31 replies to this topic

[Mossonarock]

I just acquired an Intes Micro Alter M715. I knew that wide field eyepieces don't work well with this telescope before getting it. I didn't know that its mostly because the rear aperture is only 24mm. If you use an eyepiece with a field stop > 24mm with this telescope, you get vignetting. So, I'm looking for eyepieces with a focal length of about 24-28mm, 52 to 68 deg AFOV and a field stop of not > 24mm. I'd like something with a field stop as close to 24mm as I can get. The best I've found is 22.8mm field stop in some Explore Scientific eyepieces. There's others with 27.2mm field stop and those might be acceptable as the vignetting would be on the very edges of the fov; I'd like to hear about your experiences with that if you have any. So, far I've looked mostly at the offerings from Explore Scientific and Televue. I'd like to hear suggestions from other manufacturers that you may know of. I don't care if the barrel diameter is 1.25 or 2". Its the field stop diameter that matters. 

 

It sure would be handy if retailers included the option of using field stop diameter as a search variable on their websites. hint hint.

 

I already have a couple 18mm eyepieces I can use with this telescope but I'm wanting something that's going to provide less magnification with this telescope. I'm going for about 100x mag. if you also have any suggestions for eyepieces that will provide about 50x and has a field stop <= 24mm, I'd like to hear about those too. Iirc the focal length of the telescope is 2670mm. 

 

I have had an f12 mak for awhile but I've never had any experience with an f15 mak. So, I'm not really even sure how well eyepieces with an afov in the 62 to 68 deg range will work but I'm willing to try. I don't want to go up to 82 afov (as much as I like those) because I want to maximize image brightness as I'm hoping to also use this telescope on globular clusters, planetary nebulas and galaxies, and maybe the occasional comet. Seeing conditions where I typically observe rarely let me get above 150x mag. So, I'm basically looking for eyepieces to give me 50x, 100x, and 150x mag. Well, and maybe 200x but I do have a 2x focal extender. 

 

BTW: if you know of any great threads here on CN regarding collimating these particular telescopes, please indicate some. Thank you. I've heard these are challenging to collimate. I've read the dissection thread already- very useful info there.

Edited by Mossonarock, 13 June 2025 - 01:45 PM.

[Jay_Reynolds_Freeman]

Some time ago I did a comparison of 24 mm focal-length eyepieces. My report is on line here. I did not specifically measure field stop diameter, but I suggest that a 24 mm Brandon (or perhaps even a 32 mm) might be useful for you.

 

Clear sky ...

[MisterDan]

Go here:

https://www.cloudyni...ide/?p=14049961

 

Download the Buyer's Guide and use filters to narrow down the candidates that fit (or "sort'a fit") your criteria.

 

Best wishes.

Dan

 

By the way:  vignetting is not a "Boolean" effect.  Just because it's present doesn't mean it's visible/discernible. I myself wouldn't worry about a field stop that's a fair bit larger than 24mm. -But that's me.

 

EDIT:  Have you verified that collimation is necessary? Intes and Intes-Micro Maksutovs were very robust. My own MK67 is a quarter-century old, and it has maintained collimation since day one. You may not need to collimate your M715.  -Let us know...

Edited by MisterDan, 13 June 2025 - 02:03 PM.

[balcon3]

I would recommend a Masuyama MOP 25mm. It has 53 degree AFOV, field stop of 23.1mm. I don't have this one but i do have the 7.5mm and 12.5mm focal lengths. They are 5-element eyepieces with fantastic contrast. They should be fantastic in a long focal length Mak. I prefer my Masuyamas to my Morpheus's because of the high contrast and transmissivity. 

[balcon3]

One other comment. If you have a 7 inch premium Mak you should bot be limiting yourself to 150x, unless your seeing conditions are so bad that you can rarely go above that magnification. You should easily be able to get up to 300x if seeing allows it. I would be looking also to get a 9mm or 12.5mm eyepiece. At these lower focal lengths you can go for wide AFOV eyepieces and still stay below a 24mm field stop. 

[Starman1]

I just acquired an Intes Micro Alter M715. I knew that wide field eyepieces don't work well with this telescope before getting it. I didn't know that its mostly because the rear aperture is only 24mm. If you use an eyepiece with a field stop > 24mm with this telescope, you get vignetting. So, I'm looking for eyepieces with a focal length of about 24-28mm, 52 to 68 deg AFOV and a field stop of not > 24mm. I'd like something with a field stop as close to 24mm as I can get. The best I've found is 22.8mm field stop in some Explore Scientific eyepieces. There's others with 27.2mm field stop and those might be acceptable as the vignetting would be on the very edges of the fov; I'd like to hear about your experiences with that if you have any. So, far I've looked mostly at the offerings from Explore Scientific and Televue. I'd like to hear suggestions from other manufacturers that you may know of. I don't care if the barrel diameter is 1.25 or 2". Its the field stop diameter that matters. 

