Recommendations please: 3.5 - 4mm EP

[cajen2]

I'm after a decent short f/l EP for my new-to-me Starfield 102 ED. Currently, my shortest f/l is my Pentax XW 5mm, giving me 143x and I'm sure the Starfield will handle more. It must have good eye relief and a medium to wide FOV so I can wear glasses with it and not be silly money!

I've considered an XW 3.5, which coincidentally would give me exactly 204x (twice the aperture) but has anyone got any other recommendations? 

[mikeDnight]

The 3.5mm XW is an awesome eyepiece and way better than you might expect. A Takahashi TOE is another that comes to mind, but the TOE has a narrower field which I think is 52° apparent.  Another alternative would be to use a longer focal length orthoscopic with a barlow so you maintain comfortable eye relief. A Televue 3-6 zoom is a nice eyepiece too, though it wouldn't be in the same league as the Pentax XW or Takahashi TOE.  You might also look around for a Vixen 3.4mm High Resolution eyepiece on the secondhand market.

[Mr Spock]

The 4mm SLV is a good eyepiece, but not wide field. The 4mm Nirvana is also excellent, but not long eye relief. Same with the 4mm and 3.3mm TOEs. 

Sounds like the XW 3.5 is the front runner. Another to consider is the 3mm Delite; that would give x238. The Starfield can easily handle that.

[Don Pensack]

29 minutes ago, cajen2 said:

I'm after a decent short f/l EP for my new-to-me Starfield 102 ED. Currently, my shortest f/l is my Pentax XW 5mm, giving me 143x and I'm sure the Starfield will handle more. It must have good eye relief and a medium to wide FOV so I can wear glasses with it and not be silly money!

I've considered an XW 3.5, which coincidentally would give me exactly 204x (twice the aperture) but has anyone got any other recommendations? 

When you say "good eye relief", do you mean compatible with glasses?

If so, there are some possibilities with medium to wide apparent fields:

TeleVue Delite 4mm (179x) or 3mm (238x)

TeleVue Delos 3.5mm (204x)

Pentax XW 3.5mm (204x)

Stellalyra 80° 4mm (179x)

If you mean just comfortable eye relief lone enough to avoid accidental eyelash contact with the eyepiece, I would add:

TeleVue Ethos 3.7mm (193x)

APM XWA 3.5mm (204x)

TeleVue Nagler Type 6 3.5mm (204x)

There are others, of course, at lower price points.

And, of course, adding a 2X Barlow lens to anything from 6-8mm would put you there as well.

Anything narrower that 60° of field will require a lot of pushing of the scope and smooth mount movements.  With a tracking mount, that doesn't matter.

 

I own a 102mm refractor of the same focal ratio/focal length.  I would caution you about small exit pupils and floaters.

You will experience no issues with floaters in the high power if it is for double stars.

But if it is for the Moon or planets, floaters may interfere strongly.

I cannot use a 3mm eyepiece on the Moon or planets not because the scope or seeing cannot support it but because my eye has too much junk in it to yield an image without visible floaters.

I max out at 193x (a 3.7mm eyepiece), with its 0.53mm exit pupil, and some of the time max out at 159x (0.64mm exit pupil) because of that.

I have a scope with >2.5x the focal length for when I want really high powers without floaters.  In that scope, 493x is a 0.64mm exit pupil.

 

You know your own eyes, but were I to advise an approach, I would try Barlowing a lower power eyepiece first to see if floaters interfere instead of getting an expensive wider field eyepiece with adequate eye relief.

Then you'll know if you can use such a small exit pupil without the issue of floaters.

 

 

[cajen2]

55 minutes ago, Don Pensack said:

When you say "good eye relief", do you mean compatible with glasses?

If so, there are some possibilities with medium to wide apparent fields:

TeleVue Delite 4mm (179x) or 3mm (238x)

TeleVue Delos 3.5mm (204x)

Pentax XW 3.5mm (204x)

Stellalyra 80° 4mm (179x)

If you mean just comfortable eye relief lone enough to avoid accidental eyelash contact with the eyepiece, I would add:

TeleVue Ethos 3.7mm (193x)

APM XWA 3.5mm (204x)

TeleVue Nagler Type 6 3.5mm (204x)

There are others, of course, at lower price points.

And, of course, adding a 2X Barlow lens to anything from 6-8mm would put you there as well.

Anything narrower that 60° of field will require a lot of pushing of the scope and smooth mount movements.  With a tracking mount, that doesn't matter.

