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Denkmeier II Binoviewer with Dual Arm Power Switch

Posted by Tom Hole   10/24/2004 12:00AM

Denkmeier II Binoviewer with Dual Arm Power Switch
[ARTICLEIMGR="1"]Denkmeier II Binoviewers

Here are the 3 binoviewers I owned at the time of this review. The one at the top is the Denkmeier II with dual diopter adjusters and a 2 arm Power X Switch. The one in the middle is the Televue Binovues with 2x corrector. The one on the bottom is the Denkmeier Standard with a 2" single arm Power X.

I received my Denk II's last Fri (Apr 30 2004). I had asked Russ about getting a pair a while back and he called me up and said my name was up on the list, did I want a pair? Well, sure, why not? I got the full meal deal: Denk II's, dual SCD's, Dual Arm 2" Power X Switch. They arrived and brought a weekend of rain with them.

First impression when I opened the box was yup, look like Denks. I have the Denk Stds so I knew what to expect.

The SCD's (Self Centering Diopters) were confusing at first. If you read the directions, they aren't confusing. I don't read directions, so I needed a couple minutes of futzing around to figure out which was the focusing part and which was the tightener part. I slapped in my 24 Pans to see if there was still the wiggly ep problem that my Denk stds have always had. They would wiggle if you tried hard enough, but not too much. After 6 months of steady use, I have not had an issue with eyepieces wiggling in the SCD’s.

Looking into the eyepiece holders with no extraneous pieces parts attached revealed a pink hue in the right and a blue hue in the left. Smart people figured out this was ok, so I accepted it for now.

The Power X Switch is neato keen. I was wondering how it would work in person. The machining is very precise. The optics do not move at all when the arm is seated. Zip, none, notta. That is impressive. Not sure misaligned or non-repeatable positioning of the upper elements would be a good thing.

It cleared up for about 5 minutes on Sat and I had a quick peek at Sol. I had just enough time to get focused and try out the Power Switch a few times. I was very happy when I found I could focus with the 24 Pans with 1/4" room to spare. That's actually 1/8" more than I had with the regular 2" OCS. I switched between the 3 powers and all I had to do was refocus. Now that's what I've been waiting for in binoviewing. No more OCS pieces parts swapping to get to different powers. No optical evaluation was conducted as the clouds rolled in and I was too giddy to care at that point. Very cool stuff.

I set up my yardstick on the speed limit sign across the road about 100 yds away and set up for some magnification comparisons. Here's what I found with my 11" Starmaster EL, f/5.6:

Low power mode: 1.38x
Mid power mode: 2.1x
High power mode: 2.5x

Just as expected. Not sure how useful the 2.1x mode will be, but why not, gotta have all the bells and whistles.

It was partly cloudy Mon night, so I got to have my first "dark" with the Denk II's. I also had the TV Binovues rigged up with a 2" OCS single arm Power X. Time for a showdown.

Luna was up and full. That would be my first target. Had the 24 Pans in and low power selected on the Power Switch. Centered up Luna and had my first look. WHHOOAAA!!!! What's all that color? Pink on the right side and blue/green on the left. Geesh, ooowww, oohhh, eeeeaaahhhh. I swapped eyes (actually, I just looked through the right side with my left eye) and holy crap! it's even worse. This is dreadful. I focused on the moon and alternated closing an eye and checking out the pretty pink/blue moon. Something must be wrong.

I went inside and emailed Russ Ledderman and a few other folks that I know who own Denk II's to ask about this. Got a reply back from Russ at 9:00 at night (whatsup wit dat?) and he explained about the transmission and reflectance of the beam splitter and coatings and asked me to go back out and see how much color there was with both eyes merged and settled in. I did that and things were much better. When I first put my eyes up to look at the moon, I saw the separate pink and green until the image merges. Then I just saw a white moon. Very strange, but it worked. If I closed one eye, the moon would take on the color of that side of the binoviewer (pink=right, blue=left). But open both eyes and it turned white. The mind is a wonderful thing.

I decided it was time to see what the TV's did. There was no color difference at all that I could see, but the image color looked the same as when the Denk II's were merged. I tried the Denk Stds and noticed a slight brightness difference and maybe a slight blue tint to the left side. But again, merge the images and all white.

I have had many nights of viewing to determine if this color difference is an issue and have decided that it is not. I can see a very slight hue on the moon, but everything else looks just as it should.

