APM (TMB) LZOS 115/805 Review
What’s the largest apochromat that’s truly portable? The answer is probably something like the LZOS 123/738 that I previously reviewed here. Trouble is, though that scope is compact, it’s still quite heavy. If you need to carry it a distance, that could be a problem unless you’re young, strong and fit.
Why does this matter? Well, for example, I have to go up onto a local hillside if I want good views of the planets or Moon when low in the west. Lugging the 123/738 up there is a truly tough slog; and that’s assuming someone ese is hefting the mount.
Meanwhile, most 4” refractors are too small for really detailed planetary views and some imaging applications. Is there something in between? Such intermediate sizes are rare, but this 115mm F7 LZOS lens (here in an APM tube) is one of them. So does it perform like a smaller lighter 5” or a bigger heavier 4”? Let’s find out.
At A Glance
APM (TMB) 115/805 in lightweight tube
5.65 Kg tube + 1.24 Kg rings/dovetail
Data from Me.
Design and Build
This OTA features an ED triplet objective made in Russia by LZOS (more on which below). These triplets were designed by TMB, but very similar ones are now available with just LZOS/APM branding.
Most LZOS lenses are found in tubes like this one, assembled by APM Telescopes in Germany, who has long been the main western importer of Russian and Ukrainian optics.
Both this type of objective and tube are familiar and old favourites for me – I’ve owned both a 100/800 and a 175/1400, along with another LZOS lens in a William Optics tube. All those lenses have been absolutely top-line in terms of design and fabrication.
This is quite an old OTA, but the lightweight tube design from APM Telescopes is still available with a variety of lenses. All feature well constructed and baffled tubes that are conventional until the focuser end, where there’s a 3.5” drawtube to reduce the length and make for a much more compact and portable telescope.
In this version, the focuser is a premium Starlight Instruments Feathertouch, but more recent tubes can be found with other focuser options, both cheaper and heavier-duty.
The acronym LZOS stands for “Lytkarino Zavod Optychisovo Sticklo”, which translates to Lytkarino Optical Glass Works. And it turns out they only make refractor lenses like this one as a sideline to their main business making large professional optics for the military and research. LZOS aren’t a little backstreet optical shop, they are an enormous manufacturing plant.
LZOS lenses are most frequently encountered in APM telescopes, but they have cropped up in other brands too, including Stellarvue and William Optics (the LZOS lensed version of the FLT-110 being the most common).
Part of the LZOS advantage is that they make the whole thing, including melting the glass. This means that they can tailor crowns and flints to implement a specific design very precisely – they are not dependent on existing glasses from the likes of Schott and Ohara, though they do have a catalogue of standard glass types. This also means they can make bigger lenses too, since off-the-shelf blanks often don’t exceed six inches (which is why the larger lenses from other companies like TEC and Takahashi use fluorite, which is available in larger sizes).
Of course, right now (early 2023) the big question must be whether LZOS lenses will still be available in future and perhaps whether you should buy them if they are. But this one was made years ago, so I don’t have any Ukraine-related moral issues with it.
Thread-on LZOS cell is big and heavy.
As usual, this LZOS lens is an air-spaced triplet with an OK4 ED crown sandwiched between two (different – see laser test) flints. OK4 is LZOS’ proprietary high-fluoride near-equivalent to Ohara’s commonly used FPL-53 ED glass. This is an older lens (2006), but the coatings look excellent; LZOS doubtless do their own.
LZOS lenses come in focal ratios from F9 to F6. The F9 and F8 ones are especially well corrected, but even the F6 examples show very modest false colour and spherochromatism. This intermediate f-ratio of F7 promises a good compromise for both visual and imaging.
Note that the original specification for LZOS lenses is ‘better than 95% Strehl’ and according to the supplied test certificate, this only just makes it over the bar. In the past, I’ve owned and tested other LZOS lenses up to 99% Strehl. As we will see, this theoretically lower quality isn’t perceivable in use (at least not to me).
The glass is set into a substantial (and heavy) cell - normal for LZOS, but over-engineered compared with just about any other. This makes these OTAs notoriously front heavy. Even this smaller size balances further forward than you expect, but by the time you reach the 175/1400 it needs a 10 Kg focuser weight to balance in a sensible position.
The APM lightweight tube is nicely finished in gloss white, with the drawtube, holder and sliding dewshield ring in machined and black-anodised aluminium. But the sliding dewshield and back are secured with screws, not threads. I believe these tubes are made from Krupax, a phenolic resin impregnated composite, not aluminium.
Internally, there are three large baffles. The tube interior is painted flat black, but not flocked like the high-end tube for my TMB 175.
