Louis D

2 hours ago, globular said:

I'd add APM 24 UFF into the mix. It claims 65° but I've heard it measures more like 63°. (There are other brandings of EP this too.)
If you need long eye relief for glasses then this is the one I'd go for.  
If not it still might be  

However, the APM 24mm UFF has at least as much true field as either the 24mm Panoptic or ES-68 due to much lower edge distortion.  I've measured the field stop at 27.5mm, though it tends to fade out a bit due to some vignetting.

4 minutes ago, Franklin said:

Is there much difference between the APM/Altair UFF 24mm 65deg and the ES 24mm 68deg ?

Eye relief.  You can see the entire field of the APM 24mm UFF while wearing eyeglasses.  You won't be able to do the same with the 24mm ES-68.  Correction wise, they're probably similar.

6 hours ago, Barry-W-Fenner said:

So in this design, Baader cant go shorter longer than a 17.5 - Which is a real shame, If they could produce shorter longer and it performed as well as the 17.5 they would be onto a winner.

At least not as long as they stay in a 1.25" barrel.  Were they to switch to a 2" barrel like the 17mm and 22mm NT4s, 14mm and 20mm Orion LHDs, and 22mm AT AF70/Omegon Redline SW, etc., then they probably could go with longer focal lengths.

For me, the deal breaker is no altitude clutch to allow heavy eyepiece changes.  Once balanced and the axis tensions are backed off, I don't generally use the slo-mo controls on my DSV-2B mount while tracking.  It's so much easier to just use a light, fingertip touch on the handle to track than trying to alternately mess with two slo-mo controls.

I took a pass on the DM-4 and DM-6 mounts because they have no altitude clutches.  I was with a fellow observer using a DM-6 mounted 140mm refractor at a star party and watched his contortions trying to hold two large eyepieces while trying to prevent the scope from nose diving as he swapped them.  I was appalled at how un-ergonomic it was.  It tracks fine without slo-mo controls once the eyepiece is changed, though.

My DSV-1 mount is fine for short telescopes and light eyepieces, but I wanted to be able to mount larger scopes and heavier eyepieces, so I bought the DSV-2B for them.  I wouldn't go much past a 100mm refractor with it.  I'd probably get the DSV-3 at that point.

I guess my point is the lack of an altitude clutch on the NOH CT-20 is a deal breaker for me.

1 hour ago, Deadlake said:

For BV use planning to use 24 mm UFF 

I picked up my used copy from someone who couldn't get on with a pair of them in his BV.  I don't know if it was due to an IPD issue, a nose space issue between them, or something else entirely like weight or ability to merge images.  Just temper your expectations for the 24mm UFF pair in a BV.

2 hours ago, Don Pensack said:

I recall it being measured at 74° +/- with the flashlight test.

With the other focal lengths at 78°, and just the 6.5mm at 79°

For my two Morpheus:

14mm: 77° by projection, 78° photographically

9mm: 78° by projection, 79° photographically

And before anyone suggests a systemic error between the two, the two measures match for many of my eyepieces, and the first is sometimes larger than the second.  They are generally within 1° of each other.  Eyepieces without a physical field stop are problematic for both methods because it's a judgment call to define where the usable field ends as it fades to black either in the projected or photographed image.

3 hours ago, globular said:

I know the 30mm works ok both with and without glasses with it's reported 22mm eye relief.  I guess the 24mm is recessed about an additional 7 to 10mm or so... so they're similar in use.

I measured 16mm of usable eye relief for the 30mm APM UFF, although it feels more like 17mm in use.  Both work comfortably with eyeglasses.  I think that's why the 24mm's eye lens was recessed so much, so it would have a similar feel to the 30mm and many other eyepieces with about 17mm of usable eye relief.  Too much eye relief can be a bad thing even with eyeglasses.

2 hours ago, Gfamily said:

There are astigmatism correctors that can be fitted to eyepieces if you'd rather take your spectacles off.

e.g. TeleVue Dioptrx - not cheap though.

