Takahashi Epsilon 130D Hyperbolic Newtonian Astrograph

[Ikonnikov]

So after a lot of musing I splashed out on a Tak E130D in April and this is an account of my reasoning behind buying the scope and associated problems/solutions in getting it set up for imaging….

Rationale for choosing the mini ‘nana

After a couple of years imaging with a celestron C8 plus hyperstar III adapter I was keen to try out a higher quality scope. I could produce subs up to about 10 minutes without much of a problem but the inherent sharpness of the HS system was not particularly great (although it was improved somewhat by using an aperture mask to slow things down to F2.66). Also beyond 10 minutes, mirror flop seemed to cause problems and the collimation was not always totally stable (though not too terrible). The extremely fast F ratio was great for speed of data collection but it did mean that narrower bandwidth narrowband filters weren’t really an option due to light loss from centre wavelength shift at these focal ratios and that the depth of critical focus at this speed was wafer thin.

So the main requirements for my new scope were improved  image sharpness, fixed mirror/objective system to allow longer exposures without ‘flop’, similar focal length (400-500mm) and and fastish f-ratio plus good mechanical stability to hold collimation/ focus etc well.  I also didn’t want something too large as my HEQ-5 was working well (set up on a concrete-mounted pier) and I didn’t want to have to upgrade this too. Budget was flexible but not more than £2.5K for everything.

I narrowed it down to two similarly priced Taks; either the FSQ-85 Petzval apo refractor or the newer Epsilon 130D hyperbolic Newtonian astrograph. In the end what made me (maybe somewhat controversially) go for the latter choice were two things; significantly greater aperture/faster F3.3 native focal ratio (similar to what I had been used to with the Hyperstar) and its relative rarity/novelty.

I had read a pretty positive review of the E130D in S&T which praised its excellent optics and sturdy construction and the original E130 seems to have been highly regarded, so it wasn’t a major gamble. And it was still after all a Tak.  The FSQ85 seems to be pretty fantastic and there are many superb images made using it but the (relative) novelty of the E130D appealed to me and also it would allow me to continue imaging at a speed and image scale I was happy with. Published spot diagrams seem to show similar sharpness of both scopes though the E130D might have the advantage at the edge of its (slightly larger) image circle, but the lack of central obstruction in the frac would be advantageous for image contrast. And of course there was the diffraction spikes and square star issues with the thick spider vanes of the E130D. However I am primarily interested in using the scope for narrowband imaging and star sizes/spikes through NB filters are considerably smaller and generally acceptable to my eye at least.

So in April I parted with my dosh and in fairly short order the gleaming yellow ‘nana (christened by my partner for somewhat obscure reasons as ‘Betsy’; the name has stuck) arrived courtesy of Nick at Trutek, triple boxed and complete with Tak scope rings, collimating tube/eyepiece and MEF3 microfocuser.

Getting to Know 'Betsy'

My first issue was how to mount the little beast; the scope rings were very substantial with M12 mounting bolts/holes which were too widely spaced for the Geoptik losmandy plate I had purchased. So I have ended up mounting the rings ‘upside-down’ using the smaller bolts/holes intended for mounting the guide-scope/accessory bar on the top of the scope. This is still very robust and just means that the knobs for tightening the scope rings point downward instead of upward. Also since (for balancing reasons) I keep the main CCD camera pointed upwards along the dec axis, I can’t put a guidescope on the top of the OTA anyway.  This is instead now underslung at the front of the losmandy plate.

Issue 2 was the biggie, collimation! ‘Your Takahashi scope will arrive factory collimated….’ etc etc…. If only I’d trusted the manual. Being a newt newbie I wasn’t really up on the intricacies of collimation. However I popped the Tak collimating tube/eyepiece in and things looked pretty good, everything was central etc although I noticed a couple of issues; rotating the eyepiece with the camera rotator threw everything out so I locked this down in a fixed position (something E180 owners appear to consider necessary). Also things shifted around when the scope was slewed especially near horizontal; it turned out that the primary was really quite loose in its cell and the side grub screws that hold it in place were very loose so I very carefully tightened these up trying not to impart any undue pressure on the mirror to avoid pinching. The main mirror clips were sufficiently loose and left well alone.

