Planning your ideal eyepiece collection

[25585]

9 minutes ago, Piero said:

 

From your post, it seems that you are suggesting that coma depends on the AFOV and the barrel type, hence the field stop.

If so, the latter is incorrect. Take two 100 deg eyepieces with focal lengths of 20mm and 10mm. The FOV diameter in the 10mm is half the FOV diameter in the 20mm. Therefore, one would be tempted to say that it "shows" half coma. However, the magnification is double (and double is the coma aberration), therefore the amount of visible coma is exactly the same between the two eyepieces.

My statement was made in the vein that most 2 inch eps are longish to long FL, & have wide FOV. Therefore coma will be more likely in a fast mirror, which will generally affect views through 2 inch diameter eps. 

Astigmatism is more likely in cheaper eps in faster scopes. So more expensive/upmarket models of ep would be needed to avoid that. AFAIK (not much) there are no correctors to cancel astigmatism. 

[Piero]

22 minutes ago, 25585 said:

20mm 2 inch eps are a class by themselves as not too heavy (but fairly) yet perform well. The Celestron Ultima LX 22mm & Orion Lanthanum 20mm (still to be star tested) do not have the counter balance need of longer FL 2 inchers. 

Lunt seems similar to the ES 20mm 100 deg. APM & WO also. 

 

As far as I read from Ludes' comments, APM telescope is taking over the production of Lunt XWA / HDC. Not casually, the 13mm is advertised as APM telescopes and not Lunt. ES, Lunt/APM, Myriam, WO are clones of the TV Ethos. Said this, the Lunt series introduces some valid improvements, like substantial reduction in weight (e.g. the 20mm weights just 667g) and different and effective eyecup. The 20mm Lunt goes deeper than the Panoptics I've tried as is at least on par with the Delos I had, in terms of on axis contrast. It also reveals a vibrant colour tone on stars, which is not something I expected at that extent. I've read a few times that the ES 100 line is a bit like the TV Naglers on steroids. Well, to me, the 20mm Lunt is better on axis than the Naglers T6 I had and looses nothing at the edge. 

[Piero]

9 minutes ago, 25585 said:

My statement was made in the vein that most 2 inch eps are longish to long FL, & have wide FOV. Therefore coma will be more likely in a fast mirror, which will generally affect views through 2 inch diameter eps. 

Your statement is misleading.

 

>>> most 2 inch eps are longish to long FL, & have wide FOV. 

This is generally true. 

>>> Therefore coma will be more likely in a fast mirror.

This is true. 

>>> [fast mirror], which will generally affect views through 2 inch diameter eps. 

This is incorrect.

Most of TV Naglers and Ethos have 1.25" barrels, and will show more coma than 2" MV 30mm / 40mm, 2" Panoptic 41mm / 35mm / 27mm, etc. The only thing revealing more coma is the telescope focal ratio: the shorter the focal ratio, the smaller the coma-free area. In a fast telescope, this coma-free area is sufficiently smaller than the whole FOV of the eyepiece, making the detection of coma rather obvious. The typical formula calculating the coma-free area is 0.01778mm x f/ratio^3 . Barrel size has nothing to do with coma, so implicating coma from this, is misleading. Regarding LittleGuy's F4.7 telescope, this means that the coma-free area in his telescope is just ~1.85mm. Rather small...  said this, before investing in a CC, it is important to observe and see whether this really compromising the views according to one's eye or not.

[Littleguy80]

I have to admit I don’t have a good understanding of coma, coma correctors or paracorr. Would anyone have any good links that give a basic guide to these? Or feel free to share your own understanding if you prefer  

[Littleguy80]

Answered my own question  

 

[Littleguy80]

Definitely feels like it’s something to try and see how it looks as @Piero suggests. Based on the thread above it’s most apparent at low powers so the 20mm should be a good test of how much of an issue it is. I know @alanjgreen uses a paracorr with his big dob

[Pondus]

 

https://starizona.com/acb/basics/equip_optics101_coma.aspx

http://www.telescope-optics.net/coma.htm

http://www.scopecity.com/optics-course-0028.cfm?pn=ABERRATIONS

 

Some links (abberations Scopes and eyepieces) to sites that has been helpful to me, when trying to understand what the experts talk about, and what to look for  .

[Littleguy80]

11 minutes ago, Pondus said:

 

https://starizona.com/acb/basics/equip_optics101_coma.aspx

http://www.telescope-optics.net/coma.htm

http://www.scopecity.com/optics-course-0028.cfm?pn=ABERRATIONS

 

Some links (abberations Scopes and eyepieces) to sites that has been helpful to me, when trying to understand what the experts talk about, and what to look for  .

Great links. Thank you  

[kev100]

FWIW, I don't use a paracor with my f4.7 scope, and I doubt I'll bother. The 20mm Myriad does show a tiny amount of coma at the extreme edge of the FOV, but it's so much less than, for example, my previous low power EP (a 24mm MaxVision). You really have to seek it out.

