126 replies to this topic

[Roger Belveal]

which part please sir ?

The  36.4 male to male t- thread

[Soundboy121]

Baader Takahashi / Vixen M36.4 Male to T2 Male Camera Adapter # T2-03 1508039

[Roger Belveal]

I put a Helical focuser on one and a rack-n-pinion focuser off an old Coulter dob on the other. I got real creative a put a nice paint job on the Explorer scientific twilight 1 mount and a Universal Astonomics tripod. Just got to add some decals on the tripod and she's all done...

[Roger Belveal]

She's looking good now...

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[Soundboy121]

That look beautiful please more pictures when u can. Can I ask wat are u using for a dew shield?? Just in time for Halloween 🎃

[Roger Belveal]

I picked up a piece of light weight metal flashing at my local hardware store for the dew sheild. Got my tripod re-labeled as well... I might be done with this one...

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[davidc135]

 

I've tried to find a source for it, but I'm pretty sure that it was on a posting somewhere on CN. I recall it mentioning two things specifically:

 

1.) The corrector plates for these were surplus corrector plates, possibly manufactured for Celestron's 5.5 inch Schmidt Camera (from a similar time frame) and were adapted for the Comet Catcher. Whether there is truth to that, I do not know.

 

2.) These corrector plates "appear" flat visually, but there is some method of determining that they are actually slightly curved. To do that, one needs an optical flat... and I can't recall what else.

 

3.) There is (or should be) a specific side facing the primary, due to that curvature. Both 2 and 3 I've seen mention of on here.

 

One of these days, I plan on compiling a bunch of relevant posts and links / topics here on CN regarding the Comet Catcher - mostly for my own amusement, but to also maybe to have a definitive source of information for these particular scopes, being the rarity that they are.

 

 

A very late reply but on these points:

 

1. Corrector plates need to be designed and made for their purpose. The ones for the CC have a very mild aspheric figure compared to the super fast 5.5'' Schmidt cameras.

2. There's virtually no optical advantage in imposing the Schmidt profile onto a curved surface instead of flat and I doubt that it would help in manufacturing. There'd be some slight variation.

3. It wouldn't matter which side faced the mirror unless there was some rotation involved in getting the best performance, which could be confused by reversing the corrector. Whether Celestron actually tuned the orientation of the corrector plates before sending them out? Maybe.

 

The correction in waves provided by a corrector plate with one spherical mirror is = A'' x 22.55/ f#³ with A being aperture, so

 

2.66 waves, not very much compared to, say, a 6'' sct with 12 waves. The 2.66 waves correction would appear as around 10 fringes if tested by interference against a flat. I.e ten fringes convex from centre to neutral zone and then ten fringes concave from n.z to the edge, assuming surface started flat.

 

Coma would be that of a Newtonian of 3.6 x sqrt2 = f5, still a bit. Field is fairly flat.

 

David

Edited by davidc135, 31 October 2024 - 08:48 PM.

[DAVIDG]

1.) The corrector plates for these were surplus corrector plates, possibly manufactured for Celestron's 5.5 inch Schmidt Camera (from a similar time frame) and were adapted for the Comet Catcher. Whether there is truth to that, I do not know. 

 

 

Celestron put the correction on both sides of correctors used in their Schmidt camera. The reason was that the Schmidt curve  is deep for the fast optics used in a Schmidt camera and the corrector glass they used was thin.  They used relativity thin glass because it needed to be pulled against the Master Block by vacuum.  So if they only put the correction on one side of  the corrector it  would be even thinner when the curve was ground in and the corrector could easily break during manufacturing. So they put 1/2 the correction on each side.

  So it is very possible that the correctors used in the Comet Catcher were from the 5.5" Schmidt camera and the Comet Catcher was  designed to the use the corrector plates that only had the correction  on one side.  This way they could still  use the same tooling to make them and that reduced production cost. 

 

        - Dave 

Edited by DAVIDG, 01 November 2024 - 02:46 PM.

[Soundboy121]

I put a Helical focuser on one and a rack-n-pinion focuser off an old Coulter dob on the other. 

can u please share pictures of the focuser mod

 

also how to get that celestron orange paint  

[davidc135]

1.) The corrector plates for these were surplus corrector plates, possibly manufactured for Celestron's 5.5 inch Schmidt Camera (from a similar time frame) and were adapted for the Comet Catcher. Whether there is truth to that, I do not know. 

