96 replies to this topic

[Starman1]

It doesn’t change the focus position but it changes the focus travel.

If you use a Morpheus as a 1.25", the eyepiece's shoulder rests at the focal plane of the scope.

If you use a Morpheus as a 2" eyepiece, you have to out-focus by 21mm to bring the focal plane of the eyepiece up to the focal plane.

It sounds like what is needed is a way to bring the eyepiece closer to the scope, and using the Morpheus as a 2" will bring the focal plane of the eyepiece closer to the scope.

Will is be enough?  It depends on how much additional in-focus is needed.

 

Use of a prism diagonal may gain some additional in-focus, but only a few mm.

Use of Hyperion or Morpheus eyepieces as 2" may gain a centimeter or two of in-focus.

Use of a shorter focuser would help.

Use of a drop-in 1.25" adapter would help (Astrosystems Ultra-low adapter, Tele Vue In-Travel adapter,  or Baader Push-Fix adapter) and gain several mm over the standard height adapters.

[RichD]

I think the mirrors should be altered again, and recollimated if necessary. Remember the OP used 20 to 35mm eyepieces primarily.

Surely with scopes of this type (and cost) OGS should step in and sort this out.

[ausastronomer]

Surely with scopes of this type (and cost) OGS should step in and sort this out.

Absolutely.  It's not a Cloudy Nights problem to solve, it's an OGS problem to solve, at no cost to the purchaser !

[TOMDEY]

You can cut this much off of these eyepieces:

 

TV 55mm Plössl             32mm

TV 41mm Panoptic         24mm

TV 31 Nagler T5               8mm

 

Be careful when modifying the 31mm Nagler there... the glass will "stick out" a bit in the middle. Permanently bond those three to three Lumicon Star diagonals. At work, we would just epoxy them together as a "forever" assembly. Note that you can (should) also hack a lot of the receiver on the dedicated diagonal.

 

Advantage: No modification to your RC scope whatsoever.

 

> Be sure there will still be room for your eye to get in there without bumping into the back of the telescope.

> Not a "hack saw" job --- get an experienced machinist to do the mods if you lack the tools (lathe/milling machine) or skill   Tom

[eblanken]

Hi TOMDEY & All,

 

I believe that the OP's issue is with ". . . 20-35 mm eyepieces are our workhorses." (just repeating from original post here).

 

Best,

 

Ed

 

P.S. Still waiting for a Tabular List of what eyepieces are "in hand" at OP's location. . . 

Edited by eblanken, 11 November 2024 - 08:35 PM.

[EJN]

Try a prism diagonal. Any thick piece of glass in the optical path, such as a prism, moves the focal point further back. In the diagram below, n = refractive index (1.52 for BK7).

 

 

 

 

Edited by EJN, 11 November 2024 - 10:05 PM.

[cduston44]

in the past when i've had a similar problem with some of my short fl 1.25" orthos, i've used astrosystems  2" - 1.25" adapters with deep recesses that allow the eyepiece to sit closer. 

 

here is the astrosystems adapter to show what i mean

https://www.astrosys...ieceadapter.htm

 

if you happen to have a 2.7" draw tube for instance, having recessed 2.7" to 2" adapters made with the same idea  might help.  

 

edit 11/11

if you felt like it, you could even make adapters for all of the eyepieces you use to make them parfocal - which might be nice for public viewings.  

Well, the exit diameter of our focuser is 2", so I don't think this is an option for us. At least with the current focuser. Thanks for the idea though.

[cduston44]

why not just remove the diagonal? you wouldn't have to do gymnastics to view without a diagonal; if your object is higher in the sky, then you can just sit lower, right?

Yes, but that makes it harder for children to use the telescope, and that's the primary behavior I'm trying to retain.

[cduston44]

I would take a close look at the primary mirror support cell, and the secondary mirror cell.

 

To put the focal plane a little further out you need to bring the mirrors closer together and if you have the typical 3-point collimation screws this could be accomplished by turning all three screws 1 or 2 turns. As little as 2-3mm may be sufficient, because the focal plane shifts by the delta multipled by the secondary magnification squared.

 

You will have to re-collimate the scope after doing this.

Indeed, I agree that this is an option. I am reluctant to take that on myself with an institutional instrument (I have collimated i.e. newtonian reflectors before), but I'd rather that be like plan....D? or C.

[cduston44]

cduston44 says of the factory alignment "the result is a dramatic improvement in optical quality"; they adjusted the PM-SM spacing to correct the spherical aberration. Fiddling with the alignment of the mirrors at this point would probably meaning sending this 20-inch RC right back to the factory!

