44 replies to this topic

[briansalomon1]

Both great replies. Many thanks for your time.

 

The only bit I don't understand is Eddgie mentioned 56mm aperture?

 

Also for the sake of argument if a standard pair of binoculars light grasping potential is 1.4x aperture.

This equates to 2X light capture.

For example a 15x70 is effectively 15x100.

Does this also apply to binoviewers?

If so are we not back at the square one/same amount of light?

In addition to what Edggie wrote in post #2, all optical components absorb/scatter at least a little bit of light.
 

[Sarkikos]

I have a similar problem when I am looking at the moon or Jupiter.  The view is so bright I have to add a neutral density filter - or I will lose all of my "night vision".

 

Regular binoviewers split the light into two beams and the light passes through more glass before it gets to your eye.  But my brain stitches these two beams back together in my brain to give me a single, composite view, so I am not sure how much light is actually lost. 

 

I actually love the better view through my BV.  I am much more relaxed using two eyes, I can study the object much longer with less fatigue, and I am happy to trade any small light loss for the nicer view.

 

Eddgie's numbers are as good as any.

 

Ron

My attitude when I am viewing Jupiter or the Moon is that I no longer care about preserving my night vision.  In fact, the less my eyes are dark adapted, the better.  I don't use a filter for Jupiter or the Moon except maybe to increase contrast, not to decrease the brightness.  All that brightness contributes to the color range and resolution of the image.   

 

Binoviewers also help increase the effective contrast when observing planet/lunar.  

 

Mike

Edited by Sarkikos, 19 January 2024 - 10:26 AM.

[Sarkikos]

When you use a binoviewer you are only getting 50% of the light in each eye that you would get with a regular eyepiece using one eye. This is because the binoviewer has a beam splitter that splits the light into two identical but dimmer cones, with each cone serving one eye. Binocular summation does kind of stack the two images in your brain, but the result is that your brain perceives an image that is about as bright as it would be if you were using a single eyepiece in a telescope that was 70% as big as the scope with the binoviewer.

 

What this means is that when you use the binoviewer, the image is not perceived as being  brighter than it would be for 56mm aperture and hence, the sky appears darker. You also lose about .3 magnitueds.

 

You do not alter the contrast ratio and in fact, using both eyes does slightly improve your contrast performance, though to offset the loss in brightness, you would want to use about 10% -15% lower power than you would with one eye. 

your brain perceives an image that is about as bright as it would be if you were using a single eyepiece in a telescope that was 70% as big as the scope with the binoviewer.

 

You also lose about .3 magnitueds.

 

Also, depending on the clear aperture of the binoviewer and the eyepieces used, there might be vignetting.  

 

These are reasons why I use a single eyepiece rather than a binoviewer when I'm hunting for dim galaxies and other faint DSO.   A binoviewer is better for the eye candy. 

 

Mike

Edited by Sarkikos, 19 January 2024 - 10:35 AM.

[Sarkikos]

Q1 ...

 

On the whole, refractors do transmit more light than reflectors. Like all things, it is not as simple as a yes / no.

 

Assume 98.5% transmission per surface, a good diagonal and negligible absorption. A refractor will transmit about (0.985)⁵ = 93% of the incident light. Typically, a reflector has 90% reflectivity, then it transmits 81% of the light but some of the other 19% gets scattered which degrades the contrast. If it has high reflectivity coatings (95%-ish), it will transmit about 90% of the light and less will be scattered.

 

Then you need to consider the aperture and the central obstruction from a secondary. As a rule of thumb, a refractor will about equal a reflector that has an aperture of 150%. So a 80 mm refractor is about equal to a 120 mm reflector. More or less. The image quality of the refractor will be usually be better. The refractor will be far more expensive.

 

Q2 ...

 

Hmm .. I think the effect you are seeing is related to the diameter of the exit pupil.

 

With your 15x70 bino's, the EP is 70 mm /15 = 4.7 mm while with your 20x80 bino's it is 4 mm.

 

Your 100 f/5 has an exit pupil of 5 mm with your 25 mm eyepiece and 6 mm with your 30 mm.

 

The apparent brightness of the sky goes with the square of the exit pupil, so that a 100 f/5 + 30 mm will make the sky appear 36/16 = 2,25x brighter than the 20x80 binos. That's 0.9 magnitudes brighter or nearly 2/3 of the visible stars being squashed.

 

Stopping your 100 f/5 down to 65 mm returns its exit pupil to about 4 mm so that you should see about the same number of stars as your 20x80 bino's. My explanation of it being related to exit pupil seems consistent.

