra lenses,  I don't want a "go to" & have finally decided  a 10" dobsonion would be a good choice to own, however this would mean going down the used route with the words "buyer beware " ringing in my ears, I would only buy something that I could inspect & collect so that may restrict an auction site purchase, what sort of things could go wrong with a used dob, I have seen some advertised with the words , mirror may soon require recoating, how do you spot this or is this something that happens to all scopes at some time, any advice on this or anything else that could go wrong would be appreciated, it has taken me a couple of months to get to this stage & I am happy to bide my time until the right thing comes along, thanks, mike b.

Just be warned the 250 dob is a big beast. Generally speaking Astronomers tend to look after there kit, so like already suggested Astrobuyandsell is a good way to get one. 

Also once you have 50 posts on here you will get access to the Classifieds.

[Dude_with_the_tube]

Dob is so simple construction  that there is very little to none to go wrong.All it is a piece of tube with main mirror and reflecting mirror.These are the main components you need to pay your attention on when buying second hand.People above already described the possible issues with the mirrors,as such taking all that into consideration,i would still recommend to go for a s/h unit,specially being on budget.Aperture rules as you mentioned,so get your moneys worth from s/h market as time to time some real bargains pop up and dont be worried about buying a dud one.ABS is generally a good site to look for and majority of astronomers are genuine people and will not try to flog you a daft instrument and will tell you if there are any issues with the scope.Fleebay could be a lottery sometimes.

Good luck in your new venture.

[dannybgoode]

+1 to astrobuysell.  Ask the seller plenty of questions and see if the responses seem well thought out and from a knowledgeable person.  A bit subjective I know but as per the above astronomy is one of those hobbies where there is a certain passion and a willingness to pass on experience to newbies and this comes across when buying used kit.

I was in your position, asked a couple of questions and got a very detailed response explaining the full history of the scope, what I would need in addition to the scope, how they had used it, some sample astro images they had taken with it etc.  yes it could have all been a bluff but certainly would have took more effort than it was worth.

As with anything though the old adage if it looks too good to be true applies here also.  

As a point of reference I managed to get a Skywatcher 150P OTA with the stock 10mm & 25mm EP's and the 2x Barlow and a Skywatcher AZ4 mount for £135.  Roughly half the RRP.

[mikebee]

hello, thanks for the replies, haven't seen the astrobuy site before so just had a look round on there, I have looked at the 200p on flo's website & it does seem a good buy, plus they are only 20 minutes from where I live, however for the time being I think I will hold out for  a used 250 dob as I think the extra viewing will outweigh the extra bulk, any other ideas/advice welcome, mike b.

[Northern Soul man]

Hi Mike, a very warm welcome to the SGL mate.  I think that the second hand market for scopes is quite a good start, I think you have researched well enough by the sounds of it.  You could possibly try some of the Astro Societies if its not been mentioned - just to have a look and a look through any scopes they have - they will be more than willing to let you try before you buy.

Excellent advice from above (not heavenly though !!!) pardon the pun, have a look at the event threads - some meet up, not sure how far you are away from the Norman Lockyear Observatory - they seem a very nice bunch and have a wealth of experience - I met them from my other hobby  - Amateur radio - they have open days and I think evenings as well - so might be worth a trip for you - just have to get the weather right though - as always a little hit and miss here in the UK.

The 10" dobs are very big instruments - I had a 12" for a while - I could just about manage it on my own - but really nice views through it.

Keep us informed of how you get on - try the societies if you can - really ask a lot of questions and get a feel for the purchase - they will only be too willing to help/advise you.

Paul.

[Myopicus]

There's loads of immaculate scopes out there on the 2nd hand market - many peeps buy and never use (but perhaps thats not the case for Dobs, because of their ease of use? dunno.)

A warranty and a reputable supplier is worth something, definitely.

The 200p is a fine scope, don't rule it out - it's the country's best selling scope for a reason!  

[mikebee]

just had a look on the norman lockyer observatory website, they are  only 40 minutes drive from where I live & have the south west astronomy fair on 9th August which is not too far away, so that will be pencilled on the calendar, if I haven't found anything by then hopefully there will be plenty of scopes to try out, mike .