 

I measured a bunch of commercial Star Diagonals. The 2-inch Lumicon LumiBrite Star diagonal is the shortest added path of all 2-inchers (95.5mm). I don't know if this will bring all of your eyepieces to focus, but it's certainly the best possible (both in theory and in practice) in the 2-inch format.     Tom

Super helpful. I'll post the picture in another reply, but I don't know exactly what to measure for the light path of our Meade 2" diagonal. Looking at the picture, I'm guess it's an added path of around 2", which seems much shorter than your 95.5 mm minimum (I must not know how to measure that). Do you know the light path added for a Meade 2" diagonal? That would help know if that diagonal is a possibility.

 

EDIT: Bad conversion.....

Edited by cduston44, 12 November 2024 - 02:36 PM.

[cduston44]

The focal plane position depends on the individual eyepiece and not it's focal length. 

 

Some shorter focal length eyepieces should focus.  What eyepieces do not come to focus?

 

What diagonal are you using? The optical path length of various diagonals varies quite a bit.

 

Barlows can move the location of the focal plane...

 

Jon

I'll post my measurements here. The Diagonal is an old Meade - unfortunately I don't really know how to measure the light path added by the diagonal - right now I'm going to call it 2". You can see our selection of eyepieces all have barrels less than 1.75" (the top of the diagonal), so they all get 1.75" after hitting the diagonal. I'm mostly looking at the 35 mm vs 55 mm, because that's the line between in/out-of focus.

 

So, my estimate for the (minimum) light travel before it hits another lens is 5.625" + 2" + 1.75"=9.375", and this is too long for our 35 mm. Barlows help in the *other* direction right, move the focal plane *farther* away?

 

EDIT: Tonight I'm gonna run all these straight through, without the diagonal, to better investigate the light travel distance - I'll report back and we should have a better idea how much distance we need to claw back.

 

Edited by cduston44, 12 November 2024 - 03:15 PM.

[cduston44]

There are a few lines of great 1.25” eyepieces with long ER for easy viewing. Delos, Delite, Pentax XW, Nikon SW. The Televues typically focus further out than other brands, which could be helpful, although it sounds like you can reach focus with a 1.25” diagonal. If nothing else, you might be able to keep using the 2” diagonal and still use Televue 1.25” eyepieces. However, these eyepieces only go up to 18.2mm so might not hit your sweet spot.

My ES 24mm 82 focuses pretty far out compared to 1.25” eyepieces, also my 42LVW. I mean you want eyepieces that focus farther out, right? What 2” eyepieces are you currently using that you are unable to reach focus with.

Can you confirm that 1.25" and 2" eyepieces with the same ER are "just as easy to use"? I don't know know what ER means in that sense, and that's why we use the 2" eyepieces - easier for children to use.

 

The problem is between our 35 mm (the workhorse, really) and our 55 mm.

[cduston44]

Hi All,

 

From a diagnostic approach, I suggest OP provides us with photos and/or a sketch. Also it would be helpful to have a tabular list of eyepieces and measurements of focuser settings from full-in-travel to full-out-travel (and a "go/no-go" on achieve focus). I'm a measurements guy, so details like mm and cm can sometimes uncover issues & solutions (like Jon was asking). Also a tabular list of the eyepiece specifications with barrel size (2 inch vs 1.25 inch) would be helpful. We could from eyepiece model number cross reference to Coma Corrector II Settings and get a better sense of what is happening for/to the OP. How about a 1.1x Barlow to "bump out" the focal plane ?

 

Best,

 

Ed

 

P.S. Another thing to try (as a diagnostic) is to point the RC to "an object closer than infinity" which should shift the focal plane so more eyepieces achieve focus for the tabular data sets I'm asking for . . . just saying ?

I did a first run at measurements in another reply - agree they are needed, and I didn't provide exactly all the info you want here, but place to start. Tonight I can remove the diagonal and run straight through the tube, which will give us the best estimate of the light travel length, and the difference needed to achieve focus.

[cduston44]

I'm not sure why you're being so fair to the company.  You paid a very large amount of money for something that wasn't right in the first place, when it was delivered, and it should have been!

 

When you buy a new telescope, particularly something that costs as much as they do, it should be absolutely perfect when it's delivered, and the vast majority of eyepieces should reach focus.