 

So what to do ... I'll do the sums for your 100 f/5.

 

Let's assume my understanding of the discussion in EdZ's article (linked to by Eddgie) is basically right. Binoviewers send half the light each way and using two eyes makes things appear brighter. The effective aperture of your scope will be about 100 x 6.7 /8  = 84 mm.

 

1. If you use large prism binoviewers and you can reach focus without a Barlow or corrector, you can get away with 30 or 32 mm Plossl eyepieces. Your magnification will be the same but the true field will be a lot smaller - say 3 degrees instead of 4. The effective exit pupil will then be 5.2 mm. The sky will be about 0.6 magnitudes brighter.

 

2. If you use large prism binoviewers and you can reach focus without a Barlow or corrector, you can get away with 24 mm UFF eyepieces. Your magnification will be 21x instead of 16x but the true field will be the same as a 32 mm Plossl - say 3 degrees. The effective exit pupil will then be 4 mm so the sky will have similar brightness at slightly higher magnification.

 

3. If you switched to (say) an AT 20mm 100 deg eyepiece instead of a binoviewer, the magnification would be 25x and you would have a 4mm exit pupil. So that's good. You'd also have a true field of about 4 degrees. That's good too. The primary issue is that you might get a lot of coma at the edge of your field. You might want to check the Eyepieces forum for this.

Caveat - a large prism binoviewer will cost you at least $800 (used Denk II + Baader T2 diagonal + adapter + nosepiece) and you need at least 180 mm of available inward focus travel. You will also need two eyepieces ... so going for wide fields with binoviewers easily puts you on the wrong side of a kilodollar. It would be prudent to test your system at a club meeting.

Also, the so-called 'linear binoviewers' vignette badly with longer focal length eyepieces. They're easier to use but they won't get you wide fields.

 

Also, the so-called 'linear binoviewers' vignette badly with longer focal length eyepieces.

 

I think this is due to the wider field stop of the eyepieces, not the longer focal length.

 

The clear aperture of the Orion Linears is about 17mm.  Even my old Burgess binoviewers have a wider clear aperture of 20mm.  Which is fine for me, because I virtually always use my Burgess for viewing planet/lunar, not deep sky.  Ironic for the Orion Linears, though, since the narrow 17mm clear aperture might limit deep sky viewing, and reported glare artifacts might limit their usefulness for planet/lunar.  Neither fish nor fowl? 

 

Still, the Linears do not require a Barlow or OC to reach focus.  That's an advantage in Newts and refractors, which usually cannot reach focus with binoviewers without a Barlow or OC.

 

Mike

Edited by Sarkikos, 19 January 2024 - 03:02 PM.

[noisejammer]

Also, the so-called 'linear binoviewers' vignette badly with longer focal length eyepieces.

 

I think this is due to the wider field stop of the eyepieces, not the longer focal length....

Well, sort of. If you were using (say) a 24 Pan then inserted the Linear binoviewer into the path, you would get vignetting. I'll suggest that it was the binoviewer that introduces the vignetting not the eyepiece.

 

Of course, if you use an eyepiece with a field stop that is larger than the exit pupil of a binoviewer, you also get vignetting. This happens if you use 3 5 Masuyama / Eudiascope eyepieces in a Mk V.

[Sarkikos]

Well, sort of. If you were using (say) a 24 Pan then inserted the Linear binoviewer into the path, you would get vignetting. I'll suggest that it was the binoviewer that introduces the vignetting not the eyepiece.

 

Of course, if you use an eyepiece with a field stop that is larger than the exit pupil of a binoviewer, you also get vignetting. This happens if you use 3 5 Masuyama / Eudiascope eyepieces in a Mk V.

Does the field stop of an eyepiece cause vignetting?  Or does the clear aperture of the binoviewer cause vignetting?  The answer to both questions is "Yes."   It is not a matter of either/or but both/and. 

 

The situation is similar to vignetting in Cats.  Does the wide field stop of an eyepiece cause vignetting or does the relatively narrow rear aperture of the Cat cause vignetting?  Again, the answer is "Yes."  Both/and.

 

In any case, it is NOT the long focal length of an eyepiece which would cause vignetting in a linear binoviewer.   The cause is the width of the field stop of the eyepiece interacting with the clear aperture of the binoviewer.  

 

Mike

[Eddgie]

Does the field stop of an eyepiece cause vignetting?  Or does the clear aperture of the binoviewer cause vignetting?  The answer to both questions is "Yes."   It is not a matter of either/or but both/and. 

