Louis D

8 hours ago, Don Pensack said:

One thing about zooms that keeps me from being attracted to them, other than the narrow AFOV issue, is that I really don't need the in-between magnifications.

If I have an eyepiece that yields 150x, and another that yields 185x, when I change from the 150x to the 185x, that is just fine.  The change in field size, magnification, and brightness is about the minimum I need when changing from one eyepiece to the other.

I can even put up with 150x to 200x without constantly feeling like I need a magnification in between.  For me, zooms have too many possible magnifications.

I could probably live with a quality 2" turret with a 40mm SWA, 12mm to 17mm main eyepiece (ES-92 maybe?), 8mm to 11mm mid-high power eyepiece (10mm Delos or 9mm Morpheus?), and a 4mm to 7mm high power eyepiece (5.2mm Pentax XL?).  The problem with turrets is that they are incompatible with Newts.

I haven't tried 2" eyepieces all that much in my recently acquired JOC (ES/Bresser) 127mm Mak, but my Synta (Orion/Celestron) 127mm Mak just vignettes somewhat all the way to a 46mm field stop.  It's hard to perceive visually.  There is not hard cutoff point.

Here's my well work comparison image in the Synta 127mm Mak:

As you can see, there is light falloff in the 40mm SWA which has a 46mm field stop.  I think I measured it to be about 35% falloff, IIRC.

I was digging through my archive of minus violet filter experimentation images when I came across these unpublished ones taken on a 4000K LED backlight:

The contenders:

The two deeper yellows stacked on top of the 2" Urban Sky (M&SG) along with the the lightest yellow (Meade #8) stacked on the 1.25" M&SG:

The Meade + M&SG does a pretty good job of not introducing any color cast like the BSAPO.  For achromats with modest violet fringing, it's a good, cheap alternative to the BSAPO.

The other yellows are just too strong to compensate for.

Here's the same 2" M&SG with the two lightest yellows stacked on it.  To the right is a cheap Chinese yellow stacked with the 1.25" M&SG:

Once again, anything denser than the Meade #8 can't have it's yellow cast compensated out.

Here, I substituted a Tiffen CC50B Blue (Violet) filter for the M&SB, but kept the same two yellow filters stacked on it:

It produces very similar results to the M&SG filter (if a bit ruddier and less yellow-green), but in a totally different manner (various dyes versus Didymium/Neodymium glass).  The CC50B is a rare filter (I've never seen another), but it's interesting to experiment with.  It and the M&SG act as minus yellow filters while the yellow filters act as minus violet filters.

16 hours ago, Gemineyes said:

Basically, the SV CA filter I developed has a roll on around 450nm and cuts around 690-700nm - I use a UV/IR cut with it on my bigger Achromats to drop the red fringe to almost nil. In the middle, it has a partial reduction (between ~520-580nm) in the ~25%T regime. It is a shallow camel hump in this range sort of. So basically, it passes 80-85% of the overall light (integrated across visual) acting like a 22%T neutral density filter, but color balance is retained. It apparently is VERY hard to do and so far my attempts at getting someone to replicate it has been harder than I thought...

You might have to resort to a light dye to get the mid-frequency attenuation you want.  I've got a Tiffen CC50B filter that appears violet to the eye that might be close to what you need.  It actually looks quite similar to a M&SG filter to the eye, but gets there in a totally different manner spectra-wise.  When paired with a light yellow filter, either gets you back to a muddy gray.  The CC50B cuts green and yellow the most, red a bit, and blue/violet very little.

In my experience, the closer the clear aperture constriction is to the eyepiece, the more obvious and severe the vigetting or outright cutoff will be.

I did some experiments recently and am working up a report on this subject.  Suffice it to say, someone should market a 2" diagonal with a 1.25" nose piece.  That moves the constriction far enough away from the eyepiece that all but the widest TFOV eyepieces will see only modest vignetting.  I realized this after having used widest field 2" eyepieces with my 127mm Mak.

If you just put the 1.25" adapter on the 2" filter threads of the eyepiece, you will see severe vignetting and outer field cutoff in many 2" eyepieces well before you get the widest field ones.

The effect is also true of the WO 1.25" dielectric diagonal and its other-branded brethren.  I can see quite severe vignetting when using it with my 32mm Plossls, making it rather maddening to use it while trying to find faint fuzzies.  These diagonals have a stop ring with maybe a 22mm clear aperture at the bottom of the eyepiece receiver barrel.  I can conceive of no reason to have it there.  A small lip would be sufficient to prevent a long eyepiece barrel from contacting the mirror.

In the US, a lot of smaller companies switch from the consumer market to the commercial or government contracting market as they grow and become more competent because the margins are higher, the orders are larger, and the business is more steady.  Especially as regards military contracting, they don't have to worry about competing with foreign made items.

I wonder if OO will go the way of Questar.

11 hours ago, hal9550 said:

Alas its 2" so i lose some compatibility on the MAK

Having a 28.6mm field stop, the 22mm Redlines work fine in 127mm Maks (27mm rear baffle diameter) with the SCT thread adapter and a 2" SCT visual back and 2" diagonal.

Thanks for taking one for the team. 

I have a feeling I'll be needing this done in the next decade.  I've already got a detached vitreous humor causing minor issues (black specks in my vision).  Until it gets bad, I'll probably hold off getting an operation.

Keep us updated with how your recovery is coming along.

6 hours ago, hal9550 said:

There is also some decent value Dielectric 2" Mirrors on Aliexpress - curious to know, if anyone has pulled the trigger on these!

