Explore Scientific 30mm 100deg 3" eyepiece - useable?

[raanany]

Apparently, this should be a dream-come-true for any DSO observer. The price tag is huge but if it delivers, it could be interesting.

Troubling Technical question

If you use a 2" --> 3" diagonal (or any other sort of adapter) to fit such an eyepiece to a 2" focuser wouldn't you be fooling yourself?

Reasoning

To achieve the 100deg AFOV @ 30mm, ES have set the field stop to be 52.2mm, hence the need to go above 2".

This means that the image which is formed at the focal point is 52.2mm in diameter.

The way I understand this, some trajectories associated with light beams coming from the outermost edges of the objective (mirror or lens) would have to take to reach the farthest point in this 52.2mm field are going to be blocked by the narrow passage of the 2" focuser.

Not all light will be blocked, light coming from the center of the objective will make it to all parts of the 52.2mm image but light coming from the edges will only reach the opposite side of the focal point image.

This means that the image will get gradually dimmer towards the edge of the 100 deg field. exact onset will depend on the location of the 2" stricture. This is equivalent to having less aperture. Not exactly what you might have in mind with paying $1350.

Am I missing something here?

Links

Eyepiece: http://explorescientificusa.com/collections/100-series-eyepiece/products/100-30mm?variant=589730981

Diagonal: http://explorescientificusa.com/collections/star-diagonal/products/99-reflective-3-diagonal?variant=2015683780

[John]

You would need the facility to take 3" eyepieces to make it worthwhile so a 3" drawtube and, for scopes that need them, a 3" fitting diagonal. The scope tube and focuser mount need to be able to support a 2.5 kg / 5 1/2 lb eyepiece and the diagonal (if needed) will add another .9 kg / 2 lbs to that. Then you will need a coma corrector for a fast scope like yours so thats another £900 or so for the Tele Vue Big 3" Paracorr and another .7 kg / 1 1/2 lbs of weight.

I can't see ther point of using such an eyepiece in anything less than a 3" drawtube.

Serious business !!!

I'll stick to my Nagler 31mm and Ethos 21mm I think

[raanany]

Thanks John.

What's a drawtube?

Also, since you mentioned the " a 3" fitting diagonal." I feel I haven't made my concern clear enough.

I'm saying that even if you're willing to spend that amount of money and assuming your scope and focuser can handle the weight still, you wouldn't be seeing true 100 deg at full intensity. Not all light coming from the objective can make it to all points of the object that is formed in the focal point.

[John]

The drawtube is the tube that you put the eyepieces into.

I think in the right scope the eyepiece will work well. It's aimed at really large schmidt-cassegrains and refractors perhaps, rather than dobsonians ?

[Northern Soul man]

Nice 1 , great to see they've put a WARNING label on the whole thing - probably WARNING you not to look at the price tag I bet.

Paul.

[jetstream]

You would need the facility to take 3" eyepieces to make it worthwhile so a 3" drawtube and, for scopes that need them, a 3" fitting diagonal. The scope tube and focuser mount need to be able to support a 2.5 kg / 5 1/2 lb eyepiece and the diagonal (if needed) will add another .9 kg / 2 lbs to that. Then you will need a coma corrector for a fast scope like yours so thats another £900 or so for the Tele Vue Big 3" Paracorr and another .7 kg / 1 1/2 lbs of weight.

I can't see ther point of using such an eyepiece in anything less than a 3" drawtube.

Serious business !!!

I'll stick to my Nagler 31mm and Ethos 21mm I think

I still want one for the NA neb...  even though it makes no sense...

[Chris]

I do sometimes think about keeping my ES100 14mm, and selling my ES100 9mm & 20mm to put towards the ES100 25mm! But I think it's a bit like aperture fever, where do you draw the line?

I'm thinking the ES100 30mm 3" would work well with a C11 and Moonlite maybe?   

