First Light Report: Takahashi Epsilon 180 ED

[fatwoul]

What follows is my first First Light Report, covering the initial trials of my newly-acquired Takahashi Epsilon 180. Credit is due to many people for their help, but any mistakes are my own.

Please be gentle!

Background

Having had an MN190 for a couple of years, I found myself at a point that others such as Catatonia have found themselves: As an urban astrophotographer, in my case limited almost always to narrowband imaging, I craved something faster than the mak-newt's f/5.3. I considered the Quattros and their ilk, which at f/4 are photographically almost twice as fast as the MN190.

However, all I could think about was all the time I'd spend gathering light, and pretty soon I decided my next scope had to be one of the "supernewts" - those small collection of newtonians that, through various constructions, offer f/2.8

Initially, the choice seemed obvious - the Boren-Simon 8"/2.8 was being raved about in reviews (Sky & Telescope), and was well within my price bracket. However, as my research continued, things, like a British sky during a Venus Transit, became more cloudy.

As I understand it, the Teleskop Express/Service variant of the Boren Simon is based on a GSO mirror cell. I've read enough reports from GSO owners to know that those scopes sometimes have issues with floppy/rattly primary mirrors, and it was enough to make me nervous. Since then, I have indeed read of a couple of the TS supernewts having this issue, and whilst it has been easily fixed by the owner every time, I didn't feel brave enough to take on that added challenge, nor the installation of the secondary (TS supernewts are supplied with the secondary removed, for safer transit).

Bern at Modern Astronomy was very generous with his time, and actually called me to talk about my concerns, and to suggest alternatives, such as a Quattro/ASA corrector combination. He's a very helpful chap, as others on here have observed, and I hope I can do business with him in the future (probably on a mesu 200!)

During my research, I kept arriving at reviews of Takahashi Epsilons. Way out of my price range, but still interesting to read, they did seem to tick all the boxes in terms of what I needed. The more I read, I decided I should save for as long as it took, and get one of them. The MN190 hasn't failed me yet, and would keep me going in the meantime, albeit more slowly.

Idly, I PM'd a couple of Epsilon-180 owners here on SGL. The first reply I had was from a member who, whilst happy with the scope had become involved with spectroscopy, for which the E-180 was unsuitable. He offered it to me for a very reasonable price, and before I knew it, we'd agreed to do the deal a few weeks later, when I finally had the money! Discretion prevents me from naming this SGLer - I don't wish to embarrass him with my gushing praise - but I couldn't hope to have met a nicer, more genuine guy. He was patient with my questions, and even personally delivered the telescope considerable distance for merely the cost of petrol. Thank you!

Unboxing

I'm not one for unboxing photos, but the telescope arrived in fantastic condition, and had obviously come from a very careful previous owner. Included in the original triple box (for the uninitiated, Taks come inside a Russian Doll of three cardboard boxed with polystyrene spacers between each one. All the original documentation, the collimation eyepiece and tools came with it. It didn't come with any of the fancy extras like the matching yellow finderscope (I'm using finder-guiders) or "official" tube rings, but a set of black Skywatcher rings (corked to reduce their size a little) were kindly thrown in so I could get started straight away. I was also given an E-180-specific Bahtinov, which has proved very useful. Lastly, I as provided with two "Wide T Mount" threaded tubes, one of which has already been turned into a nice little adjustable-length adapter for attaching my camera/filterwheel.

Setup

Mounting the telescope was straightforward. Initially, I used the tube rings provided with the E-180. However, due to the limited (and intolerant) backfocus of the scope, I was no longer able to use my Atik OAG. The short focal length of the E-180 allowed me to try using a finderguider with an Atik Titan as the guide camera. The Titan is, to be honest, a little wasted in this role, but it is such a fast sensor that finding a guide star is very easy.

I've always had trouble with telescope balance, and was daunted by the prospect of having the finderguider hanging off the side of the OTA on the finderscope mount. Instead, I decided to undersling the findeeguider, in order to keep everything as symmetrical as possible. To avoid collision with the mount, it was necessary to project the finderguider forward of the OTA by a few inches. To do this, I cut an 8mm aluminium bar to a suitable length, and put it between the OTA and its dovetail:

The bolts used to attach it have a different thread to the provided tube rings, so I used a set of white Skywatcher 235mm tube rings, which were already retapped. With a couple of layers of corking, they fit perfectly.

