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Binoviewer upgrade advice?

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#1 Sam M

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Posted 04 August 2020 - 03:31 PM

I have a Williams Optics BV with a Siebert 1.25x/2x/3.5x OCA.  It works well in my Dobs, C6 & 102 refractor.  I use it probably 80% for planets and the moon.  I'd like to upgrade to a higher optical quality system that is more suited to larger, fainter DSOs as well.

 

The things I'd like in my new binoviewer are:

-Can use a 24mm panoptic without vignetting

-Excellent optics

-As light weight as possible

-Reaches focus in my SCT, Refractor, and most importantly GSO Dobs (See signature)

-Can use a range of OCAs to change focal length, so I don't have to buy a bunch of eyepieces

 

Until recently, I've been resigned to the Binotron 27, which I think meets all those criteria.  Recently, I've bee looking at the Maxbright II.  However, I think (not sure) the only OCA that I can use with the Maxbright II in my Dobs is the 1.7x.  So, not optimal. 

 

I am not a wealthy man.  Any advice?


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#2 Jeff B

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Posted 04 August 2020 - 05:37 PM

It's hard to beat a used Denk II with the Powerswitch/OCS system.  Optically excellent and it can be use with all of your scopes and will do the 24 Pans justice with their 26mm prisms.  Expect to pay $550-$600 USD for a good used system.

 

Jeff


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#3 jack45

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Posted 04 August 2020 - 07:21 PM

I have the same setup, Williams Optics BV with a Siebert 1.25x/2x/3.5x OCA. A used Denk II with the Powerswitch/OCS system would be nice if I could find one for sell. Saving up for the Binotron 27 with the OCS A45.

 

Clear Skies!


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#4 bigdob24

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Posted 04 August 2020 - 08:30 PM

Denk II W/Power Switch, excellent choice 


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#5 Sam M

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Posted 04 August 2020 - 09:55 PM

My only hesitation with a Denk II is the added weight.  I fear it would be hard to balance my Z8.  Also, I don't know how my dobs' focusers will handle it.  This is also a concern with the Binotrons.  That said, a Denk II does seem sensible, if I can find one at a decent price.  Thanks for the input.



#6 Eddgie

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Posted 05 August 2020 - 08:36 AM

My only hesitation with a Denk II is the added weight.  I fear it would be hard to balance my Z8.  Also, I don't know how my dobs' focusers will handle it.  This is also a concern with the Binotrons.  That said, a Denk II does seem sensible, if I can find one at a decent price.  Thanks for the input.

The Denk II is not really lighter than the Binotron. The OCS, extension tube, and power switch are all the same, so weigh the same and the Binotron is I think actually a bit lighter than the Denk II.  Maybe I am wrong on that, but mostly they weigh about the same (I have owned both).

 

The issue with focusers is important.  The Binotron is longer than the Denk II and if heavy eyepieces are used (like 24mm Hyperion zooms) it can be a lot of load on the focuser because with the length of the binoviewer and power switch, the weight has a very long moment and will put a lot of weight on the pinion shaft of a standard Crayford. The thing though is that all binoviewers do this, but the Binotron is probably the worst because it is a very long system due to the design of the diopters and SCD lock rings. The Denk II is a bit shorter so probably a bit easier on the focuser, but light eyepieces really help with this issue. 

 

I would check for spherical aberration using your Seibert OCAs. I know that the Baader 1.7x Newtonian GPC induces some spherical aberration, and I it is likely that the Seibert does too. The Denk OCS does not, and the Televue Bino Vue 2x does not. 

 

If you can find a pair of used Denk IIs, I agree with others that it is a great way to go. 


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#7 Sam M

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Posted 05 August 2020 - 12:52 PM

Eddgie, thanks for the insight about weight.  I've read that reduced weight was one of the improvements made with the binotron.  But, I hadn't considered the length of the system.  That'll be exacerbated by the switch from the WO 20mm eyepieces to 24mm Pans. 

 

I have the stock Crayford focuser on the 8" Dob, and a GSO linear bearing focuser on the 12".  I don't love the the linear bearing GSO, as it goes from not tight enough to backlash on a tiny turn of the tensioner.  I'm planning to tear it down, and re-grease it.  But, I've been kind of lazy about it, in hopes that the Crayford will hoist the new binoviewer, and I can just sell the linear bearing, and downgrade back to a Crayford on the 12".  I'm hoping to avoid the world of more expensive focusers, but It would be good to know what I'm getting into before I commit to a binoviewer.

