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Upgrading from a 250px to....


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I'm planning on upgrading from my beloved 10" 250px dob.

My sole, only use, of my telescope at the moment is to observe from my garden in a town (NELM 4.5ish)

I'm basically looking to buy as much aperture as I can and still be able to look through the eyepiece without a height aid

I'm 6 foot dead, i guess that puts my eye height at 5' 8" ish with normal shoes on

I'm looking at a 14" flex tube dob from Skywatcher

Can anyone think of a reason why I shouldn't get this scope?

I see the weight of the OTA listed as 23.5kg. I can manage moving this from the shed to my observing spot which is 15 feet away.

The base, although heavy, deconstructs and is designed to be constructed and disassembled quickly. I can do this under light at the end of an observing session so shouldnt cause any real issues. I'm not sure if other DIY base deisgns can be used for Flextube type dobs, but I might look to get a DIY base made for this scope if the supplied base is a grind.

I feel the 16" although affordable, would have an eyepiece height which would annoy me. I read that a 16" light bridge has a lower EP height, I haven't looked at this yet as I'm still thinking 14".

I have about another month of debating myself if this is the correct choice, I dont intend to buy a bigger scope any time soon after this and if I do the next jump will likely be whatever that 18" offering Sytna are working on at the moment (prototype was at NEAF), in a few years.

Any thoughts on this? There seems to be very few people who have this scope for whatever reason.

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Hi Graham

It's not so much the eyepiece height that's the issue, its the angle. If you look at pictures of the 16" flextubes the focuser is set towards the back (top, when the tube is horizontal) of the UTA, as the scope elevates you have to be able to stretch across the OTA to reach the eyepiece.

Large dobs should have the focuser coming out of the scope PARALLEL to the ground. It means for easier access to the focuser at higher altitudes.

Where Skywatcher place theirs is of benefit when observing close to the horizon (something most of us try and avoid like the plague).

For this reason I found myself climbing steps whilst using the 16" version when my feet should have still been on the floor.

The 14" would probably be better as not only is it shorter, but because the tube is narrower reaching across it will be less of a exercise in balancing too.

Personally I would skip 14". Save my dough, then. go straight to 18", I sure wouldn't wait for synta to make one either. When buying scopes this size you want quality not mass produced stuff. I would keep your 10" as a second scope too. :)

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Wow, a lovely case of aperture fever :p

There will be a good number here that will be able to help you a lot better, Stargazer for I have absolutely no experience in this. The only thing I'm thinking is that the upgrade to a 14" would give you about half a magnitude increase in brightness. To get that full magnitude increase of 2.53, you'd need to jump from 10" to 16". So, although any increase in brightness is a lovely thing, I wonder if the 14" would give you that feeling of satisfaction.

The other concern is practicality. Would you be selling on your 10"? I feel that the smaller scope would still be very handy when you wanted just a quick peek. Also, unless the bigger scope was portable enough, I wonder if it could fit in the back of a car when you ever fancied getting out to a star-party, or a really dark site.

My feeling on this would be to look into a portable, truss dob, something that can be set up swiftly in your garden, that can be carried to darker sites if necessary and that won't take up too much room back at home.

I'm sorry I couldn't help more.

Edited by Qualia
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Some great comments, cheers.

On the 10", i might keep it or might sell it on. Certainly I wont sell it on to fund the 14" and will run with them both for a time to identify if the 10" has a spot in my arsenal still or not.

I suspect any night that warrants a dob I'll just get the 14" out so will probably convert the 10" into an eyepiece or 2 instead.

My 6" works very well for grab and go and has enough aperture to handle most brighter DSOs and is good for moon and planets. In fact i'll likey upgrade this to a 1.10 PV OOUK VX6 after I get the 14". its a perfeect G&G setup for my style.

On usability, thanks Steve you make some good points I'd not considered. I wonder if I were to get a base from a certain board member if I could wrap some rings around the mirror portion of the flex tube and then rotate the scope to the required angle. I apprecaite that the flex tube deisgn has 2 bars on the bottom, i presume to spread an equal load, and perhaps rotating the OTA within rings might put intolerable stress onto on arm more than the other.. EDIT: I'd also considered perhaps simply loading the scope upside down for high angle viewing but this would put all the stress on one pole as well. Has anyone looking into rotating the cage assembly on this scope design as an aftermarket mod?

My ideal, of course, would be to wait for a OOUK 14" solid tube to magically appear on the second hand market right now, or even a 16"! but I appreciate that's unlikely to happen and I'm unfortunately not a patient man. I wish I was but I know im not. As soon as I have the money in my bank I'll spend it on the 14". That day is likely to be the last week of June (started saving this month!) so i'll advertise in the meantime but am not that lucky I fear.

