dob question

[coffee_prince]

if I am using a dob at high mignification will I constantly be having to nudge it to keep somethign in view? How much of this is an issue?

I was planning on getting a dob with something like a powermate etc but read this might be a problem as the small field of view means I'd have to be constantly readjusting..

Thanks

[Doc]

One way round this is to use wider field of view eyepieces such as the 82° and 100° ones.

Another way is to motorise your dob with tracking.

[John]

If it's a non-tracking dob then, yes, you will need to nudge the scope to track objects at high power.

Some people find this annoying so prefer driven mounts (eg: an equatorial) and others find it no problem. I'm one of the latter sort but I do use very wide angle eyepieces which help keep objects in the field of view for longer.

Obviously as the magnification increases, the field of view decreases and tracking becomes more challenging. Most people seem to find they can track at up to 250x OK - above that and you really have to concentrate !.

Edit: Doc and I were obviously typing at the same time !.

[coffee_prince]

thats a little depressing :s

Is this a real dealbreaker? I mean I've read so much about the positives of dobs but I've only just encountered this issue, I didn't think you'd need to move it that often, would the image really move out of sight that quickly?

[Moonshane]

I have two dobs, both of which give magnifications up to about 500x which I occasionally can use on the moon. The eyepiece I get this level of power with has a field of 50 degrees which is pretty standard for plossls and other cheaper eyepieces. Although you do have to keep 'nudging' the scope, after a couple of sessions, you'll not even think about it, it's an intuitive process. More usual magnifications are maybe 100x and 150x and at these levels, it would take a target a good minute (I am guessing but it's a fair amount of time) to get across the field. The wider the field, the more time you have without nudging. Eyepieces with good sharpness across a wider and wider field are generally more and more expensive but if you can cope with slightly soft images across the outer quarter field say, you can get good 70 degree eyepieces for maybe £40-50 each.

I tend to get the target in the right of field and watch it drift across left (it's actually going the other way but the view is upside down in a reflector). Doing this you are not constantly moving the scope.

Unless you are likely to get into imaging later (in which case you can add a dob tube to an EQ mount) then a dob is a good choice as the money goes into the optics and not the mount. I love 'em.

Powermates are good but I sold mine as I felt it stuck out too much with the eyepiece in too and also, the weight was a bit much in a dob particularly. I just have eyepieces now. With four well spaced focal length eyepieces you don't really need a powermate. Horses for courses really. The powermate does not change the field of view, it's the higher magnification. EG an Ethos has a 100 degree field and using a powermate with one, the field remains at 100 degrees. But with a 2.5x bigger image you fit that factor less of sky in the view and therefore the earth appears to move 2.5x faster. hope this gibberish makes at least some sense.

[Moonshane]

thats a little depressing :s

Is this a real dealbreaker? I mean I've read so much about the positives of dobs but I've only just encountered this issue, I didn't think you'd need to move it that often, would the image really move out of sight that quickly?

if the cloud ever clears tonight I'll do some timings for Jupiter across a 50 degree field at 145x. personally, I'd say it's really not an issue. you don't ever (or rarely) feel like you are chasing things, it's a leisurely nudge and watch, nudge and watch.

[coffee_prince]

Thanks for the replies!

Going to buy the skywatcher 8 incher dob, but alot of threads have suggested that buying a barlow/powermate is the best thing as it doubles your eyepiece set?

I probably have a few bob extra (total budget around £450 with £270 for the dob) to spend so I am wondering how to divide that against any other paraphernalia I may need e.g. barlow/eps/collimator etc?

What do you all recommend?

I was also wondering whether a cheap dob will limit the benefits and use of expensive eps? You all know what I mean, some of these eps cost more than the telescope themselves!

[Moonshane]

the SW 8" dob is a fab starter scope and in fact many people would be happy with it all of their life, especially if you have a reasonably dark site - not essential but darker the better.

a barlow/powermate does indeed double your eyepieces but I prefer the simpler approach. I'd recommend a Powermate over a Barlow as in my experience I have never had a Barlow anywhere near as good (but Powermates are about £100 used and you could get three new and reasonable quality eyepieces (like the Explorer here 1.25" Eyepieces) for the same money.

I see the following as essential to make your viewing more successful and enjoyable:

Telrad / Riger Quickfinder - does not matter which - I prefer the Telrad.

Right angled finder (the Orion USA 9x50s are excellent).

Wide field low power eyepiece - maybe a 30-35mm.

Some kind of collimation tool - probably a Cheshire eyepiece.

The above should leave you with enough money to buy eg two of the explorers (maybe the 8 and 12 giving 150x and 100x) which will replace the 10mm which is not normally too good, and compliment the 25mm with the scope (usually OK) and the above wide field.

These are just suggestions and others may differ so take further advice from here and from the supplier (I recommend FLO (click the link at the top) or buying used off this forum for an even better bargain.

Regarding top quality eyepieces, John and I like Televue. These are superb but expensive. Mick (Doc) has the William Optics UWANs and these are brilliant too and a lot cheaper but almost as good as TV.

Better eyepieces can make an average scope perform to its best. Poor eyepieces can make the best scope in the world seem rubbish. My view is that we get inadequate opportunity to observe so get the best gear you can afford and make the most of the opportunities you get - buying top quality gear used is a good way to get them at discount and they also hold their value better. Finally, TV eyepieces can be used in any scope down to F4 (the lower the focal ratio - yours will probably be f6 the 'faster' the scope and the harder an eyepiece has to work to give a good image across the whole field, hence to do this they get expensive but the results from eg the Explorers and others will be pretty pleasing too)

[Moonshane]

just had a quick check now as the cloud is just thin enough to see J. it took it well over a minute to go from edge to edge in my 11mm Plossl at 50 degree field and 145x magnification. this works approximately incrementally as you increase magnification so at 290x it would take about 30 seconds. the wider the field of the eyepiece or the lower the magnification with the same field, the more time it takes to 'transit'.