Next I popped my CCD plus filter drawer on and a few spacer rings to ger the chip to corrector distance right and took a few pics. So far so good, nice image sharpness (way better than the hyperstar, Nebulosity HFR focusing values below 1 on a good night with L filter compared with ~1.4 for the HS). However not perfect; the stars in two corners weren’t quite right (slightly elongated and out of focus). Assuming the CCD and filter drawer to be pretty orthogonal I though this must be a collimation issue; it just needed a tweak… Well I got things as good as I could by eye with the Tak gear but images were still not quite right so I purchased a Hotech laser collimator and used this to collimate primary and secondary mirrors; big mistake! Maybe it works fine for both mirrors in F5 dobs but in my little F3.3 the primary/secondary positions ended up being way out and the whole image became a mess.

I tried collimating with an artificial and real stars, but with the large secondary offset in this system, out of focus star images don’t show concentric circles even when collimation is bang on (I learned the hard way) so this method was unsuccessful.

After more reading around it seemed that fast newt users swore by Catseye autocollimator systems to get things as close as possible. So the next challenge was to hook up a 2” eyepiece holder in the focuser at the right distance from the secondary to insert a Catseye autocollimator (the wide t-mount focuser comes with only a 1.25” eyepiece holder adapter).  So after more research I discovered mention of Precise Parts in these forums who produced a costly but excellently crafted E130D focuser to SCT male fitting that allowed me to attach my Baader clicklock 2” adapter purchased for my C8. However, the adapter placed the autocollimator too close to the secondary so I then needed to order an SCT threaded extender tube (from Agena Astro also in the US). The wait for all these parts (including the Catseye) took several months but thankfully this was over spring/early summer when astronomical night had disappeared. In this time I also invested in a camera titling unit and a manual filterwheel to fit in the optical path.

Once I had everything in place (and had stuck the catseye hotspot on the primary) it was fairly easy to get good stable collimation using the catseye XLKP autocollimator in conjunction with the tak collimating tube/eyepiece. However the next issue when imaging was a heavy dose of astigmatism across the whole field which I couldn’t remove with any amount of camera tilting.  Turned out that the new filter wheel connections tilted the filters in the light path and the astigmatism problem disappeared when I went back to the filter drawer system. This just left a tiny bit of coma/defocus in the corners which I have essentially ironed out by fine tuning tilt and camera spacing.

Betsy ready for imaging (but defiled with horrible insulating tape for alignment and balancing purposes!)

What Next?

My setup is now giving pretty tight stars across the whole field in short exposures. However longer exposures (1200s) are showing star elongation and 1800s are a total mess. I suspect the cause of this is the mount and I am working on this (belt mod in progress plus considering pec prep usage and sorting out drift alignment instead of Alignmaster). Not sure I can afford an Avalon but would be nice…

IC 5067, 12x1200s Ha subs showing elongated stars

I’m currently using the Baader high speed F2 narrowband filters from my hyperstar days which are recommended from F2-F3.5 but they do not give the best contrast and at F3.3 the 5nm or even 3nm Astrodons should work pretty well.  I’m not sure which ones to plump for as it seems around this speed most people stick with the 5nm but are they just being too cautious? I would really appreciate the reduced star sizes and diffraction spikes the 3nm affords but don't want to lose too much signal.

It would also be nice to have an automated focuser and filterwheel but I am going to try and get some decent images with my current setup (maybe plus some Astrodons) before worrying too much about either of these.

