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Field Flatteners for Achromats, Visual Only

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#26 Sarkikos

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Posted 28 July 2019 - 12:22 PM

While I was out last night with the ST120, I also tested my AT72EDII with the TS Flat2.  This was using the Baader 2" ClickLock Mirror Diagonal with barrel removed.  The field was flat viewing with the 8 Ethos and 10 Ethos.

 

According to the TS specs, the AT72EDII needs 128mm spacing, since it's focal length (430mm) is less than 450mm.  The spacing for my test was 94mm and 105mm.  Maybe tonight I'll retest with the diagonal barrel attached, for a spacing of 120mm and 131mm, much closer to the 128mm that TS suggests.

 

Compared to the ST120, however, the AT72EDII has a relatively flat field even without the TS Flat2.

Mike


Edited by Sarkikos, 28 July 2019 - 12:25 PM.


#27 Sarkikos

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Posted 28 July 2019 - 12:35 PM

Here are the spacing requirements for the TSFlat2 from the Teleskop-Express website:

 


The recommended distances from the M48x0.75 thread to the corrector
In principle this rule applies: the shorter the refractor´s focal length, the longer the working distance to the sensor has to be.

 

♦ focal length < 450 mm: 128 mm
♦ focal length 450-490 mm: 123 mm
♦ focal length 500-550 mm: 118 mm
♦ focal length 560-590 mm: 116 mm
♦ focal length 600-690 mm: 113 mm
♦ focal length 700-800 mm: 111 mm
♦ focal length ab 800 mm: 108 mm

 

An underrun or an overrun of the distance of up to 5% has no visible effect on the sharpness in the field of sensors with formats up to APS-C. With larger sensors, the tolerance is reduced to 1-2%.

 

https://www.teleskop...connection.html

 

I have virtually no knowledge about AP, so I'm not exactly sure what the signifcance of "the M48x0.75 thread" has for someone doing visual astronomy.  Is this where you attach the camera?  Would this be the equivalent of the location of the eyepiece's field stop?  In any case, this is what I have assumed when determining the total optical length for the spacing.

 

Note that an "underrun or overrun of the distance of up to 5%" would be 6.4mm for the 128mm spacing, and 5.4mm for the 108mm spacing.

 

Mike


Edited by Sarkikos, 28 July 2019 - 12:42 PM.


#28 Sarkikos

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Posted 31 July 2019 - 07:41 PM

Here are the two setups I'm using with the TS2FF (aka TSFLAT2):

(A) Baader 2" ClickLock mirror diagonal with diagonal barrel + TS2FF

(B)  Baader 2" ClickLock mirror diagonal w/o diagonal barrel + SCT/48mm ring adapter + TS2FF


(A) works best with AR-102xs f/4.5, ST80, AT72EDII

(B) works best with ST120, C80ED

These results agree with the spacing advised by TS.

The location of the eyepiece field stop does not appear to affect the field flattening for 10 Ethos vs 8 Ethos, which have an 11mm difference in field stop location.

I saw the greatest improvement in flatness of field for the AR-102xs f/4.5 and the ST120.  Those two telescopes had the greatest degree of FC before using the TS2FF.

Mike



#29 Sarkikos

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Posted 31 July 2019 - 07:47 PM

So there won't be any confusion over names and products, here is a link to the field flattener I'm using:

 

TS-Optics REFRACTOR 1.0x Flattener and Field Corrector - 2" connection

https://www.teleskop...connection.html

 

I've been calling this field flattener "TS2FF" in this thread, but the model name that Teleskop-Express uses is TSFLAT2.

 

Mike


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#30 tony_spina

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Posted 31 July 2019 - 08:52 PM

Here are the two setups I'm using with the TS2FF (aka TSFLAT2):

(A) Baader 2" ClickLock mirror diagonal with diagonal barrel + TS2FF

(B)  Baader 2" ClickLock mirror diagonal w/o diagonal barrel + SCT/48mm ring adapter + TS2FF


(A) works best with AR-102xs f/4.5, ST80, AT72EDII

(B) works best with ST120, C80ED

These results agree with the spacing advised by TS.

The location of the eyepiece field stop does not appear to affect the field flattening for 10 Ethos vs 8 Ethos, which have an 11mm difference in field stop location.

I saw the greatest improvement in flatness of field for the AR-102xs f/4.5 and the ST120.  Those two telescopes had the greatest degree of FC before using the TS2FF.

Mike

Do you have a link or picture is the SCT/48mm ring



#31 Sarkikos

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Posted 01 August 2019 - 07:31 AM

Do you have a link or picture is the SCT/48mm ring

Here's what I use to connect the female SCT thread of the Baader ClickLock w/o barrel to the male 48mm thread of the TSFLAT2:

 

Blue Fireball Gender Changer: SCT Male-Male Thread Adapter with Internal M48 (2" Filter) Thread # G-SM

https://agenaastro.c...8mm-thread.html

 

Mike



#32 Sarkikos

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Posted 27 August 2019 - 07:53 AM

I have yet to try the TSFlat2 on my 150 Omni XLT f/5.  Maybe I'll take it to a dark site this weekend.  This telescope has a 750mm focal length.  According to TS, a focal length 700-800 mm requires 111 mm spacing.  So the TSFlat2 should be used in a direct connection to the diagonal.

