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johninderby

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Posts posted by johninderby

  1. Too bad about that. Wonder how the lack of a future GOTO upgrade will affect sales? They're still a bargain though for a dob with tracking.

    My dob (The Blue Whale) with the ServoCAT system did have an Argo Navis as well for full GOTO, but I took the AN off as I just didn't use it very much. The tracking was the main thing that made the dob so much more useable.

    John

  2. I had a Star Sky 90. Surprisingly good sharp optics with lower than average CA for an achromat. Decent mechanical build quality with a single speed rotating crayford and retractable dewshield and lightweight as well. Not up to William Optics build quality of course, but not bad. Compared to the Star Sky 90 the Skywatcher Startravel 80 and 102 do seem a bit cheap and nasty. Great bargain at that price.

    The Celestron CD80 is also a bargain and is an APO as well, and as they've been discontinued and are being dumped off cheap by Celestron right now you couldn't go far wrong at that price. The focuser is useable for now and could always be replaced by a crayford later on.

    Tough decision, but for guiding I would take the Star Sky 90 due to it's better focuser, light weight and slightly bigger aperture. For purely imaging then it would be the Celestron CD80, but the Star Sky 90 is a lot closer in performance than you would expect and cabable of doing some decent imaging.

    John

    P.S.

    I only sold the Star Sky 90 as I found a used Megrez 72 for such a low price that I just couldn't say no.

  3. 20% plus £13.00 clearing fee is about right. One thing I have noticed recently Customs seems to have tightened up their system. I import from the US for my business (not big orders but about £500.00 to £1,000.00 at a time) and absolutely NOTHING has gotten through without charges in the past 6 months. It doesn't seem to matter what shipping method is used or if just addressed to me personally.

    Don't always assume that importing is cheaper. I took a quick look and the Stellarvue SV102ED with Feather Touch is actually about £100.00 cheaper here than it is imported after paying the shipping, import duties and VAT. Work out the costs very carefully before deciding to import. Of course if it's out of stock in the UK it may be worth importing anyway.

    John

  4. Thanks, I'm really happy with it. The optics on this particular scope are better than most Astro Physics or TEC Maks.

    Had some razor sharp views of Saturn last night for about 15 minutes before the clouds moved in. The Hyperion zoom works really well with The OMC140 as 8mm to 16mm eyepieces suit the scope, and that's right in the best range of the Hyperion's zoom settings.

    On such a long focal length planetary scope that doesn't require a wide FOV and is less demanding on eyepieces the Hyperion zoom isn't that far behind the Ethos. Close enough that I don't usually bother with the Ethos. Of course in my 4.6 f/l dob it's a different story.

    John

  5. Orion Optics UK OMC140C Deluxe Carbon Tube & Feather Touch Focuser

    Strehl 0.989 1/9PV

    Received the scope a little while ago and have been making some changes to get it just the way I wanted it. I had ordered the optional top mounting plate and added a CNC machined carrying handle and an ADM dovetail saddle and an 8x50 RA finder. Also added a 2" Baader visual back and WO 2" dielectric diagonal as I wanted something more substantial to hold an Ethos or Baader zoom eyepiece. Unfortunately it was all a bit on the heavy side for using on the Alt-Az mount (modified Manfrotto 405 geared head). Removing the mounting plate, handle, ADM saddle and 8x50 finder reduced the weight by over 2kg!

    The top mounting plate had plenty of mounting holes in it that a Manfrotto QR plate could attach to so I used it instead of the dovetail bar and ADM saddle. An Orion 6x30 RA finder (better than some 8x50 finders I've used) replaced the 8x50 and I added a laser pointer and a Rigel Quikfinder. The three finders together only added about 250g. I normally use the laser pointer if no one else is around to be bothered by it, and then the RA finder, otherwise it's the Quikfinder. Cutting the weight down reduced the vibration settling time from about 5 seconds down to about 2 seconds.

