14" Dob - Two weeks on

[kerrylewis]

I've had the big dob for exactly two weeks now and, although this is not therefore, strictly speaking, a first light report, I thought that it would be useful to share a few thoughts and perhaps get some feedback on experiences so far.

enerally speaking I have not been 'blown away' as I expected in comparison with the Celestron 9.25" but I'll be more specific below - and it is still early days.

Storage and ease of use.

There is no doubt that the Dob scores here. I have been keeping it my garage. It is much too big in any case to accommodate in the house. I already owned a small sack barrow which I bought from B&Q some time ago. This can be used in upright two-wheeled mode, or horizontal four-wheeled mode. In the 4 wheel mode the scope now sits on it permanently and I trundle it out of the garage when needed and then leave it on the barrow for observing. This means that I can move the scope during sessions to avoid obstructions  - something rarely contemplated with a fully set up mounted SCT. Cooling is not an issue either with the garage storage and not needing to supply power, do alignment etc is a real advantage and it means that I have taken advantage of short clear periods which I might not have attempted with the SCT/EQ6 set up. I am going to look at some sort of fixing to the barrow to avoid the risk of the scope toppling over during trundling but the dead weight does keep it in position and in the 'shortened' mode its centre of gravity is quite low.

Collimation

This is really simple. I already had a laser collimator which I've had for years but not been able to use much with other scopes. Now I collimate before each session, and check during a session if it's extended. The laser works simply and effectively. At first I found the alignment of the secondary to be tricky and the 'red dot' seems to want to go everywhere except in the centre of the primary but now it seems to be at least close most of the time. Is it critical to get it spot on? The red dot is then easily aligned in the collimator itself by adjusting the three thumbscrews at the bottom of the scope. 

Focus

This is tricky at times. I wanted to use my Baader Clicklock but couldn't then get the eps to focus. Most eps need some sort of extension tube to achieve focus which is surprising. Shouldn't it work 'out of the box'? Ierhaps it did with the original SW eyepieces. 

Star-hopping

With the convenience of goto, I must admit that I had got out of the habit of star-hopping buy I have slipped back into it fairly easily. The inverted finder was not easy to use in initially locating objects i found so I bought another base for the trusty Telrad and fixed this next to the optical finder. So now I quickly position the scope using the Telrad and then refine things with the finder. I have printed transparent versions of the Telrad circles and use them with the S&T Pocket Sky Atlas. I have actually enjoyed finding objects by 'dead reckoning' again but so far I have concentrated on some of the easier objects. I have found M81, 82, 78, and 51 for example without too much bother. I have also revisited the Turn Left at Orion instructions which are very good too. I look forward to ring to locate some more difficult objects.

Movement and Tracking 

I have always thought that a Dob would not suit me. Most objects, especially the planets, need some prolonged observation to achieve the best results and I thought that the manual set up of Dobs would not be conducive to this. But, having tried it, it seems to work OK. I tend to position objects on the right of the FOV and then observe them as they track across. However, while have found that movement in azimuth is fairly smooth, in altitude it's not always so. I find that I tend to over compensate in this direction and go beyond the object. But I assume that the is a matter of getting the tension correct and I will get used to it.

Observing  - planets.

I have managed a few evening and morning sessions and observed all the planets currently on show. Here I have found that it is, as always, the seeing which affects what can be seen. But in good moments it is clear that the extra aperture means that more detail can be seen. On a guaranteed clear night I intend to compare the two biggest scopes next to each other, but meanwhile on Jupiter I have seen beautiful detail around the GRS and within the cloud bands. The recent transit of Callisto was good too with the moon so dark that it looked like a shadow. So, I think that the potential for my favourite planet is promising  - just need superb seeing. An interesting feature of Jupiter at the moment is that it is located in quite a rich area for stars and looks stunning through a low-mag wide field ep - a real sense of it sitting in space

I have not been so fortunate with Mars and Saturn. There was  one period of good seeing when I glimpsed dark details and the polar cap on Mars but otherwise it has been a bit mediocre. Saturn has been similar - good at times but the Cassini only glimpsed. But I do think that things will improve as Saturn comes out of the murk a bit

Observing - DSOs 

This is where I expected to see the most difference compared with the SCT but the results have been mixed. The Orion Nebula looks spectacular as always and I think it's more so with the Dob. The green tinge is obvious and there is a 3D quality to the view. i have also seen the E and F stars in the Trapezium although I have not really looked for them before so can't compare the results.

