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Denkmeier power switch lens?

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#1 hoes

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Posted 08 February 2024 - 12:51 PM

The Barlow lens in the Denkmeier power swtich is fairly thin - can you buy something like that?   This might be for use in a filter wheel or drawer (just to have that convenience).

Steve



#2 Eddgie

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Posted 08 February 2024 - 01:06 PM

The Barlow lens in the Denkmeier power swtich is fairly thin - can you buy something like that?   This might be for use in a filter wheel or drawer (just to have that convenience).

Steve

These lenses have a very long focal length and depend on the light path length of the associated binoviewer to achieve their stated magnification and reduction fact. Finding lenses with the right thickness to fit into the filter wheel and the right focal length to work with the stated magnification might be difficult. 

 

If though, you bought some of the "Binoviewer" Barlow lenses, these could work for the power, but they may not work for the thickness.  https://agenaastro.c...ics-binoviewer/

 

Now I did manage to get a Barlow lens into a filter wheel.  To do it, I had to remove the lenses from the lens cell and mount them in an old color filter lens cell. This was not for binoviewer use, it was for use with my Night Vision eyepiece, but it does work well. 

 

As to whether the Barlow lenses sold for binoviewers fitting, I can't say, but the lenses I used were from a shorty 2x Barlow and for my own needs, that was perfect but it was a tight fit. 

This post details how I did it. 

 

https://www.cloudyni...w#entry10105053


Edited by Eddgie, 08 February 2024 - 01:06 PM.

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#3 hoes

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Posted 08 February 2024 - 02:16 PM

Thanks Eddgie-

 

Somehow I missed those threads -   It’s strange that a thin Barlow element works in the Power switch but is not available otherwise.

 

Steve



#4 Eddgie

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Posted 08 February 2024 - 04:21 PM

Thanks Eddgie-

 

Somehow I missed those threads -   It’s strange that a thin Barlow element works in the Power switch but is not available otherwise.

 

Steve

Forgive me if I gave the impression that they were not available anywhere else.  I don't know that they are not available, I have just never conducted a deep search to see if I could find them.   You might try Edmond Optics or other optical supply. 


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#5 hoes

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Posted 08 February 2024 - 04:33 PM

No worries Edggie!   Given your expertise I assumed that if you did not know of a source there probably wasn’t one.

 

thanks

 

steve



#6 faackanders2

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Posted 11 February 2024 - 02:37 PM

Thanks Eddgie-

 

Somehow I missed those threads -   It’s strange that a thin Barlow element works in the Power switch but is not available otherwise.

 

Steve

Russ Lederman designed his OCSs specifically for his denkmeiers and binotrons; but they would likely also work on Earthwins (his former partner).  Russ has no interest in providing sales to competitor products (and possibly not even used products).



#7 Sarkikos

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Posted 04 March 2024 - 08:33 AM

The Barlow lens in the Denkmeier power swtich is fairly thin - can you buy something like that?   This might be for use in a filter wheel or drawer (just to have that convenience).

Steve

Years ago, there was a small company that produced a filter wheel with different power Barlow lenses built into the openings.  Burgess?  Siebert?  I don't recall the company now.

 

Actually, I would prefer something like a filter wheel where you dial in the magnification factor you want rather than power switch arms as in the Denkmeier binoviewers.  I'd be concerned that the arms would snag on something in the dark and possibly be damaged, or at least disturb the position of the telescope.

 

If I were to rig together a Barlow wheel, I think I'd use a simple three-slot wheel.   It would provide two different power settings plus an empty slot.  The empty slot, though, would probably not allow enough in-focus for most telescopes.  It would work in Cats. 

 

For a linear binoviewer, a good design would have two different reducer settings plus an empty slot.  You would be able to come to focus through the empty slot in all telescopes, AFAIK.

 

Mike


Edited by Sarkikos, 04 March 2024 - 08:46 AM.


#8 donniesoprano

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Posted 04 March 2024 - 09:11 PM

Harry Seibert makes that.  He also makes a powerswitch sort of device.

 

https://www.sieberto...Optics-OCA.html. (Scroll down to AD#6 and AD#6a)

 

I’ve never done business with Harry, however I’ve always read good things from those who have.  The real advantage is that he will usually work with you to make the lens configurations that you want or need for your circumstance.

 

ds


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#9 Sarkikos

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Posted 04 March 2024 - 09:34 PM

Harry Seibert makes that.  He also makes a powerswitch sort of device.

