FOV Why so many increments in mm i DONT get it

[rockystar]

12 hours ago, Louis D said:

It's like anyone who has a hobby and starts collecting various examples for their subtle differences.  Think about musicians with multiple instruments, motorcyclists with multiple bikes, target shooters with multiple pistols/rifles, equestrians with multiple horses, woodworkers with multiples sets of hand tools, etc.  I enjoy comparing multiple eyepieces in multiple scopes to see how they present the same objects differently.  The objects in the sky aren't changing much over the years, so I change up how I look at them.

Or my wife and her shoes!

[Stu]

5 minutes ago, rockystar said:

Or my wife and her shoes!

But.....at least we are buying different sized eyepieces to achieve different magnifications. Surely (hopefully?) your wife has one size of feet so only needs one pair of shoes? 

I don't know why I didn't think of this before, it's a surefire winner!  

[rockystar]

1 minute ago, Stu said:

But.....at least we are buying different sized eyepieces to achieve different magnifications. Surely (hopefully?) your wife has one size of feet so only needs one pair of shoes? 

I don't know why I didn't think of this before, it's a surefire winner!  

I have no doubt that there are some on this forum with EPs of the same length in different brands and FOVs

She has the same shoe in different colours!

I don't question it anymore, then she can't question it when a new FLO box arrives at the door.

[laowhoo]

The only 2 things we considered for Barlow were field stop and glass quality. Shorties were out b/c these will often compound aberrations, unless maybe you pay top dollar? Otherwise we don't see any difference, and besides our own reading, I peeked under the covers to see what people like BillP were using and/or recommending. Sure the TVs outnumbered any other, but we went with Siebert, and keeping the power low on them--1.5x vs 2x or greater--can only help. Only issue we had was hitting the flat in the star diagonal, and had to space it with an elastic hair tie. Neither did we have to think about the 2" EPs, just the 24mm on down. Harry's Barlows are long/tall, but that didn't matter for us. Unusual looking too

http://www.siebertoptics.com/SiebertOptics-barlows1.html#Ad 1b

But yeah, we have no vignetting on the 24mm 68* and that was the largest field stop we had to consider. Others will say for the more exotic AFOVs. You should call him. He loves to talk, and I had a hard time getting off the phone. LOL Calling from the UK I imagine would really make his day, but you've been warned.

[Timebandit]

32 minutes ago, laowhoo said:

      You should call him. He loves to talk, and I had a hard time getting off the phone. LOL Calling from the UK I imagine would really make his day, but you've been warned.

 

 

In that case maybe a wise decision not to make a phone call. As a very long phone call from the UK to the US  would likely end up costing more than the Barlow itself?

A email maybe more financially prudent for UK folk , but obviously not as much fun as a one to one talk on the phone??

 

 

[laowhoo]

Hadn't thought of that. LOL You can email him or read the site and ignore the spelling. I don't know about the "high-performance" jobbies--don't think he had them 5 years ago. We just wanted to be sure we didn't need the 4-element telecentric.

[John]

I've not seen much Siebert stuff over on this side of the pond. It does seem to get great reviews though. We would have to add around 25% to the listed price for import duties etc but I guess the price would still be a bit less than a new TV Powermate 

[Louis D]

3 hours ago, rockystar said:

I have no doubt that there are some on this forum with EPs of the same length in different brands and FOVs

Guilty as charged.  For instance, I have a 17mm AT AF70, a 17mm Nagler T4, and a 17mm ES-92.  The AF70 is good for outreach, and I eventually plan to sell the NT4.  Nearby, I have an 18mm HD-60.  At 14mm, I have a Pentax XL, a Baader Morpheus, and smoothie Meade 4000 UWA.  At 12mm, I have a Meade HD-60, a Nagler NT4, and an ES-92.  Nearby, I have generic Kellner as well at 12.5mm.  At 9mm, I have another generic Kellner, another HD-60, and a Vixen LV.  I have several more focal lengths with merely duplicates.  Many of these were bought used at great prices to investigate how they compare against older or newer offerings.

