ES 24mm in 68 or 82?

[AndrewCharlton]

Hi folks,

Potentially a very newbie question here but just wanted some advice before I finalise my letter to Santa!

I'm looking to upgrade my eyepiece collection to a set of Explore Scientific 82s.  I'm currently using BST Starguiders with my Skywatcher 250px dob.

However, I'm not sure whether to go for the 24mm in the 68 or 82 variant. My thoughts are:

• 82 has the better FOV, and from what I understand does provide a better view.
• The 68 means no worrying about changing to 2" barrel and back.
• I could use the same set of filters with all my eyepieces.

 

I guess the question comes down to whether the view from the 82 outweighs the convenience of having everything in 1.25" format.  Any recommendations?

[Jimtheslim]

4 hours ago, AndrewCharlton said:

Hi folks,

Potentially a very newbie question here but just wanted some advice before I finalise my letter to Santa!

I'm looking to upgrade my eyepiece collection to a set of Explore Scientific 82s.  I'm currently using BST Starguiders with my Skywatcher 250px dob.

However, I'm not sure whether to go for the 24mm in the 68 or 82 variant. My thoughts are:

• 82 has the better FOV, and from what I understand does provide a better view.
• The 68 means no worrying about changing to 2" barrel and back.
• I could use the same set of filters with all my eyepieces.

 

I guess the question comes down to whether the view from the 82 outweighs the convenience of having everything in 1.25" format.  Any recommendations?

I am holding out for the 82 despite constantly being tempted to go for the cheaper 68. My reckoning is that with the planets out of the sky for the foreseeable future and the darker nights I will primarily be going for DSO's. I think the 24mm will provide a nice level of magnification and unlikely to want to do a lot of switching, so therefore I am not put of by the 2" barrel.

I very much doubt I will ever get one mind you, Santa isn't that generous round my way.

[Davesellars]

I'd recommend the ES68 degree.  It is a very good price and performs very well indeed with my f/4.9 dob.  Also unlike the 82 degree is not a real heavyweight eyepiece somewhat easier to balance.  I use ES82 eyepieces from 11mm down to 4.7 though.

[Paul73]

Sorry to contradict Dave. But, I would have to go with the 82°. I've had MV 68°, ES 68° and ES 82°. All excellent for their price points. The ES 24mm 82° is the only one that I would buy again / can live with a case full of TV exotica.

You owe it to your Dob to go wide.

The 2" vs  1 1/4" was a non issue for me. You just change the adaptor with the eyepiece. The 2" filter can be an issue on a handful of targets (a 2" OIII for the Veil is a must) but the majority of your filter work will be with the 1 1/4" anyway.

Don't you just love the conflicting advice! It is all down to personal preference.

Don't forget the first light report.

Paul

PS. The MV 20mm 68° is an absolute gem of an eyepiece. Don't sell that one!

[John]

I've have recently acquired an ES 24mm 68 and it shares a case with Tele Vue Delos and Pentax XW's. It provides excellent performance in all my scopes down to F/5.3 (my 12" dob). I wanted a max field 1.25" eyepiece to complete my 1.25" set and it does this job very well. It's a bit lighter than the Pentax XW's and Delos but reaches focus at close to the same point, which is handy.

I think your choice boils down to whether you want to push out the true field or not. If you do then the 2" 82 eyepiece does that although if going to 2" I'd probably go the "whole hog" and go to 28mm or more. The wider field is not necessarily "better" but it is, er, wider 

If your scope is a really fast newtonian, the wider field will show more coma of course.

For me, when I want really wide, I get my Ethos case out

[Ricochet]

If you're looking to change your whole set from BST Starguiders to ES82s I would start with one of the shorter 1.25" ES82s. That way you can assess how much the aFoV matters to you compared to the narrower aFoV of your existing eyepieces. You don't want to buy the ES68 and then later down the line discover you really like 82° and wish you'd bought the 82.

