JOC

So I've been reading through old threads and many people collecting EP's speak of wanting an EP to work with their existing Barlow, so buy a 10mm and get the apparent magnification of a 5mm with their x2 Barlow.  Not that I'd want one, but I just wondered if there was the concept anywhere of something like a reverse Barlow, where you could buy a 5mm, fit it to a minus x2 converter and get the view of a 10mm - I've never heard of one and then I wondered well why not?  I thought it sounded a wonderful question for theoretical discussion and lots of diagrams 🤪

I am a happy astronomer type person 🙂.  My son and I have just been up on the grass verge on a spotlessly clear night with my 2nd hand pair of 10 x 50 Nikons that a SGL member recently sold to me and with the help of an updated Stellarium installation on my portable, thanks again SGL we've both seen the comet 🙂 Half way between the point of the ploughshare and the horizon.  Once found we could just about see it naked eye, but that direction is my worst for light pollution.  Sort of a fat fuzzy denser greyness, with quite a long pale tail above it.  I've got my doubts that it would have all fitted into a telescope view even if I had set up on the edge of the road.  The bins certainly seemed a good tool for the job.  Quite chuffed to be able to say we've finally seen it. 

I tried tonight.  The only bank of cloud for 10 miles was sitting in a line just across the whole North/Northwest view and between that and the expected bank of leylandii there wasn't a proverbial chance of seeing the sky let alone a specific comet 😞

Wot a whopper!   Hope you have fun with it.

3 minutes ago, bomberbaz said:

legs of ursa major at a height of circa 22 degrees

ursa major is a bit more doable - I can often just about see all that above the trees.  Maybe I'll be lucky

Hmmmph................Just been upstairs with a compass - talk about just the blocked view for seeing anything 😞

7 minutes ago, bomberbaz said:

You need to look N by NW at around 15 degrees from the horizon. You should be able to pick it up from around 11 pm and the comet as you may well know is appearing to be travelling downwards. 

It is currently naked eye but best in bins or maybe a fast frac at low magnification and is currently fading as it travels away from the earth.

That's excellent Steve, many thanks for providing instructions that I can make sense of - Sorry for all stargazers in Essex, I'm sure the clouds will now descend just because I want to take a look.

So whilst I appreciate that everything moves relative in time,  if I want to see the comet say at a decent hour after sunset, roughly where have I got to look based in Essex in the UK - I was hoping it might show on stellarium on the mobile phone, but I've not had a huge amount of joy in advancing the time whilst being able to still have it as search criteria (novice stellarium user!) - I also tried stellarium online, but again didn't succeed.  I've got binoculars so it's easy enough to have a quick scan to initially find it, but roughly where do I need to look.  My NW to NE is not my best direction - distant town, next door factory lights and 50ft leylandii, but I can go out on the balcony which probably faces due West giving me best part of an 180 degree view.  If it's that good and it's best from the balcony I can always lug the telescope upstairs, but I can't creep about early in the morning here - the rest of the house inhabitants get cross.

The pictures on the first page of this thread are well worth a look for anyone having problems - it should be possible for most folks to get somewhat close to what is shown, seeing conditions permitting.

 The definitive text on collimation is from astrobaby http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

It does work, even I succeeded, but you have to carry out every little step no matter how daft it may sound.  

That's got a focal length of 400mm  with a 4mm in that's going to give a magnification of x100.  They say approximate theorectical maximum is twice the apperture in mm - your apperture is 100mm,  which would give x200, but I tend to think its about half that in the UK.  So, I guess you might get to x100 on a really good night, but I reckon you would be better off with less than that maybe something around the 8mm mark?  I don't know what sort of EP's come with these scopes, but I had Skywatchers own 10mm and 25mm come with my 8" and, FWIW, I was quite pleased with them.

