Mirror clips on OO UK scopes

[jetstream]

Don't worry about the scratch or the clips (except for glare if shiny). These OOUK scopes can give excellent views, how is the view from yours? My VX10 will support 275x-300x on Jupiter sharp and Mars over 400x...

I painted everything black, including the brass spider threads, all the stainless nuts, the mirror edge (primary) the inside of the tube rings (worth it) etc.

Have you wrote a report using your scope yet? It will work fine as is.

[Moonshane]

It never fails, the weather. making us look at our scopes rather than through them and effectively creating problems that are not really problems. I am exactly the same naturally. I doubt that the clips will have a marked effect on anything but as we all strive for the best optics and optics train we can put together every little can count just a bit.

[osbourne one-nil]

I'm still tinkering with trying to get the replacement secondary properly aligned. The initial views were gorgeous, but then the subsequent views were very dim. I think that was because it was hazy and the mirror was in the wrong place, but I'm getting there and it'll certainly be fine.

Just one thing though, the tube diameter....I've used a bit of software where I've inputted the relevant information (aperture of mirror, aperture of opening, focal length and eyepiece) and it does seem I'm not making full use of the aperture - or am I misreading that? That would be annoying - a bit of scatter or lack of contrast I can live with but at only 6" I want every photon I've paid for!

 

 

[Timebandit]

 

I would not worry to much about a couple of mm here or there of the end ring on the OO UK scope tube, and it's possible  minimal effects on the aperture .

You must remember at the heart of the scope is the mirror. And Orion Optics UK do make some great mirrors. That's why I own two of them. The minimal figure of what they consider there entry range is 1/6 wave ,and the highest I believe is 1/10 wave. This is some great optics which ever one you have. So your quality of mirror will make up for a couple of lost mm.

 

 

[Moonshane]

If you are really worried, you could buy a spare tube ring and put that in place of the top end ring. This would at least open up the tube end. I have also heard that the shape of the end rings might divert warmer air into the central area as it runs up the tube. Doing the above might also help reduce (or at least divert in a more effective way) the warmer air.

[jetstream]

17 minutes ago, osbourne one-nil said:

I'm still tinkering with trying to get the replacement secondary properly aligned. The initial views were gorgeous, but then the subsequent views were very dim. I think that was because it was hazy and the mirror was in the wrong place, but I'm getting there and it'll certainly be fine.

Just one thing though, the tube diameter....I've used a bit of software where I've inputted the relevant information (aperture of mirror, aperture of opening, focal length and eyepiece) and it does seem I'm not making full use of the aperture - or am I misreading that? That would be annoying - a bit of scatter or lack of contrast I can live with but at only 6" I want every photon I've paid for!

 

 

Dont worry (think) about this stuff IMHO-  these scopes work well as is, espc your f8 (?). Just collimate the scope-sight tube/cheshire combo- and give it a good try. If the scope is f8 it will dim objects sooner than faster ones mag wise.

[osbourne one-nil]

Here's the focuser....and my attempt at securing the secondary using what B&Q had available on a Sunday. It needs some work! 

[jetstream]

What f ratio is this scope? I'm curious what happened to the original secondary hardware?

This focuser (mine anyway) has caused me some grief- it barely works in the cold, has slop in the extension and reflects light all over the place inside the drawtube. Here's the f ratio deal- the steeper the light cone (fast f ratio) the more glare will result from reflective surfaces.

Bottom line- paint those shiny sec bolts, inside the focuser, those brass threads, stainless nuts, clip tops and at a minimum put a square of flocking behind the focuser. The sec edge should be painted too.

What do you collimate with? This scope should work well.

 

http://www.krylon.ca/products/camouflage-paint-made-with-fusion-for-plastic-technology/

 

[osbourne one-nil]

It is the original spider (or at least the one the scope came with) but it was only 25mm across so I bought a 35mm replacement. The 25mm flat had an M4 screw thread whereas the 35mm has an M6, so I opted to drill the middle of the spider out rather than use a thread adapter in the secondary. I wish I'd used the adapter. 

[jetstream]

1 hour ago, osbourne one-nil said:

It is the original spider (or at least the one the scope came with) but it was only 25mm across so I bought a 35mm replacement. The 25mm flat had an M4 screw thread whereas the 35mm has an M6, so I opted to drill the middle of the spider out rather than use a thread adapter in the secondary. I wish I'd used the adapter. 

I'm just curious, why the changes- is this the original secondary?

