FOV going wider ?

[Davekyn (David)]

Hi folks,
I can't believe how big the Carina Nebula is. Still a newbie I guess, but WOW. With my 12" Dob and the large collection of GSO EPs, I still can't get fit the whole thing in view. Acording to the fov overlay in my star atlas, it's like 3.5 degrees to just squeeze it in!

When I do the sums...I can't find any more EPs that Andrews Sell...as the largest 50 GSO - Sv (ap 68 degrees) =
12"Dob Fl- 1500/ep (50mm) MAG = 30X
APfov/mag = 2.26
2.26...still not enough. Other than turn to my ED80 to throw a shorter FL (560mm) into the equation to get a fov of a massive 6 degrees (is that right! OMG...awsome if that's true?)...what do you guys sugest.

I was looking at focal reducers for the 1st time. 0.5 both in the 1.25" & 2" version, however note that the only the 1.25" has an extension tube sold seperately? Do I need one for the 2" if I get that one as well.

How do the focal reduces work and what's the formula for working things out there? Do they effect quality for vissual?

Obtaining a 2"UHC filter for a budget price seems impossible. The cheap Bintel I use mainly on my 1.25" 25mm SV (ap68) works really well!!!

Seeing as I may need to aquire a larger 2" EP to obtain a larger FOV for my DOB...I've been strugling to find such a cheap 2" filter.

Perhaps as a newbie, my train of thought is all wrong...which is why I've tried to explain how I've been pondering on all this.

Other reasons, I'd like to get wider views in my EP, is for my new found passion of sketching.
Thanks for any help you can offer.
Cheers.

[gmbfilter (Geoff)]

In a similar situation I purchased a 32mm Panoptic
Almost the only the only eyepiece I use
Carina in the big dob is breathtaking
The same in the 80. Everything's upside down

[Davekyn (David)]

I'm getting to a stage that I have more than enough "budget gear" and used it all enough, to get a good idea of whats what...I would not mind buying quality gear, if only to view a specific target, now that I am spending more time on each. Apart from having an idea, I don't mind if anyone wants to waffle on the subject of FOV.

The view was really great out of town through my Dob, that my ED2 12mm X125/0.44" still gave some really good views...still though...will be seeking a widest angle EP as possible for this target.

[gb_astro]

David, after you have done all the maths, for 3.5 degrees you will find you are not going to do much better than those 15X70s.

gb.

[omnivorr]

Hi Dave, if you wanna keep it in the GSO cheap'n'cheerful family just yet.. try their 0.5x reducer...1.25" $29, 2" $69

[Glenn Dawes]

Hi Dave,

The exit pupil diameter should also be taken into account. This is the diameter of the beam of light leaving the e.p. Even well dark adapted eyes will not dilate more than 7mm (if you're young) maybe 5mm for the not so young.

To calculate this, take the focal length of the e.p. and divide by the f ratio. Say a 32mm at f/5 is already at 6.4mm! The same setup with a 0.5X reducer blows you out to 12.8mm. Assuming the e.p. can handle the exit pupil, you will not see eta car without having to move your head around.

Also a dob with 0.5x reducer is likely to give you bad images - I hate poor edge of fields, especially when in this case the crap stars might extend half way to the centre of the field! I don't know whether a Paracor might help? Would anyone like to comment?

I used to have a 6" f/6 rich field scope, which showed most of eta (with poor star images on the edge). This delivered some of the best visuals of eta I've seen to this day.

My advise is go for big binocs - I have a pair of 15x80s with a field of 3 degrees - fantastic!

Glenn

[mental4astro (Alexander)]

Hi David,

I've been looking at getting wide FOV EPs, and I've seen the GSO's as the cheapest, but how do they perform? Are their edges sharp.

I'm gearing up for a 17.5".

I'd like to get to some star parties to tyre-kick EPs, but so far that's been impossible.

Mental

[Davekyn (David)]

Hi guys...just taking a quick break from observing the Blue Planetary...found it...Thanks for the additional info...just what I wanted...all good points.
I'll probably go a 0.5 reducer glen, but fully agree with what you say and won't expect too much...but for the benefit of Alexander I must say...for the price, I find the GSO range quite good. I must say though, that is all I am using...I have not heard of a 17.5...I have a 1.25" 20mm Super View (68degrees) and I do believe it is sharp to the edges, however as you go wider...like glenn was saying...its does start to degrade, but then again, I think what your looking at makes or breaks the situation. Other than getting a reducer to simply see what happens...I am going to do like panaramics sketches and studdy my targets moving about like that, whilst looking into other avenues later...More Binos are definately on the cards with lower mag and higher app...