[Chris]

Scrap that, just checked out of curiosity and the 3.25" SCT Moonlite still has a 2" drawtube. 

http://www.firstlightoptics.com/moonlite-focusers/moonlite-cs-dual-rate-sct-crayford-focuser-for-large-325-inch-thread.html

[Northern Soul man]

Scrap that, just checked out of curiosity and the 3.25" SCT Moonlite still has a 2" drawtube. 

http://www.firstlightoptics.com/moonlite-focusers/moonlite-cs-dual-rate-sct-crayford-focuser-for-large-325-inch-thread.html

Yeah and not a WARNING label in sight!!

[alan potts]

I could actually use one in my LX 12 scope and my APO, both will take 3 inch fittings. I think in the case of the APO the tube rings would need to moved dramatically towards the back of the scope and and counterweights around the objective. Then in the case of the LX it will point at the zenith pretty much all the time or up to a point when the diagonal gets jammed under the lower part of the fork mount.

Sometimes I wonder why they do these things, maybe because they can. I don't think I would bother even if they were half the price for me they are not practicle.

[russ.will]

Y'know, if TV had turned this out, you wouldn't be able to beat people off it with a stick....

As a point of note a 41mm Panoptic has a 47mm field stop v the 52.2mm of the ES100 30mm - a 9% increase.

I'm using a 40mm SWA with a 46mm(ish) field stop in a telescope with an exit aperture of 38mm - 21% increase.

Under a dark sky, the vignetting in my scope with the far larger deficit is not noticeable. Whilst I wouldn't push it as far as the 30mm ES100, I'd suspect that in SCTs of 10" and up, the vignetting would be a non-issue.

Balancing, well don't take it on if you're not prepared to, but it's no more than a Denkmeier Binotron 27 with a couple of Delos and a decent 2" diagonal. I suspect when ES produced this, they had in mind the REALLY large Dobs that proliferate in the US. When you look at the cost of the EP, plus a 3" coma corrector, it looks less stratospheric if you deduct the cost of the 2" coma corrector you no longer need and set it against the backdrop of a £10k scope.

Russell

[Chris]

Russ, I've got to say, I do enjoy your posts 

[Piero]

I am sticking with my 1.25" and rather get a fast scope rather than that beast! 

You might need a case just for that!

[John]

If anyone is interested, there are some reports from owners / users on what the ES 30mm / 100 is actually like to use in this rather long "Cloudynights" thread:

http://www.cloudynights.com/topic/467613-the-monster-comes-es-30mm-100-degree/

One thing that I picked up from it is that the Tele Vue 3" Paracorr is intended for imaging only and does not have the "tuneable" capability that it's smaller versions have for visual use.

The photo in this particular post made the size of this eyepiece very clear to me  :

http://www.cloudynights.com/topic/467613-the-monster-comes-es-30mm-100-degree/?p=6099146

Scroll up and there are some photos of it in a scope that just made me envious

[alan potts]

Russell,

Had TeleVue made this and lets not kid ourselve could have, you would not have needed a stick for me. I liken it to the 2.5mm Nagler, if you have no need for one why buy it. I notice in the picture that John posted via CN, it was not exactly being used in a 200 quid scope, I see this as an eyepiece for the very well heeled.

Alan

[raanany]

Thanks Russ, now I know that what I've been struggling to explain has a proper name: Vignetting

Here's a definition I found here:

http://www.eaas.co.uk/cms/index.php?option=com_content&view=article&id=4:a-short-guide-to-choosing-eyepieces-by-neil-paterson&catid=5:learning-zone&Itemid=8

"Vignetting is caused when a lens of an eyepiece is not able to field all the light rays coming through the previous lens. Vignetting presents itself as a noticeable darkening of the field of view towards the edges."

[russ.will]

I notice in the picture that John posted via CN, it was not exactly being used in a 200 quid scope, I see this as an eyepiece for the very well heeled.

Alan

I think that was exactly the point I was making. It's horses for courses and let's be honest, with a very few exceptions, we're all messing around with amateur to lower mid market scopes at best, so it looks like an extravagant anomaly. If you have a large AP or ex-Tim Wetherall refractor, you're batting on a different quality of pitch.

To diss it, is to say that a track day Lambo is daft when you're happy with the performance of your road-going Focus ST. Sure, great little car and able to scare you on occasion, but if you had the means, you'd be sitting at the pit lane exit, waiting for the lights to go off, with your three point harness strapped up tight and a V12 burbling behind you. I would, anyway.