[osbourne one-nil]

Apparently the original purchaser ordered if from Orion as a specialist planetary scope, although the secondary came from Oldham Optical. I bought it on a spur of the moment thing without really thinking it through, but the general advice I got, both on here, CN and from Orion themselves, was that a 25mm secondary was too small for general use. 

[jetstream]

Whats the f ratio?

[Moonshane]

Assuming your centre of secondary to focal plane is 7" (this is a rough guess) and your scope f8 the min size is 7/8 of an inch so 25mm should be ok unless using very wide afov eyepieces at low magnification. I have the same one in my 6"f11. The 35mm might increase edge brightness slightly but may reduce contrast. I doubt you'll see it visually though unless you go really big or really small.

http://garyseronik.com/sizing-up-the-newtonian-secondary/

[Moonshane]

According to the diagram it is f8?

[Moonshane]

Ps here's my view down the 6" f11. My clips are pretty large. I might mid them too

 

[jetstream]

I've played around using central obstructions from about 22% to 38%. The 38% still gives VG sharp views but contrast on the dark full moon "seas" are down a bit for example, 25% obstruction in my VX10 f4.8 gives fantastic high contrast views on everything. A couple of scope/optics makers feel that while less is better an obstruction at or below 25% is optimum.

Shane nailed it describing the effect in his above post ie illumination. Either secondary will provide VG views and the larger one might offer more flexibility to your scope ( using  low power widefields). If it were me I'd collimate it, get it under the moon and enjoy! (these scopes are known as "APO" killers ).

 

ps- speaking of collimation...how do you collimate Osbourne?

[osbourne one-nil]

Yeah, it's an f8. I too read Gary Seronik's article and thought I must be getting a great combination but also read that the mirror would just be too small. My widest field eyepiece is a Panoptic 24mm and I've no intention of using 2" eyepieces, so I have probably been too hasty! I've still got the 25mm secondary of course, but I'd have to pack the hole in the middle of the spider to get the M4 bolt needed to secure properly. To be honest, I think I need a new secondary spider anyway because whatever I do, I can't get the secondary to tilt enough to align through the focuser without applying what seems like way too much pressure using the collimation bolts. I'll take a look and see if I can find anything...or talk to OO again. 

Thanks both!

[Astrobits]

Try using this web site for determining the optimum secondary size for you:

http://www.bbastrodesigns.com/diagonal.htm

Nigel

[John]

FWIW, my 12" F/5.3 has a 63mm minor axis secondary which is a 21% obstruction. I've had no difficulty in using 2" eyepieces with large field stop diameters with that scope. It does pretty well on the moon and planets too

 

[osbourne one-nil]

Thanks - I still think 16% was perhaps a bit small. I'm trying to get my head round those charts (thanks Nigel) but I need to measure the focal plane distance first. 

[Astrobits]

Basically, they show the fully illuminated area of the focal plane and how much drop off of magnitude to the edge of the field of view.

I put your figures into the boxes and initially could not get it to accept a secondary so small as 25mm, until I increased the allowed magnitude drop off figure. I assumed a secondary to focal plane of 7 inches/175mm. At that you have a fully illuminated area of about 4mm dia. in the centre of the field of view--fine for planetary. The largest secondary-focal plane distance for a fully illuminated central point in the field of view is 195mm. Anything larger and you do not get any area fully illuminated as the secondary is too small.

Nigel

[jetstream]

8 hours ago, osbourne one-nil said:

I can't get the secondary to tilt enough to align through the focuser without applying what seems like way too much pressure using the collimation bolts.

?

When I collimate I have the sec so it can be turned by hand, making it round under the focuser. The big bolt will allow the sec to be moved "fore and aft" and then centered under the focuser using a sight tube. I tighten the big bolt a bit and then line the cheshire crosshairs up in the primary mirror donut using the 3 sec adjustment screws. Line up the primary and then do it all over again. Done.

Is this how you do it?

[osbourne one-nil]

Yeah, absolutely, but I think the vanes have got twisted so no matter how I orientate the spider within the tube, I can't get the secondary to tilt towards the focuser properly; I'd need to bend the bolt the secondary is attached to. It's difficult to explain, but I've ordered a new spider and it'll all be good!

[jetstream]

I put an Astrosystems spider and sec holder in the 200mm f3.8, it sticks out a bit but works great, all flat black and covers the sec edge.

[osbourne one-nil]

I've ordered a replacement OO one for now as I'm hoping it'll just slot straight in.