Louis D

3 hours ago, PeterC65 said:

I’ve been investigating ways to maximise the FOV of the Skymax 127 with the aim of getting a proper look at M31.

As @Louis D has mentioned, one way is to upgrade to a 2” optical pathway and then use a 40mm (or longer) EP. I’ve already upgraded the diagonal to a 32mm prism and added a 1.25” helical focuser (to allow fine focussing). I’m still waiting on more parts to put both of these in to action so for now I plan to stick with the 1.25” optical pathway.

Another option seems to be the Baader Hyperion Aspheric EP. These are available at 31mm and 36mm although both would be stopped at 30mm if I stick with 1.25”. The EP FOV is 72° and that would give me an overall FOV of 1.44° compared with 0.77° for the Baader Hyperion Zoom at 24mm. That seems like a difference worth having.

What do others think of the Baader Hyperion Aspheric EP?

Based on reports I've read, the BHAs would be decent buys if they cost around $100, not $200+.  They are improved Erfles, but not enough to justify the additional cost.  There is significant astigmatism in the outer 25% of their fields.  The 1.25" adapter on them leads to heavy vignetting even in a true 2" light path, so not recommended.  It's just too close to the field stop.

The 30mm APM UFF, which is now sold under Altair, Celestron, Meade, and a few other brands, is insanely good for the same money when you get a true 2" diagonal.

The 35mm Aero ED is a better deal than the 36mm BHA at around $100+ if you can find it in stock.  They're recently discontinued, but there might be a few still available in UK/Euro stores.  Don't back order them, they won't ever come in.

5 hours ago, Don Pensack said:

The only figure where I disagree with Louis is the eye relief of the 30mm APM.  I couldn't see the entire field at 16mm effective eye relief, yet it's easy to do so.

I agree it feels like 18mm in actual use, but the point where the image circle is smallest is 16mm from the flipped down eye cup using the projection method.  I remeasured it a few times because it didn't align with my ER experience with it.  It's not the only eyepiece with this divergence between measured and "feels like" distances.  For instance, the 22mm AT AF70 also has a repeatably measured 16mm or usable ER, but feels like 18mm in use (eyeglasses just above rim).  The 22mm NT4 has 14mm of measured ER, but feels like 16mm in use (I have to push in a bit on my glasses).  The 17mm ES-92 has a measured 16mm ER, but feels like 17mm in use (eyeglasses just touching).  The 35mm Baader Scopos Extreme has 16mm of measured ER, but feels like 18mm.  That last one actually has about 35mm of design ER thanks to its 47mm diameter eye lens, but the eye lens is recessed about 17mm, IIRC.  As an experiment I screwed off the top and put a flat lens retainer over it to get to about 30mm of ER.  Even for an eyeglass wearer, that was too much ER!  I had trouble holding the exit pupil because I had no frame of reference touching either my glasses or nose.

I guess I need a measured ER and a "feels like" ER.  The problem with the latter is that it is very subjective.  I'm going to try to measure it someday with a cardboard tube wrapped around the eyepiece and pushing it down with the phone's camera until the field stop pops into view.  I would then measure and record the distance from the top of the eyepiece to the top of the tube.  After measuring a bunch of eyepiece ER distances this way, I should be able to come up with a constant offset that accounts for the location of the camera's entry pupil inside of it by comparing these numbers against the ER distances measured using the narrowest projected image circle.

2 hours ago, globular said:

How would you go about moving the EP off axis while the telescope/lens stays on axis to measure edge aberrations? 
This is really needed to stop telescope off axis aberrations being captured. (Which is much harder to minimise with careful telescope selection than is the case on axis.)
I wonder how Ernest did it?
I think we need a 3D printer to .....  are we drifting off topic??? 🤔

If you have an optics test bench as Ernest does, you just move a vernier to slide the eyepiece side to side independently of the image forming lens.  Something along the lines of putting this:

on this:

If I came across some well priced, surplused equipment in this realm, I might go this route someday.  However, I'm not really that serious about getting exact results.

Actually, I just remembered I have one of these macro focusing rails that could be used for this with a few clamps:

I believe Ernest uses a telescope with micrometer eyepiece to look into the exit pupil of the eyepiece to measure the aberration spot sizes.

I also believe he always uses the center of the lens and moves the eyepiece across its central axis to take measurements so lens edge aberrations do not figure into the equation.

I've measured the Morpheus 9mm to have a 78° AFOV both via projection and image photography.  The 14mm comes in at 77°, and the 30mm APM UFF comes in at 72°.

Usable eye relief was measured to be 20mm, 18mm, and 16mm for the three, respectively.

Your observations about AFOV and ER match up pretty well with my measurements.

I thought SA referred to Spherical Aberration, a common issue with mass produced, short tube refractors.  My ST80 from 1999 has loads of it.

