Don Pensack

The Delos 3.5-12mm have their focal planes 6.4mm below the shoulder the eyepiece sits on, requiring the eyepiece move out 6.4mm from setting 3 to compensate.

The 1.25" adapter in the P1 is 9.7mm tall, so the eyepiece needs to move in by 9.7mm to compensate.

9.7in - 6.4out = 3.3mm in.

Each setting of the P1 is 3.2mm apart, so that means the setting should be setting 4, or 1 tick up from setting 5, which is all the way down on the P1 top.

That, as it turns out, is the setting for nearly all of TeleVue's 1.25" eyepieces, and now you know why.

The focal planes in the 17.3mm and 14mm, Delos, however, are 12.2mm HIGHER in the eyepiece than the other focal lengths.

The Paracorr can only move in 3.2mm from setting 4 for the other two focal lengths, leaving them 9mm short of focus, and NOT optimized for coma correction.  Oops.

So TeleVue made the In-Travel adapter for those, which drops the shoulder of the 17.3mm and 14mm about 1.5mm BELOW the top of the Paracorr, or 11.2mm lower than the P1 adapter.

We have to move in about 12.2mm to achieve optimum correction in the P1 for the 17.3mm and 14mm, though, so the same setting as the other

Delos in the standard P1 adapter is only 1mm off from perfect.  So, using the In-Travel TeleVue adapter, we use the same setting of the P-1 as the other sizes using the standard adapter,

and just move the focuser a tiny little bit to compensate.  You could move the top in 1mm from setting 4, but, in practice, no one would bother.

So, in summary:  Delos 3.5-12mm, setting 4 (1 step from all the way down on the top) using the standard adapter, and Delos 14-17.3, setting 4 using the In-Travel adapter. 

Hope that helps understand why the In-Travel adapter was made, and why you need it for the 14mm and 17.3mm in the Paracorr 1.

You need it for the Paracorr 2 as well.

Make the caps hard plastic so that pushing the eyepiece down into the case does not push the eyepiece cap into contact with the lens and leave a smudge.

Those soft vinyl eyepiece caps will only work when the lenses on each end are a good distance in from the ends of the eyepiece.

Explore Scientific learned this the hard way, and had to provide caps to consumers for a lot of eyepieces.

APM and Stellarvue have this issue with the 20mm 100° eyepieces.  I change all the caps and clean the lenses before shipping, but I'd bet most dealers don't.

It's a very good adapter, and threaded on the bottom for 2" filters.

It also becomes a 1.25" attachment if threaded to a T2 thread, which could be useful in some camera configurations.

57 minutes ago, markse68 said:

is there a solution Don? would it be scope specific?

Well, better coatings on eyepieces might help.  But with a specific eyepiece, a drier eye will be less reflective.

It could help to look at the planet slightly off axis, as the reflection angle from the eye might put the light of the reflection somewhere outside your pupil.

17 hours ago, markse68 said:

I recently picked up a s/h but supposedly  unused XW7mm but it seems to have a problem. Or maybe not... 

when I observe Jupiter with it the image is excellent- I’m getting just about as much sharpness and detail as a 7mm ortho I think but it does this strange and quite irritating thing. It’s hard to describe but it’s like Jupiter is forming a beam of light that swishes across my eye as the disk moves across the fov and if I move my eye it kind of dances around. The 5 doesn’t do it nor the 14 or any of the others I have (I don’t have the 10 yet) I’m wondering what could be the cause? The eye lens is clean and like I say the image it produces is excellent. Anybody own the XW7 noticed something similar? I guess it could be an interaction with my scope 🤷‍♂️ Maybe it’s a reflection off my eyeball? It’s fine with less bright objects and I didn’t notice it on the moon when I first tried the ep.

Different eye lens shapes reflect back at the eye bright images that reflect from your eye.  You're seeing the reflection of Jupiter from your eye, reflected back at you from the eyepiece.  It will go all over the place if your head moves back and forth.

Other eyepieces, with different curves, may not have the same effect.