Ok, in the meantime, I talked to Russ and he mentioned a lower power lower element (part S) that might work for me and my Starmaster. It arrived today (Tues) and I immediately installed it on my dual arm Power Switch. Sol was out so I put the filter on and had a look. Hmmm, not enough back focus. I extended the OCS all the way and just barely missed focus. I had about 3/16" left on the collimation bolts, so I moved the primary up 1/8" and just got the 24 Pans to focus. 1.2x is much mo better than 1.4x. Granted, the OCS was now sticking into my light path a full 3/4", but I didn't care so much. It only does that at low power and I challenge anyone to notice the effects of an OCS sticking 3/4" into the light path of an 11” mirror at 78x. I went from 88x to 78x and from .74 deg TFOV to .84 deg TFOV. That extra .1 deg TFOV may not sound like much, but it made Sol oh so much nicer.

Now for the kicker. When you go to the mid or high power setting, it requires you to rack the focuser out to the point where the OCS is no longer sticking in the light path. So, you don't get that OCS mucking up your high power views when you are trying to track down that elusive rille in the Alpine Valley.

I measured the mags on the low power OCS and found the following:

Low power mode: 1.2x
Mid power mode: 1.7x
High power mode: 2.1x

I also took a look at whether I had any room to move the primary up in the Starmaster. I put my eye over the focuser where I thought the focal point was and looked into the focuser at the secondary. I could see a little border around the primary. I interpreted that as having a little room to move the primary up and still not vignette the light cone at the secondary. The Starmaster design is elegantly simple and moving the whole mirror cell up took 10 minutes. I just moved the 4 corner blocks up 1/2" and then re-installed the primary cell. Easy peasy. Put the magnificent ZOC primary back in, collimated with my wonderful Catseye tools and I was ready to go. I checked if I could still see the entire primary by looking in the focuser and oila, I could. It fit just perfectly in the secondary. That means that I got an extra 1/2" for free. Tonight is supposed to be clear and steady.

The benefit of moving the primary up is that I can shorten the OCS up by the same amount and it won't stick out so darn far. Not that it effects the view, it just looks darn goofy. This was such a quick and easy and penalty free (at least I think it is) mod, and I get a very low power corrector system out of it. The one I always wanted but never got.

All this was possible because I had mentioned to Russ that lower power would sure be nice. I had not heard mention (at least not that registered in my brain housing group) of Russ having a lower power option for the Newt OCS. It does require about 3/4" more backfocus vs the standard 2 arm Newtoonian Power Switch, but I found that ¾” by moving up the primary and extending the OCS 1/4".

I did find one penalty that I paid for moving the primary forward: the balance shifted. I was only using 3 speaker magnets to balance the scope. Now I need 6. I thought I had gotten off scott free, but viewing the moon low in the sky tonight proved otherwise.

Another thing I found was that the older 2" OCS's have a slightly different hollow nose piece than the newer ones. The new ones have a dual thread system that Russ said they designed to make it easier to re-configure the OCS. That was before the Power X was around. It does help when you have to re-configure, but it does take away about 3/16" of available extension. This could mean the difference between focusing and not. I used my older 2" OCS initially to get the extra length, but now that I have the primary moved up, I will swap back to the new one. That old stuff is, well, old. Gotta go with the shiny new stuff.

UPDATE, Tues night (4 May 2004)

It's clear, the moon is full and the seeing is below average, but it's a lot of fun. The moon's not out yet, but all the neighbor's porch lights are on. So, I had a peek at Jupiter to use the SCD's and compare to the TV Binovues.

I quickly learned via the SCD's that I do indeed have a difference between my eyes. I get tested annually for my flight physical and I knew there was a difference, but never really noticed anything while binoviewing. Never really looked for it either. I am 20/10 in my left eye and 20/15 in my right for far vision. For near vision, I'm getting old and I'm 20/25 in my left eye and 20/30 in my right. Not enough to warrant a different prescription in each eye for reading glasses. But, as it turns out, enough of a difference to require the use of the SCD's.

The best way I found to focus for Jupiter was to use the moons. I played with the focuser until I found exactly where in focus was for the right eye. Then I looked through just my left eye to see if it was in focus. Hmmm, a little different. I then just focused my left eye and used the SCD on the right to get that one dialed in. So, how much difference was there? Well, I had the left SCD opened up 1/16 turn. I had the right one opened up 3/8 turn. That made both eyes focus at the same time. I tried this several times and each time came up with the same difference.

