Beginner question regarding lower power eyepieces

[Richw24]

A couple of months back, I bought a Skywatcher Heritage P130 and am now looking to get a lower power eyepiece with a large field of view. I remember reading somewhere that the max field of view you would be able to get out of the P130 is 52 degrees from a 32mm EP. Is this true? Or will I be better off going for an eyepiece with a larger FOV. I'm currently thinking of getting a Bintel SuperView 30mm with a 68 degree FOV but not sure if it will provide a substantial difference with the super 25mm EP that I got with the scope. Any advice would be very much appreciated!

Cheers,

Richard

[ronin]

No, you do not "get" 52 degrees from a 32mm eyepiece.

The 32mm plossl has a field of view of 52 degrees.

What you get is (52 / Magnification)

So 130P is 650mm and a 32/52 EP gives mag = 650/32 = say 20x, so you get 52/20 = 2.5 degree.

The Bintel therefore is Mag = 650/30 = 22x, view is 68/22 = 3 degree (tiny bit more).

So about 0.5 degreee more the a 32mm plossl.

Note that 0.5 is spread across both sides so 0.25 on each.

However may depend on how good the edge quality is, if that is of concern.

[YKSE]

I'm under impression that  Heritage 130P has 1.25" focuser, meaning it can only accept 1.25" eyepieces.  While a 30mm eyepiece with 68 deg FOV can only be 2".

32mm plossl with 52 deg FOV or 24mm 68deg are about the widest FOV you can get in a 1.25" focuser. Anything noticeable wider can only be achieved with 2" eyepieces, might worth to remember.

[SpaceWalker]

YKSE is right, Bintel SuperView  is a 2" eyepiece, but your Dob has just 1.25" focuser unless you've upgraded to 2".

In addition, Bintel SuperView 30mm, 5 elements in 3 groups looks like a typical Erfle, a poor performer off-axis in f/5 scopes, so you'll have ~30-50% of outer field blurry. It looks like a rebrand of GSO SuperView or Meade QX, I'd avoid it. It works good at f/10+ though.

Indeed, the 32mm 52*AFOV Plossl will cover max TFOV of 2.4* available in your Dob. IMO, the 24mm ES68, ES Maxvision or Meade SWA (used) definitely would be a much better choice for a f/5 Dob with 1.25" focuser since you'll get max TFOV at higher magnification and exit pupil of 4.8mm, it would be a good upgrade over your stock superplossl.

[Richw24]

Well that's a bit embarrassing, I was comparing a 30mm and a 32mm and didn't realise that the 30mm was 2" so cheers for pointing that out and thanks Ronin for breaking down how all of those values are related to each other, very interesting. I see there is a lot for me to learn! Very much appreciate all the advice. Would love to own one of those above mentioned eyepieces but they are a little out of my price range at the moment, seeing as they cost more than half of what I paid for my telescope. Will have to keep a look out for any second hand ones.

SpaceWalker I see in your tag that you have 3 2x Barlows, do you stack these?

[SpaceWalker]

Would love to own one of those above mentioned eyepieces but they are a little out of my price range at the moment, seeing as they cost more than half of what I paid for my telescope. Will haveto keep a look out for any second hand ones.

What about 60*AFOV rebrands? The 25mm BST Explorer/TS25/Agena Starguider ED/AT Paradigm will give you 2.3*TFOV vs max 2.4*TFOV, just 5' less than max, you won't even notice that, and the eye relief is 5mm, just fine. Also the 25mm Celestron X-Cel LX or Meade HD-60 as an option, they perform  excellent even in fast scopes, optically pretty close to previous group and also have 60*AFOV.

SpaceWalker I see in your tag that you have 3 2x Barlows, do you stack these?

No, don't feel the need. Too many Barlows resulted mostly from my upgrades .  One of them is 2", bulky and heavy, rarely used. I purchased it *just in case*, for my few 2" eyepieces, but didn't like dealing with balance problems. The rest are 1.25", one telenegative Barlow used just for barlowed collimation. I'm mostly DSO observer and use almost exclusively my 2x TeleXtender to expand 82*AFOV EP collection or sometimes on planets and the Moon. The highest magnification that gives me acceptable results on Mars, the Moon  and some double stars is ~370x when I  2x Barlow my 6.5mm Meade HD-60. It's close to my 8" Dob theoretical limit. But usually my atmosphere doesn't allow more than ~200-240x.

