Second Time Around

Which ones of these eyepieces accept a Dioptrx? Don? Anyone?

It's not often I disagree with Louis, who's probably forgotten more than I'll ever know and has been particularly helpful to me regarding eyepieces that accept a Dioptrx. However, I prefer a Dioptrx to correct my astigmatism rather than wearing my glasses. One of several reasons is that, as Louis has pointed out, prescriptions change. In fact mine changes every year, especially the correction angle needed. With a Dioptrx one can keep up with these changes (even in mid-yea) simply by rotating it. I've also found that I need a 0.25 dioptre extra astigmatism correction at night compared with my daytime glasses. Additionally, the Dioptrx corrector is made from glass rather than the plastic lenses in my specs and so is probably better corrected. Certainly the coatings are likely to be better even than my expensive glasses. I also don't want to risk scratching my glasses on an eyepiece (don't ask me how I know!). As Louis has pointed out, one still needs an eyepiece with long eye relief as a Dioptrx eats up about 8mm of this. In practice I find I need about the same eye relief as using my glasses, despite choosing a frame design especially for telescope use. Most Televue eyepieces accept a Dioptrx as can be seen from the following chart. However ignore those with an asterisk as these have insufficient eye relief when used with the necessary adapter. Go to https://televue.com/engine/TV3b_page.asp?id=214 Non-Televue eyepieces I know accept a Dioptrx (sometimes with an O ring) include : Svbony 7-21mm zoom Baader Hyperions including the zoom Baader Morpheus APM 24mm 65 degree Many 68 and 82 degree Explore Scientific eyepieces - certainly my 28mm 68 deg does Pentax XWs Omegon 22mm 70 deg LER ( As Louis has previously pointed out the similar AF70, Omegon Redline SW, and TS-Optics Expanse WA versions with the screw-off eyecup all accept a Dioptrx, but not the Celestron Ultima LX or Olivon 70 versions with a twist up eye guard). Vixen 22mm LVW (used only) A search will reveal many others. I simply won't buy an eyepiece that doesn't take a Dioptrx when I can benefit from one. Luckily, there's a lot that will.

This in depth article by Bill Paolini, the author of a book on eyepieces, is a shootout between 12 different eyepieces with focal lengths between 24 and 26mm. Go to https://www.cloudynights.com/articles/cat/user-reviews/24-26-mm-eyepiece-comparison-r2651 Since then the 24mm APM Ultra Flat Field has come on to the market. This 65 degree FOV has particularly long eye relief (approx 20mm useable rather than the claimed 29mm), and is one of the few wide field eyepieces at this focal length where the full FOV can be seen with glasses (this being one of the problems with the 24mm Panoptic). It also accepts a Televue Dioptrx astigmatism corrector. It's garnered a fine reputation for quality and is often recommended here on SGL. It's also not expensive at less than £150.

I agree with Philip about not getting the accessory set. The eyepieces are not high quality and are too close in focal length. You can do a lot better buying 1 or 2 individual eyepieces.

Just to quantify, the ES coma corrector will increase the focal length by 6%. So your focal length will increase from 750mm to 795mm. So your figure of 800mm is almost exactly right.

It's slightly different with astronomy and it's not just convenience. Sometimes a zoom eyepiece can actually show more detail than a fixed focal length eyepiece. This is because you can dial in the exact best magnification for a given object in given seeing conditions. However I do agree with you about prime lenses being better for photography. Mind you, in the old days when magazine editors insisted on transparencies I then used zooms. This is because slides couldn't be cropped, and using a zoom could mean a better composition.

I always recommend going for the zoom first. Then you'll find out what focal lengths suit you, your scope and your observing conditions.