    At this point I was very happy with the performance of the scope except for the focuser. It is one of the best standard Mak focusers around, but it's still single speed. I looked around at what was available in 2 speed crayfords and it seemed as if the Feather Touch was the only one that would fit. A call to Starlight Instruments determined that their small diameter "shortie" adaptor would just clear the scopes focuser knob by about 1mm and the 1" travel 2" crayford would be right for this scope. 2 1/2 weeks later the focuser arrived and lo and behold it fitted, and indeed cleared the focuser knob by about 1mm. I wouldn't have minded a less expensive focuser such as a Moonlite or Baader as they're still superb focusers, but unfortunately they didn't do anything that would clear the focuser knob. The Feather Touch is very compact and light weight as well as being the best 2" crayford you can buy.

    The scope is such a pleasure to use now. Cooldown normally takes about an hour. An added benefit of the new focuser is that it takes such a light touch with just a finger tip to use the fine focus knob that vibration while focusing is almost completely eliminated.

    John

  6. Looks like you have some very interesting mods planned. Pictures to follow maybe ?

    The OO's 14" borosilicate mirror (99 Strehl) cools down really quickly and works just fine with the standard cooling fan, and has no problem in keeping up with changes in air temperature. The mirror seems to cool evenly all over. The quality and consistency of the glass seems to make a difference.

    The Lightbridge's 16" mirror is fairly thick plate glass and takes a long, long while to cool down, even with cooling fan mods. While plate glass mirrors work fine once they've cooled down, they can struggle to keep up with changes in air temperature so modding is essential. I've since also found out that many 16" Lightbridges came with poor quality secondary mirrors, so if your Lightbridge doesn't perform as well as it should the secondary mirror could be the culprit.

    John

  7. The 5mm Nagler was my most used eyepiece, which is why I sold the 8mm Ethos and replaced it with the 6mm as I thought that it would get more use. I prefer not to use barlows, but the 1.25" one is easy to add to the 13mm Ethos and it still fits into a 2" diagonal.

    I sold some Naglers on eBay recently to pay for the Ethos eyepieces and most went to Europe where the exchange rate worked in my favour, so for selling expensive eyepieces eBay is the easy way to get into the EU market. SGL's not bad and there's always Astro Buy&Sell but it seems to have more than it's share of dodgy buyers.

    John

  8. I think that with your Paracorr the Antares 2" barlow may be more straight forward, and cheaper as well, so I think that's the way to go. As you say while the AC710 is ideal with the MPCC but there's no real advantage in using it with a Paracorr.

    Re: Scopes'n'Skies

    Although they're not my favourite astro dealer, I did order something from them on Sunday (free shipping), got a shipping confirmation email on Monday and it arrived on Tuesday. OK it was only a small purchase, but it still came as quite a shock to get fast efficient service from them. Very disconcerting.

    John

  9. Hi

    It's too long if inserted directly into the Paracorr but if you use the 1.25" to 2" adaptor then it's no problem as there is plenty of room, as in this photo with the AC710 and 1.25" adaptor. Not sure about the correct setting but Televue says that a 1.25" barlow will work when used with the 1.25" adaptor and don't give a different setting.

    John

  10. One point to keep in mind if dealing with a modern commercially made dob/newt such as a SkyWatcher, is that the offset is already built in. They fasten/glue the secondary onto the holder offset by the correct amount, so if you try to add offset by adjusting the position of the secondary holder you've going to end up with double the correct offset.

    To make sure you'd have to remove the secondary and check to see if the mirror is already offset.

    John

  11. The MPCC is really only needed with the 13mm, but helps a bit with 13mm +1.5 = 8.6mm. The 6mm doesn't need it.

    Televue recommends putting a 2" barlow into the focuser first, but as the Antares is very short it will fit into the Paracorr when the tuneable top is set to the correct setting, but I think it can just contact the Parcorr lens if turned all the way down so you have to be careful.

    That's correct. With the Baader fine tuning rings on the 2" barrel, which are needed anyway to set the MPCC at the correct distance from the eyepiece, there's enough room to fit the 1.25" barlow element in-between the eyepiece and the MPCC. Very neat and compact.