[bingevader]

 Would love to own one of those above mentioned eyepieces but they are a little out of my price range at the moment, seeing as they cost more than half of what I paid for my telescope. Will have to keep a look out for any second hand ones.

Can you get the Maxvision 68° 24mm in Australia?

It would be well worth paying half the price of your 'scope for!

If it is out of your price range, then a half decent 30mm or 32mm plossl would be great, although, one of those will be about a third the price of your 'scope.

Second hand is always a very good option, quite a few of my EPs are second hand.

Just as a little aside however, it is worth remembering that the 'scope and its optics are only one half of the equation (and the 130p is a good piece of kit).

The eye piece you stick in it is the other.

As Spacewalker has said, at f5 your 'scope is on the faster side and won't benefit from poorer EPs.

Even if it means saving a little longer or waiting for something to appear on the second hand market, it will be worth the wait to compliment your decent 'scope.

Most of my EPs are between 1/4 and 1/3 the price of my 'scope, but I do have one that was half the price and it was well worth it!

[Richw24]

What about 60*AFOV rebrands? The 25mm BST Explorer/TS25/Agena Starguider ED/AT Paradigm will give you 2.3*TFOV vs max 2.4*TFOV, just 5' less than max, you won't even notice that, and the eye relief is 5mm, just fine. Also the 25mm Celestron X-Cel LX or Meade HD-60 as an option, they perform  excellent even in fast scopes, optically pretty close to previous group and also have 60*AFOV.

Are there any differences in quality between rebrands? Or is it solely just the brand that is different? Not many places I can buy locally over here but I've found a 25mm BST Explorer online. Also x370 would be amazing! I just saw Saturn for the first time last night as it has started rising earlier and it was amazing at x216.

Can you get the Maxvision 68° 24mm in Australia?

It would be well worth paying half the price of your 'scope for!

If it is out of your price range, then a half decent 30mm or 32mm plossl would be great, although, one of those will be about a third the price of your 'scope.

Second hand is always a very good option, quite a few of my EPs are second hand.

Just as a little aside however, it is worth remembering that the 'scope and its optics are only one half of the equation (and the 130p is a good piece of kit).

The eye piece you stick in it is the other.

As Spacewalker has said, at f5 your 'scope is on the faster side and won't benefit from poorer EPs.

Even if it means saving a little longer or waiting for something to appear on the second hand market, it will be worth the wait to compliment your decent 'scope.

Most of my EPs are between 1/4 and 1/3 the price of my 'scope, but I do have one that was half the price and it was well worth it!

The ES Maxvision seems like it has really good reviews but unable to get it locally and the only places I've found it online charge an incredible amount for shipping unfortunately

[Alfian]

Not sure how old your eyeballs are, but  its worth noting that a 32mm EP will give you a 6.4mm exit pupil.  A 25mm (ish) may be better for the scope.  The  ExploreScientific Maxvision 24mm/68 degree would indeed be good giving you 27x and 2.5 degrees. Cheapest costs from europe with postage I reckon would be about 255 australian dollars. Given that a 6" Dob costs bout 400 (Bintel) proportionately thats about the same as we would pay in the UK. So like bingevader, I reckon thats a fairish deal, although its still a lot of cash!  

However looking at a  BST starguider 25mm/60 degree (good EP) from the UK (skiesthelimit) looks like it would cost just over a $100 with postage. Its worth double checking that but that seems like a good deal too.

Its worth steering away from the cheaper skywatcher wide angles which are not good with fast scopes. Its  a  bit of  shame that the Bintel/GSO  Superview does not come in a 25mm.  GSO stuff tends to be good value. Not what you are looking for but noticed on Astroshop AU that they selling Vixen SLVs for $159; converting that back to sterling, they look a really good buy!

[SpaceWalker]

Are there any differences in quality between rebrands? Or is it solely just the brand that is different? Not many places I can buy locally over here but I've found a 25mm BST Explorer online. Also x370 would be amazing! I just saw Saturn for the first time last night as it has started rising earlier and it was amazing at x216.

They are all made by the same manufacturer, Barsta, so the difference should be just the name on the barrel. Just keep in mind that sample-to-sample variation used to be high within budget eyepiece lines themselves since manufacturers have to save on QC to make eyepieces cheaper. You can't go wrong with any of those brands, just find the best deal available to you.

