Louis D

I generally back off on power with Jupiter to around a 1.5mm to 2mm exit pupil due to its low contrast features.  At smaller exit pupils, they just sort of mush together most nights.  Saturn's rings and moons, on the other hand, can take much more power due to their higher contrast.  The moon is another good target for using tiny exit pupils.

It's up to you and your wallet.  The BSTs aren't that expensive, and you're not eating out as much as you used to, so treat yourself to a 3.2mm for fun's sake.

I have a 90s vintage Lumicon OIII that thankfully hasn't rusted (knock on wood) that does a fantastic job.  I've read that the problem with Lumicon is that they have had at least 5 different sources for their filters over the decades (and changed ownership recently), so it can be hit or miss on the used market as to what you will get.  It's a case of try before you buy used if possible.

I use my Lumicon UHC filter (also 90s vintage) as more of a light pollution filter in my Bortle 5/6 skies.  It helps increase contrast a bit, but no where near what the OIII does.

I also have a Zhummel OIII that is pretty pathetic.  It's not even as good as the UHC.  However, I only paid $14 for it on clearance.  Don't skimp on OIII filters.  The cheap ones don't really work at all.

Meh, I've seen plenty of astrophotos on APOD that are much more aesthetically pleasing.  I think having an eye for an appropriate foreground here on Earth really helps to connect the cosmos to our home world better than creating a faux-macro image.  I do appreciate the novel technical approach taken to capture the image; though I'm not sure it's usable more than once or twice before people would tire of the effect.

I've found that if I always wear eyeglasses, my eyepieces never fog unless I have a face covering redirecting my breath up my face.  The eyeglass lenses act as a moisture barrier.

2" is only relevant at low powers and for heavy eyepieces.  There are plenty of 1.25" 8-10mm eyepieces out there with large eye lenses and loads of eye relief.  The 8mm BST is quite good as mentioned above, but a bit tight on usable eye relief compared to some more premium offerings.  The 9mm Morpheus is excellent as is the 10mm Delos.  It all depends on your budget which you didn't specify.

14 hours ago, Charlie 2436 said:

Hi guys. I don’t want to disappoint you I’m new to this and I don’t think I would know EOFB if it walked up and kicked me on  my shin bone 😳 hopefully I am wrong.

You probably wouldn't notice it if you didn't go looking for it or didn't do an eyepiece swap with another eyepiece that didn't have it.  It just looks like a fog covering the outer field decreasing contrast.

14 hours ago, Charlie 2436 said:

Has anyone had any experience with the Altair Lightwave flat field Tele Extender Barlows 

It appears to be very similar to the discontinued Meade Series 5000 TeleXtender 2x Barlow Lens (1.25").  10 years ago, there was this thread here on SGL about it.  I would google the Meade for other reviews and discussions of it.

Altair:

Meade:

4 hours ago, Merlin66 said:

Dexter,

Sorry mate, I disagree.

There are many products today which are much better than those produced in the past.

We have good quality product available today which we could only dream of when I started back in the 1960’s

True, but the mechanical perfection of mid-century, US made Questar Maks puts today's Chinese made Maks to shame.  Of course, the price differential is enormous.

It doesn't really matter because the glass in them is generally small enough that temperature differentials don't cause stresses in the glass that would distort the image.  The reason people put dew heater strips on them is to prevent them from dewing up when they cool below the dew point.

22 minutes ago, Don Pensack said:

The "poster child" for EOFB is the 13mm Olivon 70° eyepiece (sold as many other labels, including the older Celestron Ultima LX).  If you don't notice it in that eyepiece, you need a "seeing-eye" dog.

I do have the 13mm AF70 (should be same optically as Olivon 70°), so I'll have to dust it off and go looking for EOFB sometime.  It also has pronounced edge of field chromatic aberration starting at 70% out from center.  If you like rainbows, this is the eyepiece for you.

Definitely would like to hear your impressions of the APM 12.5mm.  I've got the 12mm Nagler T4 and ES-92 and have thought about picking up the APM sometime to replace the NT4 for 1.25" usage.  Eye relief is a bit tight on the NT4 and the exit pupil is a bit on the finicky side once the field stop pops into view.  I also noticed EOFB (Edge of Field Brightening) extending all the way to center once in the 12mm NT4.  I swapped it for the 17mm NT4 which had about 50% of the amount of EFOB and practically none for the two ES-92s under the same conditions.  It looked like someone had placed a graduated vignette filter over the image, only in reverse such that the image got gradually brighter center to edge.  I haven't seen it since, but it was startling and completely repeatable during eyepiece swaps that night.

1 hour ago, AstroMuni said:

I would extend that to the night as well, as there is always stray light if used in urban areas.

Of course, but there's no risk of a child going blind at night from stray light as there is during solar viewing.  That's all I was emphasizing.  Truss Newts have their own special safety issues for solar viewing absent in solid tube Newts.

That's a tough one because I prefer affordable mid-length Barlows like the TV 2x and Meade 140 (both 90s vintage) that won't come to focus in many refractors.  I recently picked up a 3 element Japanese made shorty Barlow (Celestron Ultima, Parks Gold, etc), but I haven't had any time to try it out yet.  You could get a used Meade 140 for $50 or less and screw the optics section onto the front of a 1.25" diagonal for about 3x.  I use it at a similar power on my binoviewers to reach focus, and the images are incredibly sharp.