 

The situation is similar to vignetting in Cats.  Does the wide field stop of an eyepiece cause vignetting or does the relatively narrow rear aperture of the Cat cause vignetting?  Again, the answer is "Yes."  Both/and.

 

In any case, it is NOT the long focal length of an eyepiece which would cause vignetting in a linear binoviewer.   The cause is the width of the field stop of the eyepiece interacting with the clear aperture of the binoviewer.  

 

Mike

Please don't be offended by my input. This is not meant as an attack or challenge. 

 

The eyepiece field stop never vignettes the image. The field stop of an eyepiece is at the focal plane. Vignetting only occurs if there is a restriction (almost always circular where telescopes are involved), somewhere between the focal plane and the eyepiece field stop. Since the field stop is at the point where the image is formed, then it simply opaques 100% of the light reaching the focal plane that does not fall into the diameter of the field stop. 

 

 

The rear aperture of the binoviewer does vignette the image very slightly but because the rear aperture is so close to the focal plane, the opaquing can be a major factor. You likely would not see the opaquing using a 27mm field stop in a 26mm aperture bionviewer, but you can see it using a 27mnm field stop in a smaller prism binocular. Opaquing is identified to occur when the you drift a bright star to the edge of the field and it winks out before you get to the field stop. If it dims before it get to the field stop, that is vignetting.  If it disappears before it gets to the field stop, that is opaquing, and it would almost always be caused by the rear aperture of a binoviewer, though when using the widest field eyepieces possible  in a C8 or smaller SCT or MCT, you might see some opaquing at the very extreme edge of the field. In the C8, this will happen just before the field stop of a 41mm Panoptic or a 55mm Plossl. If you don't know what to look for, you would never notice it but the true field will be about the same as when using an eyepiece with a field stop about 3mm smaller.   

 

In fact, the primary reason for the field stop of a telescope is to block you from seeing the out of focus inside diameter of the end of the eyepiece barrel.
 

The primary source of vignetting in the SCT is the front of the baffle, not the rear. The rear baffle is there to opaque the outside of the field so no off axis light that gets through the space between the outside edge of the secondary baffle and the inside edge of the front baffle. In theory, you could make the baffle a cone shape with the larger end of the cone at the back of the scope and this would make the field wider, but the field would still be vignetted by the front of the baffle. 

 

Here is the illumination profile of a C8 type SCT. Notice that the illumination falls off outside of about an 8mm image circle. As you go further off axis, the illumination falls smoothly.  This would be the case even if the rear baffle were larger but if the illumination were allowed to fall off much more than 70%, it would not be for imaging with anything other than small sensors. 

 

The sudden downward break in the downward curve is when the rear baffle starts to opaque (completely block) the off axis rays entering the opposite side of the front of the baffle. If you were to make this larger, you would extend the gentle vignetting, but now, if you looked at an angle between the edge of the rear port through the primary baffle, you would see that you could see past the secondary baffle, and that means light could fall on to the focal plane. You could remedy that by making the secondary baffle larger, further shading the primary and lowering contrast, but the field illumination would continue to fall off until the now larger rear port once again opaqued the the front baffle opening. So, the front of the baffle vignettes, and the rear of the baffle opaques any angler larger than the angle between the outside edge of the secondary baffle and the inside edge of the primary baffle, but it does not vignette the system. That is the front of the baffle that does that. You could make the rear baffle as as large as you desire, but the fully illuminated circle size and the illumination falloff would still be the same. The only difference would be where the sharp  break in the attached graph shows.  Yes, the field would be wider, but once again, off axis light would now be able to get to the focal plane. 

 

 

 

 

The rear baffle of the SCT then is not really causing the illumination falloff It is really there to opaque the field at the point that the designer believed would provide a good compromise between keeping the contrast high and the field illumination at a practical level. 

Edited by Eddgie, 20 January 2024 - 02:16 PM.

[Sarkikos]

Please don't be offended by my input. This is not meant as an attack or challenge. 

 

The eyepiece field stop never vignettes the image. The field stop of an eyepiece is at the focal plane. Vignetting only occurs if there is a restriction (almost always circular where telescopes are involved), somewhere between the focal plane and the eyepiece field stop. Since the field stop is at the point where the image is formed, then it simply opaques 100% of the light reaching the focal plane that does not fall into the diameter of the field stop. 

