29 replies to this topic

[sunrag]

I bought this Apogee refractor from another CN member last month. There is no label on the tube other than the name "Apogee".

 

It is very well made, thick tubing, integrated sliding dew-shield. Focuser flange seems to press-fitted into the tube. The objective cell can be unscrewed from the tube and also seems to be very well made.

 

However, I am not getting very good star images. Even at low magnification of 30x, one can see that defocussed image is not symmetrical.

 

The buyer sold it with the disclaimer that it needs collimation, so I was expecting to do some work to get it collimated.  However I am finding that the objective is very different from any Achromat I have worked with. 

 

First, the front Lens (crown) is 110mm aperture, but the rear lens (flint) is only 100mm.

Second, there are two metal rings between them to act as spacers. One ring close to the front lens is ~ 10mm thick, and the second ring is ~ 2 mm thick. (These are estimates I did not actually measure them). So overall the space between the two elements is ~ 12mm!

I don't think it is common achromat like Fraunhofer because of the different element diameters and the huge spacing between them.

 

I did not find any marking on the edges of the elements, but I pencilled in the "as-found" orientation.

 

I think the only adjustments possible to collimate it is to rotate the elements w.r.t each other, or rotate the spacers. In a Fraunhofer doublet, I can use Newton's rings to  guide me how to rotate the elements or adjust the spacers. The large spacers preclude Newton's Rings method on this.

 

So anyone experienced with this before?

 

 

This picture below shows Top to Bottom:

 

100mm Flint

2mm Spacer

10mm Spacer

110mm Crown

 

 

Edited by sunrag, 05 April 2025 - 08:19 PM.

[triplemon]

Looks like a Clark-type objective.

 

Have you checked with a laser that there is actually any lens tilt in the as found configuration in the first place ?
The lens stack is likely parallel, as it only depends on the spacer - but how is the stack mounted in the OTA ?

How is the smaller lens centered in the OTA ? Reducing ring or something built into the OTA ?As there is a zillion things that can degrade image quality, objective collimation being only one of many.

And how is the focuser tilt ?

 

Any of that may be inadequately built, may not hold up under vibration of shock, but then you would have to build something better or adjustable first to get better results.

 

As there is a zillion things that can degrade image quality, objective collimation being only one of many.

Edited by triplemon, 05 April 2025 - 09:43 PM.

[RichA]

I bought this Apogee refractor from another CN member last month. There is no label on the tube other than the name "Apogee".

 

It is very well made, thick tubing, integrated sliding dew-shield. Focuser flange seems to press-fitted into the tube. The objective cell can be unscrewed from the tube and also seems to be very well made.

 

However, I am not getting very good star images. Even at low magnification of 30x, one can see that defocussed image is not symmetrical.

 

The buyer sold it with the disclaimer that it needs collimation, so I was expecting to do some work to get it collimated.  However I am finding that the objective is very different from any Achromat I have worked with. 

 

First, the front Lens (crown) is 110mm aperture, but the rear lens (flint) is only 100mm.

Second, there are two metal rings between them to act as spacers. One ring close to the front lens is ~ 10mm thick, and the second ring is ~ 2 mm thick. (These are estimates I did not actually measure them). So overall the space between the two elements is ~ 12mm!

I don't think it is common achromat like Fraunhofer because of the different element diameters and the huge spacing between them.

 

I did not find any marking on the edges of the elements, but I pencilled in the "as-found" orientation.

 

I think the only adjustments possible to collimate it is to rotate the elements w.r.t each other, or rotate the spacers. In a Fraunhofer doublet, I can use Newton's rings to  guide me how to rotate the elements or adjust the spacers. The large spacers preclude Newton's Rings method on this.

 

So anyone experienced with this before?