I've looked at M82 quite a bit recently in order to see the supernova, and through the Dob the knotty detail is more apparent where the galaxy looked just like an elongated smudge in the SCT. I have really studied the Whirlpool galaxy and saw a hint of detail but it was not obvious,  and I didn't see any dark area in the Black Eye galaxy. I've clearly seen all the galaxies that I've hunted down but there has not  been the obvious difference in detail that I expected. The Andromeda galaxy would be a good comparison and benchmark I think, but it's not best placed at this time of year from my garden.

So - I've learned that there are no instant results in this hobby and that is true of my brief experience of the Dob so far. Everything is still affected and conditioned by the conditions at any time and place and until I get some really topnotch conditions I don't think i will really see spectacular results. 

Watch this space.....

Any comments or experiences would be welcomed

Cheers 

Kerry 

[crashtestdummy]

I didn't immediately notice much difference between my 12" and 16" dob until I compared them like for on objects.the 16" shows m32 and m110 from my back garden when the 12" wouldn't.same with m51 and several others.

[Paul73]

Kerry

Thanks for the first(ish) light report. Much better to have a objective considered thoughts rather than the breathless, slightly confused ramblings that come from the genuine first contact. Also, good for all those of us with appature fever. In that, size is only part of the equation (note to self - obviously need min 16" not the previously assumed 14").

I can get the dark patch in the Black Eye with my 10" SW on a good night (mag 5 ish sky) and only moderate eyesight. So it is safe to assume that your scope has a fair bit more to give under the right conditions.

The simplicity of star hopping seems a welcome escape from the instant gratification on which modern life seems to be based.

Kick back, relax and enjoy.

Paul

[emadmoussa]

Good write up. Glad you like your Dobsonian...they're great pieces of kit, aren't they?!

I have to say we seem to share a similar experience in terms of SCT vs. Refelctor. I found that objects seemed brighter in my late 10" GSO Dob as opposed to the C11, now the 12" beats both! As a matter of fact, I preferred views in the 6" achro more than the C11...ah well, I guess it's about your sweet spot in the end

Before going for the 12" Flextube I was seirously considering the 350P, but got turned off by the size and awkwardness of the base. If I were to use a garage, I would've certainly went for the 14"...anyway, I'm happy with my little monster. Until the Explore Scientific 16" Dobs have hit the market I'm there hunting the skies with my 12" Flextube.

You'll notice more and more difference as you observe more objects by the way...

[Paul73]

Kerry

Just in case you missed this thread. Here is some idea as to what your scope can do:

http://stargazerslounge.com/topic/209561-dark-sky-session-with-faulksy-mike-barry-anne/

Paul

[swamp thing]

Hi Kerry

Darkness of sky becomes much more important with larger aperture. To get the most out of them we must get to dark skies. Shielded from local lights or hiding in city parks won't cut it. The sky must be proper dark.

No scope can improve contrast between object and sky only darker skies can do this. Aperture gives image scale not surface brightness.

Get to dark skies where the extra image scale has a chance and you'll see much more through a big scope.

[faulksy]

hi kerry nice report. i no what you mean as i had the 9.25 before my dob, viewing from home (light pollution ) not a massive difference but it was there, planets from home there was a massive difference like chalk and cheese, but when the conditions are good you will notice a big difference

[jetstream]

Hi Kerry

Darkness of sky becomes much more important with larger aperture. To get the most out of them we must get to dark skies. Shielded from local lights or hiding in city parks won't cut it. The sky must be proper dark.

No scope can improve contrast between object and sky only darker skies can do this. Aperture gives image scale not surface brightness.

Get to dark skies where the extra image scale has a chance and you'll see much more through a big scope.

