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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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Aboy
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Reged: 07/17/12

Loc: Thousand Oaks, CA
Re: new reducer/flattener from Astronomics... new [Re: CounterWeight]
      #5493472 - 10/28/12 06:11 PM

I have a question about this reducer..

I waiting for my TV pronto in the mail.. this reducer its ok to use in the TV pronto?


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WhitenerJ
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Reged: 02/06/12

Loc: Waxahachie, Texas
Re: new reducer/flattener from Astronomics... new [Re: Aboy]
      #5493574 - 10/28/12 07:28 PM

What is the difference between the new reducer and the Astro Tech 2 field flattener?

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oldstargazer
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Re: new reducer/flattener from Astronomics... [Re: WhitenerJ]
      #5493620 - 10/28/12 08:04 PM

The new one reduces the fl by about 2 tenths. Not very much but might make the difference between getting the whole target on the chip or not.

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Aboy
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Reged: 07/17/12

Loc: Thousand Oaks, CA
Re: new reducer/flattener from Astronomics... new [Re: oldstargazer]
      #5493725 - 10/28/12 09:24 PM

Ok I'll wait for my answer... But also: it's better the TV reducer that this one? Because the TV its more expensive, I know that's doesn't mean it's better.

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CounterWeight
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Re: new reducer/flattener from Astronomics... new [Re: Aboy]
      #5493885 - 10/28/12 11:27 PM

If I can use it at the spec backdistance - it reduces by 0.8x so it should take it down a from f/6 to f/4.8 - pretty good for a scope that already pretty wide. But it's in ways not so simple when mating to other brands, case of my TRF-2008 is that to keep the field flat and in focus on my ED80T-CF I have to use a working back distance well off the 'spec' distance, so I'm not getting the full reduction, maybe nearer to f/5.x. A similar scenario on my TEC 160mmm scope using the A-P telecompressor, you sometimes need to play with spacing and tradeoffs.

So it's a bit experimental, I don't assume different branded optics will match up - helps to have a lot of spacer tubes to play with backdistance. An added caution is focuser travel, the only reason the A-P optic works in my TEC is because it fits inside the focuser - otherwise I wouldn't be able to get the reducer optic close enough to the objective to get it to work properly.

So it's in ways not simple matching up sometimes, the theory might be good but the actual focuser length/location and travel... physical mechanical 'might' cause issues.

My AT flattener I've used on all my refractors to ensure flat field on the imaging chip - and it has been good on my Onyx 80 f/6.25, Orion at f/6, and TEC at F/8. Maybe a simpler job as it's not bending the light cone for focal reduction.

Some brands have reducer/flattener specifically for their scopes, this is a plus as you get matched results without worry.


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Aboy
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Reged: 07/17/12

Loc: Thousand Oaks, CA
Re: new reducer/flattener from Astronomics... new [Re: CounterWeight]
      #5494016 - 10/29/12 01:55 AM

them is better to buy the TV one after all?

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Midnight Dan
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Re: new reducer/flattener from Astronomics... new [Re: Aboy]
      #5494176 - 10/29/12 07:41 AM

Quote:

I have a question about this reducer..

I waiting for my TV pronto in the mail.. this reducer its ok to use in the TV pronto?




Hi Aboy:

Your TV pronto is F/6. If you read the information on the Astronomic website for the reducer/flattener, you'll see that it is rated to work with f/5.5 to f/7. Based on that, it should work.

-Dan


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nemo129
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Re: new reducer/flattener from Astronomics... new [Re: CounterWeight]
      #5494485 - 10/29/12 11:36 AM

Quote:

Some brands have reducer/flattener specifically for their scopes, this is a plus as you get matched results without worry.




Just my .02 and observation. I agree with Jim's opinion above. TV has tested the Pronto and the TRF2008. It should work without issue. Not that the new AT unit will not, but for $145 more you know you will be getting nice stars in all the corners..that would be worth it to me. You may be spending hundreds of hours taking pictures..nice to know you will not have to wrestle with spacing issues to get good stars. That was my .02. The observation is TV makes top shelf gear and I have never had a quality issue with it. I have had issues with machining and optical component alignment on "other" brands. Not to say all of them have it or will have issues, but you do get what you pay for and it is nice to only pay once!