Looks like you weeded out one for sure, two maybe.

I can tell you the 30mm APM would be excellent in your scope but for coma.

If you use a coma corrector already, then the 30mm APM is a true bargain in that sense of the word--it is less expensive than it should be, given its performance.

Of course, it took 9 elements to accomplish the superb correction.

*Also available from Altair Astro in an unusual green color.

I think they are merely rebadged versions of the same eyepiece.

I wouldn't buy either because of the unresolved outer field astigmatism, but they are inexpensive.

I certainly wouldn't buy one thinking they had some re-sale value  down the road, not because they wouldn't be worth anything, but because they are really not good in f/ratios

shorter than yours, and these days f/10 or longer is becoming rarer, so your resale market is constantly shrinking.

Personally, I'd save my pounds and get an APM UFF 30mm, which is a stunningly good eyepiece at any f/ratio.

Admittedly, it is in a different price range.

On 22/06/2020 at 04:19, RobertI said:

I should have mentioned, this is for visual! Apologies. 

If you want something that works well on M42/M43/M8/M20/M17/M16 and The Veil, the Crescent, Thor's Helmet, The Helix, The Owl, etc., then the UHC.

It is the closest to a "universal" nebula filter (though no filter really helps on dark nebulae or reflection nebulae).

But if your interest runs more to planetary nebulae, then the O-III.  Eventually, you'll have both.

I should more properly have said, "cotton swabs".  The problem with a lens pen is it's only clean on the first use.

Cotton swabs are cheap to throw away.  Lens pens are not.

1 hour ago, Stardaze said:

I'm just a bit particular with keeping lenses clean, always have been with my photography. It wasn't filthy by any means, just had a small smudge and dust.

Managed to find a new cloth and so have used @Don Pensack's method and it's now pristine, just like new. Whilst I pinched the better half's pure cotton pads, they weren't great, kept leaving threads of cotton in the edge. Took some time and a few careful repeated passes to clear them away. That's probably a better method to clean EP's too, though I'll need a better supply of cotton and a pack of disposable cloths. 

For eyepieces, simply use Q-tips instead.  Coatings are much harder, but stains more likely to be organic (oils, spittle, etc.), so a typical lens cleaning fluid works a tad better than pure IPA.

1 minute ago, Stardaze said:

Thanks Don. I have some isopropanol but it’s several years old now. Probably needs replacing? Just to be sure, is that a 70-90%
of alcohol, the rest being water?

Yes, water is typically the other ingredient, so 70% means 30% water.  70% may be better than 90% for avoiding residual stains, since it evaporates slower.

Figure whatever eyepiece yields an exit pupil of 1.8-3mm is likely to yield the sharpest images in the scope.

It will be a small enough exit pupil to avoid the worst astigmatism in the eye, and a large enough exit pupil to avoid floaters inside the eye and/or poor seeing.

I used 8 different eyepieces on Thursday night of focal lengths from 6 to 30mm.

Not too surprisingly, my best views were through 11-14mm (1.9-2.4mm exit pupils).

Some pure cotton balls and some high grade isopropyl alcohol will work.

No additives to the alcohol--just IPA and water, 70-90% grade.

No additives in the cotton balls either.

You will need a clean microfiber cloth--preferably the ones that feel like silk--but unused.

In a pinch, use a clean cotton Q-Tip or two in place of the microfiber cloth.

Warning: do not use a lens pen or lens cleaning paper.  These will scratch the surface.

1) blow off as much dust as possible.

2) get a cotton ball wet with alcohol and gently make a pass across the filter until you are certain the whole surface has gotten wiped with alcohol.

3) Quickly grab a 2nd cotton ball and gently wipe up the alcohol still on the filter.

4) Now that the filter has nothing on it, gently wipe the filter surface with the microfiber cloth, using your finger behind the cloth to get into the corners.

This is where a Q-Tip might work as well, but be careful.  Some swabs have polyester tips (a no-go) and some have lanolin added (another no-go).

