Louis D

They should be left "totally" loose for normal visual astronomy when using the built-in focuser.  They're mainly there for transporting the telescope and to lock up the mirror during imaging (as when a secondary focuser replaces the normal visual back) to prevent mirror shift as the telescope changes orientation while tracking across the sky.  If you lock up the mirror and try to focus using the built-in focuser, you're likely to break or bend something because the scope focuses by moving the primary mirror.

If you do decide to keep it, regardless of cleaning it, document the undisclosed fungus with macro photos clearly showing it and demand a commensurate refund of part of the purchase price as compensation for your troubles.

On 15/09/2020 at 13:55, globular said:

I'm actually thinking of a filter slider... so I'd slide in 2" or 1.25" filters (or no filter) as required.  This is independent of the EP barrel size (other than making sure the field stop of a 2" EP is < 20mm if I'm using a 1.25" filter in the slider) so I wouldn't use an adaptor like the above as such.

It amounts to basically the same thing though - except it happens a bit earlier in the light path - so I'll post back with results once I've tried it.

It will vignette the light path more as you would expect.  Most Dob filter slides are 2" for this reason.

2 hours ago, Dantooine said:

Tough call.

22 nag/21E.

Torn between two lovers!

The 22mm NT4 comes up used quite often here in the states for about $300 give or take $50, so you might want to check the classifieds over there for one.  I picked up mine for $250 just a year ago.

I'm pretty sure it's 75mm from the sensor or eyepiece field stop to the top of the M48 threads on the optical nose piece.  You may have to adjust it a bit to find the optimal spacing.

I have the High Point (now Apertura) version, IIRC.

3 hours ago, Dantooine said:

so does the 22mm feel anything like my ethos in use?

Hopefully @Don Pensack can chime in here having owned and used both.  In the meantime, I found the Ethos restricted to about 70 degrees with eyeglasses at star parties.  When I took off my eyeglasses, ignoring massively astigmatic stars, I had to push my eye into the eye cup to see the entire field.  That does cut off any perception of the non-eyepiece FOV world.  Comparatively, my ES-92s are very relaxed and seem more like looking out a bay window from up close.  The 22mm T4 views similarly, just through a smaller window.  You're aware there's a world surrounding the view due to the more generous eye relief.  It is possible to raise the Instajust eye cup if you want a more Ethos-like experience of excluding the outside world, just with a smaller AFOV.

2 hours ago, Dantooine said:

That’s very interesting for me. Would you say that the 22 Nagler is a good alternative to the 21 ethos?

I have a pan 27 at the moment and I think it shows about the same field as the Nagler. I have never used a Nagler so for me it’s venturing into the unknown. There is a big difference in price in the uk. 

Certainly if you wear glasses the 22mm NT4 is a good alternative.  It's what I ended up with at that focal length.  The difference in field stop diameter is negligible between it and the 27mm Panoptic.  They feels worlds different in usage, though.  The Nagler is just so much more immersive and easier to take in the field stop with eyeglasses than the 27 Pan.  The 30mm APM UFF is noticeably wider than either having a field stop over 5mm larger in diameter, making it just about the same TFOV as the 21mm Ethos.

The working distance is around 75mm as you say.  It magnifies 1.10x (10%).  I usually only use it visually.  I did use it to capture the 2016 Mercury transit image below, so I know it can be used with DSLRs.

55 minutes ago, Dantooine said:

well, there would be a pan27 for sale

Much prefer my 30mm APM UFF to my 27mm Panoptic.  Better eye relief, better edge correction, flatter field, and noticeably wider TFOV.  The Pan might have a slight edge in on-axis sharpness, but it is very slight.  I can't use any 100 degree eyepieces due to my strong astigmatism in my observing eye, so no comparison possible for me vis-à-vis any Ethos.

Unless you're using a Newtonian with limited back focus, you should be able to do DSLR prime focus photography with a 2" to T-thread adapter and a T-mount for your camera.  If you're using a Newt with limited back focus, you can try to use a 2" Barlow or a GSO/Revelation coma corrector with the optics section threaded onto the front of the 2" to T-thread adapter.  You won't be able to vary magnification much except with the Barlow approach.

1 hour ago, gorann said:

And then what? - just kidding!😉

Try to get it on APOD?

On 10/09/2020 at 15:59, Alan64 said:

There are no 6mm, 8mm, 10mm, or 12mm eyepieces with 2" barrels

🤔 12mm ES-92 is 2" only.  There are also the 5.5mm, 9mm, and 14mm ES-100 eyepieces as well as the 9mm ES-120.  I can't think of any 6mm, 8mm, or 10mm 2"-only eyepieces, though, as you say.

Are you thinking using a 2" to 1.25" Filter Adapter?  If so, let us know how well it works for you.  I haven't read any actual reports on their usefulness.

1 hour ago, alan potts said:

I was calling this list Shapeless, which of course most are.