 

It sure would be handy if retailers included the option of using field stop diameter as a search variable on their websites. hint hint.

 

I already have a couple 18mm eyepieces I can use with this telescope but I'm wanting something that's going to provide less magnification with this telescope. I'm going for about 100x mag. if you also have any suggestions for eyepieces that will provide about 50x and has a field stop <= 24mm, I'd like to hear about those too. Iirc the focal length of the telescope is 2670mm. 

 

I have had an f12 mak for awhile but I've never had any experience with an f15 mak. So, I'm not really even sure how well eyepieces with an afov in the 62 to 68 deg range will work but I'm willing to try. I don't want to go up to 82 afov (as much as I like those) because I want to maximize image brightness as I'm hoping to also use this telescope on globular clusters, planetary nebulas and galaxies, and maybe the occasional comet. Seeing conditions where I typically observe rarely let me get above 150x mag. So, I'm basically looking for eyepieces to give me 50x, 100x, and 150x mag. Well, and maybe 200x but I do have a 2x focal extender. 

 

BTW: if you know of any great threads here on CN regarding collimating these particular telescopes, please indicate some. Thank you. I've heard these are challenging to collimate. I've read the dissection thread already- very useful info there.

That baffle is not close to the eyepiece, so the vignetting is what you'd call "soft" vignetting, i.e. not likely to be visible until the field stop of your eyepiece is significantly larger than 24mm.

I think you would have no problem with maximum field 1.25" eyepieces.

So field stop figures (24mm =111x):

24mm Panoptic 27.0mm FS

24mm Explore Scientific 68°  27.2mm FS

24mm APM/Stellalyra/Altair/Sky Rover UFF and Celestron Ultima Edge (and the other labels this eyepiece is sold under)  27.6mm FS

24mm Baader Hyperion 28.0mm FS

 

However, with a long f/ratio scope, the issue is getting a low power and large exit pupil eyepiece, so a 32mm Plössl (=83x) would be a better choice for a maximum field eyepiece because the image will be brighter.

Or, even a 40mm Plössl (=67x), which will have an orthoscopic-narrow 40-43°apparent field, but be even that much brighter an image.

There are no longer FL eyepieces in 1.25", and 2" eyepieces would all have field stops too wide.

 

For 150x (18mm eyepiece) in 1.25", you are still using 65-68° field eyepieces, like the 18mm version of the 24mm UFF mentioned above, or an 18.2mm Tele Vue Delite, though a 20mm Pentax XW would be fine (=134x),

or a 17.5mm (actual = 17.2mm) Baader Morpheus (= 155x).

Edited by Starman1, 13 June 2025 - 02:30 PM.

[Mossonarock]

MisterDan, You know how it is when you get a new telescope- the clouds find you. So, I haven't been able to get it out yet and so don't know for sure if collimation is necessary. However, there's a chance that it is as the telescope has obviously had a major bump in its past as there is a dent and some significant damage on the tube. So, there's a chance, which may be why I got this telescope at a reasonably good price on the bay. Besides the fact that it just got shipped across the continent to me.

 

I appreciate y'alls experience that a field stop a bit larger than the rear aperture of a telescope is likely to not produce visible vignetting. There's a lot of 27mm field stop eyepieces out there; so this opens up my choices. I tried using a 31mm Nagler on my F12 mak and got obvious vignetting, stars would flare on the boundary, and all that. So, I know there is a such a thing as too wide of a field stop. That's how I learned- the hard way of course. 

 

Starman, I hadn't even gotten around to thinking about exit pupil. thank you for reminding me about that. I shall do some maths. Also, I already have a 40mm plossl. The field stop on it is almost 1.25"; its all glass edge to edge of the barrel as the barrel is 1.25". I don't know much about it as it came with a used refractor I bought. Its Orion branded if that means anything. 

[Starman1]

MisterDan, you know how it is when you get a new telescope- the clouds find you. So, I haven't been able to get it out yet and so don't know for sure if collimation is necessary. However, there's a chance that it is as the telescope has obviously had a major bump in its past as there is a dent and some significant damage on the tube. So, there's a chance, which may be why I got this telescope at a reasonably good price on the bay. Besides the fact that it just got shipped across the continent to me.

