BW-Optik Semi-Apo Triplet Kit

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Brand and Model:BW-Optik Semi-Apo Triplet Kit
Price ($USD):$735.00
Type:Achromatic Refractor
Attributes: un-checked Go-To un-checked PEC
Aperture:100mm (3.9")
f Ratio:f/6
Focal Length:600mm
Electric Power:n/a
Weight (lbs):6.5 lbs.
Dimensions (w/h/d):18" x 5" dia

Vote Highlights Vote
BW-Optik Semi-Apo Triplet Kit
[Note: Vote moved from description by scopedreamer2032]

I recently built one of these refractor kits and can offer the following comments:

1) It's _not_ an AP Traveler (it is about the same size though).

2) It has less color than an achromat, but quite a bit more than a real

APO. Bright objects (moon, Venus, have a faint purple halo - believe the

"semi" part of the description. To achieve best color correction, you

need to supply your own _prism_ diagonal (it's not included in the kit)

because the lens design assumes a 135 mm glass path before the focal

plane. My diagonal only has 60 mm of glass, but I suppose that's better

than none..

3) It is a "kit" only in the sense that you get a box with the major

parts. The machined parts are well made, but the Intes Crayford-style

focuser only has 35 mm of travel and its lock is barely adequate for the

weight of 2 inch eyepieces. Forget about photography with this focuser

because it won't hold the weight of a camera. Some people also might be

surprised when they find that their kit doesn't have any nuts, screws,

or spacer rings for the baffles. Fortunately, I have access to a machine

shop and this didn't cause me too much grief. People without these

resources might have a tougher time building this scope.

4) The "fiberglass" tube is not fiberglass at all. It's really a

phenolic coil form and is about 70 mm too short for normal eyepieces,

but I suppose it might work with a bino-viewer. A weird extension tube

is supplied to make up for this short main tube, but it fits at the

output of the diagonal, and puts way too much strain on the wimpy

focuser. I didn't like this, and added an extension to the main tube so

I could use regular eyepieces directly on the diagonal.

5) The objective is probably from a large binocular design. The elements

are fully coated and they were very clean. There is an eccentric ring

that allows it to be centered in the tube after the scope is assembled.

6) Star testing showed the objective has a turned edge, and there is

some tilt or decentering of the elements. It's not anywhere near 1/4

wave (as claimed in the ad). The dealer (ITE) ordered a replacement

objective for me, but I haven't received it yet to test. While this service is commendable, I think better quality control would save everyone a lot of hassle.

At low powers, the scope has good performance for rich-field views. At

higher power, the problems with the objective are apparent. Mars at 120X

was just a fuzzy orange ball, even in the center of the field. In a

side-by-side comparison, my 10 cm Mak showed considerable surface detail

on Mars. If the objective was really 1/4 wave, it might border on a

good deal. Hopefully, the next objective will live up to the claims on

the ITE web site and I'll have a workable RFT.

Assembly took about 20 hours. About half of that time was devoted to

making the extension tube and fixing the shortcomings of the kit. With a

few modifications, and pre-testing of the objectives, this could be a

much better telescope kit.

Overall Rating: 5
Optics:5 Ease of Use:2
Weight: 10 (Trustworthy Vote)
Link to this vote:

BW-Optik Semi-Apo Triplet Kit
Not bad Lens. Great for wide field. I bot it in 1999 and it is still my scope.
Regards Hermann

Overall Rating: 8
Optics:8 Ease of Use:7 Value:8
Weight: 1 (Unreliable Vote)
Link to this vote:

BW-Optik Semi-Apo Triplet Kit
The first objective I got would resolve stars into large icecream-cone shaped images. Bill Burnett of ITE replaced it with a better one but it was still an inferior optic. Interferometry testing indicated severe astigmatism, severe turned edge and severe spherical aberation. I was offered a better one for an aditional $250 but decided to cut my losses. The ITE website now is clearer about the variability of the quality of these kits than when I bought mine. I would not do business with ITE again. Ever.

Overall Rating: 2
Weight: 1 (Unreliable Vote)
Link to this vote:

BW-Optik Semi-Apo Triplet Kit
Despite other's experiences, I was very satisfied with the supplied kit right from the beginning. I could assemble the kit within a couple of hours, despite I had to get the right screws and paint from the next hardware store.
The focuser works to my satisfaction, as the friction can be adjusted with one screw and the another screw fixes the focuser in any given position. To achieve a large focusing range a 2-inch sliding tube was supplied (included in the kit). So, there were no parts missing and the focuser's mechanics are perhaps not up to TeleVue standards but robust and exact enough.

The optics is a three lens design intended for rich field observing! Magnifications beyond 100 x times show residual colour. But the colour fringes are much less, than with any ordinary FH/achromatic design (2 lenses). So even going beyond the 100 x limit (which is stated by the german distributor BW Optik) gives better viewing than with most standard achromatic designs. Obviously the semi-apo-design is not up to the extremly high quality of my Pentax full Apo refractor, which easily yields crisp images at considerably more than 200 x magnification.

Unfortunately there is still no glass corrector for the 100/600 available. Its optical design incorporates an additional light path through 135 mm of glass. This requairement could be met be using a binocular viewer (I got mine only recently and so haven't used it with that scope yet). Most zenith prisms are of very poor quality and their use would do no good to the image. And a mirror doesn't add anything to the glass thickness.

