Recommendations for stock 26mm upgrade

[Dibp]

Hello All 

I have a C5 bought from new as a DX5 package and really like it. The 26mm plossl it came with is pretty good but I am considering upgrading it mainly so I can pass the plossl on to my niece and her family as their one is just awful. Ideally I want to spend around £100 and would like a wider FOV. Scope is F10 5inch SCT.

Any recommendations will be gratefully received

[dobbyisbest]

Considering your stated budget, the APM 24mm UFF 65 deg eyepiece is by far the best option available. UK branded versions include:

- StellaLyra at FLO: https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-24mm-ultra-flat-field-125-eyepiece.html

- Altair Astro: https://www.altairastro.com/altair-24mm-ultraflat-eyepiece---precision-barrel-stainless-steel-237-p.asp

The resulting field of view for them would be 1.25 degrees (vs the 1.04 deg FOV that you get with that 26mm Plossl). They also punch *way* above their price class and is really only surpassed by the Televue 24mm Panoptic: https://www.firstlightoptics.com/tele-vue-eyepieces/tele-vue-panoptic-68-eyepieces.html

For a slight increase on your budget still, you could go for the Baader Hyperion 24mm 68 deg, yielding field of view of 1.31 degrees (same as the Panoptic) Solid eyepieces: https://www.firstlightoptics.com/baader-planetarium/hyperion-8.html?srsltid=AfmBOorKJiWk3eV3JUoMPE4L__Sve5amBvMaYVtJ0KKn_a0NY9DXXX6Hgvw

 

[Dibp]

Thank you so much for this Dobbyisbest

I have to say I am really tempted by the Baader Hyperion. 
Time to push the budget a bit!

[Dibp]

Not that I am at all impulsive but 

Baader Hyperion 24mm has just been ordered. I am more than a little excited to see how it compares

Thank you for the recommendation Dobbyisbest

I will update as soon as the clouds go. 

[dobbyisbest]

You’ve joined a long list of impulsive buyers in this hobby. 😂

I’m sure you’ll notice the difference in quality straight out of the box, but yes, let us know what you think, if the weather ever allows again! 🙂

[alan potts]

1 hour ago, Dibp said:

Not that I am at all impulsive but 

Baader Hyperion 24mm has just been ordered. I am more than a little excited to see how it compares

Thank you for the recommendation Dobbyisbest

I will update as soon as the clouds go. 

I tried a few Hyperions about 8-9 years ago and they were decent enough in an F10 scope but not as good any of my TeleVues. I was less than happy with them in an F6 scope though.

Alan

[mikeDnight]

And I really liked the Hyperion 24mm in my 4" F7.4 refractor and felt it was both better corrected at the edge of field and significantly more comfortable to use that the 24mm Panoptic. In fact the only person who was batting for the 24 Pan' was the chap who owned it. Goes to show how we all differ when it comes to eyepieces. I think my friend was blinded by the TeleVue black and green!

[Dibp]

Thank you both

I can’t wait for the new eyepiece to arrive. Part of me is just as excited about being able to pass the plossl on to my niece. This early on in my hobby adventure I can not justify a Televue. Not purely because of the cost but also because I am not good enough to be able to appreciate them

[Don Pensack]

4 hours ago, Dibp said:

Not that I am at all impulsive but 

Baader Hyperion 24mm has just been ordered. I am more than a little excited to see how it compares

Thank you for the recommendation Dobbyisbest

I will update as soon as the clouds go. 

A little error in the math from an earlier post.

The True field of the 24mm Hyperion will be 28/1250 x 57.2958 = 1.28°, or 1°17', at 52x.

That's a nice wide field, and good for a number of large objects--an excellent low power eyepiece in a 5" scope.

I've always liked the C5--it has great portability and enough light grasp for thousands of deep sky objects (in dark skies).

[Don Pensack]

Of course, you will need more eyepieces, because objects in the sky differ in size and brightness.