 

https://www.sieberto...Optics-OCA.html. (Scroll down to AD#6 and AD#6a)

 

I’ve never done business with Harry, however I’ve always read good things from those who have.  The real advantage is that he will usually work with you to make the lens configurations that you want or need for your circumstance.

 

ds

He needs to work with someone to improve his website and make it more customer friendly.  wink.gif   

 

Mike



#10 betacygni

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Posted 04 March 2024 - 11:00 PM

He needs to work with someone to improve his website and make it more customer friendly.  wink.gif   

 

Mike

I rather like the 90s retro vibe! lol.gif


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#11 Sarkikos

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Posted 04 March 2024 - 11:41 PM

I rather like the 90s retro vibe! lol.gif

Gives me a headache.  doah.gif

 

Mike



#12 Eddgie

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Posted 05 March 2024 - 10:23 AM

I had one of the Seibert convertible setups and the only thing I have bad to say about it is that it seemed to induce a meaningful amount of spherical aberration.

 

In most cases, I believe a relay lens setup is going to work best with a specific focal ratio. At that focal ratio, a relay will have no spherical aberration but as you move away, it will get worse. 

 

I do not know the design he uses, but I asked him about this in an email many years ago, and as I recall,  he said he could not promise that the corrector he sold would not degrade the image.

This post is not for the Seibert setup, but rather a specific and arbitrary imaginary f/5 relay:

 

https://www.cloudyni...ity/?p=6644369 

 

The easiest thing to do would be to star test it to see if it makes a lot of spherical aberration. A half a wave is OK for low power use, but you would not want to use it for high resolution observing. You could though use it for low power and switch to a Barlow or GPC for high power work. 

 

Also, this was a long time ago. Maybe 12 years?  Perhaps my memory of this is not as good as it could be, but I know that when I used the one I bought, I thought the SA was on the high side.


Edited by Eddgie, 05 March 2024 - 10:26 AM.

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#13 Eddgie

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Posted 05 March 2024 - 10:37 AM

Years ago, there was a small company that produced a filter wheel with different power Barlow lenses built into the openings.  Burgess?  Siebert?  I don't recall the company now.

 

Actually, I would prefer something like a filter wheel where you dial in the magnification factor you want rather than power switch arms as in the Denkmeier binoviewers.  I'd be concerned that the arms would snag on something in the dark and possibly be damaged, or at least disturb the position of the telescope.

 

If I were to rig together a Barlow wheel, I think I'd use a simple three-slot wheel.   It would provide two different power settings plus an empty slot.  The empty slot, though, would probably not allow enough in-focus for most telescopes.  It would work in Cats. 

 

For a linear binoviewer, a good design would have two different reducer settings plus an empty slot.  You would be able to come to focus through the empty slot in all telescopes, AFAIK.

 

Mike

It might be feasible to do it yourself.

 

I put a Barlow in the filter wheel for use with my night vision monocular. 

 

Now the problem is that for a binoviewer, you would get far higher than rated powers due to the long light path of the binoviewer.  A 2x Barlow element might give 2.6x 

 

One of the old school really long Barlow lenses that were 2x would probably give much closer to 2x. In the case of the one I made, the focal plane was a bit closer to the lens than the donor Barlow, so the power is only about .7x, but in my case, that was what I wanted. 

 

So, it can be done.

 

https://www.cloudyni...w#entry10105053

 

Here is an old school Barlow. If you could make the lens work, this would probably give close to 2x in a binoviewer.  

 

https://www.ebay.com...:Bk9SR8LEiPTBYw


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#14 Sarkikos

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Posted 05 March 2024 - 11:59 AM

I had one of the Seibert convertible setups and the only thing I have bad to say about it is that it seemed to induce a meaningful amount of spherical aberration.

 

In most cases, I believe a relay lens setup is going to work best with a specific focal ratio. At that focal ratio, a relay will have no spherical aberration but as you move away, it will get worse. 

 

I do not know the design he uses, but I asked him about this in an email many years ago, and as I recall,  he said he could not promise that the corrector he sold would not degrade the image.

This post is not for the Seibert setup, but rather a specific and arbitrary imaginary f/5 relay:

 

https://www.cloudyni...ity/?p=6644369 

 

The easiest thing to do would be to star test it to see if it makes a lot of spherical aberration. A half a wave is OK for low power use, but you would not want to use it for high resolution observing. You could though use it for low power and switch to a Barlow or GPC for high power work. 