Initially I was using the rightangle finder from my MN190 as the finderguider, but have since replaced this with an Altair Astro 10x60 finder guider:

This is a very nice little instrument, mounted more solidly than the Skywatcher finder, and much faster. Combined with the Titan, I rarely need to use the finderguider's adjustment screws, as a sufficiently bright star is always in the field of view.

Collimation

What's that?!

Having taken a long time to learn how to collimate my MN190 (with more than a little help from AndyUK and others), I felt I was ready to at least attempt to collimate a faster Newtonian. However, I have yet to try it...because so far, I haven't needed to. I had read articles that described E-180s as bomb-proof, and that one of the reasons they suit mobile set-up is because they hold their collimation well, but I assumed this was an exaggeration; that perhaps they were just a bit more stable than other f/2.8s. It isn't. I used the Takahashi collimating eyepiece when I first mounted the telescope, and nothing had budged. The scope has since been in and out of my observatory a couple of times as I reconfigured things, and I have yet to even open the packet of collimation tools.

Another E-180 owner I have spoken to claims his is so accurately made that he can actually dismantle it, clean it, put it back together, and it still doesn't always need collimating...!

Focussing

After my first imaging session, it was clear that, whilst focussing with a 1:1 focuser was possible, it meant I was racking back and forth a lot, as I kept overshooting focus. I'm used to Crayfords, so I ordered the 7:1 Micro-Edge Focuser (MEF-3) from Greenwitch. It took about five minutes to fit, and has been a big help.

As I mentioned, focussing is done using a Bahtinov mask. During the first imaging sessions, I routinely checked focus every 1-2 hours throughout the night, but after it became clear that focus wasn't changing. During a subsequent session, I forgot to check focus at all (!), but was delighted to find that the images were still useable.

So both collimation and focus are very stable. That will make things easier.

Vignetting & Internal Reflection

As mentioned earlier, I am currently running the filterwheel with 1.25" filters. On the MN190 with an Atik 314L+, these filters were plenty big enough, but when I moved up to the Atik 4000, a distinct vignette became clear. Vignetting was, therefore, inevitable with the much faster E-180 (due to its higher-angle light cone).

Flat frames were capable of eliminating the vignette on the MN190, but are struggling to do their job with the E-180. It's just asking too much.

The question is whether I need to go all the way to 2 inch filters, or whether 36mm unmounted filters will be sufficient. Not only would 36mm be much cheaper, it would also allow me to accommodate seven filters in my filterwheel. This would permit me to continue operating both narrowband and RGB in one carousel (HA, OIII, SII, L, R, G, . Using 2" filters would accommodate only five filters, so I'd have to drop RGB (I don't use them often - who can within 2 miles of a city centre? But it's nice to have the option!)

To help me decide, I examined the flat frames under each filter, having stretched their histograms so exaggerate the vignette:

The flats were taken using a Gerd Neumann Flat Panel. Most of the vignettes are comparable, but SII exhibits something peculiar on one side only, where it seems to have some kind of anti-vignette where the edge of the image actually gets brighter. I don't have an explanation for this, but I wonder if it is caused by some kind of internal reflection. Suggestions are welcome.

Field Flatness and Back Focus

This is where I fall completely out of my comfort zone. Until recently I was using a telescope with its corrector at the front, and imaging with a 285 sensor. As such, field flatness was relatively straightforward, and fairly robust.

Now, I'm operating a telescope with a 2-element corrector in the focusser, and a sensor with over three times the area...and have absolutely no idea how to interpret the pretty pictures CCDInspector gives me:

The plain itself looks pretty flat to me, certainly compared to others I've seen. But a curvature of 17.5% is much higher than the tolerable maximum of 10-12% I've read elsewhere.

