Best 3 EP's for a 300mm F5 dob

[Dobman (Simon)]

I've had my dob for 6 months and love it. I'm thinking of upgrading my EP's and would like to hear anybody's thoughts on what i should get. I currently have the 2 plossls (9 & 15mm) & the 2" 32MM supplied with the scope (Bintel) My main interset is Deeeep sky- nebs, globs, planetary globs etc and the occasional look at Jupiter & Saturn & I quite like the moon. I find myself using the 32mm 2" a lot and also the 9mm plossl. I got to have a look thru an Andrews 30mm 80' at the last Bridgenorth nite and loved the wide field.
The 3 EP's I'm thinking of are: andrews 30mm 2", 9mm & 13mmT6 Nagler and a TV 2.5x Powermate. That would give me mags of 50x, 115x, 167x, 287x & 417x.
If anyone has any advice, I'd love to hear your thoughts.

[Striker (Tony)]

Just to make it easy for everyone.

Dobman has a 12" Dob with 1500mm Focal length at F5...the 300mm may throw some people out.

There are plenty here with that dob so they can help you with Eyepieces.

[davidpretorius]

Originally Posted by Dobman

The 3 EP's I'm thinking of are: andrews 30mm 2", 9mm & 13mmT6 Nagler and a TV 2.5x Powermate. That would give me mags of 50x, 115x, 167x, 287x & 417x.

hi,

the 30mm ultra wide will be the last one i upgrade.

I am like you and thinking around 7mm, 11mm and a 2.5x powermate. I will be going a 60 degree fov i reckon because i should be tracking middle of this week, so a nagler will be a little wasted for me.

That is a good spread of magnifications. If you are going naglers for the wide view for your non tracking dob, then you are pretty right. If not just for wide views then it all gets harder as pentax, uo, meade etc all come into the mix.

Put it this way, i can't see you going wrong with what you have suggested!

Us other lonnie boys will be happy if you go that way!!!!

[jackenau]

Dobman, I have 12" also, which I also use to go deep, as that is my primary interest at this time.

Have a SV30mm GSO from bintel, which at the time was great for those wide views. IMHO it took longer to cool down to afford good views as opposed to the Naglers and Panoptics I have since purchased.

Would have to recommend the 35mm Panoptic though above this. Crisper images, and a lot lees cool down time (this is a personal thing, not grab and go)

The 35mm Panoptic works a treat. Have not had the opportunity to use a Nagler or similar for comparison, but this is a great ep for locating, before changing down (up, depending on where your coming from).

Love the view also through my 9mm Nagler if viewing conditions are good.

Have also a Nagler 16mm type 2, but not overall impressed with it, however I do use it frequently as opposed to the normal plossls


Ken M

[janoskiss (Steve H)]

Originally Posted by Dobman

The 3 EP's I'm thinking of are: andrews 30mm 2", 9mm & 13mmT6 Nagler and a TV 2.5x Powermate.:

That would leave a BIG gap between the 30mm and the 13mm. Also, the 13mm Nagler and the Powermate will give you plenty of magnification, and the 9mm in the P-mate will be too much for your scope at 99.5+% of the time. So you'd effectively be buying the rather expensive Powermate for use with only one EP. I'd recommend 19mm Panoptic, 13mm Nagler + Powermate. And if/when finances allow, the 24mm Panoptic.

Or, if you don't insist on premium EPs, the Orion Stratus EPs perform exceptionally well at less than half the price of Panoptics. They work very well in my f6 Dob, and are reported to work well in f5 and faster scopes as well. Around $175 each (incl. postage), but you need to order then from the States. Mine got here in 5 days from www.seansastronomyshop.com. Hmmm... best three ..., just get four and forget the barlow: 21,13,8,5mm.

For the widest true FOV I'm thinking of getting a Meade 5000 Plossl 32mm (with 60 deg AFOV) to keep cost somewhat on the sane side. I imagine this would be a better EP than a budget ultra-wide, but having looked through neither, who knows That's something I'll have to investigate.

