Louis D

When using the 3-8mm zoom last night, it dawned on me where I had heard that same mechanical sound at each detent.  It is the sound of my optometrist's phoropter as it changes lenses.  Since I consider those to be precision optical equipment, I think that's a pretty good achievement for the zoom to sound the same.  They certainly did not cheap out on the mechanical side of things.

3 hours ago, 900SL said:

Nice one Louis. I'm tempted by a used UNC 150mm f6 as an imaging scope for galaxies and lunar (will double my current focal length and give around 1"/px, or more with a barlow

I'm thinking it will be a noticable step up in resolution from my current 90mm f6, which is around 420mm fl with the reducer.

I am not familiar with that Newt, so I did a quick search and came across this thread on CN of someone using it for imaging.  It sounds decent, but the price is pretty steep for a 6" f/5 Newtonian with some issues that needed to be ironed out.  Hopefully, TS has resolved the issues the OP had in 2018.

On 23/02/2024 at 13:28, 900SL said:

How would you rate the 6" f5 Newt against your 90mm f6 CF Apo? I've been thinking of a 150/750 newt for longer fl...

Just got back in from a couple of hour comparison of the two scopea on Jupiter, Collinder 70, the moon, the Orion Nebula, and the Trapezium.

First, both make for excellent scopes.  I could see someone being quite happy with either, especially not having both to compare views.

The differences were more subtle than I expected.

Both are pretty much color free.  The atmosphere was causing a bit of red/blue fringing top to bottom on Jupiter and the moon in both.

Before it got reasonably dark when observing Jupiter, the central obstruction shadow of the Newt was really annoying.  Huge win for the unobstructed APO for daytime use.

Jupiter:

• Better image scale at the same exit pupil made it easier for me to see past my floaters at a particular magnification.  Aperture wins.
• As I increased magnification, the APO didn't really decrease much in contrast on the belts.  However, no new details were visible.  The Newtonian definitely had reducing contrast meaning lower powers were better.  Unobstructed wins.
• Perceived details seemed better on the edges of the belts in the Newt.  They appeared frayed instead of solid as in the APO, as if some detail was about to appear with a bit more aperture.  Aperture wins.

Collinder 70:

• Pretty much dead even.  The APO's stars looked a bit more pinpoint, but the Newtonian showed dimmer stars a bit better.  Tie

Moon:

• Looks great in both.  Perhaps a bit higher contrast in the APO, but a bit finer details visible in the Newt.  Tie

Orion Nebula:

• More nebula brightness, extent, details, and contrast visible at all magnifications.  APO didn't really show anything as good.  Aperture wins.

The Trapezium

• Stars were possibly a bit more pinpoint in the APO, but the Newt was no slouch.  Tie
• E component plainly visible in Newtonian, but no where to be seen in the APO.  It was not a subtle difference.  Huge win for aperture.

Overall, I preferred the larger exit pupil at a given magnification in the Newt due to my really bad floaters.  At really small exit pupils in the APO, I can even plainly see the shadow caused by my observing eye's vitreous humor detachment.  It wasn't as obvious for some reason in the Newt.  I confirmed what it was because it wasn't there in my non-observing eye which has no detachment.

Basically, the higher contrast of the APO just could not compensate for the extra aperture of the Newt.

The higher position of the focuser in the Newt was also easier to use standing instead of crouching as with the APO.  When using the APO alone, I extend the tripod legs to avoid crouching which leads to longer vibration settling times.

The APO's focuser tends to unravel with heavy eyepieces at high altitude angles unless I tighten the drag adjustment.  The Newt's focuser doesn't seem to have this issue, probably because of its angle relative to the ground.

Size wise, they're about the same length with the diagonal attached and the focuser extended to its typical position on the APO .  The Newt is obviously wider.  The Newt is also a few pounds heavier.

Ignore the laser sight on the Newt.  I forgot to take it off for the picture.

Yes, the APO is more svelte looking.  My grown son says it looks "legit".  The Newt looks kind of chunky in comparison.

As for Sir Patrick's assertion about the 3" refractor versus the 6" Newtonian as applied to modern scopes, I'd say "it depends".  Does slightly higher contrast and daytime use matter most?  Does light gathering and resolution matter most?  Size-wise, there's not a lot to distinguish between them.