Interestingly, I don't have a 3mm, 4mm, 5mm, 6mm, 8mm, 11mm, 15mm, 16mm, or a 21mm.  I do have 3.5mm, 4.5mm, 5.2mm, and 6.5mm.  I also have a Speers-Waler 5-8mm zoom to cover some of those as well.  I guess I need to go shopping again until I have all gaps flled in.   I keep telling myself I'll sell some, but I'm so busy I never get around to it.

I just hope our clouds clear up soon.  This Texas winter has been unusual with two snow storms, freezing sleet, and lots of drizzle.  January is typically our driest month, so I'm holding out hope for improvement.

The important thing is not to judge how others spend their time and money.  Just pick their brains for information about their experiences with different equipment instead.

[25585]

Pairs (think bino viewers) & spares (of rare eps) should not count!

I have different AFOV eps of the same focal length. A 2 inch 20mm 80 deg, & Vixen LV 1.25 50 deg. Ditto for 32mm in both barrel sizes (Erfle & Plossl). 

Cheaper versions are OK for longer fl scopes, also less worrying about loss or damage away from home. 

All the above are practical reasons..

[russp]

On 05/01/2018 at 21:32, Alan White said:

The exit pupil at under 1mm on the 8.8 may also show floaters within your observing eye, depends upon your eye health and age.

 

I know very little about eyepieces - I have a few mostly Meade HD5000 which I'm led to believe are ok but I rarely do visual .. but when I do I find the 4.5mm unusable due to what looks like lots of little short thin translucent white strands in it - are these floaters .. is it my eyes and not a dodgy lens?  9mm and 18mm of the same brand and model are great. 

 

[laowhoo]

On 1/7/2018 at 09:30, John said:

I've not seen much Siebert stuff over on this side of the pond. It does seem to get great reviews though. We would have to add around 25% to the listed price for import duties etc but I guess the price would still be a bit less than a new TV Powermate 

That, and resist the urge to lop off a bit of bottom if you refract (which would not ruin their looks). But of their performance impact on decent EPs, rest assured that's maintained, at least for our 1.5x (not much of a feat I suppose). Best we use here is the 11mm Nagler6 and it loves this Barlow, and absolutely no vignetting w/ our ES 24mm 68*. (Did I already mention that?)

[Louis D]

17 hours ago, russp said:

I know very little about eyepieces - I have a few mostly Meade HD5000 which I'm led to believe are ok but I rarely do visual .. but when I do I find the 4.5mm unusable due to what looks like lots of little short thin translucent white strands in it - are these floaters .. is it my eyes and not a dodgy lens?  9mm and 18mm of the same brand and model are great. 

 

I have the whole set, and the 4.5mm appears to be very well corrected with just the slightest bit of astigmatism at the edge.  With no knowledge of the focal ratio of your scope, I can only guess about your exit pupil.  I see no floaters at f/6 with the 4.5mm, but certainly do at f/12.

The 9mm is just about perfect across the entire field.  I'm surprised you like the 18mm.  It is abysmal from 50% out with strong astigmatism and some field curvature.  The center is decent, but so is a Plossl, and it costs a lot less.

[russp]

8 hours ago, Louis D said:

I have the whole set, and the 4.5mm appears to be very well corrected with just the slightest bit of astigmatism at the edge.  With no knowledge of the focal ratio of your scope, I can only guess about your exit pupil.  I see no floaters at f/6 with the 4.5mm, but certainly do at f/12.

The 9mm is just about perfect across the entire field.  I'm surprised you like the 18mm.  It is abysmal from 50% out with strong astigmatism and some field curvature.  The center is decent, but so is a Plossl, and it costs a lot less.

It's f7.5 (127mm refractor) - Like I said I've hardly used them - mostly for the moon and planets so the 18mm would have hardly had any use at all and I'm happy to admit I doubt I'd know a bad eyepiece as opposed to a good one if it jumped out of the scope and thumped me!.  Have just been very disappointed swapping from 9 to 4.5 .. the image produced has never ever been an improvement. Pretty much given up with visual observing (preferring imaging) , should probably give it another go.  