The 8" is useable by standing, but 100% more comfortable sitting.  I got a couple of cheap, lightweight bar stools and have a high one and a low one.   It has to be said that I don't use my scope very often, but IMO the collimation holds quite well between uses.  You def. don't need a light shroud, I think it depends on location and what you are expecting to see.  If you are somewhere pitch dark, then there won't be any stay light to enter the system.  I've got a light shroud (a home-made one), but given the relatively low ability of my 8" to capture light from DSO's anyway I don't find much difference at night with and without it - I actually think the entire system performs better at night without it. for various reasons.  You would 100% need one during day time use if used a solar filter to look at the sun - that is always when I do use the light shroud.  However, you are looking at a 250P which I think is the 10" isn't it?  Since you might therefore be more interested in DSO's that I was (I wanted a first general purpose see most things scope) then I guess you might find a light shroud might give you an edge on seeing those feint grey fuzzies particularly if you are in a light sensitive area.  

As to fitting a handle on a larger scope - in my case, I wouldn't have wanted the hassle or the fear of drilling into my brand new OTA to fit one.  Also if you look at where the handles are often positioned right in the middle of the scopes I am still not sure they look the easiest things to get on the back seat of a car.

Now talking of cars, and I've had mine in the car on several occasions what you do have to watch is not as much can you fit the OTA on the back seat? but the question that isn't so obvious is, can you also fit the Dobsonian cradle mount in the boot/on the spare passenger seat?  I have a fairly massive Estate Octavia and the Mount def. requires careful positioning - then obviously you want to add in a folding chair, EP box possibly some warm clothes and the space rapidly diminishes - I would def. say to be as aware of the size of the mount if you want to transport it as much as the size of the OTA.  Even the mount for my 8" is a respectable size and I have to lie it down in the boot - it is another awkward thing to load in the car.

With experience although it may not contribute to the problem if you look at that picture posted just above I can vouch for the potential of twiddling that big grub screw between the two focus knobs by accident in the dark.  That locks the focus and then any amount of twiddling with the big knobs won't change it - make sure it has not been tightened by accident.  I also agree that the flex tubes seem to be correctly positioned.  FWIW you are looking for yours to look like my smaller one when it's ready to use - mind does actually do the two position clicks referred to above, but if yours doesn't then providing the rods are extended apparently as much as mine they should be correct:

I've got an 8" Skywatcher flex-tube.  I've been very pleased with it and given the chance to buy again would not buy the solid tube.  I love the way it collapses - this makes storage easier - my 8" folds to about the size of a dining chair to store on its base (though your contemplated model would obviously have a wider base).  Other things I like are the folded size when it comes to moving it.  I store it inside the porch and my goto base weighs a bit and I find it easier to move the OTA and the base separately (it is a work of moments to separate the two) .  The advantage of moving the OTA comes when it collapsed - it is an easy reach to pop my fingers around the open end and under the ridge at the closed end and lift it safely within an arms width which makes it easy to move through household sized doors.  I don't know what the collapsed size of the one you are looking at is, but I imagine there would be a similar advantage - my arms are not that long and if you are a taller person than me you might still find the collapsed tube of a larger model is still an easier lift to shift through small spaces than the longer length of a tube that won't fold.  FWIW I have not found any issues with a possible loss of collimation and the tubes of the Skywatcher provide an entirely convincing rigid immovable structure when locked into place.  I'd buy again.

FWIW here is a picture of my 8" you can imagine the difference in size when folded.  The two pieces entirely butt up against each other and the whole length of the extension rods is lost.

Well at least when you decide to replace the telescope you'll have some decent kit to put it on./on it  I hope it works OK for you.

8 hours ago, Sax6M said:

The inspiration is to expand my granddaughters' apprehension of God's Creation.  I think once they see Jupiter's rings or the craters of the Moon, they will nevelr look at a night sky the same way.

