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New Denk Newtonian 1.2x 2" 45mm clear aperture OCS

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#26 johnnyha

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Posted 26 January 2013 - 09:11 AM

I was under the impression that the Siebert low mag 1.25X newt OCA does have a second element or "reducer" before the OCA, incorporated into the setup. At least that's what I see in the diagrams. :question: It's not possible to have a 1.2X OCS that works "on it's own" in a fast newt without serious vignetting.

#27 faackanders2

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Posted 26 January 2013 - 10:12 AM

Isn't Siebert's similar, an OCS in front of a reducer... :question:ng.


Maybe, but the point is that to get x1.2 from the Denk OCS you have to have a Power Switch.
Not everyone has or wants the Denk Power Switch but they might be very interested in a
45mm clear aperture OCS on it's own, especially if it was x1.2 as this thread's tile implies.

gb.


I started this thread and gave the title, because 1.2x is what Russ referred it as, since it is easier to say one number than three, and the lowest power is what decides if it will work with your telecope's infocus limits (or if internal spacers will be required to focus). Russ also initally advertised the 2" OCS for Newtonians, hence the title even though the actual OCS I am referring to has "Multi-Purpose" written on if to distinguish it from the others. If you have any questions for use with other telescopes besides Newtonian, please ask Russ at Denkmeier.

There is never a problem barlowing or going to a higher power since this just needs out focus and possibly outward extensions for the really high powers.

#28 faackanders2

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Posted 26 January 2013 - 01:55 PM

This is what Russ Lederman posted on the Vender Forum (See he even refers it as the 1.2x):

"At WSP, quite a few years ago, Mike Zammit of Star Structure along with Steve Kennedy, a fine fast mirror maker in California and user of our Denk II Binos with both 1.4X and 1.2X OCS* had let me know that the super fast scopes they were using had been shown through ray tracing to have some noticable fall off of illumination with the lower power 1.2X optical lens. Not real bad, but observable.

Basically, to transfer the image plane through the light path of the Denks (this would hold true with any binoviewer), the optical lens must be located rather deeply into the focal plane of the scope, often entering the upper cage a bit. Here's where it gets a bit tricky when deciding whether to use the 1.2X or the 1.4X lenses. The 1.2X requires .75" deeper location than the 1.4X. however, most of you who set out to have a very large and fast dob not only want a short "stepstool-ready" scope, but you want a wide true field of view (TFOV) too. Mike Z. did some on site ray tracing at WSP and determined that going with the 1.4X would be a better option due to the very steep cone in what was an F3.75 mirror, if I remember correctly. remember that it needs to go into the focal plane .75" LESS.

The clear aperture of both the 1.2X and 1.4X OCS lenses were and still are 37mm. The new optic as mentioned is 45mm clear aperture and has the same lower power 1.2X factor.

I was asked if I could make a low power 1.2X with as much clear aperture as possible to negate this clipping. I felt that in a sense, it was not a good option to make 100 optics, especially if the typical blanks that we were already using were 40mm and new tooling, New Cells, retainers, raw material etc. would be required in large numbers. For how many fast dobs? 10? Yikes!

So I sort of declined and had been telling customers with fast dobs that opting for the 37mm 1.2X or 1.4X was a decision they would have to make, weighing the tradeoffs between low power and some falloff/clipping, or less of it with the higher power 1.4X lens.

Well, things being what they are, I am a huge dob fan. I use my own 20" F/f5 with a John Hall mirror (Pegasus) for many years now. But I felt it was finally time to go ahead with this optic since more and more super fast mirrors are showing up and Steve Kennedy felt this would be a very good thing.

My opinion is that ANY dob F/5 or faster should choose this upgrade. F/5 is fast in the telescope world. Typically, large Dobs are expensive and well worth it! So, why not have the largest OCS optic possible in a 2" focuser doing the work? I need a good night to really cross test the 37mm vs the 45mm in my own F/5 but I can say I'd use the 45mm in any case to be sure there is an easily observable gain. I used the 1.2X 37mm in my scope and always had. Now of course, I will use the 45mm! It's here if people want it. Its an honest effort to make an OCS with largest possible clear aperture for a 2" focuser available for those who want one. If I'm trying to grab some photons, I want as many as possible.

*OCS=Optical Corrector System, a term that has been sort of hijacked and used by some others with slight changes. Note that the values of 1.2X and 1.4X are derived via the introduction of the low power optic in the Denk Bino's power switch, used in combination with the large OCS optic. Used alone, these OCS cells would render appx. 2.3X (lower power)vs 2.5X (higher power)in the Denk Binoviewers.
-Russ"

I did not edit Russ' above comments, and I have no affiliation with Denkmeier, except being a very satified customer with DenkII, dual powerswith, additional reducer/multiplier power switch, four 2" OCSs, and one 1.25" OCS. I wish Russ long term sucess of his company, and thank him for making the 45mm clear aperture OCS a possibility (which I have been asking him about for several years before I bought the 1.2x OCS).

