Denkmeier 2" Barlow

[ronb]

Wanting higher magnification for the moon than I could get from a couple of 19mm Panaviews and the Powerswitch with my Denkmeier STD binos and not wanting to splash out on more duplicate ep's I eventually decided to go for a 2" barlow, the larger size hopefully better supporting the weight of the binos than the usual 1.25". Then came the decision as to which barlow. I was thinking of the TV but was not sure whether it was overkill or even whether it would work with the binos. Advice was not found on any forum or Google search so I bit the bullet and emailed Denkmeier. I got a lot of help from Russ Lederer at Denkmeier and, after reading only good reviews of Denkmeier kit, I placed an on-line order for their 2" barlow. I must thank Russ for his help and prompt replies to my many questions and emails including his personal thanks for placing the order - additional to the automated response to an on-line order.

For full details of the Barlow see

The barlow arrived in a plastic bag, wrapped in two layers of 3mm foam in a white carboard box in a padded envelope. Nothing fancy. No comparison with Celestron or TV's packaging but no damage so adequate packaging with no unnecessary frills or expense. The cost from Denkmeier was at their introductory price of US$129 (full price will be US$149) with a US$46 shipping fee. There was an import VAT charge of £24.28 plus a Parcelforce VAT free clearance fee of £12.50 and the option of a Saturday delivery for an extra £12. There was also an additional non-sterling transaction fee of £3.63 on my debit card account. This comes to £2 more than purchasing a TV Big Barlow in the UK.

The barlow is well made and looks a quality piece of kit with a yellow plastic dust plug at one end and an aluminium screw cap at the other. Why not a metal cap at each end one wonders? Everything was nice and clean as should be expected and lens coatings look good (see video). The inside of the barrel is ribbed to prevent reflections. The ep is held by a single screw and a plastic compression ring which is my only critisism as when I removed the plastic plug while writing this review to see what the ring was made of I found that the ring had dropped out of its groove and fallen part way down the barrel - strange as this had not happened before even during use but will now need watching for. I have not used the barlow enough to find out whether the plastic compression ring is as good as or lasts as long as the usual brass ring.

On querying the compression ring dropping out of the groove, Russ Lederer replied to my email within 70 minutes. "As far as the internal split ring goes, I have no explanation. That's a first since it's the same ring and eyepiece holder that we use on our star diagonal. I do occasionally bend the very end of the split ring on each side INWARD to allow accessories to be inserted more easily. If the ring is not bent inward at the very ends enough, it can cause the ring to be pushed out a small amount. This is what I suspect just sort of guessing since I work on these rings myself." His response to my comment on the plastic plug: "My goal was to make a variable 2" barlow for single eyepieces, for a reasonable price. Yes, we include a machined cap on one end to protect the optical cell. This cost me about $8 to make. I am trying my best to keep the overall price as low as possible but also give the buyer something a bit special."

I will say I have never had a Barlow before (not quite true as one came with my first scope but was never used) so am not too sure where I am treading here but thought the best test I could perform was to do the following comparison using my C11: my 15mm Axiom with 2.3x barlow (6.5mm) against my 7mm Axiom, any differences showing up hopefully being due to the barlow. The targets used were M42, the Pleiades, Dubhe and Jupiter, further testing being interrupted by dew on the corrector plate. As far as I could make out, other than a slight difference in magnification, there was no difference whatsoever between the two ep's either in the centre of view or at the edge.

With no clear skies forecast for the foreseeable future I then tried my 23mm Axiom in my Equinox 80 during daylight on my usual test target - a farmhouse near the horizon some 6 or 7 miles distant. Once again, other than magnification, I could detect no difference in the quality of the view with the barlow fitted either in the centre or at the edge. With the full barlow (2.3x) as far into the diagonal as I dared go I only just managed to achieve focus on the farmhouse with the focuser wound fully in so I doubt that it would achieve focus on the sky. The 23mm Axiom plus barlow really proved too heavy and kept turning the diagonal if not held vertical - turning the focuser in the scope body at one stage and unscrewing the front barrel from the diagonal at another. No problems however when the end of the barlow was screwed directly into the Axiom to give the 1.25x, focus being achieved well within the range of the focuser and at a much reduced weight (turning moment).

If I may add that these results are what I found as a relatively new observer. Then again it could be my aging eyesight. The more experienced members of this forum may be able to detect problems with the barlow that I could not.

If I may now digress slightly for the benefit of anyone who has not bought anything on-line from the States. The barlow was ordered from Denkmeier on 19th Jan and shipped, so I was informed, on the 21st. Thanks to USPS's excellent on-line tracking system the barlow appeared at the Hauppage Sort Facility (Denkmeier's home town) on the 30th (?????) and travelled via several USPS depots to JFK then Heathrow arriving at UK customs on 3rd Feb. Customs was cleared after three days and the ep arrived in a further five days (11th Feb), the day after paying customs fees.

Verdict: I have no idea how this barlow compares to any other barlow. OK, it is expensive but, it is flexible in that you get two barlows for the price of one and as far as I can see it does exactly what it says on the tin and introduces no abberations other than those which may already be present from the equipment used with it.