These lightweight tubes feature a sliding drawtube, with a travel of about 3.5”, for coarse focusing. The advantage of this system is that this OTA is extremely compact for its optical spec and also has masses of in-focus for use with a binoviewer. Tube length is 60cm with everything retracted – not carry-on compact, but close. Weight is a modest 5.8 Kg without the rings.
I believe these lenses were (are?) also available in a standard tube with a 3.5” rack and pinion Feathertouch focuser.
Almost as compact as an AP Stowaway, the TMB 115/805 is longer in use and much weightier.
FT Crayford focuser has a 2.5” tube, 2.5” travel.
These draw-tube OTAs feature a small Starlight Instruments Feathertouch Crayford focuser with a body just 1.5” long and a 2.5” diameter drawtube with 2.5” travel. As usual with an FT, the dual-speed pinion has a gold fine focus knob and a locking thumbscrew underneath. All the parts are milled from hard stainless. It’s beautifully fabricated, if expensive, device.
For imaging with heavy cameras, one of the larger rack-and-pinion models might be preferable, but for visual use I reckon these Crayfords are even smoother and more precise.
The drawtubes in some early tubes had dodgy fit, with slop between the drawtube and bushing, but this one works perfectly, albeit a little stiff to make adjusting it tricky in use.
The 115/805 mounts fine on a medium sized mount and is very stable on my Vixen SX2, but note that it really needs the heavier counterweight, where most 4” refractors get away with the little pill-shaped one. You’d need a sturdy alt-az mount – something like an AZ-8 or Rowan.
The nice quality cast rings are standard APM and work well. Various plates can be fitted. There’s a shoe for an APM-type finder bracket (and this is the sort of focal length where I wish I’d got one for it!)
I used the Tele Vue TV-85 reducer (see below), but it’s not ideal and APM make better, dedicated, Riccardi reducers for these lenses (at a price).
The TMB 115 came in an unnecessarily large case, so I had an instrument case made for it (by Thomann) that I lined with ethafoam. The case is about the minimum size possible at 65x22x22cm plus the corner bumpers – you might get away with carrying a case this size onboard.
In Use – Daytime
Waiting for darkness, I pointed the TMB towards the west where the Sun had set behind the Barrow wind farm 20 miles away: superb views of the turbines and the offshore platforms beyond. So I stuck my DSLR in the back and got some great shots – wide and unvignetted across the full frame, with good sharpness to the edge:
Tele Vue’s TRF-2008 0.8x reducer is designed for focal lengths up to 800mm, so is marginal here and vignettes at full-frame.
In Use – Astrophotography
Many might prefer a heavier duty version of the FT focuser for imaging, but this one works fine with a DSLR although you have to use the pinion lock to avoid unexpected rack-outs.
I imaged the Pleiades and comet FTZ 2022 E3. As usual, single frames straight from the camera (an EOS 6D MkII) just reduced in size, all at 30s and ISO 3200.
Using a Baader wide T-mount, coverage is good at full-frame without a flattener – just a little vignetting in the corners. The field is substantially better corrected off-axis than an F7 doublet’s, perhaps a little better than my F6.65 triplet AP Stowaway. Violet bloat is minimal. LZOS make excellent objectives.
I tried Tele Vue’s TRF-2008 0.8x reducer, which is intended for focal lengths up to 800mm. This is a plug-and-play device with a T-thread on the camera side (so no wide option) and a 2” push-fit to the focuser.
The reducer certainly reduced exposure times and revealed more nebulosity, but added false colour bloat on the Pleiades. Stars are too distorted in the corners too. I’d need a better reducer for serious AP with the 115/805.
I’ve included 100% corner crops of the comet images, with contrast and brightness increased by the same amount, to better show the field edge performance of both configurations.
Finally, a focal length of 805 mm gives enough image scale for decent snaps of the Moon and the well corrected objective means lots of embedded detail for a small(ish) scope:
M45 at F7 (no reducer): 30s ISO 3200 Canon EOS 6D Mk2.
M45 at F5.6 with Tele Vue TRF-2008 reducer: 30s ISO 3200 Canon EOS 6D Mk2.
Comet ZTF 2022 E3 at F7 (no reducer): 30s ISO 3200 Canon EOS 6D Mk2, with 100% corner crop below it.
Comet ZTF 2022 E3 at F5.6 with Tele Vue TRF-2008 reducer: 30s ISO 3200 Canon EOS 6D Mk2, with 100% corner crop below it.
In Use – Observing the Night Sky
General Observing Notes
The drawtube is great for storage, but it’s not long enough to accommodate a 2” diagonal with a long-focal-length eyepiece, or for many cameras. Then you need an extension tube, after which finding the best setting on the drawtube is a fiddle.
That massive lens cell makes front-to-back balancing vital, otherwise the scope can swing rapidly when the RA axis clamp is loosened, even if you got the counterweight balanced right on the RA axis!