 

I appreciate y'alls experience that a field stop a bit larger than the rear aperture of a telescope is likely to not produce visible vignetting. There's a lot of 27mm field stop eyepieces out there, so this opens up my choices. I tried using a 31mm Nagler on my F12 Mak and got obvious vignetting, stars would flare on the boundary, and all that. So, I know there is a such a thing as too wide of a field stop. That's how I learned- the hard way of course. 

 

Starman, I hadn't even gotten around to thinking about exit pupil. thank you for reminding me about that. I shall do some math. Also, I already have a 40mm Plössl. The field stop on it is almost 1.25"; it's all glass edge to edge of the barrel as the barrel is 1.25". I don't know much about it as it came with a used refractor I bought. Its Orion branded if that means anything. 

Try that 40mm and check for vignetting.

The larger the exit pupil is, the brighter the field and the more visible vignetting is.

[I look at the sky in the daytime to check out vignetting.  If it's thee, you can see it.]

If you don't see it, or it's almost unnoticeable, you have a fairly wide choice of eyepieces you can use.

[RichD]

Congrats on a really nice scope. I have come close to buying the same in the past but decided the weight was a bit much for my mount.

I think you'll find the 24mm Pan would be a really nice eyepiece in that scope for mid size clusters, and Don's recommendation of the 17mm morph would be ideal on globs. I use my 14mm morph on globs in my 6" mak and it's great.

Good luck with it!

[SeattleScott]

You must be really sensitive to vignetting. I would target more like a 30mm field stop, perhaps a touch wider. 27 Panoptic, 24 Delos, 22T4 territory.

[BKSo]

Not mentioned above, the Leica HC Plan 10x/25, 25mm focal length and 25mm field stop.

[Starman1]

Not mentioned above, the Leica HC Plan 10x/25, 25mm focal length and 25mm field stop.

Not available in 1.25" as far as I know, only 30mm.

[Jeff Morgan]

I just acquired an Intes Micro Alter M715. I knew that wide field eyepieces don't work well with this telescope before getting it. I didn't know that its mostly because the rear aperture is only 24mm. If you use an eyepiece with a field stop > 24mm with this telescope, you get vignetting. So, I'm looking for eyepieces with a focal length of about 24-28mm, 52 to 68 deg AFOV and a field stop of not > 24mm. I'd like something with a field stop as close to 24mm as I can get. The best I've found is 22.8mm field stop in some Explore Scientific eyepieces. There's others with 27.2mm field stop and those might be acceptable as the vignetting would be on the very edges of the fov; I'd like to hear about your experiences with that if you have any. So, far I've looked mostly at the offerings from Explore Scientific and Televue. I'd like to hear suggestions from other manufacturers that you may know of. I don't care if the barrel diameter is 1.25 or 2". Its the field stop diameter that matters. 

 

It sure would be handy if retailers included the option of using field stop diameter as a search variable on their websites. hint hint.

 

I already have a couple 18mm eyepieces I can use with this telescope but I'm wanting something that's going to provide less magnification with this telescope. I'm going for about 100x mag. if you also have any suggestions for eyepieces that will provide about 50x and has a field stop <= 24mm, I'd like to hear about those too. Iirc the focal length of the telescope is 2670mm. 

 

I have had an f12 mak for awhile but I've never had any experience with an f15 mak. So, I'm not really even sure how well eyepieces with an afov in the 62 to 68 deg range will work but I'm willing to try. I don't want to go up to 82 afov (as much as I like those) because I want to maximize image brightness as I'm hoping to also use this telescope on globular clusters, planetary nebulas and galaxies, and maybe the occasional comet. Seeing conditions where I typically observe rarely let me get above 150x mag. So, I'm basically looking for eyepieces to give me 50x, 100x, and 150x mag. Well, and maybe 200x but I do have a 2x focal extender. 

 

BTW: if you know of any great threads here on CN regarding collimating these particular telescopes, please indicate some. Thank you. I've heard these are challenging to collimate. I've read the dissection thread already- very useful info there.

 

I’m in the same boat, picked up a Maksutov. In my case, 180mm f/15. Assuming the scope proves satisfactory I certainly would like one eyepiece for maximum practical exit pupil. Brandon and Masuyama come immediately to mind as long focal length options for larger exit pupils. But at what focal length can I “Maks out”?

 

From another thread on the Cats & Casses forum it was suggested that the rear physical opening of 32mm set a cap on usable eyepiece field stop.

 

I am wondering if this issue is similar to sizing a Newtonian diagonal for “full illumination”. Meaning yes there is real math going on, and using a camera or other instrumentation it could be objectively measured. But the real questions are: 

 

1) At what point does it become discernible to the observer; and

 

2) At what point does Discernible become Objectionable?

