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
|
Telescope |
APM (TMB) 115/805 in lightweight tube |
|
Aperture |
115mm |
|
Focal Length |
805mm |
|
Focal Ratio |
F7 |
|
Length |
60cm retracted |
|
Weight |
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.
LZOS
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.
Optics
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.
Tube
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.
Focuser
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.
Mounting
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.
Accessories
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
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.
Star
Test
The star
test was good… once the scope had cooled, but up until an hour or more it
showed significant spherical aberration.
Venus
Low to the
horizon, Venus was spoiled by lots of false colour… from the atmosphere!
The
Moon
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.
Mars
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.
Jupiter
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.
Saturn
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.
Deep
Sky
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.
Summary
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.