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CounterWeight
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Reged: 10/05/08

Loc: Palo alto, CA.
Re: new reducer/flattener from Astronomics... new [Re: nemo129]
      #5498118 - 10/31/12 05:17 PM

-update,
It still has not cleared long enough for even a rough focusing check. All I need is maybe 10 minutes of clear sky - all set up and ready to go when it finally does.


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ad701xx
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Reged: 11/22/03

Loc: Oregon, USA
Re: new reducer/flattener from Astronomics... new [Re: CounterWeight]
      #5498794 - 11/01/12 12:32 AM

Hopefully we'll get a little break in the weather on Friday. I'm not holding my breath, though.

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SMigol
sage


Reged: 07/30/10

Loc: California, USA
Re: new reducer/flattener from Astronomics... new [Re: ad701xx]
      #5503345 - 11/04/12 01:50 AM

Finally got out under the stars for some testing of this device with my SV4 (APO 102mm at F 5.71 for 581 mm FL by platesolve).

Ran it against the Pleiades for a quick and dirty test on my Pentax K10D camera.

Here's how the results look at 43 seconds:

Testing Astronomics Reducer Flattener by S Migol, on Flickr

Go here for a bigger view: http://www.flickr.com/photos/smigol/8152967121/in/photostream/lightbox/

Here are the platesolve results from PixInsight:
Code:

Iteration 3, delta = 0.013 arcsec (0.0 pixels)
Image center ...... RA: 03 46 28.591 Dec: +24 01 00.27
Resolution ........ 2.39 arcsec/pix
*****

Image Plate Solver script version 1.51
===============================================================================
Referentiation Matrix (Gnomonic projection = Matrix * Coords[x,y]):
+0.000125873835 +0.000650703735 -1.096325533721
-0.000650629315 +0.000125836022 +1.102834553734
+0.000000000000 +0.000000000000 +1.000000000000
Resolution ........ 2.386 arcsec/pix
Rotation .......... -100.950 deg
Focal ............. 466.86 mm
Pixel size ........ 5.40 um
Field of view ..... 2d 34' 55.1" x 1d 44' 1.3"
Image center ...... RA: 03 46 28.591 Dec: +24 01 00.27
Image bounds:
top-left ....... RA: 03 41 38.086 Dec: +25 06 52.28
top-right ...... RA: 03 43 51.148 Dec: +22 35 01.28
bottom-left .... RA: 03 49 09.579 Dec: +25 26 48.98
bottom-right ... RA: 03 51 14.155 Dec: +22 54 34.61



The CCDInspector shows interesting results as well:

SV4 with Astronomics Reducer Flattener Curvature Map by S Migol, on Flickr


SV4 with Astronomics Reducer Flattener Curvature 3D Map by S Migol, on Flickr

Edited by SMigol (11/04/12 01:53 AM)


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Phil Hosey
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Reged: 10/29/08

Loc: LaGrange, GA
Re: new reducer/flattener from Astronomics... new [Re: SMigol]
      #5503485 - 11/04/12 07:17 AM

The stars on the left side are quite distorted. Even the bottom-right is distored although not quite as much. This looks a lot like what I get with a William Optics Reducer/Flattener II.

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SMigol
sage


Reged: 07/30/10

Loc: California, USA
Re: new reducer/flattener from Astronomics... new [Re: Phil Hosey]
      #5503891 - 11/04/12 01:00 PM

I've used the WO and get much worse stars. I'm starting to add spacers and it's responding nicely so far. With .5 mm spacer added, the curvature improved 1% and the stars got a little tighter. Will keep working it tonight and see how it improves.

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Phil Hosey
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Reged: 10/29/08

Loc: LaGrange, GA
Re: new reducer/flattener from Astronomics... new [Re: SMigol]
      #5503973 - 11/04/12 01:55 PM

I'll be interested to see how it goes. I currently use the William Optics AFR-IV reducer/flattener which corrects the stars very well, but unfortunately it causes reflections on bright stars. I'm very interested to see how the Astrotech reducer performs.