Nor do they attach to all eyepieces.  There are various hacks out there (check CN in particular) to use them with certain Pentax, ES, and APM eyepieces.

3 hours ago, Stuu said:

I currently have a fairly mild prescription for varifocals and get on fine without them when using my telescope.

I would never use an expensive pair of varifocals at the eyepiece.  There's too high of a risk of them being damaged.  That, and they probably have lots of microscratches that cause fine stars to twinkle as your head moves through the exit pupil.

I bought a pair of distance only eyeglasses with the lowest dispersion lens I could get so my astigmatism is corrected for use at the eyepiece.  I bought them through EyeBuyDirect for about $20.  They stay in a case in my astro toolbox and only get used for astronomy, so they don't build up daily microscratches.  When I need to read something up close, I simply look under my eyeglasses because my old eyes are fixed focus at 8 inches.

41 minutes ago, globular said:

@ScouseSpaceCadet I've been mulling over this EP.  But the reported 29mm eye relief puts me off somewhat.  Sounds great for glasses... but what about without glasses? Do you end up hovering above the EP... even with the rubber in the up position?

That's the design eye relief.  The eye lens is recessed so much that it ends up having 17mm of usable eye relief.  You will need to touch the folded down eye cup to see the field of view while wearing eyeglasses.

27 minutes ago, Jiggy 67 said:

You’re absolutely right John, I’m not saying don’t get an OIII, I definitely would, but I think a UHC is a better introduction to filters. I think if I had started with an OIII I would have been turned off filters for life because it really does need a bit of aperture. I think a UHC is a good way of introducing yourself to narrowband filters 

Not so much aperture as large exit pupil.  Yes, that will mean lower magnification with smaller aperture scopes, but that can be a good thing for large objects like the Veil nebula.

If I had started with my Lumicon UHC, I probably would have written off all nebula filters as "Meh".  Some improvement, but not a dramatic improvement in the view.  The OIII is a "Wow" filter with what it can bring out.  Invisible nebula like the Veil stand out as etched on the sky.  Remove it, and the Veil disappears.

Is the OIII filter right for all emission nebula?  Certainly not.  However, more often than not, it offers a very noticeable improvement in the view.

2 hours ago, Astro_Nic said:

I'm still not sure I understand why not to use a powermate - looks like I can lose two eyepieces then!  Although I get it's a pain to change and also adds weight and length to the eyepiece.....have I just listed the reasons?!  Cheaper though!

Yes, it can be a useful way to stretch your dollars starting out.  Just be aware of how long things get with a Powermate, Paracorr, and a 100 degree eyepiece all in the focuser at the same time:

Focuser flex could become an issue.  Although as @John has pointed out, they can come in handy for other uses:

2 hours ago, Astro_Nic said:

Have no collimation tools....aaaarrrrggghhh!  What do you recommend?

I use a cheshire/sight tube to get the secondary square under the focuser.

I use a laser to get the secondary on the center of the primary.

I use a Rigel Aline to get the primary lined up with the rest of the system.

3 hours ago, globular said:

The range without the 14mm does indeed look like the usual 2x steps in fov area... i.e. root(2) = 1.4 steps in fl.

When the range first came out, however, they couldn't get the 17.5 quite right.... so brought out a 14mm instead.... as that was the longest fl they could get right.

When they finally cracked the 17.5 they brought that out too... but (rightly) didn't withdraw the 14mm.

Agreed.  Also, there's a lot of wiggle room in the 11mm to 16mm space as to what is the best workhorse focal length.  It depends on the focal length of the scope, the apparent field of view of the eyepiece, and observer preferences.  For instance, I started out with a 14mm Pentax XL at 65°, but later found that the 12mm ES-92 covers more sky at a higher magnification without shrinking the exit pupil too much in the process.

3 hours ago, Astro_Nic said:

It's weird as all the beginner guides say get barlows to reduce number of eyepieces, yet all the advice seems to be to not to bother......