I knew that I had 56mm of backfocus to play with on the E-180, with a tolerance of less than 1mm. I did a lot of research (= pestering) before the scope arrived, and tried to determine as much backfocus information as possible about the EFW2 filterwheel and Atik 4000 camera. Unfortunately, vagueness persisted in many of this information, so I decided that a variable adapter would offer the best solution, at least until I established the correct distance by trial and error:

Here's a set of images of Deneb, with the star positioned dead-centre, and to the far corners of the sensor.

I suspect the fainter stars around Deneb, and the other images I've taken will actually reveal more about the flatness than Deneb itself. I'm not sure why the top-right corner image has additional diffraction effects. I have also noticed a peculiar effect on the stars in one corner of the field, when I imaged the Cocoon Nebula (excuse the large image):

In the bottom-left corner, several of the stars have tails. I wonder if this is not a field flatness effect, but rather an effect of the 1.25" filters causing diffraction along their edge? I'd welcome opinions, but I don't think I should start working on the field flatness until I have reduced the vignette caused by the small filters.

Diffraction Spikes

I know before I got the E-180, I said that diffraction spikes don't bother me. I remember all the exciting David Malin images I saw when I was a kid, so much so that I associate spikes with that excitement. Out of morbid curiosity, I wondered just how prominent they would be in use (rather than just on isolated stars like Deneb). So at the end of a session, I swung the scope to M45 and rattled off twenty minutes' worth of exposures:

Yes, the spikes and halos are sizeable, but look at all that nebulosity in just 1200 seconds! It took me the best part of a week to produce this (incomplete) mosaic last year:

OK, so it's a little smoother, but come on! 20 minutes!

Which leads me to the last bit...

Field of View

The second most exciting thing about this telescope (after the crazy rate at which it gathers photons) is the field of view its 500mm focal length offers with the Atik 4000:

This is a hurried comparison between the field of views of the MN190 with Atik 314L+ (smallest frame), MN190 with Atik 4000 (larger square frame) and E-180 with Atik 4000 (whole image frame).

Although I love being able to cover huge sections of sky, so far this has been a double-edged sword. Mosaics may prove to be a thing of the past for me, and I can finally tackle much larger objects, but I now have to alter my mindset: the sort of objects I'm used to looking for in catalogues, and used to imaging, will often disappear in this field of view. Of course, I do also like objects to have some space around them, and even fairly small things like M27 seem to sit quite nicely in the frame:

Sky gradients might also prove a challenge now, but probably only if I start doing more RGB imaging.

Conclusions

Before it arrived, I expected the Epsilon-180 to be the same sort of challenging telescope as the other f/2.8s. It isn't. With a telescope this well engineered, I would go as far as to say it is actually easier to work with than my MN190. Whether this is because I am now more experienced now as a result of the Mak-Newt I don't know, but I can say that so far this telescope has been an absolute delight to use, and that I haven't had this much fun or such a sense of excitment since I first became interested in astrophotography about a decade ago.

[nightvision]

Great review.

[fatwoul]

Thanks Tony. I was dead nervous about posting it, considering all the knowledgeable peeps around here!

[fatwoul]

For those interested, I've just posted the results of my First Light Week with this setup:

http://stargazerslounge.com/topic/158013-hubble-palette-ngc6960/

http://stargazerslounge.com/topic/158015-hubble-palette-ngc281/

http://stargazerslounge.com/topic/158016-hubble-palette-ic5070/

http://stargazerslounge.com/topic/158019-hubble-palette-ic1805/

[nightvision]

I was thinking, couldn't you also try the Titan on the 180 for some close up images? I think the Sony sensor is more sensitive than the 4000 so you could do some dim objects even quicker, quasar hunting from the suburbs!!

[nightvision]

For those interested, I've just posted the results of my First Light Week with this setup:

http://stargazerslou...alette-ngc6960/

http://stargazerslou...palette-ngc281/

http://stargazerslou...palette-ic5070/

http://stargazerslou...palette-ic1805/

They're impressive!

[fatwoul]

That's true, Tony. I'll give the Titan a go at some point and see what I get. I dunno about quasars, but it has certainly proved its worth as a comet camera in the past, and might be good for asteroid hunting.