It boggles my mind that my ancient (90s vintage) Sky Commander DSC can do a bang-on two star alignment every time without leveling, polar alignment, or geo location.  Date is only need for solar system objects.  Objects are always within a few degrees with rough initial alignment that I then refine with "realign on object" for each centered object.  Modern DSCs should be miles ahead of it by now in accuracy.  Can you realign on an object once you center Jupiter or M31 and get good gotos after that?

1 hour ago, Mr Spock said:

All I can say is that ortho must be an inferior type. Mine are all razor sharp in a 250mm f4.8 Newt which has no field flattening or other assistance.

Here's a few images I've just taken with that scope and the 25mm, 18mm and 12.5 mm Circle-T orthos.
This test was difficult: I had to put my chart at the top of the garden and my scope in the house. The plane wasn't centred or flat and I couldn't hold my phone in the right place, or hold it steady enough. Even so, I'm sure you can see the results.

The scope is in perfect collimation, which helps a great deal with sharpness. I just wish I could capture accurately what I'm seeing through the eyepiece. I think as a demo this is good enough though.

 

I'll agree, that's more what I was expecting.  It's the first time I've gotten such a disappointing used eyepiece.

5 minutes ago, Highburymark said:

Wouldn’t a Baader clicklock solve your problems Don?

I have more problems with the 2" compression ring in the GSO CC and 2" 2x ED Barlow than with any 1.25" adapter.  I have toyed with the idea of getting a BCL with 47mm extension to replace the GSO CC eyepiece holder, but I've read of several horror stories of BCLs getting stuck in the lock position over the years.  There seems to be no agreed upon way to easily release it when that happens.

4 hours ago, astro-erago said:

Recommending a rigid storage container of the appropriate size would have been a far more positive contribution 

That's my point, I've never come across one.  Does anyone remember what brand or style he recommended?  Or, could someone post a link to the original suggestion?  It just struck me as a very odd idea based on my experiences with plastic totes over the last 30+ years.  I'm not saying the idea doesn't have merit, because it does solve two problems at the same time.  I'm just not aware of any decently rigid, and yet affordable, plastic storage bins.  If the suggestion had been for a flight case as used for transporting music gear for traveling bands, I'd have been in complete agreement as they are very tough and rigid.

Perhaps I'm not thinking of the correct thing when some says plastic storage container.  I think of the following:

Which are no where near as rigid as a tripod or pier, or even a picnic table.

However, a professional flight case flipped upside down or on end and off its wheels might be suitably rigid:

24 minutes ago, skyhog said:

Start to show your age when it's possible to remember several ring plane crossings. I remember them fully open high in taurus in the winter of 74. What I'd give for a repeat of that... 😁

Reminds me of an episode at work.  During a meeting, our team lead said "We've got a long way to go" and I finished his thought with "and a short time to get there" from the theme song to Smokey and the Bandit (1977).  Another old timer says to me "You're showing your age Louis".  We then did a quick poll of the room, and we were the only two who got the reference.  I felt so old at that moment.

Vintage binoculars were sometimes made with magnesium frames and touted how light weight they were.  Despite this, they were very heavy by modern binocular standards, probably due to often using oversized porro prisms to allow for very wide angle views.

I've also bought some of the tungsten carbide (I think that's what you meant) rings.  They are pretty awesome.  They can't normally be scratched (Mohs 9.0) and the dark reflection is really cool looking.  Their heft is pretty incredible as well.

Silicon carbide is fairly light, actually less dense than diamond.  It is known as Moissonite in the gem trade.  It has lots of industrial uses when not gem grade thanks to its extreme hardness (9.5 on the Mohs scale).  However, it is not a metal.

I have a brushed titanium band that looks really industrial thanks to that metal's rather unappealing shade of gray.  I never bought another because of that.

It reminds me of the original IBM PC keyboards that had a hefty steel plate in the bottom.  At some point, it was removed and everyone immediately equated the lack of heft to being poorer quality despite everything else being the same.

33 minutes ago, markse68 said:

maybe but it’s a wear surface so ss would be better. Brass is heavier than ss also.

Mark

Brass is barely heavier than SS, especially as either compared to aluminum or delrin.  However, SS could be made with thinner walls than brass to yield similar strength characteristics.  In that case, it would definitely be lighter overall than brass.

1 hour ago, Don Pensack said:

Stainless steel doesn't have that shiny chrome look, though.

I guess you haven't seen all the nice SS jewelry coming out of China lately.  I've bought quite a few bands and faux gemstone rings through ebay for cheap, and the SS they're using takes a very high polish and doesn't seem to tarnish at all in my experience.  It's a different "whiteness" from sterling silver, but still quite mirror-like.