    John

  12. Hi

    I would put the AC710 as being tied with the Televue 1.25" barlow, which means it's about as good as it gets in barlows. If only Televue had made the barlow element removable. The problem with the AC710's clamping ring is that it won't work at all with the William Optics type tapered barrels. It can't clamp tight enough to contact the tapered part of the barrel, which means you'd have to pull the eyepiece half way out so that the clamp would be on the straight part of the barrel. Works fine with standard eyepiece barrels though.

    I had the 8mm Ethos as well as the 13mm but sold the 8mm (for nearly what I paid for it) and got the new 6mm Ethos. With the 1.5x it now gives me 4mm, 6mm, 8.6mm and 13mm and if I use the little 1.25" barrel extension on the 6mm there's 3mm as well which pretty well covers things at the higher powers.

    John

    P.S.

    All you need now is a foot thick reinforced concrete pad to put the scope on with the Ethos, 2" barlow and Paracorr and your all set.

  13. Hi

    I have one of the AC555 Magni-Max and have tried it and actually it's not too bad for a simple doublet achro barlow, better than expected and a bargain at that price. It would hit the lens in the Paracorr, although you could probably use a Parfocal ring (or two) on the Ethos as a spacer to give enough clearance. With a bit of careful measuring perhaps?

    The AC710 APO barlow is a bit more expensive than a Televue barlow (and I can't tell any difference in performance) but has the advantage of the removable barlow element. I haven't had chance to really test it properly yet but it is noticeably brighter and sharper than the Magni-Max which you'd expect at the price difference.

    John

  14. Hi

    I had the 13m Ethos - Antares 1.6x 2" Barlow - Visual Paracorr combination and found that while it worked it was just too long and awkward and more importantly HEAVY !

    I sold the Antares 2" barlow and Parracorr and now use the AE AC710 1.25" Supreme 2x APO photovisual barlow as the barlow element can be unscrewed and put on any eyepiece making it a 1.5x barlow. Also bought the Baader MPCC. The new combination fits right into the focuser and more importantly hardly weighs any more than the Ethos on it's own, so I don't have to rebalance the dob.

    The Antares 2" barlow does work very well, but is not as good as the AE 1.25" barlow so I'm actually gaining in performance. The Paracorr and MPCC are equal in performance. The Badder 28mm and 14mm fine-tuning rings put the MPCC at the correct distance from the eyepiece and still gives enough clearance to use the 1.25" barlow element. This combination is also right for the 6mm and 8mm Ethos. The new combination actually saves over one pound in weight !

    I also bought a Mogg 0.3x 1.25" Extension Tube as this can be used in-between the 1.25" barlow element and the eyepiece to make it a 2x barlow, although the MPCC won't fit as well of course.

    Unfortunately both the Antares 1.6x 2" barlow and AC710 1.25" Supreme 2x APO are only available from Scopes'n'Skies, not my favourite astro dealer but there seems to be no other choice.

    I'm very happy :) with the combination now.

    John

  15. I've got an OO 14" dob as well.

    It doesn't actually take much airflow to cool the mirror down, and in fact too much airflow doesn't work that well. If the cooling air moves too fast it doesn't have time to pick up heat from the back of the mirror. Hence the small size of the fan that OO fits.

    Yes some of the Americans do go to crazy lengths to cool their mirrors down. Still I suppose it gives them something to do when it's cloudy :)

    John

  16. Yes it won't do much unless it is blowing on the back of the mirror. Dust doesn't seem to be a problem, but if you're concerned buy a fan filter which is only a pound or two (PC case fan filter) and stick it over the fan.

    While the main point of a fan is to cool down the mirror quicker it can also be left running while observing if the air temperature is dropping faster than the mirror is cooling. So long as it doesn't cause vibration.

    One thing that is becoming more popular in the US now with larger mirrors is to have two small fans in the side of the tube that blow across the mirror's surface while observing. Apparently it keeps the air just above the mirror's surface mixed and stops a thermal boundary layer from forming that can cause distortion. Another approach is to suspend a fan just above the front of the mirror that blows down into the centre and again stops a thermal layer from forming. A bit tricky as you have to line up the supporting wires with the secondary vanes to prevent additional diffraction spikes.

    Hope I haven't confused you but there are a lot of ways to use a fan on a dob or newt.

    John

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