[ballaratdragons (Ken)]

I have the 12" GS as well! I have mediocre/good EP's. But may I recommend a 2" Barlow. It will give you twice the variety in your mag range and you can use 2" and 1.25" EP's in it.

[Starkler (Geoff)]

I wouldnt recommend a 35mm panoptic for an f5 scope. It will give a 7mm exit pupil.
I used to have a 27mm panoptic and thats one of the nicest eyepieces I have ever used.

[janoskiss (Steve H)]

Ken, I agree. I wish I bought the UO 2" barlow too instead of the Shorty-plus. But if it's a Powermate Dobman's really after, with a 2" you are talking really big bucks. At that point I'd just buy more EPs to fill the gaps instead.

[ving (David)]

Originally Posted by Starkler

I wouldnt recommend a 35mm panoptic for an f5 scope. It will give a 7mm exit pupil.
I used to have a 27mm panoptic and thats one of the nicest eyepieces I have ever used.

true... a 27mm would be ideal

[Starkler (Geoff)]

If you want to spend money.

27mm panoptic
14mm Pentax XW
7mm Pentax XW
forget the powermate.

Or

27mm panoptic
22mm panoptic
UO 2 inch barlow (the two ep's above should work nicely in the barlow)
7mm Pentax XW for planetary.

[Dobman (Simon)]

Thanks everyone for the advice. You're quite right Janoskiss, the 9mm with the 2.5x powermate would be too much. Originally, I was thinking of the 9 & 13 mm T6& the andrews 30mm 2" with a 2x 1 1/4" barlow. That woud give me a spread of 50x, 115x, 167x, 230x, & 334x which I thought was a good spread of powers,The highest power not too extreme for my scope.Then I had to go on the TV website didn't I and convince myself that barlows were no good and I had to have a powermate which threw my plans into disarray!!
A few of you have reccommended the Panoptics. They don't give as wide a field of view do they? Are they as sharp or sharper than the naglers? I must admit I'd rather stay as wide as pos. can someone answer me this; If I use say the 9mm with a 2x barlow to look at the moon or Jupiter, will there be any diference in the image size or quality to say, using a 4.5 mm 60 degree EP of similar quality? Or will the image just stay in view longer with less tube moving?
Any opinions on the TV 2x 1 1/4" barlow?

[Starkler (Geoff)]

There are very few eyepieces sharper than the panoptics, that includes naglers.
68 degrees is wide enough for many , and the panoptics are considerably cheaper than similar focal length naglers.

I wouldnt worry too much about super high magnifications as seeing conditions rarely support powers over 250x, and 90% of my planetary viewing is done at about 200x.

[davidpretorius]

well i have just came in from viewing / imaging mars. i had my 6.5mm series 500 and a 2.4x barlow ie less than 3mm and i was able to see detail.

a very good seeing night out there at the moment!!!

i can see 6 stars in the trapezium!

given seeing conditions here in tassie, i would be tempted to have a 9 and 2.5x barlow or powermate. I have used my 6.5mm and 12.5mm in combo with my 2.4x and have been very happy on at least 6 occassions in two months.

[Stu]

Dobman, I wouldn't worry about the field of view in a big panoptic. The bigger they are the harder it is to find the field stop. Tonight through my 22mm panoptic I found it quite difficult to see the field stop when looking in the center of the eyepiece. I have to move my head to look around to the edges and at that point it is uncomfortable anyway.

Panoptics are generally slightly sharper than naglers but is all a bit of swings and round abouts. There's not much in it. Naglers are wider, slightly warmer, but have slightly less field curviture (but it's only really noticable during the day if you ask me, or, if you look though the eyepiece at a magazine which is a stupid idea anyway).

You will also get less kidney beaning in large panoptics. I find it hard to use the 31 nagler, but people that wear glasses love them. I think the advange of naglers becomes more apparent when you get into lower focal lengths because the eyerelief is better.

But as Geoff said, the pentax might be a good option at lower focal lengths. I have not compared them, but I have heard the the penax eyepieces have a more natural color tone than naglers and radians.