I've had a new telescope to try out and with (at last) some decent seeing was surprised earlier in the week how little magnification I needed to see that Saturn is ringed. I therefore decided last night (15th Sept 2020) to test exactly what magnification I needed for this, and also to see Cassini's Division. Telescopes used 1. My new scope is an Altair 72mm f/6 EDF De-Luxe with a test certificate showing a Stehl of 0.95. 2. I also set up an old Opticron 22x60 spotting scope I've used for birdwatching. Other parameters I observed for a total of 90 minutes, half before and half after Saturn reached the meridian at 20.46 local time. The maximum elevation was 15.3 degrees. I looked up that the rings are currently tilted at an angle of 21.5 degrees. Seeing was 4/5, occasionally slightly better. Eyepieces used on 72mm Baader 8-24mm Mk IV zoom Svbony 7-21mm zoom (reported to be identical to the new Orion Explorer E-series zoom) Vixen 22mm LVW Observations With zoom eyepieces I could have any magnification within their range so could get more accurate observations for this experiment. I started at the lowest power as I felt that would minimise any preconceived ideas. Baader zoom 24mm/18x magnification. Could see that Saturn had "ears", but couldn't see a ring, even in moments of better seeing. Vixen LVW 22mm/19.6x magnification. Could see that Saturn had "ears", but couldn't see a ring, even in moments of better seeing. Baader zoom 21mm/20.6x magnification. Could see a ring in moments of better seeing. This was the minimum magnification I could manage this. Svbony zoom 21mm/20.6x magnification. Could see a ring in moments of better seeing. This was the minimum magnification I could manage this. 60mm Opticron spotter 22x magnification. Could see a ring in moments of better seeing. Baader zoom 16mm/27x magnification. This is one of the click stops on the Baader zoom. I didn't try any focal lengths between 16 and 21mm. At 16mm/27x I could clearly see a ring all the time. Baader zoom at 8mm with matching 2.25x Barlow. Magnification 121x. Couldn't see Cassini Division even in moments of better seeing. The image had begun to deteriorate at this magnification and, although I could add extension tubes to get an even higher magnification, I felt this would be a waste of time, especially as this was late in the session and Saturn was getting even lower. Discussion I have very sharp eyesight, tested at 6/4 (=US 20/12 I believe). With a spherical correction of -4.00 in my dominant eye I have a fairly high degree of short sight (myopia), and a moderate amount of astigmatism. I observed both with glasses, and also without but with a Televue Dioptrx astigmatism corrector. I also tested my level of astigmatism by using 2 different strengths of Dioptrx. My daytime astigmatism prescription is for 0.75 correction, but the 1.00 Dioptrx was clearly but not hugely better. The angle I turned the Dioptrx to made a marked difference. Although my eyesight is sharper than average, my dark-adapted pupil size is under average at only 4.5mm, meaning that I can't see as faint stars as my wife. Accurate focusing made a big difference to the amount of detail I could see. The Altair has a very good dual speed rack and pinion focusser, whilst the Opticron is also dual speed with two separate focusers. Both though required frequent small corrections as the seeing varied, perhaps more so because of the low altitude. I was surprised and somewhat disappointed that the 22mm Vixen LVW wasn't quite as sharp as either the Baader or Svbony zooms at the same magnification. It was however very comfortable to use and had a much wider field of view. On the other hand I was was pleasantly surprised at the Svbony zoom. It was as good on axis at f/6 as the Baader zoom, but not quite as good off axis and had a smaller field of view. Neither the Baader nor Svbony zooms are parfocal for me, but that may be my lack of accommodation with advancing years. I was also pleased with the sharpness of the Opticron 22x60 spotter. So for me, in last night's conditions I could see that Saturn had a ring at just over 20x magnification, despite the low altitude. Yet even with just over 120x I couldn't see Cassini's division, although Saturn was even lower then.

Orion Optics UK will probably be able to make custom 130mm tube rings for you.

I'd add that my 72mm Altair EDF came secondhand with a 180mm dovetail, but even that isn't long enough with binoviewers. Mind you, mine is an earlier model with a long 97mm drawtube so the main tube is shorter than normal, making it that much harder to balance. I see that the latest version of the scope has a 75mm drawtube so should be easier to balance, although it means less backfocus.

I'm awaiting delivery of a longer dovetail for the same reason as Stu for my 72mm on a Mount Zero. It was partly due to Stu's review (what a tongue twister!) that I bought a Mount Zero. I'm very pleased with it, so many thanks for the recommendation.