 

Yes, the Seibert OCA shows (or at least fails to correct) some spherical aberration (false color fringing).  It isn't bad IMO, but I want it to go away.  Overall, I've been very happy with the Seibert / WO system.  It was relatively inexpensive, light weight, and performs very well on planets and the moon.  I'm surprised / glad you told me that the Baader 1.7x Newtonian GPC shows spherical aberration.  That's a strong push in the Denk direction.

 



#8 Eddgie

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Posted 05 August 2020 - 03:13 PM

Eddgie, thanks for the insight about weight.  I've read that reduced weight was one of the improvements made with the binotron.  But, I hadn't considered the length of the system.  That'll be exacerbated by the switch from the WO 20mm eyepieces to 24mm Pans. 

 

I have the stock Crayford focuser on the 8" Dob, and a GSO linear bearing focuser on the 12".  I don't love the the linear bearing GSO, as it goes from not tight enough to backlash on a tiny turn of the tensioner.  I'm planning to tear it down, and re-grease it.  But, I've been kind of lazy about it, in hopes that the Crayford will hoist the new binoviewer, and I can just sell the linear bearing, and downgrade back to a Crayford on the 12".  I'm hoping to avoid the world of more expensive focusers, but It would be good to know what I'm getting into before I commit to a binoviewer.

 

Yes, the Seibert OCA shows (or at least fails to correct) some spherical aberration (false color fringing).  It isn't bad IMO, but I want it to go away.  Overall, I've been very happy with the Seibert / WO system.  It was relatively inexpensive, light weight, and performs very well on planets and the moon.  I'm surprised / glad you told me that the Baader 1.7x Newtonian GPC shows spherical aberration.  That's a strong push in the Denk direction.

 

The Baader is otherwise excellent, and I can recommend for general viewing, but for planets, I would go with the Televue Bino Vue 2x or the Denk or Earthwin OCAs.

 

Yeah, the light path length of the B27 is 127mm with the diopters screwed in fully. The added length is partly a function of the built in collimation collar.  While the unit might be a bit lighter, the extra lenght does add some moment to the system.

 

Whatever focuser you use, just keep an eye on the bearings at the telescope end of the focuser tube.  These are the ones that fail.  If you can get enough tension on the pinion support bearing so that the pinion shaft does not flex so that the tube is pulling away from the eyepiece side bearings, then that will probably work as well as the Moonlight. If not, my advice is to skip the Moonlight and go to the Feathertouch. 

 

A power switch binoviewer system is a big load for a Crayford style focuser. I get away with the factory focuser on my Orion, but my setup is just for planets and it is a very light Orion Binovewer with super light Nikon zooms and a Televue 2x. The stock focuser handles this load easily. 

 

Keep your eyepieces very light though and maybe the stock focuser would be OK.  Only way to know for sure is to try it out. 


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#9 Sam M

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Posted 05 August 2020 - 10:31 PM

A few questions about the Denk OCAs:

 

-Do you think the A45 would make a noticeable difference in my 12" F5 Dob over the A37?

-Is there anywhere to buy a new A37 a la carte?

-Are the Denk A45 or A37 OCAs the same (interchangeable) for the Denk II and Binotron?  So if I can find a Denk II without an OCA, could I use an off the shelf A37, or A45?

-If I were to use a Denk OCA with a Maxbright II, would it just screw into the 2" nose piece, or would I need more to reach focus? 

-Can they be combined with Baader GPCs?



#10 Eddgie

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Posted 06 August 2020 - 06:38 AM

At f/5 you could probably go either way, but the 45mm will give a larger fully illuminated field.

 

The only people that sell the same power optic as the OCAs that I know of are Denkmener and Earthwin

 

As I recall, the OCAs both have M48 thread so should be interchangable.

 

To use it with any binoviewer, you will need between maybe 4" and 5" of spacing between the BV and the OCA.  Since the OCA uses M48 threads, you could use 2" extension tubes in place of the Newtonian mounting tube sold by Denkmeier, but this would mean having to change spacers to get the correct optical length.  The Denk tube has a threaded extension so that the spacing can be easily adjusted.   The reason this is important is because you may need more than 2.3x to reach focus in low power mode and the threading allows you to move the amplifier further away from the BV to increase power.  So, lets say you need to move it an inch forward.  I think this changes the power by around .1x, so rather than be 1.3, 2.3 and 3.1 (or whatever the power is) it would be 1.4, 2.4 and 3.2 (I forget the high power but you get the point, yes?)  If your BV had a very short light path, you might need less power.  Maybe you would get 1.2, 2.2, and 3,   So, the power you actually get is determined by the spacing, and you don't know exactly how much spacing you need until you have the system or do careful measurements.  Some Newtonians reach focus in low power with no extension, most require some small amount of extension.  Most will not reach power in all three modes, so you set up for low power, then you slip the BV out for high power.


