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Old 14-11-2018, 07:33 AM
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Logieberra (Logan)
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New tiny Tak refractor test image - thoughts?

Meet the little engine that could.

I recently picked up a small 60mm Tak for portable imaging/star parties etc, and for a bit of sneaky visual: FOA-60mm with dedicated Tak 0.93x flattener/reducer.

Here is first light. A single, 5min guided exposure with a Canon 6D. No darks/flats/bias frames. Nil post processing. Manual/eyeball focus. Full size JPG here: https://www.dropbox.com/sh/5y4szgyhb...C3M94mbGa?dl=0

Thoughts on colour correction, field flatness and resolution? Other comments?

To my eyes, it compares favourably with my TOA/FSQ shots that I’ve produced in the past... but at a fraction of the cost and size!
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Last edited by Logieberra; 17-11-2018 at 09:59 AM.
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Old 14-11-2018, 09:34 AM
JA
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Hi L,

I think that's a wonderful result, especially as you've REALLY tested the limit of its 40-44mm image circle (depending on model - you don't say which), by using a full-frame sensor. Even zoomed in tight there is no observable chromatic aberration and very even illumination of the field (except perhaps in the extreme corners, but that is to be expected with a full-frame sensor used on an optic with a full-frame image circle, even then it is very minor and easily corrected in post).

The only thing I do notice, only when tightly zoomed in near the corners, is a sort of cross or Maltese Cross shaped diffraction pattern which is more evident on brighter stars, which gives them a slightly squarish appearance. I wonder whether this is the result of using an On-axis-guider and caused by diffraction from the edges of its prism or possibly some other sharp edge in any adpators, etc in the optical path. It may even be stray light entering the edge of the optic and bouncing around and hitting things it shouldn't like the edges of internal baffles, etc. Was a lens hood used?

In any event it's an excellent result, with detail that will build as normal with more exposure. One can already tell that from the detail in the smoky reddish gas around the core. It would be great to see a head to head comparison of the same object with your other Tak optics, under the same conditions.

Best
JA

Last edited by JA; 14-11-2018 at 09:54 AM.
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Old 14-11-2018, 09:46 AM
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strongmanmike (Michael)
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Looks more than acceptable to me Logan

Mike
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Old 14-11-2018, 10:14 AM
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Quote:
Originally Posted by JA View Post
Hi L,

I think that's a wonderful result, especially as you've REALLY tested the limit of its 40-44mm image circle (depending on model - you don't say which), by using a full-frame sensor. Even zoomed in tight there is no observable chromatic aberration and very even illumination of the field (except perhaps in the extreme corners, but that is to be expected with a full-frame sensor used on an optic with a full-frame image circle, even then it is very minor and easily corrected in post).

The only thing I do notice, only when tightly zoomed in near the corners, is a sort of cross or Maltese Cross shaped diffraction pattern which is more evident on brighter stars, which gives them a slightly squarish appearance. I wonder whether this is the result of using an On-axis-guider and caused by diffraction from the edges of its prism or possibly some other sharp edge in any adpators, etc in the optical path. It may even be stray light entering the edge of the optic and bouncing around and hitting things it shouldn't like the edges of internal baffles, etc. Was a lens hood used?

In any event it's an excellent result, with detail that will build as normal with more exposure. One can already tell that from the detail in the smoky reddish gas around the core. It would be great to see a head to head comparison of the same object with your other Tak optics, under the same conditions.

Best
JA
JA, thanks for this. I wonder if I’m undesampled? And that’s the pixels coming through? Hmmm... I also updated the above with scope details: FOA-60mm. Essentially, a baby TOA. Agreed, more data needed, and a comparison would be interesting...
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Old 14-11-2018, 12:10 PM
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Firstly, glad you kept it. I was so tempted the SECOND time around (after letting you get it the first time )

Looks VERY good to me - with a polychromatic Strehl of 0.99, you'd expect it to be sharp, which it is. These are EXCEPTIONAL telescopes.

The field flatness looks pretty darned good too.
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Old 14-11-2018, 12:35 PM
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Firstly, glad you kept it. I was so tempted the SECOND time around (after letting you get it the first time )

Looks VERY good to me - with a polychromatic Strehl of 0.99, you'd expect it to be sharp, which it is. These are EXCEPTIONAL telescopes.

The field flatness looks pretty darned good too.
Yes thanks mate. I’m happy. I only listed her to help get into the full “Q” model, but following talks with Claude the change out/$ was negligible. I’ve now got the Q module as an add on.
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Old 14-11-2018, 12:37 PM
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Looks more than acceptable to me Logan

Mike
Thanks Mike. Compared to your famous “ultra deeps”, I’ve got the “ultra shallow” end covered
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Old 16-11-2018, 07:28 PM
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Wow for a 60mm scope that looks like a wonderful result. Well done.
Geoff
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Old 16-11-2018, 08:27 PM
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Yeah, the FOA-60 certainly is the pinnacle of the 60mm-class scopes.

Now, I am hoping for an FOA-100 or 120
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Old 16-11-2018, 09:01 PM
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Congratulations!

