New member of the Dob Mob

[estwing]

Nowt wrong with being a fraccer also..I'll be bringing the telly!!

[swamp thing]

Nothing wrong with Fracs.......they make great finder scopes

[Laurie61]

Nice to see you have sorted a dob base Stu  Did it need to be specially made for the longer tube or is it a standard size. As mine came with the scope I was not aware if OO had to make a special for an f6 or not.

[Stu]

Fab looking scope Stu! The scuffing of the trunnions is a common issue and sometimes can be adjusted out using the little inset grub screws (I think you need to back off the fixing bolts first though). It's one of those jobs that can drive you mad though so be warned.

Hope you enjoy it as much as I enjoy my OOUK scopes. My own 12" f4 is used far more than any of my other scopes - my 16" f4 has not even had a run out since PSP 13 in October!

Thanks Shane, will have a play next time I have a chance. Seems like they just need to make the spacing between the uprights a mil or two wider and it wouldn't be a problem!

I expect this will become my regular big scope, with the Vixen for those nights when I know I can get a long session in.

Stu

[Stu]

Nice to see you have sorted a dob base Stu Did it need to be specially made for the longer tube or is it a standard size. As mine came with the scope I was not aware if OO had to make a special for an f6 or not.

Thanks Laurie.

I spoke with OO and we decided a standard one was fine. I may have to add a little weight to the base for heavy eps but I have all I need to make up a sliding system so should be no problem.

Stu

[Mike73]

Did you look any further into the curved spider veins Stu?

I asked OO about them and they said they just did the standard spider veins these days because the curved ones gave halos rather than spikes but I guess he was talking more about imaging rather than visual.

I'm not worried about spikes because they dont bother me and I dont do double stars but I recall you mentioning curved veins before?

[Stu]

I spoke with OO too, and they were very negative about them. I understand that you can't cheat the laws of physics, and any reduction in spikes will see an increase in smeared diffraction around objects. The thing is, anyone who has tried them seems to think they are an improvement so there must be something in it.

Funds are a little tight right now, so I won't do anything for a while but I think I will try to source a Protostar single curve vane support at some stage to give it a go.

http://www.fpi-protostar.com/crvmnts.htm

Stu

[John]

I had no idea you had an EQ6! I use Tapatalk so don't often see signatures. Do you use it much? Thought you just used the Bray for the big frac?

I must admit, I love the Atlux mount. So solid, very easy to setup and use. The Losmandy plate and clamp are rock solid too.

It's only just arrived and the Bray will be off soon. I'm putting the EQ6 on the Meade Giant Field tripod. The driven mount will benefit the big refractor with it's long focal length. I may well use the Losmandy approach too, if the current dovetail bar is not up to the task.

[John]

I spoke with OO too, and they were very negative about them. I understand that you can't cheat the laws of physics, and any reduction in spikes will see an increase in smeared diffraction around objects. The thing is, anyone who has tried them seems to think they are an improvement so there must be something in it.

Funds are a little tight right now, so I won't do anything for a while but I think I will try to source a Protostar single curve vane support at some stage to give it a go.

http://www.fpi-protostar.com/crvmnts.htm

Stu

Mine has the OO curved vane design from 2006 when the scope was made. I prefer the views without the spikes and the scope shows me Sirius B and other really challenging stuff when the seeing co-operates so I'm entirely content with their performance. If they produced much in the way of halos or other ill effects "the Pup" star and the sub-arc second stuff would simply not be visible I assume.

One thing I have noticed about suppliers is how negative they can be about stuff they have decided not to offer any more. When they were selling it, it's the bees knees of course, but now they have dropped it, then it's "oh no, you don't want that ...."   

[Stu]

It's only just arrived and the Bray will be off soon. I'm putting the EQ6 on the Meade Giant Field tripod. The driven mount will benefit the big refractor with it's long focal length. I may well use the Losmandy approach too, if the current dovetail bar is not up to the task.

From my brief experience with the Atlux, I think that is a wise move John. I do enjoy the ability to track objects for long periods without touching the scope. You can really focus and catch those moments of good seeing. Did you consider the AZ-EQ6? I had been pondering one of these before going for the Atlux

Stu

[cotterless45]

Yo! I keep my frac for those bleached Moonlit nights for lunar, planets, stars .... The Newts come out to play when it's properly dark. Set up time with eq mount aligned is about 12 minutes. The Meade goes on those trips out to the sticks and Scotland.

Still prefer fracking,

Nick.

[Stu]

Mine has the OO curved vane design from 2006 when the scope was made. I prefer the views without the spikes and the scope shows me Sirius B and other really challenging stuff when the seeing co-operates so I'm entirely content with their performance. If they produced much in the way of halos or other ill effects "the Pup" star and the sub-arc second stuff would simply not be visible I assume.