 

Given the YMMV factor, the only way to know is to test eyepieces with large field stops. For me, this is a 40 Paragon (46mm) and 26 Nagler (35mm). 

Edited by Jeff Morgan, 14 June 2025 - 05:30 PM.

[SeattleScott]

I think he did try it with 31 Nagler and there was obvious vignetting, as expected. The question is where does the vignetting cease to be obvious between 25mm and 42mm field stop.

[luxo II]

I have had an f12 mak for awhile but I've never had any experience with an f15 mak. So, I'm not really even sure how well eyepieces with an afov in the 62 to 68 deg range will work but I'm willing to try.

They will work fine. You're overthinking this IMHO.

 

So, I'm basically looking for eyepieces to give me 50x, 100x, and 150x mag. Well, and maybe 200x but I do have a 2x focal extender. 

These scopes will handle 300-350X  just fine. If yours is a deluxe, maybe more.

 

50X: 54mm - filling the field fully will be a bit optimistic, but you could get close with a 2" Masuyama 50mm or Brandon 48mm.

100X: 27mm (24-30) - APM 2" UFF 30mm is a spectacular choice, alternatively the 24mm UFF gives the widest possible field in a 1.25" barrel.

150X: 18mm - an APM UFF 18mm is an obvious choice.

200X: 13mm - I'd opt for the APM UFF 15mm (180X).

250X: 11mm - I'd opt for the APM UFF 10mm (270X).

300X: 9mm

340X: 8mm - Brandon 8mm.

 

For a very "classic set" you could run with Brandons 8, 12, 16, 24 and add the UFF 30mm.

Edited by luxo II, 15 June 2025 - 01:49 AM.

[IslandPink]

For a vintage option, the Meade Super Wide 24.5mm from the original 4000 series is a nice unit, I've always enjoyed using it on my 6" f/20 Schief. It does exceed your field stop target slightly at 26.0 , though.

[Brent Campbell]

For my SCT I recently purchased ( actually repurchased) an explore scientific 24mm 68 degree and a 16 mm 68 degree.  Combined with a Barlow they give me 24 mm, 16 mm, 12 mm, 8 mm.

[T1R2]

I don't think you'll notice much vignetting, especially with DSO views, but maybe...just maybe you might notice a little drop in brightness on stars at the very edge of the fov when panning through the Milky Way , Maybe only on fainter star fields, maybe not at all on brighter star fields. 

 

I think you'll be fine with any FS of 24-27mm.  

 

25mm HD60's /Celestron X-Cel, 24mm Panoptics or as long as you don't go to far over 27mm FS. will all be fine, I wouldn't put much weight into being bothered by vignetting at med exit pupils with dark sky background. the fact the stars will be virtually perfect edge to edge really does make up for a lot BS you might come across or hear about, even with what results to a couple 2-3-4 degrees of AFoV being slightly dimmer at the edge. You'll just have to see for yourself, so go for it, get what you want with a FS of 24-27+ish mm FS.

[RichA]

Not available in 1.25" as far as I know, only 30mm.

the only thing they could use to make adapters (0.5mm walls) would be stainless steel or some kind of avionic aluminum alloy.

[MisterDan]

1.25 inches ~ 31.7mm, so walls can be a smidge thicker (~0.85mm).

 

Poly film cannisters (with their bottoms cut off) have been used as friction-fit 30mm barrel "sleeve" adapters for decades. 30mm-format eyepieces with such sleeves fit 1.25-inch ports perfectly.

 

-Perhaps not a high-tech or "elegant" solution, but cheap and functional.

 

Best wishes.

Dan

[Astrojensen]

I’m in the same boat, picked up a Maksutov. In my case, 180mm f/15. Assuming the scope proves satisfactory I certainly would like one eyepiece for maximum practical exit pupil. Brandon and Masuyama come immediately to mind as long focal length options for larger exit pupils. But at what focal length can I “Maks out”?

 

From another thread on the Cats & Casses forum it was suggested that the rear physical opening of 32mm set a cap on usable eyepiece field stop.

My 6" f/15 Zeiss Maksutov has a rear opening of 33mm (measured with calipers) and it can use 2" eyepieces with no apparent vignetting. At least in some of the eyepieces. 

 

30mm ES82 and 32mm Masuyama 85 shows no visible vignetting. 

 

42mm and 50mm GSO Superview Erfles show no visible vignetting.

 

40mm ES68 shows mild vignetting. 

 

All eyepieces used in a 2" Baader prism diagonal. 