As I begin to want to know more about each star...The quality of image is starting to become more important...when the time is right though...I think my next move will be to get a 2" UHC as the GSO 42mm SV is pretty good for the price, and despite maybe not razor sharp to the edge, it does give a bright image and I would be lost without it.

At 40 my pupils are most likely 5mm in the dark...if I am lucky...That info means a lot glenn......THANKS...when I start spending hundreds on one EP alone...I guess I better start thinking along those lines...as well as it impacting me with what I have now...I'll bear that in mind as I do my obs...going back to my sketches now...thanks again

Later guys.

[Glenn Dawes]

Originally Posted by mental4astro

Hi David,

I've been looking at getting wide FOV EPs, and I've seen the GSO's as the cheapest, but how do they perform? Are their edges sharp.

I'm gearing up for a 17.5".

I'd like to get to some star parties to tyre-kick EPs, but so far that's been impossible.

Mental

Hi Mental,

As you might gather I'm fairly fussy when it comes to e.p. performance. I was once given 2 GSOs for free, a 15mm and 25mm (I think). Let's just say .. I got my money's worth!

wrt wide fov e.p., I haven't looked through many, but I do love my 16mm Meade series 5000. I think it cost me at the time about $250. Also, of course the 9mm Nagler ($400?). These 2 e.p. are my workhorses for deep sky in my 16 LB. I know it is said that realistically 300x is about the max for large dobs, I must admit, even at only 200x mag with the 9mm, I find I am fighting the seeing a lot.

Regards

Glenn

[ngcles]

Hi All,

Originally Posted by Glenn Dawes

Hi Dave,

The exit pupil diameter should also be taken into account. This is the diameter of the beam of light leaving the e.p. Even well dark adapted eyes will not dilate more than 7mm (if you're young) maybe 5mm for the not so young.

To calculate this, take the focal length of the e.p. and divide by the f ratio. Say a 32mm at f/5 is already at 6.4mm! The same setup with a 0.5X reducer blows you out to 12.8mm. Assuming the e.p. can handle the exit pupil, you will not see eta car without having to move your head around.

Also a dob with 0.5x reducer is likely to give you bad images - I hate poor edge of fields, especially when in this case the crap stars might extend half way to the centre of the field! I don't know whether a Paracor might help? Would anyone like to comment?

I used to have a 6" f/6 rich field scope, which showed most of eta (with poor star images on the edge). This delivered some of the best visuals of eta I've seen to this day.

My advise is go for big binocs - I have a pair of 15x80s with a field of 3 degrees - fantastic!

Glenn

Well said that man!

But a paracorr won't help -- it will reduce the true FOV because it acts as a mild barlow of x1.15.

The focal reducer used visually will introduce stunning amounts of aberrations into the image which will defeat the purpose of the exercise-- don't go there -- they are designed for imaging!

As for exit pupil as Glenn has said, 6mm should be a practical upper working limit -- which means you want an eyepiece that gives x50 in the 12" GSO which has a fl of 1500 = a 30mm ep. If you go longer in fl than this, there is a strong probability that your iris within your own eyeball will vignette the beam coming out of the eyepiece before it hits your retina = light lost. It's like cutting down the aperture of your 'scope. You may as well place an aperture-stop over the top end of the tube and mask out the outer few inches of the mirror -- it will have the same nett effect.

There are quite a few "economy versions" of wide-field 30mm eyepieces with about 80 deg apparent FOV which will give you a bigger True FOV -- a true field of about 1.6 degrees diameter is the result with 300fl ep in a 12" f/5 GSO.

The premium quality versions (several brands) do the same job but with pin-point star images edge-to-edge right across the fov and higher contrast. The more economical versions generally introduce quite a bit of astigmatism in the outer 1/3 to 1/2 of the FOV and a brighter background. The premium quality wide-field eps are expensive for a reason -- you're not just paying for a name ...

Weigh your choices accordingly ...


Best,

Les D

[JD2439975 (Justin)]

Hi David

As a pretty green newbie I wouldn't put too much weight on what I say but I have a little viewing time through a 42mm GSO SV (65-68 deg ApF) & a 28mm William optics UWA (82 deg ApF).

Not having viewed through a Nagler or Meade UWA (wish I had) I can't give a true comparison between the higher end 82 deg EP's.

The 42mm GSO is brighter but suffers at the edge of field as expected of a budget EP, but for the money not a bad eyepiece.

The 28mm WO is sharp across the field but does seem to have a greenish tinge on fainter objects, the 9mm SWA version is the same though bright objects don't show any green tinge.
Jupiter the other evening was stunning, banding, sharp edged and the shadow of one of the moons on the surface gave me a real buzz.

