John

3 hours ago, johninderby said:

You don’t want to pour water over a mounted filter. Much better to use the proper stuff. Spray a little bit onto the cloth then clean the filter. Never spray directly onto the filter.

As above. Keep the ionised water for mirrors.

What do you want to use it for ?

If I had been able to mount it in in observatory like @Rusted has I would probably still have my Istar Perseus 150 F/12

As a free standing scope that needed to be setup and taken down each session it was just not a practical proposition

I have a Berlebach Uni 28 and a 2 inch steel tubed EQ6 tripod. The Berlebach looks fabulous but the 2 inch steel tube tripod gives pretty much the same stability I reckon. The Uni 28 goes a lot taller of course but the EQ6 is not really a "shorty" either.

21mm is my favourite eyepiece focal length with my 12 inch dob. Add an 8mm to it and I can be happy for a whole session of Ethos magic

1 hour ago, NGC 1502 said:

That’s an excellent example of a properly ventilated cell.  It’s very different from older OO UK cells that were poorly ventilated, a solid closed back with just one central 10mm hole.

Ed.

The Orion Europa range had the "mirror cell" that you describe. They dropped that range when they moved to the VX series a few years ago. My scope was what used to be known as the SPX series.

+ 1 for @johninderby's recommendation. That's what I use on my eyepieces and filters along with a hurricane blower for the initial dust removal.

2 hours ago, NGC 1502 said:

Having said that, my OO UK 10” Dob is a great scope that I enjoy using,  but would be better without those issues.  I lessened those problems by increasing the primary cell ventilation (earlier OO mirror cells had a solid back with just a single 10mm diameter hole) and removing the lip from the upper tube trim.

Ed.

 

My OO primary cell could not be more ventilated really. There is a small fan there but I don't use it.

That's the nice thing about a zoom - you can try a range of magnifications out instantly and find what is working best at that time and on that target. On nights of very good seeing conditions you have more in hand, if you want to use it.

The other great thing about the Nagler zoom in particular is that it gives very little away in performance terms to specialized fixed focal length eyepieces such as orthoscopics.

1 minute ago, Ruud said:

....A guide ring like the one that Don showed is intended for use near the exit pupil and is wide enough to allow all beams through. It's an aid for finding the exit pupil.

To be fair to Don, it was me who introduced that into the thread, and I wish I hadn't because it's not really relevant.

5 minutes ago, Don Pensack said:

But the pupil guide had to be used at or near the exit pupil or it would vignette the image.

Yep, I realize that now !

I hardly used the things when I had TV eyepieces that came with them and that was quite a few years back now.

Wish I'd not mentioned them .......

Good stuff !

With regard to the zoom, at 4mm you are at 200x and 3mm 267x. These are very high magnifications for an 80mm aperture scope to support so I think their usefulness will be somewhat more limited. 

Ah, yes that's true. I didn't used to use the things but I recall that the instructions said that they should be used with the top section of the eyepiece raised ie: not close to the eye lens. It's been a long time since I owned a TV eyepiece that came with them - T4 Naglers and Radians I think.

It is indeed to help find the exit pupil, hence it's name

I'll get me coat ......

Should there be a link to and adapter or something Simon ?

2 inch diagonals do have longer light paths than 1.25 inch ones but that should not pose a problem for the mak-cassegrain because they have a lot of of focus travel.

4 minutes ago, Pixies said:

Is that little dovetail moulded into the main part, or bolted on?

 

I was thinking just that !

13 minutes ago, Louis D said:

Okay, I missed the point of the second diagram taking into account the exit pupil diameter.  Basically, just a one to one linear offset for EP diameter.

I think what @andrew s is saying, what if the edge of the eye lens were masked with a circular aperture mask?  The telescope and eyepiece focal lengths would remain the same since none of the curves changed, and the exit pupil would remain the same, but some of it would have to be vignetted.  Any thoughts on the validity or speciousness of this argument @Ruud?

The pupil guides that Tele Vue supply with some of their eyepieces do mask quite an area around the edge of the eye lens but you can still see the full field and, from what I recall, with no vignetting

23 minutes ago, Robindonne said:

Those weird looking open or flex tubes aren’t that weird at all🙂

The truss design has advantages with cooling. In the winter months warm currents of air from the body can get into the light path though. I found that a light shroud helped with that and keeping stray light out of course. Also for keeping debris off the primary mirror.

I'm just not sure that, in the apertures that we amateurs generally use, that the cooling of the optics themselves, in terms of the optical figure, makes a lot of difference 

Keeping the light path clear of air currents certainly does make a lot of difference though.

17 minutes ago, Ruud said:

It's impossible if you consider how the exit pupil is formed.

 

Yes, that's what I thought

Interesting experiment.

The ultimate low scatter, high transmission eyepiece is reputed to be the "ball" eyepieces comprising a single spherical element. Miniscule AFoV and eye relief though.

Siebert produced a commercial version, the Planesphere series:

https://www.siebertoptics.com/Planesphere.html

Makes sense to me Kev

I don't find that I need to use the fan on the primary cell of my 12 inch dob. The tube seems to cool quite effectively in 30 minutes with the top cap off.

Perhaps the label should state "Do not consume this telescope eyepiece or attempt to use it as a drinking vessel" to be sure.

Sort of thing that made "Wonko the Sane" the person he was. Funnily enough, he lived in California

Douglas Adams was ahead of his time ........

Do you have a 2" diagonal ?

The 2 inch fitting gives you the wider field of view so is good for low to medium power viewing but for higher powers there is no advantage to the larger fitting.

I've used my Lunt 1.25" Herschel Wedge quite often with my ED120mm refractor and the combination works well and safely.

2 hours ago, InterstellarTim said:

....looks impressive, not sure what the wife would think having that in the back of the lounge here ha....

 

The scope is a 130mm F/9.2 triplet so about the same size as the 127L. Perhaps a touch heavier at 9.5kg.

Is the cooling about removing warmer air from within the tube and, if possible, disrupting the boundary layer or is it about actually cooling the glass temperature ?

I've always considered the former to be the key thing rather than the latter ?