My resumee: a very good and compact and fast refractor for low power use. The ideal choice for "strolling" through the milky way under really dark skies. It's not the best choice for high magnification planetary or lunar observing, but that is evident from the text in the original German cataloge! May be the American distributor should submit some more revealing information to its customers. And by the way: the service and advice by BW Optik in Germany is excellent, whereas sometimes a bit technical. Good value for money and a good companion for many clear nights!

Overall Rating: 7
Weight: 1 (Unreliable Vote)
Link to this vote:

BW-Optik Semi-Apo Triplet Kit
Background leading to purchase of B-W kit.

I have been looking for a portable scope for travel, and quick look-sees that gives good images but doesn't cost way over $1000. I already own a high quality 6" APO and am spoiled by it's performance. I have tried a 4" Schmidt-cass, a 4" Mak, a 80mm refractor without satisfaction, so this refractor kit sounded promising to me - I placed my order and continued researching. I was experienceing a growing concern, due to several bad postings I had read, stating poor color correction and bad optical quality.

When the scope arrived I put the kit together in a couple hours with no problems. My unit's focuser suffered from excessive clearances that made for a wobble when focusing. I corrected the problem and the focuser works well now. I have been using this refractor for a few weekes now and was pleased to find its optical quality is quite good. The instructions that came with the kit explained that squaring and centering the lens was a requirement for good performance, and indeed this is the case. Before "tweeking it right-on" there was quite a bit of color and the images were soft, but now that it is adjusted the images show very little color especially when you consider this is a 4' f/6 lens! I find that with such a short focal length, focusing is very critical and there is more color unless your focus is "spot-on", but then this is to be expected in a f/6 optic. Jupiter and Saturn are almost completely color free and the moon's edge shows just a tiny thin violet edge, which is outstanding for such a fast lens. NOTE: I purchased a 2" prism diagonal specifically for this scope because the lens correction was designed to be optimal for an additional 135mm of bak-4 optical path. (this lens was apparently designed to be used with a prism bino-viewer with those specs) Using a mirror diagonal shows considerably more color. Color error seems to be more toward the red end of the spectrum, but is still much, much, much better than that of my 80mm f/7 doublet.

Performance is surprisingly good for such a fast lens and Images of Jupiter, Saturn and the moon are very good. Under good seeing I have viewed both planets up to about 280X with nice results. Cassini's division was visible all the way around and multiple cloud-belts were seen on Jupiter.It does however seem to have a long cooldown time, not unexpected in a triplet lens. The startest is somewhat strange and difficult to decipher so I'm holding off on that opinion for now - I simply don't have enough experience testing.

Anyway, I keep waiting to find something wrong with this scope and just when I think I've found it, it turns out to be just poor seeing and the scope ends up surprising me once again.

On top of the good optical performance, throw in the fact it's a 4" refractor that will fit in a small carry-on case and costs under 1K, I have to say I'm very pleased at this point and just may have found the scope I have been looking for!

Overall Rating: 8
Weight: 1 (Unreliable Vote)
Link to this vote:

BW-Optik Semi-Apo Triplet Kit
I also assmebled one of these kits and I agree with all the previous comments. I also had to return the objective, at major cost from a foreign country, because the first one had a gross fault in the figure. It had a major radial zone as will as turned edge, and gave only lopsided diffraction patterns. The replacement has a turned edge and fails to meet the 1/4 wave P-V error claimed by ITE.

The crayford focusser problem can be fixed. There is an extra threaded hole (for which a machine screw was lacking) which allows you to tighten a screw against the focussing shaft bearing block. The bearing is a low-friction plastic (teflon?) cushion in which the shaft rests. After tightening this, my focusser can hold EP, camera and all without slipping.

The color is certainly obvious in planets and the moon as described previously. I wouldn't believe the testimonial letters provided by ITE, since they describe a far better lens than the two I've been provided with. However, I can say that after using a Panoptic 27mm on the scope, I get a flat nearly coma-free field. I would ascribe that to Al Nagler's talent, not to the BW Optik product! Their quality control is hopeless.

Overall Rating: 6
Weight: 1 (Unreliable Vote)
Link to this vote:

BW-Optik Semi-Apo Triplet Kit
the objective of this telescope was in origin planned for military binoculars. These binoculars have 4 prisms of Porro for a total of optical way in the glass (Bak4) of 135 milimeter.
The objective SEMI-APO-TRIPLET are calculated holding account of the glass of the prisms. I have calculated (in ZEMAX) the secondary spectrum of this objective without the prisms and the result is not good. This telescope is truly optimal only if the optical bundle crossing an optical element of glass to flat faces for a total of 130/140 milimeter. I have used a pentaprisma of glass BK7 40x40 milimeter (I can supply other correct new pentaprisms to lambda/4) and the image in the focus is EXCEPTIONAL for the price of the telescope. It does not have sense to use and to speak about this telescope without to put 130/140 milimeter of glass in the optical way, is like speaking about a objective Zeiss or Astro-Phisics after to have removed one lens.

Antonello Satta

Overall Rating: No Vote
Weight: <none>
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