One thing I have noticed about suppliers is how negative they can be about stuff they have decided not to offer any more. When they were selling it, it's the bees knees of course, but now they have dropped it, then it's "oh no, you don't want that ...."

I think you are right about that, and as an approach all it does is to undermine your belief in what they tell you!

I shall certainly give the Protostar a go when I can afford it. I think it is optimized in terms of shortest arc which still 'obeys' the 180 degree rule to cancel out the spikes.

Stu

[AlexB67]

I posted some research paper on one occasion I found very enlightening, Stu, if you want it I can post it again, but it does some in depth analysis on the topics of curved versus straight designs and many others. While the curved spider gets rid of spikes  the moral of the story in that paper for the drawback of the curved is that supposedly takes more energy out of the central airy disk, therefore reducing contrast

BUT

since the amount of energy taken out depends largely on the area of the obstruction caused by the veins there is a counter argument to this. The total area of the veins is quite  negligible in comparison to the total obstruction size of the secondary, therefore, the effect can largely be ignored in terms of contrast, this was not pointed out in that original paper, but I read about it elsewhere, and with some calculations/simulations in more recent papers showed this indeed to be true. 

If you had a rather heavy secondary (should not be really an issue in the 12 inch )  one of the other issues is that the curved veinswill need to be thicker compared to the straight design for a stable design, so for very large scopes it may become factor in order to keep the secondary stable and the increase in area will be more of a factor.   

The conclusion I get from this, you'll have to make up you own mind what you think, is that for the scopes in the size that you have at least the curved solution is the way to go on the whole I feel, but there are compromises, pros cons for each.

Like many things spikes may not bother some until you see through a scope without them and you realise it is actually quite nice. My little Heritage 130p has a single strut design which is rather thick, it will cause some other issue like an asymmetry in the diffraction pattern, but its thick enough to smear out the effect from the single strut to result in a clear single spike. I find it is lovely when I look a Jupiter through it as I did this weekend without the spikes

Besides, john's experience saying it works nicely is the ultimate proof. Without having such a design or used it myself there is theory to support the argument for it though.

[Moonshane]

I have the curved spider on my 6" f11 and it removes the thick diffraction effects (almost as wide as the planet when there was moisture in the air) and creates a much more aespethic view of Jupiter. I have yet to be convinced if the double star images are quite as tight as they were but I have not used it for long enough to rule out seeing yet. in the case of a 12" f6, I am not sure the curved one would be worth it but see how you go. I hardly get any difftection spikes on Jupiter with my 12" f4. I should clarify that they only bugged me a bit on Planets.

[Stu]

You are right in that I don't have enough experience with the 12" yet to know what it is like on a variety of targets. I did not find them annoying on Jupiter when I tried it, so may just stick with it's it is. I'm pretty keen to just get observing with the kit I've got now, since the weather seems to be improving quite a bit!

Stu

[Stu]

I have the curved spider on my 6" f11 and it removes the thick diffraction effects (almost as wide as the planet when there was moisture in the air) and creates a much more aespethic view of Jupiter. I have yet to be convinced if the double star images are quite as tight as they were but I have not used it for long enough to rule out seeing yet. in the case of a 12" f6, I am not sure the curved one would be worth it but see how you go. I hardly get any difftection spikes on Jupiter with my 12" f4. I should clarify that they only bugged me a bit on Planets.

Forgot to say, did you manage to create one which goes through exactly 180 degrees Shane? I think that's important to cancel out diffraction evenly.

In theory, the single curved 180 degree vane is the shortest possible obstruction so should produce least smearing. John's seems to work very well, but the two circles are, again in theory, producing a longer obstruction.

I guess this is all a case of analysis paralysis and we should just get on an observe :-)

Stu

[Naemeth]

Just seen this Stu, I do think the dobsonian mount is the right way to go with this one .

As for reflectors vs refractors, I don't see the problem - they both have their uses .

[As of this moment, I have 4 refractors and 4 reflectors - one of the reflectors being a Maksutov ]

[John]

I guess this is all a case of analysis paralysis and we should just get on an observe :-)

Stu, I think you have hit the nail on the head there 

It's fun to debate these fine points of scope design but getting observing time and experience under your belt is better still. I've read plenty of reports from skilled observers who use standard spec scopes and fairly ordinary eyepieces but by putting the time in and honing their skills are able to produce really great results 

[Stu]

Alex, would you mind posting a link to that research?

Cheers,

Stu

[Stu]

Stu, I think you have hit the nail on the head there

It's fun to debate these fine points of scope design but getting observing time and experience under your belt is better still. I've read plenty of reports from skilled observers who use standard spec scopes and fairly ordinary eyepieces but by putting the time in and honing their skills are able to produce really great results

Despite my last post to Alex, I do agree with this point but I also like understanding the theory behind it.

I've been on a bit of a mission over the rubbish winter to rationalize my kit into a state where I have what I want and can do just what John says, forget about it and get on and observe.

Stu