Yes, I use my Starpals with finder rings. Apologies for the bum steer, I thought these were called mini Vixens.

Wow, that's stunning! Many congratulations!

Yes, StarPal do both standard and mini Vixen dovetails with slots. It was finding the mini ones that had slots rather than holes that I struggled to find.

Starpal on AliExpress do them up to 30cms. I recently needed a shorter version and couldn't find any with slots in the right place in the UK or EU. They came within 2 weeks.

Wow!

I'd very much recommend that you actually measure your pupil size as it varies hugely from person to person, even of the same age. It's not at all difficult to do. Just stay in darkness for a couple of minutes at your observing site for your pupils to dilate; you don't need to get fully dark-adapted as that's a chemical process that occurs after your pupils have fully dilated. Then just put a ruler above your eyes and take a flash photo - the flash is so fast your pupils won't react. But do make sure that you have red-eye and pre-flash turned off if your camera has these settings. Why is pupil size important? Well, if the exit pupil of your scope is greater than your pupil size you'll be wasting some of the aperture of your scope (although the field of view is likely to be bigger). So it's a good idea to have an eyepiece that matches exit pupil and pupil size. You also need to take into account that the magnification and therefore the exit pupil will change if you use a coma corrector. For instance, a Paracorr reduces the exit pupil by 15%, an Explore Scientific coma corrector by 6%. To give an example I measured my dark-adapted pupil at 4.5 mm. I have a 10 inch f/4.8 Dob fitted with an Explore Scientific coma corrector. So the calculation is 4.5 x 4.8 x 1.06 = 22.9 mm eyepiece. As there are few 23 mm eyepieces available, plus my pupil size will almost certainly get even smaller with age I rounded this down to 22mm. Mine has a 65 deg FOV. However, I do also use a 28mm/68 deg eyepiece. This gives me a 33% wider field by diameter, 77% by area. As Pixies said, there's a limit how far you can go with a reflector though before you see the shadow of the secondary mirror. There's no such limit with a refractor.

Thanks.

Thanks, Franklin.

Many thanks! Have just checked the size with Rother Valley Optics who measured the ones they have in stock and say they'll fit. I've therefore just ordered them. Thanks again.

I've just bought a ScopeTech Mount Zero but, having queried whether it came with slow motions, it turned up without. Unfortunately, the retailer has none in stock and isn't expected to get resupplied for some time. Can you help please? I'll willingly pay you for them, alternatively make a donation to charity - my wife is an ambassador for Demelza children's hospice.

I've just bought a ScopeTech Mount Zero and wanted a carbon fibre tripod for it. This invaluable site purely lab and field tests a lot of camera tripods for stability and portability: https://thecentercolumn.com/ As a result I've just ordered a tripod from the Leofoto Ranger range. These have no centre column and so fold to a very compact size. They're now imported into Europe with 16 in the range in various weights and sizes, all but 3 having ball and socket heads in a package deal. This page on the new European Leofoto website has a chart giving the full specs: https://www.leofoto.com/products_detail.php?id=362 There are also a lot of other Leofoto ranges. I don't need a ball and socket head but do need a heavy duty tripod so went for the Leofoto LS-364C. This is a full size 4 section tripod with the top section being made from 36mm carbon fibre, but weighing only 1.77kgs/3.90lbs. It's rated to 25kgs/55lbs. Not all the Leofoto range are available in the UK, including this model. However London Camera Exchange and Wex Photographic stock many of them. I was happy to buy from an EU country and pay on PayPal so I've ordered it from Dext in Sweden for a cost of £320. It arrived within a couple of days. Go to https://www.dext.se/sv/stativ/ranger-tripod/https://www.dext.se/sv/stativ/ranger-tripod/https://www.dext.se/sv/stativ/leofoto-ls-364c-trebenstativ-i-kolfiber.html for a wide selection of Leofoto tripods.

I wouldn't be without an observing chair. AFAIC, a necessity rather than an option.

Done.

You can also use the Baader Classic Q at 1.3x I believe by unscrewing the lens and screwing it onto the filter thread of the eyepiece. How does it compare with other Barlows?