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#11 Sam M

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Posted 06 August 2020 - 04:13 PM

So, right now I'm looking at three options:

 

1) Used Denk II or Earthwin with powerswitch and hopefully A45 OCA

Pro:

-Probably the cheapest

-Turn-key system

-Three magnifications with convenient switch

Con:

-Hard to find one for sale

-Heavy

-Risks associated with buying used

 

2) New Binotron 27

Pro:

-Turn-key system

-Three magnifications with convenient switch

-Benefits of buying new

Con:

-Most expensive

-Heavy

 

3) New or used Denk A45 (or A37) OCA + Maxbright II + Baader 2.6x GPC (used in tandem with Denk OCA)

So 1.3x approximately with Denk OCA for wide field, and 2.9x (unknown) with Denk OCA combined with 2.6x GPC for high magnification.

Pro:

-Medium Price

-Lightest weight

-Benefits of buying new

Con:

-Unproven concept

-Only two magnification options that require switching parts

-Have to buy, build, and figure out the right nosepiece extension for the Denk OCA

 

Also, I'm assuming the Denk II or Earthwin will work in my refractor with 2" diagonal, and C6 with 1.25 diagonal.  Is that true?


Edited by Sam M, 06 August 2020 - 04:19 PM.


#12 Eddgie

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Posted 06 August 2020 - 04:30 PM

Yeah, I think you have it about right.

 

The Denk OCS will make the binoviewer more or less parfocal with a regular eyepiece when used with a 2" diagonal in a refractor.  

Now Denk's marketing used to suggest that the powers were 1.3x, 2.3x, and 3.1x (or whatever the high power was) but the Owner's Manual has the more complete picture.  If you use the OCS with a standard diagonal, the OCS is threaded to the filter thread in the nose of the diagonal, but this actually will give more like 1.4x, 2.4x and 3.2x (or wahtver the high power is).  The clue to this is the pitch in the Owner' Manaul for the Denk Diagonal.  See, the Denk Diagonal has a 2" nose that screws on to the diagonal housing using a standard M48 thread, so this means you can remove the nose from the diagonal, screw the OCS directly to the front of the housing, then screw the nose of the diagonal on to the front of the OCS for better support.   In this section of the manual it says that doing this lowers the power to 1.3x, 2.3x and 3.1x (or whatever. I forget if it is 3x, or 3.1x but whatever high power is, just add .1x)

 

Still, most refractors that use a 2" diagonal should reach focus in all three modes using the OCS. 

 

I have used pretty much all of the configurations in a Newtonain and I don't think anything comes close to using a power switch type system.  You can do a aweful lot of observing with just three powers and the power switch just makes it easy. I eventually sold my Mark V simply because even if I had to use the OCS in my refractors, having three powers and not having to change eyepieces all the time was more beneficial to me than having a field that was wider when in most refractors, far more things fit into the field than don't.   Now that is my own preference.  I just enjoyed the freedom to simply sit and observe without having to constantly change eyepieces.  That is a very personal preference though, but once you have used a power switch system, you will find the convenience of it to be quite excellent. 


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#13 Sam M

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Posted 06 August 2020 - 04:52 PM

Thanks for sharing your time and expertise!



#14 aa5te

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Posted 06 August 2020 - 07:15 PM

3) New or used Denk A45 (or A37) OCA + Maxbright II + Baader 2.6x GPC (used in tandem with Denk OCA)

So 1.3x approximately with Denk OCA for wide field, and 2.9x (unknown) with Denk OCA combined with 2.6x GPC for high magnification.

 

Maybe I'm missing something here, but, based on older threads about the Denk Low Power OCA, and by seeing that if you remove it from the power switch diagonal you get 0.66x for use in your SCT, it seems that the A37/A45/Low Power OCS is somewhere around a 1.5-2x barlow factor. If it's in the diagonal, or the binoviewer optical train in the correct location, with the powerswitch, you get 1.3x as your lowest power (1.3x/2.3x/3x), and, without, you get 0.66x/1.15x/2x.

https://www.denkmeie...tar-diagonal-r1



#15 Sam M

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Posted 06 August 2020 - 07:50 PM

Dunno?  I was under the impression that 'low' on the powerswitch was just a clear aperture + the OCA.  Maybe that's not true.  Also, don't know if the diagonal powerswitch is different than the Supersystem powerswitch.



