Questions For The Dob Mob.... (Particularly Oo Dob Owners)

[Helen]

I am loving my new dob (well the twice I've managed to use it so far because of poor weather   ).  I've just ordered a secondary mirror dew heater though as dew has been a problem on both nights, the fan did seem to make a difference for the primary second time out

I've got a  few questions though....

Firstly, a really basic one about collimation for the OO owners - ummmm which of the knobs are the collimation knobs and which the locking    I would have thought the thumb knobs were the collimation, but there's a little sticker that says 'finger tight only' under the thumb knob which makes me wonder whether its the locking knob...

The scope is fully flocked, but is unsticking in a few places, with one particularly sticky-outy bit, but its a long way down (and I only have short arms!) - any suggestions on ways to get it stuck back without taking the mirror off?

And thirdly, much more generally, what is your favourite eyepiece for these big fast-ish scopes?  I've got a 28 UWAN, and have enjoyed my 24 Pan in it too so far, but wondering whether a longer focal length might be good and whether I'll need a coma corrector?

Thanks

Helen

[brantuk]

What aperture is your dob Helen - and how long are your arms? lol. You've got two very nice eyepieces there that work well in most dobs of 8" plus. I like the 35mm Panoptic in my 16" - M31 is particularly spectacular.

For a peeling flock one of the best things to use is a can of carpet glue spray. But I wouldn't recommend doing it with the mirror in situ. Sorry I'm not familiar with OO colli/lock screws but hope I've helped a bit.

[John]

Hi Helen,

Mine might be an older design mirror cell but my collimation knobs are knurled brass and around 15mm in diameter and and the locking screws (which I don't use) are plain hex screws. I have a fan on the back of the cell but thats something else that I don't use. I've not had dewing issues with my scope to be honest with you.

I have mine flocked opposite the focuser and around the primary but not the whole tube. I guess a pole with rounded end might be OK for pressing down the flocking that is sticking up in yours ?. That is a disadvantage with the solid tubes when they get large !

I don't use a coma corrector with mine (it's F/5.3) but the favourite eyepiece bit is tricky because it depends on the target, conditions etc, etc. I have the 31mm Nagler and the 21mm Ethos and the latter is much more often in the scope because of the moderate LP my garden suffers from. The 8mm Ethos is another firm favourite being a great small DSO / globular busting eyepiece.

I'll be interested to see what other OO dob owners come up with

[Helen]

What aperture is your dob Helen - and how long are your arms? lol. You've got two very nice eyepieces there that work well in most dobs of 8" plus. I like the 35mm Panoptic in my 16" - M31 is particularly spectacular.

For a peeling flock one of the best things to use is a can of carpet glue spray. But I wouldn't recommend doing it with the mirror in situ. Sorry I'm not familiar with OO colli/lock screws but hope I've helped a bit.

It is a 14 inch f4.6 and as for my arms, well given the tube is longer than I am tall

The 35 Pan sounds good

Helen

[Helen]

Hi Helen,

Mine might be an older design mirror cell but my collimation knobs are knurled brass and around 15mm in diameter and and the locking screws (which I don't use) are plain hex screws. I have a fan on the back of the cell but thats something else that I don't use. I've not had dewing issues with my scope to be honest with you.

I have mine flocked opposite the focuser and around the primary but not the whole tube. I guess a pole with rounded end might be OK for pressing down the flocking that is sticking up in yours ?. That is a disadvantage with the solid tubes when they get large !

I don't use a coma corrector with mine (it's F/5.3) but the favourite eyepiece bit is tricky because it depends on the target, conditions etc, etc. I have the 31mm Nagler and the 21mm Ethos and the latter is much more often in the scope because of the moderate LP my garden suffers from. The 8mm Ethos is another firm favourite being a great small DSO / globular busting eyepiece.

I'll be interested to see what other OO dob owners come up with

Thanks John. I've got an 8mm ethos, which actually hasn't had a huge amount of use - it framed the double cluster brilliantly in my Megrez 90 when that was my main observing scope.. I have found that too dewed very easily - I may just breathe too much!!

