Louis D

There's a lengthy thread on CN about these low cost Chinese refractors.

The only use for the 45mm over the 30mm that I can think of would be in conjunction with a nebula filter.  The lower power and larger exit pupil will lead to a higher surface brightness of the object's nebulosity, but at a smaller image scale.  Without the nebula filter, sky glow would dominate in the 45mm negating any possible advantage.  With the nebula filter in place, much of the sky glow would be eliminated leaving only the brighter nebulosity.

1 hour ago, Alan64 said:

Again, a parabolic mirror can focus all of the incoming rays of light to a single focal-point, via its exotic curvature, which then results in the sharpest and most pleasing images possible.

With one caveat.  It does this only on axis.  Off axis, there is coma aberration necessitating a coma corrector for pinpoint focus across the field.  Refer to my post in another thread about spherical vs. parabolic mirrors and off axis coma in parabolic mirrors:

20 hours ago, jaydee3839 said:

Thanks for the input all.  Doesn't sound like anyone wants to endorse the 17-22mm eyepiece in the $100-$150 (USD) range, that the $240 Morpheus is much better (yet out of my price range).  Other threads suggest the Vixen NPL 20mm and Baader Classic Ortho 18mm are excellent in the $50-$65 (USD) range (albeit much narrower FoV).  Barlows seem to have mixed reception (except for higher end) here, so maybe I should pass on this for now also.

 

Based on the above (and reading lots of other threads), I'll skip my original plan of "low-medium" 17-22mm + barlow, and instead get a "high-medium" ES 82 deg 11mm for $150 USD right now.  It seems universally praised as a great piece and give me some diversity as I already have a "low" mag 30mm piece. 

 

Eventually I'll fill out a "low-medium" 17-22mm and a "high" ~7mm, but for now, I'll enjoy the Vixen NPL 30mm plossl and 11mm ES 82 deg.  

If you ever get a ~2000mm focal length scope, then a 17mm to 22mm eyepiece would make a lot of sense.

I played with one of these at an October star party, and the image is mostly unusable outside the inner 30% of a Plossl's field of view due to severe spherical aberration, so keep your subject centered as best you can.  I was able to make out Jupiter's disk and four main moons, but I don't recall if I could discern any banding on Jupiter.

Just download and learn to run Stellarium to find the positions of the planets.  I believe if you zoom in enough, it also shows the positions of their major moons as well.

If it is astigmatism in your observing eye that necessitates you wearing eyeglasses at the eyepiece, I'd stay away from the 30mm ES-82.  The new version has a recessed eye lens that makes it impossible to use with eyeglasses.  I have the original mushroom top version that is the same as the 30mm Meade 5000 UWA and 31mm Celestron Axiom.  The eye lens is basically flush with the top of the housing and is just barely usable with eyeglasses if you push in a bit.  The 27mm Panoptic is even tighter on eye relief.  I've scratched a couple of pairs of eyeglasses on the exposed metal retaining ring around the eye lens trying to take in the field stop.

I much prefer the 30mm APM Ultra Flat Field at this focal length when wearing eye glasses.  It's comfortable to use, sharp across the field at f/6, has no ring of fire like the 30mm UWAs (31mm Nagler T5 included), is compact, and relatively light weight in comparison to the UWAs.  I've found it might be a slightly bit less sharp than the 27mm Panoptic in the center, but it is sharper in the outer 15% of the field.

I doubt the 40mm ES-52 would do well at f/5 in you Dob.  It's a modified Plossl or Astroplan design that is already falling apart at 75% out in an f/6 scope if it's the same as the older 40mm Meade 5000 Plossl.  It does have excellent eye relief for eyeglass wearers and is super sharp in the central 50% and has basically zero distortion across the field.  The moon stays circular from edge to edge rather being oblate or egg shaped near the edge.

A better option at this focal length is the 40mm Explore Scientific MaxVision 68° which is the same as the discontinued 40mm Meade 5000 SWA.  If you hunt around, you might locate one still in stock since it appears to have been discontinued as well.  It is very well corrected at f/6 and would probably work well at f/5 as well.  It is also super easy to use with eyeglasses.

9 hours ago, Eugene69 said:

Ok thanks for enlightening me! Would you class it as an essential piece of kit?

Pretty much for star hopping.  I've always used either a Telrad or QuikFinder on every one of my scopes.

19 hours ago, Waldemar said:

Most of the time ventilation alone is enough to prevent mold, but there needs to be an airflow, a kind of draft so to speak. All fungi hate airflow.

I've got heavy duty fungus growing one of my bush's roots in the winter here.  It's on a slope and we're in a drought, so mold is devastating here even during our drier months.  I'm going to err on the side of caution and keep everything stored indoors.