Steve I'm in the market for a bigger dob down the road but I don't have a handle on the meaning of image scale...is it because of the longer FL,using a short Fratio?Any insight would be great

[Caldwell14]

Thank you Kerry for your obviously well thought out and honest review. I am sure that a great many readers will appreciate your observations on the pay off between aperture and convince of use of large aperture telescope. An excellent review imho.

[AlexB67]

Steve I'm in the market for a bigger dob down the road but I don't have a handle on the meaning of image scale...is it because of the longer FL,using a short Fratio?Any insight would be great

Gerry, the way I would look at it as a guide, your scope with a 10mm eyepiece would give a brightness factor of 0.12 ( a brightness of 1 being the value at which the exit pupil matches your own maximum pupil dilation, and thus appears at the same brightness as it would appear the naked eye at that magnification in the scope). In your scope this setup with the 10mm gives a mag 120x with exit pupil around 2mm and brightness factor of 0.12. 

A 500mm aperture scope with focal length 2000mm would give the same brightness factor of 0.12 in a 8.33mm eyepiece at 240x, and the same exit pupil of around 2mm and power per inch of aperture, therefore the object would appear twice as big at the same apparent brightness to the eye in both these setups, added to that the extra resolution of course and detail you should get.

No doubt Steve will tell you the 20 inch will swamp the 10 inch in performance terms 

edit; and nice review Kerry, no doubt once you get it to a good site it will impress you. 

[Northern Soul man]

Nice 1 Kerry, really honest and interesting review mate - WELL DONE.  before I had the 11, I used to own a 12" dob and an 8" SCT - I always felt that the dob was "under performing".  I found where you lose on 1 you gain on the other.  It wasn't really fair to compare the dob (optics not the best, much shorter focal length) against the 8" SCT, for me, there really wasn't a lot in it, I just found the whole SCT package was giving me more than the extra bit of aperture, looking at the whole picture, the SCT won hands down for me.  Nearly all of my observing is done under light polluted skies and over the years i have just put up with the light pollution and geared my observing to more of the "surburban" targets, with the GOTO accuracy checked on brighter targets I can then try to pick off the fainter objects, usually picking a constellation and going through the M/Caldwell/NGC/IC usually getting down to around 10.5 11 ish depending on how big or diffuse each object is.

A really good review Kerry thanks again.

Paul.

[jetstream]

Alex thanks...I was thinking if the scope specs stayed the same except FL and if the exit pupil remained the same then the magnification would go up giving a larger image,which at some point then the sky conditions may come into play on DSO-not sure about that either....question-does a bigger aperture mirror make its abberations more apparent than a smaller one?Kerry sorry to go off topic,your post was/is great

[Mike73]

As others have said thats a very good and honest review Kerry, I think its all too easy to get a new 'toy' and be a little over the top when writing a review.

I think that as you increase in aperture you also need to improve the skies you use it in.

My 16" shows galaxies in a very similar way to my old 8" and 12" scopes from home with moderate LP, they are still faint fuzzies but the opposite happens when I take the 16" to a dark site where it shows spiral arms but my old 12" and 8" still showed faint fuzzies! 

I think you can spend a fortune in this game and still not get great views, its all about putting the scope in the right place.

[kerrylewis]

Thanks everyone for the interesting comments. Thanks for the compliments too. I did deliberately wait rather than rush into first impressions.

You would think that increased aperture would mean a significant improvement whatever the conditions. I certainly noticed an immediate difference between my 4" refractor and the SCT - but there obviously is a limit. I do not regret getting the Dob - the quick and convenient way of getting excellent views is worth it alone. I now have four scopes (which my wife cannot understand!) and have one 'for all seasons' I think. I tell myself that I therefore don't need any more equipment(!)

I need to try a dark site - Shaun (Pig) from Northampton has mentioned one a couple of times and I will take up the opportunity at some point (thanks Shaun and I hope last night went well) and also I'm going to SGL9, which will be my first experience of such an event, and hopefully we will be blessed with clear skies. And one of these nights we are going to get superb steady seeing and then you will get the 'oh my gosh!' report.