There are plenty of quality shorty barlows, but they aren't cheap.  Start with this list to see what I mean:

1.6x 1.25" Nikon EIC Barlow

3.0x 1.25" Televue Barlow

2.4x 2.0" Vernonscope Dakin Barlow

2.0x 2.0" AP BARCON (BARADV) Barlow

2.5x 2.0" Siebert Telecentric

2.0x 1.25" Carl Zeiss Abbe Barlow

2.0x 1.25" & 2" Baader VIP Barlow

2.25x Baader Hyperion Zoom Barlow

18 hours ago, Dippy said:

Baader optical wonder solution is practically Isopropyl alcohol. Instead of £12 for a 70mL of it, buy a 1000 mL of Isopropyl alcohol for £22 (before pandemic it was only £5). They have also smaller bottles which will be cheaper of course. The Baader solution and Isopropyl alcohol don’t remove the toughest of fungi on optics, only a few of the less deep set ones can be treated with them. 

According to Baader Wonder Fluid's MSDS, it's 25% Ethanol and 35% Propan-1-ol.  The latter is an isomer of propan-2-ol (isopropyl alcohol), so not quite the same thing as pure isopropyl alcohol.

On 08/09/2020 at 04:39, Pryce said:

Not looking to hijjack the post, but why do you say that? I just sat here looking at the sun with my newtonian.  Can be just as exciting as looking at the moon or planets! 

With a Heritage truss type Newt, you'd have to make sure they're using a well fitted shroud around the truss poles to keep stray light out of the light path for daytime usage.  This is especially true if you're going to do solar observing with a full aperture solar filter.  What good is a filter if the sun can come in from an angle via the open tube?

Glad to hear you got it sorted enough to resume observing.  You may want to fill in the undercuts with pinstriping tape to make it easier to get good alignment when swapping eyepiece pairs in the dark.

2 minutes ago, Charlie 2436 said:

One last thing do you think it would be worth getting a 3mm giving 300x on a good night or would it just be a waste and never get used. Or should I just barlow the 9mm or 6.5mm.

If you use a very high quality Barlow, the combination would probably work very well.  You do end up with a long lever arm sticking out of the diagonal which can complicate balance at high altitudes.

1 hour ago, johninderby said:

If the aperture remains the same it is the focal length that affects the amount of CA. If you change the aperture then that does effect the amount of CA as well.

Further reading on the subject.

http://www.maa.clell.de/Scholar/chromatic_aberration.html

But your original post on the subject simply stated that "false colur becomes more of a problem the shorter the focal length" without reference to holding the aperture constant.  This made it sound like any shorter focal length scope will have higher CA than any longer focal length scope as is the case for field curvature (shorter always has more FC for a simple doublet design regardless of aperture).  More accurately, the shorter the focal ratio (or commensurately, focal length) for a given aperture increases the amount of CA.

1 hour ago, Don Pensack said:

Magnification-wise, though, the 12.5mm Morpheus is closer to the in-between magnification from the 9 and 17.5, so I'd go 12.5mm Morpheus instead of 14mm.

Agreed.  My 14mm Morpheus gets little use because it is just too close to both the 17mm and 12mm ES-92s I use.  I then jump to either my 10mm Delos or 9mm Morpheus.  I kind of want to get an 8mm Delos to bridge to the 7mm Pentax XW I have.

1 hour ago, Neil H said:

John what CA ?

1 hour ago, johninderby said:

CA (chromatic aberation) or false colur becomes more of a problem the shorter the focal length with a achromat which is more important for lunar / planetary observing as you will be using higher magnifications.  Not such a problem with DSOs at lower magnification.

CA (chromatic aberration) is a function of aperture and focal ratio.  Focal length alone won't give you any indication of a scope's CA.  The following table shows how CA behaves as a function of aperture and focal ratio:

You can cross reference individual telescope's specs with this table to get a feel for how good or bad the CA will be for it.  Additionally, moving to FPL-51 or FPL-53 doublets or even triplets allows the green and yellow areas to slide to the left.

Field curvature is strictly dependent on focal length.  It's roughly FL/3.

@Don PensackHow does the APM 12.5mm compare to the Apollo 11mm?

1 hour ago, paul mc c said:

Its labeled Astro-tech,but they look identical,thank you, M4 is the width isn't that right ?,would you know what length i need.

M4 is the width and thread pitch combined (technically, M4-0.70).  Length?  Probably no more than 5mm assuming thin wall tubing for the refractor.  Just measure the thickness of the scope's tubing and the depth of the threads in the focuser (thickness of the focuser flange) and add them together.  It's probably okay to go a few millimeters beyond that.  You just don't want long screw tips protruding into the light path.  I'd also get stainless steel screws to avoid corrosion issues.

The 22mm Nagler is nice.  I was able to find one second hand for about $270, IIRC.  It has a ding on the outer housing, but the optics and insertion barrel are fine.  I find I do have to touch my glasses to the top of the eyepiece and push in slightly to see the entire field (the eye lens is only 30mm in diameter compared to 36mm/37mm for the Morpheus).  However, it does not have the finicky exit pupil of its 17mm and 12mm stablemates, so it is usable to the field stop.  It feels about like 16mm of usable eye relief compared to the Morpheus's 18mm or more of usable eye relief.  The ES-92s are right in between at about 17mm of usable eye relief with their 43mm eye lenses.  If you don't push in, you can easily see 70 degrees as with the AT AF70 (both have 30mm eye lenses).

Probably would make for an interesting discussion in the lounge as to why Bresser and TS-Optics don't market their wares more in the US.

If it's a GSO focuser, they're M4 sized.

26 minutes ago, johninderby said:

Bresser had two lines of refractors. The ones with a basic focuser with plastic wheels and the better line with the all metal CNC R&P focusers. My focuser is totaly stock with the dual speed option.

 

Excellent.  Unfortunately, neither made it to this side of the pond. 🙄