Written by people who haven't spent a good chunk of their lives out under the stars, I suspect.  I tend to leave mine in the focuser the entire night when I want to use all of my eyepieces at double their normal magnification, which isn't very often.

3 hours ago, Astro_Nic said:

So say I get all 100 degree APMs - what targets would I use for each of the sizes - 5mm, 9mm, 13mm and 30mm ?  Is that a good spread?  340x, 170x, 123x, 53x ?

25x to 50x is good for very large open star clusters, solar system conjunctions, typical solar observing (with safe solar filter) sweeping rich star fields, and detecting comets.

50x to 100x is good for large open star clusters, emission nebula, the whole moon at once, and large galaxies from dark sites.

100x to 150x is good for small open star clusters, planets on nights of average seeing, smaller galaxies from dark sites, viewing the moon in large swaths, and splitting many double star systems.

150x to 200x is good for planets on nights of above average seeing, planetary nebula, lunar details, starting to resolve globular clusters, and splitting tighter double stars.

200x+ is good for planets on nights of exceptional seeing, bright planetary nebula details, challenging lunar details, interacting galaxies from dark sites, fully resolving globular clusters, and splitting the tightest double stars.

I'm sure I missed someone's favorite type of observing in there.  That, and folks will argue about what magnification works best for each.  It's nice to have an assortment of eyepieces to try out to match the seeing conditions with the object at hand.

3 hours ago, Astro_Nic said:

What's the main difference between OIII and UHC filters?  Do you use both at once or just one at a time?

OIII only pass the two oxygen emission lines while UHC filters add one or both hydrogen emission lines.  As a result, the OIII filter has a narrower passband and a higher rejection of light pollution.  However, some emission nebula just don't emit much in the oxygen lines, so the UHC or even an Hß filter comes into play.

You don't use them together.  It's either one or the other.  The OIII is a subset of the UHC.  The OIII and Hß are mutually exclusive.

A lot of folks like the Baader Contrast Booster on planets and other objects to make it easier to pick out low contrast details, but I've not tried one personally.  I've had some luck with an 80a filter on Jupiter to bring out the Great Red Spot better.

3 hours ago, Astro_Nic said:

Are the APMs suitable for binoviewers if I went that way?

Probably not.  They're heavy and fat.  You might not be able to get two of them close enough together for your IPD.  That, and your nose or at least its bridge between your eyes might not fit between the eyepieces, either.  Most folks use smaller, lighter weight eyepieces in their BVs.  Adapted microscope eyepieces can even work quite well I've found.

Also, most folks tend to use lower powered eyepieces with BVs because it's easier to merge their images.  Higher powered eyepieces tend to reveal any slight miscollimation in the BV.  You can always boost the power by adding a Barlow element ahead of the BV.  They also help you to reach focus in Dobs which don't usually have enough in-focus for BVs natively (about 100mm required).

On 29/08/2021 at 12:44, vlaiv said:

I borrowed the idea from @Louis D who did wonderful set of comparison photos thru the eyepiece. Only difference is that I would advocate using large lens instead of phone camera because phone camera can act as aperture stop and reduce aberrations created by eyepiece.

We went round and round on this in another thread, and I tried to use large lenses and presented the mediocre results there, but the results were inconclusive.

I will restate that the image from the camera phone exactly mirrors my visual impression of the field of view, right down to where some eyepieces have zones around 70% out that go soft and then get sharp again toward the edge.  Visually, those areas look "jittery" depending on how you move your eye.  Clearly, there's some sort of aberration going on at the exit pupil, possibly SAEP related.

The one exception as I've previously stated is the portrayal of field curvature.  Eyepieces with a curved field look much flatter in the small camera lens than to my presbyopic eyes.  It probably mirrors how younger eyes perceive the field of view.  I suspect the enormous depth of field/focus of these tiny, wide angle lenses are able to bring the curved field into focus from center to edge.  Despite these lenses operating at f/1.7 to f/2.5, they still have lots of depth of field because of their incredibly short native focal lengths of around 4mm or less.