 

IMG_3946.jpg

 

This picture below shows Top to Bottom:

 

100mm Flint

2mm Spacer

10mm Spacer

110mm Crown

 

 

IMG_3945.jpg

How on Earth could they get that thing to work without either cementing it or having lateral alignment screws?  Would have to be a very good two-tiered cell and even then, unless the elements were completely symmetrical it would be hard to achieve a good, round diffraction pattern.

Edited by RichA, 05 April 2025 - 09:51 PM.

[triplemon]

Well, thats a prototype of their richest field series. Only the 80 and 90mm seem to have ever made it into production.
Fast achromats at a price point below ordinary achromats, intended for low power, guidescope or finder duty, only.
 

Even the 80mm and 90mm versions have quite amusing test reports. Basically just good enough for the intended purpose.

 

https://www.cloudyni...ractor-problem/

[sunrag]

Triplemon & RichA - thanks for your comments.

Before I disassembled, I checked the focuser alignment with the objective using a laser. It was nicely centered. Then I used a cheshire to check the reflections from the elements. That was inconclusive. I could only see one reflection.


Interesting post above. My 110mm (or is it 100mm) looks exactly like the 80mm in that post!

I don’t understand the purpose of the over-sized crown element. The 2-tier spacer is also strange. Too many degrees of freedom that can be messed up.

[sunrag]

Looks like a Clark-type objective.

 

Have you checked with a laser that there is actually any lens tilt in the as found configuration in the first place ?
The lens stack is likely parallel, as it only depends on the spacer - but how is the stack mounted in the OTA ?

How is the smaller lens centered in the OTA ? Reducing ring or something built into the OTA ?As there is a zillion things that can degrade image quality, objective collimation being only one of many.

And how is the focuser tilt ?

 

Any of that may be inadequately built, may not hold up under vibration of shock, but then you would have to build something better or adjustable first to get better results

 

As there is a zillion things that can degrade image quality, objective collimation being only one of many.

This whole stack fits into the cell. The retainer ring is more than just a ring. It is pretty thick, with an ID to match the rear element, and OD to match the front element. So the rear element goes inside the retainer ring completely. This is how it is kept centered.

 

I will post a picture of the cell and retainer when I take it apart again.

Edited by sunrag, 06 April 2025 - 07:35 AM.

[davidc135]

I don’t understand the purpose of the over-sized crown element. The 2-tier spacer is also strange. Too many degrees of freedom that can be messed up.

By the time the converging rays have travelled through the crown glass and past the 12mm spacers they should be contained within the 100mm aperture flint.

 

Can the cell be tilted wrt to the tube with shims?

 

David

Edited by davidc135, 06 April 2025 - 07:56 AM.

[sunrag]

The cell screws into the OTA. It cannot be tilted.

[sunrag]

By the time the converging rays have travelled through the crown glass and past the 12mm spacers they should be contained within the 100mm aperture flint.

Yes, that makes sense. 
So it is really a 110mm refractor then. 

[sunrag]

After reassembling it last night (I kept the “as found” orientation), I did an indoor star test. It looked the same as it was on my previous real star test.
Two things that were promising:

I did not detect any color

The inside and outside focus were both circular.  There was no sudden elongation and 90 degrees rotation to indicate astigmatism.

 

At focus, stars showed flaring even at 30x.

 

When assembling, I noticed that it was very easy to slide the elements into the cell & retaining ring. So there must be a gap ~ 0.5mm. This Maybe too much and could allow the elements to get de-centered. So I am thinking of putting thin paper shims spaced 120 degrees apart between the cell and the elements.

Edited by sunrag, 06 April 2025 - 08:59 AM.

[KerryR]

Triplemon & RichA - thanks for your comments.

Before I disassembled, I checked the focuser alignment with the objective using a laser. It was nicely centered. Then I used a cheshire to check the reflections from the elements. That was inconclusive. I could only see one reflection.


Interesting post above. My 110mm (or is it 100mm) looks exactly like the 80mm in that post!