 

Cheers

I know - and I don't want to tell you the price tag of building a crate, shipping a 20" RC, having it at the factory for 6 months, and having it returned. Needless to say, we are not happy. But at this point, in-house solutions might just be wiser.

[cduston44]

Is this scope primarily intended for imaging and not optimised for visual use from the manuf?

Seems strange that eyepieces worked fine with incorrect mirror spacing and now don't with the correct mirror spacing. Is this scope just intended to have a camera/sensor at the rear and no diagonal?

I too can't see what difference a computer controlled focuser would achieve. It wouldn't change the focal plane position.

Otherwise agree with ausastronomer above.

Ok great thanks for that answer about the computer controlled focuser, because that's also my understanding.

 

It's primarily an observational instrument (visual, rather), but we do have small research projects that involve cameras. The cameras don't seem to be a problem here, as they don't have the additional optics to shorten the light path (haven't checked them all, I guess).

[cduston44]

This may sound drastic... but considering it's a precious 20-inch RC >>> You could take your longer focal length eyepiece and literally "cut the end off" --- which may well include its field stop going in the scrap bin. Might also need to then cut down the receiver end of a 2-inch star diagonal so that eyepiece can nestle in farther than usual. Permanently mate that dedicated pair as a "custom 90^o eyepiece". It would come to focus nicely and become part of the dedicated eyepiece kit for the 20" RC, without modifying the valuable telescope at all. The edge of the visible field will be defined by the star diagonal... which is often the case anyway with a very long wide field eyepiece. As long as you are removing only metal structure, and not glass... this should work nicely!    Tom

 

PS: At work (Kodak Research Labs) we often butchered stock hardware to custom fit our concoctions. We'd take the parts to the opto-mechanical machine shop and the tool & die makers would perform the surgeries with operating room skill.

Ha, I had not thought about that yet. Fortunately, we have quite a few 2" diagonals lying around, and even probably some excess eyepieces. Certainly worth thinking about!

[cduston44]

Here is another thought.  When I purchased my OGS they were all supplied with Astro-Physics focusers.  If the OP has such a focuser all that may be required is an alternative adapter that provides more in-travel.  Specifically, this is one that I use when I have a focal reducer in the train:  https://www.astro-physics.com/ada20132

The focuser is Astro-Physics, but the exit barrel is 2" already, so no room for such an adapter, unfortunately!

[cduston44]

Ok so the options are:

 

1. Alter the mirror spacing to shift the focus back out.

2. Swap the focuser for a shorter one. 

3. Find a diagonal with shorter light path.

4. Hack the eyepieces to sit further in.

 

#1. Is feasible but means recollimating. No hardware mods.

#2. The VSI focuser isn’t the lowest profile possible which suggests a swap. Requires an adapter to be made and might yield  just a few mm.

#3. Might be possible, might not.

#4. Personally I would not start chopping eyepieces. They’ll never be the same afterwards.

 

My money is on #1, you’ll have to learn to collimate it.

But if the relative positions of the mirrors are important (something OGS was very clear about), it seems that going in and futsing around is not a brilliant idea. Sure, I could *maybe* move both of them the same distance, or....not, and then I just blew some thousands of dollars of our money!

[cduston44]

If you use a Morpheus as a 1.25", the eyepiece's shoulder rests at the focal plane of the scope.

If you use a Morpheus as a 2" eyepiece, you have to out-focus by 21mm to bring the focal plane of the eyepiece up to the focal plane.

It sounds like what is needed is a way to bring the eyepiece closer to the scope, and using the Morpheus as a 2" will bring the focal plane of the eyepiece closer to the scope.

Will is be enough?  It depends on how much additional in-focus is needed.

 

Use of a prism diagonal may gain some additional in-focus, but only a few mm.

Use of Hyperion or Morpheus eyepieces as 2" may gain a centimeter or two of in-focus.

Use of a shorter focuser would help.

Use of a drop-in 1.25" adapter would help (Astrosystems Ultra-low adapter, Tele Vue In-Travel adapter,  or Baader Push-Fix adapter) and gain several mm over the standard height adapters.

Ahhhhh I didn't understand this when I read it before. These eyepieces are like, *combos* 1.25/2, nested. That's interesting - indeed, that might be a solution. Maybe once I have a better idea what the legths are, I'll have a better sense of how workable a solution this is.