But having said that I'm about to get a 4mm radian and 35mm panoptic. I would try them first if possible because you might like something better. I think panoptics are the best (at the moment).

[Dobman (Simon)]

The Panoptics sound good. A query on FOV. I'm talking about the actual FOV you see when looking thru the EP. You get wider FOV with longer F.L EP's amd narrower FOV with shorter FL EP's. Am I right? If so, (remembering I like Wide Fov's) if I,m getting 2 good EP's & I'm tossing up between Naglers & /or a Panoptic, should I get say, a 15mm Panoptic & a 9mm Nagler? My reasoning behind this is this; the 15mm Panoptic has a narrower FOV but because of its longer FL this wont be as noticeable and the 9mm nagler has a wider FOV but the shorter FL will counteract this. Does any of this make sense? I'm also thinking of a TV 2x barlow & a 30mm 2" Andrews EP. This combo would give me 50x, 100x, 167x, 200x & 333x. Any thoughts out there?

[Stu]

Originally Posted by Dobman

You get wider FOV with longer F.L EP's amd narrower FOV with shorter FL EP's. Am I right?

I have been thinking about this since I posted my last post (above) last night. I can't explain why this is so... But I definitely notice a difference when I look through EP's with different focal lengths and the same AFOV.

Why? Why!

I thought that it might have something to do with the EP relief. Maybe when I look though some naglers I have a tendancy to view from too close to the lens. This make makes it easier to see the field stop. Could this be it?

My experience at star camps looking through lots of different naglers is that sometimes it is impossible to see the field stop and other times it's way too easy. That's one of the reasons why I'm happy with the 22mm pan, because the field is way bid enough, getting the extra bit from the nagler would be a waste. But with another focal length comparison the nagler would kick it's buttt. I can't remember whether it was longer or shorter FL that made the difference now...

I would be intrested to hear if anyone else has had the same experience. Is it an eye relief issue?

[Starkler (Geoff)]

Dobman, I suggest you do a lot of research before laying out the kind of funds we are talking about here. All the premium eyepieces types are not equal and have varying characteristics, even within the same line. eg there are different series of naglers, all different.

I advise you to do some comparisons in the field and see what characteristics are important to you, especially:

FOV
eye relief
sharpness across field
2inch or 1.25
contrast (mainly for planetary)

[Starkler (Geoff)]

Originally Posted by Stu

My experience at star camps looking through lots of different naglers is that sometimes it is impossible to see the field stop and other times it's way too easy.

The definition of eye relief is the farthest distance from the eyepiece that the full field stop becomes visible. Correct eye placement should be at around this distance. As you get closer it becomes harder to hold the image.

Stu , yes it sounds like you are used to short ER eyepieces and are getting too close.

[ausastronomer (John Bambury)]

Originally Posted by Stu

I have been thinking about this since I posted my last post (above) last night. I can't explain why this is so... But I definitely notice a difference when I look through EP's with different focal lengths and the same AFOV.

Why? Why!

Stu/Dobman,

You need to understand the difference between Apparent Field of View (AFOV) and True or Actual Field of View (TFOV).

The AFOV is that specified by the eyepiece manufacturer and is determined by the eyepiece design and its field stop diameter. This does not change regardless of which telescope you use the eyepiece in. Hold the eyepiece in front of a light source and look at the size of the light circle through the eyepiece. This basically represents the angle that the light source enters the field lens of the eyepiece. This is around 45° for an orthoscopic, 50° to 55° for a plossl design, 60° for a TV Radian, 65° degrees for the Vixen LVW, 68° for the TV Panoptics, 70° for the Pentax XW series and 82° for the TV Naglers and Meade UWA.

The TFOV is the actual angular size of the targets' field that you see through the telescope. It is calculated by dividing the magnification that the eypiece gives in a particular telescope by the AFOV. Consequently as the focal length of the eyepiece increases the magnification drops and the TFOV is increased. eg a 30mm 50° Plossl gives a larger TFOV than a 20mm 50° Plossl, when used in the same telescope, because it gives lower magnification in that telescope.

Example:

Assume a 200mm (8")/F5 newtonian. The aperture is 200mm the focal length (FL) is 1000mm.