 

 

The rear aperture of the binoviewer does vignette the image very slightly but because the rear aperture is so close to the focal plane, the opaquing can be a major factor. You likely would not see the opaquing using a 27mm field stop in a 26mm aperture bionviewer, but you can see it using a 27mnm field stop in a smaller prism binocular. Opaquing is identified to occur when the you drift a bright star to the edge of the field and it winks out before you get to the field stop. If it dims before it get to the field stop, that is vignetting.  If it disappears before it gets to the field stop, that is opaquing, and it would almost always be caused by the rear aperture of a binoviewer, though when using the widest field eyepieces possible  in a C8 or smaller SCT or MCT, you might see some opaquing at the very extreme edge of the field. In the C8, this will happen just before the field stop of a 41mm Panoptic or a 55mm Plossl. If you don't know what to look for, you would never notice it but the true field will be about the same as when using an eyepiece with a field stop about 3mm smaller.   

 

In fact, the primary reason for the field stop of a telescope is to block you from seeing the out of focus inside diameter of the end of the eyepiece barrel.
 

The primary source of vignetting in the SCT is the front of the baffle, not the rear. The rear baffle is there to opaque the outside of the field so no off axis light that gets through the space between the outside edge of the secondary baffle and the inside edge of the front baffle. In theory, you could make the baffle a cone shape with the larger end of the cone at the back of the scope and this would make the field wider, but the field would still be vignetted by the front of the baffle. 

 

Here is the illumination profile of a C8 type SCT. Notice that the illumination falls off outside of about an 8mm image circle. As you go further off axis, the illumination falls smoothly.  This would be the case even if the rear baffle were larger but if the illumination were allowed to fall off much more than 70%, it would not be for imaging with anything other than small sensors. 

 

The sudden downward break in the downward curve is when the rear baffle starts to opaque (completely block) the off axis rays entering the opposite side of the front of the baffle. If you were to make this larger, you would extend the gentle vignetting, but now, if you looked at an angle between the edge of the rear port through the primary baffle, you would see that you could see past the secondary baffle, and that means light could fall on to the focal plane. You could remedy that by making the secondary baffle larger, further shading the primary and lowering contrast, but the field illumination would continue to fall off until the now larger rear port once again opaqued the the front baffle opening. So, the front of the baffle vignettes, and the rear of the baffle opaques any angler larger than the angle between the outside edge of the secondary baffle and the inside edge of the primary baffle, but it does not vignette the system. That is the front of the baffle that does that. You could make the rear baffle as as large as you desire, but the fully illuminated circle size and the illumination falloff would still be the same. The only difference would be where the sharp  break in the attached graph shows.  Yes, the field would be wider, but once again, off axis light would now be able to get to the focal plane. 

 

 

Screenshot 2024-01-20 122504.png

 

 

The rear baffle of the SCT then is not really causing the illumination falloff It is really there to opaque the field at the point that the designer believed would provide a good compromise between keeping the contrast high and the field illumination at a practical level. 

Front of the baffle or rear of the baffle, the baffle of the SCT restricts the light cone that is available at the focal plane.  In future, I'll just say "baffle."    

 

But doesn't the front of the baffle have the same ID as the rear of the baffle?  That is the important point.  

 

If the observer uses an eyepiece with a field stop much wider than the light cone presented by the telescope at the focal plane, isn't there is a drop in illumination in the outer field of the image?  So, you are saying this should not be called vignetting?  Should it be called opaquing?  Or should it be called something else?  

 

In my post, I said "Cats" not "SCTs."  I meant to include Maks as well.  I have definitely seen a reduction in outer field illumination when viewing through a C90 with some eyepieces, especially if a 0.63x R/C is in the stack and/or wider field 2" eyepieces are used.  The rear aperture of the C90 is only 16mm, as I measured it with a digital caliper.  I don't know about restrictions on the light cone anywhere else.  

 

The only binoviewer I have now is an old Burgess with a 20mm clear aperture.   I don't have any with a 26mm aperture.   I am thinking about getting an Orion Linear Binoviewer because it can come to focus without a Barlow or OC.   I like the idea of binoviewing at native magnification with Newts and refractors ... without having to do drastic surgery on the OTA.  But the clear aperture in the Linear is only 17mm, even less than the Burgess.  How will this affect the image when viewing with eyepieces which have field stops much wider than 17mm?   A reduction in the outer field illumination?  Vignetting?  Opaquing?   Should we even bother with binoviewers for low-power deep sky if they have such narrow clear apertures?   

 

Mike

Edited by Sarkikos, 20 January 2024 - 04:53 PM.