I don’t understand the purpose of the over-sized crown element. The 2-tier spacer is also strange. Too many degrees of freedom that can be messed up.

Here's useful trick I stumbled on several years ago that can help with seeing and aliginging the cheshire reflections: Mask off 1/2 of the opening in the side of the cheshire (easy) or 1/2 of the reflective surface (better, but harder). It's best to use completely opaque tape, like foil or electrical. When you look through the chesire under these conditions, you'll now see the first bright reflection cut in half, and the dimmer second reflection also cut in half but opposing the first. Under these conditions, it's easy to see minor misalignments that can be lost in the brighter first reflection. If you have collimation screws (which I know you don't, but I'll explain anyway), and you align the edge of the mask with long axis of the ota, you can rotate the ep to align the split in the reflections to the screws, one at a time, and see which screw needs the most attention. (Here's a very old post with an illustration of what you see...)

 

On another note: I think you could be on the right track by shimming the elements accurately in place to maintain centering. I did exactly that with my old Meade ED127, which was incredibly sensitive to tiny centering issues in it's slightly loose cell, to great effect.

 

If that doesn't fix the issue, I'd try to figure out of there's any lens wedge. Sometimes you can do this in real time on a star by leaving the front element a little loose in the cell, star test, and, using latex or nitrile gloves for cleanliness and friction, contact the face of the front element and rotate (only the front element) and retest.

[sunrag]

Thank you! That is a great idea with the Cheshire mask! I will try that.

I think one of the reasons the second reflection is faint/invisible is because of the huge space (~12mm) between the elements.

I will try next time at night in a pitch black room.

[KerryR]

Thank you! That is a great idea with the Cheshire mask! I will try that.

I think one of the reasons the second reflection is faint/invisible is because of the huge space (~12mm) between the elements.

I will try next time at night in a pitch black room.

I hope you find it useful... probably not on this scope so much, because of the un-adjustable cell, but maybe on a different scope.

 

Along these lines, the new(?) ColliDream collimator looks like it might help with this kind of thing, too, with it's adjustable brightness and cross-hair design. I haven't decided if I "need" one yet or not...

[Jon Isaacs]

I would contact the proprietor of Apogee Inc, Sheldon Farowski.  This is his CN Profile.  He is still active. 

 

https://www.cloudyni.../25634-masilmw/

 

I am not sure how much I would expect out of the scope.  I think my old Sky and Telescopes from that era (~20 plus years ago) but as I recall, those were very inexpensive and mostly plastic.  

 

The fact that the seller told you it needed collimation was only the seller's guess.. 

 

Jon

[sunrag]

Thanks Jon.  The seller sold it really cheap, and half it was for shipping cost. He said he could not collimate it, so i thought I would take a shot. I have restored collimation on a lot of refractors but those were all the common Fraunhofer doublets. I have never seen a Clark doublet until now. I Still have a lot to learn I think.
 

Mine is made entirely of metal, and built like a tank. Even the baffles appear to be solidly attached, not the typical friction hold.

[KerryR]

I wonder what the deal is with the two different sized elements?

 

Maybe the elements were pre-existing, and paired after the fact because they had the right curves.

 

I remember that several years ago, there was a short period of time where aespherizing some lower-cost fast achromat elements- ostensibly for better performance for the cost- was a thing. I don't think it continued due to the proliferation of "cheap" fast ED scopes. But maybe that's part of the reason for this scope's odd design...

[sunrag]

Still working on the Apogee refractor collimation. Everything I have tried so far has only worsened the collimation. 

 

I am beginning to think it is predominantly a cell Tilt issue, and not elements issue (such as centering or spacing or clocking). I am excluding the elements issues not because of extensive testing of these effects, but because these are hard to adjust! 

 

The reason I think it is a tilt issue is because I unscrewed the cell a little bit to induce some play and was able to tilt the cell by hand - the focussed image quality varied quite a bit (nothing improved just got worse). So even with the cell screwed in tight, perhaps it is tilting the elements a little bit.

