10395 replies to this topic

[clamchip]

Be careful that you're not looking at an enlarged image of the ronchi screen off the flat.  That's happened to me more times than I care to admit.

What would tip me off if I'm looking at an enlarged image of the ronchi screen off the flat?

It's definitely going thru the right channels I'm sure of that, and I tested multiple times and got the same results.

It's just odd I can change the mirror spacing as much as I did without introducing spherical aberration. I can

move the primary a total of 1/2" inch, and dead straight jail bars the entire travel. 

I'm very new to DPAC and have only tested a few Mak's so I'm not exactly sure what to expect. I look at the test

take notes and if I have questions I hunt for the answer. 

When I read about some of the mirror spacing tolerances in the thousandth's you would think moving the mirror

a 1/2" you would see some bending in those bars, as sensitive as DPAC is. 

 

Robert

Edited by clamchip, 04 May 2025 - 05:40 PM.

[Eddie_Concatenate]

I stared at my new FF107 as it served it's "time-out" in the corner. 8 days of rain in the forecast. Still waiting on the OAG.

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[CHASLX200]

I stared at my new FF107 as it served it's "time-out" in the corner. 8 days of rain in the forecast. Still waiting on the OAG.

Not a classic.

[Garyth64]

This is an old CG-5 hub sitting on one of my tripods:

 

 

Here's an 826 (or 628) Meade mount.  I drilled and tapped a hole and added in a long bolt:

 

 

The 826 mount fits perfectly onto the CG-5 hub:

 

 

I initially thought that the post on the CG-5 mount would interfere, but it doesn't.  It helps to stabilize the 826 mount.

Edited by Garyth64, 05 May 2025 - 11:58 AM.

[tim53]

What would tip me off if I'm looking at an enlarged image of the ronchi screen off the flat?

It's definitely going thru the right channels I'm sure of that, and I tested multiple times and got the same results.

It's just odd I can change the mirror spacing as much as I did without introducing spherical aberration. I can

move the primary a total of 1/2" inch, and dead straight jail bars the entire travel. 

I'm very new to DPAC and have only tested a few Mak's so I'm not exactly sure what to expect. I look at the test

take notes and if I have questions I hunt for the answer. 

When I read about some of the mirror spacing tolerances in the thousandth's you would think moving the mirror

a 1/2" you would see some bending in those bars, as sensitive as DPAC is. 

 

Robert

First question:  Do you see the secondary shadow?  I actually wasted an hour or so on the 6" Kludgescope looking at what I thought was a terrific ronchigram, only to have Dave point out to me that there was no secondary shadow, so I couldn't have been looking at reflections through the system.

 

With my 6" Gregorian, the problems I've had testing it for figuring the secondary have been exacerbated by the fact that none of the surfaces are coated, and the secondary is made from a 2" flat, so I can get reflections off the back of the secondary that fool me.  I've never found the dpac reflection so I think I'll need to build an ota, collimate the optics on an insulator in daylight, then put it on the bench and align it with the test flat.

 

-Tim.

[Garyth64]

Tim, fine grind the back of the secondary.  Then you can null the Gregorian secondary.

[clamchip]

First question:  Do you see the secondary shadow?  I actually wasted an hour or so on the 6" Kludgescope looking at what I thought was a terrific ronchigram, only to have Dave point out to me that there was no secondary shadow, so I couldn't have been looking at reflections through the system.

 

With my 6" Gregorian, the problems I've had testing it for figuring the secondary have been exacerbated by the fact that none of the surfaces are coated, and the secondary is made from a 2" flat, so I can get reflections off the back of the secondary that fool me.  I've never found the dpac reflection so I think I'll need to build an ota, collimate the optics on an insulator in daylight, then put it on the bench and align it with the test flat.

 

-Tim.

I do see the secondary and everything does seem to be running like it should.

I'll see how it looks in a star test which is coming up soon.

 

Robert

[deSitter]

I do see the secondary and everything does seem to be running like it should.

I'll see how it looks in a star test which is coming up soon.

 

Robert

 

You'll be happy

 

-drl

[clamchip]

I know the star test from this scope will be a thing of beauty, the DPAC sure is.

But what has me wondering is why I can't change the jail bars in a 1/2 inch of mirror movement.

There's a optimum spacing and I know where that is, and it's perfectly corrected there, and

everywhere around it too! 

Maybe it takes more mirror movement before I'll see some bent bars, I only have 1/2 inch.

If I unscrew the front and rear cells and line the cells up on the bench I can have any mirror

separation I want. I'm not willing to do that unless another reason pops up like a mirror cleaning.

I might use another Mak for a guinea pig. Problem is I only own one other Mak with a perfect

DPAC and it has fixed mirrors.

 

Robert

Edited by clamchip, 05 May 2025 - 06:22 PM.