[NGC 1502]

A Dob with smooth motions is great to use, but if the movements are sticky

it can be a real pain, so it's worth spending time to sort this as best you can.

If the azimuth movement is sticky, then a centre bearing, often made from

thin plastic, can ease the weight from the teflon, and help a lot.

The Meade Lightbridge Dobs have a "lazy susan" bearing, some don't like

this, but I've tried a clubmates and found it good.

Some do use Dobs at high power, but most observing is done at lower

powers, I use 44x, 92x and 150x most of the time, so tracking objects

is not much of an issue for me.

HTH, Ed.

[John]

Great advice from Shane there. The Skywatcher dob may not cost a lot but it's a great instrument - at F/6 it's a really good all round performer and, like practically all scopes, will benefit from good quality eyepieces.

On the tracking issue - dobs are amazingly popular scopes worldwide - if this issue was really a "dealbreaker" then they would have never achieved that level of popularity.

Anyway, you can always put the optical tube from the 8" dob onto a driven equatorial mount at a later date if you find you would like a driven scope.

You don't need to spend a fortune on eyepieces to get satisfying views - with an F/6 scope there are a number of eyepieces in the £30-£60 range that perform very well.

[great_bear]

I'm not a dob owner.

I'm one of those with a scope mounted on a powerful, tracking equatorial mount.

However, what I gain in precision tracking, I also lose in convenience: I always have to think twice about going outside because of the length of time not only setting up, but in breaking the kit down afterwards when I am tired.

Also, there are some targets - such as the moon for example - which look very dramatic when you allow them to drift past.

If I were starting again from scratch I would probably get a Sky-Watcher 200P Skyliner, and a small collection of three or four widefield eyepieces.

Since the 200P is an F6 scope, the widefields need not be the most expensive ones.

[Beulah]

I'm a happy dob owner and those high mag viewing sessions doesn't really bother me as it's only though brief moments of atmospheric stillness you capture those details, although I am seriously thinking about making an equatorial platform...

[coffee_prince]

Okay guys thanks for all the helpful messages!

I'm on my way to check out the telescope shop, I have no idea what ep's to buy so probably going to get them later but I was thinking the powermate 2.5 and also an WO uwan ep but not sure which size, I think 16mm will give me 75X

I don't mind splashing out on one or two nice ep to start me off with

Telescope comes with 10mm and 25mm which will obvious get replaced after time

Thanks

[Chris H]

Just get the scope first worry about ep's and barlows/powermates later. Good luck.

[great_bear]

I was thinking the powermate 2.5 and also an WO uwan ep but not sure which size, I think 16mm will give me 75X

Well, I'm selling my 16mm WO UWAN for £99 here on SGL <click here>. Eyepieces bought second-hand tend to keep their value.

[lguise]

Buy the scope but hold off on the powermate!

Try it first and enjoy it. As advised play around to get the motion as smooth as possible then you will not have a problem just sliding the scope to track an object.

There are loads of good but relatively low price eyepieces for high power. I use the Burgess/TMB 9, 6 (and 5mm on occasions when the seeing is good). They cost £40-£50 each have a field of view around 60degrees and are fantastic on planets.

A powermate is an expensive item (assuming you mean a Televue Powermate) A second hand Barlow may be OK but on a smaller Newtonian I don't like to have too much sticking out the focusser.

Good luck and enjoy!

Linton

[johnkirkpatrick]

I agree get the scope first I went from eq to dob and its fantastic mate, the "nudging" is easy and not that bad at higher mag, wider angle eps are fantastic though I have the meade 5000 swa 20mm and have fell in love with it

[LukeSkywatcher]

I have to agree with everyone else who said that manually tracking an object with a Dob is not really that much of an issue. In fact i wouldnt consider an issue at all.

[twotter]

I've got a Skyliner 200P dob and I've turned out to be more of a 'drifter' than a 'nudger'

With EPs I've spent ages looking at the pros and cons of various models, trying to decide which ones I will eventually buy. I also opted to buy a range of cheaper EPs to see which sizes I use the most. Hopefully that way I will be able to narrow down what to buy in the future.

I've also found myself toying with ideas for new scopes....maybe a goto Flextube, or a SCT, or maybe put my OTA on HEQ5 Pro???

Decisions, decisions

[coffee_prince]

Hi guys, I'm back from the shop.

Unfortunately most of their stuff isn't in stock as its ordered in or shipped straight from the supplier. They didn't have any telescope I could play around with.

They did have an Orion Dob Intelliscope in the display window, I was tempted but had little information on it so stuck with the Skywatcher.

I ordered the Skyliner 200, so it will arrive next week!

Will hold off on the EPs for now

Yes, I was interested in the televue powermate, will probably buy at a later date

[Moonshane]

this is a great move. you'll not regret this purchase.

I agree on holding off and buying eyepieces to meet your needs based on your observing.

the Telrad though would be a smart purchase from day one - it just makes it so much easier to put the scope in the right place.

[johnkirkpatrick]

You will love it mate, such a great scope, the supplied eps are not to bad but still not great, but try them out then decide on the eps at a later date, I went for individual ones and got a few good ones for the same price of a set, anyways fantastic buy

[dweller25]

Great choice and £265 well spent.

[Merlin999]

Hi coffee,

Just read through your thread. You got some very useful comments there. I'll be looking forward with interest to see how you get on with the dob, especially as you had the same concerns as me about tracking.

You must be very excitied now you've made the purchase.