(Eyepiece magnification is calculated by dividing FL of scope/FL of eyepiece)

lets go back to the 20mm and 30mm 50° plossls.

The 30mm Plossl gives a magnification of 33.3X (1000/30)
The 20mm Plossl gives a magnification of 50X (1000/50)

Hence the 30mm Plossl gives a TFOV of 1.5° (50/33.3)
and the 20mm Plossl gives a TFOV of 1° (50/50)

I hope this helps, if its not clear let me know.

CS-John B

[ausastronomer (John Bambury)]

Originally Posted by Dobman

I've had my dob for 6 months and love it. I'm thinking of upgrading my EP's and would like to hear anybody's thoughts on what i should get. I currently have the 2 plossls (9 & 15mm) & the 2" 32MM supplied with the scope (Bintel) My main interset is Deeeep sky- nebs, globs, planetary globs etc and the occasional look at Jupiter & Saturn & I quite like the moon. I find myself using the 32mm 2" a lot and also the 9mm plossl. I got to have a look thru an Andrews 30mm 80' at the last Bridgenorth nite and loved the wide field.
The 3 EP's I'm thinking of are: andrews 30mm 2", 9mm & 13mmT6 Nagler and a TV 2.5x Powermate. That would give me mags of 50x, 115x, 167x, 287x & 417x.
If anyone has any advice, I'd love to hear your thoughts.

Dobman,

I will make a couple of very important assumptions in recommending the following eyepieces:

1. You do not need glasses on at the eyepiece to observe ?
2. Your normal observing conditions are under dark skies (ie Mag 6 or better)
3. You are under 50 years of age. (Pupil dilation reduces as you age)

If the above 3 assumptions are not correct then my recommendations would be a lot different and for very important reasons.

I would forget about the Andrews 30mm 80° eyepiece. It's not at its best in a scope as fast as F5 and is not nearly in keeping with the quality and EOF performance of the other eyepieces you are considering. A bit like buying a new Jag and then putting a $30 CD player in it.

For low power widefield viewing I would recommend the 35mm TV Panoptic, which will work very well as a finder eyepiece and also for low power views of extended objects. This gives 43X with a TFOV of 1.6° and a 7mm exit pupil, so you will need dark skies.

For medium power the 13mm Nagler T6 gives 115X with a TFOV of .7° (42') and a 2.6mm exit pupil.

For medium/medium high power the 9mm Nagler T6 gives 167X with a TFOV of .5° (30') and a 1.8mm exit pupil.

Basically I think you were pretty much on the money excepting the 30mm 80° Andrews Eyepiece which is not near the standard of a TV Nagler or Panoptic, mind you its not near them in price either. If you wanted a cheaper option the 30mm GSO Superview (also available from Andrews) performs a lot better in an F5 scope than the 80° Andrews eyepiece, but it only has an AFOV of 65° thus giving you a magnification of 50x with a TFOV of 1.3° and a 6mm exit pupil.

The barlow. With the eyepieces chosen I think you are wasting your money on the 2.5X TV powermate, which is an exceptional barlow BTW, as the powers with the 2 Naglers will be too high IMO on most occasions. The 13mm T6/2.5 PM combo gives 290X and the 9mm T6/2.5PM combo gives 417X. I doubt that the seeing would allow you to use these powers very often. I would forget about the barlow and put the money into 2 or 3 specialist planetary eyepieces like the 5mm, 6mm and 7mm UO HD orthoscopics at about $120 each, consequently 2 of them will cost less than the barlow. They will give the following mags 7mm=214x, 6mm=250X, 5mm = 300x. If I was to only buy 2 orthos in your case it would be the 6mm and the 7mm. Another option may be the 7.5mm and 5mm Takahashi LE's again an outstanding planetary/high power eyepiece.

CS-John B

PS: I personally prefer the 10mm Pentax XW over the 9mm and 11mm Nagler T6's, by a small margin but they are both exceptionally good. If you are heartset on a couple of Naglers they are an outstanding eyepiece so go for 'em.