5 hours ago, Don Pensack said:

eAFOV is NOT what you see.  What you see is the apparent field of view, i.e. what angle the eye has to make from side to side to see the edge with direct vision.

ALL eyepieces above about 40° AFOV have distortion, and the wider the field, the more there is.  The ES 25mm is a 100° eyepiece (measured 103°), as that is the angle you see, not 94°.

I see no purpose to even figure an eAFOV, since it doesn't relate to anything, unless you are merely using the TF = AF/M formula to compute TFOV.

And you could just as easily use TF = (FS/Tel.FL) x 57.3 to compute an accurate true field without creating a fictitious eAFOV, since the field stop diameter is known, and this formula excludes any consideration for distortion.

Meade 26MWA--44.6mm field stop, ES 25x100--40.8mm field stop.  So the 26mm MWA has a larger true field.  

The SAEP would kill it for me.  You're more patient.

You read the wrong line off of Ernest's report:

Light diameter of the field lens, mm 44.6

The field stop diameter is as follows:

Light diameter of field clearance* 1 star, mm 41.2

I measured 41.0mm for the field stop, so the same within the margin of error.  That also puts it at the same field stop within the margin of error as the 25mm ES-100.

The field lens of the Meade is larger than the effective field stop.

I suppose eFS is just as fictitious of a construct as eAFOV when you think about it.  It simply makes using the standard TFOV calculation easier than using the physical field stop diameter and accounting for the magnification distortion effect of the Smyth lens.

You're right, you see 100° in the ES and 83° in the Meade, but the same true field of view in both at the same power (at least in the center).  eAFOV is simply another way of stating the field stop for comparing TFOV.

The Meade's SAEP is not bad as I'm finding out if I view at 17mm to 18mm of eye relief and live with the resulting 79° AFOV which is very similar to most Morpheus eyepieces at 78°.  That's a loss of only 4° AFOV which I can live with.  What is the AFOV at 17mm to 18mm of eye relief with the 25mm ES-100?  Is it only 4° less than at the design usable eye relief?  If it is, I may consider buying one.

As a follow-up, I had the 26mm Meade MWA out a few nights back.  I think I've made my peace with it three years later.  For an astigmatic eyeglass wearer, it views like a 25mm Morpheus would in many respects, but with compressional distortion at the edge instead of expansional distortion.  As such, the moon gets squashed instead of stretched as it approaches the field stop.

It is surprisingly well corrected over the vast majority of the field of view, certainly the portion viewable without scanning around the field by swiveling your eye.  It provides a nice boost in power over the 30mm ES-82 while maintaining almost the same true field of view in the "Easy View" mode.  I tried to see that last few percent of the AFOV, and was thwarted once again by SAEP.  You simply can't see more than a fraction of that additional field at one time.  Other parts will go dark to see to the true field stop.

I'll try to get it out more often now to make more use of it.  The more I use it, the better I become at working around its limitations.  Of course, if ES came out with a 25mm ES-92 as good as the 12mm and 17mm versions, I'd ditch the Meade in a heartbeat. 😄

28 minutes ago, SwiMatt said:

Let's put it like this: after few long sessions (probably more than 10 sessions at this point), I find Jupiter quite boring since I can never tease out more than just the equatorial bands. I have seen possible traces of festoons and GRS, but far from conclusive certainty.

That's pretty much my experience with my 127 Mak as well.  I've only seen festoons and barges clearly starting at 8" of aperture (needs to be exceptionally well corrected and acclimated), becoming blatantly obvious by 12" of aperture in an exceptionally well corrected scope on nights of exceptional seeing.  If collimation, figure, polish, seeing conditions, etc. don't all align, fine, low contrast details will turn to mush guaranteed.  All you can do is buy or make the finest scope you can, use the best eyepieces possible, get yourself to places with the best seeing conditions, wait for opposition, make sure everything is well collimated and aligned, and then hope for the best if you want to see low contrast details on Jupiter.  When everything does align, it's hard to stop taking in the view because it's so mesmerizing to see such detail.  It's quite sublime.  Mars is the same way, except that dust storms on Mars can ruin our best laid plans here on Earth.

