36 replies to this topic

[Maxtrixbass]

ID confirmed. Nice call Robert!

 

"Hi William,

 

Yes that is one of our 6" F4 OTA which we made about 300 and it was made in the late 70s. It looks like it is in good shape.

 

Good luck,

Paul T. Jones, Owner/Optician

Star Instruments"

 

 

Having spent more time on the collimation I must say the view is quite good, superb really. The outer edge does show coma, but the central 7/8ths is impressive for such a fast scope.

Edited by Maxtrixbass, 04 May 2022 - 10:22 AM.

[CHASLX200]

Odd that mirror does not have the center bolt holding it in place.

[Maxtrixbass]

Well, I beefed up the probably homemade rings, put a 2" focuser on it, spent some time getting it properly collminated, inserted  a coma corrector (a basic Apertura I had on hand), put in an eyepiece and later an aps-c sensor camera. Completely stunning. There is some softness on the images in one corner  (tilt?), but for a scope this fast its surprisingly sharp across the frame. Visually there is some softness around the edges even with the CC, but one would be hard pressed to guess this as f/3.8 .

 

The whole setup even with the new larger focuser and heavier eyepieces/camera really isn't that heavy. Perhaps some of that is the fiberglass tube. The primary is certainly on the thick side.

 

The CG4 mount seems to handle it no problem.

 

Now to get a break in the endless clouds....

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Edited by Maxtrixbass, 06 May 2022 - 08:12 PM.

[deSitter]

Well, I beefed up the probably homemade rings, put a 2" focuser on it, spent some time getting it properly collminated, inserted  a coma corrector (a basic Apertura I had on hand), put in an eyepiece and later an aps-c sensor camera. Completely stunning. There is some softness on the images in one corner  (tilt?), but for a scope this fast its surprisingly sharp across the frame. Visually there is some softness around the edges even with the CC, but one would be hard pressed to guess this as f/3.8 .

 

The whole setup even with the new larger focuser and heavier eyepieces/camera really isn't that heavy. Perhaps some of that is the fiberglass tube. The primary is certainly on the thick side.

 

The CG4 mount seems to handle it no problem.

 

Now to get a break in the endless clouds....

Softness in one corner - definitely collimation. At f/4 the allowed error is about a millimeter. I have tweaked my collimation by making the coma even around the edges. You need an adjustable coma corrector - a Paracorr. I have come to consider my f/4.5 as a catadioptric telescope. 

 

-drl

Edited by deSitter, 07 May 2022 - 08:19 AM.

[Maxtrixbass]

It may be beyond my abilities as it is really close, although I do plan to keep trying. Pic attached (although the detail is somewhat lost at this reduction). These houses are about 2 miles away. I won't bias a response by saying which corner I find soft..  I rotated the camera for the lower left water corner to expose detail, but it looks pretty good.

 

If I go with my 4/3rds QHY I really think the image would be crisp to the edges. I guess I could always crop the DSLR aps-c, but again, for an F/3.8 scope with a pretty basic CC I find the results quite good.

 

I found binoculars at Goodwill years ago, leather case, Japanese made, maybe from the 60s (?). The view through those is similar to this scope. Its rather hard to describe, crisp, almost 3d.

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[deSitter]

It may be beyond my abilities as it is really close, although I do plan to keep trying. Pic attached (although the detail is somewhat lost at this reduction). These houses are about 2 miles away. I won't bias a response by saying which corner I find soft..  I rotated the camera for the lower left water corner to expose detail, but it looks pretty good.

 

If I go with my 4/3rds QHY I really think the image would be crisp to the edges. I guess I could always crop the DSLR aps-c, but again, for an F/3.8 scope with a pretty basic CC I find the results quite good.

 

I found binoculars at Goodwill years ago, leather case, Japanese made, maybe from the 60s (?). The view through those is similar to this scope. Its rather hard to describe, crisp, almost 3d.

Can't tell from such a heterogeneous image, but the upper right appears unfocused, which could be field curvature. Need point sources to identify coma. 

 

-drl

[Maxtrixbass]

Can't tell from such a heterogeneous image, but the upper right appears unfocused, which could be field curvature. Need point sources to identify coma. 

 

-drl

Agreed.

 

Weather=cloudy/rain until the end of time. Am looking forward to an actual star image.

[Maxtrixbass]

As a follow up..  I'm pleased with the performance of the scope and it promises some good imaging. The collimation, including secondary offset (as mentioned) is really touchy in large part due to the fast optics and in part due to the overall resolution (it really shows everything with little fudge factor) . Overall a really great instrument.

 

First light image here:

https://www.astrobin.com/k26via/

 

I'm using a GSO coma corrector which is adequate.  Something a bit better would likely do a better job, but at this point I can either crop it down to a 4/3rds sensor size and/or just correct some of the abberation in post processing.

Edited by Maxtrixbass, 25 May 2022 - 10:34 AM.

[tim53]

That’s a keeper!

[Maxtrixbass]

As a follow up..

 

I decided to get a Sharpstar .95 coma corrector. Finally a brief break in the clouds, so here is a star test.  Overall I am very pleased.  A tiny bit of abberation/coma in the corners of the APS-C sensor, but I can either crop it to to 4/3rds or (more likely) 

correct in post processing. I consider it a success especially since the Sharpstar reduces the scope to F/3.6.

 

Full spectrum 500d, 10 seconds. Pixel scale 1.7 arc seconds/pixel.

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Edited by Maxtrixbass, 21 June 2022 - 09:20 AM.

[Maxtrixbass]

Pixel peeping the corners. Oddly, the corners aren't totally consistent, but the variation is rather minimal.

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[Craigar]

Very nice!.. possibly pinched primary or very slight astigmatism?

 

I just got what looks like a Cave Astrola 6" F4 and once I got the collimation half decent it seems really good for this fast.. definitely want to get it a CC.. Here's some pics - any ideas on what it is will be appreciated Thanks

 

Album: CAVE 6" F/4 RFT (maybe)?

8 images

0 comments

Edited by Craigar, 03 August 2022 - 07:18 PM.