All my gear is stored in two downstairs coat closets at the back of each.  It's not the most convenient, but it keeps it all in a climate controlled area (A/C and heat).  Our summers are swamp-like here, and everything in the shed develops a covering of mold.  I don't know if it would be possible to have enough ventilation to stop this without active heating to keep things dry in there.

I have and use both the Rigel QF and Telrad.  The Telrad is better in some respects (larger 4 degree outer circle, no parallax, easier to find circles image), but much larger.  That 76mm diameter scope is fairly small in diameter, so I recommended the QF as the better fit for it as I would for most refractors.

@Eugene69 The QF and Telrad are just unit power finders that project circles on the sky via a glass plate.  They're only there to help you figure out where the scope is pointed on the sky.  You still have to do all the translations from star maps to the sky yourself.

12 hours ago, joe aguiar said:

but if it is that model that has the OLD 0.965 inch ep which will not fit 99% of todays eps

he will have to get a 0.965 adptor to 1.25" adptor first b4 getting any eps

my personal opnion is i wouldnt upgrade the finder or eps on that scope that would be more then the whole scope costs and i would just upgrade the scope to somthing better BUT i know alot people wont like to hear that BUT sometimes the trurth hurts and its better to restart over then fix something that will prove to make most people to get out of the hobby verses stay in it.

joejaguar

If it is that model, Amazon specifically states the following:

Extendable because of the 31.7mm (1.25“) accessory socket: for astrophotography, usage of filters, etc.

I checked that before making my recommendations since I had the same thought after seeing that focuser.  Of course, Amazon could be completely wrong.  Until we hear back from the OP, it's all speculation on our part.

It could also be that the knurled black ring has to be removed to access the 1.25" fitting.

I wouldn't worry about the upgrade costs of finders and eyepieces since they can be moved on to other scopes.  On the other had, I would not recommend upgrading the focuser on such a scope because it would be difficult to move it to a new scope.

In the winter, I cap everything and close my sealed Pelican-style eyepiece case(s) before bringing everything inside.  The dewpoint outside is super low in the winter compared to the dewpoint inside the house, so I seal that dry air in with the optics as they warm up.  In 20+ years, I've had zero mold issues.

In the summer, I bring everything in caps-off and cases-open since the dewpoint outside is generally much higher than inside my air conditioned house.  I then leave them out to dry until morning when I cap and close everything and put them all away.

In the shoulder seasons, it really depends on the dewpoint.  Anytime there is noticeable dampness, I err on the side of allowing things to dry out inside rather than trapping that moisture with the optics.

This applies to Texas which swings from swamp-like summers to desert-like winters.  I haven't dealt with dry summers and wet winters or non-air-conditioned houses.

4 hours ago, John said:

Hello and welcome to the forum.

What aperture is the main mirror on your seben scope ?

 

I am going to guess it's the Seben 700-76 Reflector Telescope which comes with SR4mm, H6mm, H12.5mm, and H20mm eyepieces and a 2x Barlow in 1.25" sizing.  Based on that, I recommend getting a 32mm Plossl, and 8mm and 15mm BST Starguider eyepieces.  The existing eyepieces will slot in between these, and you'll be able judge the difference in performance and ergonomics between them and the new eyepieces.  You can even try using the 2x Barlow with each to see if any combinations are usable.

I'd also recommend getting a Rigel QuikFinder to help aim the tube and aid in star-hopping, and downloading and learning Stellarium to find out what's up on any given night.

@Jibber Go ahead and get the two parts listed above and give it a try on terrestrial targets first, like a distant tower or tree.  I would probably try to focus with an eyepiece first to get it close.  For astrophotography, you normally remove the diagonal and insert the 1.25" adapter straight into the focuser tube.  However, for terrestrial testing, you may need to keep it in the imaging chain to achieve enough back focus when focusing on objects much closer than infinity.  For daytime photos, you can put the camera in aperture priority and let the camera select the shutter speed.  I'd probably put the ISO in auto mode to start with as well for testing purposes.  This setup will probably work for the moon, although you may need to use exposure compensation if the black sky around it fools the camera to overexpose the moon.  Once you note what shutter speeds and ISOs it is using to best effect, you can then switch to full manual and dispense with the exposure compensation.  Set the shutter and ISO to those values that worked best and start experimenting with both in single steps to see what exposure combinations work best.  The planets will be much more challenging, so perfect your moon shots first.  Deep Space Objects (DSOs) will be orders of magnitude more difficult beyond that.  Instead, I'd probably just put the camera on a tripod and put the 18-55mm lens on it at 18mm, point it at the sky, and take some 30 second or shorter exposures (depending on the ISO).  You'll be surprised by what the sensor will pick up.