8 hours ago, lvan said:

Refractor > Reflector

As far as price, you got that right.  My 6" f/5.9 achromat cost 3 times what my 6" f/5 Newt cost (both used).

7 hours ago, 900SL said:

How would you rate the 6" f5 Newt against your 90mm f6 CF Apo? I've been thinking of a 150/750 newt for longer fl...

Funny you should mention that.  I'm going to try mounting them on either side of my DSV-2B mount the next chance I get and compare the views for aesthetics as well as for absolute sharpness, contrast, resolution, etc.  I'm curious if Sir Patrick was on to something.  I figure a 90mm f/6.9 FPL-53 triplet APO should be similar to an old 3" f/15 or longer achromat as far as color correction goes.  The focal length will obviously be completely different, though.  The Newt is probably faster than the Newts of old as well.

Ultimately, it comes down to what the market will bear.

I always laugh when I see ads saying "Final price reduction!" as if that makes any difference to most buyers.  Generally, it's sellers who way overprice in the first place on non-in-demand items who do this.  I especially chuckle when they're trying to sell at a higher than new current price when the same item goes on sale or the price has come down drastically since new.  I've contacted some to point this out, and they get all indignant saying they sticking to their guns asking 75% to 80% (or more) of the price they paid.

5 hours ago, Nicola Fletcher said:

Thanks @AstroKeith! The price is very close to the new price - plus I have a voucher for FLO so I don’t think I’d save anything from new. I appreciate you letting me know!

Especially when you consider you need to subtract the 20% VAT from the new price.  It's highly unlike the seller is going to collect it again, so you really need to work from the pre-tax price to establish the tax-free used price.

Just be aware that type of diagonal often has a restriction to about 23mm clear aperture:

If you do buy one, check it immediately to make sure it doesn't have a stopped down clear aperture.

I bought one used to use with a 22mm clear aperture binoviewer, so I'm okay with the aperture restriction.

5 hours ago, John said:

Maybe things were different in the UK in the 1950's though ?

I suspect Sir Patrick's advice stemmed from that era.

 

I think the choice was biased by poorly figured, coated, and aligned Newtonians of the day.  3" slow achromats of that era tended to be of very good quality in comparison.  A 6" Newt of the day would have been very long and unwieldy.

Some old Unitron cartoons along these lines:

I just checked a bunch of recent ads for these vintage black C8s on CN classifieds, and with few to no accessories, they tend to go for $400 to $500, so keep that in mind.

I've been observing with Meade Safari Pro porro-prism 8x42 bins for over 25 years and still love them.  I managed to snag a second pair off of ebay a couple of years ago as a backup pair.  I like their 65 degree field and 18mm of usable eye relief.

20 minutes ago, aleixandrus said:

I started wearing glasses two years ago (myopia, 2 diopters) and I've never done visual wearing them. As I'm not very familiar with visual observation in general, I suppose I need to try first and check if I feel comfortable.

Check your cylinder (CYL) diopter amount for your observing eye in your eyeglass prescription.  It is a measure of how much astigmatism you have in each eye.  I have around 2.0 diopters in each eye, so I need to wear eyeglasses all the way down to fairly small exit pupils to avoid seeing spiky stars and blurred fine details.

Tele Vue has this chart for their DIOPTRX™ line:

It's fairly accurate for most observers.  For instance, I can get by without correction below 1mm exit pupil.  It still improves the sharpness a little bit by putting eyeglasses back on at sub-1mm exit pupils, but not tremendously as at larger exit pupils.

1 hour ago, Naughty Neal said:

The ep has only 10mm eye relief so specs wearers will likely not get on with it.

On planets and other small objects, I find it doesn't matter much because I can still see enough of the field of view while wearing eyeglasses to see what I want to see.  On the moon, I'll agree, it doesn't work very well unless I'm just focusing in on a single feature to study.  On my undriven alt-az mount, I just tilt my head to follow objects as they drift through the FOV from edge to edge.