Kev

[niallk]

In my 10" f4.7, my 24mm Panoptic and Nagler 13mm T6 were just a joy to use. I also use a pair of 15mm TV plossls in my Baader Maxbright binoviewer with 2.6x GPC for solar system targets: works well for me.

I've now gone for a 31T5 - 17E - 10E - 8E - 6E lineup for my 15" f4.5 with a Paracorr2, and added a 2xPM for higher powers.  They all get use on various objects. I've definitely fallen for the allure of 100° views

[Littleguy80]

3 minutes ago, kev100 said:

FWIW, I don't use a paracor with my f4.7 scope, and I doubt I'll bother. The 20mm Myriad does show a tiny amount of coma at the extreme edge of the FOV, but it's so much less than, for example, my previous low power EP (a 24mm MaxVision). You really have to seek it out.

Kev

Thanks Kev. I haven’t noticed anything with the ES68 24mm but haven’t looked for it either. I guess this in itself suggests it’s probably not an issue!

[Littleguy80]

4 minutes ago, niallk said:

In my 10" f4.7, my 24mm Panoptic and Nagler 13mm T6 were just a joy to use. I also use a pair of 15mm TV plossls in my Baader Maxbright binoviewer with 2.6x GPC for solar system targets: works well for me.

I've now gone for a 31T5 - 17E - 10E - 8E - 6E lineup for my 15" f4.5 with a Paracorr2, and added a 2xPM for higher powers.  They all get use on various objects. I've definitely fallen for the allure of 100° views

That’s a great line up. Nice and simple for the 10” too  

[kev100]

5 minutes ago, Littleguy80 said:

I haven’t noticed anything with the ES68 24mm

To be fair, I didn't notice it to begin with either (is yours the MaxVision type?). It took a couple of years before I got to the point that I always saw it and struggled to not see it. Maybe I'll start noticing it more with the Myriad after a while...

[Littleguy80]

7 minutes ago, kev100 said:

To be fair, I didn't notice it to begin with either (is yours the MaxVision type?). It took a couple of years before I got to the point that I always saw it and struggled to not see it. Maybe I'll start noticing it more with the Myriad after a while...

Mine is the Explore Scientific version. I’ll probably start noticing it now too haha 

[kev100]

1 minute ago, Littleguy80 said:

I’ll probably start noticing it now too

Maybe not. I believe the ES versions are better corrected for fast scopes than the MaxVision variety. 

[scarp15]

2 hours ago, 25585 said:

Horrible thought. What if EU increases tariffs on TV eps as imports from the US

Making reference to the weak pound versus strong dollar, hopefully the threatened trade war is just hot air and will not materialise. 

Probably good not to place emphasis (and yet more initial expense) on a coma corrector for now Neil, just gain time, becoming increasingly accustomed to enjoying the scope and aspiring new eyepieces, particularly when next at a dark site.

[jetstream]

3 hours ago, 25585 said:

Plossls (apart from TV 55mm which would have too large an exit pupil) don't need a CC. 

In my f3.8 the TV plossls could benefit from a coma corrector

[Littleguy80]

7 minutes ago, scarp15 said:

Making reference to the weak pound versus strong dollar, hopefully the threatened trade war is just hot air and will not materialise. 

Probably good not to place emphasis (and yet more initial expense) on a coma corrector for now Neil, just gain time, becoming increasingly accustomed to enjoying the scope and aspiring new eyepieces, particularly when next at a dark site.

Thanks Iain. Good advice as always. I’d be surprised if coma was something that bothered me. At this point, I’ll be very excited to get a forecast that allows me to get the dob to a dark site for the first time. The weather hasn’t been so kind this month. All good things comes to he who waits though  

[Littleguy80]

3 hours ago, Floater said:

Yes, Neil, I am. ?

Always love to see the different input and how it helps to focus (couldn’t resist) the mind. Although, sometimes the choice and the suggestions are so diverse they can have a frying effect! ?? 

As before, with those powerful keywords in your first post I knew this one had legs ...

It’s been a great thread and unusually has a fairly clear consensus. The Lunt 20mm HDC looks to be the smart first purchase. Although I started the day looking at a secondhand Ethos 13mm wondering if I’d been too hasty in writing off the green and black! However, with such strong support for the Lunt and it’s quality, I find it hard to find a reason to part with the extra money for an Ethos.  

This thread has taught me about coma too which is I’ve heard of but never really knew it meant. 

There have been some surprises too. I thought something like the ES82 30mm would be a high priority. Now it’s down the bottom of the list. Possibly not needed at all. I also thought there’d be a lot of support for the Nagler zoom. It seems to be very popular. Perhaps it’s better suited to other telescope types? 

I’ll be looking for a 4mm eyepiece at some point for my Triton hunt but that’s low down on the list too. 

After I get the 20mm, I’ll probably be keen on a 2” OIII filter for it. The Veil and NAN will be calling my name by then   

[25585]

2 hours ago, Piero said:

Your statement is misleading.