[Northern Soul man]

28 minutes ago, Ricochet said:

If you're looking to change your whole set from BST Starguiders to ES82s I would start with one of the shorter 1.25" ES82s. That way you can assess how much the aFoV matters to you compared to the narrower aFoV of your existing eyepieces. You don't want to buy the ES68 and then later down the line discover you really like 82° and wish you'd bought the 82.

Totally agree with this, ive just bought 3 82's and i only have compared true FOV with my set of hyperions at F10 and found that the comfort of the hyperions do really work well at this focal length, with the 82's you really do need to get your eye right up against the eye lens at the scope to have a look around to get the full field in, as said ive only had a couple of nights to compare so not the best test but my initial thoughts are that maybe the 68's are much more comfortable in that respect but may just be me being used to 70 degree .

You could do with someone who has both the range but i think that once you settle on one particular range, if your like me, i tend to do the same and get all one particular set.

I really do have to get right up against the eyecup to get the benefit of the extra field in comparison to the hyperions but they are nice EP's for the price.

[F15Rules]

I've owned both 68s and 82s (though not all in the same focal lengths and I prefer the 68s. The 24mm one of my favourite 3 eps, along with a Pentax 10.5mm XL and a Morpheus 14mm. It can live with all the "premium" brands IMO. It's also a nice size, not too big but very solid and has very bright views, I think the coatings are excellent. Finally, the eye relief is better on the 68s and I find this makes prolonged viewing very comfortable. It's virtually the same as the Pentax XWs, and I think their combination of AFOV and optical quality especially in shorter focal lengths is pretty special.

But as said above, it's all down to personal preference :-)

Dave

[bingevader]

82° for me.

The other added bonus is the drift time.

[cloudsweeper]

The ES 24/82 comes in at 870g; the 24/68 is just 390g - and that's with the Revelation 1.25 to 2" adapter (twist to fit, no screws) which I leave on it.  (My six lowest mag EPs are thus all 2" fitting, which makes for easier change-over.)

(I have the 82* in 18, 14, 11, 8.8, and 6.7mm.)

Doug.

[rob0971]

I have the 82 deg & it's my favourite eyepiece in my 12" dob

[Ben the Ignorant]

I have the Explore 24/68 and a Meade 24/82; the Explore 68 is for my 1.25" achro, the Meade 82 is for my f/5 dob. The point of those eyepieces is to show the maximal field with the lowest power and largest practical exit pupil (5mm for the dobsonian). If you don't get the 24/82 you lose some field, you'll always know your scope is making a larger image than you see, and the remainder just dies on the outside of your 68° eyepiece's field stop.

Think of all the large clusters and nebulas you won't frame well because of this.

[John]

28 minutes ago, Ben the Ignorant said:

... If you don't get the 24/82 you lose some field, you'll always know your scope is making a larger image than you see, and the remainder just dies on the outside of your 68° eyepiece's field stop....

 

So how large an apparent field would you need to ensure that this does not happen at all - 100, 110, 120 degrees ?

 

[cloudsweeper]

The 68* would give TFOV = 1.36*, whereas the 82* would give 1.64* - not a huge increase, I believe.

A 30/82 would give 2.05*, but costs a lot more - and weighs a lot more.

As usual, it's a juggling act - cost, quaility, angle, weight.

Doug.

 

[AndrewCharlton]

Thanks for all the excellent advice!  It sounds like people have their favourites but they're both excellent eyepieces.

 

I think I'll follow Ricochet's advice and start with the 11mm ES82 - the 12mm BST is the eyepiece I use most atm, and I figure this would be the best replacement/upgrade.  I suspect my collectionitis will then force me to get the 24mm in 82 as well, but we'll see how I get on with it.

 

Thanks again, will make sure to let you know how I get on with them.  Now just wish M42 would rise a bit earlier ...

[michael.h.f.wilkinson]

I have a MaxVision 24mm 68 deg which has the same optical design of the ES version (although coatings may differ). The MV is very good indeed for the price, and the eye relief is comfortable. It can match TV EPs well down to F/5, but when tested in a fast dob (at F/4.1) it showed a lot of astigmatism. The 68 deg was only rated for F/5 and slower, so no real surprise there. The MaxVision 24mm 82 deg is rated to F/4, and so I would expect it to do better in a really fast dob.