Kerry

[astronymonkey]

Hi kerry,

ill be on the pitch next to you at sgl with my 16inch, and I can swy a big dob under dark skies is fantastic.

the main things I have found have been:

a decent finder arrangement ( I use a red dot, the raci, then onto the scope), next would be a good cover ( go to a bed shop and get a plastic cover that comes with a double mattress),

good 82 degree eyepieces ( to allow the image to stay in the fov longer),

a light shroud to cover the open fram ( I made one from a blackout roller blind for £15),

and finally ive found dew control for the secondary can help extend a viewing session ( I use a 12v hairdryer for energencies like the frozen secondary I had at kielder when I woke up, but a permament kendrick ellipse heater I have retro fitted behind the secondary ismfantastice and is all I need if I swithc it on early in the night)

Cheers,

[YKSE]

Very interesting report Kerry, a big dob down the road is kind of in my mind too.

As to the performance of the increased apertures, it's quite different between your two upgrades, from 4" to 9.25", light grasp increased by 545%, that is 1.82 magnitude increase, while from 9.25", light grasp incraded by 229%, only 0.9 magnitude increase.

[kerrylewis]

Yes Yong that does put it into perspective! Thanks for the maths - not my strong point.

Astromonkey - I look forward to meeting you at SGL9 - I presume that I'll recognise you by the glasses! It'll be quite an adventure as I'm hiring a motor home which I've never done before either.

In fact I do have most of the items that you mention:

I have supplemented the finder with a Telrad as I mentioned

I have also got some wide angle eyepieces and must resist the temptation to get more! I looked at some 100 degree ones at Astrofest but they were expensive - and big!

The scope came with a light shroud and I do have a large plastic sheet - all I have to do is fix it somehow so it doesn't blow off

And one morning last week the dew was horrendous and both mirrors were completely fogged. I used my wife's hair dryer and an extension lead. Goodness knows what the neighbours made of that! Are the 12v ones any quieter? Or perhaps the Kendrick that you mention is the answer.

Edited to remove the reference to the Kendrick hat - but, thinking about it, perhaps not a bad idea!

[astronymonkey]

Hi kerry,

the 12v hairdriers are very quiet and much safer in the damp. To be honest they are too weak to dry hair but ideal for gently taking the dew off optics .... I think go outdoors do them for about £10. The kendrick is a really neat solution, but are about £30 plus another £60 or so for the controller but I can also run a heater tape for my finder and another two tapes off the same unit as its 4 channel.... and in my eyes is worth the cost.

cheers

[faulksy]

Hi kerry,

the 12v hairdriers are very quiet and much safer in the damp. To be honest they are too weak to dry hair but ideal for gently taking the dew off optics .... I think go outdoors do them for about £10. The kendrick is a really neat solution, but are about £30 plus another £60 or so for the controller but I can also run a heater tape for my finder and another two tapes off the same unit as its 4 channel.... and in my eyes is worth the cost.

cheers

can i ask which secondary heater you bought for £30, and have you got a link, thanks. sorry kerry

[astronymonkey]

I used the kendrick s3 http://www.kendrickastro.com/astro/newtonian.html which green witch sell for £31.

This model fits inside the secondary holder on my lightbridge but there is also a split version for secondary holders which are stuck directly to the back of the mirrors.

This then connects to the dew controller to vary the heat and once switched on it works a treat.

As previously mentioned my secondary frosted up at kielder in november but 3 mins with the hair dryer then kendrick on for the rest of the night meant i had no further problems ...note to self - dont catch 2hrs kip without dew heater left on !

Cheers

[faulksy]

I used the kendrick s3 http://www.kendrickastro.com/astro/newtonian.html which green witch sell for £31.

This model fits inside the secondary holder on my lightbridge but there is also a split version for secondary holders which are stuck directly to the back of the mirrors.

This then connects to the dew controller to vary the heat and once switched on it works a treat.

As previously mentioned my secondary frosted up at kielder in november but 3 mins with the hair dryer then kendrick on for the rest of the night meant i had no further problems ...note to self - dont catch 2hrs kip without dew heater left on !

Cheers

thank you for that

[crashtestdummy]

My secondary heater was a dew not one and was less than 30 notes