The 44mm image circle would illuminate a lot bigger chips than my ICX814; there’s always the 8300 series cameras to consider although I would lose some of the resolution I enjoy with the Atik 490 and risk squarer stars…

Brief Summary

Overall I am very happy with my little Epsilon; now I have the Catseye and am at stage where I can competently collimate the scope my main gripe is the camera rotator which can’t be used without destroying collimation. The looseness of the primary when I first got the scope was a bit annoying but it seems to be fine after adjustment without obvious mirror pinching. And I guess Takahashi should really provide the hardware to accurately collimate the scope themselves. However the plus points greatly outweigh the negatives;  the optics are excellent, the build quality is superb with very robust and precise collimation adjustment, solid high capacity focuser that shows no sign of creep, little evidence of temperature induced focus shift, and the finish is beautiful (if a little ostentatious!). Once my mount is sorted I just need some more clear nights, the usual story!

Paul

[Chris]

Great write up, I'm sure this info will be very valuable to future E130D owners. What a roller coaster ride you've been on with it, glad it's pretty close to being sorted now

I like the banana yellow, it makes it instantly recognisable

[Ikonnikov]

Thanks Chris, hope it is of some use to others. Intend to post an update or two when I have a few more images under my belt.

[sharkmelley]

Great review and very fair.  I'm a very happy Tak Epsilon 180ED owner.  I use Tak's own collimation eyepiece - it's a variation on a Cheshire eyepiece and screws into position very solidly.  I assume they have one for the 130ED?

The good news is that once collimated, it holds collimation because it is so solidly built.  I've driven it to the South of France, to Kelling Heath and to other dark sky sites, all without need for re-collimation.  I've even removed the primary mirror for cleaning and it goes back into position still collimated.

I sure you'll love the scope!

Mark

[Ikonnikov]

Great review and very fair.  I'm a very happy Tak Epsilon 180ED owner.  I use Tak's own collimation eyepiece - it's a variation on a Cheshire eyepiece and screws into position very solidly.  I assume they have one for the 130ED?

The good news is that once collimated, it holds collimation because it is so solidly built.  I've driven it to the South of France, to Kelling Heath and to other dark sky sites, all without need for re-collimation.  I've even removed the primary mirror for cleaning and it goes back into position still collimated.

I sure you'll love the scope!

Mark

Yes, maybe I'm being a little unfair to Takahashi, I do have the their collimation tube/eyepiece and it does get the things pretty close; it's likely that incorrect CCD sensor spacing & tilt were the main reason I wasn't getting a good flat field when collimating with them. The Catseye I used subsequently is reassuring to get the collimation bang on although it remains to be seen whether that degree of accuracy is essential for good images if sensor tilt/spacing are right (but it doesn't hurt!).

Paul

[laudropb]

Very nicely written report. A joy to read. Thanks for posting.

[ollypenrice]

A truly superb report. I read it with some relief, having taken the 'other' path (FSQ) which is the coward's alternative! I think you have to be up for one of these scopes and shouldn't buy one if you're not. In my situation I'm too nervous about lost time with people waiting, though perhaps I'm overy concerned about that. But then, if you are up for an Epsilon, you get a truly mighty instument. And with UK weather the speed has to be a big bonus.

Trivia corner: I actually like the 'nana colour and I like Tak Hospital Green as well. However, I'm not too sure about the two together...

 lly

[mftoet]

Thanks for the review, sums it all up. Another happy Epsilon-180 owner over here. Having owned an FSQ-106ED, I wouldn't trade back for one. Mainly because yellow happens to be my favourite colour. ;-)

Though perfect collimation is difficult to achieve, I agree with Mark the Epsilons hold their collimation very well. A friend of mine owns an Epsilon-160 from the Nineties. Has been in perfect collimation ever since. The light gathering power of these instruments is amazing!

[Ikonnikov]

Thanks for the positive comments, I was afraid I had rambled on for a bit too long!