At first, I didn't realize Sharpless was a person's name.  I thought it was a description of the type of objects, as in "These are less sharp objects".

4 hours ago, gorann said:

Lovely shot indeed! I really should put my Samyang 135 more to work. One problem with it, and as Kinch suggested, is that with such a wide field you will finally one day run out of object as it covers such a waste area and almost all good targets are in the Milky way. Of course, at that point of time you could always move to the southern hemisphere😉

At that point, it would be time to stitch them together into an all-sky panorama. 😉

You never specified where you would be observing from and if transporting the telescope would be an issue.  For example, I put together a 127 Mak on an alt-az mount for my daughter and her fiancé to take along on camping trips in her CUV.  There wouldn't be room in the back for an 8" Dob with all of their camping gear.  I also thinking of sending along my AT72ED if the 127 Mak's narrow field of view becomes an issue for them.

And first 10 units of the 9mm ES-120 didn't have their field stop inserted, so they actually have a 140 degree AFOV.  The observers who got them aren't letting them go from what I can tell.

1 hour ago, Dantooine said:

when first see about the bag of washers as a counter balance I imagined a swinging pendulum. It must act as dead weight. 

That's why I have to dampen its swing when moving quickly in azimuth to a new target (by dampen, I mean grab it and stop it from swinging).  It is indeed a swinging pendulum.  Fortunately, moving slowly in azimuth to track doesn't induce the swinging motion to it.  Moving in altitude has no effect on its side to side motions no matter how abrupt.

22 hours ago, John said:

Will that show you any more sky than your current 35mm 2 inch though ?

Let's run the numbers for TFOV:

35mm Orion DeepView: 37mm Field stop (Orion's claim) = 1.77°

30mm APM UFF: 36.4mm FS (my measurement) = 1.74°

30mm ES-82: 42.4mm FS (my measurement) = 2.03°

30mm 80° Wide Field III clone: 44.2mm FS (my measurement) = 2.11°

31mm Nagler T5: 42.0mm FS (Tele Vue specs) = 2.01°

35mm Panoptic: 38.7mm FS (Tele Vue specs) = 1.85°

35mm Aero ED: 44.4mm FS (my measurement) = 2.12°

40mm Meade 5000 SWA (Maxvision SWA): 46mm FS (my measurement) = 2.20°

I have my doubts about Orion's field stop diameter claim because that would imply either a 61° AFOV with little distortion, or large amounts of edge distortion to squeeze in that additional 5° of AFOV at the edges in the claimed 56° AFOV.

The OP has lots of options of varying degrees of edge correction, eye relief, weight, and price to choose from.  My preference would be the 30mm APM UFF to start with.  It may not be much wider, but it will be so much better corrected and will feel much wider with its measured 72° AFOV.  That, and it has very comfortable eye relief.

Have you tried to put a 1.25" insertion barrel cap on top?  I know that some of these style eyepieces are close to symmetrical top to bottom as far as diameter.  The rubbery yellow/red vinyl caps might stretch enough to fit if the upper barrel is a bit oversized.

3 hours ago, Rob_UK_SE said:

I recall once seeing an ingenious homemade solution bu Stu that added a counterweight on the opposite side of the focuser. I once tried to replicate this, but failed spectacularly!

I have a 6" bolt that I screw into a threaded hole on my alt-az mount at 90 degrees to the OTA (on the bottom, rotating up to the front at high elevations).  I then hang a plastic grocery bag filled with a pound to two pounds of metal washers and bolts I had laying around to counteract the backward tilt of heavy eyepieces near zenith.  At lower elevations, it has little to no effect other than to bang into the tripod legs as I rotate in azimuth.  Being a plastic bag, it just moves out of the way.  I do have to dampen the swinging manually when that happens, though.  It works like a charm to prevent my rig from turning turtle near zenith, though.  It just looks literally trashy.

On 12/09/2020 at 12:52, Don Pensack said:

I can successfully use eyepieces that have long eye relief and yield a <0.5mm exit pupil, but the eyecup has to touch my nose or eye socket to help hold my eye in the right place.

I have so many bulbous, long eye relief eyepieces and a long enough nose that I get to know the right eye position by the feeling of my nose touching the upper body of the eyepiece while hovering.

Not sure what you mean by "light reflection".  Based on the price, I would think it has a budget first surface mirror.  I have no idea how well collimated it would be nor how optically flat it is.  I would think it performs best at 90 degrees, getting slightly worse toward the 45 degree end of things.  I would be concerned about vignetting at 45 degrees if the mirror wasn't made large enough.

I think it's based on an oversized mirror, so it's not going to flip the image left for right like the Amici prism diagonal.  As such, it won't introduce a spike on bright stars.  Also, it wouldn't be a replacement for an Amici prism for terrestrial use since it doesn't flip left for right.

Depends on the condition of the finish at that price point.  Are there blemishes or other wear marks aside from the dovetail?  Don't forget to account for your costs to pick it up compared to shipping costs.