 

 

Celestron put the correction on both sides of correctors used in their Schmidt camera. The reason was that the Schmidt curve  is deep for the fast optics used in a Schmidt camera and the corrector glass they used was thin.  They used relativity thin glass because it needed to be pulled against the Master Block by vacuum.  So if they only put the correction on one  sides the corrector would be even thinner when the curve was ground in and the corrector could easily break during manufacturing. So they put 1/2 the correction on each side.

  So it is very possible that the correctors used in the Comet Catcher were from the 5.5" Schmidt camera and the Comet Catcher was  designed to the use the corrector plates that only had the correction  on one side.  This way they could still  use the same tooling to make them and that reduced production cost. 

 

        - Dave 

The 5.5'' f1.65 Schmidt camera corrector needed a correction of 27.6 waves as compared to 2.66 waves in the Comet Catcher. I don't think the vacuum and master block method can aspherise both sides.

 

David

 

Has anyone measured the corrector thickness of the comet catcher.

Edited by davidc135, 01 November 2024 - 11:09 AM.

[DAVIDG]

The 5.5'' f1.65 Schmidt camera corrector needed a correction of 27.6 waves as compared to 2.66 waves in the Comet Catcher. I don't think the vacuum and master block method can aspherise both sides.

 

David

 

Has anyone measured the corrector thickness of the comet catcher.

 Here is a  quote from the Celestron's  patent on the Master Block method and how the Schmidt corrector for the Schmidt camera were made. So yes this method can be used to place the correction on both sides of the  corrector.

 

           "As an illustration, an 8 inch fl l .5 Schmidt camera calls for a corrector having a curve in excess of the amount that 0.l25 glass can be deformed. In this case a portion of the correction is ground onto one side of the glass and then the balance of the correction is ground onto the other, i.e., ground and polished." 

 https://patents.goog...t/US3889431A/en

 

          - Dave 

Edited by DAVIDG, 01 November 2024 - 08:29 PM.

[davidc135]

 Here quote from the Celestron's  patent on the Master Block method and how the Schmidt corrector for the Schmidt camera were made. So yes this method can be used to place the correction on both sides of the  corrector.

 

           "As an illustration, an 8 inch fl l .5 Schmidt camera calls for a corrector having a curve in excess of the amount that 0.l25 glass can be deformed. In this case a portion of the correction is ground onto one side of the glass and then the balance of the correction is ground onto the other, i.e., ground and polished." 

 https://patents.goog...t/US3889431A/en

 

          - Dave 

OK. Thanks for that. I see that they used two separate blocks.  David

[deSitter]

 Here quote from the Celestron's  patent on the Master Block method and how the Schmidt corrector for the Schmidt camera were made. So yes this method can be used to place the correction on both sides of the  corrector.

 

           "As an illustration, an 8 inch fl l .5 Schmidt camera calls for a corrector having a curve in excess of the amount that 0.l25 glass can be deformed. In this case a portion of the correction is ground onto one side of the glass and then the balance of the correction is ground onto the other, i.e., ground and polished." 

 https://patents.goog...t/US3889431A/en

 

          - Dave 

This is fascinating. Did they try this because they needed to figure something out that came up unexpectedly?

 

-drl

[CrossoverManiac]

I'd like to see astrophotos taken with one of these.  I haven't seen any for sale recently, though there was one several months back in the inland empire craigslist.

 

How do they compare with other fast imaging systems?  I love my Tak Epsilon 130, but even used it was rather expensive.  But even just fiddling with it and my Olympus micro 4/3rds camera can result in some fabulous deep sky images.  If a CC can come close, for a couple orders of magnitude less money, I want one.

 

-Tim.

https://app.astrobin...n-comet-catcher

 

Those are all of the images on AstroBin taken with a Comet Catcher.  So far, I'm disappointed with what few images that were taken with the Comet Catcher.  I had high hopes for a telescope with a focal length of 500 mm at f/3.6.  You will probably be better off with an f/4 astrograph Newtonian with a Starzona 0.75× Coma Corrector.  Then again, maybe the Comet Catchers weren't properly collimated.  But I would suggest caution when purchasing one.