Under a bright light, look for residual stains,  and see if the swab or cloth simply wipes them away.  If not, you might have to repeat the whole process.

I have used those little tear-packs containing a small piece of cloth soaked in alcohol when I had nothing else, and they worked fine as well.

5) If it looks clean and free of stains or spots, you're done.

Thee are many lens-cleaning fluids out there.  I've used ROR when a stain was really bad, like smeared pollen.

The surface is not as hard or durable as the coatings on an eyepiece, so be careful not to rub two dry surfaces together, though once the filter is clean, a silk-like microfiber cloth

will not likely scratch at all.  None of the cleaning methods outlined will work on a pre-2000 Lumicon filter.  These were not designed to be cleaned, so if you clean one, expect scratches.

Ditto for filters from the long-gone company Sirius Optics.

If you can avoid getting your fingers on the filter, the cleaning procedure need not be a regular thing--only when the filter seems to get a haze on it, or otherwise looks very much like it needs cleaning.

Mine seem to go a few years between cleanings other than merely blowing off the dust.

If you are a smoker, you may need to do it a lot more often.

1 hour ago, Stardaze said:

The APM 13 arrived this morning and certainly is a nice chunk of glass. I’ll have to rethink my EP case when I add the 20 and probably 9. The 3 of them would  pretty much fill it!

Given it’s long length I found the 3 retaining grub Screws a bit of a faff to secure it into the focuser, seemed to not engage very well? Is there a better clip-lock 2” replacement available that secured a large EP better than the bresser standard?
 Edit: just seen this. Quite expensive but do they work well?

https://www.firstlightoptics.com/adapters/baader-clicklock-m68-clamp-for-hexafoc-focusers-bresser-omegon-and-explore-scientific.html

Yes, that works well, but the issue is with the 3 screw binding.

One screw binds the eyepiece, but presses the eyepiece against one point on the other wall of the focuser, creating two pressure points 180° apart, so the eyepiece can wiggle back and forth 90° from that line.

Two screws press the eyepiece into contact with the focuser wall opposite, but the pressure points are 120 degrees apart and there is no plane to allow wiggle of the eyepiece in the focuser.

Three screws 120° apart makes no sense.  Two screws press the eyepiece into contact with the other wall of the focuser, but the 3rd screw presses the eyepiece away from contact with the wall at the very point it needs to be tightly pressed against that wall.

So if you have 3 screw binding, remove one of the screws and only use two screws to bind the eyepiece and it will be tighter.

If there is a brass split ring inside the focuser between the thumbscrews and the eyepiece, slide it around so both screws contact the brass ring.

An eyepiece can be constructed with an eye lens larger than is necessary to field the entire light cone to the exit pupil.

The TeleVue Delites are a case in point.

The eyeguard has an opening smaller than the eyelens, yet does not vignette the field.  It does add a "light trap" when the eyeguard is raised, though.

One note about eye relief: If the eyelens is concave or convex, a pure calculation of the necessary lens diameter does not follow from the diameter of the visible eye lens.

The lens diameter merely defines the approximate eye relief and/or apparent field.  True eye relief is measured from the center of the top surface of the eye lens.

So if it is concave, the concavity would be added to the eye relief of the eyepiece (i.e. the eye lens diameter may not calculate the eye relief).

Likewise, if the eye lens is convex, the convexity would be subtracted from the eye relief derived from the eye lens diameter.

43 minutes ago, John said:

 

The pupil guides that Tele Vue supply with some of their eyepieces do mask quite an area around the edge of the eye lens but you can still see the full field and, from what I recall, with no vignetting

 

But the pupil guide had to be used at or near the exit pupil or it would vignette the image.

22 hours ago, Aaqib_A said:

Hey all! 

Getting more and more into this awesome field and as such getting better equipment, and want to keep that new gear look.

My question is regarding eyepiece retention and the marks it leaves on the eyepieces.