#16 Jeff B

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Posted 06 August 2020 - 08:48 PM

The Denk power switches are all basically the same regardless of vintage.   The "logo" slide switch arm has the Denk logo imprinted on it.  It has a reducer element in it, ~.66X.  The other switch, called the high power arm, has a barlow element in it.  The OCA is actually a barlow lens too with an amplification of around 1.8X by itself.  

 

For an SCT,  you a couple power switch choices in configuration, basically with and without the OCA. 

 

Without the OCA you just screw the power switch into the bottom of the viewer and then the 2" nose piece into the bottom of the switch.  That whole assembly is then placed in the 2" star diagonal.  When you push in the "logo" slide switch in, you get ~ .66X.  You can get a focal reduction and still be able to reach focus because  most SCTs and Maks have a very large range of available back focus because they focus by moving the primary mirror.  This movement is amplified by the power of the secondary mirror.  The advantage of focal reduction is the lower power.  However that usually comes at the price of clipping the aperture of the scope a little.

 

When the switch arms are pulled out, there is no extra element in the optical path so the beam from the scope goes directly into the viewer.  This actually results in about a 1.1X amplification as you need to refocus the scope (over that of single eyepiece use) to make up for the extra 5" of optical path length a typical viewer has.  

 

With the high power arm is pushed in, you ~2.0X amplification, and, again, you have to refocus.

 

With the OCA, you simply screw the OCA into the bottom of the 2" nose piece with the configuration above, then, just like above, insert it into the 2" star diagonal.  Now since you are stacking the OCA element (which is a barlow) with the other elements of the switch arms, you will get different magnifications.  Specifically ~1.4x with the low power switch arm pushed in, 1.9X with both switch arms pulled out and 3.0x with the high power switch arm pushed in.   This is also the same configuration you will be using with a typical refractor with a 2" diagonal, however, the magnifications will be slightly different (~1.3X, 1.8X, and 2.6X) as you are not shoving a primary mirror around to focus.  The low power, 1.3X, mode will require a bit of focuser in-travel relative where you would focus with a single eyepiece, the 1.8X about the same, and the 2.6X mode will require you to run the focuser out a bit.

 

With a newtonian, you use the same system as the refractor system except you need to add an adjustable spacer tube between the 2" nose piece and OCA because almost all newts just don't have the range of focus you get with a refractor and you need to push the focus plane out a bit more from the side of the tube as a result.  You will also typically need to adjust the spacer tube length to fit the range of focuser travel that's unique to your newt. But this is easy to do really.  Magnification factors will be a little higher than those for a refractor. 

 

I hope this helps.

 

Jeff


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#17 Sam M

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Posted 06 August 2020 - 09:32 PM

OK, so it's the middle magnification that is a clear aperture through the power switch.  That's both arms out. That would be only the OCA, assuming you're using one.  Then the Denk OCA ranges roughly from 1.8x - 2.4x, depending on the scope, and how far it's placed in front of the binoviewer.  Thanks, that does change my understanding, and probably nixes my idea of using it with a Maxvision II for low power.



#18 junomike

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Posted 07 August 2020 - 08:12 AM

OK, so it's the middle magnification that is a clear aperture through the power switch.  That's both arms out. That would be only the OCA, assuming you're using one.  Then the Denk OCA ranges roughly from 1.8x - 2.4x, depending on the scope, and how far it's placed in front of the binoviewer.  Thanks, that does change my understanding, and probably nixes my idea of using it with a Maxvision II for low power.

This is correct however not all P X S are "normal".

I bought a used Earthwin and found the highest mag was with no sliders (just the OCS).

Turns out the seller  had Bill (EarthWin) put in two reducers (instead of a Reducer + Barlow lens) as he had a C14 and didn't need the magnification, but

quite the opposite.

 

Also, If used in a Newt the OCS will need to be threaded out (or in) a certain amount to reach focus in all three settings.

This changes the magnification in the OCS and thus the sliders as well, so all magnification settings are a close guideline.


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#19 Eddgie

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Posted 07 August 2020 - 02:30 PM

This is correct however not all P X S are "normal".

True. 

 

And some Denkmeier power switches were set up with a different set of optics that had a high power of something like 2.3x and that was provided with both arms out as I recall.

 

To make matters worse, Russ told me that he had on several occasions set up units with custom powers.  Now this was not normal production, but that means that what is out on the used market is not always going to follow the formula mentioned by Jeff. 

 

This means that when buying used, it is important to ask.. I bought a used Denk once that had the three lower powers and I thought it was actually a better match for SCTs, where the high power is often a bit too high.  Now the seller did not mention it and in I had the impression that he did not even remember it so no foul on his part but of course I was expecting the standard configuration and it was an older PS. configuration. 