I recommend, with that size of scope, steps of 40x magnification up to about 200x.

So, since you have 50x covered, eyepieces yielding 90x, 130x, and 170x at least.

That is focal lengths of 14mm, 10mm, and 7mm

The Pentax XW eyepieces fit right in with the 24mm Hyperion.

For less money, the 13mm Baader Hyperion plus 2 fine tuning rings can provide focal lengths of 13mm, 10.8mm, 9.2mm, and 8.1mm in one eyepiece.

The 10mm Hyperion can yield 10mm, 8.4mm, 7.1mm and 6.1mm.

If you don't mind threading the rings on in the dark, that makes the Hyperion eyepieces very versatile, reducing your cost for eyepieces significantly

https://www.baader-planetarium.com/en/baader-hyperion-finetuning-ring-14.html

Click on the graph on the left to see the details about every Hyperion with the Fine Tuning Rings added.

 

The 24mm Hyperion isn't used with the rings, as it has no lower lenses to move farther from the upper section of the eyepiece.

[Roy Challen]

I've never used Hyperions, but the fine tuning rings sound like a great idea. Why don't other manufacturers use them? Patents?

[John]

3 minutes ago, Roy Challen said:

I've never used Hyperions, but the fine tuning rings sound like a great idea. Why don't other manufacturers use them? Patents?

I think the main drawback is that you are opening the eyepiece up to install the FT ring. It goes between the upper body optical set and the lower set. Except for the 24mm which, as Don says, does not have a lower optical set.

I guess it's a fiddly thing to do in the dark and there is always the possibility of dust getting onto the internal lenses of the eyepiece.

 

[Carbon Brush]

I have used Hyperions in all FL available. To me the big things were long eye relief and (certainly some years back) a really good FOV for the ££ spent.
The ability to use them in 1.25" or 2" barrels was useful. Then of course they can have a camera hang on the front.
Actually this was the only way I could get a Coronado PST to interface with my DSLR - again a long time back.
I probably used them more in an F8 scope than anything else and was always happy with the views.
Yes the FT rings are nice to have, but not essential. The rings are though low cost so for trying that different magnification.
 

[lunator]

I have the 24mm Hyperion and am very happy with it. I have used it in F6 and F9 scopes.

Cheers

Ian

[Don Pensack]

4 hours ago, John said:

I think the main drawback is that you are opening the eyepiece up to install the FT ring. It goes between the upper body optical set and the lower set. Except for the 24mm which, as Don says, does not have a lower optical set.

I guess it's a fiddly thing to do in the dark and there is always the possibility of dust getting onto the internal lenses of the eyepiece.

 

Though because the eyepieces coma apart easily and the lenses are held in with retaining rings, they are easy to clean if necessary.

I think many use them to create a different focal length for a night, and don't change them often in the dark.

 

[dobbyisbest]

6 hours ago, Don Pensack said:

A little error in the math from an earlier post.

The True field of the 24mm Hyperion will be 28/1250 x 57.2958 = 1.28°, or 1°17', at 52x.

That's a nice wide field, and good for a number of large objects--an excellent low power eyepiece in a 5" scope.

I've always liked the C5--it has great portability and enough light grasp for thousands of deep sky objects (in dark skies).

Hi Don,

Original responder here. Would you perhaps mind elaborating on the math/logic?

My workings are 1250mm/24mm = 52.083, and then 68deg/52.083deg = 1.30568 FOV.

Am I missing something?

I was trying to give a good, honest answer to OP, but if I didn’t succeed, I’d be grateful to know where I went wrong.

If I didn’t manage to provide the OP with the best recommendation, I’d be happy to buy the eyepiece from them if there is something better. 

 

 

 

 

Edited April 7 by dobbyisbest

[Dibp]

I am so grateful that everyone is taking the time to help me with this. 
I have to admit that the fine tuning rings are completely new to me and will definitely be exploring those options when considering my next eyepiece purchases. 
As always this is proving such a great hobby and every time I think I may have a decent idea of what is possible I discover there is so much more to discover.
All your advice is being greatly appreciated and digested!