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CounterWeight
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Reged: 10/05/08

Loc: Palo alto, CA.
Re: new reducer/flattener from Astronomics... new [Re: Phil Hosey]
      #5504153 - 11/04/12 03:59 PM

SMigol - what is your spacing that are starting with? is your imaging trane 'all threaded'?

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Mike7Mak
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Reged: 12/07/11

Loc: New York
Re: new reducer/flattener from Astronomics... new [Re: SMigol]
      #5504226 - 11/04/12 04:59 PM

Quote:

With .5 mm spacer added...




Is that correct? That's about the thickness of a fingernail.


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SMigol
sage


Reged: 07/30/10

Loc: California, USA
Re: new reducer/flattener from Astronomics... new [Re: CounterWeight]
      #5504228 - 11/04/12 05:01 PM

I haven't measured the spacing "vanilla." Here's what it's supposed to be by common standards:
Pentax K mount flange distance: 45.46 mm
K mount to T thread adapter: 10 mm

This camera has been full spectrum modified, I've computed the glass thickness as 1.4 mm based on reflections of bright stars.

Given the usual rule of thumb about glass adding 33% of its thickness to the optical train for backfocus, then I should be adding .46 mm.

By these numbers, I should be trying to remove about .9 mm of backfocus to bring it to the proper setting. However, when I added the .5 mm spacer, the flatness went down by 1% and the star images improves, it leads me to think that there are other factors in play.

I should measure the actual flange distance of the camera. I've had disagreement with a ronchi screen set to proper distance so there may be issues with this camera from the factory.

Nearly all the devices are threaded. The only two parts that are not threaded is the reducer/flattener to the feathertouch focuser and the camera mount is a flange device. I've wrapped that flange with teflon tape to tighten it up a little, as well. I do have a way to support the camera so that there is no weight resting on the focuser. I will do that as a part of my full testing once I get proper spacing. That will be the exercise to center the camera and get it flat.


EDIT: the .5 mm thickness is correct, I'm using brass rings from Edmund Optics for tweaking. I have a .5, 1, and 1.5 available. I also have some screw on spacers that start at 5 mm.

Second Edit:
I've measured my camera setup and here's what the values are:
Camera flange distance to the glass: 46.91 mm
T Ring thickness is 9.3 mm

My stock non-converted camera has a flange distance to the front surface of the IR filter of 47.2, so this seems to make sense.

Edited by SMigol (11/04/12 06:24 PM)


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SMigol
sage


Reged: 07/30/10

Loc: California, USA
Re: new reducer/flattener from Astronomics... new [Re: SMigol]
      #5504905 - 11/05/12 03:45 AM

I ran through a battery of tests this evening, using spaces from 6 mm through 2 mm and a baseline again of no spacers.

I think that some of my numbers from the previous night were misleading. By going through the whole set again under one night and matching the practice carefully, I can see that spacers don't effect flatness. While this should not be a surprise, I wasn't sure what to expect.

So it appears that the flatness of this device does not work well for my SV4. It may work well for other scopes in my setup, including the SV 70 ED and the ST 80. I'll have to try these out.

In the meantime, I'll keep using the flattener that I have that gives very nice stars across the field and work on mosaics.


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Midnight Dan
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Re: new reducer/flattener from Astronomics... new [Re: SMigol]
      #5505014 - 11/05/12 07:21 AM

Quote:

In the meantime, I'll keep using the flattener that I have that gives very nice stars across the field and work on mosaics.




Which one is that?
-Dan


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CounterWeight
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Re: new reducer/flattener from Astronomics... [Re: Midnight Dan]
      #5505182 - 11/05/12 10:13 AM

I was able to do a rough focus check finally (coming in from too close/too far)- but nothing qualitative, shooting through rapidly moving holes in the clouds/high haze with 3 sec bin*2 exposures. 'Desperation imaging'. No issues with in/out focus and I think critical focus will be near where I found it using the TRF. Having done this will make it that much easier when the weather clears.

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