[Princess Leah]

The 56mm is 70% of the 80mm and this is the aperture that would give the same brightness when using one eye as the 80mm does when using two eyes with a binoviewer.

 

No, does not apply to binoviewers. 

Not sure if you made a wee mistake here.

 

56mm would be less than 50% of the aperture of a 80mm refractor.

[kroum]

Front of the baffle or rear of the baffle, the baffle of the SCT restricts the light cone that is available at the focal plane.  In future, I'll just say "baffle."    

 

But doesn't the front of the baffle have the same ID as the rear of the baffle?  That is the important point.  

 

If the observer uses an eyepiece with a field stop much wider than the light cone presented by the telescope at the focal plane, isn't there is a drop in illumination in the outer field of the image?  So, you are saying this should not be called vignetting?  Should it be called opaquing?  Or should it be called something else?  

 

In my post, I said "Cats" not "SCTs."  I meant to include Maks as well.  I have definitely seen a reduction in outer field illumination when viewing through a C90 with some eyepieces, especially if a 0.63x R/C is in the stack and/or wider field 2" eyepieces are used.  The rear aperture of the C90 is only 16mm, as I measured it with a digital caliper.  I don't know about restrictions on the light cone anywhere else.  

 

The only binoviewer I have now is an old Burgess with a 20mm clear aperture.   I don't have any with a 26mm aperture.   I am thinking about getting an Orion Linear Binoviewer because it can come to focus without a Barlow or OC.   I like the idea of binoviewing at native magnification with Newts and refractors ... without having to do drastic surgery on the OTA.  But the clear aperture in the Linear is only 17mm, even less than the Burgess.  How will this affect the image when viewing with eyepieces which have field stops much wider than 17mm?   A reduction in the outer field illumination?  Vignetting?  Opaquing?   Should we even bother with binoviewers for low-power deep sky if they have such narrow clear apertures?   

 

Mike

Before I upgraded to a denk 2 with OCS and power switches (regular and focal reducer switches) I used an old Orion prism binoviewer wirh 20mm prisms and 22mm field stops at the eyepiece end. I believe it’s optically identical to the burgess one you have.

I found that I could use eyepieces with field stops up to ~23mm without noticeable vignetting. (25mm Plossls and 18mm UFF eyepieces work without noticeable vignetting)

In addition to the 2x OCS/barlow that came with that binoviewer, there is a 1.6x available from Omegon that is relatively affordable.  It was ~$30 when I bought it and it’s about $50 now on Amazon.  It requires more back focus than the 2x OCS, but still significantly less than trying to use the binoviewer without an OCS. I was able to use this configuration with both my 6” f5 reflector (with a low profile focuser), as well as with my 80mm f7 SVBONY ED refractor if I use a 1.25” prism diagonal.

 

If this works for you, you’re almost at the same effective eyepiece field stop of the linear binoviewer. (14.4mm vs. 17.5mm)

 

Personally, for the price I don’t think the linear binoviewer is a good choice.

I got my denk 2 with the power switches and a bunch of adapters and accessories used, for about the same price on the CL classifieds and I’m thrilled with the performance and versatility. Every eyepiece pair gives me 6 different power options, the lowest of which is ~1x, so I can use eyepieces at their native focal lengths and while it’s not quite a full 27mm clear aperture, it’s pretty close.  I can use 30mm Plossls and there is just a little vignetting with the focal reducer switch + lowest power arm of the power switch.  I’m looking at 25mm 60 degree eyepieces next as my lowest power pair without any vignetting, though the previous owner used a pair of 24mm Panoptics ‍♂.

 

if you have a 25mm Plossl already, I’d say it might be worth trying getting a second one to use with your Burgess binoviewer, and then checking how much extra back focus you have with the optical path corrector that came with it to see if it might be worth investing in the 1.6x Omegon for an even bigger exit pupil and wider field with the 25mm Plossls.

[Sarkikos]

Before I upgraded to a denk 2 with OCS and power switches (regular and focal reducer switches) I used an old Orion prism binoviewer wirh 20mm prisms and 22mm field stops at the eyepiece end. I believe it’s optically identical to the burgess one you have.

I found that I could use eyepieces with field stops up to ~23mm without noticeable vignetting. (25mm Plossls and 18mm UFF eyepieces work without noticeable vignetting)

In addition to the 2x OCS/barlow that came with that binoviewer, there is a 1.6x available from Omegon that is relatively affordable.  It was ~$30 when I bought it and it’s about $50 now on Amazon.  It requires more back focus than the 2x OCS, but still significantly less than trying to use the binoviewer without an OCS. I was able to use this configuration with both my 6” f5 reflector (with a low profile focuser), as well as with my 80mm f7 SVBONY ED refractor if I use a 1.25” prism diagonal.