EDIT: Oh, and glad you like the pics, too!

[Ibbo!]

A very comprehensive review which I like you obviously like your new baby

also the images are very very good

[NickK]

Banana scope

[Zul]

Great review! Congrats with new tube

[AndyUK]

A very professional and informative review Robin, and those images aren't exactly too shabby either! Excellent job... and obviously a LOT more to come from the Epsilon!

[Auntystatic]

I agree with Andy, great review. Some very impressive pictures there too, but a bit of a pink cast on the stars in the images. If these are just from quick imaging sessions I can not wait to see what comes out of a dedicated run :grin:

[fatwoul]

Thanks, all. I can breathe a sigh of relief that I didn't come across as a complete idiot in the report.

Dani - yes, the pink stars, particularly in the Pacman image. That's mostly an effect of using Hubble Palette; I'll post some HSO and HOO palette versions in the corresponding threads for a comparison.

[AndyUK]

You should be able to minimise those magenta stars by:

a) using Filter/Noise/Reduce Noise and setting the Reduce Colour Noise slider to 100%

b ) Opening a Hue/Saturation layer, selecting magenta from the drop down list and then pulling the saturation down

(If you're looking at doing other versions, don't forget to try out an Ha, synthetic green, OIII version - It doesn't work for all NB images, but some look great!)

[fatwoul]

Thanks, Andy, that's a good tip. I'll give it a bash when I get home.

[Gina]

Excellent review - I really enjoyed reading it - thank you for writing and posting it

[laser_jock99]

Thankyou for this interesting review, sounds like a great scope but way over my budget.

Interestingly your research on fast imaging Newtonians sort of led you where I'm going though- the ASA Keller 'Supernewt' route.

[SamAndrew]

Great first light report. A very interesting scope.

I had also been considering a Supernewt and was also put off by the GSO underpinnings on such a fast scope, so I've opted for the ASA/Quattro combo after speaking to Bern at Modern Astronomy too.

Initial tests are very encouraging, and I hope to have some results to share within the next few weeks if we get a clear night

[fatwoul]

Thanks again for the kind words, all.

SamAndrew - I'm really glad someone is giving that combination a go. That was actually the combo Bern talked to me about, but I didn't want to give too much away in case he was keeping it quiet until the testing is complete. Bern definitely seems to know his stuff, so I'm sure you've got a winning double-act there.

[russ.will]

I dabbled in imaging, before realising that with my lifestyle pressures meant it restricted my time at the eyepiece. None the less, this is a fantastic, informative piece of writing that deserved to be pinned for future reference.

Russell

[fatwoul]

Thanks Russell. I hope people found/find it useful.

[ollypenrice]

Ah, I missed this one. It is a superb review.

I entirely concur in your conclusion that fast is good but only if the engineering is up to the job. I'm at a loss to know why so many of the fast Newts are built down to such low prices. They need to be a little more expensive and then they'd be a lot more attractive. I'm full of admiration for those who take on the fast, cheap scopes knowing that they are buying a work in progress. I'm not such a person and, besides, when people come here they want to do astronomy, not watch me fiddle with difficult kit!

The Atik4000 at around 500mm is a great format. You have endless extended objects at your fingertips. You'll love it.

Olly

[fatwoul]

Thanks Olly. I already do! The mindset is my main obstacle at the moment, I'm so used to little objects. Tonight I'm on Andromeda by request. Don't hold out a lot of hope, but I've got a few more minutes before the Moon wrecks it!

[fatwoul]

Among other things on the to-do list is to sort out the field flatness, and to choose what size filters to upgrade to. I get the feeling that they are chicken/egg things, and that one will affect the other.

So two questions are:

1) Based on the little vignette illustrations I posted in the report, what filters should I move to? Do I have to upgrade to 2 inch, or can I get away with 36mm unmounted?

2) Referring to the CCD Inspector 3D plot I posted, should I expect to move the CCD further away from the back of the corrector, or closer to it? Most plots I see have the corners raised, not dipped, and I'm not sure how to interpret it. A starting point would be really helpful.

Thanks everyone.