Doesn't it have a 3/8"-16 mount on the base underside to attach it to a wide range of photo tripods?  If not, my apologies.

4 hours ago, Astro_Nic said:

9mm ES 100 degree FOV 2 inch - this would give me 170 x magnification;

Don't overlook the 9mm APM XWA 100°.  It's lighter and cheaper than the ES alternative, and most reports rank it as just as good if not better.

4 hours ago, Astro_Nic said:

30mm APM UFF 2 inch - this would give me 53 x magnification;

Excellent choice.  My preferred eyepiece at that focal length.  The ES-82 is wider, but has issues with CAEP (Chromatic Aberration of the Exit Pupil) aka, ring of fire at the edge.

4 hours ago, Astro_Nic said:

2x Televue powermate 2 inch - this would then increase the above magnification options to 340, 170, 106 and 53

You'll find yourself either leaving it in the focuser for extended observing periods or removing it.  PMs and Barlows are just too clunky to be swapping in and out regularly.  I would spend the money on dedicated eyepieces, myself.  That, and you'll have a really long optics train hanging off your focuser.  I would probably recommend 13mm and 4.77mm APM XWA 100° to fill the power gaps instead.  The latter is 110° which will be really helpful at high powers with a nondriven Dob.

4 hours ago, Astro_Nic said:

Moon filter - suggestions please?

Pick up a cheap moon filter off of ebay or similar if you feel the need.

4 hours ago, Astro_Nic said:

Nebula filter - ES CLS

Pick up a quality OIII first and UHC second.  Don't go cheap on either one.  Astronomik, Lumicon, and several others are quite good.

4 hours ago, Astro_Nic said:

I don't wear glasses.  Wife does but only long sighted so eye relief shouldn't be an issue.

As long as neither of you has astigmatism (CYL correction), you'll both be fine without eyeglasses at the eyepiece.  You can just focus out the distance correction.  Depending on how strong the prescription is, the field stop may get a bit fuzzy because you're moving the image circle away from it to compensate for the observer's eye.

On 30/08/2021 at 09:52, Pixies said:

What the flip was going on with Vixen in 1991? 

Don't ask, don't tell.  It was the 90s afterall.

Found a good clip of the self-destructing tape for our younger contributors:

Also remember that as the f-ratio goes down, the central obstruction goes up, and contrast on planetary details goes down with it.  Below is a simulation of the effect CO has on planetary details:

The effect is subtle but real.

Does anyone know why Synta hasn't switched over to a GSO style focuser that actually makes sense when switching between 2" and 1.25" mode?  It would prevent a multitude of problems for users of their Dobs.

8 minutes ago, PIRISH33 said:

Hi there, sorry I know that I might sound like a little bit silly, but, what is the best telescope to view Saturn's rings????

One located in Australia or in orbit, I would think.  Right now, the planets are a bit low from the northern hemisphere, so you really need to get south.

They're generally listed for $4000 to $5000 in the US astro classifieds, although that doesn't mean they sell for that.  Thus, £2,000 would be a quite a bargain.

4 hours ago, Mr Spock said:

One thing to note about undercuts. Some Skywatcher tubes have the screw very close to the top. This means the screw can land on the top of the undercut meaning the eyepieces doesn't go all the way in as the screw pushes against the undercut forcing the eyepiece outwards.

I've got that same situation with a $50 dielectric diagonal from Amazon.  It's a very nice diagonal except for the fact it pushes all 2" undercut eyepieces up and out of the holder because the compression ring is too close to the top.  I'll have to try removing the ring and replacing the screw with nylon one to see if that improves matters.

6 hours ago, Barry-W-Fenner said:

I am to stupid to understand any of the above 🤣 👍

Just try to find eyepieces that you like the view through and are comfortable to use and you'll be fine.