 

If this works for you, you’re almost at the same effective eyepiece field stop of the linear binoviewer. (14.4mm vs. 17.5mm)

 

Personally, for the price I don’t think the linear binoviewer is a good choice.

I got my denk 2 with the power switches and a bunch of adapters and accessories used, for about the same price on the CL classifieds and I’m thrilled with the performance and versatility. Every eyepiece pair gives me 6 different power options, the lowest of which is ~1x, so I can use eyepieces at their native focal lengths and while it’s not quite a full 27mm clear aperture, it’s pretty close.  I can use 30mm Plossls and there is just a little vignetting with the focal reducer switch + lowest power arm of the power switch.  I’m looking at 25mm 60 degree eyepieces next as my lowest power pair without any vignetting, though the previous owner used a pair of 24mm Panoptics ‍♂.

 

if you have a 25mm Plossl already, I’d say it might be worth trying getting a second one to use with your Burgess binoviewer, and then checking how much extra back focus you have with the optical path corrector that came with it to see if it might be worth investing in the 1.6x Omegon for an even bigger exit pupil and wider field with the 25mm Plossls.

I have a wide selection of Barlows and OCS's, including the 1.6x that came with the Burgess, which is probably effectively the same as the Omegon 1.6x.   I also have a wide selection of eyepieces, many of them in pairs for binoviewing.  I experimented with many different setups using the Burgess on my 10" f/5 Dob, so I know what it is capable of.  What it's not capable of is coming to focus at native magnification in the Dob.  Also, the narrow clear aperture makes it prone to vignetting and the binoviewer itself decreases the effective light grasp.  All these factors limit its value for deep sky.   

 

For many years, I binoviewed planet/lunar with the Burgess and the Dob.  I never did much binoviewing for deep sky because I'm well aware of the limitations of the Burgess for deep sky.  I never thought it was worth the trouble.   Monoviewing will give lower-power and a wider field and will allow you to go deeper.   

 

On the other hand, at least a linear binoviewer allows the Dob - or refractor - to perform at native magnification, which is an advantage for deep sky over other types of binoviewer which require a Barlow/OCS.  

 

I prefer to buy new, not used, when possible.   But it would be nice if Orion put their Linear on sale. 

 

One thing I don't like about the Denks is that they appear to require different setups for Newtonian vs other telescope types.  I want something that's a simple plug-n-play among different types of scopes.  The Orion Linear is simple plug-n-play.

 

I checked the Orion website this morning.  Their Linear Binoviewer is not available until March 10th.   I put in an order for one.  I made sure to use a credit card directly, not through PayPal, so the credit card won't be charged until the item is shipped.  I hate ordering something and having my CC be charged long before shipment.  

 

At least this puts me in the door for the Orion Linear.  I have time to cancel if I change my mind.

 

Mike

Edited by Sarkikos, 21 January 2024 - 12:09 PM.

[betacygni]

I have a wide selection of Barlows and OCS's, including the 1.6x that came with the Burgess, which is probably effectively the same as the Omegon 1.6x. I also have a wide selection of eyepieces, many of them in pairs for binoviewing. I experimented with many different setups using the Burgess on my 10" f/5 Dob, so I know what it is capable of. What it's not capable of is coming to focus at native magnification in the Dob. Also, the narrow clear aperture makes it prone to vignetting and the binoviewer itself decreases the effective light grasp. All these factors limit its value for deep sky.

For many years, I binoviewed planet/lunar with the Burgess and the Dob. I never did much binoviewing for deep sky because I'm well aware of the limitations of the Burgess for deep sky. I never thought it was worth the trouble. Monoviewing will give lower-power and a wider field and will allow you to go deeper.

On the other hand, at least a linear binoviewer allows the Dob - or refractor - to perform at native magnification, which is an advantage for deep sky over other types of binoviewer which require a Barlow/OCS.

I prefer to buy new, not used, when possible. But it would be nice if Orion put their Linear on sale.

One thing I don't like about the Denks is that they appear to require different setups for Newtonian vs other telescope types. I want something that's a simple plug-n-play among different types of scopes. The Orion Linear is simple plug-n-play.

I checked the Orion website this morning. Their Linear Binoviewer is not available until March 10th. I put in an order for one. I made sure to use a credit card directly, not through PayPal, so the credit card won't be charged until the item is shipped. I hate ordering something and having my CC be charged long before shipment.