Well, experimenting with magnifications on planets of course worth it, but I wouldn't be so excited about 370x since it exceeds even the theoretical limit (260x) for your scope. Our atmosphere in 90%+ cases allows 300x max independently on the scope size. You can successfully use magnifications like that, probably on the Moon only.  The magnification you've used (216x or 42x/inch of aperture) on Saturn would be pretty close to your reasonable max limit (38x/inch). Mars usually requires high magnifications (~250x+), Saturn needs less, but tolerates high magnifications well, but Jupiter is more picky (IMO, ~150-180x for your scope in most observing conditions).

[Jimtheslim]

I just acquired a Meade 32mm Plossl for my 90mm refractor. First glance at the moon and it looked great, even better than my 26mm Meade. The only problem is that the 32mm suddenly blackens out if you start looking 'around' in the eyepiece which is frustrating. I've had a look at the eyepiece and there is nothing visibly wrong with it, I'm assuming it's just the longer barrel. Anyone else get this problem? 

[Stu]

No, you do not "get" 52 degrees from a 32mm eyepiece.

The 32mm plossl has a field of view of 52 degrees.

What you get is (52 / Magnification)

So 130P is 650mm and a 32/52 EP gives mag = 650/32 = say 20x, so you get 52/20 = 2.5 degree.

The Bintel therefore is Mag = 650/30 = 22x, view is 68/22 = 3 degree (tiny bit more).

So about 0.5 degreee more the a 32mm plossl.

Note that 0.5 is spread across both sides so 0.25 on each.

However may depend on how good the edge quality is, if that is of concern.

Just to clarify/correct this point.

The maximum field of view in a 1.25" eyepiece is determined accurately by the field stop, not the formula quoted above. The field stop is the physical aperture available limited by the barrel of the eyepiece, either 1.25" or 2".

The easiest eyepieces to quote as examples are Televue, not because they are premium but because they publish field stop sizes.

The formula to calculate field of view is :

True field of view = eyepiece field stop diameter ÷ telescope focal length x 57.3

32mm Plossl has a 27mm fieldstop

24mm Panoptic also has a 27mm fieldstop

Both therefore have the same true field of view at 27/650*57.3 = 2.38 degrees which is the maximum in a 1.25" barrel.

Using the magnification and AFOV route gives 2.46 (assuming 50 degree afov) and 2.51 degrees respectively which is overstated.

I would question the point about the significance of 0.5 degrees of true field of view being a 'tiny bit more'. It is a 20% increase and is the difference between framing certain large clusters or nebulae nicely or having them only just, or not fit at all.

Example of a 2.5 and 3 degree field on the North America Nebula.

The Televue 32mm Plossl is not expensive if picked up on the used market and is 'good' down to f4.

Hope that's of some use.

Stu

[Stu]

I just acquired a Meade 32mm Plossl for my 90mm refractor. First glance at the moon and it looked great, even better than my 26mm Meade. The only problem is that the 32mm suddenly blackens out if you start looking 'around' in the eyepiece which is frustrating. I've had a look at the eyepiece and there is nothing visibly wrong with it, I'm assuming it's just the longer barrel. Anyone else get this problem?

The eyerelief on Plossls is a function of their focal length, approx x0.7 of the focal length. The 32 and 40mm Plossls have quite long eye relief as a result which can make the placement of your eye a little tricky at times. There is nothing wrong, just takes a little practise.

[Jimtheslim]

The eyerelief on Plossls is a function of their focal length, approx x0.7 of the focal length. The 32 and 40mm Plossls have quite long eye relief as a result which can make the placement of your eye a little tricky at times. There is nothing wrong, just takes a little practise.

I thought this might be the case, I was just surprised that it seems so much more obvious on the 32 than the 26 (on which it doesn't seem to happen at all). I must say however that the moon in the 32 is absolutely stunning when it's lined up

[Stu]

I thought this might be the case, I was just surprised that it seems so much more obvious on the 32 than the 26 (on which it doesn't seem to happen at all). I must say however that the moon in the 32 is absolutely stunning when it's lined up

Yes, I think once you get over about 20mm it can get more difficult. You need that much if you wear glasses, but if not then it is almost too much.

Some eyepieces have adjustable eyeguards which extend out to make eye placement easier, and to cut down the reflections which happen when your eye is further from the exit lens. Televue sell a nicely expensive eyeguard extender for their 32 and 40mm Plossls which helps too.