With my deep set eyes, I have about a 15mm gap between my eyeglass lens and my cornea.  This makes 17mm of usable eye relief about the least I can comfortably get by with.  Of the BST Starguiders, I've measured 12mm of usable eye relief for all but the 25mm, which has 17mm and is comfortable to use.

If 12mm of usable eye relief is enough for an observer wearing eyeglasses, I consider them lucky.  It opens up a huge number of eyepieces for them from Nagler T6 to Ethos with sub-17mm usable eye relief.

On 20/02/2024 at 19:16, Franklin said:

4" achro for me. Why? Because decades ago I was brainwashed by Patrick Moore into believing that a 6" reflector was about as good as a 3" refractor so obviously the 4" frac must be better. Also, I believe telescopes are devices for looking at things and looking into the side of scope at 90deg from the object I'm looking at just seems silly. Sorry Sir Isaac.

In my experience, my 6" f/5 Newtonian runs huge circles around my 80mm (3.1") f/5 refractor.  To equate them in performance in any way is a complete insult to the Newtonian.

5 hours ago, aleixandrus said:

Sorry for the late reply, busy week 😅 Wow, thank you so much for all reply and comments, I appreciate it so much. Very valuable info there. Some thoughts:

• I've never done visual except for some very-very casual observations using a very old 1000/100 eq1 manual newton and a 12" dobson from a friend, time ago. I know that the dobson is in another league, I get my 'wow' moment with Saturn using it and I do know the 90 APO will no provide anything similar.
  • Saturn's ring will wow you even in a smaller scope.  Keep in mind, they're closing down to a thin line over the next year.
• But it is fine. In addition and to be fair, I don't know any of those features of the target objects: bands, transits, divisions, etc. In the past I've just enjoy the object itself so my expectations are quite low, probably more in the "I want bigger" than "I want details". Of course I'm probably wrong thinking this way.
  • You can certainly go bigger, but aperture still limits resolution.
• Never try sun observation, it's not high on my priority list but I'll take a note on this for the future.
  • Can be quite rewarding with just a Baader Solar Film front filter.
• Based on your comments, I'll discard the Mak 90 for know, give first the APO 90 a try.
  • I found 90mm Maks dim for their aperture compared to refractors.  I do have a 127 Mak and find it quite handy for camping trips at dark sites due to its compactness.
• I don't have the scope yet so I have time to rob borrow some oculars from friends. I'll try to get something such 4-6-10mm ocular plus x2 barlow just to test magnification in the range of x90 to x180. Scope specs mention "up to x300", this may be just a marketing scam but I'll try to push the "aperture x 2" magnification limit if I find the right oculars. Here in north of Spain, close to the Ocean Atlantic, I think seeing is similar to UK (clouds and rain most of the year) so I don't probably could go that far with magnification very often. Time will tell.
  • Bummer about your weather.  I've always pictured Spain being semi-arid like parts of western Texas.  Apparently, that's mainly in the Tabernas Desert.
• That Svbony 3-8mm zoom seems quite appealing at least for casual use. The Baader Hyperion zoom is simple out of my budged for now. I'll probably need to open a thread in the future before purchase anything as I said, never did visual and I'll probably screw it up. Can't figure out yet how the take into consideration things such as 'exit pupil', 'field of view' or 'eye relief'.
  • I was actually using my Svbony 3-8mm zoom last night to speed up checking high power viewing.  It is excellent from 5mm to 8mm and very good from 3mm (really 3.5mm) to 5mm.
  • Exit pupil is simply the eyepiece focal length divided by the scope's f-ratio.  It tells you how big the exit beam of light is coming out of the eyepiece.  I was struggling at tiny exit pupils with the zoom set at 3.5mm to 4mm last night due to the wealth of dense floaters I have in my observing eye.  It made using those powers very frustrating.  At larger exit pupils, floaters don't tend to bother much at all.
  • The zoom's eye relief was tight enough that I had to tilt my head around while wearing eyeglasses to see the outer parts of the field of view.  This isn't a big deal when observing planets, but it is a distraction with the moon, though.  At the highest powers, I could remove my eyeglasses due to the tiny exit pupil negating the effect of my eye's astigmatism.
• Do I need a diagonal (or prism?) or it will simply prevent me from doing the kamasutra with my scope? The focuser as almost 150mm of travel so I should do focus without extenders. Isn't it?
  • Exactly.  Apparently, Japanese observers tend to prefer straight through viewing.  If you can recline in a beach chair, you might be able to make it work while remaining comfortable.