1 hour ago, joe aguiar said:

holy cow $16 shipped sounds so cheap. I guess for this price it could be something that's better than nothing for a brand new person.

mine were all about $149 to $169 BEFORE taxes so that's just shy of $200 cdn

joejaguar

Misremembered.  It was actually $10 shipped.  I think Hayneedle was clearing them out 6 years ago.

Avoid the cheap OIII filters.  I picked up a Zhumell OIII for $16 shipped a while back just to compare to my 1990s Lumicon OIII.  It was no contest.  The Lumicon is actually an interference filter that looks mirrored and has a really narrow passband and high transmission within that band making many nebula really stand out in light polluted skies.  The Zhumell looks sort of like a dark green filter with no obvious mirroring.  It acts like a somewhat stronger light pollution filter, so nebula stand out ever so slightly better.

Or mount a longer dovetail bar with it sticking out the back below your imaging train.  You may need a riser to get the needed clearance.  As long as it's a solid, machined bar rather than an extruded one, it should be plenty rigid.

4 hours ago, LDW1 said:

I learn something new every day, I didn’t know there was two types, I will have to read up on that !

Here's a couple of links on the topic of battery sulfation:

https://www.crownbattery.com/news/sulfation-and-battery-maintenance

https://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it

On 06/01/2020 at 08:10, Richard136 said:

Thanks for the update - appreciated and interesting findings.

My 70mm shows an apparently flat visual field to about 80%. I have relatively narrow fov eyepieces, and this may factor into how noticeable is the effect.

It also matters a great deal if you do or don't have presbyopia (lack of focus accommodation in older eyes).  Younger eyes can refocus when shifting attention from center to edge.

For example, when I bought my 14mm Pentax XL 20+ years ago, I never noticed the curved field of focus thanks to my relatively young eyes.  My eyes could compensate "on the fly", so to speak, as I gazed around the field.  Once my presbyopia settled in about 7 years ago, I noticed that the outer 20% of the Pentax's field needed refocusing for my newly fixed focus eyes.

I'm sure had I bought my AT72ED (or its equivalent) 20+ years ago, I probably wouldn't have noticed its curved field, either.  Getting old is no fun in so many ways.

19 hours ago, LDW1 said:

All batteries sulfate as part of the chemical reaction between the plates and battery acid, its a natural process ! 

Sorry, I thought it was clear I was referring to permanent sulfation rather than reversible sulfation.

On 31/12/2019 at 13:59, Louis D said:

I did find that stars were ever so slightly tighter at very high powers without the flattener in place in the 600mm scope.  This is the same as with my GSO coma corrector in my Dob.  In both cases, curvature and coma at high powers matter very little when attention is focused on axis, so I remove them temporarily at the very highest powers.

I was out again with the 600mm refractor Friday night, and I paid close attention to when the flattener switched from being a help to a hindrance.  With my 10mm Delos and 9mm Morpheus, I noticed a nice flat field and no image degradation with the flattener in place.  When I removed it, stars were noticeably defocused in the last 25% to the edge.  However, with my Pentax 7mm XW, 5.2mm XL, and 3.5mm XW, the flattener introduced slight yellow/purple color fringing that disappeared when it was removed.  There was no discernible defocusing of stars at the field edge without it in any of those three.  I didn't have an 8mm widefield eyepiece handy to see which way it would have tilted.  I'll have to try this with my Speers Waler 5-8mm zoom the next time I'm out.

That's a newer Pentax PR XL zoom for which there are no reports whatsoever.  It was introduced a few years ago.  Who wants to go first buying and testing it?

Here's the Pentax SMC XL zoom on FLO, Bristol Cameras, and Agena Astro.  You would also be correct to simply refer to it as the Pentax SMC 8-24mm Zoom as B&H Photo and several others do.  However, I've never seen a single commercial reference to it being labelled the Pentax XW zoom anywhere, and that was simply my point.  As far as I can recall, Pentax has never put the XW appellation on any zoom eyepiece.

2 hours ago, Merlin66 said:

I use a Pentax XW 8- 24mm zoom for Ha observing.

Technically, it's a Pentax XL.  The 8-24mm zoom was never updated with the XW release, so it's a 20+ year old design rather than 16+ years for the XWs.

4 hours ago, Tenby2 said:

Any suggestions to help stop this? I will buy suppression pads for the tripod, there are so many out there, with prices varying from £15-£80 I wonder if there's really a great deal of difference justifying the prices! 

Look for pure Sorbothane pads and just put them under each tripod foot.  I bought some new old stock Sorbothane insoles from the 90s off ebay and cut them into pads for multiple tripods.  It cuts dampening time from 3 to 5 seconds to 1/2 second.