A truly superb report. I read it with some relief, having taken the 'other' path (FSQ) which is the coward's alternative! I think you have to be up for one of these scopes and shouldn't buy one if you're not. In my situation I'm too nervous about lost time with people waiting, though perhaps I'm overy concerned about that. But then, if you are up for an Epsilon, you get a truly mighty instument. And with UK weather the speed has to be a big bonus.

Trivia corner: I actually like the 'nana colour and I like Tak Hospital Green as well. However, I'm not too sure about the two together...

 lly

Yes, the Takahashi-Green rings, yellow scope, orange losmandy plate and red camera make for an 'interesting' combination of colours. Maybe a purple mount would create some kind of Fauvist masterpiece...

[dodi]

Nice report, but I do not think the bolts for the Tak rings are M12. They are M8. Smaller, but still no easy fit for most dovetails, let alone Vixen ones. I will use riser blocks on my Epsilon, which just arrived.

Dodi

[Ikonnikov]

Nice report, but I do not think the bolts for the Tak rings are M12. They are M8. Smaller, but still no easy fit for most dovetails, let alone Vixen ones. I will use riser blocks on my Epsilon, which just arrived.

Dodi

Indeed you are right the main mounting bolts are M8, my mistake. The (large) spacing between is the main problem for me though!

[NickK]

Firstly, let me get this over with --- drool.

Nice report If I was in the market for a new scope I'd be seriously tempted by the mini banana having seen one at Astrofest. Maybe.. some day... in the distant future.

[nicks90]

firstly let me say thats an insane piece of equipment and it must feel great to own something as precious as that. But i dont like the colour - reminds me of cheapy Konus telescopes.........

[ollypenrice]

Firstly, let me get this over with --- drool.

Nice report If I was in the market for a new scope I'd be seriously tempted by the mini banana having seen one at Astrofest. Maybe.. some day... in the distant future.

Time is an illusion. So is the idea that you won't buy one...

lly

[Michael36]

diffraction spikes i just cant do it captain

[ollypenrice]

diffraction spikes i just cant do it captain

No, nor can I on widefield. But some people like them.

Olly

[Ikonnikov]

Well I'll see what kind of spikes I get with the 3nm Astrodon NB filters soon...

[sharkmelley]

As I understand it 3nm filters have far too narrow a pass band for an F/2.8 scope.  There will be a frequency shift for the wider angles of incidence which means that H-alpha will actually be cut.

Mark

[Ikonnikov]

The little E130D is F3.3 so I'm hoping I'll scrape through by the skin of my teeth... On the Astrodon website they seem to think that 3nm is usable down to F3 (although the test scope is an E-180 which is actually F2.8) http://www.astrodon.com/uploads/3/6/0/7/3607549/astrodonnarrowbandfaq.pdf

[Ikonnikov]

Update: October 2015

Following on from my first post I have made a number of alterations to my setup to improve things, the main issue being lack of round stars and a generally sharp image after 30 minute subs which I am aiming to use for my narrow-band images.

Mount:

First thing was to get my HEQ5 up to scratch. This seems to have gone quite well; the backlash and tracking were improved considerably by tightening the belts that I had recently installed and I also improved my polar alignment using the automated drift alignment function of PHD2. Thankfully the alignment seems to hold reasonably well after removing and re-attaching the OTA to my pier (being sans observatory). These improvements seemed to improve tightness of stars in my images but I still noticed an asymmetric shape to all the bright stars that looked like a result of pinched optics.

Primary mirror adjustment:

This indeed proved to be the cause as I had very slightly over tightened the primary mirror side screws in an attempt to stop the primary mirror movement I noted above. Turns out those guys at Takahashi knew what they were doing when they shipped the scope with a slight amount of movement in the primary! I now have the mirror in a state where it is no longer pinched but still retains collimation when the scope is slewed around the sky. However there is a proviso to this which is that below about 30 degrees elevation the primary starts to tilt slightly and collimation/focus begin to drift. This is a bit of a pain but obviously the great majority of the time I would want to image objects above this elevation.