I know some focusers use collar/collet style retention systems, but I only have a 2 screw retention screw that marks my current EPs pretty heavily (A skywatcher 130p). Also, thinking a repurposed feeler gauge as a physical barrier between the two surfaces, but my issue is with the efficacy and if it would actually fit with an EP in there.

Are there any tips and tricks to minimise this gouging? 

Thanks in advance! 

 

Yes, nylon thumbscrews or nylon-tipped steel ones.

1) don't grind up the eyepiece and eat it.

2) don't drink out of the eyepiece

It just means there is a material in the item that can be carcinogenic.

Lead in paint won't harm you unless you eat it, drink it, or chew dry paint (which, apparently, many small tots did).

25 minutes ago, Louis D said:

Okay, can you quote the geometric equation to ensure this doesn't happen as I've never seen it quoted anywhere?  You're saying that just because you've got a 4mm eye  lens, you may not be able to pass an entire 4mm exit pupil without vignetting which I'll grant you might be the case.  However, what is the required width to ensure that there is no vignetting for a given exit pupil?

You won't run into that because the eyepiece that yields a 4mm exit pupil will not be a short focal length eyepiece.

The diameter of the eye lens is directly related to eye relief and apparent field.

If the eye relief is longer, the lens is larger.  If the eye relief is the same but the apparent field is larger, the eye lens must be larger.

if long eye relief is desired in an ultrawide eyepiece, the eye lens will be enormous.

Ruud gave the formulas in an earlier post to determine the diameter of the lens for a given apparent field or desired eye relief.

If you don't need long eye relief or wide fields, the lenses can be quite tiny.

40 minutes ago, John said:

Guess what my first target is going to be when I next have the 12 inch dob out ? - the Cats Eye with the Lumicon O-III filter

Just be aware that if you use magnifications above about 15x/inch of aperture, your best view will be without the filter.

The contrast enhancement at high powers is very minor, and the dimming of the nebula more important when the magnification is large.

My best view of the Catseye has been at 493x in the 12.5" but without a filter.

It's been done for over a century.  However, rarely on a scope > 6" in size.

I see you used the term "back focus" to indicate "out focus".

Back focus is a photography term and it means gaining additional focus room outside the focuser, i.e. back focus.

It implies in focus of the focuser.  Sorry for my confusion.

In that case, there are a couple solutions:

1) add an extension tube to the focuser.  These pull the eyepiece out of the focuser by at least the length of the eyepiece's barrel, so the focuser would need to move in at least that far.

2) use only the 2" adapter for the focuser (the tall one provided by the manufacturer) and add a standard 2" to 1.25" adapter to that and do not use the 1.25" adapter that came with the scope again.

This would raise the eyepiece and cause you to lower the focuser.

However, to the point of the large extraneous spike in the image.  It is obviously not caused by the focuser, so what else protrudes into the inside diameter of the tube?

4 hours ago, bomberbaz said:

Sorry @Don Pensack surely if you add height to the focuser you are then having to wind the focuser in further to compensate or did I misunderstand what you meant?

Would pushing pushing your primary mirror up 5mm not be another option assuming that is there is enough travel!

Steve

The new 2" to 1.25" adapter would be SHORTER than the one currently used.   You are shortening the focuser thereby, not adding height.

So you misunderstood what I meant.

Pushing the mirror up 5mm wouldn't be enough unless the focuser only protruded 5mm inside the UTA, and the spike says it sticks in more than that.

My adapter switch would likely make a 15mm different or more.

On 09/06/2020 at 10:35, Barry-W-Fenner said:

I do have the 25mm version, I use it quite a lot to view almost the entire area of M45 & The double cluster. It is also useful for using to locate your targets before changing to higher power. I did notice an improvement over the stock 25mm, The image is definitely sharper, However I have noted that the 25mm isnt clear all the way to the edge of the field, I would say around 70% with the outer edge slightly degraded. I dont know if that is the eye piece and 200p combination doing this or just the eye piece.

Cheers

Baz

It's how the eyepiece handles the light cone from the primary.  This eyepiece works fantastic in an f/15 Maksutov.