Saw photos and read an article yesterday about how tight collimation screws appear in star photos. To apply my new "knowledge", I investigated your photo.
And guess what I found: Tight collimation screws.
Or not?

The first screenshot is the bottom right corner of your image.

The second is taken from the mentioned article. http://interferometrie.blogspot.com/...l?view=sidebar

I'm that far from being an expert as we are from traveling to Andromeda galaxy.
So what do the others say? Is that negligible? That it doesn't show in the center stars might just be because they're over-exposed in this test shot.
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Old 17-11-2018, 04:54 AM
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Logieberra (Logan)
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Originally Posted by silv View Post
Congratulations!

Saw photos and read an article yesterday about how tight collimation screws appear in star photos. To apply my new "knowledge", I investigated your photo.
And guess what I found: Tight collimation screws.
Or not?

The first screenshot is the bottom right corner of your image.

The second is taken from the mentioned article. http://interferometrie.blogspot.com/...l?view=sidebar

I'm that far from being an expert as we are from traveling to Andromeda galaxy.
So what do the others say? Is that negligible? That it doesn't show in the center stars might just be because they're over-exposed in this test shot.
That’s not my image. Looks filthy. There is no comparison... See below.

This is a 44mm, full frame imaging chip with OAG and flattener/glass elements in between. It’s is a big ask for a 60mm compact scope.

Nice of you to come out of the woodwork and share though

Thank you.
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Last edited by Logieberra; 17-11-2018 at 09:14 AM.
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Old 17-11-2018, 09:03 AM
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Silv, notice in Logan's image the "lighthouse effect" as it is known, is NOT present over the entire image, notable not the bright central stars. This is indicitive of it NOT being collimation screws or similar, and is more than likely an artefact of a little tilt (top left), not QUITE flat (the flattener was not designed for such a large sensor) and also most likely a small intrusion into the light path by the OAG's prism or prism housing (a common issue). notice the Lighthouse ONLY appears on the right side.

If Logan had used a camera with a slightly smaller sensor, you would not see these artefacts.
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Old 17-11-2018, 09:09 AM
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Quote:
Originally Posted by LewisM View Post
Silv, notice in Logan's image the "lighthouse effect" as it is known, is NOT present over the entire image, notable not the bright central stars. This is indicitive of it NOT being collimation screws or similar, and is more than likely an artefact of a little tilt (top left), not QUITE flat (the flattener was not designed for such a large sensor) and also most likely a small intrusion into the light path by the OAG's prism or prism housing (a common issue). notice the Lighthouse ONLY appears on the right side.

If Logan had used a camera with a slightly smaller sensor, you would not see these artefacts.
The little engine thanks you Lewis.
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Old 25-11-2018, 09:26 PM
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FSQ106N used to have that type of artefact. Bright stars long the edge of the image had a black bar going through them like a wormhole.

Roland Christen said it was vignetting. FSQ106ED does not do this.
I would have thought it fits the definition for astigmatism where a star forms a line towards the centre of the image or at 90 degrees to it.

Are your spacings spot on?

A full frame sensor is a big ask for a small scope. In my experience with Taks they needed a 4 inch focuser to be happy with full frame no matter what the brochure said.

Its very impressive overall.

Greg.
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Old 26-11-2018, 05:20 AM
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FSQ106N used to have that type of artefact. Bright stars long the edge of the image had a black bar going through them like a wormhole.

Roland Christen said it was vignetting. FSQ106ED does not do this.
I would have thought it fits the definition for astigmatism where a star forms a line towards the centre of the image or at 90 degrees to it.

Are your spacings spot on?

A full frame sensor is a big ask for a small scope. In my experience with Taks they needed a 4 inch focuser to be happy with full frame no matter what the brochure said.

Its very impressive overall.

Greg.
Some did Greg, mist don’t. I’ve seen FSQ85s and 106EDs do it as much if not more.

It’s the foil spacers in the objective. I mitigated it in one FSQ85 by making a very small aperture mask that masked off the foil edge (literally it became an FSQ84.5).

My current FSQ106N does not show any artefact even with an APS-C sized SX sensor. Might with a 16803 but that’s not going to happen
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Old 29-11-2018, 06:27 PM
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Logieberra (Logan)
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Quote:
Originally Posted by gregbradley View Post
FSQ106N used to have that type of artefact. Bright stars long the edge of the image had a black bar going through them like a wormhole.

Roland Christen said it was vignetting. FSQ106ED does not do this.
I would have thought it fits the definition for astigmatism where a star forms a line towards the centre of the image or at 90 degrees to it.

Are your spacings spot on?

A full frame sensor is a big ask for a small scope. In my experience with Taks they needed a 4 inch focuser to be happy with full frame no matter what the brochure said.

Its very impressive overall.

Greg.
Greg, if a 4” focuser is ideal for full frame, I’m way off it! The tiny Tak comes with nothing like that. If Roland says it’s vignetting, then that would definitely apply for this tiny tube setup. Re spacing, it’s bang on. Tak flattener to Tak #33 wide/Canon mount. 100% per Tak system chart.

Last edited by Logieberra; 29-11-2018 at 07:44 PM.
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