As I said, thank you so much for all your insights.

See inline comments in yellow.

Because of this thread, I went out tonight with my 90mm APO and looked the moon, Jupiter, Collinder 70, and the Orion Nebula.  It was basically color free compared to my 6" f/5.9 achromat, no surprise.  It showed a wealth of detail on the moon with excellent contrast.  It showed the main two bands of Jupiter quite clearly along with obvious size differences among its moons.  However, I could not discern any detail in the main bands.  Collinder 70 was rendered beautifully and in context at low power with pinpoint stars.  The Orion Nebula looked great from low power right up to the highest powers.  The Trapezium was always obvious as multi-member.  However, I could not get even a hint of the E and F components tonight.  I loved how light and compact it is compared to my 6" achro.  It makes for a terrific grab and go scope.

I forgot to mention that the 90mm APO shows exceptionally nice solar images with an affordable 1.25" Herschel wedge.

I've extensively compared my 6" f/5 Newt to my 6" f/5.9 achromat over the past year, and it is no contest.  The Newt runs circles around the achromat.  It's color free, half the weight, one third the price, wider field of view, spherical aberration free, holds collimation exceptionally well, and is well corrected with a coma corrector.  I have spent countless hours and hundreds of dollars on various filters trying to make the achromat somewhat sharper without cutting out too much of the spectrum.  I honestly don't get the hype for large, fast achromats.  Either buy an APO refractor, or stick with a fast Newtonian.

On 18/02/2024 at 11:13, bosun21 said:

If you wear glasses while observing them buy a 5mm Starguider rather than the Svbony 3-8mm zoom.

I've found that the 12mm of usable eye relief in the 5mm Starguider BST to be too little while wearing eyeglasses to comfortably take in the entire FOV at once.  I've found that the 8mm to 9mm of usable eye relief of the Svbony 3-8mm to feel similar in use.  I would be concerned about trying to use its zooming action in a helical focuser, though.  You'd have to firmly hold the focuser while zooming.

By pinched optics, I mean that bright stars have spikes emanating radially in oddball orientations from the center of each of them.  I was panic stricken the first time I looked through mine because of it.  However, I noticed it getting better over time, so I went back inside to let it acclimate for 20 or 30 minutes.

I haven't noticed color correction changing during acclimatization, but it would be hard to discern among the bright spikes with my scope.

One other observation I made accidentally while observing the moon was thinking I had the LP470 in my fingers when in fact I had the BP500.  I was mystified why I was seeing only about 50% of the violet disappearing.  I then realized I had the wrong filter.  However, I had a much greater epiphany in retrospect.  Why was I seeing any violet reduction when the BP500 blocks no violet at all, just orange and red?

I went back to the BP500 to try and figure it out by blinking it in and out of the light path from the eyepiece to my eye.  I noticed when adding the LP470 that it was attenuating red and orange fringing quite well, but when I removed the LP470 from the stack by blinking it in and out, the red fringing turned to purple/violet!  I then tried the really weak Meade #8 Light Yellow by itself.  It cut the far violet fringing, but none of the near-blue violet fringing.  I then added the BP500 to the stack blinking it in and out.  Suddenly, the amount of residual purple/violet fringe dropped way down to near acceptable levels.  Near-blue violet fringing I had been seeing with the weak yellow #8 filter was actually red fringing combining with blue that was fairly well focused creating the impression of near-blue violet fringing via purple fringing.  It's just that my eye can't discriminate violet fringing from purple fringing.

Now I'm thinking a weaker yellow may be sufficient if a strong enough cyan is applied at the same time to avoid red fringing creating the impression of near-blue violet fringing.

I'll have to try more experimentation with smaller objects such as the bright planets and stars before drawing any stronger conclusions.  I just thought it weird that red fringing could manifest itself as violet fringing on an extended object like the moon.