Helen

[John]

.... I have found that too dewed very easily - I may just breathe too much!!

It might just be the Welsh climate !

Have you tried wearing a mask and snorkel when observing ?

It doesn't help but we could all have a giggle at SGL XI

[Peter Drew]

Just a comment on long focus eyepieces on fast telescopes. You don't really want to go below 4x the aperture on magnification or the exit pupil gets too large and wastes aperture. This equates to about a 28mm eyepiece for 56x on a 14" F4.5. A 35mm eyepiece would provide only about 46x.

[Scooot]

On mine the collimation knobs are spring loaded so there's resistance when you turn them either way. The locking knobs are fairly loose once loosened and I also have the "finger tight warning" next to them.

I tend to use my 17.3 and 13mm the most with my 16".

The inside black ones are the collimation knobs

Ooh that's a funny pic, uploading it has stretched it lol

[johninderby]

Hi Helen

I found a 26mm Nagler worked rather well with it.

Also found a Hotech collimator made collimation very easy.

John

[faulksy]

hi helen, i love the 13, and 8mm ethos the most with my scope and the 5mm pentax is ace as well. as richard and john says the hex bolt locks the mirror and the thumb screw is the adjuster.i use a secondary heater and a ep heater all the time. hope this helps

[estwing]

in a 14" I'd say either a 26 nag or that 28 uwan are just about right for low power...the bigger the App the less ep's you need I find...for me a 17mm ethos suits a 14/16" as a goto ep anything above,eg 18/22" its the 21 ethos . At F4.5 the coma is there but its something that you will live with or wont!!...its your choice!...BTW that 8E will soon become your fave power eyepiece..

[scarp15]

Hi, just to confirm what others have said really, 26mm nagler is just about perfect for low power, for medium and high power, 13mm and 8mm Ethos.

The inside bolts are the collimating bolts, after collimating I hand tighten the others prior to loading into the car. 

As said I think some kind of stick with a pad on the end for compressing any loose flocking material

I rarely bother using the fan and haven't really encountered drastic dew issues with the secondary, but could if required use my 12V battery for my 12V hair dryer.

In terms of coma corrector, I would personally spend the money on eyepieces. the views you get are great without, though a paracorr will clean up the image a little, perhaps something to maybe consider for a much later stage. 

I have the astrozap dust covers, breathable and more importantly do not fall off as do the supplied plastic ones

Enjoy the scope look forward to any reports

[Helen]

Thanks guys . Its clear now, but freezing, so trying to decide whether to risk it.... just getting the imaging stuff running, so will decide shortly ;-)  Mike is home early tonight though,so I should take the opportunity 

Helen

[Helen]

It is out cooling    I'm in cleaning my 8mm ethos

Helen

[estwing]

slowly increase the power on 42 and watch the detail come popping out...

[estwing]

ps....isn't it great when you start to inject excitement back into this hobby...

[Drop Of Sun]

We sold our lovely 35mm Panoptic because it looked pretty washed out to us (exit pupil too high?) in our Skywatcher 400P F4.3 dob, though I guess it will vary depending on how owl-esque your eyes are? We find the 21mm Ethos rather nice at F4.3! Sometimes I'd like to go a bit wider but it gives me something to look forward to with the smaller scopes!

Congrats on the dob!

Luke

[Helen]

ps....isn't it great when you start to inject excitement back into this hobby...

Yep, nothing like a lovely new toy to get the enthusiasm back up (thanks Johninderby for putting this brilliant  scope up for sale at just the right time   )

I managed 15 minutes before the potential snow clouds gathered, so packed away only for it to clear again   but the snow is due shortly so will leave it for now.  Good fun 15 minutes though - M42, M45, M31 and generally starfield surfing    Didn't get to use the E8 yet, started with UWAN 28....   It does need collimating properly though - so will get the hotech out tomorrow and give it a go.

Helen

[estwing]

cant wait to see it at SGL Helen...just think last year we were raving about our 63mm telementors!