Ken

#29 gb_astro

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Posted 26 January 2013 - 07:09 PM

"This is what Russ Lederman posted on the Vender Forum (See he even refers it as the 1.2x):"

Yes, but he finally clarifies it in the footnote.
Perhaps it is just his marketing instinct to promote it's lowest possible magnification (in his system)
since that is usually the holy grail of binoviewing.

gb.

#30 faackanders2

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Posted 26 January 2013 - 08:33 PM

"This is what Russ Lederman posted on the Vender Forum (See he even refers it as the 1.2x):"

Yes, but he finally clarifies it in the footnote.
Perhaps it is just his marketing instinct to promote it's lowest possible magnification (in his system)
since that is usually the holy grail of binoviewing.

gb.


And with an additional reduer switch this can be brought down to 0/87x? The decision which one you are able to use is based on infocus ability of your scope at lowest power. Hence the low power side is the critical deciding factor; hence I don't see any issue with how he refers it to Newtonian uses with dual power switch. I did not buy the 1.2x OCSs for any other reason than its' lowest power ability (accepting vignetting at 37mm clear aperture), and then upgrading same 1.2x with 45mm clear aperture. You DO NOT need 45mm clear aperture for the higher powers, since those don't vignette due to infocus. There is no deception, and he used to list all the powers with the old Denk II when you selected your 2" OCS (for your Newtonian).

For SCTs and Refractors everything is different, please contact Russ or refer to denk site.

#31 faackanders2

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Posted 10 February 2013 - 01:09 PM

Last night I decided to compare the 1.2x2"45mm Multipurpose OCS (with 1 extension) to the 1.4x2" 38mm Newtonian OCS (no extension) with the views of M45, Jupiter, M42/M43 [and NGC1981(HT30), Col72(HT31); could NOT see NGC1977(HT32), NGC1999(HT33) nor NGC2024(HT34)]. I used my Denk II with dual 3x3 power switch on my 17.5" f4.1 Dob and 24mm 68 AFOV Panoptic eyepieces and astrocrumb/denk filter switch from my driveway. At the end there was slight ice dew on my scope tube and chair, but neither ice/dew efffected the viewes of my eyepiece nor telrad.

M45 Pleadies: Actually last object observered.
*1.2x(really 0.87x in LL powerswith mode) - able to see most of the dipper and easily recognized as M45, but not able to fit all of M45 in same FOV. Required panning.
*1.4x(really 1.0x in LL powerswith mode) - able to see some of the dipper and less recognizabled as M45, beeing able to fit lesl of M45 in same FOV. Required more panning.
* Did not use any of the other higher powerswith modes for M45.

Jupiter and 4 moons:
*1.2x/1.8x/2.3x(really 0.87x in LL, 1.2x in LM, x? in ML, ?x in HL, 1.8x in MM, and ?x in HM powerswith mode) - able to see jupiter 2-3 dark bands and dark polar caps with skyglow filter, and 4 moons cosisting of three in a slightly elongated isocoles triangle pointing to the outer moon. Unfiltered provided natural colors but with less band/pole detail. Ultrablock and OIII too dark and less band detail.
*1.4x/2.0x/2.5x(really 1.0x in LL, 1.4x? in LM, 1.43x?x in ML, 1.79x? in HL, 2.0x in MM, and 2.5x? in HM powerswith mode) - Overall larger and better view of Jupiter with 3 dark bands and dark polar caps with skyglow filter, and 4 moons cosisting of three in a slightly elongated isocoles triangle pointing to the outer moon. Unfiltered provided natural colors but with less band/pole detail. Ultrablock and OIII too dark and less band detail.
*Did not use LH, MH, nor HH power swith modes for either OCS.
*Did not use 1.8x/2.6x/3.2x Multiplier OCS which would have provided best higher powers of Jupiter based on past viewing experiences.

M42/M43 Orion Nebula:
*1.2x/1.8x/2.3x(really 0.87x in LL, 1.2x in LM, x? in ML, ?x in HL, 1.8x in MM, and ?x in HM powerswith mode) - 4 star trapezium visible in all powers, M42 visible unfilered but skyglow, ultrablock, and OIII bring out M43 head, and M42 awings and notch in diamond body, with losing stars. OIII especially brightened body. LL with extension only setting not able to use astrocrumb(denk version) filter switch. All other power switch modes enabled use of filters which were preferred views. All view up to MM mode did not crop the wings and higher power provided greater detail without increasing fuzziness.
*1.4x/2.0x/2.5x(really 1.0x in LL, 1.4x? in LM, 1.43x?x in ML, 1.79x? in HL, 2.0x in MM, and 2.5x? in HM powerswith mode) - 4 star trapezium visible in all powers, M42 visible unfilered but skyglow, ultrablock, and OIII bring out M43 head, and M42 awings and notch in diamond body, with losing stars. OIII especially brightened body. LL without extension able to use astrocrumb(denk version) filter switch and hence this is the preferred OCS for this size nebulae in my 17.5" dob, since all views up to MM mode did not crop the wings and higher power provided greater detail without increasing fuzziness.
*Did not use LH, MH, nor HH power swith modes for either OCS.

Ken






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