Off axis Guider:

To prevent any small movements of the primary causing issues in imaging and to achieve a more compact set-up I decided to switch to an off axis guider. This also seemed like a good idea since the scope has a large image circle with plenty of space for an OAG prism, it obviously provides appropriate focal length for accurate guiding and is also very fast so should be easy to find a bright guide star. This has proved to be the case and I am getting very good snr for guiding with my asi120mm (typically 30-60 in PHD2, considerably better than with my finder-guider) and gives a significantly lower RMS guiding error than the previous set-up. What proved tricky was the incorporation of the OAG into the imaging train with the limited back-focus of the corrector (56mm). I managed to fit the TS ultra short OAG into the set-up even though with T2 adapter it took up 14mm of back focus (a lot more than the quoted 9mm thickness of the main OAG body) but couldn't also fit the titling unit I was using in addition to the filter drawer and the corrector-to-t-thread adapter. Since the tilting unit has proved vital to get flat images at F3.3 I had to make another (much more expensive!) change, a new camera...

CCD upgrade:

The only way I could figure out how to get everything into 56mm was to use a Starlight Xpress Trius camera that has the titling unit built in to the front of the camera body (total back focus= 17mm instead of 13mm for the Atik camera body plus 10mm for t2 camera tilting unit. Thankfully I managed to sell my Atik for a good price second hand to cover a large part of the cost. I decided to go for the ICX694 version of the Trius as this gave me a slightly faster setup (2.2 versus 1.8 arc seconds per pixel and also lower noise and higher QE chip)  and also gave the option of ~1.1 arc seconds per pixel (just above the maximum res of the scope) if using 2x drizzle integration in PixInsight. The Trius is performing very well (maybe there's scope for a separate review if I have the time) it seems to be noticeably cleaner than the Atik 490EX and with its better cooling I can run it at -20C (inside and out) which seems to hep for very long subs. Getting the CCD spacing and tilt right took quite a lot of time but it is essentially correct now with small tight star across the whole chip. There does however appear to be some slight distortion of stars at the edges which becomes more noticeable when drizzle integration is used to increase resolution so at some stage I will probably have another go at fine-tuning tilt and collimation. But for now I just want to get more images at native resolution.

Picture of current camera setup

Filter upgrades:

I have bitten the bullet and gone for the 3nm Astrodon Ha and OIII filters to replace my Baader F/2 versions. This post http://blog.astrofotky.cz/pavelpech/?p=207 plus the Astrodon literature tipped me over the edge (though I'm not sure if I'd have made the same choice if I had the E180ED at F2.8). The contrast with this filters is clearly superior to every other filter I've tried and stars are smaller although the overall signal strength seems somewhat weaker. Initially I had my IDAS filter in line with the 3nm Ha and this plus a hazy night gave pretty faint subs.  However removing the IDAS plus better sky conditions seem to have given much brighter images. Below is a link to an  image comprising 20x 30min subs on NGC281, (a fainter target than I had remembered and one I am finding quite hard to work with!) quickly processed with image calibration, mild de-convolution and stretching then some local histogram equalization and curves.

http://www.astrobin.com/full/220217/0/?real=&mod=

Here is a comparison from a crop of the same region of NGC281 imaged with my old C8 hyperstar setup (F2.66 for 5h, 30 x 10 min subs with Atik 428EX) with 12nm Ha filter) and with my current E130D setup (F3.3, 10h, 20x 30 min subs with 3nm Ha filter and Trius 694) with only basic image calibration and auto STF stretches in PI. Both images have identical pixel scale and CCD QE and both scopes were carefully focused using minimum FWHM method in Nebulosity (hyperstar using JMI motofocus and epsilon by hand).

C8-Hyperstar

E130D

Now I just have to learn how to squeeze the most out of the data without making a mess of it (plus a few clear nights for some OIII in the near future wouldn't hurt)!