The Telescopes

As outlined in my introduction to the site, I started stargazing decades ago, and of course throughout these years I have acquired many items of equipment.

Unlike many others who trade, buy and sell to substitute one piece of equipment with another, I have perhaps bought less stuff, but I have also never given away one either, with the only sad exception of my first scope, a 1984 Meade 826, I had to get rid of because of logistics in 2008.

Meade826

Another scope that has seen its fair share of activity but that is now on storage and out of active duty is the nice little Meade ETX-80, the first scope I used to image DSOs.

etx80_1.jpg

The only survivor of my past stargazing activities that is still performing active duties, and very well indeed, is my third Meade scope: a vintage 2045D SCT.

Bought second (or perhaps third or fourth) hand in 2006 for 360€ (not exactly a bargain, I know), I originally used it for visual observation of DSOs, where it was limited by the small aperture, and of the moon and planets, where perhaps the big central obstruction (close to 45%) was of even greater hindrance than the small aperture.

I also tried some lunar and planetary imaging with the LPI both at his native 1000 mm focal length and at 1500 and 2000 mm with the help of a Meade 140 barlow, with moderately satisfying results.

I put it back into service with its original clock drive mount in 2017, this time for DSO imaging only and with the help of a F 6.3 focal reducer (a SCT classic).

Meade2045D-fork

I doubt many people ever took the little (and indeed quite sturdy) fork mount seriously, but laying down on the floor of the balcony I was able to get 10s exposures with the DSLR: enough to image both globular and open clusters.

To go beyond that I needed to “unfork” it and put it on my AZ-GTI mount, to rather comfortably achieve 30s exposures.

Meade2045-OTA

I really like this small, light, stubby and sturdy SCT: to collimate it has been a bit of a chore, but now, used only at home, it is keeping collimation very well and taking nice pics at 640 mm of focal length.

The big central obstruction has indeed an advantage (which was by design in the original project), namely the capability of vignetting only peripherally an APS-C format sensor.

I also successfully paired what is probable the smallest SCT ever produced for the consumer market with a cheap 0.5X focal reducer and an extension to obtain an overall reduction factor of 0.4X, which means that in this case the Meade 2045D works as a F4 scope with a focal length of about 405-410mm and without appreciable distortion when used with small sensors like those of a ZWO ASI 178MM or 385MC.

The other catadioptric scope of my small (in more sense than one) armada is the trustworthy Skywatcher MAK-90.

MAK-90

This little Maksutov-Cassegrain has a well deserved fame for possessing sharp optics and I think to have reached on the Moon (particularly with the craterlets inside Plato) the physical limits of its aperture.

But, its exceedingly slow focal ratio of almost F14 notwithstanding, I have also used it a few times with big globular clusters and planetary nebulas: it is dark but always quite sharp.

Its focal length is at least partially compensated but its very light weight (1.2 kg) and its compactness, making 20s exposures possible with the AZ-GTI mount.

Indeed, with a simple and cheap 0.5X focal reducer the small Maksutov can obtain surprising and unexpected results as a true astrograph.

Then come the products of my insane passion for the short achromats: it is on the one hand a matter of money, but I also think that imaging with these rather despised (in AP) short focal ratio doublets is a challenge worth the try.

The first is a classic of the last twenty years, one of the many declination of the ubiquitous 80/400, specifically a Skywatcher Startravel-80 .

Skywatcher ST80

It being rather light (1.5 kg) and rather short and well balanced, it allows 45s exposures (and at times even 60s ones) at 400 mm of focal length, even when one add the 0.5 kg weight of the Canon EOS 1300D body plus T2 ring adapter.

It is probably the best balanced for AP among my scopes, surely the easiest to manage.

Of course it displays chromatic aberration, of course it has coma and field curvature … of course it is not an apochromatic.

Of course I know it, but I like it very much and I use it with personal satisfaction.

The latest addition, as of 2018, is the relatively new on the market Bresser AR 102-XS , a 102/460 F4.5 fast achromat, with, according to the producer, some sort of ED lens in the doublet to at least limit chromatic aberration.

BresserAR102XS

Mine is perhaps not a lucky sample: it definitely has some collimation issue and coma and field curvature outside perhaps 25% of dead center are quite an issue.