 

 

Clear skies!

Thomas, Denmark

[Mossonarock]

I really appreciate y'all sharing your experience and suggesting that 27mm field stops ought to be fine when the rear opening of the telescope is only 24mm. I'm not so worried about "noticing vignetting". Rather, I feel that, when a field stop on an eyepiece is larger than the light cone of the telescope, its a bit of a waste of glass as the light won't reach the full diameter of the field stop. So for example, when you have an eyepiece with a 36mm field stop and the diameter of the telescope's light cone at the eyepiece is only 26mm, well that's 10mm of glass diameter that isn't being used. I know from experience that you'll notice vignetting. 

 

The reason I was wanting an eyepiece of smaller AFOV is because I didn't want to put too much demand on bending the light path. Also, I know that widening the afov spreads out the light which can make the image appear dimmer. As my eyes get older, I want all the help I can get. Iow, optical efficiency and brightness. 

 

Explore Scientific has a 26mm 62* afov eyepiece with a 27.2mm field stop. That's top of my list right now. If I did my math right, the exit pupil will be about 1.8mm and magnification about 103x.

[ABQJeff]

Masuyama, ES68, TV Pans, APM UFF.

 

Experiment with 32mm Plossl (which everyone should have in their kit) to see if vignetting bothers you.

[Astrojensen]

Rather, I feel that, when a field stop on an eyepiece is larger than the light cone of the telescope, its a bit of a waste of glass as the light won't reach the full diameter of the field stop. So for example, when you have an eyepiece with a 36mm field stop and the diameter of the telescope's light cone at the eyepiece is only 26mm, well that's 10mm of glass diameter that isn't being used. I know from experience that you'll notice vignetting. 

 

On my 6" f/15 Zeiss Maksutov with 33mm rear opening, the full 2" eyepiece is being used, right out to the field stop. There is no visible vignetting. Not even in daylight. Stars are tight and sharp, right until they exit the field of the 32mm 85° Masuyama. The whole field is visible. It is not stopped down by the rear opening.

 

Now, with a rear aperture of only 25mm, it's quite likely that an eyepiece such as the 32/85 Masuyama will show some stopping down of its AFOV, but I'd still encourage you to try some 2" eyepieces with larger than 1.25" lenses. 

 

A determining factor is how far away from the rear opening the eyepiece field stop is located. The further away, the less visible vignetting and stopping down becomes.  

 

 

Also, I know that widening the afov spreads out the light which can make the image appear dimmer.

This is incorrect. A larger AFOV doesn't "spread out the light" just like looking out a large window to see a wider view of the outside doesn't make the view dimmer than through a smaller one. The view in a 32mm 85° eyepiece and a 32mm 50° eyepiece are exactly the same, everything else equal, except the field in the 32/85 is a lot bigger. 

 

 

Clear skies!

Thomas, Denmark 

[Starman1]

I really appreciate y'all sharing your experience and suggesting that 27mm field stops ought to be fine when the rear opening of the telescope is only 24mm. I'm not so worried about "noticing vignetting". Rather, I feel that, when a field stop on an eyepiece is larger than the light cone of the telescope, its a bit of a waste of glass as the light won't reach the full diameter of the field stop. So for example, when you have an eyepiece with a 36mm field stop and the diameter of the telescope's light cone at the eyepiece is only 26mm, well that's 10mm of glass diameter that isn't being used. I know from experience that you'll notice vignetting. 

 

The reason I was wanting an eyepiece of smaller AFOV is because I didn't want to put too much demand on bending the light path. Also, I know that widening the afov spreads out the light which can make the image appear dimmer. As my eyes get older, I want all the help I can get. Iow, optical efficiency and brightness. 

 

Explore Scientific has a 26mm 62* afov eyepiece with a 27.2mm field stop. That's top of my list right now. If I did my math right, the exit pupil will be about 1.8mm and magnification about 103x.

You are only thinking about the on-axis light cone.

Light also comes from the side and bypasses the 24mm opening to hit a circle larger than 24mm.

That means though the light is not at the 100% level at a 27mm field, it will be so high in % you won't see the dimming at the edge.

I used an SCT with a rear baffle opening of 38mm with eyepieces having 46mm and 46.5mm field stops, and though I could see the vignetting in the daylight, I could not at night.

Illumination was probably 20% down from the center of the field, but that is only 0.2 magnitudes, and it wasn't apparent in star images.

 

The 26mm 62° ES eyepiece has a bit of intrinsic vignetting that will add to the scope.  Even with that, I doubt you'll see it at night.

Edited by Starman1, 16 June 2025 - 10:43 AM.