I picked up one of these off of Amazon about 6 years ago for $50.  While there's nothing wrong with the mirror or housing, the compression ring is too close to the end.  For eyepieces with undercuts, it tends to push them up at angle off the lip of the receiver tube.  As a result, I never use it.  I ended up paying $70 to $75 for used copies of GSO made 2" dielectrics.

5 hours ago, hal9550 said:

I trawled Aliexpress numerous times, and did find a 2" 45 degree Erecting Prism, which was very reasonably priced - aprox 70 euro - most places i have read recommend AGAINST these for astronomical use though

I'm looking at picking up one of these to use with my 127 Mak when in spotting scope mode, so I can get a larger, unvignetted FOV when using widest field 1.25" eyepieces or mid-focal length 2" eyepieces like my 20mm Founder Optics Marvel 80°.  Despite being a 2" diagonal, it only has 31mm of clear aperture.  However, this is a major improvement over the 1.25" 45 degree Amici diagonals that have only 17mm of clear aperture.

Check a bit over on CN Eyepieces forum for reports on these 70° eyepieces.  I've seen some feedback on them over there, but not much.  They're the same as the Oberwerk 70° eyepieces.

Let's put it this way, I haven't seen a plethora of glowing reports on them pushing me to buy one or more of them to try out like I saw for the Svbony 3-8mm zoom and Founder Optics Marvel 20mm 80°.

Agreed.  The Morpheus' AFOV looks nice and wide until I switch back to one of them from one of my ES-92s.  Then I suddenly get a bad case of claustrophobia. 😄

I guess it depends on how much stray light you have shining into the back of your tube.  I've read imagers really hate stray light making its way in from the back of the tube, ruining their images.  You've still got the problem of light coming around the edges of the mirror, though.

Here's a couple of lunar eclipse images I took with my Canon DSLR and 55-250mm lens tonight:

10 minutes before maximum:

Just a couple of minutes before maximum:

I love my GSO 6" f/5 Newtonian with GSO CC.  It does pretty much everything very well for a modest cost.  It is also not very heavy or bulky.  My DSV2B mount has no issues with it.

I don't have a 120ST, but I do have a 152mm f/5.9 achromat, and I have yet to find anything it does better than the Newtonian.  The CA and SA are just too much to overcome in the frac.  Even low power star field sweeping isn't very satisfying because the star colors are messed up and they're not pinpoint.  Add in the fact it weighs roughly double the Newt and cost 3 times as much even when bought used, and it's a no-brainer to go for the Newt.  Once set, I haven't detected any collimation shift in the Newt, either.

One post I place particular weight on for the 3.2mm is Jon Isaacs's take on the 3.2mm Paradigm (BST Starguider) here on CN.

The 3.2mm doesn't get the best reviews compared to the 5mm and 8mm.  It's the only one of that line I don't have, and I've never felt the need to get one.  I would try Barlowing first.

@Spad The best analogy I can think of is the use of a Barlow.  Have you ever used a Barlow with either an eyepiece or a camera?  Once you've focused with the eyepiece or camera alone and then inserted the Barlow, did the focus position change or was the image still in focus?  Usually, the focus position changes in my experience.  Often with a Barlow, you have to rack the focuser outward from the objective.  With a focal reducer or flattener, you often have to rack the focuser inward toward the objective.  That's what I'm thinking the 16.2mm distance is about with your flattener.

With my TSFLAT2 flattener, I have to rack my focuser inward to reach focus as compared to when it is not present.  I've never measured the actual amount, but it is on the order of 10mm to 15mm.

With my GSO coma corrector, I have to rack my focuser inward 11mm to reach focus as compared to when it is not present.

Does that help to clear things up for you?

I'm guessing that the 16.2mm of focus shift is the additional inward focus distance relative to the distance without the flattener needed to achieve proper focus.

I MacGyvered together an adapter using a macro extension tube, a short length of PVC tubing, and 6 thumbscrews.  Three screws to hold the PVC pipe to the rear of the extension tube and three to hold and center the eyepiece.  It worked reasonably well as a spotting scope.

There's generally not enough back focus to use a diagonal, so straight through is your only option short of creating a relay lens or removing the back part of the lens.

It's most likely you haven't aligned the finder scope to the main scope.  I recommend doing this during the daytime using a distant object to get them at least near each other.

2 hours ago, Ratlet said:

Most of the time we stick to fractions but for data entry it's more common to make them decimal.

Then they should be in powers of two fractions to avoid rounding errors when converting to binary.

1 hour ago, CraigT82 said:

What’s the cause of the dark centre donut in the Nirvana image? Also the LVW but there it’s more of a disc than donut. 

Generally they're caused by exit pupil aberrations such spherical aberration of the exit pupil (SAEP), also known as kidney beaning.  Obviously, both have it very mildly.  When a field of view is described as needing critical eye positioning to take in the entire field of view, it's generally due to SAEP.  It's more critical in the daytime or with bright objects that cause your eye's iris to constrict.  This can cut-off mid-field light rays.

See the following post for some animations created by @Ruud:

I've done custom length coax ethernet cables with the proper tools and supplies at work.  That was pretty easy.  Unless kits (supplies and tools) are widely available as with coax ethernet cables, I wouldn't know where to begin with your cable situation.

I checked CN Classifieds, but I didn't find any 130 f/6 Starfire EDFs.  I did find some newer Gran Turismos going for $7000 and 130 f/8 Starfire EDFs going for $5000.  So, between $5000 and $7000 in the US, I would think.

On 06/09/2024 at 03:32, TiffsAndAstro said:

Thanks Google says yes and no

 

Run it through one of them thar new fangled AI websites to see what it has to say. 😉