Edited by sunrag, 16 April 2025 - 09:38 AM.

[sunrag]

I wonder what the deal is with the two different sized elements?

 

Maybe the elements were pre-existing, and paired after the fact because they had the right curves.

 

I remember that several years ago, there was a short period of time where aespherizing some lower-cost fast achromat elements- ostensibly for better performance for the cost- was a thing. I don't think it continued due to the proliferation of "cheap" fast ED scopes. But maybe that's part of the reason for this scope's odd design...

I think the reason for the smaller rear element is because the front element is very steeply curved and the exiting light tapers very quickly from 110mm to 100mm in just 12mm.

Edited by sunrag, 16 April 2025 - 09:56 AM.

[Jon Isaacs]

I think the reason for the smaller rear element is because the front element is very steeply curved and the exiting light tapers very quickly from 110mm to 100mm in just 12mm.

 

It would be interesting to measure the effective aperture.  I have fixture based on a laser collimator I use.  I focus at infinity with a 4.8 mm Nagler and then illuminate the eyepiece with the laser.  It's quite accurate. 

 

 

 

Jon

[KerryR]

That's a very cool fixture for the laser, Jon. My "solution" has always resorted to stacks of books and magazines to get everything lined up, which makes the test tedious. I've not tried a laser as the light source- without a cool fixture it's a little tougher to set up with a laser instead of an LED flashlight.

 

I'd be curious about the results in this scope. I have a suspicion the effective aperture is going to be that of the smaller element...

 

I got into a little hot water with this test a few years ago in a very long thread about the effective aperture of my Synta 127 Mak, with some optical experts that questioned the test's efficacy. But I performed two other tests using different methodologies, and the results were within a mm or two, so I feel pretty confident that the test works. Plus, out of all the scopes I tested with the laser (flashlight) test, the only one to "fail" was the 127-- everything else came out to the stated aperture +- a mm or two. (+- 1mm because the edge of the disk using an LED is a teeny gradient, so I had to estimate the center of the gradient for the measurement. Using a laser dramatically reduces this minor problem and increases accuracy..)

Edited by KerryR, 16 April 2025 - 11:07 AM.

[Jon Isaacs]

Kerry:

 

Not to get too far off topic but I believe the consensus is that the 127 mm Synta Mak had an effective aperture of about 120 mm.

 

My fixture is based on the fact that the 4.8 mm Nagler has both a 1.25 inch barrel and a 1.25 inch body so I can mount a 2 inch laser collimator to the eyepiece with a 2 inch -1.25 inch adapter plus a sleeve.

 

Jon

[CollinofAlabama]

Be VERY careful

[sunrag]

Be VERY careful

Interesting thread! It did not say so explicitly, but the OP adjusted the centering screws which made the Airy rings not lop-sided? 

 

Also cool tip about using a prism diagonal to eliminate color aberration...got to try that next. But that is opposite of conventional wisdom - using prism diagonals in fast F actually makes color aberration worse? The OP said he saw red flare around bright stars, which is also opposite of my experience with Achros - i see purple flare. Could be the two opposites cancel in that case.

Edited by sunrag, 16 April 2025 - 03:52 PM.

[CollinofAlabama]

Bear in mind his Orion was an ED scope -- FPL-51, and a 110mm doublet at F/6, so not exactly color-free, but ED just the same.  It would have less CA than any achromat.

[Terra Nova]

Kerry:

 

Not to get too far off topic but I believe the consensus is that the 127 mm Synta Mak had an effective aperture of about 120 mm.

 

My fixture is based on the fact that the 4.8 mm Nagler has both a 1.25 inch barrel and a 1.25 inch body so I can mount a 2 inch laser collimator to the eyepiece with a 2 inch -1.25 inch adapter plus a sleeve.

 

Jon

I thought that measurements had shown it to be closer to 114mm.