[December 2018 update: during the latest photographic session with the Bresser AR 102-XS, after about 4 months since the last previous use, it looks like the general quality of the optics has improved: collimation issues look mostly (even completely) gone and even the corrected field looks at least doubled. Possibly the doublet stabilized in place during the months it laid unused?]

However, it is quite fast and luminous and I am a lazy guy, so for now I have decided to keep it as it is and try to get from it all it can give.

StarTools module “Repair” comes in very handy to compensate collimation as far as star shape is involved and when paired with the big pixels of the Meade DSI Pro this is less of an issue, while at the same time the pair makes for a quite fast astrograph.

So much so that in a stack of 30s exposures taken with the DSI Pro under my 17.6 mag/arcsec^2 sky, I was able to identify 16.3 magnitude stars, and there where even fainter ones, but they were not present on my sky charts.

The negative side of the Bresser is that at 2.8 kg (+0.5 of DSLR and T2 ring) it really starts to be a load for the AZ-GTI. Of course visually that weight would be no problem at all (the mount has been tested with more than 6 kg of load), but for DSO imaging it really is at the limit, probably also because of the size and balance of the scope (a Celestron C5 perhaps would do better).

I have used the EQ2 counterweight shaft and a 2 kg weight to try and counterbalance the scope, but so far 30s exposures with the DSLR have been the absolute maximum, 20s ones being definitely safer. Of course with the DSI Pro one can essentially double those times.

On the other hand it feels better built than the very “plastic” Startravel-80 and it also has a much smoother focuser, which always helps astrophotography.

I do not exclude to buy a small ED refractor in the future, or maybe a C5, or perhaps even both, given enough time, but for now I am busy squeezing even the last digitized photon out of my “Cheap Four”.

UPDATE 2020

It has been a difficult year and astrophotography has at times been my only distraction from the grim reality around. So, with travel and vacations much reduced, I could channel more resources in the hobby and bought two scopes, quite at the opposite end of the spectrum.

First I decided to be brave and buy the largest (aperture wise) telescope an AZ-GTi could reasonably handle for astrophotography.

The choice was the Celestron C6 in the same version sold as Nexstar 6SE.

At 3.5 kg on the scales it is heavier than the Bresser AR102-XS, but more balanced and allows exposures of up to 20 seconds at a focal length of about 1020 mm with a 0.63X focal reducer.

M33-20201116-140x20s-C6F68-lpc-cbg-csc-2
M33 – 140x20s – Celestron C6 with Canon EOS 2000D
M1-C6F71
M1 – 139x20s – Celestron C6 at F7.1 and ZWO ASI 178MM

Obviously it also allows more resolution on the Moon and the planets, and it arrived just in time for the queue of the Martian Opposition 2020.

Mars-20201107-0010-3587f-3000mm-LR
Mars – 20201107 – Celestron C6 at 3000mm

The AZ-GTi mount is impressively loaded when paired with the C6 and a 2kg counterweight, but it works with good tracking accuracy, even for planetary use at 3000 mm, albeit vibration during focusing may require 10 seconds to subside.

At the other opposite of the scopes that can be paired with my AZ-GTi lies the Skywatcher Evoguide ED 50.

This small ED scope was originally conceived as a guidescope, but then, thanks to its performances and good price, was rebranded as a potentially standalone scope for astrophotography.

Indeed the new version comes already mounted on a Vixen dovetail bar, just like the one you see above, that is mine.

It is well known that without a flattener the little scope suffers of substantial field curvature.

Honestly it looks like it is even more than I expected, the totally corrected circle possibly not exceeding a degree and a half in diameter, which could be a little short even for a sensor with a 9 mm diagonal.

On the other hand the flattener Skywatcher makes for this scope has a backfocus of just 20 mm and hence cannot be paired with a DSLR and there could be issues even with dedicated cameras if filters have to be used.

Also Starizona sells a flattener for this scope, but it is not completely clear if it allows a DSLR to focus at infinity, besides costing about twice as much as the Skywatcher one.

So for now I will go without flattener, even if this limits the useful field the scope can image.

A great bonus of the little scope is, on the other hand, its limited weight, which, paired with a small size, easily allows the AZ-GTi to achieve 60 seconds exposures.

M337h50m
M33 – 470x60s – Evoguide ED50 and ZWO ASI 178MM

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