I don't recall it being brought up earlier in this thread, but the rings have been "closing" for several years now, making it harder and harder to make out ring details:

2 hours ago, Nugs said:

Decided to pass on the 25mm starguider as there has been some mixed reviews, so 25mm GSO super plossl  added to the order, being express shipped thanks to our friend Zoltan at 365astronomy. 👍

I would have gone with a 32mm GSO Super Plossl to max out the field of view in that case.  I have one, and it's a very nicely made eyepiece.

7 hours ago, astro-erago said:

He keeps his in plastic storage containers to move them, then flips the box/barrel over and puts the scope on the container.

He must have found some really rigid plastic storage containers, then.  All the plastic storage bins I've used are made from very flexible plastic that deforms easily.  Maybe they're rigid enough for a lightweight scope to sit on top of.

2 hours ago, Don Pensack said:

Some collet style adapters do not, so they can tip:

https://www.highpointscientific.com/baader-clicklock-2inch-to-1-25inch-adapter-t2-15b?utm_source=google&utm_medium=cse&utm_term=BAD-T2-15B&gclid=CjwKCAjwmqKJBhAWEiwAMvGt6AskBk8OqRTcxNGFBH7EoNEHB3a3oJr9vtaDY0obQwvjOTP1qLrtfxoCFi4QAvD_BwE

With that one, the fit depends solely on tolerances of fit of barrel through the opening.

On top of possible tipping, one European user on SGL posted a video review where he complained that the Baader Clicklock pushes the barrel of whatever it's clamping to the side.

So, the BCL isn't even self-centering.

1 hour ago, johninderby said:

Did some testing using 2” diagonal on a 127 mak and found that while you could get a slightly wider fov with the right 2” eyepiece it wasn’t a lot more and decided it wasn’t worth bothering with. 

To each their own, but I found as stated above that using a 40mm SWA eyepiece with a 46mm field stop increased the linear TFOV from 1.1° to 1.8° and made it a lot easier to get objects centered after getting the telescope in the general vicinity with either an RDF or GLP.  Since I already had the 2" diagonal and 2" eyepiece, all it took was adding the step ring and SCT 2" visual back.  When I went to buy another one for my daughter to take on her camping trips, it arrived with everything but a max field 2" eyepiece.  I'm letting her borrow a couple of mine until she decides what she wants to buy for herself.  At f/12, most wide field eyepieces look pretty good.

The 1.8° TFOV also makes scanning rich star fields more rewarding.  It's obviously not as good as with a short refractor, but it is better.

11 minutes ago, floyd fan said:

Just within your price range is an Astro Fi 6 from Rother Valley optics.

 

https://www.rothervalleyoptics.co.uk/celestron-astro-fi-6-sct-wifi-telescope.html

It's certainly very cool looking in black with that snazzy graphic on its side:

13 minutes ago, Captain Magenta said:

Fair enough; I also haven't dared for similar reasons

Most eyepieces I've dealt with use the lower base plate to hold the eyepiece lenses in place in lieu of a separate retaining ring, so caveat emptor.

10 minutes ago, JamesF said:

To expand on this a little, M31 is about 3°x1° whereas the full Moon is about 0.5° in diameter, so if you think about how the Moon appears in any given eyepiece, that gives you some idea of how much of M31 you can see with the same eyepiece.

James

But unless you're in quite dark skies, you won't see much beyond its core.  It's surface brightness just isn't enough to overcome most skyglow.  You should be able to make out one or both of its two brighter satellite galaxy cores as well.

3 hours ago, PeterC65 said:

@Louis D can you tell me what step-up ring you used? I've just received a Baader SCT to 2" ClickLock which was recommended by my scopes supplier in the UK (First Light Optics), but it doesn't fit. The SCT thread is bigger than the one on the visual back of the scope so I need to know what that thread size is (clearly not SCT).

39 minutes ago, Zermelo said:

This one?

https://www.firstlightoptics.com/adapters/lynxastro_makcas-sct_adptr.html

@Zermelo nailed it.  You just screw that adapter onto the existing rear thread, and presto-chango, you have an SCT thread that accepts myriad attachments.

Once attached, it does look like the image below from the thread referred to above:

4 hours ago, John said:

The Ethos SX 4.7 and 3.7 use just that approach as well. I was using my 4.7 last night and it's a great high power eyepiece with my 12 inch dob

It appears that the TV Apollo 11 also comes with a 2" sleeve:

Maybe it would have been $50 cheaper without it?

15 minutes ago, Don Pensack said:

TV looked into this and over a decade ago the barrels were about $50 apiece at TeleVue's cost.

Then there is the labor of changing the barrel.

 

This might be a solution for a machinist who can make his own, but it's not commercially viable.

 

That "discontinued" 17mm AF70 shown above in my pic has a removable 2" barrel without an undercut.  I seriously doubt it added $50 to the cost of that eyepiece.  Was TeleVue considering having Starlight Instruments CNC machine them at that price?