The 14" offers a 98% light grasp increase over my 10" so I expect it will be a massive increase. A 16" is a 125% increase over the 10" for an additional £500 and more weight, and harder to use. I think the 14" in this design is the right choice for what I can handle and use although I believe a solid tube 16" would be equally manageable were I lucky enough to get my hands on one.

I also noticed that the skywatcher website lists the 14" specifically as having hand polished mirrors, which it doesnt show for other models. I think this says more about their bad content management on the website than anything special about the scope (as the 16" shows pyrex mirrors and not hand polished)

Edited by Stargazer_00
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When Shane designed built the base for my OO 12" F/5.3 SPX tube we went for measurements that keep the eyepiece at the optimum position for my height (6 foot). Consequently it's a very comfortable scope to observe with. I moved to it from an OO 10" F/4.8 OTA which I used on my Giro-style mount. The eyepiece with that rig was nice and high too. The 12" is optically higher quality than the 10" so that, combined with 2" more aperture has given me a performance "hit" that I was looking for, particularly on the planets and moon. My garden (where I observe from 99% of the time) is not great for DSO's due to surrounding trees, houses and some LP so I've not, as yet, turned into an avid DSO hunter.

I have to move my scopes from my house onto the garden and then, during a session around the garden from time to time (on the level) to see objects in certain parts of the sky. When I had a Meade Lightbridge 12" I could not lift the whole lot in one go - nowhere near really. It needed to be moved in two pieces. With the OO 12" on the "Moonshane" dob mount I can lift the whole lot up and (carefully) re-position it 10 feet away or so. This is very important to the way I observe. The whole scope weighs around 26kg, which is very light for a 12" dob. This is not at the expense of stability either (thanks Shane !) as 300x plus is quite manageable and pretty stable with this scope, conditions allowing.

I've seen the 14" and 16" Skywatcher dobs a few times at the SGL star party and other events. They look great scopes and offer really significant performance but I know that I could not manage to observe the way I need to with one.

Thats just my situation really and it may not mirror yours but, from my experience with the 12" Lightbridge, having a great scope which is just not practical is a rather frustrating experience :embarrassed:

OO scopes do come up used and are great buys. They are also quite a bit lighter than their chinese equivalents. If you can manage a chinese 14" or even a 16" though, go for it and enjoy it :smiley:

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We have the 16 inch flextube. I'm 6ft5 and I only just get away without using steps. Sometimes I still go up a step anyway as it can be more comfy than standing upright and my missus needs a step ladder anyway, so it's already out.

Would you get away without the steps with something like Moonshane's 16 inch setup?

If you did go 16 inch, do you have to sell the 10 inch? I use my 10 inch dob just as much as the 16 inch, as it's a bit less hassle and goes out on the iffy nights or when I just want a quick look.

Edited by Luke
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Certainly I dont have a financial or storage need to sell the 10" to fund an upgrade. But with a 6" on a tripod for nights when it isnt perfect I can't think of a reason I'd ever need to get a 10" out that wouldn't be better with a 14". The setup time looks very low, more than a 10" sure but still less than 5 minutes.

Too few people have a 14" flex tube and there is literally nothing on the internet either in terms of reviews of even size comparison photos so should I get it I'll certainly do my level best to rectify that situation so others dont fall into the same void I have while looking for info.

I did see a 16" solid tube when I was in the widescreen centre and I believe I could easily handle that size/bulk. I wish a 16" OOUK popped up today in my budget but I appreciate the higher up you go the less chance you actually have of this happening. I think the 14" will be good and if it's not everything I want then I can always sell it for a small loss and save up again for something else.

If any of you hear of anyone selling a 14" / 16" OO please do let me know.

the one option ive completly discounted is continuing to save up and buy a VX14 brand new. At twice (or more) the price of the chinese equivalent I really don't think it's worth considering

Edited by Stargazer_00
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A friend just told me to look at these:

Does anyone have any experience of these scopes?

http://www.sumeriano...s.com/products/

I've heard of them but dont see many people with them. the 14" and 16" are both in my budget (on second thoughts it appears you need to supply mirrors and focusers at additional cost)

EDIT: Canopus model

Are there any other telescope suppliers that do afordable scopes to order? I'd much prefer to get a solid tube scope just can't stretch to OO prices

Edited by Stargazer_00
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Lovely bit of kit. I think Mike 73 got himself a 16" and Umadog a 10". Might be worth dropping them a line - although I haven't seen Mike around for a wee while.

You might find this, this useful.

If I recall, the prices are without the mirrors and focuser, so you will have to include these in the final sum.