No need to wait until you build your scope, hand her a pair of binoculars and see what she can see on the moon, also, if only building for your granddaughter she might get on better with a small tabletop Dobsonian, which may well be sufficient to see rings around Saturn and moons around Jupiter and could come in around £100 second-hand - could you build for less?  You would also have a solution for her far quicker.  You could always sell it once you have your own larger model.  For that matter you can buy a brand-new 200P for £289 or many decent scopes for less than that second-hand.  It just sounds a rather long-term project for a first telescope when you could both be enjoying the sky a whole lot sooner with an off-the-shelf solution that would be guaranteed to work and get finished!  Just a thought 😄 

I'd love to know how you all get the foam cut so neatly and flat in the bottom of your 'holes'.  I couldn't work out how to achieve that and dug the snips in and cut the upright bits of foam at an angle, but it makes the case look less than tidy

2 hours ago, paul acreman said:

It's always nice to have and look after from new,but second hand would allow perhaps one more

I guess so if you have cash to burn, but I've never picked up a 2nd hand EP that wasn't within a whisker of being like a brand-new one (all mine have come via SGL) and I have a set of Morpheus for around half the cost of buying new - it's well worth considering.

That's one bold choice as a first scope - hope it's everything you hope it will be. 

FWIW:

On 23/06/2020 at 21:20, paul acreman said:

looking like the Pentax Xw first choice or Baader Morpheus .I guess you have to be lucky to find them second hand as most are keepers.Any suggestions where to look apart from here or Astrobuyandsell ?

The Pentax come up from time to time second-hand - that's where I got my one and only, but the Baader Morpheus I can tell you that I kept an eye on SGL classifieds and in about 18mths or so I had amassed the complete collection of these in nearly new condition, so it depends what time you have to spend on things.  Maybe get a decent long and shorter length EP now and then bide your time and see what comes up second-hand?

2 hours ago, KevS said:

Dependent upon the particular circumstance Saturn and Jupiter may be problematical but Mars is some 40 degrees at opposition in October so unless the Hertfordshire Matterhorn is in the way I don't envisage any problems.

LOL, I was also kind of looking at it from the persepctive of using the degrees up and down (and left to right, though that won't so affected) that are published for any given object.  If you have some form of marker on the telescope for vertical degrees and a reference says that Saturn is at 10 degrees altitude it won't be any good setting the marker on the telescope for 10 degrees if the telescope is already sitting hundreds of metres up.  There must be a standard adjustment that can be used, i.e. subtract 1 degree from the published figure for the object for every x metres the scope is sitting above sea level?

23 hours ago, Tomatobro said:

Compass, cheap angle finder and a guide scope with cross hairs.

That won't account for altitude though will it?

You can make a home-made shadow finder with a nail tapped into a piece of wood that casts a shadow onto a back plate - get the sun where you want it and mark on the backplate where the top of the nail's shaddow is - or for not of cash you can buy a simple solar finder - I strap mine to my scope with a bungee, but you have to adjust it with each use.  However, just as a tip - and it only works safely if you have a solar filter that covers the whole of the front of the scope like mine 

I find a useful thing to do is to take out the EP and look directly through the focus tube - with the shadow finder getting you close and I also find you can use anything that sticks up on the telescope to help, like a nut head it seems far easier to adjust the tube to find the sun in the mirror if you don't have it magnified, you can sort of see the glow as you approach and then big circle sun directly in the mirror - I have a huge amount more success that way, but you ABSOLUTELY MUST have the whole of the OTA covered with solar filter like in my picture

Won't it be necessary to adjust the measured horizon relative to how high the OP is to begin with .  Surely the star measurements are taken relative to sea level horizon.  If the OP is in a Valley which is still 100m above sea level then does this need to be adjusted for.  For example in some instances you might be looking down to a horizon?   Either that or I've missed something huge in my thinking.

I don't know what you can use software wise, but I have had experience that sometimes USB leads are very specific for certain applications and you can't just use any old USB lead in certain situations.

Just an idle thought - if the OP is imaging I imagine this calls for a very calm and stable environment.  Is there any potential problem arising from possible vibration from the proposed fans?

That's quite lovely, you are so clever - I can't sew for toffee.  Well done, I'm sure it will be a much appreciated square.