My point is that for some, the stakes are higher and what looks like preposterous solution at our level, is simply another option at that level.

Russell

[alan potts]

Russell,

Beautifully put as always. I think I could have been more interested in this type of eyepiece if it had been done a different way. I feel many of us with large SC scope and their long focal lengths yearn for a wider FOV, I feel if they had done say a 60mm (if that would be possible) with say a 68 degree field, then I would be more interested. The 30mm  100 degree doesn't really give such a massive advantage over the 41mm Panoptic. I mean I have the latter and this is my starter for 10 at a power of X74, it would be nice to have something a bit lower.

However I do agree and see this has been pointed mainly at lucky people with 6 inch plus APO's.

Alan

[John]

I don't think the ES 30 / 100 is going to be in a different performance league to the other ES 100's. It's just had to be made in a larger format to accomodate the optical path and field stop. Because more materials are used and the anticipated market is smaller this results in a higher price.

The above is not dissing it in any way because the ES 100's are excellent. The 30 / 100 is just, currently, the largest one. If they did a 50mm / 100, say for observatory type instruments, it would need to use a 4 inch format I guess.

My Istar 6" F/12 refractor made my 2" diagonals and eyepieces look rather small so the 3" 30 / 100 would have been right at home in that 

It would still "only" have showed a 1.67 degree true FoV though.  My Nagler 31 gave me 1.41 degrees so not a huge difference. for hte additional cost.

[Stu]

I actually don't agree Russ. If TV had made one I would still be thinking 'Why?'

As others have said, it seems to be more of a because they could, or just to outdo TV.

I would not buy one even if I had the money or the scope to use one in, from either company.

It's been said before, but I would far rather someone designed a top quality 2" 100 degree zoom eyepiece, perhaps 8 to 21mm, plus a 2 to 8mm in 1.25" format, again 100 degree, both with 20mm eye relief. I would then be able to use two eyepieces for any scope.

I'm not an optical designer so have no idea about the practicalities of these but something like this would really change the game in a practical way rather than just bigger/wider as the ES seems. They just need to use a bit more imagination I think.

[alan potts]

Stu,

Antares did actually make a 5-8mm zoom and an 8.5-12mm with what they called an 84 degree FOV. I had the shorter one and it was not half bad though it was a bit heavy on CA at the edges. You could also use an extention sleeve to give you the shorter one down to 4mm. I don't know what happen to them, when I sold mine it got snapped up quickly. I would not say it was of the optically quality of the 3-6mm Nagler but I never had them together and there is a large difference in the FOV.

So this is an area that has been visited if not beaten. 

[russ.will]

I actually don't agree Russ. If TV had made one I would still be thinking 'Why?'

A lot of people say the same thing about any 100deg AFOV EP full stop. I'm obviously not one of them, but it doesn't make them wrong.

Russell

[Stu]

A lot of people say the same thing about any 100deg AFOV EP full stop. I'm obviously not one of them, but it doesn't make them wrong.

Russell

Not totally sure of your meaning there Russ? I love 100 degree fov eyepieces, but also love 42 degree Orthos and a range in between.

My comments are simply that this is a highly impractical eyepiece which is irrelevant to the vast majority of astronomers, requiring significant hardware upgrades or changes to use.

Would I like to look through one? You betcha, but for practical purposes I would rather see advances in other directions that just the continued wider/bigger race.

I had a 110 degree 3.7mm ethos SX for a while, and found the extra field annoying and the whole thing quite difficult to get the best out of.

[rwilkey]

Having used my ES82 30mm (only once!) and seen a great view of a very flat sky, I really can't see the benefit of going to a 3" 100 and an expensive ep like this one.  Used in a good refractor, by the way.

[bingevader]

There must be a market, if extremely limited, for this EP, or they wouldn't have gone to the trouble of producing it! 

It may well be totally impractical in most amateur kit. 

I bet it's rather splendid in the right gear!
 

Robin, are you not impressed with the ES 82° 30mm EP, surely it's better than the Panaview?

Why doesn't it get more of a look in?