[bomberbaz]

I would go for a zoom but use it with the hyperion 24mm as your next eyepiece. Baader Hyperion Zoom Eyepiece | First Light Optics

Something I notice no one has asked, are you using a bog standard diagonal or a dielectric version.  Personally I found the dielectric versions offer a much cleaner image on planets and marginally brighter response, especially on dimmer objects. 

Something to consider.

Steve

[Dibp]

Hello Steve 

I am using the bog standard diagonal that came with the Celestron package. Looks like something else I can explore! 
One of the first eyepieces I bought was the Celestron zoom which I really like. I now know there are better options available but have become so attached to the Celestron one I am unable to upgrade it. I fully appreciate this sounds insane but it is still my most used eyepiece 

[Highburymark]

I seem to remember that the Hyperion 10mm was my first upgrade eyepiece when I bought a C6. At a relatively slow focal ratio of F/10, the 10mm Hyperion was excellent. 
I totally agree with Steve’s recommendation for a dielectric diagonal - you could pick one up from the classifieds for not much money, and it will make a noticeable difference to views with any eyepiece. Be aware that although they come under a wide range of brands, they are all of similar quality - unsurprising as they are built in the same Chinese factories. 

[Don Pensack]

On 07/04/2024 at 14:24, dobbyisbest said:

Hi Don,

Original responder here. Would you perhaps mind elaborating on the math/logic?

My workings are 1250mm/24mm = 52.083, and then 68deg/52.083deg = 1.30568 FOV.

Am I missing something?

I was trying to give a good, honest answer to OP, but if I didn’t succeed, I’d be grateful to know where I went wrong.

If I didn’t manage to provide the OP with the best recommendation, I’d be happy to buy the eyepiece from them if there is something better. 

 

 

 

 

It's very simple.

The TF = AF/M formula is only accurate if there is no distortion in the eyepiece.  Since all eyepieces have distortion, this formula overstates the True Field by 5-10%.

IF the Field Stop in the eyepiece is known, this determines the true field of the eyepiece since the field stop is laid on the focal plane of the scope in the same manner a sheet of paper with a hole cut in it, laid on a map,

determines how much map is seen.

So the Field stop formula ignores distortion and yields an accurate true field for the eyepiece.

TF = (FS/TFL) x 180/pi

or True Field = (field stop/telescope focal length) x 57.2958

You can use 57.3 for the last number, which converts radians to degrees.

 

In this case, the 24mm Hyperion's field stop is known--28.0mm, so the true field calculation follows.

You'll notice that this formula also ignores eyepiece focal length, which can be in error by several tenths of a mm.

The 24mm APM Ultra Flat Field is labeled 24mm, but actually measures 24.7mm, so the magnification formula will be way off.

In tests, the 24mm Hyperion focal length seems accurate, but the field stop measured 28.8mm !!

That means the true field will be 28.8/1250  x 57.3 = 1.32°, or 1°19' !

 

In truth, the Field Stop formula isn't going to be dead accurate either because we rarely know the EXACT focal length of the scope.

When scopes are made, there is always a variation in mirror and lens focal lengths.  Unless it has been measured on a test bench, it is likely not known exactly.

 

There is only one easy, non-instrument, way to accurately assess true field exactly, and that is to time the passage of a star on the celestial equator across the field of the eyepiece from edge to edge.

You would take 3 timings and use the longest one.  Then convert it to decimal minutes (e.g. 1 minute 13 seconds = 1.217minutes) and divide by 3.99 to convert to degrees.

 

If you want, you could then find the exact field stop diameter in your eyepiece by using the true field formula and solving for field stop:

FS = (TF x TFL)/57.3

 

Knowing the field stop means you can figure out the true field seen in any telescope by merely plugging in the focal length of that scope.

Just be aware it won't be any more accurate than the stated focal length of the scope.  That error is tiny compared to the TF = AF/M formula, however.