[Ben the Ignorant]

6 hours ago, John said:

So how large an apparent field would you need to ensure that this does not happen at all - 100, 110, 120 degrees ?

My 24/82 has a 37mm field stop but a 45mm field stop would fit the barrel since its inner diameter is 47mm. 45 / 37 = 1.21, thus the apparent field could be 82° x 1.21 = 100°, and the focal length would have to be reduced to 24mm / 1.21 = 20mm. 20mm and 100° are the Ethos and Explore clone specs.

[alan potts]

Having had both Meade eyepieces which have the same elements though the coating could be different I would say the 24mm 82 degree was a better eyepiece. Wish I had kept mine to be honest.

[bingevader]

12 hours ago, AndrewCharlton said:

I think I'll follow Ricochet's advice and start with the 11mm ES82 - the 12mm BST is the eyepiece I use most atm, and I figure this would be the best replacement/upgrade. 

I'm sorry to disagree, but I'm not sure that would be the best upgrade!

If you have a 12mm, the 11mm will be pretty close in terms of the focal length.

Why not fill a gap that you don't already have filled instead?

From the reviews, I'm sure there isn't anything wrong with the BST, if it's the EP you use the most why replace it?

Fill the gaps, and if you decide you like the 82° EPs, then replace the ones you have.

[SpaceWalker]

On ‎11‎/‎1‎/‎2016 at 19:16, Ben the Ignorant said:

My 24/82 has a 37mm field stop

I'm afraid that's not true. Check out the 24mm ES82 specs on the Explore Scientific website (http://explorescientificusa.com/collections/82-series-eyepiece/products/82-24mm?variant=589728169), it says 33.5mm.

[Ben the Ignorant]

My 24/82 is a Meade.

[John]

2 hours ago, Ben the Ignorant said:

My 24/82 is a Meade.

To deliver an 82 degree AFoV in a 24mm eyepiece the field stop should be 33.5mm in diameter. A 37mm field stop in that focal length would give an AFOV of around 90 degrees I think. Maybe yours is an UUWA ?

 

[YKSE]

34 minutes ago, John said:

To deliver an 82 degree AFoV in a 24mm eyepiece the field stop should be 33.5mm in diameter. A 37mm field stop in that focal length would give an AFOV of around 90 degrees I think. Maybe yours is an UUWA ?

That's a very interesting question actually.

My lastest understanding (could be wrong as well) is that we can calculate an eyepiece's True Field of View(TFOV) by using the formular

57.3*(field stop diameter)/(focal length)

and this formula is usually referred as calculating Apparent field of view (AFOV)

My understanding is that AFOV vill vary somewhat depending on what distortion type(s) an eyepiece has. E.g. Docter UWA 12.5mm with field stop 19.2mm, gives 88° according to the above calculation, while the AFOV specification from Docter is 84°, and my measurement here support their claims too, this 88° is TFOV (the actually sky it shows), but the outer edge is somewhat compressed (AMD), so it looks like only showing 84°.

 

There's a thread about AFOV, FS and distortions in other site if interested:

http://www.cloudynights.com/topic/553874-afov-fs-and-different-distortions/

Having some scope time with some measurements when cloudy can be quite fun

[Peter Drew]

Surely the 88 degrees must be the apparent FOV?, a true FOV would need a "fisheye" lens.   

[cloudsweeper]

1 hour ago, YKSE said:

 

My latest understanding (could be wrong as well) is that we can calculate an eyepiece's True Field of View(TFOV) by using the formula

57.3*(field stop diameter)/(focal length of telescope)

I recently saw this too, and it does seem to work quite well.

A bit of algebra applied to it gives us:

AFOV = (FS dia x 57.3)/(FL of EP)      -  which gives it in terms of EP parameters only. 

Again, this appears to work to a reasonable accuracy.

For example, using data for the ES 68* series, we have, for the 20mm EP, an AFOV of 65.3* instead of 68*.

Doug.