Edited by CrossoverManiac, 01 November 2024 - 05:41 PM.

[telesonic]

1.) The corrector plates for these were surplus corrector plates, possibly manufactured for Celestron's 5.5 inch Schmidt Camera (from a similar time frame) and were adapted for the Comet Catcher. Whether there is truth to that, I do not know. 

 

 

Celestron put the correction on both sides of correctors used in their Schmidt camera. The reason was that the Schmidt curve  is deep for the fast optics used in a Schmidt camera and the corrector glass they used was thin.  They used relativity thin glass because it needed to be pulled against the Master Block by vacuum.  So if they only put the correction on one side of  the corrector it  would be even thinner when the curve was ground in and the corrector could easily break during manufacturing. So they put 1/2 the correction on each side.

  So it is very possible that the correctors used in the Comet Catcher were from the 5.5" Schmidt camera and the Comet Catcher was  designed to the use the corrector plates that only had the correction  on one side.  This way they could still  use the same tooling to make them and that reduced production cost. 

 

        - Dave 

Dave -

Thanks for the additional possible confirmation / info.

 

I remember reading all of that stuff somewhere, a few years back. I don't recall if it was on here... in the archives somewhere, or some blog post. It would be nice to have a confirmation on that.

 

At that time, I was also researching the rather elusive 5.5" Schmidt Camera... so that information lead me down some rabbit hole unknown. Perhaps it's in the "History Of Celestron" book? I don't have that publication, but at the time of my sleuthing, I did have a few screenshots saved from a PDF posted..... so that rings a bell for a lead.

 

 

https://app.astrobin...n-comet-catcher

 

Those are all of the images on AstroBin taken with a Comet Catcher.  So far, I'm disappointed with what few images that were taken with the Comet Catcher.  I had high hopes for a telescope with a focal length of 500 mm at f/3.6.  You will probably be better off with an f/4 astrograph Newtonian with a Starzona 0.75× Coma Corrector.  Then again, maybe the Comet Catchers weren't properly collimated.  But I would suggest caution when purchasing one.

 

Well, that is a very valid point. For someone wanting to Image - there are no doubt better options out there for imaging scopes, these days. For those interested in history, the CC is a cool piece though.

 

My experience in collimating these.... well, I wouldn't be surprised that many of them are not properly collimated. They are also kind of a bugger to do unless you:

 

1. Center spot the primary (with something like a CatsEye)

2. Have good tools - cheshire / sight tube / lightpipe / laser / autocollimator

3. Have the will of an ox, and the patience of a sloth to get it done (adjusting mirrors)

 

And I'm sure my two aren't perfectly collimated.... but they were way waaaaaaay out of whack when I got 'em. There are so many variables but the sled / stalk secondary is the bit that needs to be as best you can get - and that takes some trial and error.

 

 

 

 

With reflective sight cap tool

 

 

With autocollimator (1.25")  slightly de-collimated to show reflections.

 

 

Cheers,

T

[Roger Belveal]

I agree with you that these are a bugger to get collimated. One of the problems is that one doesn't know if the corrector plate and mirror are in their original position. Truly a painstaking task. After a lot of work, I've got both of mine as close as I possibly can. The views are pretty good with these scopes IMO... I'm using a 16mm type5 Nagler and a 4mm Radian most of the time and am more than happy with the performance. 

[Roger Belveal]

can u please share pictures of the focuser mod

 

also how to get that celestron orange paint  

This focuser is off an old Coulter dob. It's a perfect fit for this scope and works very well indeed. I had to grind the base down a lot to get it to sit flat on the base. It is secured with epoxy. This the orange paint I used is from what I've learned from other forum post, it's as close as one can get to the original... Cheers..

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[Roger Belveal]

This focuser is off an old Coulter dob. It's a perfect fit for this scope and works very well indeed. I had to grind the base down a lot to get it to sit flat on the base. It is secured with epoxy. This the orange paint I used is from what I've learned from other forum post, it's as close as one can get to the original... Cheers..

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[DAVIDG]

This is fascinating. Did they try this because they needed to figure something out that came up unexpectedly?