At least this puts me in the door for the Orion Linear. I have time to cancel if I change my mind.

Mike

I’ll preface this by saying I don’t own the linear style binoviewer. But the reaching focus at native focal length is a bit misleading. The aperture of the linears is only 17mm, so you’re effectively limiting yourself to eyepieces with this field stop. Using standard prism binoviewers with a 1.6x amplifier will give you an identical effective field stop (~17mm) with a 27mm field stop eyepiece (ie 32mm plossl, 24mm panoptic, etc). The linears also seem to have some reflection issues and other oddities. Again maybe I’m missing something with the linears, but I can’t see how they make sense, even in a newt. Now if they had a full 27mm aperture that would be another story entirely. But as is your effective longest focal length eyepiece is the same with the linears as a prism binoviewer with 1.6x amplifier (20mm plossl in linear, 32mm/1.6x=20mm is standard prism style).

Edited by betacygni, 22 January 2024 - 12:15 AM.

[Sarkikos]

I’ll preface this by saying I don’t own the linear style binoviewer. But the reaching focus at native focal length is a bit misleading. The aperture of the linears is only 17mm, so you’re effectively limiting yourself to eyepieces with this field stop. Using standard prism binoviewers with a 1.6x amplifier will give you an identical effective field stop (~17mm) with a 27mm field stop eyepiece (ie 32mm plossl, 24mm panoptic, etc). The linears also seem to have some reflection issues and other oddities. Again maybe I’m missing something with the linears, but I can’t see how they make sense, even in a newt. Now if they had a full 27mm aperture that would be another story entirely. But as is your effective longest focal length eyepiece is the same with the linears as a prism binoviewer with 1.6x amplifier (20mm plossl in linear, 32mm/1.6x=20mm is standard prism style).

Reaching focus at native magnification is literally true for the linears.  Being able to binoview natively is not just about field stops, AFOVs and TFOVs.  The exit pupil will be wider, which has some value sometimes in itself.

 

But in any case, you can use eyepieces with field stops somewhat wider than the clear aperture of the binoviewer.  No one is going to stop you.    There may be some drop off for illumination in the outer field, which you might or might not notice.  

 

What is a "standard" prism binoviewer?   I don't think 27mm clear aperture is standard.  I think that is high end.   My Burgess binoviewers might be considered old outliers - they probably are!  - but their clear aperture is only 20mm.

 

Besides, TOMDEY liked the Orion Linears!   https://www.cloudyni...er-mini-review/    Maybe his most succinct takeaway - yes, difficult to find for TOMDEY - is this:

 

Howdy! By far the greatest advantage of this Linear is that you just plug it in and use it. It's absolutely parfocal with your telescope as-is, no need to change anything.

Mike

Edited by Sarkikos, 22 January 2024 - 10:09 AM.

[betacygni]

Reaching focus at native magnification is literally true for the linears. Being able to binoview natively is not just about field stops, AFOVs and TFOVs. The exit pupil will be wider, which has some value sometimes in itself.

But in any case, you can use eyepieces with field stops somewhat wider than the clear aperture of the binoviewer. No one is going to stop you. There may be some drop off for illumination in the outer field, which you might or might not notice.

What is a "standard" prism binoviewer? I don't think 27mm clear aperture is standard. I think that is high end. My Burgess binoviewers might be considered old outliers - they probably are! - but their clear aperture is only 20mm.

Besides, TOMDEY liked the Orion Linears! https://www.cloudyni...er-mini-review/ Maybe his most succinct takeaway - yes, difficult to find for TOMDEY - is this:

Mike

True, but if your goal is exit pupil, and you don’t care about TFOV or AFOV, then this can also be accomplished by 40mm plossls (and even some 45mm plossls if you find a pair of old Celestron silvertops).

The models I had in mind with standard were the Maxbright II, which are middle of the road price wise, and do indeed have close to 27mm prisms (26mm or so), and not much more expensive than linears.

By all means I hope the linears work out well for you. I just often see them recommended as a solution to amplifiers, and except in unique cases like perhaps chasing larger exit pupils or not caring about getting a hard vignette limiting AFOV, I’m not convinced they are really all they are cracked up to be. But like I prefaced my post with I’ve never used them, so could be off base.

One of these days I’m going to have to try out a pair, so then I could criticize with better authority 

Edited by betacygni, 22 January 2024 - 11:15 AM.