These factors (along with the slow cooldown) make the 115/805 more involved and time consuming to set up than its small size would suggest.
Cool down was slow. Initially, it produced very soft images. After 45 minutes or so, the scope was usable, but wasn’t giving its best (see note on the star test) until well over an hour. Until cool, planetary sharpness was noticeably down and Mars showed some false colour that it didn’t when fully cooled.
I don’t want to labour the point, but this is a consideration with larger triplets. I recently enjoyed a planetary viewing session with several telescopes, including a friend’s LZOS 123/738 (reviewed by me here) and a Takahashi FC-100DC. Surprisingly, the Takahashi gave the best views, almost certainly because the triplet failed to cool properly in rapidly dropping temperatures. Don’t buy a triplet over about 80-90mm for quick looks.
The star test was good… once the scope had cooled, but up until an hour or more it showed significant spherical aberration.
Low to the horizon, Venus was spoiled by lots of false colour… from the atmosphere!
The TMB 115/805 is over the aperture threshold where the Moon’s rugged landscapes are explorable in sufficient detail for long sessions at the eyepiece. I lingered over the terraced walls of crater Tycho, Promontorium Laplace and a little field of domes west of Copernicus. I easily found Hadley Rille, landing site of Apollo 15.
With Mars at 16.9” near the 2022 opposition, near transit at 57° altitude in fine seeing, the TMB 115 remained sharp at 322x with the 2.5mm Pentax XO in steady moments. The incredibly precise Feathertouch Crayford focuser was essential at this power – just the slightest nudge on the gold fine focus knob to get best focus.
My best views, though, were predictably with the 4mm Zeiss Abbe Ortho’ giving 201x. The troubling red blur you get with ED doublets on Mars was absent, with just the faintest trace of red blur outside focus at high power.
Mars showed its classic ‘bikini’ of Syrtis Major just off centre, extending into the lighter equatorial regions of Arabia to the north, with its dark point and hook in steady moments. Hellas to the south was noticeably brighter and a stronger orange colour than the deserts to the north and revealed its clearly defined arc of northern boundary to the south-west. To the west, I noted the twin ‘bikini straps’ of dark albedo – Sabaeus Sinus and Mare Sarpentis according to my atlas – leading to the prominent dark area of Meridiani Sinus on the limb. I also noted some limb cloud over the north west.
At 161x with a Nagler T6 5mm, Jupiter showed a lot of detail in the equatorial belts, fine banding in the polar hood and the GRS nicely defined.
A perfect view of Saturn, with the rings and ring shadow sharply defined, the Cassini Division visible most of the way around. The planet itself revealed it pinky cream colour and darker polar hood with hints of fine banding.
The flat field of the 115/805 gives wonderful deep sky views and the extra aperture over a 4” is noticeable. Optical quality is superb with dazzlingly pin-point stars across the field and no false colour. With a 19mm Panoptic giving 42x, M42 shows colour and knots in the nebulosity, wide arms and central spike.
Auriga’s Starfish cluster reveals its arrow-head shape and a frosting of dim stars and pin-sharp bright ones. The Pleiades are brilliant jewels, embedded in wisps of nebulosity and velvety-black space. The Crab Nebula shows off its shape, standing out from the background more clearly than through smaller APOs.
The Double Double gave a good split at 161x, with a perfect diffraction ring in fine seeing and black space in between.
The TMB 115/805 is typical of LZOS objectives. That means it’s the very best in all but two things: weight and cool-down time. This is a heavy cell and it takes a good hour or more to give its best from a warm house. So, despite its compact size, this isn’t a quick-look scope (unless you store it somewhere cold).
Otherwise, it’s superbly sharp and very well corrected for high power visual use and delivers a surprisingly well-corrected field for imaging, even without a flattener.
Perhaps it’s not politically correct to say so, given the Ukraine war, but LZOS certainly know what they’re doing. It will be a real loss to the astronomy community if we can’t get these lenses anymore.
The tube is well made and finished. It is properly baffled to supress stray light but without vignetting, something that could easily have gone wrong with the drawtube. That drawtube makes it super compact and there’s no play in the bearing. The focuser is the very best for precision and feel, so long as you’re not using very heavy camera or bino’.
But the drawtube is not ideal if you’re swapping between long and short focal length eyepieces, or between visual and imaging, because the action is stiff and it can hard finding the right setting given the shortish focuser travel.
In terms of performance, the 115/805 goes deeper for deep sky and gives noticeably more detailed and involving views of the Moon and planets – a genuine step-up from a 4” refractor, but also not quite up to the all-purpose level of a 5”.
The 805/115 LZOS objective is another superb one. The drawtube and small focuser make for a light and compact OTA, but imagers might prefer the fixed tube version with a heftier r&p focuser.