Edited by Qualia
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the best thing you can spend when looking for a scope is patience. honestly, you'll eventually get a serious bargain with a 14-16" scope in a month or two I'd bet. there's a huge difference between my 12" f4 and my 16" f4 in terms of everything - bulk, weight, impressiveness and of course wonderful views of (in my opinion) all objects so I think your jump from 10-14" will be a satisfying one. personally I see the 16" f4 as a handful in the solid tube but I like it as it's easy to use and a breeze to set up. I'll not go bigger as budget and getting through doors are both issues. I could sell all my stuff to fund a mega dob but don't want to - I like diversity.

in your shoes I'd recommend a 16" f4 and to wait for one to come up. I bought the mirror, tube and focuser, spider and secondary and made the base and cell for less than your budget.

if you are ever up north, send me a PM, you'd be welcome to come and look at my scopes.

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i have a few months until im on budget but can access money sooner if needed. i'll keep saving and if something comes up in the meantime then great :) I suspect when im on budget i'll take another look at where I am and see what is appropriate. ultimately its not the best time of the year to buy a scope and maybe id benefit from continuing to save until september or so in which case i could probably close to double the budget. its just knowing what to get. I didnt really want to invest much more than 1400 on a scope really, less would obviously be better and more than that feels like diminishing returns.

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Probably about £1400 but then there are VAT and duty to consider.

Also may be a bit too lightweight, sort of a Sumarian on a crash diet.

Hubble

Someone on CN bought the 16" waiting for a full first rport for them to be posted.

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I was having a think about this.. is there any issue getting a larger aperture reflector for use in an urban environment. Im thinking light pollution basically.

As the aperture increases and the focal length increases the exit pupil at the magnifications I have now is going to be larger in the bigger scope. So lets say 150x now in a 10" compared to 150x in a 14", the objects will look brighter but the background sky will also appear brighter/more orange.

So in my 10" F4.7 scope right now 150x is achieved with a 8mm eyepiece. I dont own that eyepiece but I can do the math. This gives a 1.69mm exit pupil.

150x in a 14" F4.5 is achieved with 10.666667mm eyepiece (this is theory only). This gives a 2.37mm exit pupil.

So to get an idea how bright the sky background will be at the same exit pupil in my 10" I need to use an 11.2mm

Obviously these focal lengths are not existant except the 8mm which I dont own anyway but is the logic sound? Will the sky background brightness increase as well as the exit pupil increases?

If so this means my low end magnification will get even more orange and the point at which this doesnt become sickening to my eye will become narrower.

My current 10" shows appreciable orange at around a 3.8mm exit pupil with an 18mm giving 67x, and its not too bad with a 14mm giving 2.9mm exit pupil, 86x.

In a 14" F4.5 to get those magnifications this translates to 24mm gives 67x with 5.33mm exit pupil and now an 18mm gives 89x and a 3.99mm exit pupil. So to maintain magnification across scopes im increasing exit pupil size by approximately 40%. which means not only does target brightness increase but also background oranginess

I'm wondering, after all that, if i shouldn't get a 12" instead so I can boost brightness of DSOs a bit without bringing in significantly more orange.

Obviously in a really dark site the larger aperture wins hands down everytime. But I wont do that very often if ever with this scope and I should be realistic about my usage.

It's early in the morning so maybe I missed something here i just wanted to go into my next purchase with my eyes fully open. I know after buying the 10" I realised the speed of the scope which I didnt consider before and I promised myself then that my next scope I'd look at every angle for suitability first.

Maybe the larger aperture dob is for use in the realm of 140x + and for rich field views I should just use my 6"? Or keep the 10"just for a certain magnification range? Is my logic above even sound?

Edited by Stargazer_00
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I think your logic makes sense but you are over-thinking it I reckon. I don't buy into the 'aperture sucks up more light pollution' argument. this is based on looking at things through scopes rather than worrying about what things might look like (I don't mean that to sound confrontational by the way but it does sound a bit like that).

There is a lot to be said for more than one scope and as mentioned previously, my preference is for three. my two bigger scopes are f4 and although the exit pupil is bigger at lower mags, resulting in light pollution taking its toll, the views of all objects are improved with the larger scope - if they fit in the field. I really enjoy the view for example through my 26mm Nagler in both my 16" f4 (71x 1.1 degree field and exit pupil 5.9mm) and my 12" f4 (51x 1.6 degree field and same exit pupil) as well as all my other eyepieces. of course they are all better at darker sites.

shame you cannot visit me to try them.

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Was having a conversation with Shane about something similar to this about a week ago..

For your height, a 16" F/4 should be ideal (right eyepiece height level), and I'd personally go for a Sumerian dob too, see Mike73's review for his Sumerian:

One thing to consider:

Add the cost of a paracorr to whichever large dob you get that's faster than F/5. You don't want to spend, maybe, 3k or 4k on a big dob and have the views spoiled by coma.

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I kinda agree with Shane here. Nearly any object that the LP allows through will be improved on with aperture.

LP is no more sucked up by large scopes than small. As extended objects are no brighter in a scope, so that horrid orange glow will be the same.

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