[Louis D]

4 hours ago, russp said:

It's f7.5 (127mm refractor) - Like I said I've hardly used them - mostly for the moon and planets so the 18mm would have hardly had any use at all and I'm happy to admit I doubt I'd know a bad eyepiece as opposed to a good one if it jumped out of the scope and thumped me!.  Have just been very disappointed swapping from 9 to 4.5 .. the image produced has never ever been an improvement. Pretty much given up with visual observing (preferring imaging) , should probably give it another go.  

Try the 4.5mm on a large, bright globular cluster like M13 or M15.  It just might start to resolve the core in your telescope whereas it will still be a fuzz patch in the 9mm.

[Saganite]

On 1/7/2018 at 16:49, 25585 said:

Pairs (think bino viewers) & spares (of rare eps) should not count!

I have different AFOV eps of the same focal length. A 2 inch 20mm 80 deg, & Vixen LV 1.25 50 deg. Ditto for 32mm in both barrel sizes (Erfle & Plossl). 

Cheaper versions are OK for longer fl scopes, also less worrying about loss or damage away from home. 

All the above are practical reasons..

That makes me feel better !

My binoviewers have 1.4x and 2.5x OCS and so 4 pairs is all I need across 3 scopes with f5.3, f9, and f15 focal ratios ( the latter scope shortened thanks to Dave -f15 Rules so they all work at native as well), which, with a handful of Orthoscopics , Konigs, and just plain favourites for cyclops observing, the total is less than 20. 

The problem is I enjoy trying different eyepieces. 

[tuckstar]

So this my ideal for my 10" dob f4.7

All explore scientific 100° with the exception of the 30mm which would be 82°. Don't have a 3" focuser, nor the budget for the 30mm 100°.

Shouldn't need anything else after that, except a paracor at some point.

Just the 5.5 and 30 to acquire yet.

 

[John]

That looks a good selection for the 10" dob. Personally I'd want a couple more high power options because it's at high power that you seem to need to have more options to find the "goldilocks" one for the target / prevailing conditions. I'd be looking to add something around 250x-260x and something around 170x as well. Sorry !

You could try the set you have mapped out and see if you feel that any additions / revisions are required - thats the best way !

 

[tuckstar]

17 minutes ago, John said:

I'd be looking to add something around 250x-260x and something around 170x as well. Sorry !

Don't be sorry John. I do also have 25mm, 16mm, 10mm, 6mm and 4mm claves to fall back on. But I tend to keep these for my telementor rather than the dob.

[25585]

2 hours ago, Saganite said:

That makes me feel better !

My binoviewers have 1.4x and 2.5x OCS and so 4 pairs is all I need across 3 scopes with f5.3, f9, and f15 focal ratios ( the latter scope shortened thanks to Dave -f15 Rules so they all work at native as well), which, with a handful of Orthoscopics , Konigs, and just plain favourites for cyclops observing, the total is less than 20. 

The problem is I enjoy trying different eyepieces. 

I enjoy trying as well, too much! Also I am on a nostalgia trip, wanting to recapture my first scope viewing, so have bought and am looking for 80s, 90s eps. Still have old scopes (but one) and bins, sadly the Internet has run dry of older Erfle's. 

Guess a zoom is a duplication, but less FOV than prime at most of the FLs it covers.

 

[Louis D]

On 1/7/2018 at 03:23, 25585 said:

So disregarding price, physical size and weight, what of all makes and designs of EPs and ordinary Barlows, is the supreme combination giving effective longer eye relief (at least 22mm) to an effective short focal length (13mm max), but still having a large AFOV (over 70 deg), an optical combination that would surpass any manufactured prime EP?

The problem I've found with ordinary barlowing long focal length wide fields is edge of field cut-off.  It's not vignetting.  It looks like there is literally a new, hard edged field stop inboard of the normal field stop.  I get this with both my 30mm ES-82 and 40mm Meade 5000 SWA.  Eye relief might get longer, but it was already fairly long.  With a telecentric magnifier, this cut-off effect goes away.