 

Edited April 8 by Don Pensack

[dobbyisbest]

1 hour ago, Don Pensack said:

It's very simple.

The TF = AF/M formula is only accurate if there is no distortion in the eyepiece.  Since all eyepieces have distortion, this formula overstates the True Field by 5-10%.

IF the Field Stop in the eyepiece is known, this determines the true field of the eyepiece since the field stop is laid on the focal plane of the scope in the same manner a sheet of paper with a hole cut in it, laid on a map,

determines how much map is seen.

So the Field stop formula ignores distortion and yields an accurate true field for the eyepiece.

TF = (FS/TFL) x 180/pi

or True Field = (field stop/telescope focal length) x 57.2958

You can use 57.3 for the last number, which converts radians to degrees.

 

In this case, the 24mm Hyperion's field stop is known--28.0mm, so the true field calculation follows.

You'll notice that this formula also ignores eyepiece focal length, which can be in error by several tenths of a mm.

The 24mm APM Ultra Flat Field is labeled 24mm, but actually measures 24.7mm, so the magnification formula will be way off.

In tests, the 24mm focal length seems accurate, but the field stop measured 28.8mm !!

That means the true field will be 28.8/1250  x 57.3 = 1.32°, or 1°19' !

 

In truth, the Field Stop formula isn't going to be dead accurate either because we rarely know the EXACT focal length of the scope.

When scopes are made, there is always a variation in mirror and lens focal lengths.  Unless it has been measured on a test bench, it is likely not known exactly.

 

There is only one easy, non-instrument, way to accurately assess true field exactly, and that is to time the passage of a star on the celestial equator across the field of the eyepiece from edge to edge.

You would take 3 timings and use the longest one.  Then convert it to decimal minutes (e.g. 1 minute 13 seconds = 1.217minutes) and divide by 3.99 to convert to degrees.

 

If you want, you could then find the exact field stop diameter in your eyepiece by using the true field formula and solving for field stop:

FS = (TF x TFL)/57.3

 

Knowing the field stop means you can figure out the true field seen in any telescope by merely plugging in the focal length of that scope.

Just be aware it won't be any more accurate than the stated focal length of the scope.  That error is tiny compared to the TF = AF/M formula, however.

 

Wow! 

Thank you for the comprehensive answer and taking to the time to do so. That has been very interesting and enlightening - much appreciated. It’s one of those posts that I’m sure will become a timeless reference point for myself and others in the future.

What you say makes sense after a first reading, but I’ll have to go ‘put it to practice’ to remember properly. Thanks again 🙂

Edited April 8 by dobbyisbest

[Louis D]

21 hours ago, Don Pensack said:

The 24mm APM Ultra Flat Field is labeled 24mm, but actually measures 24.7mm, so the magnification formula will be way off.

I measured 24.1mm FL in the center and 20.5mm FL at the edge for my 24mm APM UFF.  I measured the FS at 27.5mm, the AFOV at 63°, eAFOV at 65°, and the usable eye relief at 17mm.

[Don Pensack]

1 hour ago, Louis D said:

I measured 24.1mm FL in the center and 20.5mm FL at the edge for my 24mm APM UFF.  I measured the FS at 27.5mm, the AFOV at 63°, eAFOV at 65°, and the usable eye relief at 17mm.

Not too far from Ernest Maratovich's measurements.

He got 27.6mm for the field stop, AFoV at 64°.

I also measured 17mm as effective eye relief.

I can't explain why he found a focal length of 24.7mm.  I think he uses an instrument to measure that.

(a calculated focal length makes assumptions about other measurements and can often be wrong).

Since the eyepiece has some AMD due to its low RD, I'm inclined to think your focal length measurement may be close to accurate.

It does make my earlier point, however, that the TF = AF/M formula is simply not an accurate one.  In the absence of field stop dimensions, however, it's probably

best to do a star-timing if you want to know the accurate true field size.