[Garyth64]

Robert, I have a question.  Where is the focus when you move the secondary?  Which way are you moving the secondary? (ok, two questions)

 

I know you know, that in these types of scopes moving the secondary a little moves the focus a lot.  I'm thinking that if you move the secondary 1/2", the focus would move very much, maybe even several inches.  So, let's say you see straight lines before you move the secondary.  Then you move the secondary, and depending on the direction you moved the secondary, did you move the ronchi to the new focus?  If not, then you could either be far inside the focus, or far outside the focus, and then the lines might continue to look straight.

Edited by Garyth64, 05 May 2025 - 07:48 PM.

[clamchip]

I didn't measure where in the 1/2" of mirror movement I found infinite focus with the supplied 26mm, I wish

I had. I did move the Ronchi to the new focus every time I moved the mirror. And at every new focus I observed

the bars both sides of this new focus looking for any change in the bars. My flat is uncoated but I can see

very well in white light. I see no color fringing on the bars the meniscus might add, no CA, so I did all the testing

with white light.

I did remove the control box so I could get right up to the port in the rear cell, and the other direction I add

quite a few inches of back focus by changing the mirror spacing. Still though I was limited to 1/2" mirror

movement by the focusing mechanism and the clip on the sky end of the baffle tube.

 

Robert

Edited by clamchip, 05 May 2025 - 06:50 PM.

[starman876]

I moved some scopes from one side of the room to the other side 

[deSitter]

I moved some scopes from one side of the room to the other side 

 

A man's reach should exceed his grasp.

 

-drl

[ericb760]

A recent thread here regarding 60mm tube rings got me remembering that I had a set from a Celestron CO-60 I picked up awhile ago. I also scored a Bushnell SkyChief Jr. 60/700 in the original box last year. Unfortunately, the mount is in need of repair and I haven't got around to it yet. Instead, I mounted the Bushnell OTA onto my Svbony 225 mount with the 60mm rings. I also swapped out the original .965 visual back with a 1.25" that fit perfectly, allowing for 1.25 EP use. 

I gotta say that for a scope nearing 60 years old, the views of the moon are nothing short of astonishing. No CA at all and the view is almost freaky sharp.

 

 

 

 

 

Edited by ericb760, 06 May 2025 - 11:00 PM.

[norvegicus]

Those are amazing scopes.  Modern 1.25" eyepieces really wake them up.  Mine always made me smile every time.

Edited by norvegicus, 07 May 2025 - 10:17 AM.

[deSitter]

Those are amazing scopes.  Modern 1.25" eyepieces really wake them up.  Mine always made me smile every time.

 

I am amazed by my 80/900mm Vixen, which can get to lower powers with long Plossls. It is harder to appreciate the virtues of classic refractors at f/16 instead of f/11. 

 

-drl

[CHASLX200]

I rolled the AP900 2 feet to put on a wall plate just now.

[starman876]

I rolled the AP900 2 feet to put on a wall plate just now.

what was the rolling speed

[scout]

I've taken apart the alt-az mount to my Asahi-Pentax 60mm f/13.3 to adjust the alt motion. It was getting a bit jerky. After 65 years the original grease is black sludge, so I need to clean and relubricate it.

 

I've been using the refractor on another mount lately and I miss using the classic mount with the unique clutches. I've always wanted a modern long-fl 60mm Takahashi, but every time I use the old Asahi-Pentax I lose that urge. It's such a sharp refractor.

[deSitter]

what was the rolling speed

 

Chas has a go-to mount after all - "Go to the living room."

 

-drl

[Bomber Bob]

I've taken apart the alt-az mount to my Asahi-Pentax 60mm f/13.3 to adjust the alt motion. It was getting a bit jerky. After 65 years the original grease is black sludge, so I need to clean and relubricate it.

 

I've been using the refractor on another mount lately and I miss using the classic mount with the unique clutches. I've always wanted a modern long-fl 60mm Takahashi, but every time I use the old Asahi-Pentax I lose that urge. It's such a sharp refractor.

I haven't tested one of the A-P 60x800 refractors yet, but I doubt you'd be blown away by my 1972 TS-65S / 1000.  IME, with these top-tier old scopes, the differences are more aesthetic than analytical.  This Triplet has better color-correction than the '56 GOTO 60 F20 that I had, but both showed the same very fine lunar & planetary details.  Ditto comparing the FC-50 F8 vs my TS-50 F14.

[starhunter50]

building a new spider vane system for my Taiwan 8 inch F3.75 , scope.

 

 

 

 

 

 

[CHASLX200]

what was the rolling speed

2" a sec.

[deSitter]

2" a sec.

 

Everyone in Florida drives like a maniac!

 

-drl

[deSitter]

building a new spider vane system for my Taiwan 8 inch F3.75 , scope.

 

 

 

F1.jpg

 

F2.jpg

 

F3.jpg

 

F4.jpg

 

What is the effect on the diffraction pattern of non-radial vanes? That would worry me.

 

-drl