Maybe this was due to a difference in the path lengths between the sides of the Denk II's. Easy to verify, I guess. I put the TV Binovues in that I have been using for a year without adjusting between the sides (pulling out an ep to focus it). I focused my right eye and looked through my left. Sure enough, there was a slight difference in the focus point. I'm sure it's always been there and my brain took care of it, but I didn't really nail it down until now.

Does it matter? Dunno for sure. Seeing isn't good enough right now to get a definitive answer. First impression, which is the one I always trust, the image of Jupiter snaps into focus more crisply with the SCD's than without. If I leave the SCD's bottomed out to simulate the same mismatch as the Binovues, the image loses the crisp snap and resembles the Binovue focus. It will take better seeing to determine if there is a difference in the fine detail visible with and without SCD compensation.

I can say that one SCD would have been plenty for me. A fixed left with an SCD right would have worked just fine. I did not know that before, but now I do. Now, I just leave the left bottomed out and after the ep's are in, I turn the right one 1/4 + skosh turn to match the sides. So, the SCD's are keepers.

The Views

Well, the seeing was pretty good, 4-5 on the Pickering scale, and I did a comparison between the Denk II's and TV's. I was using the Denk II's with the 2 arm, low power OCS in high power mode for 2.1x and the TV's had the 1 arm regular power OCS in 2.5x mode. I used 18mm UO orthos in the TV for 212x and 15mm Pans in the Denk II's for 215x. I also used the 15 Pans in the TV's for 255x and the 13 Naglers in the Denk II's for 248x. The views were better in both binoviewers with the lower power (212x and 215x) so I did most of my comparisons there.

I think the SCD's on the Denk II's won the day here. The details were about the same between the two, but the fine details were more often seen and easier to see in the Denk II's. It's hard to explain, but I felt I could see more details, more easily in the Denk II's. I tried to adjust the ep's in the TV's so I got an accurate focus between the two sides, but the accuracy of positioning was just not there as it was with the SCD's. I should wait until I get a night of great seeing to be sure, but I don't know that that is necessary at this point. The SCD feature has me sold on the Denk II's.

I also did a comparison of the 1.66x mode of the dual arm Power Switch and much to my surprise, it was very good. I am going to keep the Denk II's and sell the TV's and Denk stds, so I will have more time to compare the mid power mode in the future. Ah, who am I kidding, I'm going to head out right now and check it out. More to follow...

I did a quick comparison of the 13 Naglers at mid power mode (195x) and the 15 Pans at high power mode (215x) and noticed no difference. It will take a good night of seeing to make a definitive determination.

I did some more investigation on the color issue. There is definitely a slight off color hue to the moon in the Denk II's in low power mode with the 24 Pans. It is subtle compared to the Denk stds and TV Binovues, but it is definitely there. On Jupiter, it is not noticeable with both eyes. No color on stars. So, I will live with it because the benefits of the Denk II far outweigh this.

Here are some pics I snapped with a digicam through the ep holders on my 3 binoviewers. You can see the definite color difference between the sides of the Denk II’s.

I merged the images in Photoshop and made the right one 50% transparent. This is to simulate what might be happening when the brain merges the two sides of the binoviewer.

Not sure if I can conclude anything other than the merged images do look different than the separate ones.

I played around a lot with the SCD's and have decided the left will stay locked down all the way. The right consistently required a skosh over 3/8 turn to match the left. IMHO, this feature should be on all binoviewers. It is the biggest factor for why I am keeping the Denk II's. The shorter path length, which allows me to use the 1.2x OCS is the other. Although I haven't done a rigorous comparison of the views on deep sky. I don't plan to, either. I know the Denk II's are no worse than the TV's on Jupiter and that's good enough to divest in the other 2 binoviewers.

I also compared the Denk stds with the 1.4x OCS and 24 Pans to the Denk II's with the 1.2x OCS and 24 Pans. I was looking at the moon to see if that extra .1 deg TFOV really mattered. It was noticeable and framed the moon more easily, but it wasn't a big deal. It made a wonderful improvement with the sun. So, not a big deal, but it was practically a no brainer to go with the 1.2x OCS.


I kept the Denk II's with the 2 arm low power OCS and SCD’s. I sold my Televue Binovues here an Astromart and donated the Denks with the single arm Pwer Switch to my local astronomy club.

NOTE: Full size versions of the above test images can be viewed at: