Best scope for planetary and star doubles

[CraigT82]

This...!

http://ensoptical.co.uk/telescopes/-lyra-102mm-f11

[Moonshane]

just make the largest hole that can fit between your vanes and avoid the secondary. I'd think 90mm would be doable which would be 1200mm / 90mm = f13.3

[bomberbaz]

cheers shane, new job to do next week 

[Stu]

4 minutes ago, bomberbaz said:

For what it is though and as an interim I will try it. Not sure what aperture I need to take 250 from f4.7 into an f10 - f12. 90mm ?

Whats the calculation again anyone

Not sure there's a simple calculation, it's a case of getting the largest aperture which fits between two of the secondary vanes so you get an unobstructed light path. A bit of trial and error me thinks

[Moonshane]

if making one, you might as well try different apertures

https://stargazerslounge.com/topic/143780-aperture-mask-for-16-f4-dobsonian/

 

 

[mikeDnight]

Sell the house, sell the wife, sell the kids, live in a shed, buy a Tak. Problem solved! 

Mike

 

[CraigT82]

Opticstar 102mm F9.8 achro for £165 new... could be worth a punt?!

 

http://www.opticstar.com/Run/Astronomy/Astro-Telescopes-Opticstar.asp?p=0_10_1_1_230

[bomberbaz]

http://www.ebay.co.uk/itm/tal-refractor-telescope-/351666090901?hash=item51e0eeb395:g:2lMAAOSwuAVW1J91

this just came up on flea bay

[SkyGibbon]

I have a 78mm mask here in the photo of my 10"/250mm dob, which also I can double as a helpful but weak exhaust fan, as pictured. When I look down the focuser it seems I can get about 4mm more diameter before either cutting into either the vane, secondary, or outer edge of the mirror. So, I would say between 80-85mm mask at most on a 250mm.

 

[YKSE]

On 2016-02-28 at 00:23, Stu said:

Not sure there's a simple calculation, 

There is a simplified calculation, here's a picture for illustration:

The bigger circle with radius R is a Dob, with 4-spider vane, small circle is the mask with radius r, the diagonal of the rectangular can be calculated as

square root of (r**2+r**2), i.e. square root of 2 times r, or 1.414r, so we have 

R=1.414r+r=2.424r

rewrite to Diameter, we have D=2.424d.

in a more convinient way, we can say

10" dob can be masked down to 4", 12" to a 5", 14" close to 6", etc.

With other spider vane, e.g.curved ones, the mask diameter can be made close to as large as (R-s), where s is the secondary radius.

[Moonshane]

roughly true but don't forget to miss the secondary.

[YKSE]

Yes, that's one of reason I called it simplied calculation.

to take into account of secondary size, just check if its diameter is bigger than 40% of of the intended mask, if it is, then you have maximum mask diameterof R-s, as mentioned above (which incidentally can be the maximum mask size if the secondary is small).

[bomberbaz]

I will probably take a more technical approach with some cardboard and a system called trial and error 

[Moonshane]

Just take a pic down the tube and then work to approx scale.

[bomberbaz]

still got my eye on the 2nd hand 100ED shane, might be in with a shout. Do I need it, maybe no. Having read so much about them this last few days do i want it, probably yes 

[Moonshane]

You cannot go wrong at the price. Maybe buy it, try it and sell it if not.

As you know I have definitely changed my views on fracs since using EDs for a time. I blame solar as without that, I'd probably never have tried them.

[bomberbaz]

On 02/03/2016 at 09:08, Moonshane said:

You cannot go wrong at the price. Maybe buy it, try it and sell it if not.

As you know I have definitely changed my views on fracs since using EDs for a time. I blame solar as without that, I'd probably never have tried them.

Looks like I have just become the owner of a 100ED 

Erm now its a case of which mount. hahahaha.

[mikeDnight]

25 minutes ago, bomberbaz said:

Looks like I have just become the owner of a 100ED 

Erm now its a case of which mount. hahahaha.

An EQ 5 would carry it and if it was driven in RA so much the better. If you want an altaz, I'd suggest an AZ4 just as a grab and go. I'm not keen on vixens Porta or Porta ll as with the ED100 they would both vibrate like a tuning fork.

Mike

[YKSE]

37 minutes ago, bomberbaz said:

Looks like I have just become the owner of a 100ED 

Erm now its a case of which mount. hahahaha.

Congratulations Steve, that's a very one

In addition to a mount, you might have accidentally dig a hole or two among your EPs too

[bomberbaz]

1 minute ago, YKSE said:

Congratulations Steve, that's a very one

In addition to a mount, you might have accidentally dig a hole or two among your EPs too

hahaha, the only EP hole from research already done lies in my mind, covered in my EP box along with the PMate.#wieght

However given time I am sure I will manage to find something 

[nightfisher]

congrats on the ED100, re the mount if your purely visual go with AZ4 mount, though this mount does need s little "tuning"as it cn be a bit notchy just a case of cleaning and regreasing the axis with mly grease

[mikeDnight]

9 hours ago, bomberbaz said:

hahaha, the only EP hole from research already done lies in my mind, covered in my EP box along with the PMate.#wieght

However given time I am sure I will manage to find something 

How about these for starters!

 

[Stu]

1 minute ago, mikeDnight said:

How about these for starters!

 

Hmmm, x562 for the 1.6 might be a tad optimistic Mike!! ??????

[YKSE]

16 minutes ago, mikeDnight said:

How about these for starters!

 

That's even bigger hole in his wallet

[mikeDnight]

1 minute ago, Stu said:

Hmmm, x562 for the 1.6 might be a tad optimistic Mike!! ??????

I agree! However I keep looking at them and that's a bad sign. It's more the price that's holding me back from trying them out (almost €300 each). I'm not sure of the price in £, I daren't do the conversion, because I know I'm stupid enough to do it. 

The only advantage I imagine they may have over a sharper lower power eyepiece could possibly be in splitting close binaries. Over magnifying a planet is a sure way to destroy the finer detail, coupling that with our temperamental seeing, probably means they're be a pricey novelty. However, that shouldn't stop Steve from buying a set, as I can then buy them off him for a greatly reduced price. 

Mike