434 replies to this topic

[Jason D]

Via BlackCat

Attached Thumbnails

• 

[rockethead26]

I think I'm liking the clarity of this design!

[Starman1]

The proof will be "in the pudding", as they say.
I look forward to Jason's test.

[Jason D]

One interesting advantage of Hotspot is assisting the user to optimally place the XLK. In previous posts at CN, I have already established that the optimal placement of the AC mirror is on or close to the focal plane. I also have shown that reflection sizes will change as the AC mirror moves away from the focal plane in either direction. When the AC mirror is below the focal plane, reflection 2 will look larger than reflection P. When the AC mirror is above the focal plane then reflection 2 will look smaller. The Hotspot will make it easier to compare both P&2 relative sizes as shown in the attachment and in the next post.
I need to clarify that both POVRay simulation figures are for cases where the AC mirror is 5% Focal-Length (FL) above and below the Focal-Plane (FP) which is excessive for visual scopes. 5%FL was selected for simulation to magnify the difference in size.

So, if Hotspot reflection 2 is larger than reflection P, then rack-out the AC. If Hotspot reflection 2 is smaller than reflection P, then rack-in the AC. Stop when both reflections are sized about the same.

Jason

Attached Thumbnails

• 

[Jason D]

.

Attached Thumbnails

• 

[Jason D]

I decided to pull out my old XT10 stock primary mirror and replace the original stock donut center spot with Hotspot. But first I decided to check how centered is the original stock donut spot. It was 1.5mm off center which is disappointing. That means even if I achieve perfect collimation using whatever method and tool my PAE will be 0.75mm. The 0.75mm might still be within the “coma-free” zone spec for my F4.7 scope but it also means I have lost 0.75mm from my scope’s mechanical tolerance.
I do not understand why the manufacture can’t install a machine to place these center spots with high precision!!!

Attached Thumbnails

• 

[Jason D]

Anyway, I went ahead and replaced the stock donut with Hotspot.
I will do my best to set aside time to replace my premium mirror with my stock mirror this weekend and give the Hotspot a test drive.

Attached Thumbnails

• 

[Jason D]

Behold the first “radioactive” primary mirror !@#$%

Attached Thumbnails

• 

[CatseyeMan]

Behold the first “radioactive” primary mirror !@#$%

... not quite - my 6" has that claim to fame.

Attached Thumbnails

• 

[CatseyeMan]

... just a technicality, Jason. You have the template "upside down" (unless you reversed the pic). It certainly doesn't make any difference on centering accuracy but with it right side up (text not reversed) because of the way the holes are punched in the template, the center spot is a bit easier to affix to the exposed "sticky" of the cellophane tape.

[Jason D]

... not quite - my 6" has that claim to fame.

... just a technicality, Jason. You have the template "upside down" (unless you reversed the pic).

Because of the direction the template was rolled-in, I felt I was going to get little more puffiness at the center to keep the sticker away from the mirror while positioning it. So, I did what I did for a reason. However, in retrospect I don't think it really made much of a difference.

Jason

[Jason D]

First installment of photos.

BLACKCAT Cheshire

Attached Thumbnails

• 

[Jason D]

INFINITY XLK offset pupil

Attached Thumbnails

• 

[Jason D]

INFINITY XLK central pupil

Attached Thumbnails

• 

[Jason D]

CDP via central pupil

Attached Thumbnails

• 

[cheapersleeper]

Great thread but no longer concise.

[Jason D]

My first impressions:

Hotspot is definitely more accurate when using it with the cheshire. It has the best of both the donut and triangle center spot advantages.

Hotspot is definitely more accurate when using it for stacking P+2 reflections via the XLK offset pupil. Small shifts are easier to detect with the Hotspot shape compared to the triangle/donut shapes.

Hotspot wins again when it gets to stacking P+1 reflections since there is more perimeter to reference compared to both triangles and donuts spots

However, when it gets to CDP the triangle wins because a typical CDP view is already busy with reflections around P+3 and the large size of the Hotspot cluttered the view. But the Hospot wins over donut spots.

I like the yellow color because of its contrast against the cheshire ring but I felt successive reflections of the yellow color in the XLK where not as bright as the white color.

Above are first impressions. I am continuing with my evaluation.

Jason

[Jason D]

Attachment shows how small and even smaller P+2 shifts can be easily detected with Hotspot

Attached Thumbnails

• 

[Jason D]

Attachment shows how little extra effort is needed to avoid pupil reflections and to clear the clutter around P+3 CDP with Hotspot. Right photo is a better CDP setup.

Attached Thumbnails

• 

[CatseyeMan]

Jason,

As always - GREAT PICS! Once again ... another of your innovative concepts is now a reality!

Were these pics taken with just "room" lighting or did you have any supplemental source directed at the spot?

[CatseyeMan]

... Left photo is a better CDP setup.

Actually, I prefer the "Right" pic queues.

[Starman1]

Do I understand correctly, though, that the diameter of the hotspot centermark has to be calibrated to the focal length of the scope to actually correspond well to the inside diameter of the central dark area in the cheshire?
If that's the case, then several different sizes of marker would be necessary.
Though the ability to find the focal point of the scope by matching sizes of reflected spots would seem to be a definite plus of this center mark.
The field could be a little "busy" if this mark were employed with the CAM modification, though.

[Jason D]

another of your innovative concepts is now a reality!

And thank you for encouraging innovation, Jim.

Were these pics taken with just "room" lighting or did you have any supplemental source directed at the spot?

Just room lighting though the OTA was poiting close to a source light but not directly at it. As part of my continued evaluation I will use a diect light source (white and red) in the dark. Stay tuned.

[Jason D]

Actually, I prefer the "Right" pic queues.

I meant to say "right". I made the edit.

[Jason D]

Do I understand correctly, though, that the diameter of the hotspot centermark has to be calibrated to the focal length of the scope to actually correspond well to the inside diameter of the central dark area in the cheshire?
If that's the case, then several different sizes of marker would be necessary.

No.
The Cheshire reflection's apparent size is one focal length away but located at infinity.
The Hotspot reflection's apparent size is one focal length away and located one focal length away.
Therefore, one Hotspot size will work for all scopes regardless of their focal lengths.
Think of it this way, if your thoughts are correct then Jim would have been selling different triangle sizes depending on your scope's focal length over the past years.

Though the ability to find the focal point of the scope by matching sizes of reflected spots would seem to be a definite plus of this center mark.

I still need to evaluate this benefit. Stay tuned.

The field could be a little "busy" if this mark were employed with the CAM modification, though.

Good point. My XLK+CAM is inaccessible to me at the moment. I will evaluate and post photos in few days. Stay tuned.

Jason