 

So, there are absolutely units out there that are not 1.3, 2.3x and 3x when used in a dob or refractor.  

 

Now these variations in the power switch were mostly in the Denk Standards and early Denk IIs, but again, there are a fair number out there with one of the older configurations and at least a few with some custom tweaked PS lenses. 


Edited by Eddgie, 07 August 2020 - 02:32 PM.

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#20 junomike

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Posted 07 August 2020 - 04:51 PM

The nice thing about EarthWin is that Bill will fix/retrofit the existing units for cheap.

My original unit was in "Newt" config and I had Bill retrofit it with a Diagonal as well as the "normal" P X S lenses/magnifications.

This was several yrs ago when I mainly used SCT's and Refractors however I just had Bill refit it back to Newt config as that's my main use (for Filters and BV's now.

Great to deal with.  Maybe Russ (Denk) does the same, but I have no experience there.



#21 Sam M

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Posted 07 August 2020 - 05:16 PM

Is EarthWin (Bill) still in business?  I live in Maryland, and I think they were located not far away in Ocean City, if I remember right.  But, I tried to check their website recently, and couldn't find anything.  I'd be curious to know if he has anything for sale.



#22 faackanders2

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Posted 07 August 2020 - 10:53 PM

It's hard to beat a used Denk II with the Powerswitch/OCS system.  Optically excellent and it can be use with all of your scopes and will do the 24 Pans justice with their 26mm prisms.  Expect to pay $550-$600 USD for a good used system.

 

Jeff

Denk II w/ 2" OCS works great w/ dob!

I remember they used to have a universal system for SCTs (known to vignette), Reflector, and Dobs.

With binotron they started making only one type.

Russ will only give advice with new systems or original customers (never say you bought used).


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#23 faackanders2

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Posted 07 August 2020 - 11:04 PM

A few questions about the Denk OCAs:

 

-Do you think the A45 would make a noticeable difference in my 12" F5 Dob over the A37?

-Is there anywhere to buy a new A37 a la carte?

-Are the Denk A45 or A37 OCAs the same (interchangeable) for the Denk II and Binotron?  So if I can find a Denk II without an OCA, could I use an off the shelf A37, or A45?

-If I were to use a Denk OCA with a Maxbright II, would it just screw into the 2" nose piece, or would I need more to reach focus? 

-Can they be combined with Baader GPCs?

Denk OCS are Multipurpose (lower power), Newtonian (mid power), Multiplier (high Power), Starsweeper (low power for SCT).

The A45 is Multipurpose and I would recommend that one for widest Newtonian view (never use the A37 multipurpose anymore), but "Multipurpose" requires more in focus.  A37 are all the other options above, and Newtonian and Multipler are nice alternatives.  All are 48mm thread.  Never had an SCT, so never got star sweeper OCS.


Edited by faackanders2, 07 August 2020 - 11:05 PM.

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#24 faackanders2

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Posted 07 August 2020 - 11:07 PM

The nice thing about EarthWin is that Bill will fix/retrofit the existing units for cheap.

My original unit was in "Newt" config and I had Bill retrofit it with a Diagonal as well as the "normal" P X S lenses/magnifications.

This was several yrs ago when I mainly used SCT's and Refractors however I just had Bill refit it back to Newt config as that's my main use (for Filters and BV's now.

Great to deal with.  Maybe Russ (Denk) does the same, but I have no experience there.

Russ helps if you bought original equipment from him, but don't mention used equipment.



#25 faackanders2

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Posted 07 August 2020 - 11:11 PM

True. 

 

And some Denkmeier power switches were set up with a different set of optics that had a high power of something like 2.3x and that was provided with both arms out as I recall.

 

To make matters worse, Russ told me that he had on several occasions set up units with custom powers.  Now this was not normal production, but that means that what is out on the used market is not always going to follow the formula mentioned by Jeff. 

 

This means that when buying used, it is important to ask.. I bought a used Denk once that had the three lower powers and I thought it was actually a better match for SCTs, where the high power is often a bit too high.  Now the seller did not mention it and in I had the impression that he did not even remember it so no foul on his part but of course I was expecting the standard configuration and it was an older PS. configuration. 

 

So, there are absolutely units out there that are not 1.3, 2.3x and 3x when used in a dob or refractor.  

 

Now these variations in the power switch were mostly in the Denk Standards and early Denk IIs, but again, there are a fair number out there with one of the older configurations and at least a few with some custom tweaked PS lenses. 

Believe Russ used to make different Denk II power switches for Newtonians, SCT, Refracors, Universal; or perhaps change OCSs.  He went common with binotron and other dealers to make it simple (rather than optimized for specific scopes).




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