Price-wise I guess it's more a mid range EP than high end.
28mm WO UWA approx $550
30mm Meade UWA approx $750
26mm Nagler appox $850

As I said before my inexperienced eye can't say 'go out & buy one' but I'd love to hear from someone who has had the pleasure of all these EP's.

As for your wanting a wider FOV...use the ED80.

JD

[Astrolabe]

Originally Posted by Davekyn

Hi folks,
I can't believe how big the Carina Nebula is. Still a newbie I guess, but WOW. With my 12" Dob and the large collection of GSO EPs, I still can't get fit the whole thing in view. Acording to the fov overlay in my star atlas, it's like 3.5 degrees to just squeeze it in!

When I do the sums...I can't find any more EPs that Andrews Sell...as the largest 50 GSO - Sv (ap 68 degrees) =
12"Dob Fl- 1500/ep (50mm) MAG = 30X
APfov/mag = 2.26
2.26...still not enough. Other than turn to my ED80 to throw a shorter FL (560mm) into the equation to get a fov of a massive 6 degrees (is that right! OMG...awsome if that's true?)...what do you guys sugest.

I was looking at focal reducers for the 1st time. 0.5 both in the 1.25" & 2" version, however note that the only the 1.25" has an extension tube sold seperately? Do I need one for the 2" if I get that one as well.

How do the focal reduces work and what's the formula for working things out there? Do they effect quality for vissual?

Obtaining a 2"UHC filter for a budget price seems impossible. The cheap Bintel I use mainly on my 1.25" 25mm SV (ap68) works really well!!!

Seeing as I may need to aquire a larger 2" EP to obtain a larger FOV for my DOB...I've been strugling to find such a cheap 2" filter.

Perhaps as a newbie, my train of thought is all wrong...which is why I've tried to explain how I've been pondering on all this.

Other reasons, I'd like to get wider views in my EP, is for my new found passion of sketching.
Thanks for any help you can offer.
Cheers.

Hi David

My experiences are as follows:

1. I cannot get the full Eta Carina in either the 10" F5 Dob or 12" F5 Dob, even when I use a 35mm Panoptic. The true field of view is not large enough.
2. I can get the whole of Carina in any of my 105mm F7 refractor, 120mm F5 refractor, 6" F5 Dob, ST80 F5 refractor or my ex ED80. The best views are with a 35mm or 27mm Panoptics combined with a 2" UHC filter. The larger objectives obviouly give more enjoyable views.
3. I also enjoy the wide views though a mounted 15X70 binoculars, especially from a semi dark or dark site.

(EDIT) I also use the GSO 30mm 2" eyepiece instead of the 27 or 35 Panoptic. The TFOV is not the same but close to Panoptics. The optical quality of GSO is quite good.
If you decide to use a short focal length scope then a 32mm or 25mm Plossl will give you wide enough FOV to fit Carina in. You can also get a GSO 1.25" UHC filter quite cheaply these days

I hope that this helps.

George (astrolabe)

[ngcles]

Hi All,

Originally Posted by JD2439975

Hi David



Not having viewed through a Nagler or Meade UWA (wish I had) I can't give a true comparison between the higher end 82 deg EP's.

The 42mm GSO is brighter but suffers at the edge of field as expected of a budget EP, but for the money not a bad eyepiece.

The 28mm WO is sharp across the field but does seem to have a greenish tinge on fainter objects, the 9mm SWA version is the same though bright objects don't show any green tinge.
Jupiter the other evening was stunning, banding, sharp edged and the shadow of one of the moons on the surface gave me a real buzz.

Price-wise I guess it's more a mid range EP than high end.
28mm WO UWA approx $550
30mm Meade UWA approx $750
26mm Nagler appox $850

Re the UWAN -- I have had the chance to compare the 28mm UWAN with the 26mm T5 side-by-side and am happy to report the UWAN is a superb eyepiece. There is a small difference in fl between to two but as to fit, finish, optical quality and the view, I thought the UWAN every bit as good as the big Nagler.

If the UWAN had been available at the time I purchased the 26mm T5, I'd have bought it over the T5 because it is somewhat cheaper but the same in quality to my eye, but also because it offered a slightly wider true field (due to the longer fl) in my 'scope while still producing an exit pupil under 6mm (5.75mm at x79).

Haven't tried the Meade series 5000 28mm so can't comment on them personally. The reports on them are quite mixed. Some people prefer them to the older Series 4000, but a majority seem to prefer the older design (I emphasise that can't comment personally). Most seem to think the 5000s inferior to the "more premium" brands. I thought the old 14mm series 4000 UWA (discontinued several years ago) was an excellent ep - only available 2nd hand now.


Best,

Les D

[JD2439975 (Justin)]

Thanks for that info Les, nice to know I got value for money.

JD