 

>>> most 2 inch eps are longish to long FL, & have wide FOV. 

This is generally true. 

>>> Therefore coma will be more likely in a fast mirror.

This is true. 

>>> [fast mirror], which will generally affect views through 2 inch diameter eps. 

This is incorrect.

Most of TV Naglers and Ethos have 1.25" barrels, and will show more coma than 2" MV 30mm / 40mm, 2" Panoptic 41mm / 35mm / 27mm, etc. The only thing revealing more coma is the telescope focal ratio: the shorter the focal ratio, the smaller the coma-free area. In a fast telescope, this coma-free area is sufficiently smaller than the whole FOV of the eyepiece, making the detection of coma rather obvious. The typical formula calculating the coma-free area is 0.01778mm x f/ratio^3 . Barrel size has nothing to do with coma, so implicating coma from this, is misleading. Regarding LittleGuy's F4.7 telescope, this means that the coma-free area in his telescope is just ~1.85mm. Rather small...  said this, before investing in a CC, it is important to observe and see whether this really compromising the views according to one's eye or not.

Piero, I am surprised as I always regarded larger TFOV in fast Newtonians to be the main cause of coma, upsetting visual astronomers who pay a lot, only to need spending more for that unflawed view. 

Current Nagler & Ethos ranges I have not tried at any focal length, due to their shallow eye relief &/or eye placement, &/or kidney bean reports. Ditto for other make/models. 

Also 35 eps is enough!

[TheLookingGlass]

I know if I ran into some "unexpected extra cash", I'd be springing for some TeleVue and Baader Morpheus!

I already have some of my "dream" eyepieces already. IMO, it's best to "mix 'em up" and not just stick to one brand, although I do prefer long eye relief and 70-76 degree EP's myself. 

[Piero]

9 hours ago, 25585 said:

Piero, I am surprised as I always regarded larger TFOV in fast Newtonians to be the main cause of coma, upsetting visual astronomers who pay a lot, only to need spending more for that unflawed view. 

Current Nagler & Ethos ranges I have not tried at any focal length, due to their shallow eye relief &/or eye placement, &/or kidney bean reports. Ditto for other make/models. 

Also 35 eps is enough!

 

Don, who is also a member here on SGL ( @Don Pensack ), explains this very well in my opinion: 

https://www.cloudynights.com/topic/565194-focal-ratio-and-coma/page-3#entry7710217 

[Littleguy80]

I've continued to think about what my "finished" collection might look like. With the Nagler zoom now looking like it'll be cut, I'm left considering a 4mm eyepiece for those rare occasions where the seeing allows 300x. There are three contenders:

1. The cheap option. 4mm Ortho. Will be sharp but short on eye relief. There's a noticeable drop in eye relief between my 6mm and 5mm BGO. I fear a 4mm ortho may be a step too far with regards to eye relief

2. The inbetweener. 4mm Vixen SLV. These seem to have a great reputation. I've heard them compared to the BGOs in terms of sharpness. 20mm eye relief and 50 degree AFOV. £100 new

3. The expensive option. 4mm Televue Delite. @Stu suggested this yesterday. No arguing with the quality. 20mm eye relief and wider 62 degree AFOV. There's one on ABS for £190 at the minute

The Vixen feels like the sensible choice. Should be very reasonably priced if I can find one secondhand. It'll definitely be more of a niche eyepiece but worth having I think. 

Any other contenders?

Not a priority purchase, of course. The Lunt's will come first.

[Stu]

I reckon the Vixen is probably the most sensible choice. It’s a very sharp but comfortable eyepiece and will only get used occasionally, so would keep some budget for other areas.

[25585]

1 hour ago, Littleguy80 said:

I've continued to think about what my "finished" collection might look like. With the Nagler zoom now looking like it'll be cut, I'm left considering a 4mm eyepiece for those rare occasions where the seeing allows 300x. There are three contenders:

1. The cheap option. 4mm Ortho. Will be sharp but short on eye relief. There's a noticeable drop in eye relief between my 6mm and 5mm BGO. I fear a 4mm ortho may be a step too far with regards to eye relief

2. The inbetweener. 4mm Vixen SLV. These seem to have a great reputation. I've heard them compared to the BGOs in terms of sharpness. 20mm eye relief and 50 degree AFOV. £100 new

3. The expensive option. 4mm Televue Delite. @Stu suggested this yesterday. No arguing with the quality. 20mm eye relief and wider 62 degree AFOV. There's one on ABS for £190 at the minute

The Vixen feels like the sensible choice. Should be very reasonably priced if I can find one secondhand. It'll definitely be more of a niche eyepiece but worth having I think. 

Any other contenders?

Not a priority purchase, of course. The Lunt's will come first.

How much AFOV do you want at a 4mm ep magnification? Orthk 40ueh, SLV 50, Delite 60ish. Of those 3 Delite is best, but if you already own a 9mm, maybe a 2x Barlow is all that is needed, until you know how much use around 4mm will be.