 

Also, this was a long time ago. Maybe 12 years?  Perhaps my memory of this is not as good as it could be, but I know that when I used the one I bought, I thought the SA was on the high side.

Relay Lens https://en.wikipedia...o the eyepiece.

 

In optics, a relay lens is a lens or a group of lenses that receives the image from the objective lens and relays it to the eyepiece. Relay lenses are found in refracting telescopes, endoscopes, and periscopes to optically manipulate the light path, extend the length of the whole optical system, and usually serve the purpose of inverting the image. They may be made of one or more conventional lenses or achromatic doublets, or a long cylindrical gradient-index of refraction lens (a GRIN lens).

A Barlow, whether in a tube or a wheel, is still a Barlow.  It increases the effective magnification of an eyepiece, without changing the orientation of the image.  A relay lens apparently changes the orientation of the image.  

 

For astronomy, I'm not concerned about the orientation of the image, except in finderscopes, or maybe in low-power refractors for deep sky viewing.   In those cases, a natural orientation is provided with an Amici diagonal.  Using SkySafari on my iPhone or tablet, I can easily switch orientation of the screen image on-the-fly as needed depending on the orientation of the instrument I'm looking through at the moment.  

 

Mike


Edited by Sarkikos, 05 March 2024 - 12:05 PM.


#15 Sarkikos

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Posted 05 March 2024 - 12:04 PM

It might be feasible to do it yourself.

 

I put a Barlow in the filter wheel for use with my night vision monocular. 

 

Now the problem is that for a binoviewer, you would get far higher than rated powers due to the long light path of the binoviewer.  A 2x Barlow element might give 2.6x 

 

One of the old school really long Barlow lenses that were 2x would probably give much closer to 2x. In the case of the one I made, the focal plane was a bit closer to the lens than the donor Barlow, so the power is only about .7x, but in my case, that was what I wanted. 

 

So, it can be done.

 

https://www.cloudyni...w#entry10105053

 

Here is an old school Barlow. If you could make the lens work, this would probably give close to 2x in a binoviewer.  

 

https://www.ebay.com...:Bk9SR8LEiPTBYw

The major obstacle is to find Barlow lenses that can be screwed into filter cells and have a low enough profile to allow turning the filter wheel.   After that, it's gravy to test the device in a telescope in the field. 

 

Mike



#16 Sarkikos

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Posted 05 March 2024 - 12:10 PM

An alternative to a Barlow wheel is a variable Barlow.   https://www.cloudyni...-variable-zoom/

 

But I wouldn't want to mount a binoviewer on top of a variable Barlow.   I think a Barlow wheel would be a better option for a binoviewer.  

 

Mike

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Edited by Sarkikos, 05 March 2024 - 12:23 PM.


#17 Sarkikos

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Posted 05 March 2024 - 12:21 PM

There is also this.  hmm.gif

 

Mike

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#18 Sarkikos

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Posted 05 March 2024 - 12:28 PM

OK, so what are the available Barlows (or OCS's, etc) which have lens assemblies that could be screwed into a filter cell and be low enough to be used in the typical 1.25" filter wheels?  thinking1.gif

 

I have several Barlows, Barlow lens assemblies and OCS's, but I doubt if any would be low enough to work in a filter wheel.  

 

Mike


Edited by Sarkikos, 05 March 2024 - 12:32 PM.


#19 Eddgie

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Posted 05 March 2024 - 10:00 PM

The major obstacle is to find Barlow lenses that can be screwed into filter cells and have a low enough profile to allow turning the filter wheel.   After that, it's gravy to test the device in a telescope in the field. 

 

Mike

I removed the lenses from a Barlow lens cell and mounted them into an old 1.25" filter cell. Worked fine. I detailed that in a link in the Night Vision forum.  

 

Of course not all lenses will fit, but because most 1.25" Barlows are going to have rather small lenses to fit into the Barlow cell, then I would think that they would fit into the filter cell as long as they were not to thick. 

 

In mine, not only did the lens doublet fit, but I even had room for a red filter. Because I use it for the image intensifier, the Red filter acts as kind of like a light pollution rejection filter. 

 

One of these days I intend to replace it with a real long pass filter. 

 

Anyway, that is the way I did it. I just took the doublet out and mounted it into an old color filter cell. I used a small O'ring to hold it in place. 


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