[cduston44]

You can cut this much off of these eyepieces:

 

TV 55mm Plössl             32mm

TV 41mm Panoptic         24mm

TV 31 Nagler T5               8mm

 

Be careful when modifying the 31mm Nagler there... the glass will "stick out" a bit in the middle. Permanently bond those three to three Lumicon Star diagonals. At work, we would just epoxy them together as a "forever" assembly. Note that you can (should) also hack a lot of the receiver on the dedicated diagonal.

 

Advantage: No modification to your RC scope whatsoever.

 

> Be sure there will still be room for your eye to get in there without bumping into the back of the telescope.

> Not a "hack saw" job --- get an experienced machinist to do the mods if you lack the tools (lathe/milling machine) or skill   Tom

Oh yes, a machinist job for sure. How in God's name would you perfect metal dust from impacting the optical surfaces? Lots and lots of painters tape?

[cduston44]

Try a prism diagonal. Any thick piece of glass in the optical path, such as a prism, moves the focal point further back. In the diagram below, n = refractive index (1.52 for BK7).

 

 

 

 

Ohhhh THAT'S a good suggestion, we might even have a prism diagonal somewhere in our bin of diagonals!

[chemisted]

The focuser is Astro-Physics, but the exit barrel is 2" already, so no room for such an adapter, unfortunately!

The 2" adapter that is shown in your photo can be removed from the drawtube by simply unscrewing it in the counter clockwise direction. The alternative adapter that I recommended will then screw on with ease. This is such an inexpensive and easy solution for you that I suggest you try it first.

Edited by chemisted, 12 November 2024 - 07:59 PM.

[luxo II]

But if the relative positions of the mirrors are important (something OGS was very clear about), it seems that going in and futsing around is not a brilliant idea. Sure, I could *maybe* move both of them the same distance, or....not, and then I just blew some thousands of dollars of our money!

In which case I would be writing a very stern letter to them to say thank you for screwing up your scope and it is now unusable, and suggest they send a fellow to visit you and correct it, at their cost.

 

And point out the issue is now all over CN, and up to them if they want to salvage a little reputation. 

Edited by luxo II, 12 November 2024 - 04:57 PM.

[Starman1]

I suspect that 99.999% of their scopes are ONLY used for astrophotography.

Ironically, cameras usually need additional in-focus from eyepieces, so the rear focuser is definitely too tall.

[ausastronomer]

I'm not sure why you're being so fair to the company.  You paid a very large amount of money for something that wasn't right in the first place, when it was delivered, and it should have been!

 

When you buy a new telescope, particularly something that costs as much as they do, it should be absolutely perfect when it's delivered, and the vast majority of eyepieces should reach focus.

 

Cheers

 

 

I know - and I don't want to tell you the price tag of building a crate, shipping a 20" RC, having it at the factory for 6 months, and having it returned. Needless to say, we are not happy. But at this point, in-house solutions might just be wiser.

 

 

In which case I would be writing a very stern letter to them to say thank you for screwing up your scope and it is now unusable, and suggest they send a fellow to visit you and correct it, at their cost.

 

And point out the issue is now all over CN, and up to them if they want to salvage a little reputation. 

 

Maybe the Consumer Protection Laws in the USA are different to Australia.  I don't know about that and you'd need to investigate.

 

In Australia, despite any express or implied warranties or guarantees from the manufacturer or distributor, there is legislation in place that protects the consumer from exactly this type of occurrence.

These Laws have been in place since 2011.  Unfortunately, less than 5% of the Australian Population are aware of them and only about 50% of manufacturers and wholesalers are aware of them.

 

It's worth reading the attached webpage as something similar may exist in the USA.

 

If this happened in Australia it would be up to OGS to make good and everything including shipping and packaging would be recoverable from OGS. Under the Legislation you are entitled to recover all of your out of pocket costs or damages in addition to the cost of the equipment.

 

The legislation is lengthy but it says, inter alia, "the product must be of merchantable quality and fit for purpose".  In Australia this would be a "no brainer" and OGS would be footing the bill for everything.  There are government departments that deal with this and enforce the legislation.  Another example might be if a product has a 1 year manufacturers warranty.  About 2 years ago I had a friend that had a cappuccino machine, which cost just over $3,000 that was just over 2 years old die and they wanted $1,400 to fix it, as it was outside the 1 year warranty.  He wasn't aware of the Consumer Protection Laws and neither was the Australian Distributor. I said to him that he needed to deal with it under Consumer Protection Law as there was protection under the Legislation that a $3,000 coffee machine should last longer than 2 years. He got a new machine free of charge !

 

Maybe the laws are different in the USA, but you should be investigating it before you start hacking expensive accessories to bits !