 

Mike



#33 Sarkikos

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Posted 31 August 2019 - 08:24 AM

I took the 150 Omni XLT f/5 to a dark site this past Thursday.  The sky was clear and cloudless all night.  I connected the TSFlat2 to the Baader 2” BBHS Sitall Mirror Diagonal without barrel.  I used the Blue Fireball SCT Male-Male Thread Adapter with Internal M48 for the connection.

 

Stars were sharp from edge to edge, even for the 120 degree field of my 9mm ES!   The field did show barrel rectilinear distortion, but I think that was from the eyepiece.  I also viewed through my Leica Zoom, 32 Masuyama and 25 ES 100 degree.  Sometimes I removed my eyeglasses to get an easier view of the edge of field.  Then my astigmatism tended to kick in.  But other than that, the stars were sharp. 

 

By the time I started to pack up at 2am, I had observed 80 DSO. No goto.  I did initial pointing with a laser finder, and then star hopped with a 9x50 RACI. 

 

Mike


Edited by Sarkikos, 31 August 2019 - 08:26 AM.

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#34 Sarkikos

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Posted 26 October 2019 - 08:08 PM

Before I bought the 150 Omni XLT f/5, I thought about getting the Bresser 152 mm f/5.  The Bresser has a "Petzval-like" element to provide a flat field, with no distorted stars at the edge.  On the other hand, the Bresser is nearly twice as heavy as the Omni and 30% longer … which are the reasons why I decided to buy the Omni instead.

 

Sometimes I have thought back and wondered if I should have bought the Bresser for the flat field, despite the extra weight and length. 

 

Nope.  No sir.  Now that I have the TSFlat2, the Omni gives a flat field without the extra weight and length! grin.gif

 

Mike


Edited by Sarkikos, 26 October 2019 - 08:10 PM.

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#35 tony_spina

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Posted 31 October 2019 - 12:06 AM

Well I got a chance to test the TSFLAT2 with my ST120 tonight. Unfortunately there is something wrong with it.  Star test shows a teardrop start image when using with a perfectly collimating scope and diagonal frown.gif

 

Sent a message to TS about getting a replacement 



#36 Sarkikos

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Posted 31 October 2019 - 06:06 AM

Sorry to hear it.  I didn't see anything like that through my TSFLAT2.   This past Sunday night at a dark site I had the TSFLAT2 in an Omni XLT 150 f/5 achro.  It nicely flattened the field.  An observing buddy in the field verified it.

 

I noticed the TSFLAT2 has a discount now.  I paid full price.

 

Mike


Edited by Sarkikos, 31 October 2019 - 06:07 AM.


#37 tony_spina

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Posted 05 November 2019 - 12:15 AM

Well still try to get this resolved with TS.. the latest is tech support telling me that this product is not for visual use!  Really?!  Told them to look at what they state on their website

 

Very frustrating 



#38 Sarkikos

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Posted 05 November 2019 - 07:17 AM

The product description says the TSFLAT2 can be used for visual.  My experience in the field tells me the TSFLAT2 flattens the field nicely in several of my telescopes.

 

Mike



#39 Sarkikos

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Posted 29 November 2019 - 02:38 PM

A couple nights ago I took out my ST80, which has a 2" Crayford focuser.  A Baader 2" ClickLock Mirror Diagonal was in the focuser.  I put a 10mm Ethos in the diagonal.  Yes, there was noticeable field curvature.  If I focused on a star at the center of field, and then moved that star to edge of field, the star was no longer sharply in focus. 

I tried it again, but this time I screwed the TSFLAT2 onto the barrel of the diagonal.  Now the stars were sharply in focus from edge of field to center of field.  My test objects were the Pleiades, Hyades, Double Cluster and the Mellote 20 open cluster around Mirfak in Perseus.

Mike


Edited by Sarkikos, 29 November 2019 - 02:38 PM.

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#40 tony_spina

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Posted 29 November 2019 - 05:54 PM

The product description says the TSFLAT2 can be used for visual.  My experience in the field tells me the TSFLAT2 flattens the field nicely in several of my telescopes.

 

Mike

I shipped it back to TS.  Per their reply it was NOT meant to be used visually.   They cited translation for the misinterpretation 



#41 Sarkikos

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Posted 29 November 2019 - 08:16 PM

I shipped it back to TS.  Per their reply it was NOT meant to be used visually.   They cited translation for the misinterpretation 

I suspect they were blowing smoke, possibly to cover for a defective sample.  I have used the TSFLAT2 successfully in several telescopes.   I believe my own eyes and my own field experience above anything else.  But in any case, I bought a TSFLAT2 because I had read other threads on CN in which other observers said they were able to use it successfully for visual.  Otherwise I wouldn't have known about it.

 

Here is the English translation from the TS website:

 

 

Also visually usable, depending on the eyepiece. Often the sharpnesss in the field can be improved.

 

Here is the original German:

 

 Abhängig von der verwendeten Okularbauart auch visuell einsetzbar, oft kann auch hier die Feldschärfe verbessert warden.

 

Seems like pretty much the same meaning to me.  shrug.gif

 

https://www.teleskop...connection.html

 

Mike


Edited by Sarkikos, 29 November 2019 - 09:10 PM.


#42 RUS+7

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Posted 03 December 2019 - 02:26 AM

Good day . Is there any kind of finished pipe achromat with an aperture of 200 mm  1\5.....1\6  suitable for observation with a bin attachment?

Extension 2 "?

thanks




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