 

I own a 102mm refractor of the same focal ratio/focal length.  I would caution you about small exit pupils and floaters.

You will experience no issues with floaters in the high power if it is for double stars.

But if it is for the Moon or planets, floaters may interfere strongly.

I cannot use a 3mm eyepiece on the Moon or planets not because the scope or seeing cannot support it but because my eye has too much junk in it to yield an image without visible floaters.

I max out at 193x (a 3.7mm eyepiece), with its 0.53mm exit pupil, and some of the time max out at 159x (0.64mm exit pupil) because of that.

I have a scope with >2.5x the focal length for when I want really high powers without floaters.  In that scope, 493x is a 0.64mm exit pupil.

 

You know your own eyes, but were I to advise an approach, I would try Barlowing a lower power eyepiece first to see if floaters interfere instead of getting an expensive wider field eyepiece with adequate eye relief.

Then you'll know if you can use such a small exit pupil without the issue of floaters.

 

 

Yes, as I said in my OP, I will need to wear glasses. 

Taking into account eye relief, FOV and cost, the XW does seem the best compromise.

Or I could Barlow my Morpheus 6.5 mil. I'm a bit hazy on the difference in effect of a Barlow v. a focal extender. I already have a 2x ES Focal Extender. Would that be better or worse for exit pupil than a standard Barlow?

[Mr Spock]

14 minutes ago, cajen2 said:

Would that be better or worse for exit pupil than a standard Barlow?

An extender would keep eye relief the same; a Barlow increases eye relief.

[cajen2]

But neither affects exit pupil?

[Mr Spock]

1 hour ago, cajen2 said:

But neither affects exit pupil?

Both affect exit pupil the same - x2 magnification = ½ exit pupil.

[cajen2]

That's what I thought but I supposed I'd better check....

[John]

At or around that focal length I currently have the XW 3.5mm along with a Nagler zoom 2-4mm and a TOE 4mm. The latter 2 have 10mm of eye relief and a 52/50 degree AFoV so might not quite tick all your boxes. 

The XW 3.5 mm ticks all of them and is optically right up there as well. That would be the one that I would recommend in your case. I'm sure that your Starfield 102 would handle the 204x magnification that a 3.5mm eyepiece delivers effectively as long as the seeing is decent.

[Don Pensack]

2 hours ago, cajen2 said:

Yes, as I said in my OP, I will need to wear glasses. 

Taking into account eye relief, FOV and cost, the XW does seem the best compromise.

Or I could Barlow my Morpheus 6.5 mil. I'm a bit hazy on the difference in effect of a Barlow v. a focal extender. I already have a 2x ES Focal Extender. Would that be better or worse for exit pupil than a standard Barlow?

A Barlow can be telecentric or telenegative.

As far as a 2X magnification is concerned, either type will do the job.

Your ES is a telecentric Barlow but will work fine to provide the magnification you need (Focal Extender is merely an advertising name).

Morpheus eyepieces work fine in Barlows.

Assuming that you have the seeing conditions to support a 3.25mm eyepiece (220x), it will be a good test of whether floaters are a problem for you at that high a magnification.

If they aren't, the 3.5mm XW would be a possibility, though there isn't anything wrong with using the Barlow, either.

[Louis D]

I have the 3.5mm Pentax XW, and it is aberration free across the field as near as I can tell under close scrutiny.  It also has very good contrast and stray light control.  It might not be quite at TOE or HR levels, but it is very good for us eyeglass wearers.  It does not have any SAEP issues, so holding the exit pupil is a breeze.  However, I use it so rarely due to seeing conditions and floaters at that tiny exit pupil that I sometimes wonder why I bought one.  I highly recommend extending(?) some longer focal length eyepieces in your collection with your 2x ES Focal Extender first before buying a 3.5mm XW as recommended above.  You may find it to not be a very useful view.  I've found that observing with a larger aperture scope of longer focal length works much better for higher power views at larger exit pupils than trying to squeeze out the last bit of magnification at smaller apertures.

[cajen2]

Thank you both for your insights. I'll try the telecentric with both the Morpheus 9 and 6.5 mm and see how it goes first.

[Alan White]

I have a Pentax XW 3.5 and it’s superb, equal to the other XWs that I have, 10, 7, 5 and 3.5
The only issue I have is that some nights I wish it were 3 or even 2.5mm.
I barlowed the 3.5 on Lunar on a recent stable seeing night and it was still good, not bad in my ed103,
227x in native and 454x barlowed, which was crazy mad.
Shows how a good image train on the right night work.