 

-drl

 Those that understand Schmidt optics know that the correction can be placed on both sides of the corrector  So it was the  understanding that the amount of deflection needed for the fast f1.5 system would be too much when the glass was pulled down against the Master Block and the glass would break. So with this understanding they put less correction on each side that equaled the total optical correction needed. Since the correction was less, the curve is shallower and hence the glass  doesn't need to be deflected as much when pulled down against the Master Block. 

   The correction doesn't have to  be equal on each side of corrector just the total correction equals what is needed. So it is possible that Celestron had a Master Block that was used to make one side  of the 5.5" Schmidt camera corrector  that they repurpose to make the correctors for the Comet Catcher. 

   One a side note the corrector on the Meade SCT I have tested has the correction on both sides as well Also Meade had their own version of Comet Catcher as well. 

 

                   - Dave 

Edited by DAVIDG, 02 November 2024 - 07:11 PM.

[davidc135]

I played around with the idea of cutting down sct corrector plates but a c.p from a C8 would be too strong by 1 wave, whilst a C11 c.p reduced to 5.5'' is too weak. 8.8'' f2/10 sct would be just right but that's not much help. Correction is proportional to fourth power of aperture.

 

I expect that they made new tooling for the job.

 

David

[deSitter]

I played around with the idea of cutting down sct corrector plates but a c.p from a C8 would be too strong by 1 wave, whilst a C11 c.p reduced to 5.5'' is too weak. 8.8'' f2/10 sct would be just right but that's not much help. Correction is proportional to fourth power of aperture.

 

I expect that they made new tooling for the job.

 

David

It very much depends on the zone right? So cutting down would relocate the zones of spherical correction outward. Is that wrong?

 

-drl

[Terra Nova]

 Here is a  quote from the Celestron's  patent on the Master Block method and how the Schmidt corrector for the Schmidt camera were made. So yes this method can be used to place the correction on both sides of the  corrector.

 

           "As an illustration, an 8 inch fl l .5 Schmidt camera calls for a corrector having a curve in excess of the amount that 0.l25 glass can be deformed. In this case a portion of the correction is ground onto one side of the glass and then the balance of the correction is ground onto the other, i.e., ground and polished." 

 https://patents.goog...t/US3889431A/en

 

          - Dave 

Could the corrector plate be ditched and the primary refigured to a parabola? The secondary is just a flat isn’t it?

[DAVIDG]

Could the corrector plate be ditched and the primary refigured to a parabola? The secondary is just a flat isn’t it?

 Sure, but then you lose the coma correction that a Schmidt Newtonian has which  for  a given focal length is less. So at F3.6 that coma would be much worse. The reduced coma is one of the reasons that Comet Catcher was  designed for wide field viewing.

 

            - Dave 

Edited by DAVIDG, 02 November 2024 - 07:16 PM.

[deSitter]

 Sure, but then you lose the coma correction that a Schmidt Newtonian has which  for  a given focal length is less. So at F3.6 that coma would be much worse. The reduced coma is one the reasons that Comet Catcher was  designed for wide field viewing.

 

            - Dave 

I seem to remember that the Meade SN reduced it more or less by 1/2, for some reasonable definition of 1/2. Imagers seemed happy with it. I had a 10" which was very average optically, but the imager I sold it to was very satisfied.

 

-drl

[davidc135]

It very much depends on the zone right? So cutting down would relocate the zones of spherical correction outward. Is that wrong?

 

-drl

It's a convention that the position of the neutral zone is measured in reference to a plane surface, for instance by contact interference.

 

So when the centre and edge are at the same height, the nz must be at 0.71r. If the same aspheric is placed on a slightly convex surface, the neutral zone appears to move out when tested against a flat. But if the surface was tested against the appropriate concave sphere, the nz would return to the 0.71r position.

 

If an 8'' sct c.p Schmidt profile was cut down to 5.5'', which is close to the original 0.71 n.z position, and tested against a sphere which touches the edge and centre, the greatest deviation when measured parallel to the optical axis will be at the new 0.71r, n.z position, 1.944'' from the axis.

 

David

Edited by davidc135, 02 November 2024 - 03:44 PM.