[Hwunkzeep]

True, but if your goal is exit pupil, and you don’t care about TFOV or AFOV, then this can also be accomplished by 40mm plossls (and even some 45mm plossls if you find a pair of old Celestron silvertops).

The models I had in mind with standard were the Maxbright II, which are middle of the road price wise, and do indeed have close to 27mm prisms (26mm or so), and not much more expensive than linears.

By all means I hope the linears work out well for you. I just often see them recommended as a solution to amplifiers, and except in unique cases like perhaps chasing larger exit pupils or not caring about getting a hard vignette limiting AFOV, I’m not convinced they are really all they are cracked up to be. But like I prefaced my post with I’ve never used them, so could be off base.

One of these days I’m going to have to try out a pair, so then I could criticize with better authority 

I think you'll like it.  I've used it with an 8" and 12" Dob.  "Up" to 40mm Plossls with the 8", and 32 mm with the 12'.  I've also used it with with a pair of zooms (24 to 8mm) on both scopes.

 

I'll be the first to admit it IS a bit fussy to do.  Having a Starbound chair and keeping the binoviewer parallel to the ground is very helpful.

 

It's not a configuration I start newbies with.  Takes a couple minutes of "hassle".  But it's really good once you get there...

[betacygni]

I think you'll like it. I've used it with an 8" and 12" Dob. "Up" to 40mm Plossls with the 8", and 32 mm with the 12'. I've also used it with with a pair of zooms (24 to 8mm) on both scopes.

I'll be the first to admit it IS a bit fussy to do. Having a Starbound chair and keeping the binoviewer parallel to the ground is very helpful.

It's not a configuration I start newbies with. Takes a couple minutes of "hassle". But it's really good once you get there...

I’ll have to give them a try one of these days. I’ve somehow found myself becoming a binoviewer collector for some odd reason, guess I should just embrace it!

That said to your point about newbies I really wish the Televue Binovues still existed new. Except for the linears there doesn’t seem to be any off the shelf binoviewers that just simply reach focus with all scopes like the Binovues did.

Maybe I should try to talk Televue into at least reintroducing their t2 2x binovue amplifier.

Edited by betacygni, 16 February 2024 - 10:58 PM.

[Sarkikos]

I think you'll like it.  I've used it with an 8" and 12" Dob.  "Up" to 40mm Plossls with the 8", and 32 mm with the 12'.  I've also used it with with a pair of zooms (24 to 8mm) on both scopes.

 

I'll be the first to admit it IS a bit fussy to do.  Having a Starbound chair and keeping the binoviewer parallel to the ground is very helpful.

 

It's not a configuration I start newbies with.  Takes a couple minutes of "hassle".  But it's really good once you get there...

I always observe sitting.   

 

I don't think binoviewers would be good for outreach, given the range in IPDs and the general fussiness of trying to align the images.   

 

Mike

[Sarkikos]

I’ll have to give them a try one of these days. I’ve somehow found myself becoming a binoviewer collector for some odd reason, guess I should just embrace it!

That said to your point about newbies I really wish the Televue Binovues still existed new. Except for the linears there doesn’t seem to be any off the shelf binoviewers that just simply reach focus with all scopes like the Binovues did.

Maybe I should try to talk Televue into at least reintroducing their t2 2x binovue amplifier.

But didn't the TV Binoviewers have a built-in 2x power factor?  (That's my understanding from previous posts.)  That's why they can reach focus.  I could have the working equivalent of this by just keeping an OCS on my old Burgess Binoviewer, or pretty much any standard binoviewer that's available.  But they would not be running at native magnifications.  

 

Mike

Edited by Sarkikos, 17 February 2024 - 11:11 AM.

[betacygni]

But didn't the TV Binoviewers have a built-in 2x power factor? (That's my understanding from previous posts.) That's why they can reach focus. I could have the working equivalent of this by just keeping an OCS on my old Burgess Binoviewer, or pretty much any standard binoviewer that's available. But they would not be running at native magnifications.

Mike

Yes, for your case where you don’t mind the vignette of the Linears the binovues might not make sense. I meant from a stand alone, someone wanting a plug and play system, the binovues did that with any scope. Binoviewer options available today generally are not that simple.

[noisejammer]

... I don't think binoviewers would be good for outreach, given the range in IPDs and the general fussiness of trying to align the images.  ...

That's my experience too - even folk who are comfortable with an eyepiece and binoculars seem to struggle getting the IPD and dioptre setting correct. I suspect this is because a scope usually produces a smaller exit pupil.